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• System analysis guided to a set of measures to revert lake eutrophication. • Coordinated measures were implemented instead of a single intervention. • Five years pre-intervention water quality was compared with five years after. • Water quality strongly improved and no cyanobacteria blooms after intervention. • A combination of measures is powerful in controlling eutrophication in lakes. Controlling lake eutrophication is a challenge. A case-specific diagnostics driven approach is recommended that will guide to a suite of measures most promising in restoration of eutrophic lakes as exemplified by the case of the shallow lake Groote Melanen, The Netherlands. A lake system analysis identified external and internal nutrient load as main reasons for poor water quality and reoccurring cyanobacterial blooms in the lake. Based on this analysis, a package of restoration measures was implemented between January 2015 and May 2016. These measures included fish removal, dredging, capping of peat rich sediment with sand and an active barrier (lanthanum-modified bentonite), diversion of two inlet streams, reconstruction of banks, and planting macrophytes. Dredging and sand capping caused temporarily elevated turbidity and suspended solids concentrations, while addition of the lanthanum-modified clay caused a temporary exceedance of the Dutch La standard for freshwaters. Diversion of inflow streams caused 35 % less water inflow and larger water level fluctuations, but the lake remained water transporting with strongly improved water quality as was revealed by comparing five years pre-intervention water quality data with five years' post-intervention data. Total phosphorus concentration in the water column was reduced by 93 % from 0.47 mg P l -1 before the intervention to 0.03 mg P l -1 after the intervention, total nitrogen by 66 % from 1.27 to 0.21 mg N l -1, total chlorophyll- a by 75 % from 68 to 16 µg l -1, cyanobacteria chlorophyll- a by 88 % from 32 to 4 µg l -1. Turbidity had declined by 58 % from 23.5 FTU to on average 9.9 FTU. No cyanobacteria blooms were recorded over the entire post-intervention monitoring period (2016–2021). Submerged macrophytes increased from complete absence before intervention to around 10 %–15 % coverage after intervention. Repeated fish removal lowered the fish stock to below 100 kg ha-1 with 12 % of bream and carp remaining. Hence, the package of cohesive measures that was based on a thorough diagnosis resulted in rapidly, strongly and enduringly improved water quality. This case provides evidence for the power of combining measures in restoring eutrophic lakes. [Display omitted] [ABSTRACT FROM AUTHOR]

Eutrophication and cyanobacteria blooms are considered major problems for the biodiversity and water quality of urban ponds. While biomanipulation techniques such as drawdown with fish removal have great potential to restore turbid ponds to a clearwater status, it remains difficult to predict if and how macrophytes will recover naturally. Here, we used individual genotyping and population genetics based on 20 nuclear microsatellite loci to investigate the recruitment and recolonization strategies of the submerged macrophyte Stuckenia pectinata (L.) Börner. More specifically, we compared the founder genetic diversity of recovering populations just after biomanipulation to the genetic diversity of spontaneous, contiguous populations that settled over an extended period of time and were within the same catchment. Our results showed that turbid ponds may contain a persistent propagule bank that allows for an immediate re-establishment of genetically diverse populations of S. pectinata once a desired clearwater state is restored. Therefore, biomanipulation without sediment removal proved to be successful for founding populations to become immediately integrated with their established populations, thus maintaining the overall diversity of this species within local areas. Additionally, our results demonstrated an excess of heterozygotes in established populations that may be caused by substantial drift in albeit small effective population sizes of this predominantly outbreeding species. • Persistent seed banks accumulated past-generation diversity. • Seed banks acted as a source for spontaneous population re-establishment. • Spontaneous establishment was sufficient for maintaining genetic diversity. [ABSTRACT FROM AUTHOR]

Infochemicals refer to chemicals responsible for information exchange between organisms. We evaluated the effects of Daphnia magna and Daphnia galeata infochemicals on Microcystis aeruginosa for 15d. The Daphnia infochemicals were obtained from spent medium after culturing Daphnia in Elendt M4 medium for 48 h. Both Daphnia infochemicals significantly increased (p < 0.05) the intracellular reactive oxygen species level and microcystin-LR concentration in M. aeruginosa. This cellular effect increased colony formation of M. aeruginosa , thereby inhibiting the growth of M. aeruginosa. D. galeata infochemicals provoked significantly greater (p < 0.05) adverse effects on M. aeruginosa than those of D. magna infochemicals, which were further exaggerated by pre-exposure of Daphnia to M. aeruginosa. This result seems to be related to the different compositions and concentrations of Daphnia infochemicals. Several Daphnia infochemicals, such as methyl ferulate, cyclohexanone, 3, 5-dimethyl, hexanedioic acid, and bis(2-ethylhexyl) ester, showed a high correlation with M. aeruginosa cell concentration (| r | >0.6), suggesting that they may play a key role in controlling harmful cyanobacteria. Additionally, pre-exposure of D. magna and D. galeata to M. aeruginosa produced oleic acid, methyl ester, and n-hexadecanoic acid, with a highly correlation with M. aeruginosa cell concentration (| r | >0.6). p-tolyl acetate and linoleic acid were detected only in the pre-exposed D. galeata infochemicals. These findings suggest that some of Daphnia infochemicals identified in this study can be a promising tool to control M. aeruginosa growth. However, further studies are required to verify the specific actions of these infochemicals against cyanobacteria. [Display omitted] • Daphnia infochemicals inhibited the growth of Microcystis aeruginosa. • Daphnia galeata showed higher growth inhibition compared with Daphnia magna. • Pre-exposure of Daphnia to M. aeruginosa increased growth inhibition. • Some Daphnia infochemicals were well related to growth inhibition of M. aeruginosa. [ABSTRACT FROM AUTHOR]

The fish and plant communities in a pond contaminated with polychlorinated biphenyls (PCBs) in East Tennessee, USA, were manipulated to reduce ecological and human-health risk associated with exposure to the chemical contaminants. We evaluated the success of the remedial action using a habitat valuation approach, as well as measuring PCB concentrations in fish. Risk reduction objectives included: alter the fish community to favor fish that do not resuspend, bioaccumulate, or biomagnify PCBs; stabilize contaminated sediments to improve water quality; and stabilize shoreline soils and enhance riparian habitat. Fish targeted for removal included gizzard shad, largemouth bass, and nonnative carp. Reduced PCB concentrations in fish have characterized the new bluegill-dominated community, although a weir-overtopping event led to the need for additional removals of gizzard shad and largemouth bass. Sunfish abundance is high, as was intended. Moreover, amphibian and waterbird diversities have increased in the years following biomanipulation, possibly owing to improvements in the riparian zone and increased structural (vegetation) complexity in both the aquatic and terrestrial environment. Thus, the remedial action has improved aspects of habitat value, and PCB concentrations in sunfish have dropped below the remediation level (risk-based target value) for this pond (1 µg/g in fish fillets or 2.3 µg/g in whole body fish). [Display omitted] This paper addresses an uncommon but effective option for remediation of environmental contaminants in aquatic environments, biomanipulation. PCBs have important implications for human health and ecosystems. The paper combines analyses of PCB concentrations, habitat valuation, and water quality metrics, following biomanipulation of a pond. The 10-year study is longer than most published studies of environmental contaminants. The relevance is confirmed through funding from the US Department of Energy's Environmental Management program, and federal and state regulatory agencies have shown interest in the findings. Biomanipulation is a less expensive and effective remediation alternative, compared to excavation of chemical contaminants. This paper addresses an uncommon but effective option for remediation of environmental contaminants in aquatic environments, biomanipulation. PCBs have important implications for human health and ecosystems. The paper combines analyses of PCB concentrations, habitat valuation, and water quality metrics, following biomanipulation of a pond. The 10-year study is longer than most published studies of environmental contaminants. The relevance is confirmed through funding from the US Department of Energy's Environmental Management program, and federal and state regulatory agencies have shown interest in the findings. Biomanipulation is a less expensive and effective remediation alternative, compared to excavation of chemical contaminants. • An ecological manipulation in a contaminated pond reduced PCB concentrations in fish. • Habitat value metrics were measured over a 15-y period. • The pond transitioned from gizzard shad and largemouth bass dominance to sunfish. • PCB concentrations in bluegill decreased below risk-based targets. • Habitat metrics for most taxa are at least equal to those before biomanipulation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fish biomass were driven by fish stocking, catches, and ecological effects. • The ecosystem was unstable and showed a decreasing trend in maturity. • The ten-year fishing ban may fail to achieve the expected goal of restoration. • Fish of different feeding types require different targeted policies. With increasing anthropogenic activities, freshwater ecosystems around the world are becoming increasingly affected by various pressures, including eutrophication, overfishing, and irrational stocking, which may have a negative impact on the food web structure. Despite the extensive research and proposed management measures for eutrophic lakes, there are only few analysis on long-term monitoring data regarding fishery resources. Additionally, there is a lack of evaluation and prediction of the effectiveness of current fish management policies. To remedy this, we analyzed long-term monitoring data from Lake Taihu, China, a severely eutrophicated lake with a skewed fish size structure exhibiting dominance of small individuals. We first constructed 14 Ecopath models to investigate how trophic interactions and biomass fluxes changed from 2007 to 2020. Subsequently, the Ecosim model was used to predict how the biomass of fish and the ecosystem network respond to the initiated 10-years fishing ban. Our results demonstrate long-term changes in fish biomass and ecosystem stability. The analyses revealed that 1) the biomass development in different feeding types of fish is controlled by human activities (mainly catches and stocking) and trophic interactions and 2) the rate of decline in ecosystem network stability slows down during the fishing ban. The primary focus of this study was to fill the gap in long-term serial studies of fish monitoring data and ecosystem stability in the lake and, for the first time, to predict the outcome of the fishing ban from an ecosystem perspective using the Ecosim model. Overall, our results emphasize the importance of rational stocking and fishing policies and provide a better understanding of the changes in the ecological dynamics in Lake Taihu of relevance for the management and restoration of the lake. [ABSTRACT FROM AUTHOR]

