Search

Introduction: Water depth (WD) and snail abundance (SA) are two key factors affecting the growth of submersed aquatic plants in freshwater lake ecosystems. Changes in WD and SA drive changes in nutrients and other primary producers that may have direct or indirect effects on submersed plant growth, but which factor dominates the impact of both on aquatic plants has not been fully studied. Methods: To investigate the dominant factors that influence aquatic plant growth in plateau lakes, a one-year field study was conducted to study the growth of three dominant submersed macrophyte (i.e., Vallisneria natans, Potamogeton maackianus, and Potamogeton lucens) in Erhai Lake. Results: The results show that, the biomass of the three dominant plants, P.maackianus, is the highest, followed by P.lucens, and V.natans is the lowest. Meanwhile, periphyton and snails attached to P.maackianus are also the highest. Furthermore, WD had a positive effect on the biomass of two submersed macrophyte species of canopy-type P.maackianus and P.lucens, while it had a negative effect on rosette-type V.natans. Snail directly inhibited periphyton attached on V.natans and thereby increasing the biomass of aquatic plants, but the effect of snails on the biomass of the other two aquatic plants is not through inhibition of periphyton attached to their plants. Discussion: The dominant factors affecting the biomass of submersed macrophyte in Erhai Lake were determined, as well as the direct and indirect mechanisms of WD and snails on the biomass of dominant submersed macrophyte. Understanding the mechanisms that dominate aquatic plant change will have implications for lake management and restoration. [ABSTRACT FROM AUTHOR]

Shallow freshwater ecosystems emit large amounts of greenhouse gases (GHGs), such as carbon dioxide (CO2) and methane (CH4), yet emissions are highly variable. The role that aquatic macrophytes play in regulating aquatic GHG emissions is uncertain despite their ability to dominate shallow waterbodies. Here, we studied the effects of submersed macrophyte (Ceratophyllum demersum) density on CO2 and CH4 concentrations and fluxes. We conducted a 61‐days experiment using mesocosms containing one of the following C. demersum density treatments: 0, 10, 20, or 30 individual shoots (n = 3). We found that high density C. demersum had the highest CO2 and CH4 surface water concentrations and emissions while there was no significant difference in CH4 in the low and medium densities and no plant control. The high density treatment lost biomass over the course of the experiment, indicating die‐off and additions of organic matter to the sediment. High organic matter loading and low dissolved oxygen likely stimulated GHG production in the high density treatment. Our results emphasize that submersed macrophyte density and periods of growth and dieback are important in regulating GHG emissions, which may help explain why shallow waterbodies are high yet variable sources of GHGs to the atmosphere. Plain Language Summary: Shallow freshwaters release large amounts of greenhouse gases. These shallow waterbodies are often dominated by submersed plants, yet the role these plants have in affecting greenhouse gas release is unclear. We conducted a 2‐months experiment to determine the effects of a submersed plant on two greenhouse gases, methane and carbon dioxide. We manipulated the number of plants (plant density) and measured gas release, gas concentrations in the water, plant growth, and several characteristics of water chemistry. When plants were most dense, we observed the greatest release of methane and carbon dioxide, likely due to competition and plant die‐off. Our results show the importance of plant growth and density on greenhouse gases. Key Points: In systems dominated by non‐rooting plants, plants may have a larger effect on water column CO2 and CH4 dynamics than on greenhouse gas production in the sedimentHigh density stands of a submersed macrophyte (Ceratophyllum demersum) emit more CO2 and CH4 than lower density standsPeriods of macrophyte growth and die‐off influence CO2 and CH4 dynamics [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hydrobiology / Shuisheng Shengwu Xuebao is the property of Editorial Department of Journal of Hydrobiology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Benthivorous fish disturbance and nitrogen loading are two important factors that influence the community structure of submersed macrophytes, but their interactive effect is not well elucidated. We conducted an outdoor mesocosm experiment to examine the individual and combined effects of these two factors on the growth of two submersed macrophytes of different growth forms, i.e., the rosette-forming Vallisneria natans and the canopy-forming Myriophyllum spicatum. The treatments involved two levels of fish (Carassius auratus) disturbance crossed with two levels (0 and 12 g NH4Cl per month) of ammonium (NH4+-N) loading. For M. spicatum, we found that maximum height (MH) was reduced by 30.7%, 26.4%, and 51.0% in fish addition alone (F) and nitrogen addition treatments (N, F + N), respectively, compared with the control (C) treatment. The density of M. spicatum declined by 20%, 62% and 68.8% in the F, N and F + N treatment. The above-ground biomass (AGB) of M. spicatum respectively reduced by 56.7%, 94%, and 96.5% in the F, N and F + N treatments, and the roots/shoots ratio (R/S) increased by 114%, and 176% in N and N + F treatments, respectively. Regarding V. natans, only the MH in the N treatment was reduced (71.9%), and the density exhibited a reduction of 59.1% and 64.5% in the N and F + N treatments, respectively. The AGB of V. natans was significantly lower in the N (90.3%) and N + F (78.4%) treatments compared with the C treatment, while increased by 60.3% in F treatment. The R/S of V. natans increased by 227%, and 74.4% in the N and F + N treatments compared with the C treatment. The interactive effect of fish disturbance and high N on MH and AGB of V. natans and density of M. spicatum were antagonistic. However, the interactive effect on density and BGB of V. natans and AGB of M. spicatum were negatively synergistic. Moreover, fish activity significantly increased the concentration of total suspended solids (TSS) in the water, while total nitrogen (TN), ammonium, total phosphorus (TP), light, pH and salinity were unaffected. When fish and nitrogen were combined, TN, TP, TSS and salinity increased significantly, while pH decreased. Our study reveals that the interactive effects of fish disturbance and high N are synergistic and/or antagonistic, suggesting that the same stressor interaction may vary from synergistic to antagonistic depending on the response variables and growth forms of the macrophytes examined. Our study contributes to the understanding of how different factors can interact with each other and affect submersed macrophytes in aquatic ecosystems. This is timely and relevant knowledge, considering the range of multiple stressors involved in the decline of aquatic ecosystems worldwide at present.

