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Submerged macrophytes can improve water quality and buffer the effects of external nutrient loading, which helps to maintain a clear-water state in shallow lakes. We constructed 12 large enclosures with contrasting coverages (treatments) of submerged macrophytes (SMC) to elucidate their buffering capacity and resilience to nutrient pulses. We found that aquatic ecosystems with high SMC had higher buffering capacity and resilience, vice versa, i. e, the enclosures with high SMC quickly buffered the nutrient pulse and rebounded to clear-water state after a short stay in turbid-water state dominated by algae, while the treatments with low SMC could not fully buffer the pulse and rebound to clear-water state, and they slowly entered the transitional state after staying in turbid-water state. This means that the enclosures with high SMC had a better water quality than those with low SMC, i.e., the levels of nutrients and Chl-a were lower in the treatments with high plant coverage. In addition, plant coverage had a significantly positive buffering effect against nitrogen and phosphorus pulses, i.e., the nutrient concentrations in the treatments with high SMC took shorter time to return to the pre-pulse level. Overall, our results evidenced that the higher that the SMCs is, the better is the water quality and buffering capacity against nutrient pulses, i.e. the more stable is the clear-water state. However, low SMC may not be able to resist the impact of such strong nutrient pulse. Our results provide reference and guidance for water pollution control and water ecological restoration.

The global surface temperature has increased by about 0.74°C over the past 100 years, and the frequency of extreme weather has increased as well. We used the state-of-the-art complex, dynamic, mechanistic model GOTM-FABM-PCLake to quantify the impacts of extreme summer warming on a summer-stratified temperate Danish lake. Simulated values of all calibrated parameters (water temperature, DO, NO3, NH4, TN, PO4, TP and Chl.-a) agreed well with observed values over the whole calibration and validation period and generally exhibited the same seasonal dynamics and inter-annual variations as the monitoring data. A series of climate scenarios with different summer heat wave frequencies and duration were set up to quantify the effects on the ecosystem state of the lake. Our simulations showed that summer surface mean TN will decrease with rising summer heat wave frequencies, while summer surface mean TP and Chl.-a and the biomass and proportion of cyanobacteria will increase. Following a summer heat wave, the lake approached baseline conditions in the autumn, but with increasing frequency of heatwaves the recovery period increased. Our results suggest that compliance with existing legislation, such as EU’s Water Framework Directive, will become increasingly challenging in a future scenario with increased temperatures and more frequent heatwaves.

Antioxidant systems are vital in life activities of macrophytes. Species with different life forms need to cope with distinct environments by modifying physiological characters, especially antioxidant systems. In order to find differences among life forms and consequence of lake eutrophication, we studied three antioxidant enzymes activity (superoxide dismutase SOD, ascorbate oxidase APX and catalase CAT) and total soluble phenolics (TP) content in leaves of 26 macrophyte species in September 2013 in Lake Erhai, China. We found that antioxidation varied accordingly with life forms. The activities of SOD and APX in emergent macrophytes (EM) and floating-leaved macrophytes (FM) were much lower than those of submerged macrophytes (SM). On the contrary, TP content was much higher in EM and FM species. There was a negative correlation between TP and antioxidant enzyme activities (CAT and APX). The results suggested that EM and FM species rely on phenolics might to adapt to adverse environments (higher herbivores predation pressure and UV radiation intensity), while SM species more rely on antioxidant enzymes possibly due to lower demand for antioxidation and/or lack of light and inorganic C availability for phenolics synthesis. We also found FM species represent highest fitness in term of antioxidant system, which would lead to overgrowth of FM species and littoral zone bogginess during lake eutrophication. Finally, it is necessary to carry out the verification experiment under the control condition in the later stage, especially for the dominant ones in eutrophic lakes, to understand the exact adaptive mechanisms of them.