Promotion of successful examples of biomanipulation and long-term monitoring is important for encouragement of similar activities, which are still relatively scarce. A project to improve water quality in the Velky Bolevecky pond (Plzeň, Czech Republic) began in 2006. The main activities in this project were: large scale fish reduction; stocking of predatory fish; usage of phosphorus binding coagulants; and reintroduction of macrophytes. During five years the impact of a eutrophic system with massive cyanobacterial blooms with low water transparency transformed into a clear water system with high water transparency and well developed macrophyte cover. All aspects relating to the ecological status of the water body such as total phosphorus concentration, chlorophyll- a concentration and cyanobacterial and other phytoplankton density improved significantly during or immediately after the project realization. For example, water transparency increased three fold. Zooplankton density also increased, however the difference was not significant. Oligotrophication of the system became evident also in the species composition of zooplankton and phytoplankton. Species adapted to nutrient reduction and macrophyte cover developed. Seven years after the project was over, the fish stock remained on the low densities naturally. A good ecological stage was achieved with low nutrient levels, high water transparency, very low densities of cyanobacteria and other phytoplankton together with a well-developed macrophyte cover. All of which has been maintained without any expensive impact. The highest expenditure is, paradoxically, due to macrophyte harvesting because their massive explosion in the pond is not in accordance with recreational and sporting utilization. It seems, that reduction of nutrient loading and switching of a formerly eutrophic system to an oligotrophic one is possible and sustainable over a relatively long time period in a shallow temperate pond. Subsequent good management of the system will, of course, be necessary. [ABSTRACT FROM AUTHOR]

Highlights • Simplified community and body size diminution occurred in the zooplankton community. • Unusual dynamics of diversity and biomass coincide well with carps' feeding rhythm. • Community traits related significantly to carp releasement in history. • Community traits related weakly to environmental factors. • Zooplankton-based indicators tend to overestimate trophic level under feeding stress. Abstract Zooplankton is widely used in indicating environmental changes and energy flow efficiency in aquatic ecosystems. Species composition and body size spectrum of zooplankton assemblage are sensitive to the changes of physico-chemical variability and fish feeding stress, and thus have in turn a prime bearing on water quality and cultured fishes. To study the response of zooplankton community to the introduction of planktivorous carps, monthly surveys were conducted in 2015 at six traditionally monitored locations in Miyun Reservoir, the unique surface drinking water of Beijing. There was a decrease in species richness, diversity, density and biomass, suggesting simplification of the community structure. Species diversity, density, and biomass declined significantly through the growth season, illustrating the great pressure imposed on the zooplankton. Regression and canonical correspondence analysis (CCA) showed low relationships between community traits and environmental variables. Zooplankton biomass had a significantly negative relationship with the stocking intensity of the filter-feeding carp. The different responses of the subgroups of Protozoa, Rotifera, Cladocera and Copepoda indicated that they responded differently to environmental stress. Seasonal variations in the density and biomass of the four subgroups and biomass size spectrum (BSS) indicated that planktons with medium and large body sizes were more sensitive and suffered more stress from the filter-feeding carp. The filter feeding by the silver and bighead carp disrupted the natural equilibrium of the zooplankton community, decreased diversity and stocks, altered the seasonal dynamics of all quantitative traits and suppressed the dominance of medium- and large-sized species or functional groups. The impacts of the fishery mode and the responses of different functional groups of zooplankton must be considered in ecological assessments and biomanipulation studies based on the zooplankton community structure and dynamics. [ABSTRACT FROM AUTHOR]

• Combining conventional and ecohydrological restoration maintained good water status. • Limiting nutrient inflow reduced the number of days with cyanobacteria bloom. • Sediment removal increased the phosphate level and induced overgrowth of Hydrodictyon reticulatum. • Trapping external nutrient loads was the most cost-effective restoration measure. • The SSBS and hybrid system reduced the cost of siltation treatment. The study presented in this paper aimed to improve the water quality of a small, stormwater-fed urban river and a cascade of ponds and reservoirs (Łódź, Poland) that are intensively used for recreation. We tested a combination of conventional restoration methods (bottom sediment removal and biomanipulation) and comprehensive ecohydrological restoration methods (hybrid systems, sequential sedimentation-biofiltration systems (SSBS), floating islands, landform-adjusted shoreline vegetation and plant harvesting). As a result of sediment removal (9795 m3, cost: €80761), almost 12.5 tons of nitrogen and 197 kg of phosphorous were eliminated from the reservoirs. The hybrid systems and SSBSs reduced the nutrient transport and suspended solid levels by 49%–98.5% and 89.6%–98.6%, respectively, from the upstream catchments to the reservoirs (investment cost: €63929). Generally, restoration improved most of the water quality indicators, although an increase in the phosphate concentration was observed from 0.06 to 0.17 mg L−1 before restoration to 0.13–0.28 mg L−1 immediately after restoration as a result of disturbances resulting from bottom sediment removal. Four years after restoration, the concentrations of the total forms of nutrients and ammonium were still considerably lower than before restoration. The number of summer days with microcystins and with chlorophyll a concentrations above the WHO limits for recreational waters decreased. However, there was a gradual decline in the physicochemical parameters of the water due to the local impacts of human use (swimming and duck and fish feeding), rather than from other external or internal loads, which were effectively controlled. [ABSTRACT FROM AUTHOR]

Abstract The presented research is part of the LIFE project ("EH-REK" LIFE08 ENV/PL/000517) on innovative restoration methods for small urban impoundments in the city of Łódź (Poland). The objective was to evaluate the usefulness of zooplankton as a biological quality element, when assessing the effectiveness of restoration efforts in three urban reservoirs and a one pond. The fifth unrestored pond was used as an example of the progressive eutrophication of an urban ecosystem. Studies were conducted during two periods: before (2010−2012) and after (2013–2016) restoration. A selection of zooplankton indices, including the rotifer trophic state index (TSI ROT), was used. The influence of the supplying river resulted in the negligible responses of biological parameters to the restoration efforts in the Upper Arturówek (UA) reservoir, which is the first in cascade of reservoirs. However, clear symptoms of water quality improvements were observed in the other two reservoirs (the Middle Arturówek, MA; the Lower Arturówek, LA) and in the Bzura-17 (B17) pond. After restoration, the contribution of species indicative of high trophic levels decreased in these ecosystems. The TSI ROT was strongly positively correlated with the trophic state index based on chlorophyll a , and both parameters significantly decreased in the MA, LA and B17. In the unrestored pond (B11), the successive increase in the concentrations of chemical parameters indicated progressing eutrophication. Interestingly, since 2013, the TSI ROT values clearly decreased in B11, but the strong negative correlation between ammonium concentration and rotifer density indicated that the reduced TSI ROT values didn't result from improvements in water quality; rather, they resulted from the increases in pollution and the associated harmful impacts on Rotifera. In conclusion, the TSI ROT can be a useful tool for assessing the ecological quality of small urban ecosystems; however, the use of biological indices must be supported by also monitoring physicochemical parameters. Graphical abstract Unlabelled Image Highlights • Zooplankton can be a useful indicator of ecological conditions in restored ecosystems. • Rotifer trophic state index was positively correlated with trophic state index based on chlorophyll a. • The biological indices should be used along with physicochemical monitoring when assessing water quality. • Rotifer trophic state index was not reliable in ponds with high concentrations of ammonium. [ABSTRACT FROM AUTHOR]

Abstract Fish manipulation has been used to restore lakes in the temperate zone. Often strong short-term cascading effects have been obtained, but the long term-perspectives are less clear. Fish manipulation methods are far less advanced for warm lakes, and it is debatable whether it is, in fact, possible to create a trophic cascade in warm lakes due to the dominance and high densities of fast-reproducing omnivorous fish. However, removal of benthic feeding fish also reduce disturbance of the sediment, which not only affects the nutrient level but also the concentration of suspended organic and inorganic matter with enhanced water clarity and potentially better growth conditions for submerged macrophytes. We conducted a biomanipulation experiment in one of the basins in Chinese Huizhou West Lake that have remained highly turbid after extensive nutrient loading reduction. Another basin was used as control (control-treatment pairing design). Removal of a substantial amount of plankti-benthivorous fish was followed by planting of submerged macrophytes and stocking of piscivorous fish. We found strong and relatively long-lasting effects of the restoration initiative in the form of substantial improvements in water clarity and major reductions in nutrient concentrations, particularly total phosphorus, phytoplankton and turbidity, while only minor effects were detected for crustacean zooplankton grazers occurring in low densities before as well as after the restoration. Our results add importantly to the existing knowledge of restoration of warm lakes and are strongly relevant, not least in Asia where natural lakes frequently are used extensively for fish production, often involving massive stocking of benthivorous fish. With a growing economy and development of more efficient fish production systems, the interest in restoring lakes is increasing world-wide. We found convincing evidence that fish removal and piscivores stocking combined with transplantation of submerged macrophytes may have significant effects on water clarity in warm shallow lakes even if the zooplankton grazing potential remains low, the latter most likely as a result of high predation on the zooplankton. Graphical abstract Image 1 Highlights • Biomanipulation was used to restore a eutrophic shallow lake in tropical China. • Substantial reduction in TP and Chl a concentrations, and turbidity were observed. • Low densities in crustacean zooplankton indicated minor grazing effects on phytoplankton. • The increased bottom-up effect is likely the mechanism for success in restoration in this warm lake. [ABSTRACT FROM AUTHOR]