Ammonium (NH4-N) produces a paradoxical effect on submersed macrophytes because it is not only the preferred nitrogen source for the growth of plants but also threatens the growth of plants at high concentration. Whether short-term and smallscale physiological toxicity experiments at an individual level can reflect the effects of high ammonium on populations of submersed macrophytes in natural conditions is still unclear. In this study, an 18-month experiment was conducted in six 600 m2 ponds subjected to different levels of ammonium loading. The effects of high ammonium on populations of canopy-forming Myriophyllum spicatum and rosette-forming Vallisneria natans were explored. The results showed that M. spicatum and V. natans populations can develop high cover and height at high ammonium concentration (7 mg/L) at shortterm exposures, and V. natans may be tolerant to 18 mg/L ammonium concentration. However, the cover of M. spicatum and the height of both species were inhibited at 2.4 mg/L at long-term exposures. The height of M. spicatum was two to six times higher than that of V. natans across all treatments and control by the end of the experiment, and the cover of M. spicatum was 7-11 times higher than that of V. natans in most NH4-N loading treatments, except the cover of M. spicatum in the highest NH4-N loading treatment with 18 mg/L NH4-N. The rosette-forming V. natans resists ammonium stress by slow growth (shoot elongation) to reduce consumption, while canopy-forming species resist ammonium stress by shoot elongation and canopy development to capture light. Although increasing ammonium concentration may induce severe stress on M. spicatum, the morphological characteristics of this species may, to some extent, release the plants from this stress. Our present study indicates that the negative effects of ammonium stress on the development of populations increased with exposure duration, and the submersed macrophyte community with stronger ability for light capture and dispersal may resist high ammonium stress. Nevertheless, in strongly ammonium-enriched systems, competition and succession cannot be neglected. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hydrobiology / Shuisheng Shengwu Xuebao is the property of Editorial Department of Journal of Hydrobiology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Hydrobiology / Shuisheng Shengwu Xuebao is the property of Editorial Department of Journal of Hydrobiology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract The knowledge about the impacts of ammonium loading on microbial food webs in biofilms attached to submersed macrophytes is limited. In the present study, Illumina sequencing method was employed to investigate bacterial and eukaryotic communities in biofilms attached to leaves of Vallisneria natans (V. natans) exposed to 1–16 mg L−1 NH 4 +-N for 10 days, and 8 mg L−1 NH 4 +-N for 21 days. Ammonium loading stimulated biofilms growth, enhanced the relative abundance of nitrifying genus Nitrospira and several denitrifying genera. Eukaryotic kingdom Metazoa, Viridiplantae, Chromista, Fungi and super group SARNU (Stramenopiles, Alveolata, Rhizaria, Nucleariidae and Fonticula group and unknown eukaryotes) were obtained. Relative abundance of Metazoa decreased with the increased ammonium concentration and exposure time. Redundancy analysis revealed that ammonium, dissolved oxygen (DO) and pH had a key role in determining microbial community structure. Network analyses revealed that there were complex interactions including feeding, parasitism and predatism among organism in biofilms, and the microbial food webs were disturbed by inhibiting metazoan growth but stimulating bacteria and algae growth. These results suggest that ammonium-disturbed microbial food webs in biofilms may contribute to the growth of biofilms and algae, and thus contribute to the decline of submersed macrophyte and provide "algal seeds" for the algae burst in water column. These data will be helpful in understanding the macrophytic region transform into algal region in water column polluted by ammonium. Graphical abstract Unlabelled Image Highlights • Ammonium increased relative abundances of nitrifiers and denitrifiers in biofilms. • Ammonium decreased relative abundance of Metazoa in biofilms. • Ammonium stimulated the growth of algae in biofilms. • Ammonium altered microbial food web in biofilms attached to leaves of plants. [ABSTRACT FROM AUTHOR]

Due to excess nutrient loading, loss of submersed macrophytes is a worldwide phenomenon in shallow lakes. Phosphorus is known to contribute significantly to macrophyte recession, but the role of nitrogen has received increasing attention. Our understanding of how high nitrogen concentrations affect the growth of submersed macrophytes, particularly under natural conditions, is still limited. In this study, we conducted experiments with canopy-forming Potamogeton crispus in 10 ponds subjected to substantial differences in nitrogen loading (five targeted total nitrogen concentrations: control, 2, 10, 20, and 100 mg L-1) and compared the results with those of our earlier published experiments with rosette-forming Vallisneria natans performed 1 year before. Canopy-forming P. crispus was more tolerant than rosette-forming V. natans to exposure to high NH4 concentrations. This is probably because canopy-forming species reach the water surface where there is sufficient light for production of carbohydrates, thereby allowing the plants to partly overcome high NH4 stress. Both the canopy-forming P. crispus and the rosette-forming V. natans showed clear declining trends with increasing chlorophyll a in the water. Accordingly, shading by phytoplankton might be of key importance for the decline in submersed macrophytes in this experiment. Both experiments revealed free amino acids (FAA) to be a useful indicator of physiological stress by high ammonium but is not a reliable indicator of macrophyte growth.

Due to excess nutrient loading, loss of submersed macrophytes is a worldwide phenomenon in shallow lakes. Phosphorus is known to contribute significantly to macrophyte recession, but the role of nitrogen has received increasing attention. Our understanding of how high nitrogen concentrations affect the growth of submersed macrophytes, particularly under natural conditions, is still limited. In this study, we conducted experiments with canopy-forming Potamogeton crispus in 10 ponds subjected to substantial differences in nitrogen loading (five targeted total nitrogen concentrations: control, 2, 10, 20, and 100 mg L-1) and compared the results with those of our earlier published experiments with rosette-forming Vallisneria natans performed 1 year before. Canopy-forming P. crispus was more tolerant than rosette-forming V. natans to exposure to high NH4 concentrations. This is probably because canopy-forming species reach the water surface where there is sufficient light for production of carbohydrates, thereby allowing the plants to partly overcome high NH4 stress. Both the canopy-forming P. crispus and the rosette-forming V. natans showed clear declining trends with increasing chlorophyll a in the water. Accordingly, shading by phytoplankton might be of key importance for the decline in submersed macrophytes in this experiment. Both experiments revealed free amino acids (FAA) to be a useful indicator of physiological stress by high ammonium but is not a reliable indicator of macrophyte growth. [ABSTRACT FROM AUTHOR]

Phytomass and specific diversity of macrophytes of the Yenisei River on the stretch from Krasnoyarsk to the mouth of the Angara River were estimated. The investigation showed that littoral macrophyte vegetation clearly differs in specific composition and biomass in the deep water (H>0,8 m) and shallow water (H

Loss of submersed macrophytes is a world-wide phenomenon occurring when shallow lakes become eutrophic due to excess nutrient loading. In addition to the well-known effect of phosphorus, nitrogen as a trigger of macrophyte decline has received increasing attention. The precise impact of high nitrogen concentrations is debated, and the role of different candidate factors may well change over the season. In this study, we conducted experiments with Vallisneria natans during the growing season (June–September) in 10 ponds subjected to substantial differences in nitrogen loading (five targeted total nitrogen concentrations: control, 2, 10, 20, and 100 mg L − 1 ) and compared the results with those obtained in our earlier published study from the low-growth season (December–April). Like in the low-growth season, growth of V. natans in summer declined with increasing ammonium (NH 4 ) concentrations and particularly with increasing phytoplankton chlorophyll a (Chl a Phyt ). Accordingly, we propose that shading by phytoplankton might be of key importance for macrophyte decline, affecting also periphyton growth as periphyton chlorophyll a (Chl a Peri ) decreased with increasing Chl a Phyt . Free amino acid contents (FAA) of plants tended to increase with increasing NH 4 concentrations, while the relationships between FAA with growth indices were all weak, suggesting that FAA might be a useful indicator of the physiological stress of the plants but not of macrophyte growth. Taken together, the results from the two seasons indicate that although a combination of high nitrogen concentrations (ammonium) and shading by phytoplankton may cause severe stress on macrophytes, active growth in the growing season enabled them to partly overcome the stress. [ABSTRACT FROM AUTHOR]

