Increase In Water Transparency Research Articles

Potential effects of climate change and eutrophication on a large subtropical shallow lake

In many aquatic ecosystems, increased nutrient loading has caused eutrophication, which is reflected in the trophic structure of the ecosystem. In Lake Mangueira, a large shallow subtropical lake in Brazil, nutrient loading has also increased, but it is still unclear what the effects of this increase will be and how this relates to climate change. To evaluate the effects of increased nutrient loadings in such large lake one would need to integrate hydrological and ecological processes into one model, an approach that has rarely been used before. Here, we apply different versions of a complex 3D ecological model, called IPH-TRIM3D-PCLake, which describes the integrated hydrodynamic, water-quality, and biological processes in the lake. First, the nutrient loadings from the watershed were estimated using a separate hydrological water quality model of the watershed based on field data. Second, we calibrated the 3D ecological model for a 6-year monitoring period in the lake using a simplified non-spatial version of the model. Finally, the calibrated ecological model was applied to evaluate the spatial explicit effects of different scenarios of land use, water pumping for irrigation, and climate change. On short term (1.5 year), the system seemed to be rather resilient, probably because of the lake size related to its high inertia. Our simulations indicated warming can increase water transparency in Lake Mangueira which may be related to two factors: (a) the current meso-oligotrophic state of the lake which may easily lead to nutrient limitation; and (b) submerged macrophytes grow during the whole season. The combined effect of climate change and increased nutrient loading, less strong than increased nutrient loading alone. The model can only be used for qualitative predictions of the effect of management scenarios, such as maintenance of water levels in the dry season, and water-pumping rules for irrigation in order to maintain the ecosystem structure and functions in the future under additional stress caused by increased use or climate change.

Structural and successional variability of periphytic algal community in a Amazonian lake during the dry and rainy season (Rio Branco, Acre)

The colonization process and successional patterns of a periphytic algal community were evaluated in a Amazonian Viveiro Lake (Rio Branco, Acre, Brazil). Sampling was performed over a period of 35 days; at four-day intervals for 20 days, and then at five-day intervals. Water sampling for physical, chemical and biological analyses was done during the dry and rainy season. Glass slides were used as artificial substrates for periphyton colonization. The structural community was evaluated through population density, algae class, diversity indices and descriptive species. Species richness, diversity and evenness increased as succession progressed. While density of Bacillariophyceae, Euglenophyceae and Zygnemaphyceae increased with succession, Cyanobacteria remained dominant. Synechocystis aquatilis, Synechocystis diplococcus and Navicula pseudolanceolata were the main descriptive species in both the dry and rainy season. Cymbela tumida, Frustulia rhomboides, Trachelomonas lacustris and Closterium acicularis was correlated with an increase in hydrologic level during the rainy season. Conversely, the density of Chlamydomonas sp., Chroomonas nordstedtii, Trachelomonas volvocinopsis, Trachelomonas volvocina and Synechococcus linearis was correlated with an increase in water transparency during the dry season. In general, the periphytic algal community showed high diversity and species richness independent of season. Season also had little influence on representation of algae class and main descriptive species. However, successional patterns varied by season, and changes in hydrologic levels acted directly on the succession path of periphytic algae. More research on periphyton dynamics is needed to improve our understanding of tropical lake ecosystems, especially in Amazonian.

Enclosure Study on Phytoplankton Response to Stocking of Silver Carp (Hypophthalmichthys molitrix) in a Eutrophic Tropical Reservoir in South China

AbstractA 10‐week enclosure experiment was conducted in the dry season (October to December) to assess the impact of fish stocking on water quality and phytoplankton community at three stocking levels of silver carp (Hypophthalmichthys molitrix) (0, 16 and 50 g m–3) in a shallow, eutrophic tropical reservoir (Guangdong, South China). The nanophytoplankton (< 20 μm) accounted for 60 ± 5% of total biomass and Scenedesmus quadricauda was the predominant species (size: 16.5 ± 5 µm, relative biomass 27 ± 10%). Phytoplankton biomass was markedly suppressed in high fish stocking level and the grazing effect of silver carp on the nanoplankton was significant from the sixth week to the end of the experiment. The high fish density treatment significantly increased water transparency and somewhat reduced total phosphorus. Indirect effects of silver carp on the phytoplankton community involved excretion of nitrogen that favored small species of Chlorophyta. Colonial Cyanobacteria were reduced in the high fish treatment, but enhanced in the low fish treatment.Our results suggest that the widespread practice of harvesting fish from October to December in reservoirs of South China releases phytoplankton from consumption by filter‐feeding fish, and consequently prompts algal blooms. Conversely, harvesting fish just before monsoon, around the time of restocking with small fish, would make more sense since no interruption in grazing pressure would occur. This would help to control excessive phytoplankton biomass just before monsoon. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Submerged aquatic vegetation in Cook's Bay, Lake Simcoe: Assessment of changes in response to increased water transparency