• A calibrated zooplankton groups module was utilized to estimate seasonal dynamics. • Macrophyte reestablishment indicated on improvement of balance in SWE. • Zooplanktivorous fish manipulation had a seasonal heterogenous impact on zooplankton. • Fish-zooplankton-macrophyte-phytoplankton biomanipulation mitigated eutrophication. Eutrophication leads to algae blooms and reduces the transparency of water bodies, which seriously affects water quality and ecosystem equilibrium, especially in shallow water body ecosystems (SWE). Controlling foodwebs by manipulating fish and macrophytes provides a feasible method to mitigate the effects of eutrophication. The response of zooplankton as the primary consumer to biomanipulation is mostly conceptualized and lacks detailed observation. Mesocosm experiments that altered the biomass of planktivorous fish and macrophytes were set up and their boundary conditions were extended into a series of scenarios for modeling biomanipulation. Thus, this study utilizes a one-dimensional lake ecosystem model Water Ecosystems Tool (WET) which considered each zooplankton group: rotifers, cladocerans, and copepods, to predict the seasonal dynamic effects of biomanipulation on zooplankton in SWE, and the model results are analyzed in comparison with the mesocosm results. Observed data from mesocosm experiments set up in a temperate pond, including water temperature, dissolved oxygen (DO), total nitrogen (TN), total phosphorus (TP), chlorophyll a (Chl a), macrophytes, zooplankton, and fish, were used to calibrate and validate the models. The modeled results showed that in spring and summer zooplanktivorous fish removal would increase all three categories of zooplankton and consequently cause a decrease of phytoplankton, whilst an increase in fish biomass would increase phytoplankton, and concomitantly water turbidity. However, in autumn, rotifers and phytoplankton increased in response to fish removal, but cladocerans and copepods decreased, 27% and 41%, respectively. Across all three vegetated seasons, increasing the biomass of macrophytes revealed a similar pattern: all three categories of zooplankton increased and phytoplankton subsequently decreased. Our study proposes a "fish-zooplankton-macrophyte-phytoplankton" trophic cascade and quantitatively predicts the dynamics of each zooplankton group under biomanipulation through this pathway, and provides support for establishing macrophyte beds and removing zooplanktivorous fish (in spring and summer) as an effective approach to mitigate eutrophication. [Display omitted] [ABSTRACT FROM AUTHOR]

Ecological networks are useful for describing the complex trophic interactions within an ecosystem and hold great potential for ecosystem-based management. However, owing to the complexity and limited knowledge on the trophic interactions of natural food webs, it is challenging to make quantitative predictions about ecological community response to management interventions. Here, we use stable isotope mixing models in conjunction with Bayesian Belief Networks (BBN) to develop and examine the trophic interactions for six empirically determined aquatic food webs in tropical reservoirs. Using BBN, we predicted potential trophic cascade outcomes to predator removals, validated the predictions against data observed from in-situ biomanipulation experiments, and identified influential species using sensitivity analyses. Comparisons among various food web modelling frameworks demonstrated the importance of weighted connectance and network-centric approach for quantitative predictions, suggesting that the Bayesian Belief Network framework can play an important role in ecosystem-based management. [ABSTRACT FROM AUTHOR]

Due to sea water eutrophication and global warming, the harmful Phaeocystis blooms outbreak frequently in coastal waters, which cause a serious threat to marine ecosystem. The application of rotifer to control the harmful alga is a promising way. To investigate the influence of initial rotifer density and temperature on the ability of rotifer Brachionus plicatilis to eliminate Phaeocystis globosa population, we cultured P. globosa with different initial rotifer densities (1, 3, 5 inds mL −1 ) at 19, 22, 25, 28, and 31 °C for 9–16 d. Results showed that the population of rotifer feeding on Phaeocystis increased rapidly and higher temperatures favored the growth of P. globosa and B. plicatilis . With increased initial rotifer density and temperature, both the clearance rate of rotifer and the reduction rate of P. globosa increased, and thus P. globosa were eliminated earlier. Both temperature and initial rotifer density had significant effects on clearance rate of rotifer and the time to Phaeocystis extinction, and there was a significant interaction between the two factors on the two parameters, i.e., the effect of initial rotifer density on eliminating Phaeocystis decreased with increasing temperature. The rotifer in 5 inds mL −1 at 28 °C eliminated P. globosa in 4 d, whereas the rotifer in 1 ind mL −1 at 19 °C spent about 16 d on eliminating P. globosa . In conclusion, higher temperature and bigger initial rotifer density promote rotifer to eliminate the harmful P. globosa , and the optimal temperature for rotifer to clear P. globosa is 28 °C. [ABSTRACT FROM AUTHOR]

Feldberger Haussee (NE Germany) was polluted for almost a century. During the late 1970s, the nutrient input reached a maximum of approximately 1.9/11.5 g TP/TN m −2  yr −1 . As a result, the lake became a hypertrophic ecosystem and had largely lost its recreational value. In 1980, the sewage discharge was stopped, decreasing the external loading by approximately 90%. Because of vast amounts of phosphorus stored in the sediment, the lake remained highly eutrophic until 1985 with a TP concentration of ca. 1 mg L −1 . To accelerate recovery, biomanipulation was applied from 1985 to 2002 but was successful to only a minor extent. Eventually, due to sediment sequestration and discharge to downstream lakes the TP spring maximum (2006–2010) dropped to 0.112–0.078 mg L −1 . However, given the trend, it was obvious that it would take another 10–15 years for the concentration to approach the desired mesotrophic level. Thus, it was suggested to inactivate the surplus phosphorus by treating the lake with poly-aluminium chloride (PAC) as precipitant. To ensure good water quality, the objective was to decrease concentrations below 0.035 mg TP L −1 , while optimising the amount of PAC applied (as much as needed, but as little as possible). As a prerequisite, the status of the lake was carefully studied; external phosphorus loading and the amount of mobile phosphorus stored in the sediment being of specific interest. Laboratory experiments, modelling studies and field observations eventually resulted in an estimated dosage of 27 g Al m −2 (molar Al/P 12). Following the treatment in April 2011, prime water quality parameters showed two opposing trends: (1) TP concentration immediately dropped below the restoration target (≤0.025/0.035 mg L −1 ), primary production and phytoplankton biomass declined substantially. (2) However, water clarity did not improve for another four years. The likely reason for the delay was the structure of the phytoplankton community. It was dominated by cyanobacteria with the potential to trigger intensive calcite precipitation and thus impair transparency. In spring 2015, the cyanobacteria suddenly disappeared and transparency increased significantly. We speculate that these changes of the planktonic community shifted the ratio of assimilation and respiration in favour of the latter. This allowed an increase of free CO 2 * (dissolved CO 2 & dissociated carbonic acid) altering the carbonate buffering system and thus halting the formation of calcite crystals. Also, the phytoplankton, now represented by small readily ingestible taxa, promoted a flourishing Daphnia population inflicting heavy grazing losses, resulting in clear water stages (2015 June, 4.20 m; 2016, August 3.70 m; 2017 August, 4.5 m). We conclude that the drastic decrease of phosphorus availability in concert with structural and functional changes of the plankton community eventually improved the water quality of Haussee significantly. The lake is now in a mesotrophic status; well in accordance with the aim of the restoration project. [ABSTRACT FROM AUTHOR]

Accelerated eutrophication and requirements of the Water Framework Directive impose searching for effective restoration methods Recently positive effects are achieved by means of sustainable restoration methods that are cheap because they are limited to activities initiating natural changes in the ecosystem. Despite previous research, there is still not enough accurate data on ecosystem response (i.e. changes in the physico-chemical variables and phytoplankton composition in shallow lakes) to the sustainable restoration based on simultaneous application of several methods The restoration of shallow urban hypertrophic Swarzędzkie Lake started in autumn 2011. Three methods: were applied: (i) aeration of waters above the bottom sediments using a wind-driven aerator, (ii) phosphorus inactivation in water column using small doses of iron sulphate and magnesium chloride and (iii) biomanipulation with cyprinids catching and pike fry stocking. The aim of the study was to analyse the phytoplankton succession as well as physico-chemical variables of water quality in a shallow urban lake as a response to restoration measures. Samples were taken monthly from 2012 to 2014 at the deepest place of the lake, every 1m in the depth profile. Due to the restoration process, the Secchi depth increased to 1.00m. The oxygenation improved, as the anaerobic period in the deep water layer shortened to one month. The concentration of nutrients slightly decreased (mainly total nitrogen, from 5.5 to 4.0 mg N l −1 ), especially above the bottom. These changes had an impact on phytoplankton, which decreased twofold. The dominating cyanobacteria was eliminated or reduced and an increase in the number of chlorophytes, chrysophytes and cryptophytes has been observed. Nevertheless, the observed changes were not stable yet, so the restoration process should be continued to achieve permanent improvement. [ABSTRACT FROM AUTHOR]