Evaluating plant community response to atmospheric CO2 rise is critical to predicting ecosystem level change. Freshwater lakes offer a model system for examining CO2 effects as submersed macrophyte species differ greatly in their growth responses to CO2 enrichment, and free CO2 concentrations among these habitats show a wide range of natural, spatial variation. We determined free CO2 concentrations in the water column and sediment porewater in littoral zones with pH < 6.0 in Adirondack Mountain (New York, USA) lakes, and derived a community CO2 responsiveness index (CCRI) based on quantitative sampling of 15 submersed macrophyte communities coupled with greenhouse-derived growth responses to CO2 enrichment of constituent species to test two hypotheses: (1) CCRI, which is higher for communities dominated by species with greater growth responses to CO2 enrichment, is positively correlated to free [CO2] in the water column, and (2) in natural communities, the percent of sediment CO2-using species, which are relatively unresponsive to CO2 enrichment, is negatively correlated to free [CO2]. A significant positive correlation ( P = 0.003) between our physiologically based CCRI and the concentration of free CO2 in the water column supported our primary hypothesis that sites with higher levels of free CO2 are dominated by species with greater growth responses to CO2 enrichment. Our CCRI is also highly significantly correlated ( P < 0.001) to the first axis scores for the same vegetation data from polar ordination. Finally, the relative importance of species that use sediment CO2 as a photosynthetic carbon source is significantly negatively correlated ( P = 0.029) with the concentration of free CO2 in the water column. Our results indicate that natural variations in CO2 levels are important determinants of submersed macrophyte community composition. Further, we demonstrate the utility of a physiologically-based index of community composition, our CCRI, as an ecologically valid measure of community response to CO2. [ABSTRACT FROM AUTHOR]

The Chinese mitten crab ( Eriocheir sinensis (H. Milne Edwards, 1854)), is a highly invasive species and poses a great threat to endemic species and infrastructure in Europe and North America. Although it is partly herbivorous and prefers to live in lakes with abundant submersed macrophytes, little is known about its effect on macrophytes. We used its native range, the mid-lower Yangtze Basin where the species has been cultured intensively for decades, as our study site to test the hypotheses that (1) high crab densities weaken the positive feedback between macrophytes and water transparency, and that (2) the effects of crabs become apparent only on decadal timescales and (3) are density dependent. We used correlative analyses based on 12 years of monitoring and multi-lake comparisons among 20 sub-areas in 4 lakes. High crab densities were found to cause negative effects on submersed macrophytes and transparency, and to weaken the positive relation between macrophytes and transparency. High densities of macrophytes showed resilience to disturbance from crabs. This resilience, however, reduced with continuous presence of high crab densities. Crab densities were strongly positively related with total phosphorus and negatively with transparency and total nitrogen. Phosphorus concentrations and transparency were not related with phytoplankton chlorophyll a , suggesting that crab’s bioturbation strongly influences water quality. The apparent resilience of the dense macrophyte stands should however, not delay attempts to eradicate the crab where it is invasive as this becomes more difficult once they have become established. When macrophyte abundance is already low at the time of invasion, immediate loss of macrophytes may occur. [ABSTRACT FROM AUTHOR]

The present study was carried out to determine the efficacy of root foraging and the physiological response of Vallisnaria natans grown in heterogeneous sediments. V. natans was cultivated in two homogeneous and two heterogeneous sediments. The results suggested that V. natans grown in heterogeneous sediments presented a significantly higher root proportion in its total biomass, exhibited root foraging, and grew well, as indicated by a total biomass, ramet number, and plant height very close to those of plants grown in nutrient-rich clay sediment. Moreover, the more sensitive physiological response of the roots than the stems or the leaves to sediment nutrients suggested that root foraging occurred, and the approached values between the two heterogeneous sediments and the homogeneous clay sediment indicated that V. natans could satisfy its nutrient requirements via root foraging. The results may be useful in the recovery of macrophytes that remodel part (rather than all) of the substrate and can potentially improve habitats that are unsuitable for plant growth. [ABSTRACT FROM AUTHOR]

In aquatic ecosystems, ecological processes such as organic matter mineralization and nutrient cycling are regulated by benthic O 2 in sediments, and application of in situ techniques in field environments has the potential to better define the links between O 2 dynamics and the unique biogeochemical phenomena occurring in these regions. The effects of benthic O 2 on sediment nutrients release were identified on the basis of field specific observations conducted over one and a half years at Taihu Lake. Sediment dredging (SD) practices have sharply reworked the benthic boundary oxidation layer, and the oxygen penetration depth (OPD) in the SD responded as expected to the new-born surface, increasing immediately (7.5 ± 0.8 – 10.5 ± 0.6 mm) after dredging, then further increasing with an unusually high heterogeneity when a significant submersed macrophytes (SM) coverage of about 40% was implemented. Multiple correlation analysis revealed that OPD was responsible for PO 4 3− and NH 4 + release. A lower benthic oxygen flux was immediately observed in dredging-related sediments in the case of dredging compared to SM or the control (CK), which suggested that oxygen demand is low in the uppermost sediments because of the degradable fresh organic carbon removal. SD and SDSM implementation was most successful at continuously reducing the size of PO 4 3− released from sediments over one and a half years, and a significant seasonal-dependent release was also observed. The direction of flux was consistent among SD and SDSM, suggesting the potential to reduce internal PO 4 3− release even further with the invasion of SM communities. Our results indicated that ecological engineering practices could alleviate internal nutrient loads from the contaminated bottom sediment, which was probably in positive response to benthic oxygen changes. [ABSTRACT FROM AUTHOR]

For submersed macrophytes, carbon (C) and nitrogen (N) metabolism is a central factor affecting growth and survival under low light availability. Three common submersed macrophytes, Vallisneria natans , Potamogeton maackianus , and Potamogeton malaianus , were grown at five water depths (1.0, 2.5, 4.0, 5.5, and 7.0 m) to explore mechanism of low light adaptation in terms of C/N metabolism by examining relative growth rate (RGR) and contents of soluble carbohydrate (SC), starch, total carbon (TC), free amino acid (FAA) and total nitrogen (TN) in leaf, stem and root of the plants. With increasing water depth, P. malaianus , P. maackianus and V. natans initiated dying at 4.0 m, 5.5 m and 7.0 m water depths, respectively. V. natans showed higher RGR than the other two species. For all the plants, the FAA contents increased with increasing water depth, except for the roots of P. maackianus . The TN contents showed a unimodal curve along water depths with the highest in moderate water depth, except for P. malaianus and the roots of V. natans . For V. natans and P. maackianus, the C metabolic indices (SC, starch, and TC) showed a unimodal curve along water depths with the lowest in moderate water depth in the leaves and stems, except for TC contents in the leaves of P. maackianus . Compared with P. maackianus and P. malaianus , lower SC and FAA contents and higher starch storage in V. natans contributed to its higher tolerance to deeper depths. The nonlinear changes in metabolite contents along water depths for V. natans and P. maackianus demonstrated complex mechanism for low light adaptation, and thus partly explained the wider ranges of colonizing water depths than P. malaianus . [ABSTRACT FROM AUTHOR]

Eutrophication of lakes leading to loss of submersed macrophytes and higher turbidity is a worldwide phenomenon, attributed to excessive loading of phosphorus (P). However, recently, the role of nitrogen (N) for macrophyte recession has received increasing attention. Due to the close relationship between N and P loading, disentanglement of the specific effects of these two nutrients is often difficult, and some controversy still exists as to the effects of N. We studied the effects of N on submersed macrophytes represented by Vallisneria natans (Lour.) Hara in pots positioned at three depths (0.4 m, 0.8 m, and 1.2 m to form a gradient of underwater light conditions) in 10 large ponds having moderate concentrations of P (TP 0.03 ± 0.04 mg L −1 ) and five targeted concentrations of total nitrogen (TN) (0.5, 2, 10, 20, and 100 mg L −1 ), there were two ponds for each treatment. To study the potential shading effects of other primary producers, we also measured the biomass of phytoplankton (Chl a Phyt ) and periphyton (Chl a Peri ) expressed as chlorophyll a . We found that leaf length, leaf mass, and root length of macrophytes declined with increasing concentrations of TN and ammonium, while shoot number and root mass did not. All the measured growth indices of macrophytes declined significantly with Chl a Phyt , while none were significantly related to Chl a Peri . Neither Chl a Phyt nor Chl a Peri were, however, significantly negatively related to the various N concentrations. Our results indicate that shading by phytoplankton unrelated to the variation in N loading and perhaps toxic stress exerted by high nitrogen were responsible for the decline in macrophyte growth. [ABSTRACT FROM AUTHOR]

The ecological responses of aquatic macrophytes and benthic macroinvertebrates to deep-release dams in three impounded rivers of the Henares River Basin (Central Spain) were studied, specially focusing on the effects of nutrient enrichment caused by deep releases on these two freshwater communities. Three sampling sites, one upstream and two downstream from the reservoir, were established in each impounded river. Sampling surveys to collect submersed macrophytes and benthic macroinvertebrates at each sampling site were carried out in spring-summer of 2009 and 2011. Water temperature tended to decrease downstream from dams, whereas nitrate and phosphate concentrations tended to increase. These abiotic changes, particularly the downstream nutrient enrichment, apparently affected the macrophyte and macroinvertebrate communities. In the case of submersed macrophytes, total coverage and taxa richness increased downstream from dams. In the case of benthic macroinvertebrates, total density and total biomass also increased downstream, but taxa richness tended to decrease. Scrapers appeared to be the macroinvertebrate feeding group most favored downstream from dams as a probable consequence of the positive effect of nutrient enrichment on periphyton and perilithon abundance. Nutrients would ultimately come from water runoff over agricultural lands and over semi-natural forests and pastures, being subsequently accumulated in the hypolimnion of reservoirs. [ABSTRACT FROM AUTHOR]

Strategies of carbon (C) and nitrogen (N) utilisation are among the factors determining plant distribution. It has been argued that submersed macrophytes adapted to lower light environments are more efficient in maintaining C metabolic homeostasis due to their conservative C strategy and ability to balance C shortage. We studied how depth distributions of 12 submersed macrophytes in Lake Erhai, China, were linked to their C-N metabolic strategies when facing acute [ABSTRACT FROM AUTHOR]

Highlights: [•] Fluoride and turbidity levels significantly increased downstream from the effluent. [•] Macrophytes exhibited slighter ecological responses than macroinvertebrates. [•] Fluoride was significantly bioaccumulated in macrophytes and macroinvertebrates. [•] The amphipod Echinogammarus calvus was very sensitive to fluoride toxicity. [•] This sensitivity would be due to its great capacity to take up and retain fluoride. [Copyright &y& Elsevier]

Bicarbonate plays a crucial role in limiting the growth of submersed aquatic macrophytes in eutrophic lakes, and high ammonia is often toxic to macrophytes. In order to evaluate the combined effect of HCO and total ammonia (i.e., the total of NH and NH) on submersed macrophytes Vallisneria natans, the growth and physiological response of V. natans in the presence of HCO and ammonia were studied. The results showed that with the increase of ammonia, morphological parameters of V. natans declined. In contrast, increased HCO concentration stimulated the growth of V. natans, especially when the NH-N/NO-N ratio was 1:7. High ammonia concentration induced excess free amino acids (FAA) accumulation and soluble carbohydrates (SC) depletion in plant tissues. However, the elevated HCO promoted the synthesis of SC and rendered the decrease of FAA/SC ratio. The results also suggested that HCO could partially alleviate the stress of ammonia, as evidenced by the decrease of FAA/SC ratio and the growth enhancement of V. natans when the ammonia concentration was 0.58 mg L. Given the fact that HCO is probably the dominant available carbon source in most eutrophic lakes, the ability of V. natans to use HCO for SC synthesis may explain the alleviating effect of HCO on V. natans under ammonia stress. [ABSTRACT FROM AUTHOR]

To map the aquatic vegetation of Bavarian (Germany) freshwater lakes in a large-scaled and quick way, remote sensing is a helpful tool. For interpretation of the data, a spectral library of different macrophyte and sediment reflectances is under development. Therefore. multi-temporal in situ remote sensing reflectances were sampled from May to October 2011 with hyperspectral RAMSES spectroradiometers. Occurring spectral variations during the growing season could be linked to biometric and phenological data of the particulate species. Principal component analyses showed that, by applying the presented method, differentiation of the macrophytes from sediment and among each other is possible and can be improved by multi-temporal data. [ABSTRACT FROM PUBLISHER]

The relationships between relative growth rate and its components across 11 submersed macrophytes were examined in a short-term experimental study. Plants were grown in identical conditions in pots that were submersed in tanks. The average values for relative growth rate ranged from 17.4 to 94.5mg g-1d-1. The net assimilation rate, based on the increase in plant dry weight per unit leaf area in a fixed time, varied fivefold among species and showed a strong, positive correlation with relative growth rate. The leaf area ratio, leaf mass ratio, and specific leaf area were not significantly correlated with the relative growth rate, although these parameters were important in the adaptive responses of macrophytes to environmental stress. These results suggest that the physiological components (net assimilation rate) would be the main determinant of relative growth rate in submersed macrophytes, which highlights the importance of net assimilation rate in explaining differences in macrophyte species performance in freshwater habitat. [ABSTRACT FROM AUTHOR]