A high frequency echo sounding method was employed to assess the extent of SAV cover and depth of colonization in Cook's Bay, Lake Simcoe during the late summer of 2006 and 2007. Results from this study are compared to historical echo sounding surveys in Cook's Bay conducted in 1984 and 1987, prior to reductions in point source phosphorus loads to the lake and before dreissenid mussel invasion. This study revealed that the total area of inner Cook's Bay covered by SAV has increased 65% since 1987, and SAV coverage extends to depths approaching 10 m. The areal expansion of SAV and increased depth of colonization are consistent with observations of increasing water transparency documented by the Ontario Ministry of Environment since the 1980s. Tissue nutrient content (N and P) of SAV growing in Cook's Bay during 2006 was found to be significantly lower than nutrient content measured in 1984 suggesting that light availability has increased relative to nutrient availability to SAV. The results of this study support are consistent with other studies demonstrating an areal expansion and increased depth of SAV colonization in response to increased water transparency.

Effect of chlorophyll sampling design on water quality assessment in thermally stratified lakes

In order to adequately assess the ecological status of thermally stratified lakes based on chlorophyll, the sampling must cover all productive layers of the water column. Missing the deep chlorophyll maxima (DCM) that often occur in the meta- or hypolimnion of transparent lakes supported by sufficient illumination and good nutrient availability may cause serious underestimation of the productivity and lead to misclassification of the lake ecological status. There is no commonly accepted sampling design for stratified lakes, and various monitoring guides suggest controversial designs. Our aim was to find some robust criteria to assess the probability of occurrence of a DCM and estimate the differences in measured mean chlorophyll concentrations caused by various sampling designs. Our theoretical model showed that the probability of occurrence of a DCM increases with increasing water transparency and decreasing lake size. Empirical data from Italian and Estonian stratified lakes confirmed the results. Testing of different sampling designs on lakes with full measured chlorophyll profiles available showed that taking only surface layer samples will lead with a high probability to an underestimation of the chlorophyll concentration in the trophogenic layer. In order not to miss the Chl peak in stratified lakes, in most cases it would be more precautious not to limit the sampling to the well-mixed epilimnion but to extend it to the whole euphotic layer. Sampling the epilimnion instead of the euphotic zone could cause up to a 70% underestimation of the chlorophyll concentration, an error that would cause a misclassification of the lake by one or even two status classes in a 5-class assessment system. In most cases, the 2.5 * Secchi depths proved a suitable criterion of the sampling depth and only in the case of surface scums, would sampling of a 3 * Secchi depth layer be recommended in order not to miss the deep chlorophyll maximum.

Can Submerged Macrophytes Influence Turbidity and Trophic State in Deep Lakes? Suggestions from a Case Study

Feedback between submerged macrophytes and water transparency stabilizing the clear, macrophyte-dominated regime has been described so far for shallow lakes. Based on data of total phosphorus (TP) concentrations, underwater light supply, phytoplankton and submerged macrophyte abundance from narrow, stratified Lake Scharmützelsee (mean depth: 9 m, retention time: 16 yr) of the period 1994-2006 we hypothesize that submerged macrophytes may influence transparency and trophic state in deep lakes. The lake was characterized by summer epilimnion TP concentrations of 38 to 57 mug L(-1), turbid water due to mass development of cyanobacteria, and low abundance of few submerged macrophyte species until 2003. Thereafter, a sudden increase in water transparency was followed by a rapid submerged macrophyte colonization of the littoral down to about 5 m depth corresponding to the depth of a light supply of 3 E m(-2) d(-1). Initially, this recolonization was probably a consequence of decreased turbidity. We argue that the increase of submerged macrophyte coverage from < 10% in 1994 to 2003 to about 24% in 2005-2006 has contributed to the stabilization of the clear-water regime during the subsequent years. This is supported by the fact that earlier shifts to clear-water regimes in 1994 and 2000 without a significant spread of submerged macrophytes were not stable. We discuss potential mechanisms that may have resulted in a positive effect of plants on transparency such as P uptake and immobilization by the dominant rootless macrophyte species Nitellopsis obtusa and Ceratophyllum demersum and other macrophyte-related mechanisms such as increased zooplankton grazing and allelopathy.

15N isotope fractionation in an aquatic food chain: Bellamya aeruginosa (Reeve) as an algal control agent

15N isotope tracer techniques and ecological modeling were adopted to investigate the fractionation of nitrogen, its uptake and transformation in algae and snail ( Bellamya aeruginosa Reeve). Different algal species were found to differ in their uptake of nitrogen isotopes. