State In Shallow Lakes Research Articles

The dual role of benthic fish: Effects on water quality in the presence and absence of submerged macrophytes

Rebuilding a clear-water state dominated by submerged macrophytes is essential for addressing eutrophication, yet the impact of benthic fish on water quality is complex. We conducted two experiments to explore the interaction of submerged plants and benthic fish on the water quality. Experiment I investigated the water clearing effects of submerged macrophytes with varying coverage (from 0% to 40%) before and after the removal of benthic fish. Experiment II explored the impacts of benthic fish at different densities on aquatic ecosystems with and without submerged macrophytes. The results showed that an increase in submerged macrophytes coverage significantly enhanced the reduction of some major water quality parameters. We assert that the coverage of submerged macrophytes should not be lower than 40% to establish and sustain a clear-water state in shallow lakes. However, benthic fish significantly weaken the ability of submerged macrophytes to improve water quality. Surprisingly, the presence or absence of macrophytes may reverse the role of benthic fish in freshwater ecosystems. When macrophytes are present, benthic fish can cause water quality to deteriorate. Conversely, when macrophytes are absent, benthic fish with a density of ≤ 10 g/m3 can restrict the growth of phytoplankton by directly consuming algae or by disturbing sediments to increase turbidity, thereby potentially improving water quality. But the detrimental effects of benthic fish with higher densities may gradually outweigh their benefits to water clarity. Therefore, the percentage of submerged macrophyte cover in combination with the density of benthic fish play crucial roles in shaping the ecological effects of benthic fish and overall ecosystem dynamics. These findings underscore the importance of understanding ecosystem interactions and have practical implications for the management of shallow lakes.

Food quality upgrade of carbon from submerged macrophytes by flagellates via a heterotrophic pathway can stimulate growth of Daphnia magna.

Submerged macrophytes play crucial roles in maintaining the stability of clear-water states in shallow lakes. Recent stable isotope studies have shown that crustacean zooplankton can utilize submerged macrophyte carbon, but macrophytes alone cannot support the growth and reproduction of such grazers, being deficient in highly unsaturated fatty acids (HUFA). We hypothesized that flagellates feeding on macrophytes can synthesize HUFA and thereby support crustacean zooplankton. To test this hypothesis, we conducted a feeding experiment in which Daphnia magna were provided with a diet of submerged macrophyte Hydrilla verticillata detritus which had been degraded by lake microbes. The chlorophyte Scenedesmus bijuga and undegraded macrophyte detritus were used as controls for comparison of Daphnia's performance. Using biochemical analysis, we examined how the degradation process affected the food quality of the macrophyte. Flagellates were subsequently isolated from the degraded macrophyte and cultured heterotrophically to detect their HUFA synthesis. The 5-day degraded H. verticillata showed significantly higher HUFA concentrations than undegraded macrophyte detritus. They supported better Daphnia performance than undegraded macrophyte, being comparable with S. bijuga. Two isolated flagellates (SL-1 and SL-2), identified as Ochromonas sp. and Poterioochromonas sp., were found to contain HUFA when cultured heterotrophically without dietary sources of fatty acids, suggesting their HUFA synthesis ability. Our results demonstrate that submerged macrophytes may thus indirectly support crustacean zooplankton via flagellate mediation. As crustacean zooplanktons are of key importance for water quality in the grazer control of phytoplankton, this microbial facilitation may contribute to the maintenance of macrophyte clear-water conditions in shallow lakes.

Analysis of tsagaan lake sediment, valley of the gobi lakes, Mongolia, to determine past environmental changes and the effect of ongoing global warming