Interspecific trait variability (e.g., functional diversity) is often correlated with community productivity and thus promotes ecosystem stability. However, we know little about how intraspecific trait variability mediated the effects of environmental gradients on population stability. We applied generalized multilevel path models to investigate multivariate causal hypotheses that environmental effects on population stability of a macrophyte species - Potamogeton maackianus - are mediated by physiological and morphological traits variability. Using a hierarchical nested design, we measured quarterly nine physiological traits, and monthly ten morphological traits from 9720 individuals at 27 plots along water depth gradients in Lake Erhai, China. Results showed that changes in water depth and light availability caused significant shifts in intraspecific trait variability, with cascading direct and indirect effects on temporal stability of P. maackianus. Water depth exerted major control over population stability, both directly and indirectly via shifts in morphological and physiological traits. Light availability affected population stability indirectly by altering morphological traits. Size traits (shoot morphology and root/shoot ratio) and metabolic traits captured the effect of water depth and light availability on population stability with a relative high accuracy. Our study provide a strong support to the hypothesis that intraspecific trait variability mediate the combined effects of variations on water depth and light conditions on the temporal stability of a dominant macrophtye species in Lake Erhai. Maintaining and enhancing trait variability within plant populations may help to buffer negative effects of anthropogenic environmental changes on population stability.

In shallow eutrophic lakes, submersed macrophytes are essential for maintaining a clear water state, and they are affected markedly by fishes directly through herbivory and indirectly by fish-invertebrate-periphyton complexity, a pathway that presently is not well understood in subtropical lakes but probably vital to lake managements. We conducted a mesocosm study involving benthic fish (Misgurnus anguillicaudatus), snails (Radix swinhoei) and submersed macrophyte (Vallisneria natans), aiming to examine whether benthic fish is detrimental to reestablishment of clear-water macrophyte-dominated state in eutrophic degraded lakes. In addition, we aimed to investigate the cascading effect that benthic fish might have on periphyton and phytoplankton and to what extent snails can alleviate this effect. Our results showed that benthic fish promoted nutrient release from the sediment and thereby facilitated the growth of phytoplankton and periphyton, leading to reduced growth of submerged macrophytes due to shading. Snails consumed the periphyton attached on the leaves of macrophytes, thereby being beneficial to the plant growth, albeit it could not fully counteract the adverse effects from benthic fish. The water quality indicators in terms of nutrients concentrations, phytoplankton biomass and light extinction coefficient along the water column was affected primarily by benthic fish, followed by macrophytes and snails. To target a clear-water condition, the water quality was best at the presence of macrophytes alone or in combination with snails, and worst at the presence of benthic fish. Our results implied that the removal of benthic fish should be a useful ecological restoration method for rehabilitation of submersed macrophytes and water quality improvement in subtropic, eutrophic, shallow lakes following external nutrient loading reduction.

Adaptations to low light and water depth stresses are crucial for the survival of submerged macrophytes. To determine the phenotypic responses of Vallisneria natans to such stresses, we combined a field investigation, a light control experiment and an in situ response experiment to evaluate adaptive variations in fresh weight and morphological and physiological characteristics. In the field investigation and the light control experiment, water depth and light intensity were the main environmental factors affecting the fresh weight and morphological characteristics of V. natans. Fresh weight and leaf length were the most significant responding variables, and they were positively correlated with water depth and negatively correlated with underwater light intensity, although the root length and leaf number exhibited no variation. The leaf length elongated more rapidly at sites with intermediate water depth and low light intensity, and the allometric slopes were steeper. Furthermore, the in situ response experiment results showed a unimodal distribution of the chlorophyll-a concentrations of V. natans along with increasing water depths (from 0.5 m to 8.5 m). The turning point of the chlorophyll-a concentration occurred at 5.5 m, which is almost the maximum water depth at which V. natans occurs in Lake Erhai. Overall, our results evidenced that light availability is an important driving factor that controls the status of V. natans by affecting not only its morphology and physiology but also its biomass allocation and ramet production. An alternative resource allocation pattern of V. natans could be a shift between light acquisition and clonal reproduction.

Carbon (C) and nitrogen (N) metabolism are essential for the growth and maintenance of submersed macrophytes. They are affected by nutrient and light availability and seasonal changes. In this study, we investigated the changes of C/N metabolism and growth of three natural submersed macrophyte populations (i.e., each in a different site), Potamogeton maackianus, in response to water depth gradients with 0.5 m interval in a freshwater lake for four seasons. Changes were identified by measuring the biomass of the sampled macrophytes and metabolite contents of soluble carbohydrate (SC), starch, and free amino acid (FAA) in their organs. Results showed that no significant and consistent changes were found in the SC and FAA contents in leaves and stems from 1.0 m to 5.5 m water depth, as compared to previous results of controlled studies, suggesting a relative stable C/N metabolism in response to the depth gradients in studied natural populations of P. maackianus. The metabolite contents with the most variations appeared mainly because of seasonal changes. The metabolite contents of the macrophyte populations were more closely correlated with the chemical parameters than with the light parameters in water columns. No significant correlations were found between the metabolite contents with the light attenuation coefficient ($K$) and Secchi depth (SD) in water columns. The NO3-N and total phosphorus (TP) contents in water columns were positively correlated with the SC and starch contents in leaves, respectively. The NH4-N content in water columns was negatively related to the FAA content in leaves. Metabolite contents had weak correlations with depth gradients and light parameters, probably because of the physiological integration among individuals by developed stolons and the canopy-forming characteristic of this species. Our results highlighted the importance of water quality to the C/N metabolism in natural population of submersed macrophyte. (C) 2017 Elsevier B.V. All rights reserved.

Benthivorous fish disturbance and snail herbivory are two important factors that determine the community structure of submersed macrophytes. We conducted an outdoor mesocosm experiment to examine the separate and combined effects of these two factors on water quality and the growth of two mixed-cultivation submersed macrophytes, Vallisneria natans and Hydrilla verticillata, with different growth forms. The experiment involved two levels of fish (Misgurnus anguillicaudatus) disturbance crossed with two levels of snail (Radix swinhoei) intensity. The results revealed that fish activity rather than snail activity significantly increased the overlying water concentrations of total suspended solids (TSS), total nitrogen (TN), ammonia nitrogen (N-NH4), total phosphorus (TP) and phosphate phosphorus (P-PO4). However, no differences among treatments were observed for chlorophyll a (chl a) concentrations. Fish disturbance or snail herbivory alone did not affect the relative growth rate (RGR) of H. verticillata, but their combined effects significantly decreased the RGR of H. verticillata. Although snail herbivory alone did not affect the RGR of V. natans, fish disturbance alone and the combined effects of these factors drastically reduced its RGR. Both species exhibited increased free amino acid (FAA) contents and decreased ramet numbers, soluble carbohydrate (SC) contents and starch contents in the presence of the fish. Moreover, compared to H. verticillata, V. natans showed exceedingly low ramet numbers and starch contents in the presence of the fish. H. verticillata had a higher RGR and summed dominance ratio (SDR2) than V. natans in all treatments; H. verticillata also displayed a larger competitive advantage in the presence of fish disturbance. The present study suggests that (1) fish disturbance rather than snail activity increases water nutrient concentrations, (2) low snail density may be harmful to submersed macrophyte growth when the plants are under other abiotic stress conditions and (3) the competitive advantage of H. verticillata over V. natans is more preponderant in a turbid environment.

It is of great significance for real-time sensing and visualization of electromagnetic situation to grasp the battlefield situation. The most important procedure is to deal with multi-source mass electromagnetic perception data and realize the point to space electromagnetic situation data refactoring. The basic idea of this paper is to estimate the electromagnetic field intensity of any concerned position by space domain fusion of multi-source data fusion after time domain fusion. Firstly, the Grubbs criteria is used in the pretreatment of single sensor data, and then the Bootstrap re-sampling methods is used for single sensor information fusion. This method can eliminate the vagueness and uncertainty of a mass of sensing data in a short period of time. Secondly, by the D-S evidence theory, the multi-sensor perceptual data combined with the wave propagation model and expert information are fused, and finally the prediction of space electromagnetic situation data is reconstructed. Finally, calculation examples of single sensor fusion and multi-sensor fusion are given to illustrate that the developed methods can increase the credibility of the reconstructed electromagnetic situation.

Plant nutrient concentrations and their stoichiometric characteristics are often used to predict nutrient availability and nutrient limitation. However, there is still debate because plants, especially submersed macrophytes, can store excess nutrients and exhibit different survival strategies. To determine the extent to which the trophic status of lakes affect nutrient concentrations of submersed macrophytes and to estimate the relative contribution of lake and interspecific differences to variation of plant nutrient concentrations, we investigated four common submersed macrophytes, Potamogeton maackianus, Potamogeton pectinatus, Potamogeton malaianus and Myriophyllum spicatum, in three plateau lakes with contrasting trophic statuses (i.e. oligotrophic: Fuxian Lake; mesotrophic: Erhai Lake; eutrophic: Dianchi Lake) in Yungui Plateau in southwest China. The results indicated that the average C: N ratios were not different among the three lakes. However, the C: P and N: P ratios in Erhai Lake and Dianchi Lake were significantly lower than those in Fuxian Lake. The N: P ratios of P. maackianus and P. pectinatus did not significantly differ among the lakes. By contrast, the N: P ratios of P. malaianus and M. spicatum indicated different levels of interspecific stoichiometric homeostasis. The C and N concentrations and C: N ratios were mainly determined by the species, while the P concentrations and C: P ratios were mainly determined by the trophic status of lakes. Our study suggested that the C: N: P stoichiometric characteristics of submersed macrophytes exhibit high interspecific differences but substantial homoeostasis in response to different trophic conditions in plateau lakes.

Carbon (C), nitrogen (N) and phosphorus (P) are the three most important essential elements limiting growth of primary producers. Submerged macrophytes generally absorb nutrients from sediments by root uptake. However, the C:N:P stoichiometric signatures of plant tissue are affected by many additional factors such as taxonomy, nutrient availability, and light availability. We first revealed the relative importance of taxonomy, sediment, and water column on plant C:N:P stoichiometry using variance partitioning based on partial redundancy analyses. Results showed that taxonomy was the most important factor in determining C:N:P stoichiometry, then the water column and finally the sediment. In this study, a significant positive relationship was found between community C concentration and macrophyte community biomass, indicating that the local low C availability in macrophytes probably was the main reason why submerged macrophytes declined in Yangtze floodplain shallow lakes. Based on our study, it is suggested that submerged macrophytes in Yangtze floodplain shallow lakes are primarily limited by low light levels rather than nutrient availability.

Electric fields (EFs) are widely used in human activities, and all organisms are potentially affected by EFs. The effects of an EF on terrestrial plants, seeds and water animals are well documented, whereas the effects of an EF on aquatic macrophytes remain unknown. We wanted to determine the effects of an EF, generated by backpack electrofishing equipment, on the growth and metabolism of three submerged plants (Vallisneria natans, Myriophyllum spicatum and Potamogeton maackianus). The results showed that the shoot heights, shoot dry weights, root dry weights, root:shoot ratios and contents of soluble proteins and soluble carbohydrates of the three tested submerged plants were influenced by the EF, and these effects were significantly different among the study plants. Thus, our results indicated that submerged macrophytes might be suppressed by EFs released by electrofishing. Accordingly, we highlight that the growth, development and metabolism of submerged macrophytes might be inhibited by EFs, although the results were obtained from a simulated experiment, and more extensive field experiments are needed.

The anaerobic-anoxic-oxic (AAO) process was used to investigate the variation of the parameters of water quality when the dissolved oxygen (DO) in the aerobic tank was controlled at a low concentration. The results indicated the system still had good phosphorus and nitrogen removal efficiencies when the DO concentration in the aerobic tank was decreased from 2.00 mg·L

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. 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. (C) 2015 Elsevier B.V. All rights reserved.

This study evaluated the effects of sediment capping with local unpolluted soil and re-vegetation with Vallisneria natans on the water quality in a two-month in situ experiment in a mesotrophic lake. Water quality was improved substantially by sediment capping whether alone or along with re-vegetating using V. natans, although varied greatly with time. Sediment capping was an effective technique to reduce nitrogen (N) and phosphorus (P) release from fertile sediment, which thus inhibited phytoplankton growth in the water column. Re-vegetation using V. natans helped to improve water quality slightly more. Sediment capping alone or along with re-vegetating also changed interactions of the water quality parameters substantially. Compared to the control, sediment capping alone enforced the relationships between Chia and both SD and K, but along with re-vegetation weakened the relationships. In addition, sediment capping alone enforced the relationship between Chl-a and N-NH4, but with or without along with the re-vegetation the relationships between Chl-a and both TN and N-NO3 decreased. (C) 2015 Elsevier B.V. All rights reserved.

Submerged macrophytes mainly distribute in the wind-protected littoral zones, rather than continuously distribute around the lake due to mechanical damage by strong wave. However, it is unknown how the biomechanical properties, the key targets against mechanical stress, contribute to its survival and distribution in natural aquatic ecosystem. In this study, the distribution, plant growth, and leaf biomechanical and morphological traits of different segments of Vallisneria natans were examined at 25 sites with three wind strength [sites exposed to strong ES wind (HW), sites exposed to moderate ES wind (MW) and sites sheltered by lakeshore with weak wind disturbance], in Lake Erhai, of Yunnan Province, China. Results showed that V. natans mainly distributed in the wind-protected eastern and northern littoral zones within 5 m water depth. The smallest plant growth, strongest and least flexible leaves were at MW, indicating that V. natans is prone to dominate the littoral zones exposed to strong but short wave. Additionally, the high plant growth and relatively stronger and less flexible leaves at HW suggested that the maximization of photosynthesis was at the cost of reduced biomechanical properties and increased drag forces from similar waves, which were unfavourable to complete their life cycles and ultimately reduce the survival and distribution of V. natans under strong wave disturbance. The significant associations between the biomechanical and morphological traits may trigger trade-offs between the mechanical resistance and other plant functions, such as photosynthesis, ultimately determining survival and distribution of submerged macrophytes in natural aquatic ecosystems.

Variability in biomass allocation and growth rate of submersed macrophytes along water depth gradients may lead to different carbon (C), nitrogen (N) and phosphorus (P) stoichiometric characteristics. We conducted a field investigation to evaluate long-term effects of water depth on C, N and P stoichiometry of three submersed macrophytes, Potamogeton maackianus, Myriophyllum spicatum and Ceratophyllum demersum. The results indicated that shoot C:N, C:P and N:P of the plants tended to increase with elevated water depths, and patterns of biomass allocation along water depth gradients were more important than biological dilution of increased growth rates in affecting shoot C:N:P stoichiometric characteristics of the plants. Partial correlation analysis using shoot height and biomass as covariates revealed that water depth significantly affected C:P ratios in shoots of P. maackianus and M. spicatum and C:N ratio in shoots of M. spicatum, but did not affect N:P ratios of all the plants. Shoot stoichiometry of M. spicatum was most sensitive in response to water depth, followed by P. maackianus, and that of C. demersum was really unchanged with elevated water depths. Our results suggested that strategies in biomass allocation in organs, which depend largely on the species identity, rather than growth rates of the plants, contributed mainly to variation in the observed element stoichiometry along the water depth gradients.

As external nutrients inputs above a critical level may drive shallow lakes to shift from clear water to a turbid state, it is important to detect ecological changes of the lake at an early stage of the eutrophication process. In this way, it is possible to assess the stress tolerance of the system and thereby improve the possibilities for proper management. In this study, water quality parameters and the biomass of submerged macrophytes were examined monthly in two bays receiving contrast amounts of nutrient input of a large mesotrophic lake from August, 2011 to July, 2012. We found that effects of external nutrient input could not be explained by differences between the two bays in water quality parameters, such as total nitrogen, total phosphorus, chlorophyll a, light attenuation coefficient and water transparency (Secchi depth), but by the species composition and temporal variation of submerged vegetation. In the progress of eutrophication, the submerged macrophyte community changed from Potamogeton maackianus dominance to co-dominance of Ceratophyllum demersum and P. maackianus, and became more seasonally variable in biomass and coverage due to the shorter survivorship of C. demersum. We suggest that in the early stage of eutrophication, when submerged macrophytes are still abundant, water quality parameters should be coupled with monitoring of submerged vegetation to examine the effects of external nutrient loading on shallow lake ecosystems.

Occasional and sharp increase in NH 4 + availability due to massive input of sewage and agricultural runoff is not uncommon in inland aquatic systems; and its aftermath effects on the system should be evaluated as high NH 4 + concentration is toxic to many animals and plants. In this study, an experiment mimic of natural NH 4 + pulse was used to examine its effects on carbon (C) and nitrogen (N) metabolism of two submersed macrophytes, Myriophyllum spicatum L . and Ceratophyllum demersum L., by determination of NH 4 N, free amino acid (FAA), starch, and soluble carbohydrate (SC) contents. Results showed that FAA contents were significantly higher even on the 10th day after stopping of NH 4 + pulse. Both species accumulated large amounts of NH 4 N and FAA mainly in the leaves in response to the NH 4 + pulse. M. spicatum accumulated more FAA than C. demersum despite both species accumulated similar amounts of NH 4 N. The higher starch and SC reserves in M. spicatum benefited its higher NH 4 + capture and assimilation compared to C. demersum . The C source for N assimilation came mainly from SC in the roots of M. spicatum . The species-specific strategy in CN metabolism and the long-lasting effects of NH 4 + pulse on the CN metabolism would affect growth, distribution, and interaction of the plants in lakes.

Few studies have focused on the biomechanical responses of submerged, rosette-forming macrophytes to wave action, water depth, or their co-occurrence in naturally eutrophic systems. The plant architecture, root anchorage strength-related traits, leaf morphology, and biomechanics of Vallisneria natans inhabiting a range of water depths were examined along three transects (T1, T2, and T3) in a eutrophic lake, Lake Erhai, in Yunnan Province, China. These transects were exposed to weak wave action and hyper-eutrophication (T1), moderate wave action and eutrophication (T2), or strong wave action and eutrophication (T3). The results showed that V. natans was mainly distributed at intermediate depths, with the widest colonization depth in T1. The values of plant architecture, root anchorage strength-related traits, leaf morphology, and biomechanics were generally highest in T3 and smallest in T2. Along the depth gradient, these values were generally highest at 3.5, 2.5, and 2.5 m for the plants growing in T1, T2, and T3, respectively. These findings suggest that V. natans adopts a “tolerance” strategy to cope with the effects of strong wave action in eutrophic habitats and an “avoidance” strategy when exposed to moderate wave action in eutrophic areas. Since the absence of an avoidance strategy increases the resistance to low-light stress at the expense of increased drag forces, there is a limit to the wave action that V. natans can withstand. This study indicates that biomechanics could be important when determining the distribution pattern of V. natans in Lake Erhai.

Eutrophication and hydrodynamics determine the final distribution patterns of aquatic macrophytes; however, there is limited available knowledge regarding their interactive effects. Morphological and biomechanical responses to eutrophication and hydrodynamic stresses were assessed by sampling five abundant and dominant species, Potamogeton maackianus , P. pectinatus , P. lucens , Ceratophyllum demersum and Myriophyllum spicatum , in three macrophyte beds in Lake Erhai, Yunnan Province, China: one exposed to eutrophication and moderate southeast (SE) wind; one with mesotrophication, but sheltered by the lakeshore, with weak wind disturbance; and one with meso-eutrophication and strong SE wind. The results showed significant interactive effects of eutrophication and hydrodynamics on most biomechanical traits and some morphological traits, suggesting that aquatic macrophytes preferentially undergo biomechanical adjustments to resist the coexisting eutrophication and hydrodynamic stresses. In particular, hydrodynamics increased both the tensile force and tensile strain of P. maackianus under meso-eutrophication and dramatically decreased them in eutrophic areas, suggesting that eutrophication triggers mechanical failure in this species. Additionally, P. pectinatus , C. demersum and M. spicatum showed the lowest and highest values for the biomechanical variables (greater values for M. spicatum ) in the most eutrophic and hydrodynamic areas, respectively, implying that increases in hydrodynamics primarily induce mechanical damage in eutrophic species. The plants generally exhibited greater tensile strain in both shallow and deep waters and the greatest tensile force at moderate depths. The stem cross-sectional area, plant height, stem length, internode length, and branch traits were all responsible for determining the biomechanical variables. This study reveals that hydrodynamic changes primarily induce mechanical damage in eutrophic species, whereas eutrophication triggers mechanical damage in sensitive species.

The geo-engineering approach of modified soil flocculation has been widely applied to mitigate algal blooms and eutrophication in relatively small lakes. Nevertheless, its potential ecological risks and feasibility should be examined and identified prior to its application in large natural lakes given the multiple functions of these water bodies in human health and welfare. In situ mesocosm experiments on modified soil flocculation were performed in Lake Taihu during summer 2010 and 2011. Chitosan-modified kaolinite (CMK) soil was used to flocculate algal blooms and improve water transparency to facilitate the re-establishment of the submersed macrophyte Vallisneria natans in this shallow eutrophic lake. Moreover, the ecological effects of CMK soil were assessed. Results showed that repeated additions of CMK (0.3g/L for each time) improved water quality in terms of Chl-a, TN, and TP concentrations; TN/TP ratio; turbidity; redox conditions; and nitrification and denitrification activities. These effects lasted for 48days. After the fourth dose of CMK, the biomass of all phytoplankton categories, except for that of Cryptophyta, decreased by >90% (ca. 1-2×106cell/L or 0.38-0.55mg/L of wet weight). Zooplankton biomass markedly decreased after the first CMK addition, and copepods became dominant. These effects, however, did not last for the long term. Most importantly, submersed V. natans was restored successfully when water clarity and quality were improved through repeated CMK flocculation. Nevertheless, the indices of carbohydrate depletion and free amino acid accumulation indicated that the plant experienced physiological stresses. The reestablishment of V. natans reinforced the positive effects of repeated CMK dosing on water quality, and promoted a clear water state. V. natans is recommended for vegetative restoration in shallow eutrophic lakes given its facile transplantation, high stress tolerance, and physiological traits, which can be applied as indices of post-flocculation effects. In summary, the combination of repeated CMK dosing and revegetation of V. natans can feasibly improve water quality and initiate the restoration of a clear water state in shallow eutrophic lakes.

Low underwater light availability and benthivorous fish-mediated disturbance are two important factors that influence the growth of submersed macrophytes. However, the combined effects of these factors remain unclear. To determine the combined effects of low light and fish-mediated disturbance on the growth of two submersed macrophytes with contrasting growth forms, i.e., Vallisneria natans and Hydrilla verticillata, we conducted an outdoor mesocosm experiment with a two-by-two factorial design. The experiment involved two fish-mediated disturbance levels (0 and 1 Misgurnus anguillicaudatus) crossed with two levels of light intensity (ambient light and a low-light environment created by culturing the macrophytes under a shelter). The results showed that the chlorophyll a (chl a) concentration in the overlying water showed no difference among treatments for each macrophyte species. The fish-mediated disturbance significantly decreased the relative growth rate (RGR) of both species in the low-light environment but showed no effects in the ambient light environment. Low light availability and/or fish-mediated disturbance led to increased plant heights of both species compared with the heights under the ambient light regime. Low light availability combined with fish-mediated disturbance significantly reduced the ramet number and soluble carbohydrate (SC) content of both species; however, the free amino acid (FAA) content was not affected. Compared to V. natans, H. verticillata exhibited a high RGR and high ramet numbers in a low-light environment combined with fish-mediated disturbance. Our results indicated that the adaptability of H. verticillata is better than that of V. natans in turbid, shallow and hydrostatic water. Fish-mediated disturbance can negatively influence submersed macrophyte recovery in lakes when light is not abundant.

Trait-based approaches provide a framework for integrating the distribution of functional traits associated with ecological strategies into the responses of plant community dynamics along environmental gradients. We used a trait-based approach to unravel the processes governing macrophyte community assembly along a water depth gradient. We sampled 42 plots and 1513 individual plants and measured 12 functional traits and abundance of 17 macrophyte species. The results showed significant evidences of habitat filtering (i.e. a significant reduction in the range and variance of trait values) and of niche differentiation (i.e. trait values distributed more evenly than expected), both of which affected the functional responses of macrophyte communities associated with different sets of traits in significant different patterns along the gradient. Habitat filtering effects increased significantly for specific leaf area and leaf carbon content along the gradient. Niche differentiation effects increased significantly for leaf dry mass content, but decreased for ramet size, shoot height and leaf carbon content with increasing water depth, implying that the relative strength of biotic competition in a specific functional niche would vary with water depth. Intraspecific trait variability promoted significantly the detection of habitat filtering effects on stem diameter, lamina thickness and stem dry mass content, and niche differentiation effects on specific leaf area, leaf dry mass content, shoot height, stem diameter, stem dry mass content and ramet size. Community assembly processes shape the functional trait distribution within communities along environmental gradients through hierarchical effects of habitat filtering and niche differentiation. Our study highlights that niche differentiation plays a structuring role in macrophyte community assembly and that intraspecific trait variability is an important factor influencing macrophyte community dynamics. 10.1111/(ISSN)1365-2427