Rapid recruitment of small fish after biomanipulation in warm lakes may delay the reestablishment of submerged macrophytes, not least at high nutrient concentrations. Success has recently been obtained in controlling phosphorus (P) loading to many lakes, but nitrogen (N) inputs often remain high. To determine the interactive effects of N loading and the abundance of small-sized fish on the growth of the submerged macrophyte Vallisneria natans , we conducted an outdoor mesocosm experiment with a factorial design on the north shore of Lake Taihu, China. The experiment involved two densities of small crucian carp – low (10 g m − 2 ) and high (40 g m − 2 ) – crossed with two levels of N loading – present-day external nutrient loading (P: 5 μg L − 1 day − 1 , N: 130 μg L − 1 day − 1 ) and P: 5 μg L − 1 day − 1 with a three times higher N loading (N: 390 μg L − 1 day − 1 ). The results showed that nitrogen-fish interactions significantly hindered the growth of V. natans , particularly at the high N loading. At low N loading, high densities of fish decreased the relative growth rate, mean leaf length, leaf mass and root mass of V. natans by 16%, 5%, 8%, and 23%, respectively, compared with these measures at low fish densities. The effect of fish was even stronger when N loading was high, with decreases of 232%, 32%, 57%, and 47% for the respective plant growth measures. The stronger effect at high N loading was attributed to higher turbidity due to enhanced phytoplankton biomass and to increased consumption or damage of plants by the fish in response to the more nutrient-enriched plant tissue. Our results indicate that high abundance of small crucian carp in warm lakes may reduce the resilience of submerged macrophytes to external N loading, thereby lowering the chances of successful restoration by biomanipulation. [ABSTRACT FROM AUTHOR]

Temperate and tropical shallow lakes differ in several fundamental aspects with respect to management of eutrophication. High altitude tropical shallow lakes are a special case, showing similarities with temperate and tropical lakes. We studied the ecology of the eutrophic high-altitude tropical lake Yahuarcocha in the Ecuadorian Andes and evaluated the potential of biomanipulation to control eutrophication. With a toxin-producing Cylindrospermopsis bloom, low Secchi depth and low submerged macrophyte cover, Yahuarcocha is clearly in a turbid ecosystem state. Relatively low nutrient concentrations should theoretically allow for a shift to a clear water state through biomanipulation. Top-down control of phytoplankton by zooplankton, however, is complicated by the (1) absence of predatory fish, (2) fish community dominated by small poecelid species, (3) lack of a refuge for zooplankton from fish predation within the macrophytes, and (4) persistent, grazing resistant bloom of the cyanobacterium Cylindrospermopsis . In these aspects, lake Yahuarcocha is more similar to tropical shallow lakes, probably because water temperature is high relative to the mean air temperature and because of the absence of a cold season. The fish and macrophyte communities consisted almost entirely of exotic species. The exotic fish species probably stabilized the turbid state in the lake. [ABSTRACT FROM AUTHOR]

Biomanipulation is a tool decision makers use to achieve desirable management goals. In lakes, one of the most common goals is the improvement of water quality, an objective that can be achieved mainly by reducing the amount of phytoplankton in the water. Although it is a very clear goal that is achievable by using actions that affect the phytoplankton biomass, experience shows that primary biomanipulation goals are rarely achieved. A biomanipulation program was conducted in Lake Kinneret over a 12-year period with the goal of improving water quality by reducing the population of the dominant fish species in the lake. However, the biomanipulation failed to achieve the goal and the program was stopped. We used Ecopath with Ecosim (EwE) scenarios to examine the effect of biomanipulation on the ecosystem. The results of these scenarios show that biomanipulation actions, such as those used in the lake, indeed fail to improve water quality; furthermore, they will actually increase the amount of phytoplankton in the water and decrease water quality. The development of the method described in the present article provides managers with the means to evaluate the effect of biomanipulation on an ecosystem. This method enables researches to conduct a pre-action analysis of the planned measures and examine whether the goal can be achieved, saving money and time and preventing damage to the ecosystem. [ABSTRACT FROM AUTHOR]

Three shallow basins in Huizhou West Lake, China, were compared with respect to phosphorus (P) cycling between sediment and water, binding forms of P in sediment, and macrophyte biomass. The basins had similar sediments and similar depths, but two of the basins were restored by carp fish removal and macrophyte transplantation. These two basins have had clear water, low Chl.a and high macrophyte coverage for seven and ten years, whilst the unrestored control basin had turbid water and higher Chl.a. Judged by diffusive ammonium efflux, sediments in restored basins had higher mineralization rates than the unrestored basin, but the release of total dissolved P were more similar. However, sediments of restored basins released primarily dissolved organic P, while the sediment from the unrestored basin only released dissolved inorganic P. One third of the P release in the unrestored basin occurred from resuspended sediment, while this pathway contributed less than 3% in restored basins where resuspension rates were 10 times lower and the surface sediments affinity for phosphate higher. Besides from the presence of carps in the unrestored basin, the main differences were a large pool of P (700–850 mg P m −2 ) in macrophyte biomass and a smaller pool (∼150 mg m −2 ) as loosely adsorbed P in the sediment of restored basins than in the unrestored (0 in macrophytes and 350 mg P m −2 as loosely adsorbed). Also, a tendency of higher concentrations of oxidized iron was observed in the surface sediment from restored basins. The study underlines the potential of trophic structure changes to alter internal nutrient cycling in shallow lakes. [ABSTRACT FROM AUTHOR]

Life-history traits like dominance of certain reproductive modes (e.g. vegetative, specialized, unspecialized or sexual propagules) and overwintering strategies (evergreen or re-sprouting) determine the success and timing of the ability of aquatic plants to colonize new areas. In the present experiment the distribution of these reproductive modes was examined in-situ, where new gaps were experimentally formed and establishment of new vegetation observed on a monthly bases in ten plots. During a period of 126 days, altogether 73% of all established plants (n = 1822) colonized by rhizomatic growth and 11% by rooting of vegetative fragments. Myriophyllum spicatum was observed to use mostly fragment rooting (81%), while Potamogeton perfoliatus followed a more mixed strategy combining re-rooting fragments and rhizomatic growth (31% and 41%, respectively). Stuckenia pectinata also preferred colonisation by rhizomes (84%). No colonisation by specialized vegetative units (tubers or turions) was observed during the study period The importance of surrounding vegetation was shown by comparing colonisation on inner and marginal sections of the plots (30% vs.70%). Three different patterns of timing of peak colonisation intensities were observed, related to species’ life-history traits. While several experimental works have been done on the regeneration and colonisation abilities of different species under laboratory conditions, information on the in-situ application of the different strategies is scarce. Insights on the modes by which plants succeed in colonising gaps helps us understand how (re)establishment of aquatic vegetation might function in lake ecosystems recovering after eutrophication. [ABSTRACT FROM AUTHOR]

The responses of plankton communities and nutrient loads to different biomass levels of silver carp and tilapia (0, 25, 70, 130 g/m 3 ) were evaluated in situ , using enclosures in Lake Taihu, and the effects of fish feces on algal biomass were assessed using in situ dialysis culture. Both silver carp and tilapia significantly suppressed zooplankton biomass, after which zooplankton grazing was too low to suppress algal populations. Both fish also played an important role in accelerating nutrient circulation, and their feces directly contributed to algal growth. In fact, after passing through the digestive tract of silver carp, the cyanobacteria Microcystis remained viable, and their photosynthetic activity was even stimulated; however, no viable algae were detected in the tilapia feces. Overall, algal biomass increased with increasing biomass levels of the tilapia, whereas the medium biomass level of silver carp (70 g/m 3 ) was most effective in controlling cyanobacteria. Our results indicate that stocking with silver carp, rather than with tilapia, is an appropriate strategy for reducing summer cyanobacteria blooms in eutrophic lakes that lack large crustaceous zooplankton, such as Lake Taihu. In addition, stocking with 70 g/m 3 of silver carp was most effective for suppressing cyanobacteria blooms and improving water quality, which suggests that this moderate biomass level can be used to achieve a beneficial balance between the positive effects of filter feeding and negative effects of feces-derived nutrients on the growth of algae. Statement of relevance Good for algae control and aquaculture yields increase. [ABSTRACT FROM AUTHOR]

The water balance, with large seasonal and annual water level fluctuations, has a critical influence on the nitrogen and phosphorus dynamics of shallow lakes in the semi-arid climate zone. We constructed seasonal water and nutrient budgets for two connected shallow lakes, Lakes Mogan and Eymir, located in Central Anatolia, Turkey. The study period covered 20 years with alternations between dry and wet years as well as restoration efforts including sewage effluent diversion and biomanipulations in Lake Eymir. Both lakes experienced a 1–2 m water level drop during a drought period and a subsequent increase during the wet period, with seasonal water level fluctuations of 0.60 to 0.70 m. During wet years with high water levels, small seasonal differences were observed with a nutrient peak in spring caused by external loading and nutrient loss via retention during summer. During years with low water levels, nutrient concentrations increased due to internal and external loading, exacerbated by evaporative water loss. In Lake Eymir, a shift to eutrophic conditions with turbid water occurred under low water level conditions and consequent internal loading of P from the sediment, causing high nutrient concentrations in summer. Our results indicate a threat of lakes drying out in the semi-arid climate zone if evaporation increases and precipitation decreases as anticipated from the global climate change predictions. In addition, our results show the influence of the water balance on the eutrophication of shallow lakes in the Mediterranean climate zone and highlight the ultimate consequences for lake management. [ABSTRACT FROM AUTHOR]

Many urban ponds experience detrimental algal blooms as the result of eutrophication. During a two year field experiment, the efficacy of five in situ treatments to mitigate eutrophication effects in urban ponds was studied. The treatments targeted the sediment phosphorus release and were intended to switch the ponds from a turbid phytoplankton-dominated state to a clear-water state with a low phytoplankton biomass. Two eutrophic urban ponds were each divided into six compartments (300–400 m 2 ; 210–700 m 3 ). In each pond the following treatments were tested: dredging in combination with biomanipulation (involving fish biomass control and the introduction of macrophytes) with and without the addition of the flocculant polyaluminiumchloride, interception and reduction of sediment phosphorus release with lanthanum-modified bentonite (Phoslock ® ) in combination with biomanipulation with and without polyaluminiumchloride; biomanipulation alone; and a control. Trial results support the hypothesis that the combination of biomanipulation and measures targeting the sediment phosphorus release can be effective in reducing the phytoplankton biomass and establishing and maintaining a clear-water state, provided the external phosphorus loading is limited. During the experimental period dredging combined with biomanipulation showed mean chlorophyll- a concentrations of 5.3 and 6.2 μg L −1 , compared to 268.9 and 52.4 μg L −1 in the control compartments. Lanthanum-modified bentonite can be an effective alternative to dredging and in combination with biomanipulation it showed mean chlorophyll- a concentrations of 5.9 and 7.6 μg L −1 . Biomanipulation alone did not establish a clear-water state or only during a limited period. As the two experimental sites differed in their reaction to the treatments, it is important to choose the most promising treatment depending on site specific characteristics. In recovering the water quality status of urban ponds, continuing attention is required to the concurrent reduction of external phosphorus loading and to maintaining an appropriate fish community. [ABSTRACT FROM AUTHOR]

Phosphorus (P) removal structures have been shown to decrease dissolved P loss from agricultural and urban areas which may reduce the threat of eutrophication. In order to design or quantify performance of these structures, the relationship between discrete and cumulative removal with cumulative P loading must be determined, either by individual flow-through experiments or model prediction. A model was previously developed for predicting P removal with P sorption materials (PSMs) under flow-through conditions, as a function of inflow P concentration, retention time (RT), and PSM characteristics. The objective of this study was to compare model results to measured P removal data from several PSM under a range of conditions (P concentrations and RT) and scales ranging from laboratory to field. Materials tested included acid mine drainage residuals (AMDRs), treated and non-treated electric arc furnace (EAF) steel slag at different size fractions, and flue gas desulfurization (FGD) gypsum. Equations for P removal curves and cumulative P removed were not significantly different between predicted and actual values for any of the 23 scenarios examined. However, the model did tend to slightly over-predict cumulative P removal for calcium-based PSMs. The ability of the model to predict P removal for various materials, RTs, and P concentrations in both controlled settings and field structures validate its use in design and quantification of these structures. This ability to predict P removal without constant monitoring is vital to widespread adoption of P removal structures, especially for meeting discharge regulations and nutrient trading programs. [ABSTRACT FROM AUTHOR]

Many urban ponds in The Netherlands and other countries suffer from eutrophication, resulting in harmful algal blooms which are often dominated by cyanobacteria. A sufficient reduction of nutrients, as prerequisite to mitigate cyanobacterial blooms in urban ponds, is not always feasible. Water managers are in need for applicable alternatives to mitigate these cyanobacterial blooms. The quagga mussel ( Dreissena rostriformis bugensis ) is a rapidly expanding bivalve species in many standing waters and rivers in The Netherlands. Because quagga mussels feed on algae, they could become a useful tool in controlling harmful algal blooms in urban ponds if provided with the appropriate substrate. We tested the hypothesis that quagga mussels can reduce phytoplankton biomass and induce a clear water state in a shallow hypertrophic urban pond. We executed an in situ enclosure experiment using eight enclosures (750 L) in an urban pond: four enclosures contained quagga mussels (0.3 g ww L −1 ), and four control enclosures were set up without mussels. We used artificial substrate for the breeding of mussels and the transfer from the breeding location to the experimental site. In contrast to the controls, the enclosures with mussels showed significantly lower concentrations of total chlorophyll- a (2.4 μg L −1 in mussel enclosures versus 84.1 μg L −1 in controls), cyanobacterial chlorophyll- a (1.0 μg L −1 versus 7.3 μg L −1 ) and total phosphorus (0.08 mg L −1 versus 0.17 mg L −1 ), and had higher transparency (>0.80 m in mussel enclosures versus 0.57 m in controls) and higher soluble reactive phosphorus concentration (0.03 mg L −1 versus <0.01 mg L −1 ). No effect of the mussels on microcystin concentrations was shown. The results show that quagga mussels are able to reduce the phytoplankton biomass in a hypertrophic urban pond, including cyanobacteria and induce a clear water state. We conclude that quagga mussels can be a promising tool in controlling algal blooms in urban ponds, in particular when a sufficient reduction of nutrients is not feasible. A preferred next step in the scaling up of the method is the determination of long-term effectiveness and side-effects in a controlled application in an urban pond. Because the quagga mussel is an invasive alien species, new introductions should be considered carefully and water purification using quagga mussels is preferably applied in water systems where the species is already present. [ABSTRACT FROM AUTHOR]

The physiochemical and planktonic community responses of the water column to the introduction of silver and bighead carp at a biomass of 50 g m −3 were studied in enclosures in the hypereutrophic Meiliang Bay of Lake Taihu over a 54-day period. Groups of silver carp and bighead carp stocked at weight ratios of 1:0 (G1), 1:1(G2) and 1:2 (G3) as well as a control group with no fish were established. The results showed that the chlorophyll- a levels were significantly decreased in the groups containing fish, and the lowest total phosphorus was detected in the G1 group. The fish in all of the groups stocked with fish grazed rapidly on crustacean zooplankton. The diversity and density of the phytoplankton decreased in the enclosures containing fish, and the phytoplankton abundance was higher in the G3 group than in the G1 and G2 groups but lower than that in the control group. The less effective ability of bighead carp to collect small sized algae caused consumptive separation between the two fish and resulted in the less efficient in collection and digestion of Microcystis by bighead carp. To control nuisance cyanobacteria blooms and bring some economical benefits, silver carp should be artificially enhanced prior to bighead carp. [ABSTRACT FROM AUTHOR]

Artificial enhancement of lakes using filter-feeding silver carp is a technique that is widely used to manipulate and/or promote fisheries' production in Chinese lakes. To evaluate the impact of this enhancement on nutrient cycling in the water column, we analyzed two silver carp biomass gradient testing sites by stocking experimental enclosures within Lake Taihu (eutrophic) with 0, 35, 70 and 150 g m − 3 of silver carp biomass and those within Lake Erhai (mesotrophic) with 0, 20, 50 and 100 g m − 3 of silver carp biomass. Total phosphorus and dissolved nitrogen were obviously influenced by the fish density. At relatively low densities, the silver carp were able to graze for particles of food directly, resulting in a decline in phosphorus and chlorophyll- a levels within the Lake Taihu enclosures. When fish were introduced to the Lake Erhai enclosures, chlorophyll- a levels increased. Increased dissolved nitrogen levels were recorded in the Lake Taihu enclosures during the experiment, while the enhanced uptake of nutrients by increased algae resulted in decreased dissolved nitrogen levels in the Lake Erhai enclosures. We hypothesize that although silver carp could potentially reduce cyanobacteria in water bodies with large algal blooms, the relatively small change in fish in Lake Taihu is still too minor to control severe algal blooms. In relatively clean water bodies such as Lake Erhai, artificial ecological enhancement using silver carp should be evaluated carefully before action is taken in order to assess the risk of increasing small algal blooms and nutrients. [ABSTRACT FROM AUTHOR]

The improvement of water quality in recreational and drinking water reservoirs has been a main priority of river basin authorities for some time. One measure commonly applied is biomanipulation, which aims to improve water quality by adjusting fish community structure. Effective reduction of cyprinid density, with a resultant increase in filtering zooplankton development, has already proved successful in many lakes. In this paper, we document progress in a project to evaluate the feasibility and efficiency of biomanipulation through parallel use of age-selective fish removal and predator stocking to improve water quality in a 42 ha drinking water reservoir. Between 2009 and 2012, cyprinid and young perch ( Perca fluviatilis ) density was reduced through removal of early-stage planktonophagous fish and perch eggs, along with removal of adult bream ( Abramis brama ) and roach ( Rutilus rutilus ) during spawning. Predatory fish were also stocked to increase juvenile mortality of the target species. As a result, cyprinid biomass was significantly reduced (ca. 2/3 of adult bream removed; biomass now estimated at <25 kg ha −1 ). This study showed that biomanipulation was successful at the reservoir and that it is a feasible method for other water bodies of similar area and depth with suitable capture sites. While reduced cyprinid biomass has resulted in a continuous increase in zooplankton density and biomass, however, phytoplankton dynamics appear to be dependent on additional factors such as nutrient input (especially phosphorus). Over the coming years, therefore, attention will focus on both external (catchment) and internal (sediment) nutrient sources, in addition to continuing fish biomanipulation. [ABSTRACT FROM AUTHOR]

