Clearwater Lake Research Articles

Cooling lakes while the world warms: Effects of forest regrowth and increased dissolved organic matter on the thermal regime of a temperate, urban lake

Depending on the magnitudes and directions of changes in air temperatures, winds, and underwater light attenuation, lakes may either warm or cool. Here we report a 28‐yr decrease in the whole‐lake average temperature of Clearwater Lake, Canada, despite regional signatures of climate warming. Using a one‐dimensional lake mixing model, we demonstrate that this pattern was attributable to a 35% reduction in surface wind speeds, itself explained by forest regrowth following local SO2 emission reductions and tree planting, and a 10‐fold increase in dissolved organic carbon concentrations causing a substantial increase in vertical light attenuation following deacidification of the lake. Long‐term trends in lake temperatures do not necessarily follow those of air temperatures. The Clearwater Lake data demonstrate that any factors that influence local wind speeds and underwater light attenuation should be considered as modifiers of the effects of climate warming on lake thermal regimes.

Three decades of recovery of the phytoplankton community in Clearwater Lake (Sudbury, Canada) from acid and metal contamination

Three decades of recovery of the phytoplankton community in Clearwater Lake (Sudbury, Canada) from acid and metal contamination

Calibrating the Dynamic Reservoir Simulation Model (DYRESM) and filling required data gaps for one‐dimensional thermal profile predictions in a boreal lake

One‐dimensional vertical heat transfer and mixing models, such as the Dynamic Reservoir Simulation Model (DYRESM), have seldom been applied to lakes in the boreal region even though this region houses the majority of global freshwater lakes. In order to employ DYRESM to predict the thermal structure of a boreal lake located near Sudbury, Ontario, Canada, we overcame two methodological challenges. First, we developed models to predict the vertical light extinction coefficient (Kd) from dissolved organic carbon (DOC) concentrations and hydraulic retention time. We also developed models to predict stream temperatures from local meteorology, and to predict the discharge of lake inflows and the lake outflow from runoff per unit area at gauged streams nearby. We then re‐calibrated several DYRESM parameters which had been tested previously primarily in the Southern Hemisphere, and explored the sensitivity of the re‐calibrated model to all of the remaining uncalibrated inputs implicated in heating and mixing processes. The mean difference between values predicted with the re‐calibrated model and field measurements (± 1 standard deviation), 1.09 m (± 0.89 m) for thermocline depth and 1.98°C (± 1.58°C) for bottom water temperature, was relatively small compared with other North American studies, and likely due to the model rather than our parameterization. Our calibration of DYRESM for Clearwater Lake, and supplementary models, provide a demonstration for and guidance to those wishing to simulate changes in thermal regimes of boreal lakes in response to climate change or other broad‐scale environmental stressors of importance both to local fisheries and freshwater resource management.

Does terrestrial organic carbon subsidize the planktonic food web in a clear‐water lake?

Allochthonous organic carbon can subsidize consumers in aquatic systems, but this subsidy may only be significant in relatively small systems with high organic matter loading. We tested the importance of allochthonous carbon to consumers in a relatively large (258,000 m2) clear‐water lake by adding H13CO3 daily for 56 d. Dissolved inorganic carbon (DIC) was substantially enriched in 13C by the addition, but it was also variable over diel cycles because of exchange with the atmosphere and photosynthesis. By measuring the δ13C value of a physically separated phytoplankton concentrate as well as the δ13C of phospholipid fatty acids, we were able to follow 13C‐labeling dynamics of specific groups of phytoplankton and bacteria. The δ13C values of particulate organic carbon (POC), dissolved organic carbon (DOC), phytoplankton, bacteria, zooplankton, and the invertebrate predator, Chaoborus spp. all increased to a maximum during the addition and declined once the addition ceased. Autochthony (% C derived from internal primary production) of carbon pools (POC, DOC) and consumers was assessed by fitting dynamic models to time series of δ13C. Autochthonous carbon was the dominant source (88‐100%) for POC, gram‐positive bacteria, a copepod, zooplankton biomass, and Chaoborus spp. Autochthonous carbon provided a lower fraction (<70%) of carbon to DOC, gram‐negative bacteria, and cladoceran zooplankton. In comparison to smaller and more humic lakes, terrestrially derived allochthonous C was less significant to the pelagic food web in this larger, clear‐water lake. Among lakes, the relative importance of autochthonous versus allochthonous carbon to planktonic consumers is positively correlated to the ratio of color (absorbance of light at 440 nm, an indicator of terrestrially derived organic carbon) to chlorophyll.