Seasonal variations in the abundance of cyanobacteria and catch per unit effort (CPUE) of bluegill (Lepomis macrochirus) were investigated in Lake Biwa of Japan. High CPUE occurred from late spring to autumn when cyanobacteria dominated the community of photosynthetic plankton. However, the CPUE decreased substantially when the population density of cyanobacteria increased dramatically within an hour. Seasonal variation in the body weight of the fish with a fixed length was estimated from the length-weight relationships, revealing that body weight increased rapidly in early spring and reached its first peak in late spring, eventually decreasing in autumn after reaching the second peak. In May, bluegill fed on extremely large numbers of Bosmina longirostris when it dominated the zooplankton community. From June, the main diet of the bluegill became epiphytic filamentous green algae, which are the competitors for cyanobacteria. The biomass of submersed macrophytes in Lake Biwa has increased recently, potentially affecting cyanobacteria adversely since submersed macrophytes release allelochemicals and provide a habitat for cladocerans. However, propagation of submersed macrophytes also benefits bluegill, possibly contributing to the dominance of cyanobacteria by reducing the amounts of cladocerans and epiphytic algae. [ABSTRACT FROM AUTHOR]

The necessity of assessing the accuracy of spatial data derived from remote sensing methods and used in geographic information system (GIS) analyses has been regarded as a critical component of many projects. In this article, supervised classified QuickBird satellite imageries of submersed macrophytes of the Gavaraget region of Lake Sevan (Armenia) during 2006-2008 are validated in a GIS environment. The results of this assessment are represented by error matrices presenting the overall accuracy, the user and producer accuracies in each category, as well as the kappa coefficients. The assessments were done at three levels: the vegetation types, the growth (vertical) type, and the species levels. At the vegetation level, an overall accuracy of more than 86% was achieved in 2006 and 2007, while that in 2008 was about 72%. Substantial agreements were achieved between the classified remote sensing data and the reference (groundtruth) data for both 2006 and 2007. Only a fair agreement was attained in 2008. The kappa coefficients ranged from 0.39 to 0.89. At the growth type level, only the 2006 classification attained a substantial agreement, with an overall accuracy of 80%. The 2007 and 2008 classifications had above average and average overall accuracies of 72 and 64%, respectively. The kappa coefficient had a lowest value of 0.35 and a highest value of 0.70 at the growth type level. At the species level, Chara spp . or Zannichellia palustris and Potamogeton pectinatus had high user accuracies of more than 90% and a high overall accuracy of 82% in 2006. High user accuracies (>80%) occurred for P. pectinatus (for 2007 and 2008) and No Vegetation (for 2007). The remaining species, however, had low user and producer accuracies of less than 64%. The kappa coefficients ranged between 0.36 and 0.73 at the species level. [ABSTRACT FROM AUTHOR]

The Common Carp ( Cyprinus carpio) is an exotic benthivorous fish that can have negative impacts in aquatic ecosystems. This study examines the direct and indirect ecological impacts of Common Carp on water column nutrient concentrations, suspended solids, sedimentation, and submersed macrophytes in large (5–7 ha) experimental wetlands in Delta Marsh, Manitoba, Canada. In general, the effects of Common Carp on water quality were similar to those encountered in systems undergoing cultural eutrophication. With increasing densities of Common Carp, water column nutrient concentrations, suspended solids, and chlorophyll a increased while dissolved oxygen concentrations, submersed macrophyte density, and photic depth decreased. The wetlands did not become noticeably more turbid, contrary to our expectation, probably due to the mitigating effects of dense submersed macrophyte beds, and to high water color that likely prevented phytoplankton from flourishing. [ABSTRACT FROM AUTHOR]

The Upper River Paraná Floodplain System comprises the rivers Ivinheima, Baía and Paraná, which with their associated waterbodies form three subsystems, each showing individual characteristics. Hydrilla verticillata recently invaded the Upper Paraná Floodplain, while Egeria najas is the native most abundant submersed macrophyte. A large flood-pulse, during January–March 2007, abruptly reduced macrophyte stands in many areas to near-zero and dispersed propagules over the entire floodplain. From April 2007 to April 2008, we conducted three surveys sampling for the presence–absence of H. verticillata and E. najas and environmental variables aiming to answer: (1) How rapid is the colonization–regeneration process for both species? (2) Which habitats seem to be more susceptible to their colonization? (3) Which environmental factors can best predict their occurrence? Neither H. verticillata nor E. najas colonized the Ivinheima subsystem. In the Baía subsystem, E. najas had only two occurrences while H. verticillata was not present. In the Paraná subsystem, E. najas predominantly occurred in river channels, but it was also common in floodplain lakes. In April 2007, it was found in 13% of the sites in the Paraná subsystem, increasing to 30% in November 2007 and reaching 34% in April 2008. H. verticillata did not successfully colonize floodplain lakes of the Paraná subsystem. In channels, it had 34% occurrence in April 2007, increasing to 62% in November 2007 and remaining at 62% in April 2008. The role of environmental variables in predicting species occurrence changed depending upon the scale of the analysis. Considering the whole Upper Paraná floodplain, water transparency followed by electrical conductivity were the strongest predictors for both species. Colonization by submersed plants seems improbable in the Ivinheima subsystem owing to its low water transparency besides frequent localized floods; in the Baía subsystem, it seems inhibited by transparency and low alkalinity. Considering just the Paraná subsystem, the proportion of organic matter in sediment, ten times higher in floodplain lakes than in channels, was the best predictor for H. verticillata occurrence (also related to water pH and transparency), while E. najas was only significantly explained by transparency. [ABSTRACT FROM AUTHOR]

In this study the effects of common carp (Cyprinus carpio) on water transparency, chlorophyll a, macrophyte, phytoplankton and zooplankton densities, and nutrients were examined for a six-week period in a shallow Turkish soda lake with the use of enclosures. Four fish-flee and four fish enclosures were constructed in the lake. Fish enclosures contained approximately 1000 kg/ha1 of common carp. Physico-chemical and biological variables of the lake were measured at the beginning and the end of the experiment. Common carp caused significant increases in turbidity and chlorophyll a levels and decreases in macrophyte density. Carp had no effect on total phosphorus, nitrate or ammonium. [ABSTRACT FROM AUTHOR]