The arid region of Mongolia is sensitive to climate change. Understanding of climate variations in the past plays an important role in predicting further climate changes. In this study, we aim to investigate the relationship between the climatic factor and sedimentation history in the late Holocene. We analyzed the 18TS1 core sample (136 cm in length) from the Tsagaan lake in the Valley of the Gobi Lakes, Mongolia. The sediment core mainly consists of clay and silt sediments, occasionally interrupted by the sand-dominated layers. 210Pb dating method is applied and indicates that the upper 24 cm sediment spans the sedimentation history of the last 87 years. Along-core variations in sediment characteristics such as organic matter, carbonate, and amorphous silica abundance are indicative of the drought -inducing period based on the significant correlations between sediment characteristics and Self-calibrated Palmer Drought Severity Index. Moreover, the enrichment of carbonates is a great indicator of shallow lake conditions prior to the lake disappearance during the dry period. The chemical composition of sand-dominated units in the sediment core well agrees with that of sand sheets and sand dunes in the catchment. Modern expansion and migration of sand sheets are identified by aerial photo imagery. The insufficient sediment chronology is limiting our interpretation, though; the comparison with the other paleoclimate records helps the establishment of environmental changes in the last millennium.

Do submerged macrophyte species influence crustacean zooplankton functional group richness and their resource use efficiency in the low-light environment?

During the high grazing of epiphytic zooplankton in submerged macrophyte beds, the changes in crustacean zooplankton functional groups are crucial for stabilizing a clear water state in shallow lakes. However, submerged macrophytes often experience low-light stress due to many ecological processes. It is unclear whether submerged macrophytes alter the zooplankton functional group and their resource use efficiency in the low-light environment. We conducted two mesocosm experiments involving the treatments of low-light and submerged macrophyte species (Vallisneria natans and Potamogeton maackianus). The results show that abiotic factors (e.g., light) were the most important variables in explaining the change in the zooplankton community. Specifically, zooplankton functional group (i.e., pelagic species, plant-associated species, and substrate scrapers) richness and zooplankton species diversity decreased with the decreasing light intensity, especially for low substrate scraper abundance. In addition, structural equation models showed that low-light stress reduced zooplankton resource use efficiency by reducing zooplankton functional group richness and species diversity. Compared to species diversity, zooplankton functional group richness had a greater influence on their resource use efficiency (Zp/Chl-a) in the low-light environment. Our results suggest that the low-light stress reduced zooplankton resource use efficiency by changing their functional group richness. Moreover, the abundance of substrate scrapers shaken from V. natans was higher than that from P. maackianus. Therefore, submerged macrophyte species influence crustacean zooplankton functional group richness and their resource use efficiency in the low-light environment. Selecting appropriate aquatic plant species to assure the high diversity of zooplankton should be considered when conducting lake restoration using submerged macrophytes.

Buffering capacity of submerged macrophytes against nutrient pulses increase with its coverage in shallow lakes

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.

Regime shifts in shallow lakes explained by critical turbidity

Worldwide, water quality managers target a clear, macrophyte-dominated state over a turbid, phytoplankton-dominated state in shallow lakes. The competition mechanisms underlying these ecological states were explored in the 1990s, but the concept of critical turbidity seems neglected in contemporary water quality models. In particular, a simple mechanistic model of alternative stable states in shallow lakes accounting for resource competition mechanisms and critical turbidity is lacking. To this end, we combined Scheffer's theory on critical turbidity with insights from nutrient and light competition theory founded by Tilman, Huisman and Weissing. This resulted in a novel graphical and mathematical model, GPLake-M, that is relatively simple and mechanistically understandable and yet captures the essential mechanisms leading to alternative stable states in shallow lakes. The process-based PCLake model was used to parameterize the model parameters and to test GPLake-M using a pattern-oriented strategy. GPLake-M's application range and position in the model spectrum are discussed. We believe that our results support the fundamental understanding of regime shifts in shallow lakes and provide a starting point for further mechanistic and management-focused explorations and model development. Furthermore, the concept of critical turbidity and the relation between light-limited submerged macrophytes and nutrient-limited phytoplankton might provide a new focus for empirical aquatic ecological research and water quality monitoring programs.

Interactions between suspended sediments and submerged macrophytes-epiphytic biofilms under water flow in shallow lakes

Suspended sediments (SS) pollution is one of the factors affecting the transfer from turbid water state to clear water state in shallow lakes. However, the interactions between suspended sediments and submerged plants are far from clear. In this study, we investigated the settlement laws of SS in overlying water and its impact on the epiphytic biofilm of Myriophyllum verticillatum and Vallisneria natans under water flow. At least 90% of turbidity can be removed from overlying water, and the decreasing trend of water turbidity fitted the logarithmic decay model in all treatments. The size distribution of SS fit the log-normal distribution model in the first 240 min after SS addition. It should be noted that the main peak particle sizes were lower in treatments with submerged macrophytes (8.71-13.18 μm) than without plants (15.14-19.95 μm). Water flow and SS addition significantly increased the thickness of biofilms attached to M. verticillatum (p < 0.05), but they together significantly reduced the biofilm thickness on V. natans (p < 0.05). SS increased the bacterial α-diversity but decreased eukaryotic one in epiphytic biofilms. However, water flow had a more significant impact on microbial communities (especially eukaryotes) than SS and plant species. The relative abundances of dominant phylum Proteobacteria, class Alphaproteobacteria and Betaproteobacteria, and class Verrucomicrobiae increased in epiphytic biofilms after SS addition. Co-occurrence networks reveal that photosynthetic microbes in epiphytic biofilms played an important role in microbial communities under water flow and SS, and many hub microbes were increased by SS addition but reduced by water flow. These data highlight that SS decline can be predicted by the logarithmic decay model and, SS and water flow can affect the epiphytic-biofilm on submerged macrophytes.

Physical Factors and Microbubble Formation Explain Differences in CH4 Dynamics Between Shallow Lakes Under Alternative States

Submerged macrophytes play a key role in maintaining clear vegetated states in shallow lakes, but their role on methane (CH4) dynamics is less explored. They might enhance methanogenesis by providing organic matter but they can also supply oxygen to the sediments increasing methanotrophy. They may also affect gas exchange by diminishing wind turbulence in the water column. We previously measured seasonal CO2 and CH4 partial pressure (pCO2 and pCH4) and diffusive fluxes from two clear vegetated and two turbid algal shallow lakes of the Pampean Plain, Argentina, and we reported that clear lakes had higher mean annual pCH4 despite states having similar mean annual CH4 diffusive flux. In this study we explore the contribution of physical and biological factors regulating surface pCH4. Mean annual CH4 diffusive fluxes and CH4 fraction of oxidation (Fox) were similar between states, implying a comparable mean annual CH4 input. kCH4 was significantly higher than kCO2, suggesting occurrence of CH4 microbubbles, yet kCH4 was higher in turbid lakes than in clear lakes, implying a higher microbubble formation in turbid lakes. Furthermore, in turbid lakes there were positive relationships between k and wind speed, and between k and pCH4, yet in clear lakes these relations were absent. Results suggest that submerged vegetation suppresses wind induced turbulence in clear vegetated lakes, decoupling kCH4 from wind and reducing microbubble formation, therefore augmenting pCH4 in their surface waters. Overall, physical rather than biological factors appear to control the observed differences in pCH4 between states.

Late Holocene vegetation, climate, and lake changes in northern China: Varved evidence from western Loess Plateau

High-resolution archives deepen the understanding of past climate variability. We report new sedimentological and paleoecological data from Chaona Lake in northern China. The record represents the annually laminated (i.e., varved) archive from the western Loess Plateau spanning the Late Holocene, allowing insights into critical time intervals of decadal to centennial-scale climate instability. After developing a robust, continuously chronology supported by radioisotope dating and varve chronology, we used high-resolution palynological and sedimentological data to decipher the specific climate and ecosystem evolution over the last 2800 years. Our results show a general forest decline and climate deterioration intercalated with a series of oscillations during the Late Holocene, which may have profoundly influenced the eco-social development of northern China. In addition, lake development changes that mainly reflect the transformation from deep to shallow lake conditions generally match the regional vegetation, which is probably driven by climate-related processes. However, fluctuations in well or poor and the absence of varved sediment indicate variations in the water circulation in the lake catchment. Periods of predominantly well-varved sediments are considered to reflect reduced lake circulation and more anoxic conditions, coinciding with warmer and more stable climate intervals, such as the Roman Warm Period and the Medieval Warm Period. Conversely, periods of poor or even non-varved preservation indicate strengthened lake circulation, which may be influenced by strong winds (e.g., 2800–2000 cal yr BP) and cold/drought conditions (e.g., the Little Ice Age). Integration of our data with those of published climatic reconstructions in northern and eastern monsoon China suggests that this variability in climate can be explained by shifts in solar insolation and large-scale ocean-atmospheric coupling dynamics that affect the Loess Plateau (e.g., the East Asia Summer Monsoon and El Niño-Southern Oscillation).

Submerged macrophytes benefit from lanthanum modified bentonite treatment under juvenile omni‐benthivorous fish disturbance: Implications for shallow lake restoration

Abstract The re‐establishment of submerged macrophytes is crucial in shallow lake restoration transforming a turbid into a clear water system, but it might be inhibited by juvenile omni‐benthivorous fish. These fishes disturb the sediment, and even uproot new sprouts, creating turbid water through sediment resuspension and release of nutrients stored in the sediment. Lanthanum modified bentonite (LMB), an in‐situ capping material, can immobilise phosphate and consolidate sediments, potentially weakening the negative effects of juvenile omni‐benthivorous fish. We hypothesised that applying LMB would improve water quality and promote the growth of submerged macrophytes by eliminating or weakening the increase of suspended solids, nutrient concentration, and algal reproduction due to juvenile omni‐benthivorous fish disturbance. To test our hypothesis, a two‐by‐two factorial mesocosm experiment with two densities of juvenile crucian carp (absence and 10 g/m3) and two doses of LMB (absence and 800 g/m2) was conducted. Juvenile crucian carp significantly inhibited the growth and reproduction of the macrophyte Vallisneria natans by reducing the underwater light and direct effects such as uprooting. No significant inhibition or promotion by LMB on the growth of V. natans in the absence of juvenile crucian carp was observed. However, LMB significantly inhibited the fish‐induced sediment resuspension and nutrients increases. Consequently, algal production was reduced and underwater light conditions were improved, which promoted the growth and reproduction of V. natans, e.g., more ramets, biomass, and leaves of V. natans. Our results indicated that submerged macrophytes could benefit from LMB application under high intensity disturbance by juvenile omni‐benthivorous fish, thereby conducive to the maintenance of a clear water state in shallow lakes.

The effect of climate change on Galaxias maculatus thermal habitat availability in northern Andean Patagonian lakes

Abstract Temperature is a prime driver of biological systems, and has implications for populations, community dynamics and stability across entire lake food webs. Galaxias maculatus is a keystone prey species in Patagonian lakes due to its trophic and habitat coupling roles. Adverse effects on this species could cascade through food webs, threatening the biotic integrity of Patagonian lakes. Our aim was to define the current use of available thermal habitats by three G. maculatus life stages in three morphologically dissimilar lakes of the Andean range and to simulate potential shifts in thermal habitat availability. Thermal habitat availability simulations derived for the 4.5‐ and 8.5‐W/m2 radiative forcing values of greenhouse gas Representative Concentration Pathway scenarios up to 2099 were run for the three lakes. The availability of simulated thermal habitats for 2099 was used to analyse possible consequences for G. maculatus, using thermal habitat suitability index curves. The curves were defined from the temperature dependence of the maximum consumption of each life stage of G. maculatus considered. Our results showed that thermoclines would form at greater depths in the two deep lakes and remain stable for longer periods than at present. For the shallow lake, which does not currently form a thermocline, Representative Concentration Pathway scenarios predict higher water temperatures and absence of winter freezing. Galaxias maculatus currently encounters better thermal habitat for food consumption in the shallow than the deep lakes. Simulations for the deep lakes indicated that future climate change will not be detrimental to any G. maculatus life stage. However, in shallow lakes its earlier life stages will encounter lower quality thermal conditions. Lower quality thermal conditions in shallow lakes could result in a reduction in G. maculatus numbers, which could affect entire food webs given that this species is a keystone prey species. In turn, this could threaten the biotic integrity of these lakes. Our results raise the question: what happens in other lakes around the world that have low food web complexity, dynamic processes, and structure, which depend on a single vulnerable keystone prey species? The lack of research addressing the role of keystone species in relation to global climate change suggests that this question has not been thoroughly addressed and requires further study around the world.

Use of artificial-substrate samplers to identify relations between periphytic diatom community composition and hydro-limnological conditions in shallow lakes of Old Crow Flats, Yukon Territory (Canada)

Use of artificial-substrate samplers to identify relations between periphytic diatom community composition and hydro-limnological conditions in shallow lakes of Old Crow Flats, Yukon Territory (Canada)

Structure of phytoplankton functional groups in shallow lakes with different equilibrium states

Changes in equilibrium states in shallow lakes are associated with disturbances and resilience. The study evaluated the structure and composition of phytoplankton functional groups in two lakes, Lagoa do Paó (turbid waters) and Santa Lúcia (clear waters). Monthly collections of limnological variables and phytoplankton occurred between August 2014 and June 2015 in the pelagic region. The lakes shared five functional groups: K, S1 , X1 , W2 and P, formed by coccoid and filamentous cyanobacteria, coccoid chlorophytes and euglenophytes, and desmids, respectively. The canonical correspondence analysis evidenced a clear separation, highlighting the groups TD, N, W2 and S1 in Santa Lúcia and functional groups composed of potentially toxic cyanobacteria in Lagoa do Paó (SN, Lo), indicating that the submerged macrophyte coverage can act promoting the phosphorous stabilization in the sediment in Santa Lúcia, reducing its contribution to the water column and inhibiting the dominance of the mentioned species. Temperature, pH, phosphorus and light attenuation coefficient influenced the occurrence of H1 , SN, S1 , W2 , X1 , D, and Lo , in the Lagoa do Paó. The composition and structure of the functional groups responded in the two lakes with some functional groups associated with toxic cyanobacteria occurring exclusively in Lagoa do Paó, having also been observed the sharing of some functional groups.

Optimal submerged macrophyte coverage for improving water quality in a temperate lake in China

Submerged vegetation is essential for maintaining a clear water state in shallow lakes. To determine the optimal submerged macrophyte coverage required to improve water quality, field investigations and a simulation experiment were carried out in a sub-lake of Baiyangdian Lake, China. The effects of two seasons and five submerged macrophyte coverage gradients (0 [C-0], 25 [C-25], 50 [C-50], 75 [C-75], and 90% [C-90]) were examined in the field study, while the five submerged macrophyte coverage gradients were examined in an 80-day simulation experiment. In the field study, plant coverage, season, and their interaction all had a significant effect on most physicochemical parameters. Compared with C-0, the Secchi depth and pH of the water were higher, while the total nitrogen and total phosphorus concentrations were lower when submerged vegetation was present. Lowest values of total nitrogen, total phosphorus, and conductivity all appeared under C-50. Meanwhile, in the simulation experiment, the total nitrogen content decreased by 76.43, 90.98, 88.28 and 84.32%, and the total phosphorus content decreased by 85.15, 88.48, 87.76 and 79.00% at C-25, C-50, C-75 and C-90 compared with C-0, respectively. Moreover, plant coverage and time had a significant effect on all eight physiochemical parameters. There were no significant differences in the total nitrogen content among C-50, C-75 and C-90, but values were significantly lower than at C-0 and C-25. In contrast, the total phosphorus content was significantly higher at C-0 than all other groups, and the lowest value was observed at C-50. Overall, these findings suggest that 50% is the optimal submerged macrophyte coverage for improvements in water quality in temperate shallow lakes.

Shifting states, shifting services: Linking regime shifts to changes in ecosystem services of shallow lakes

Abstract Shallow lakes can shift between stable states as a result of anthropogenic or natural drivers. Four common stable states differ in dominant groups of primary producers: submerged, floating, or emergent macrophytes or phytoplankton. Shifts in primary producer dominance affect key supporting, provisioning, regulating, and cultural ecosystem services supplied by lakes. However, links between states and services are often neglected or unknown in lake management, resulting in conflicts and additional costs. Here, we identify major shallow lake ecosystem services and their links to Sustainable Development Goals (SDGs), compare service provisioning among the four ecosystem states and discuss potential trade‐offs. We identified 39 ecosystem services potentially provided by shallow lakes. Submerged macrophytes facilitate most of the supporting (86%) and cultural (63%) services, emergent macrophytes facilitate most regulating services (60%), and both emergent and floating macrophytes facilitate most provisioning services (63%). Phytoplankton dominance supports fewer ecosystem services, and contributes most to provisioning services (42%). The shallow lake ecosystem services we identified could be linked to 10 different SDGs, notably zero hunger (SDG 2), clean water and sanitation (SDG 6), sustainable cities and communities (SDG 11), and climate action (SDG13). We highlighted several trade‐offs (1) among ecosystem services, (2) within ecosystem services, and (3) between ecosystem services across ecosystems. These trade‐offs can have significant ecological and economic consequences that may be prevented by early identification in water quality management. In conclusion, common stable states in shallow lakes provide a different and diverse set of ecosystem services with numerous links to the majority of SDGs. Conserving and restoring ecosystem states should account for potential trade‐offs between ecosystem services and preserving the natural value of shallow lakes.

Relationship between epipelon, epiphyton and phytoplankton in two limnological phases in a shallow tropical reservoir with high Nymphaea coverage

Macrophytes and phytoplankton are recognized as having roles in determining alternative stable states in shallow lakes and reservoirs, while the role of periphyton has been poorly investigated. Temporal and spatial variation of phytoplankton, epipelon and epiphyton was examined in a shallow reservoir with high abundance of aquatic macrophytes. The relationships between algae communities and abiotic factors, macrophyte coverage and zooplankton density were also analyzed. Monthly sampling was performed in three zones of the depth gradient of the reservoir. Two phases of algal dominance were found: a phytoplankton phase and epipelon phase. The phase of phytoplankton dominance was characterized by high macrophyte coverage. Rotifera was the dominant zooplankton group in all the zones. Flagellate algae were dominant in phytoplankton, epipelon and epiphyton. Macrophyte coverage was found to be a predictor for algal biomass. Changes in biomass and species composition were associated with macrophyte cover variation, mainly the Nymphaea. In addition to the abiotic factors, the macrophyte coverage was a determining factor for changes to the algal community, contributing to the alternation between dominance phases of phytoplankton and epipelon. The macrophyte–phytoplankton–periphyton relationship needs to be further known in shallow reservoirs, especially the role of epipelon as an alternate stable state.

Mapping paleo-lacustrine environments and long-term climate trends using groundwater chemistry

Groundwater chemical and isotopic variability are used to identify and map temporal changes in the paleo-lacustrine environment and the long-term climate trends in the Closed Basin of the San Luis Valley, Colorado, USA. Total dissolved solids, water color, δ13C, SO42−, Cl−, and Na+ excess are used to identify chemical reaction zones. The reaction zones include methanogenic zones, which represent organic-rich reducing shallow lake conditions; gypsum and halite dissolution zones, which represent saline and playa lakes; and ion exchange zones, which represent organic-rich lakes. The reaction zone maps and vertical stratification depict both long-term and rapid changes in the paleo-lacustrine environmental conditions and changes in the climate regime of the Closed Basin. Based on the reaction zone mapping, the general scheme of the late Pleistocene-Holocene environmental regime of the Closed Basin has been worked out. The upper portion of the confined aquifer was deposited in the organic-rich late Pleistocene Lake Sipapu, which filled the Closed Basin after the draining of the Plio-Pleistocene Lake Alamosa. As the organic-rich lake shrank in size due to the drying climate, the unconfined aquifer sediments were deposited as fluvial sediments and in a series of smaller string lakes. In the string lakes, organic-rich sediments were deposited, and gypsum and halite precipitated as the lakes fluctuated between swamps, fresh and saline lakes, and playas.

Indirect effects of extreme precipitation on the growth of Vallisneria denseserrulata Makino

Submerged macrophytes are important for maintaining a clear water state in shallow lakes but are now threatened by the ongoing climate changes involving more extreme weather events. We explored the effects of extreme precipitation (higher water level, higher loading of nutrients (phosphorus and nitrogen)) on the growth of the submerged macrophyte Vallisneria denseserrulata Makino in a 10-month long mesocosm experiment. We used three macrophyte communities (one, three and six species) and four simulated scenarios of water level and nutrient loading (constant 75 cm, no nutrient loading; gradual water level increase from 75 cm to 150 cm over three months; extreme water level increase to 150 cm within one day at the same nutrient loading as in the gradual increase; constant 75 cm and the same nutrient loading as in the two former treatments). Leaf chlorophyll fluorescence, biomass, morphology of macrophytes and periphyton biomass were recorded. In the treatment with an extreme increase in water level, macrophyte biomass declined, whereas plant height and leaf number remained unchanged compared with the treatments where only nutrient but not water levels were increased. The combined effect of increased water level and enhanced nutrient loading (gradual and extreme change) did not differ significantly from the constant 75cm treatment without additional nutrient loading. No significant differences were found in epiphyton biomass among the water level treatments, while epipelon biomass was marginally higher and plant volume inhabited lower in the two treatments with a water level increase. Changes in macrophyte assemblages only had limited effects on maximum leaf width and the relative electron transport rate of V. denseserrulata. In conclusion, V. denseserrulata was overall resilient to the major simulated changes in precipitation, except when the water level increased suddenly, and only marginally influenced (leaf chlorophyll fluorescence parameter) by the composition of the macrophyte assemblage.

Assessment of water levels and the effects of climatic factors and catchment dynamics in a shallow subtropical reservoir, Manjirenji Dam, Zimbabwe

Abstract Natural water level fluctuations have associated effects on water quality and resident aquatic communities, although their impacts are magnified if the dams have other non-seasonal designated multiple uses. Research demonstrates that excessive water level fluctuations impair ecosystem functioning, ultimately leading to shifts between clear-water and turbid states in shallow lakes. However, these data lack for Manjirenji Dam in Zimbabwe, thus hampering efforts towards effective freshwater resources management in the shallow reservoir. This study analyzed water levels and their fluctuations, and assessed the effects of climatic factors and catchment dynamics using a combination of historical and remote sensed data for the shallow Manjirenji Dam in Zimbabwe. Time series and multiple regression analysis were used to determine water level trends, and the influence of catchment and climatic components in Manjirenji Dam. Lake levels have increased since construction, though their non-significant seasonal variation in the Manjirenji Dam reflects the overlapping effects of catchment and climatic variables. Despite the inferred high stability and resilience, the high fluctuation widths expose the dam to hydrodynamic and climate shocks which have major ecological and conservation implications. A climate change based integrated water resources management approach is necessary for sustainable water resources utilisation in the Manjirenji Dam.

Effects of water level and climate on the hydrodynamics and water quality of Anvil Lake, Wisconsin, a shallow seepage lake

ABSTRACTRobertson DM, Juckem PF, Dantoin ED, Winslow LA. 2018. Effects of water level and climate on the hydrodynamics and water quality of Anvil Lake, Wisconsin, a shallow seepage lake. Lake Reserv Manage. 34:00–00.Interannual differences in the water quality of Anvil Lake, Wisconsin, were examined to determine how water level and climate affect the hydrodynamics and trophic state of shallow lakes, and their importance compared to anthropogenic changes in the watershed. Anvil Lake is a relatively pristine seepage lake with hydrology dominated by precipitation, evaporation, and groundwater exchange enabling the typically subtle effects of water level and climate to be evaluated. Groundwater and hydrodynamic models were used to describe lake water and phosphorus budgets and how its hydrodynamics are affected by water level and air temperature. Decreases in water level are expected to cause Anvil Lake and other shallow lakes to stratify fewer days, and have warmer bottom temperatures and more deep-mixing events. Increasing air temperatures should cause these lakes to have shorter ice cover, longer summer stratification periods, and warmer bottom temperatures. How water level affects water quality depends on how nutrient loading and lake volume vary: during drier, low-water years, lakes with large interannual changes in loading should have better water quality, whereas lakes with small changes in loading should degrade slightly. Anthropogenic changes in Anvil Lake's watershed over the past ∼100 yr were about 1.5 times the effects of changes in water level when levels were low, but the effects were similar when levels were high. Climate warming is expected to increase productivity in shallow lakes because warmer air temperatures will likely increase bottom temperatures increasing sediment phosphorus release and deep-mixing events enabling this phosphorus to reach the epilimnion.