Tracking long-term acidification trends in Pockwock Lake (Halifax, Nova Scotia), the water supply for a major eastern Canadian city

Pockwock Lake, the drinking water supply for the city of Halifax (Nova Scotia, Canada), has been impacted by the deposition of strongly acidic anions. Because long-term monitoring data are lacking, we used diatom-based paleolimnological techniques to track changes in water quality variables in this important water source. Similar to other acidified lakes in this region, Pockwock Lake has undergone changes in diatom assemblages starting ~1940 with a corresponding lakewater pH decrease of 1.2 units. Before ~1940, Pockwock Lake had a diatom-inferred pH ~6.3 and a diatom assemblage dominated by Cyclotella stelligera and Asterionella ralfsii var. americana (>45 μm). With the onset of acidification, diatom-inferred lakewater pH decreased to ~5.8 and there was a shift to dominance by A. ralfsii var. americana (>45 μm) and Tabellaria flocculosa. A subsequent shift in diatom assemblages and inferred lakewater pH was recorded ~1990 suggesting a decrease in dissolved organic carbon (DOC) and water colour. Since ~1992 Pockwock Lake has undergone further acidification, as evidenced by a shift in the diatom assemblage to dominance by Fragilaria acidobiontica, Eunotia spp., and Frustulia pseudomagaliesmontana. Both diatom-inferred and measured lakewater pH = 5.1 during this time interval. The first (~1940–1992) acidification period followed the trend observed in other humic (high DOC) Nova Scotia lakes, whereas the second (post ~1992) acidification event resulted in a diatom assemblage more common in acidified clearwater (low DOC) lakes. Thus, the acidification signal observed in Pockwock Lake likely indicates a change in diatom assemblage resulting from a loss of DOC, and the sudden drop in diatom-inferred pH suggests that the weak acid buffering system of humic DOC had been exceeded. Further acidification and loss of DOC in this lake has the potential to increase the availability of metals in this important water source.

Physical and chemical limnology of alpine lakes and pools in the Rwenzori Mountains (Uganda–DR Congo)

This study describes the physical and chemical properties of 17 Afroalpine lakes (>2 m deep) and 11 pools (<2 m deep) in the Rwenzori mountains, Uganda-DR Congo, with the aim to establish the baseline conditions against which to evaluate future environmental and biological changes in these unique tropical ecosystems, and to provide the foundation for lake-based paleoenvironmental studies. Most Rwenzori lakes are located above 3,500 m elevation, and dilute (5–52 μS/cm specific conductance at 25°C) open systems with surface in- and outflow. Multivariate ordination and pairwise correlations between environmental variables mainly differentiate between (1) lakes located near or above 4,000 m (3,890–4,487 m), with at least some direct input of glacial meltwater and surrounded by rocky catchments or alpine vegetation; and (2) lakes located mostly below 4,000 m (2,990–4,054 m), remote from glaciers and surrounded by Ericaceous vegetation and/or bogs. The former group are mildly acidic to neutral clear-water lakes (surface pH: 5.80–7.82; Secchi depth: 120–280 cm) with often above-average dissolved ion concentrations (18–52 μS/cm). These lakes are (ultra-) oligotrophic to mesotrophic (TP: 3.1–12.4 μg/l; Chl-a: 0.3–10.9 μg/l) and phosphorus-limited (mass TN/TP: 22.9–81.4). The latter group are mildly to strongly acidic (pH: 4.30–6.69) waters stained by dissolved organic carbon (DOC: 6.8–13.6 mg/l) and more modest transparency (Secchi-disk depth: 60–132 cm). Ratios of particulate carbon, particulate nitrogen and chlorophyll a in these lakes indicate that organic matter in suspension is primarily derived from the lakes’ catchments rather than aquatic primary productivity. Since key features in the Rwenzori lakes’ abiotic environment are strongly tied to temperature and catchment hydrology, these Afroalpine lake ecosystems can be expected to respond sensitively to climate change and glacier melting.