Abstract: The toxicological sensitivity and variability of a range of macrophyte endpoints were statistically tested with data from chronic, non-axenic, macrophyte toxicity tests. Five submersed freshwater macrophytes, four pesticides/biocides and 13 endpoints were included in the statistical analyses. Root endpoints, reflecting root growth, were most sensitive in the toxicity tests, while endpoints relating to biomass, growth and shoot length were less sensitive. The endpoints with the lowest coefficients of variation were not necessarily the endpoints, which were toxicologically most sensitive. Differences in sensitivity were in the range of 10–1000 for different macrophyte-specific endpoints. No macrophyte species was consistently the most sensitive. Criteria to select endpoints in macrophyte toxicity tests should include toxicological sensitivity, variance and ecological relevance. Hence, macrophyte toxicity tests should comprise an array of endpoints, including very sensitive endpoints like those relating to root growth. [Copyright &y& Elsevier]

This study investigated the interactions of submersed plants with environmental factors using structural equation modeling (SEM) and evaluated the effect strength of respective factors in an aquatic ecosystem using a data set collected at a fourth order stream in Japan. A model that simultaneously examines the relative importance of factors of the system has developed. The investigated factors included plant biomass (Biomass) of submersed macrophytes ( Potamogeton malaianus and Potamogeton oxyphyllus) and other environmental factors, i.e. water velocity and water depth (Hydraulic), pore water nitrogen (TNL), pore water phosphorus (TPL), sediment organic matter (Organic) and sediment particle size (Texture). The estimated model showed that the Biomass was negatively correlated with Hydraulic but positively correlated with Organic whilst TNL and TPL affected the Biomass with almost equal strength. The effects caused by Hydraulic to Texture were greater than the ones caused by Biomass. At the narrow ranges of water velocity (0–7 cm s−1) and shallow depth (0–35 cm), the effect of wash-away of Organic by Hydraulic were smaller than the retention effect of Organic by Biomass. These results provide more insights into interactions of the submersed macrophytes with environmental factors. [ABSTRACT FROM AUTHOR]

American wildcelery (Vallisneria americana Michx.) is a valuable submersed aquatic plant that was negatively affected by pollution and urban runoff in the lower Detroit River for much of the 20th century. Following 25 years of water-pollution and urban-runoff abatement initiated in the early 1970s, we postulated that water clarity had increased and that this would allow restoration of wildcelery in the lower Detroit River. In addition, water clarity increased in the late 1980s due to water filtration and particulate removal by exotic dreissenid mussels (Dreissena polymorpha and D. bugensis), which could contribute to potential wildcelery restoration. We sampled wildcelery in 1996-97 and compared these data to wildcelery data from 1950-51 and 1984-85. Over the 48-year period of comparison, areal density of wildcelery tubers decreased 72% (from 51.2 million to 14.4 million tubers) between 1950-51 and 1984-85 then increased 251% (from 14.4 million to 50.5 million tubers) between 1984-85 and 1996-97. As a result, overall areal abundance was about the same in 1950-51 as in fall 1996-97. However, tuber densities in spring 1996 were similar to historical low abundances in springs of 1984-85. Then between spring and fall 1996, tuber densities increased 333% and remained relatively abundant through October 1997 indicating the beginning of the restoration of wildcelery in the lower Detroit River. In addition, we believe further reductions of turbidity through continued pollution-abatement programs and water filtration by dreissenid mussels combined with habitat protection and active management of wildcelery will contribute even further to the restoration of wildcelery in the Detroit River in the 21st century. [ABSTRACT FROM AUTHOR]

The submersed macrophyte Utricularia inflata (inflated bladderwort) is a recent invader of Adirondack Mountain lakes (NY, USA). A 15-week greenhouse experiment and a 7-week field experiment were conducted to test the hypothesis that this rootless species fundamentally changes sediment chemistry through its suppression of the native short-statured species, Eriocaulon aquaticum. E. aquaticum has an extensive root system that releases oxygen into the sediment. In greenhouse conditions, E. aquaticum raised the porewater redox potential of otherwise bare sediment from 25 to 324 mV, lowered the sediment porewater pH from 5.7 to 4.6, and depleted the dissolved inorganic carbon and ammonium concentrations in the sediment porewater by 68.4 and 96.0%, respectively ( P<0.001 for all four parameters). A cover of U. inflata over E. aquaticum, however, greatly reduced the latter’s effect on redox potential ( P<0.001), dissolved solutes ( P<0.001), and pH ( P<0.05). E. aquaticum biomass increased during the greenhouse experiment in the absence of U. inflata, but decreased in its presence ( P<0.001). Redox and growth rate results from the field experiment paralleled those from the greenhouse experiment. Our data suggest that U. inflata may change nutrient cycling in Adirondack lake ecosystems by reducing the growth of native isoetid macrophytes, such as E. aquaticum, and consequently altering key features of sediment chemistry. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the relationship between Charophytes and herbivorous waterbirds in the littoral zone of Lake Constance by quantifying their seasonal dynamics. The waterfowl extensively consumed Charophyte vegetation in shallower areas (<1m water depth) at the beginning of the winter season, while deeper regions were only used in late winter. By the end of winter, the waterfowl had almost completely depleted the available Charophyte biomass down to a water depth of approximately 2m (relative to average mean water level (AML)). Enclosure experiments revealed that senescence processes had a negligible influence on Charophytes biomass loss until early February. Coot, Red-crested Pochard and Pochard are the main avian Chara consumers in winter. Despite their great influence on biomass in winter, their influence on subsequent Charophyte regeneration is probably limited in Lake Constance, since Charophytes as typical pioneer species produce innumerable diaspores forming dense Charophyte meadows at a depth of between 1 and 4m every year. [Copyright &y& Elsevier]

Abstract: Submersed macrophytes in Yangtze lakes have experienced large-scale declines due to the increasing human activities during past decades. To seek the key factor that affects their growth, monthly investigations of submersed macrophytes were conducted in 20 regions of four Yangtze lakes during December, 2001–March, 2003. Analyses based on annual values show that the ratio of Secchi depth to mean depth is the key factor (50% of macrophyte biomass variability among these lakes is statistically explained). Further analyses also demonstrate that the months from March to June are not only the actively growing season for most macrophytes, but the key time the factor acts. Five key-time models yielding higher predictive power (r 2 reaches 0.75, 0.76, 0.77, 0.69 and 0.81) are generated. A comparison between key-time models and traditional synchronic ones indicates that key-time models have higher predictive power. Analyses of transparency thresholds during macrophyte growing season and the limitations of the models are presented. The models and other results may benefit the work concerning submersed macrophyte recovery in Yangtze lakes. [Copyright &y& Elsevier]

We conducted an analysis of dabbling duck food habits in the fall of 2002 and 2003 in the Heron Lake system. Gizzard contents of hunter-harvested birds were analyzed using the percent aggregate volume method to determine what food items were consumed and in what quantity. Curltop Ladysthumb (Polygonum lapathifolium) was the food item consumed most often (82.2%) and in the greatest volume (34.2 ml). Sago Pondweed (Stuckenia pectinata) was the only food item of which multiple plant parts were consumed. However, the seeds and tubers only comprised 1.27 and 0.07 of the total aggregate percent. [ABSTRACT FROM AUTHOR]

A model for vertical turbulent diffusion and stratification in a shallow lake with submersed macrophytes is formulated on the basis of a one-dimensional equation for production, transport, and dissipation of turbulent kinetic energy, coupled with a vertical heat transfer equation. Numerical solutions of the coupled equations allow simulation of the hourly variation of water temperature profiles in a shallow lake as a function of varying weather parameters. The model can be used to simulate water temperature and turbulent kinetic energy profiles in locations of a shallow lake with either dense macrophyte beds or relatively open water. The water temperature simulations are in good agreement with field data from a shallow lake. During the day, macrophyte beds are found to increase the strength of temperature stratification and to reduce the mixed layer depth compared to open water. Macrophyte beds are found to have relatively little effect on nighttime deepening of the mixed layer because of surface cooling. Lateral transport between open water and macrophyte beds of finite horizontal dimensions (patchiness) may limit the accuracy of one-dimensional transport models. Vertical diffusivity coefficient profiles found in this study may be useful to investigate mass transport in shallow lakes with macrophytes. [ABSTRACT FROM AUTHOR]

The submersed vegetation of mesotrophic, alkaline Chenango Lake in New York, USA, was monitored at two spatio-temporal scales: a 200 m2 grid censused annually from 1978 to 1993 and again in 2001 (12,800 quadrats), and a 1.8 ha littoral zone sampled every 6–10 years (1978, 1984, 1991, and 2001; 3600 quadrats). The grid vegetation fluctuated rather erratically for the first 11 years with each of the dominant species showing a different pattern of change. Frequency values for Chara vulgaris were the most dynamic, while those for Vallisneria americana were the most stable. After 1989, grid vegetation declined, so that by 2001, only four of the original 11 species were present (including the original dominants), and the total number of observations declined to <10% of the maximum recorded. This decline is attributed to vigorous benthic feeding by carp (Cyprinus carpio), not noted in 1978 but relatively abundant by 2001. Frequency changes of species in the 200 m2 grid were positively correlated with corresponding frequency changes in the 1.8 ha littoral zone, indicating that a small, carefully chosen area may reflect vegetation at a larger scale. This was particularly true when vegetation change was appreciable. [Copyright &y& Elsevier]

Abstract: The effect of density on the growth, recruitment of new ramets, biomass allocation, rhizome spacer length and rhizome branching of the submersed macrophyte Potamogeton perfoliatus L. was experimentally evaluated in a mesocosm with three different initial shoot densities. The findings suggest that the number of primary shoots available in the beginning of the season can strongly influence patterns of growth and clonal reproduction. In contrast to many studies that found decreasing production parameters with plant density, ramet and biomass production of Potamogeton perfoliatus plants were highest at medium plant density. This is probably due to negative feed-back through crowding at high density and unclear negative effects at low density. Shoot allocation tended to increase with density, rhizome allocation tended to decrease with density and root biomass remained unchanged. At low density Potamogeton perfoliatus produced longer rhizome spacers and more branchings than at higher densities. Shorter rhizome spacers at high plant density probably restrict patch expansion and cause discrete patch shapes. A likely mechanism for plastic changes in clonal architecture is increasing competition for light at increasing density, but other density-dependent factors may also contribute. Investigations on propagule numbers of tubers and turions show that self-regulation of ramet number was associated with self-regulation of propagule number in both Potamogeton perfoliatus and Potamogeton pectinatus, with higher densities producing less propagules per plant. [Copyright &y& Elsevier]

Spatial variation in the distribution and abundance of submersed macrophytes in the Mary River, a subtropical Australian river, was examined at 29 sites on four occasions (116 samples) over a 1 year period. Thirteen submersed macrophyte taxa representing seven families were recorded during the study period. Submersed macrophyte cover was generally patchy and mean quadrat cover per sample was below 7% for every recorded taxon. Classification and ordination identified four distinct groups characterised by differences in submersed macrophyte abundance and associated environmental variables. Three of the four groups were characterised by different abundances of three core taxa, Myriophyllum verrucosum, Vallisneria nana and Potamogeton crispus. The distribution of the four sample groups within the Mary River catchment was associated with two environmental gradients, the first gradient representing discharge intensity, discharge variability and total Kjeldahl nitrogen (TKN) concentration and the second gradient representing discharge intensity, substrate composition, riparian canopy cover and total phosphorus (TP) concentration. Both environmental gradients were constrained by geomorphology at the catchment as well as the reach scale. Our findings are consistent with a general conceptual model that highlights the importance of major environmental gradients in structuring submersed macrophyte assemblages. [Copyright &y& Elsevier]

Photogrammetrical methods were combined with field studies to map macrophytes in a medium-sized river, which has not been practised prior to our studies.In August 2001, aerial photos were made at a 15 km long section of the Lower River Spree. In the same time, we described the spatial distribution of submersed macrophytes along two 50 m long river stretches within the photographed section, and correlated the results of both methods. Macrophytes were harvested above defined areas, and their biomass and nutrient concentrations were determined for various degrees of river bottom coverage. Field data and photogrammetrical data were combined to determine nutrient retention by macrophytes.Aerial photos provided results of the same magnitude as field observations, but underestimated plant coverage by as much as 36.8%. The large error was mainly due to the occurrence of trees partly overshadowing and overhanging the water surface. Changing water levels and turbidity caused minor errors (11.2%). According to field data, macrophytes had high small-scale spatial heterogeneity, but this could not be measured using aerial photos.Phosphorus retention due to biomass fixation amounted to 1.9% of total phosphorus load during the vegetation period between May and August, and the nitrogen retention was 1.2%. In comparison to nutrient retention due to sedimentation, nutrient incorporation into biomass contributed little to total nutrient retention. The considerable discrepancy between nutrient pools and spatial distributions of some macrophyte species underlines the necessity to combine photogrammetrical methods with field studies, if the aim is to quantify nutrient retention. [Copyright &y& Elsevier]

1. We grew the submersed freshwater macrophyte Vallisneria americana under controlled conditions at low and high [CO 2 ] to produce litter with high and low tissue nitrogen concentration ([N]), respectively. We then followed mass and nitrogen dynamics in situ in this litter to test the indirect effect of [CO 2 ] on its subsequent decomposition and colonisation by macroinvertebrates. 2. Litter from plants grown in high CO2 initially lost mass and N at a significantly lower rate but, by day 30, both litter types had lost about 90% of mass and N. Litter [N] did not appear to govern decay rate. 3. There was no effect of CO2 on the pattern of macroinvertebrate colonisation. 4. The potential exists for high [CO2 ] to increase rates of C and N cycling and, thereby, to increase internal N loading in macrophyte-dominated shallow water ecosystems. [ABSTRACT FROM AUTHOR]

1. We grew the submersed freshwater macrophyte Vallisneria americana under controlled conditions at low and high [CO 2 ] to produce litter with high and low tissue nitrogen concentration ([N]), respectively. We then followed mass and nitrogen dynamics in situ in this litter to test the indirect effect of [CO 2 ] on its subsequent decomposition and colonisation by macroinvertebrates. 2. Litter from plants grown in high CO2 initially lost mass and N at a significantly lower rate but, by day 30, both litter types had lost about 90% of mass and N. Litter [N] did not appear to govern decay rate. 3. There was no effect of CO2 on the pattern of macroinvertebrate colonisation. 4. The potential exists for high [CO2 ] to increase rates of C and N cycling and, thereby, to increase internal N loading in macrophyte-dominated shallow water ecosystems. [ABSTRACT FROM AUTHOR]

The independent and interactive effects of nutrient concentration and epiphyte grazers on epiphyte biomass and macrophyte growth and production were examined in Zostera marina L. (eelgrass) microcosms. Experiments were conducted during early summer, late summer, fall, and spring in a greenhouse on the York River estuary of Chesapeake Bay. Nutrient treatments consisted of ambient or enriched (3× ambient) concentrations of inorganic nitrogen (ammonium nitrate) and phosphate. Grazer treatments consisted of the presence or absence of field densities of isopods, amphipods, and gastropods. epiphyte biomass increased with both grazer removal and nutrient enrichment during summer and spring experiments. The effect of grazers was stronger than that of nutrients. There was little epiphyte response to treatment during the fall, a result possibly of high ambient nutrient concentrations and low grazing pressure. Under low grazer densities of early summer, macrophyte production (g m d) was reduced by grazer removal and nutrient enrichment independently. Under high grazer densities of late summer, macrophyte production was reduced by enrichment only with grazers absent. During spring and fall there were no macrophyte responses to treatment. The relative influence of epiphytes on macrophyte production may have been related to seasonally changing water temperature and macrophyte requirements for light and inorganic carbon. [ABSTRACT FROM AUTHOR]

• We examined the relationship between wet and dry mass of 13 submersed macrophyte species. • Standardized major axis tests indicate predictable relationship between wet and dry mass. • Dry mass can be estimated from fresh mass for submersed species. • Species-specific dry mass ranged from 5-13% of wet mass. • Additional research will permit examination of sources of within-species variation in dry matter. Submersed freshwater macrophytes can provide numerous crucial ecosystem functions and influence biotic assemblages across multiple trophic levels. These functions are dependent on abundance, which has been most often reported as biomass in terms of dry mass per unit area. Determining dry mass is a time- and labor-intensive process that may not be practical at the assessment scale of interest. We examined the relationship between wet and dry mass during the approximate peak growing season for thirteen submersed species common on the Upper Mississippi River and other aquatic systems in the midwestern USA and beyond (Ceratophyllum demersum , Elodea canadensis , Heteranthera dubia, Myriophyllum sibericum , Myriophyllum spicatum , Narrow-leaf pondweeds (likely included Potamogeton foliosus , P. pusillus), Potamogeton crispus , Potamogeton nodosus , Potamogeton richardsonii , Potamogeton zosteriformis, Ranunculus longirostris , Stuckenia pectinata , and Vallisneria americana). All species exhibited a predictable linear relationship between wet and dry mass. The species-specific dry: wet mass ratios of 5.0–13.1% presented here supplement previously published data for some species, represent novel information for others and allow for estimations of dry mass from fresh material when direct measurement of the former is impractical. Pairwise comparisons of the individual estimates indicated four distinct groups of species within the overall gradient of dry:wet mass ratios. Lowest estimates of percent dry mass were for species previously associated with higher flow (V. americana and H. dubia) and highest values were for species typically found in still water (P. zosteriformis and the P. foliosus / P. pusillus group). [ABSTRACT FROM AUTHOR]

• Water flow enhanced NH 4 +-N and COD removal but inhibited TN and TP removal. • Turnover had greater contribution than nestedness to beta-diversity dissimilarity. • Bacteria in biofilms were less stable than eukaryotes. • The effect of temperature on the bacteria in the biofilm was the main reason for the reduction of purification capacity. • Temperature had a greater influence on the microbial community than water flow. The mechanisms behind water flow on contaminant removal by a submerged macrophyte-biofilm complex in surface flow wetlands remain to be fully elucidated. In this study, water flow (2.02 ~ 2.12 or 4.06 ~ 4.5 L s−1; hydraulic retention time, 7d) significantly enhanced NH 4 +-N and COD but inhibited TN and TP removal compared to the static ones. No more than 30% of TN and TP were assimilated by V. natans -biofilm complex in wetland system. Water flow remarkably affected alpha-diversity of microbial community in epiphytic biofilm. As revealed by beta-diversity analysis, turnover played greater contribution to the total dissimilarity than nestedness. Network analyses revealed that the microbial interactions including predation, symbiosis and competition in epiphytic biofilms were much more intensive in the Sept.- Oct. than the Nov.-Dec group. Redundancy and Mantel correlation analyses revealed that temperature played a key role in determining microbial community structure, especially for bacteria. [ABSTRACT FROM AUTHOR]

Microbes in epiphytic biofilms and surface sediments play crucial roles in the biogeochemical cycles in wetlands. However, little is known about the compositions of microbial community in wetlands dominated with submersed macrophytes. In this study, bacterial and eukaryotic community in epiphytic biofilms and surface sediments were investigated in wetlands with artificial plants and Myriophyllum verticillatum from September (~27 °C) to January (~9 °C). A total of 30 (including 13 bacterial and 17 eukaryotic) and 34 (including 14 bacterial and 20 eukaryotic) phyla were detected in epiphytic biofilms and sediments, respectively. Microbial community in epiphytic biofilms shifted with decreasing temperature, and biofilms on M. verticillatum were generally similar to those on artificial plants. Though the OTUs and Shannon values were significantly higher in sediments than epiphytic biofilms (p < 0.05), numbers of strongly correlated edges detected in biofilms (64 nodes with 182 edges) were at least three times of those in sediments (40 nodes with 57 edges) as revealed by co-occurrence networks analysis (|r| > 0.7, p < 0.05). These data suggest that there were complex interactions among microbes in epiphytic biofilms than sediments. Positive relationships among microbes revealed the predation, symbiosis, parasitism relationships and the collective degradation of organic matter, while negative ones may be ascribed to their different lifestyles. These results highlight that artificial plants play a similar role as submersed macrophytes as microbial carriers and can be potentially used an alternative substitutes to submersed macrophytes in wetlands. Unlabelled Image • Abundant bacteria and eukaryotes inhabited on surface of artificial plants in water column. • Microbial community in epiphytic biofilms shifted with decreasing temperature. • Shannon values and OTU numbers were significantly higher in sediments than epiphytic biofilms. • There were more complex interactions among microbes in epiphytic biofilms than in surface sediments. • Metazoa genera were somewhat positively and negatively related to bacteria and Viridiplantae in biofilms, respectively. [ABSTRACT FROM AUTHOR]