Eutrophication transforms clear water into turbid water in shallow lakes. Current restoration techniques focus on re-establishing the clear-water state rather than on its maintenance. We investigated the response of submerged macrophytes to temporary grass carp (Ctenopharyngodon idella) and scraping snail (Bellamya aeruginosa) introductions. We also explored the impacts of herbivores on underwater light conditions to identify their long- and short-term potential to halt regime shift from clear to turbid after clear-water state reestablishment. Herbivores reduced both the biomass of submerged macrophytes and accumulated nutrients in the tissue of submerged macrophytes. This potentially avoided the pulse of endogenous nutrient release which would have exceeded the threshold required for the regime shift from clear to turbid. However, herbivores had a non-significant impact on submerged macrophyte-reduced light attenuation coefficient, which has a positive linear relationship with water chlorophyll a. Further, grass carp and snails enhanced the inhibition ratio of submerged macrophytes to phytoplankton by 3.96 and 2.13 times, respectively. Our study provides novel findings on the potential of herbivore introduction as an indirect biomanipulation tool for halting the regime shift of shallow lakes from clear to turbid after the restoration of submerged macrophytes. [Display omitted] • Lake management focus few on clear-water state maintenance. • We studied the potential of herbivores for regime shift prevention of clear-water. • Herbivores reduced endogenous nutrient accumulation rather than underwater light. • Herbivores enhanced submerged macrophyte inhibition ratio of phytoplankton. [ABSTRACT FROM AUTHOR]

Gillnetting is a technique commonly used in relative abundance and biomass estimates of fish. However, due to its passive nature, the direct recalculation of the catch to reservoir volume or area is not trivial. This issue is often solved by using hydroacoustics, which provides information about fish density, though without the ability to distinguish species. However, the precision of such density estimates are also questionable. In this study, we estimated the abundance and biomass of dominant fish species before and after a biomanipulation program (fish removal) in 2020 using gillnetting and hydroacoustic surveys in a temperate reservoir. Between the two sampling periods, nearly 27,000 individuals (9000 kg) older than 0 + of bleak (Alburnus alburnus) and bream (Abramis brama) were removed during the biomanipulation program. Decreases in abundance and biomass estimates were expected for both techniques and both species. The gillnet decrease was 68% in CPUE (catch per unit of effort) and 48% in BPUE (biomass per unit of effort) for both species and all gillnets grouped together. Hydroacoustic observations showed a decrease of approximately 79% in abundance and 74% in biomass after fish reduction. Considering the numbers and biomass of fish removed, the absolute hydroacoustic estimates were underestimated for fish abundance but credibly estimated for biomass. The average weight of the fish taken was between the values of the fish caught with gillnets and the weights determined by hydroacoustics. In terms of results, both methods appear to be a suitable tool for estimating fish abundance and biomass in large inland waters, although the spatial and temporal distribution of fish of different sizes should be considered when using different sampling methods for fish monitoring. • Fish abundance and biomass estimates before and after mass reduction were compared. • More than 50% of bleak and bream were removed both in abundance and biomass. • Abundance and biomass decrease was observed in gillnets and hydroacoustics. • Higher decrease of bleak was observed in benthic habitat, of bream in pelagic habitat. • To minimize bias in fish estimates, intercalibration between techniques is needed. [ABSTRACT FROM AUTHOR]

Abatement of external phosphorus (P) loading and biomanipulation are measures that are often applied with the aim to restore a macrophyte dominated clearwater state in turbid, anthropogenically eutrophied lakes. The recovery of such lakes, however, is often hampered by ‘internal eutrophication’, as a result of the release of historically accumulated P from the sediment into the water column. One way to combat this internal P loading is by adding iron (Fe) into the lake, which naturally binds to phosphate. Although studied in the laboratory or mesocosms, the effects of iron addition on a whole-lake scale are largely unknown. In this study we therefore compiled lake monitoring data to evaluate the effect of a gradual dose of 33 g Fe m −2 on the water quality and biotic communities (phytoplankton, zooplankton and macrophytes) of Lake Terra Nova. During and after the Fe-addition, we also carried out assays to evaluate the effect of the Fe-addition on sediment P-release rates. Lake Terra Nova is a eutrophied, shallow peaty lake that has been subjected to biomanipulation measures for 10 years. The large scale addition of iron during 2010 and 2011 resulted in a substantial reduction of dissolved P, suspended matter (SM), phytoplankton biomass and relative Cyanobacterial biomass, whereas macrophytes reappeared. Fe-addition also resulted in strongly reduced sediment P-mobilisation rates. Nevertheless, reductions of water column TP in response to the Fe-addition were short-lived. This discrepancy between the observed TP-levels in the water column and sediment P-release rates could indicate that sustained loading with external P and interactions of chemical compounds with Fe may jeopardize long term restoration success by depleting the water column reservoir of reactive Fe. Ecological processes can in addition enhance this process by shunting P from the sediment to the water column. [ABSTRACT FROM AUTHOR]

This paper focuses on assessing a lake biomanipulation and introduces self-organizing maps (SOMs) as an analytical tool. In 2000, the biomanipulation using herbivorous plankters ( Daphnia galeata ) and piscivorous fish ( Oncorhynchus mykiss ) was implemented to improve water quality in Lake Shirakaba, Japan. We aimed to identify the relationships among dominant zooplankton and environmental conditions during the study period (pre-: 1997–1999, intermediate-: 2000–2002, and post-biomanipulation: 2003–2006, sampled between May and October on the biweekly basis, N = 122). From the SOM, the limnological characteristics of the lake were categorized into five features. The results accommodated that the newly introduced non-native grazers, D. galeata , were well stabilized by introducing O. mykiss which helped D. galeata survive away from predation pressure of Hypomesus transpacificus nipponensis . The interplay and relationship between variables projected by the SOM were also supported by the previous research and evidences in compliance with competitions and predations. Hence the results manifest that a regime shift of zooplankton communities in this lake has occurred since the biomanipulation. Furthermore, the present study highlights the applicability of contemporaneous introduction of both top-down cascade regulators (i.e. D. galeata and O. mykiss ) as an alternative choice for the successful biomanipulation. [ABSTRACT FROM AUTHOR]

• Using biomanipulation to restore a eutrophic highland lake in subtropical China was tested. • Fish removal led to increased abundance of cladoceran (Daphnia spp., especially Bosmina spp.). • Enhanced top-down control was found leading to lower phytoplankton and cyanobacterial biomass. • Fish removal may be a feasible additional restoration tool to nutrient loading reduction such lakes. Removal of planktivorous fish is used extensively in northern temperate lakes to reduce phytoplankton abundance via enhanced zooplankton grazing. However, whether this method would work also in large subtropical highland lakes to alleviate cyanobacterial blooms is unknown. We conducted a one-year pilot in situ experiment where we removed a substantial biomass of fish in a fenced-in area, followed by a 3-year whole-lake experiment where the dominant fish species (Japanese smelt) was removed in Lake Erhai in southwest China. The fencing experiments showed that between July and November, when the biomass of the removed stock reached 4 g/m2, the zooplankton biomass inside the fence increased significantly compared to a control fence. In the full-lake experiment, we found that sustained removal of Japanese smelt led to an increase in the biomass of cladocerans (Daphnia spp. but especially of Bosmina spp.) and a significant decrease in the biomass of Cyanobacteria and Chlorophyta. Additionally, a marked increase in the ratio of zooplankton to phytoplankton biomass, as well as an increase in the body size of cladocerans, emphasising the importance of enhanced top-down control for mitigating cyanobacterial blooms following extensive fish removal. Our results reveal that removal of small fish (here Japanese smelt) can lead to a reduction of the phytoplankton and cyanobacteria biomass through a trophic cascade in highland deep subtropical lakes. Thus fish removal may be a feasible additional restoration tool to external nutrient loading reduction in such lakes. [Display omitted] [ABSTRACT FROM AUTHOR]

With the rapid progression of bionanorobotics, manipulation of nano-scale biosamples is becoming increasingly attractive for different biological purposes. Nevertheless, the interaction between a robotic probe and a biological sample is poorly understood and the conditions for appropriate handling is not well-known. Here, we use the molecular dynamics (MD) simulation method to investigate the manipulation process when a nanoprobe tries to move a biosample on a substrate. For this purpose, we have used Ubiquitin (UBQ) as the biomolecule, a single-walled carbon nanotube (SWCNT) as the manipulation probe, and a double-layered graphene sheets as the substrate. A series of simulations were conducted to study the effects of different conditions on the success of the manipulation process. These conditions include the tip diameter, the vertical gap between the tip and substrate, and the initial orientation of the protein. Also we have studied two strategies for the manipulation of the protein by a nano-scale probe that we have named pushing and pulling. Interaction force between carbon nanotube (CNT) tips and the biomolecule, the root-mean-square deviation (RMSD), and the radius of gyration of the protein are monitored for different conditions. We found that larger tip diameters, smaller gaps between tip and substrate, and a pulling strategy increase the chance of a successful manipulation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Zooplankton in wastewater reservoirs may cause severe clogging in irrigation systems. [•] We studied clogging and particle size distribution in 9 treated wastewater reservoirs. [•] Factor analysis identified 2 sets of environmental conditions that lead to clogging. [•] One set is related to thermal stratification and copepods, the other to cladocerans. [•] Potential management procedures to avoid filter clogging are discussed. [ABSTRACT FROM AUTHOR]

Most in-lake restoration projects use deeply intrusive methods. They include the removal of bottom sediments and the use of high doses of precipitants. They are very radical, causing extinction of many organisms, and are very expensive. Alternative methods described in this paper are inexpensive, easy to use, effective, and sustainable (energy-efficient, not destructive for most of the biota). They have been applied to three lakes located in Poznań and the surrounding area (Western Poland) and their effectiveness has been documented. They include: (i) use of biomanipulation to increase trophic influence of zooplankton on phytoplankton, and small doses of iron sulphate to reduce phosphorus content in the water column, used in Maltański Reservoir, (ii) delivering water rich in nitrates from small tributaries to the deepest part of the lake, thus increasing redox potential and limiting the release of phosphorus from bottom sediments, used in Uzarzewskie Lake, (iii) oxygenation of hypolimnetic waters using wind aerators, iron treatment with small doses of coagulant and biomanipulation, used in Durowskie Lake. Use of limited doses of an innovative solid phosphorus precipitant called Sinobent ® is also possible. These methods, in accordance with the intermediate disturbance hypothesis, increased the diversity of flora and fauna in the lakes and contributed to improvements in water quality. Simultaneous application of several methods, which prevented feedback mechanisms, increased the efficiency of lake restoration. [ABSTRACT FROM AUTHOR]

Abstract: Toxin-producing cyanobacteria have frequently been hypothesized to limit the ability of herbivorous zooplankton (such as Daphnia) to control phytoplankton biomass by inhibiting feeding, and in extreme cases, causing zooplankton mortality. Using limnocorral experiments in hyper-eutrophic ponds located in Alabama and Michigan (U.S.A.), we tested the hypothesis that high levels of cyanobacteria and microcystin, a class of hepatotoxins produced by several cyanobacterial genera, prevent Daphnia from strongly reducing phytoplankton abundance. At the start of the first experiment (Michigan), phytoplankton communities were dominated by toxic Microcystis and Anabaena (∼96% of total phytoplankton biomass), and concentrations of microcystin were ∼3 μg L−1. Two weeks after adding Daphnia pulicaria from a nearby eutrophic lake, microcystin levels increased to ∼6.5 μg L−1, yet Daphnia populations increased exponentially (r = 0.24 day−1). By the third week, Daphnia had suppressed phytoplankton biomass by ∼74% relative to the no Daphnia controls and maintained reduced phytoplankton biomass until the conclusion of the five-week experiment. In the second experiment (Alabama), microcystin concentrations were greater than 100 μg L−1, yet a mixture of three D. pulicaria clones from eutrophic lakes in southern MI increased and again reduced phytoplankton biomass, in this case by over 80%. The ability of Daphnia to increase in abundance and suppress phytoplankton biomass, despite high initial levels of cyanobacteria and microcystin, indicates that the latter does not prevent strong control of phytoplankton biomass by Daphnia genotypes that are adapted to environments with abundant cyanobacteria and associated cyanotoxins. [Copyright &y& Elsevier]

Abstract: Piscivorous fish may drive trophic cascades and maintain good water quality in lakes and reservoirs. Biomanipulation by stocking piscivores has been therefore suggested as a useful tool to regulate phytoplankton biomass in anthropogenically eutrophicated systems. We evaluated the top-down effects of piscivores on lower trophic levels in 13 deep, stratified Czech reservoirs that were built by damming rivers. In addition, the importance of piscivores was assessed in three deep, bank-side Dutch reservoirs that are artificially destratified. All the Czech reservoirs are regularly stocked with piscivores while the Dutch reservoirs have never been stocked. The piscivores had no significant top-down effect on the biomass of planktivorous and benthivorous fish and on phytoplankton biomass (measured as chlorophyll-a concentration) in the Czech reservoirs, although the proportion of piscivores in the fish community was high in half of them. The planktivore and benthivore biomass and the phytoplankton biomass correlated strongly with phosphorus concentration, which is in line with bottom-up control by nutrient supply. On the other hand, piscivores in the Dutch reservoirs dominated the fish community and apparently contributed to good water quality. Nevertheless, the primary cause of relatively low phytoplankton biomass in the Dutch reservoirs was the artificial destratification inducing light limitation on phytoplankton. We conclude that biomanipulation cannot substantially reduce phytoplankton biomass in the eutrophicated systems with high external nutrient input. The input should be reduced to control phytoplankton and if it is not possible, artificial destratification can be applied. [Copyright &y& Elsevier]

Abstract: A 3-year ecological engineering project was carried out from 2003 to 2005 in the drinking water source in Meiliang Bay, Lake Taihu, China. The project area was divided into three zones: Zone C (outside the area), Zone B (pelagic part within the area) and Zone A (littoral part within the area). The community composition, density and biomass of zooplankton were studied as a part in the lake restoration study. Also, the abundance, biomass and composition of fish in the engineering area were annually analyzed in the littoral zone (Zone A). The average density of cladocerans decreased from the outer part to the inner part of the lake, i.e., from Zone C to Zone A, while the average density of copepod did not significantly vary among the 3 zones. The average densities of rotifer and ciliate increased from Zone C to Zone A. RDA analysis indicated that Microcystis biomass more impacted the zooplankton compositions after temperature. In Zone A, many planktivorous fishes, e.g., Coilia nasus, Hemiculter leucisculus, Pseudorasbora parva, dominated the fish community, which caused a marked decrease in the abundance of cladocerans, especially large-sized cladoceran Daphnia galeata and Daphnia obtusa. Our results suggested that both fish predation and other environmental factors such as the Microcystis bloom greatly affected the zooplankton community during the restoration of subtropical eutrophic lakes. [Copyright &y& Elsevier]

Abstract: To evaluate the ecological consequences of engineered use of water hyacinths in Lake Taihu, China, we conducted a systematic survey of the dynamics of the zooplankton community (mainly copepods, cladocerans, and rotifers) inside (INE), around (ARE), and far-outside (FAE) a large-scale enclosure of water hyacinths in Zhushan Bay, Lake Taihu from August to November 2009 and calculated five response variables for the zooplankton community for each area. INE, ARE, and FAE differed little in their zooplankton composition at the genus level: the 16 of 21 identified genera were common and the same 6 zooplankton genera were dominant in all three areas, and only 5 sparse zooplankton genera were not collected from all three areas. The average abundance of each zooplankton faunal group and their annual trends displayed similar patterns in INE, ARE, and FAE. The only significant difference (p <0.05) detected was between INE and FAE in the average abundance of cladoceran fauna (INE>FAE) and rotifer fauna (INE

Abstract: Inter-specific and intra-specific differences in the filtering activities of two unionid bivalves, Unio douglasiae and Anodonta woodiana, which thrive in small agricultural canals, were compared using a flow-through chamber system of ambient eutrophic lake water. The mean filtration rates (FRs) of these two species, size-matched for similar shell length, were not significantly different (t-test, t =0.024, P =0.981), whereas there were significant differences in the FRs between mussels of different ages (t-test, t =5.137, P =0.001), different densities (t-test, t =8.297, P <0.0001), and different currents (t-test, t =3.898, P =0.005). The FRs of A. woodiana increased significantly more with higher temperatures in younger mussels (P <0.01, maximum FR=0.352±0.157L/h at 13.5–20.4°C) than in adults. However, the mortality of the mussels was comparatively higher in younger mussels due to a low tolerance to ammonia. Correlation coefficients and PCA results collectively indicate that the two dominant unionid mussels in the canal had a strong relationship with the seston level in the lake (turbidity, suspended solids and chlorophyll-a), resulting in a higher FR, pseudo-faeces production, and ammonia tolerance and a lower mortality. In addition, the validation of the biomanipulation used in the mussel-controlled system is discussed in an effort to improve the water quality of eutrophic lakes and streams and the conservation of the benthic mussel community. [Copyright &y& Elsevier]

Abstract: We address restoration of eutrophic lakes and reservoirs through the formulation of dynamic optimization problems subject to complex PDAE systems representing biogeochemical processes in the water bodies. The model includes phytoplankton, zooplankton, fish, nutrients, DO, particulate and dissolved carbon dynamics. The PDAE has been transformed into an ordinary differential algebraic equation system by spatial discretization into two water layers. An optimal control problem for the implementation of three different restoration techniques and their combinations has been formulated within a control vector parameterization approach. Numerical results for the different problems provide optimal profiles for tributary deviation flowrate through a nearby wetland, aeration rates and fish removal rates, as restoration strategies. [Copyright &y& Elsevier]

Abstract: Most stock assessment models are solely age-based and ignore variability in length-at-age, but the incorporation of length structure can improve parameter estimates. Here, we present an age- and length-structured population model to estimate fish recruitment, von Bertalanffy growth parameters, natural mortality, and gear selectivity from survey length- and age-specific catch, fishery length distributions, and total harvested biomass. We evaluated parameter bias when fitting the model to simulated data with variable fish longevity, survey sampling duration (i.e., years of data), survey gear selectivity (i.e., asymptotic or dome-shaped), instantaneous fishing mortality rate and fishing mortality trend (i.e., stable or increasing). Median proportional bias in mortality (fishing and natural), growth, and gear selectivity parameters did not exceed 0.05 across all scenarios. Median recruitment bias ranged up to 0.12 and was greatest for the short-lived species and for scenarios with increasing fishing mortality, but bias for all other scenarios was less than 0.1. The model was demonstrated using data from a whole-lake biomanipulation of gizzard shad (Dorosoma cepedianum) at a 2300-ha lake in Florida, USA. Model estimates of gizzard shad exploitation rate were similar to an independent estimate from an in-season depletion analysis. Estimates of gizzard shad natural mortality and growth parameters were within the range of literature values for the species. The model could be useful for estimating growth, mortality, and recruitment parameters that account for gear selectivity and the cumulative effects of size-selective harvest. [Copyright &y& Elsevier]

Abstract: In this work, we develop a lake eutrophication model to determine restoration policies for water quality improvement. This hybrid biogeochemical model has been formulated within a simultaneous dynamic optimization framework as an optimal control problem, whose solution provides limiting nutrient inflow profiles to the lake, as well as in-lake biomanipulation profiles. The water quality model comprises a set of partial differential algebraic equations in time and space, which result from dynamic mass balances on main phytoplankton groups, nutrients, dissolved oxygen and biochemical demand of oxygen. Spatial discretization has been performed in two layers. The simultaneous approach proceeds by discretizing control and state variables by collocation over finite elements and solving the large scale nonlinear program with an interior point method with successive quadratic programming techniques. [Copyright &y& Elsevier]

Abstract: A large-scale enclosure experiment for lake restoration was carried out in Lake Wuli, a northern bay of shallow and eutrophic Lake Taihu in China. The large enclosure with an area of 10ha was set up in the littoral zone and was bordered by waterproof fabric which did not cover the sediments. Multiple approaches were used and included fish removal, piscivorous fish stocking, shoreline reconstruction, aquatic macrophyte planting, benthic macro-animal stocking, and silver carp cultivation in pens for reduction of cyanobacteria. The results showed that the coverage of aquatic macrophytes increased from 0% to 45.7%. Mean concentrations of TN and TP inside the enclosure from May 2004 to May 2008 were 22.2% and 26.0% of those outside, respectively. Secchi depth was 0.40m outside the enclosures and 0.75m inside. However, responses of phytoplankton to the restoration project lagged behind improvement of water quality and reestablishment of aquatic plants. The phytoplankton biomass gradually decreased after the third year of the restoration. Stocking piscivorous fish and planting submerged macrophytes could not increase zooplankton biomass and enhance graze pressure on phytoplankton, most likely due to high omnivorous fish density and lower nutrition inside the enclosure. Higher grazing pressure of zooplankton on phytoplankton was observed in May and October every year. Zooplankton to phytoplankton biomass ratios were significantly negatively correlated with phytoplankton biomass outside (r =−0.440, p <0.01) and inside the enclosure (r =−0.336, p <0.05) from February 2004 to March 2007. Therefore, phytoplankton biomass inside and outside the enclosure was lower in May and October. Higher grazing pressure of zooplankton on phytoplankton in spring may result in occurrence of the clear-water phase that facilitated growth of submerged macrophytes in the littoral in Lake Wuli, and a clear-water state and improved water quality would likely be sustained throughout the year after reestablishment of submerged macrophytes. [Copyright &y& Elsevier]

Abstract: Silver and bighead carp were stocked in a large pen to control the nuisance cyanobacterial blooms in Meiliang Bay of Lake Taihu. Plankton abundance and water quality were investigated about once a week from 9 May to 7 July in 2005. Biomass of both total crustacean zooplankton and cladocerans was significantly suppressed by the predation of pen-cultured fishes. There was a significant negative correlation between the N:P weight ratio and phytoplankton biomass. The size-selective predation by the two carps had no effect on the biomass of green alga Ulothrix sp. It may be attributed to the low fish stocking density (less than 40gm−3) before June. When Microcystis dominated in the water of fish pen, the pen-cultured carps effectively suppressed the biomass of Microcystis, as indicated by the significant decline of chlorophyll a in the >38μm fractions of the fish pen. Based on the results of our experiment and previous other studies, we conclude that silver and bighead carp are two efficient biomanipulation tools to control cyanobacterial (Microcystis) blooms in the tropical/subtropical eutrophic waters. Moreover, we should maintain an enough stocking density for an effective control of phytoplankton biomass. [Copyright &y& Elsevier]

Abstract: This paper reports on seasonal changes in stable carbon and nitrogen isotope ratios of seston and muscle tissue of silver carp and bighead carp during 2004 and 2005, focusing primarily on the carbon sources and trophic relationships among phytoplankton, zooplankton and silver carp and bighead carp in a large fish pen of Meiliang Bay (Lake Taihu, China). δ 13C showed a minimal value in March 2005 and a maximal value in August 2005 in seston both inside and outside the pen, whereas δ 15N of seston showed the minimum in winter and the maximum during algal blooms. A positive correlation between δ 13C of silver carp and that of seston suggested that temporal variation of δ 13C in seston was preserved in fish via the food chain. The differences of δ 13C among seston, zooplankton and muscle tissue of silver carp and bighead carp ranged only 0.2–1.7%, indicating that plankton production was the primary food source of filter-feeding fishes. According to a mass balance model, we estimated that the contributions of zooplankton to the diets of silver carp and bighead carp were 45.7% and 54.3%, respectively, based on the δ 15N values of zooplankton and planktivorous fishes. [Copyright &y& Elsevier]

[Display omitted] • Widespread contamination of PFASs was found in environmental compartments in Wuliangsuhai Lake. • Biomanipulation through species introduction changed food web structure in Wuliangsuhai Lake. • Lower concentrations of PFASs in fish species were observed in biomanipulation area in Wuliangsuhai Lake. • Biomanipulation through species addition increased trophic magnification factors of PFASs. Manipulation of freshwater food web through species introduction has been used to control the increasing algae in the Wuliangsuhai Lake, which affects not only the pathways of carbon source and energy transfer, but also the transfer of contaminants through food web. Food web relationships between biomanipulation area (BMA) and non-biological manipulation area (NBMA) were investigated using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis. In BMA, the δ13C values in fish species were enriched while δ15N depleted due to the increased inter-species competition. Among the same fish species between BMA and NBMA, lower trophic levels were observed in BMA. Concentrations of target PFASs (ΣPFAS) in fish from BMA were significantly (p < 0.05) lower than those from NBMA. Whilst elevated trophic magnification factors (TMFs) of PFASs, especially for perfluoroalkyl carboxylic acids (PFCAs) with long carbon chain length (C9-10), perfluorooctane sulfonate (PFOS), and 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) were exhibited in BMA. We found that biomanipulation through species introduction played an important role in control over lake eutrophication and trophic transfer patterns of PFASs in biota from the altered aquatic ecosystem. [ABSTRACT FROM AUTHOR]

Driven by global warming and eutrophication, Microcystis blooms have posed a severe threat to freshwater ecosystems, especially their derived pollutants cause serious harm to aquatic organisms, thus it is urgent to develop an effective strategy to eliminate nuisance Microcystis. Some protozoa can efficiently graze on toxic Microcystis aeruginosa and degrade cyanotoxins, and play a vital role in regulating harmful cyanobacteria. In the process of protozoa feeding on harmful algae, both temperature and protozoa population density are critical factors that affect the consequences of harmful M. aeruginosa population dynamics. In this study, we first found that Paramecium multimicronucleatum has strong ability to feed on M. aeruginosa , and then studied the interactive effects between temperature and initial density of P. multimicronucleatum on controlling M. aeruginosa. Results showed that increasing temperature accelerated the elimination of M. aeruginosa by P. multimicronucleatum , e.g. the time for M. aeruginosa elimination at 32 °C was shortened to 3.5–4 days. The higher temperatures (26, 29, and 32 °C) were more conducive to improve the efficiency of controlling M. aeruginosa by P. multimicronucleatum with low initial density (10 inds mL−1). Furthermore, P. multimicronucleatum can rapidly degrade microcystins, and the degradation ratio approximately 100% at 32 °C after 6 days. This is the first study to discover that P. multimicronucleatum can high efficiently graze on M. aeruginosa and has a much higher grazing rate (3.5–5.5 × 104 Microcystis Paramecium −1 d−1) than other protozoa. These findings contribute to the establishment of a new feasible method for the biological control of M. aeruginosa , and provide a theoretical guidance for the practical application of P. multimicronucleatum in the removal of M. aeruginosa. The removal of Microcystis aeruginosa and degradation of microcystins by Paramecium showed an initial density-dependent temperature effect. [ABSTRACT FROM AUTHOR]

Abstract: Water level fluctuations in a drinking water reservoir (Saidenbach Reservoir, Saxony, Germany) and length–frequency data of roach (Rutilus rutilus) derived from gillnet catches were studied over a period of eight succeeding years and subsequently analysed with respect to level change and cohort establishment. The results indicate a strong impact of water level on the year class strength of roach. Constantly high water level with large areas of inundated plants led to a very strong roach year class. Conversely, decreasing water level shortly after the spawning period was found to result in a total loss of the new roach year class. Any other possible factors influencing year class strength of roach (such as food, temperature, winter duration) may only play a role if the water level after spawning remained relatively stable. Consequently, water quantity management in reservoirs can be used as a biomanipulation tool to reduce the planktivorous fish stock and to improve water quality, which should be an interesting option especially in drinking water reservoirs. [Copyright &y& Elsevier]