Food quality for Daphnia in humic and clear water lakes

Summary1. Growth and reproduction of Daphnia fed lake seston were measured in two categories of meso‐ to eutrophic lakes differing with respect to terrestrial organic matter influence (humic and clear water lakes). The content of highly unsaturated fatty acids (HUFA), P and N, as well as the taxonomical composition of seston were analysed.2. Seston HUFA and C : P ratios were similar between lake categories, whereas C : N ratios were lower in the clear water lakes in both spring and summer. Despite the similarity in HUFA and P content of seston, Daphnia growth rate, clutch size and the proportion of gravid females were, respectively, about 1.5, 3 and 6 times higher in the clear water lakes.3. Differences in growth and reproduction were related to a combination of higher N content and good fatty acid quality of the seston in the clear water lakes. Relatively high biomass of edible algae, such as Rhodomonas sp. and Cryptomonas sp., in the clear water lakes, and differences in water pH likely contributed to the observed differences in Daphnia growth and reproduction between lake categories. Additionally, it is possible that Daphnia was energy limited in the humic lakes despite high particulate organic carbon (POC) concentrations, as the contribution of non‐algal and detrital C to the POC pool was high.4. Our results suggest that dietary HUFA content has the potential to improve herbivore growth and reproduction if N and P are not limiting. N merits more attention in studies of zooplankton nutrition.

Essential fatty acids and phosphorus in seston from lakes with contrasting terrestrial dissolved organic carbon content

Summary1. It is often assumed that lakes highly influenced by terrestrial organic matter (TOM) have low zooplankton food quality because of elemental and/or biochemical deficiencies of the major particulate organic carbon pools. We used the biochemical [polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA) – 20:5ω3] and elemental (C : P ratio) composition of particulate matter (PM) as qualitative measures of potential zooplankton food in two categories of lakes of similar primary productivity, but with contrasting TOM influence (clear water versus humic lakes).2. C : P ratios (atomic ratio) in PM were similar between lake categories and were above 400. The concentration (μg L−1) and relative content (μg mg C−1) of EPA, as well as the particulate organic carbon concentration, were higher in the humic lakes than in the clear‐water lakes.3. Our results show high fatty acid quality of PM in the humic lakes. The differences in the biochemical quality of the potential zooplankton food between lake categories can be attributed to the differences in their phytoplankton communities.4. High biochemical quality of the food can result in high efficiency of energy transfer in the food chain and stimulate production at higher trophic levels, assuming that zooplankton are able to ingest and digest the resource available.

Primary production in two shallow lakes with contrasting plant form dominance: A paradox of enrichment?

We estimated total lake plant biomass and primary net production in two shallow Swedish lakes that differ in nutrient loading and plant form dominance. In clearwater Lake Krankesjon (10 µg chlorophyll a L‐1), submerged macrophytes contributed more than phytoplankton and epiphyton to the estimated plant biomass. Estimated net primary production during May to September was 90‐130, 1.2, and 14 g C m‐2 for phytoplankton, epiphyton, and submerged macrophytes, respectively. In turbid Lake Bö rringesjön (60‐80 mg chlorophyll a L‐1), primary production by submerged macrophytes and periphyton was negligible. Although gross primary production of phytoplankton was high close to the water surface, estimated areal net primary production during May to September was low, ‐40 to +25 g C m‐2, as a result of self‐shading and high respiration. Grazing pressure from zooplankton rarely exceeded 15% d‐1 in both lakes, indicating that phytoplankton production was not limited by grazing. Low gross epiphyton production could result from high grazing by macroinvertebrates and thus higher trophic transfer efficiency through the benthic than through the pelagic food web. Provided that conditions in Lake Börringesjön reflect previous turbid state conditions in Lake Krankesjon, our results may explain why a shift to a clearwater state was followed by increased biomass of higher trophic levels. Our results also support the paradox of enrichment hypothesis, which predicts lower productivity at high nutrient loading. Contrary to former investigations, we found lower production at a higher nutrient loading already at the trophic level of primary producers.

Vertical distribution of phytoplankton in a clear water lake of Colombian Amazon (Lake Boa, Middle Caquetá)

Vertical distribution of phytoplankton is highly influenced by physical and chemical factors, but the knowledge about these aspects remain unknown in Colombian Amazon lakes. In this work, the relations between the physico-chemical variables and the vertical distribution of phytoplankton community of a clear water lake (Lake Boa) are analyzed. Samples were taken at every 30 cm from surface to bottom in the center of the lake at different times of the hydrological cycle. Phytoplankton transformed from a diluted community dominated by cyanobacteria in high waters to one with elevated abundance of coccal chlorophytes in low waters. In the low water phase, the vertical distribution of Cryptomonas spp., Peridinium cf. umbonatum and Chlamydomonas spp. had significant statistical associations with the redox potential (RP), reactive phosphorus (PO4), and hydrogen sulfide (H2S) (p ≤ 0.05). During the flood stage the conditions were more varied and significant associations were detected between the vertical arrangement of Botryococcus braunii, Oscillatoria splendida, Dinobryon serturlaria, Euglena acus, and Trachelomonas volvocina with conductivity, dissolved oxygen (DO), pH, temperature, dissolved organic carbon (DOC), PO4, RP, and ammonia (NH4). The vertical structure of the Lake Boa’s phytoplankton responds to annual changes produced by the flood pulse, and to the vertical environmental variations, which are stronger during the high water phase.

Inorganic nutrient acquisition in a shallow clearwater lake – dominance of benthic microbiota

This mesocosm study from the oligotrophic Lake Eckarfjarden in Sweden shows, in contrast to many previous studies, that benthic microbiota dominated production following elevated nutrient concentrations in the water. Increased nutrient concentrations favoured microphytobenthos, whereas phytoplankton biomass remained roughly the same. Microphytobenthos biomass and production were clearly stimulated by nitrogen addition, while phytoplankton showed signs of phosphorus limitation. There were tight interactions between pelagic and benthic habitats and between organisms, and pelagic as well as benthic heterotrophic bacteria were disfavoured when microphytobenthos had access to nitrogen. We conclude that increased nutrient concentrations in the water column may trigger immediate responses in both habitats, altering the tight interactions between microbiota, but not necessarily resulting in a shift towards pelagic production.

The Influence of Bauxite Tailings on the Growth and Development of Oryza glumaepatula in an Amazonian Lake

The influence of bauxite tailings on the growth and development of Oryza glumaepatula was studied in Lake Batata, a clear water lake of the Amazon. Lake Batata is an unusual lake because 30% of its total area was covered by bauxite tailings as the result of aluminum mining, influencing many communities and ecological processes. Changes in length, growth rates, total biomass production, density, culm diameter, net primary production and percentage of different plant organs of Oryza glumaepatula were studied for two consecutive flood pulses in natural and impacted areas of Lake Batata. The aim of this research was to test the hypothesis that the growth and development of this aquatic macrophyte is negatively affected in the areas impacted by bauxite tailings. This hypothesis was rejected because most studied parameters were higher in the impacted area, indicating that the growth and development of O. glumaepatula was not negatively affected by the presence of the bauxite tailings. The better development of O. glumaepatula in the impacted area was attributed to the less available space for germination than in the natural area. The lower density of individuals at the impacted area prevented future density dependent mortality that was observed in the natural areas and did not seem to occur in the impacted area.

Increasing trends of total organic carbon concentrations in small forest lakes in Finland from 1987 to 2003

Trends in total organic carbon (TOC) concentrations over the period 1987–2003 were studied in 13 small forest lakes. Recovery from acidification (reduced SO 4 deposition) and long-term changes in runoff as potential drivers for the trends were examined. The results showed that TOC concentrations have increased throughout Finland. Ten of the 13 lakes showed a significant increasing TOC trend ( p < 0.05), and included both clear water and humic lakes. The largest annual increase in TOC occurred in lakes with the largest average concentrations. The magnitude of the TOC trends were not significantly related to the proportion of peat soils in the catchment but the catchment size was an important predictor. Decreasing SO 4 deposition and improved acid–base status in soil due to the recovery from acidification implied an increased mobilisation of organic acids and TOC. There was little evidence that the long-term increasing trend in TOC concentrations was related to long-term changes in runoff. However, large seasonal and inter-annual fluctuations in runoff did appear to affect TOC concentrations for a number of years.

A carbon budget for an oligotrophic clearwater lake in mid-Sweden

A carbon budget for an oligotrophic clearwater lake in mid-Sweden

A carbon budget for an oligotrophic clearwater lake in mid-Sweden

In this study, a whole-lake carbon budget for the oligotrophic, clearwater Lake Eckarfjarden was established both on an annual and seasonal basis. For budget calculations, the lake was divided into three habitats (pelagial, littoral and benthic) and the biota into 19 functional groups. In the lake, major parts of biomass (97%) and primary production (91%) are concentrated in benthic and littoral habitats and to a few functional groups. Respiration on the other hand, is focused on benthic and pelagial habitats where 60% and 39%, respectively, of the respiration took place. Our conceptual model indicates strong interactions between habitats. For instance, the pelagial is fed with carbon fixed by primary producers in the benthic and littoral zones. On an annual basis, total primary production exceeds total respiration and the lake is net autotrophic. However, there are clear differences between habitats and between seasons. For instance, the littoral is net autotrophic during spring, summer and autumn, the benthic habitat is net autotrophic only during summer, and the pelagial is always net heterotrophic. Our results demonstrate clear couplings between habitats and organisms and the importance of a holistic view when studying lake ecosystems.

An evaluation of the role of daphnids in controlling phytoplankton biomass in clear water versus turbid shallow lakes

Phytoplankton and zooplankton were monitored during 2 years in four eutrophic shallow lakes (two turbid and two clear water) from two wetland reserves in Belgium. In each wetland, phytoplankton biomass was significantly higher in the turbid lake than in the clear water lake. Although total macrozooplankton biomass and the contribution of daphnids to total zooplankton biomass was comparable in the clear water and the turbid lakes, the grazing pressure of macrozooplankton on phytoplankton as estimated from zooplankton to phytoplankton biomass ratios was higher in the clear water lakes. Estimated grazing by daphnids in the clear water lakes was always high in spring. In summer, however, daphnid biomass was low or daphnids were even absent during prolonged periods. During those periods phytoplankton was probably controlled by smaller macrozooplankton or by submerged macrophytes through nutrient competition, allelopathic effects or increased sedimentation rates in the macrophyte vegetation.

Responses of the fish community to the flood pulse and siltation in a floodplain lake of the Trombetas River, Brazil

The distributions of the fish species were examined in relation to environmental variables, to evaluate the effects of environmental degradation on the fish community of Batata Lake, a typical Amazonian clearwater lake. From 1979 to 1989, tailings composed of water and clay, extracted from bauxite by water jets, were discharged into Batata Lake. The tailings spread into about 30% of the lake’s area, where the level of the lake bottom rose and turbidity increased. In the present study, multivariate analyses were performed on data for environmental parameters and fish density and biomass. Fish were collected with gillnets during the annual hydrological cycle (filling, flood, drawdown and dry periods), in the silted area, the partly silted area (intermediate) and the natural area. Values of the Shannon index, density and biomass were compared among areas and periods to evaluate the effects of the tailings on community structure. Sediment resuspension, which reduces transparency, is accentuated in shallow water, and was the main factor regulating differences in the community structure between the natural and silted areas. The decrease in transparency occurs mainly during the filling period in the silted area and during the low-water period in the silted and intermediate areas, when sediment resuspension increases concentrations of nutrients and chlorophyll-a. The strong influence of migratory and piscivore species in low-transparency waters is likely associated with the greater bacterioplankton productivity and turnover rate observed by other authors in the silted area, increasing the importance of the heterotrophic food chain in Batata Lake. Reduction of transparency in the silted area was a selective factor for fish species. The death of part of the flooded forest vegetation was decisive in lowering densities of the igapo-associated species in the silted area. The unconsolidated substrate, the death of part of the igapo forest and the negative effects of low transparency – inhibiting resident visually oriented species in the affected areas – are the main factors causing the low diversity in the silted area as a whole. The correlations between CPUEs, conductivity and nutrients and chlorophyll-a concentrations do not appear to reflect cause–effect relationships, indicating that these environmental parameters are poor predictors of fish density in Batata Lake.

Allelopathy of filamentous green algae

Allelopathy of filamentous green algae (FGA) has been less studied than that of macrophytes. Little Budworth Pool, Cheshire, UK is a small, shallow, clear-water lake with high TP concentrations, very high NO3-N concentrations, only moderate phytoplankton density, high FGA growth (mainly Spirogyra sp.) and no submerged plants. Experiments were carried out to test the possible allelopathic effects of Spirogyra on the phytoplankton of this lake and on a submerged plant Elodea nuttallii. Changes in phytoplankton growth, phytoplankton species dynamics and species composition were apparently not influenced by allelopathy of live or decaying Spirogyra. A shift from diatom (Cyclotella sp) – cryptomonad (Chroomonas acuta and Cryptomonas erosa) dominance to Chlorococcales (Micractinium pusillum, Monoraphidium contortum and Scenedesmus opoliensis) – Volvocales (Chlorogonium elongatum and Pandorina morum) dominance was recorded in both control and FGA treatments, suggesting an effect of nutrient enrichment. Nutrient concentrations and differences in competitiveness among phytoplankton species can also explain differences in their growth rates in Spirogyra filtrate. Spirogyra also did not influence apex number per plant, shoot length or growth rate of E. nuttallii. This FGA species probably cannot control phytoplankton or E. nuttallii growth in nutrient rich conditions through allelopathy.

Applicability of Littoral Food-web Biomanipulation for Lake Management Purposes: Snails, Macrophytes, and Water Transparency in Northeast Ohio Shallow Lakes

Seven shallow-to-intermediate-depth, meso-eutrophic lakes in northeast Ohio were surveyed July-August 1998 to evaluate a macrophyte-based littoral food-web (and its possible manipulation) role in increasing or maintaining water transparency. Macrophyte and periphyton growth were determined from pre-weighed C. demersum sprigs and biomass developed on glass tiles, respectively; littoral snail densities were estimated from assemblages in large-mesh cages at 1-m depth. Other variables were monitored weekly in situ. Lakes were generally phosphorus (P)-limited, but differed significantly in perceived state (turbid, stable or unstable clear-water), water transparency (SD), total phosphorus (TP) and chlorophyll a concentration (chla), vegetation cover (VC), snail density, sprig growth and periphyton biomass. The most richly vegetated lake was also the most stable (seasonally and long-term) clear-water lake, but midsummer SD was more strongly correlated with watershed:lake surface area. C. demersum growth was negatively correlated with periphyton biomass; meristem production was lower in turbid lakes, but was influenced by TP. Snail abundance tended to follow food (periphyton) and substrate (VC) availability, but was lower in crayfish-present lakes. Correlations between lake-describing variables were nonlinear with frequent outliers. When integrated with information from the literature, the results suggest that littoral food-web biomanipulation may be employed as a management technique in some cases. More often, macrophytes and the macrophyte-driven, snail-mediated clear-water stable state may (re)establish naturally in suitable lakes after conditions are brought above a “threshold” for plant growth. Frequent exceptions in observed patterns in this study and elsewhere suggest that applicability of littoral food-web biomanipulation should be evaluated on a case-by-case basis.

A filamentous green algae-dominated temperate shallow lake: Variations on the theme of clear-water stable states?

Shallow lakes can have two alternative stable states over wide range of nutrient concentrations: a macrophyte-dominated clear-water state and a phytoplankton-dominated turbid-water state. Little Budworth Pool, Cheshire, UK is a small (surface area 3 ha), shallow (max. depth < 1m), clear-water lake with very high nitrate concentrations (annual mean 9.2 mg NO 3 -N 1 -1 ), relatively low phytoplankton growth (annual mean 13.5 μg chlorophyll-a 1 -1 ) and high metaphytic filamentous green algal abundance (FGA, mainly Spirogyra), but without any submerged plant-beds. To understand the mechanism limiting phytoplankton biomass in summer, the lake was sampled every two weeks for two years (November 2001-October 2003) for water chemistry, phytoplankton, zooplankton, benthic macroinvertebrates, FGA and benthic diatoms. Phytoplankton growth was mainly dominated by small species like Cyclotella spp., Chroomonas acuta and Cryptomonas spp., whereas among the zooplankton Cladocera showed high abundance of both small and large species (Bosmina longirostris and Daphnia longispina) especially in summer and autumn. FGA attained highest biomass in the warmer months and showed negative correlations with nitrate-N and total nitrogen concentrations suggesting nutrient removal ability of these plants, but also possible increased denitrification in summer. While phytoplankton growth was negatively correlated with FGA biomass, cladoceran densities were positively related to the latter. A comparison among macrophyte-dominated lakes and FGA-dominated lakes showed similarities among them regarding water clarity, nutrient concentrations, phytoplankton growth and species composition, zooplankton assemblage and abundance, but not for abundance of benthic macroinvertebrates. We suggest that in a lake lacking submerged plants, abundance of FGA may act as a buffer against a forward switch to phytoplankton dominance, thus maintaining a clear-water state. The control of phytoplankton growth was primarily not through FGA removing nutrients from the water because sufficient available nutrients were recorded in water during summer. Rather it was by intense grazing by cladocerans ostensibly supported in refuges provided by FGA.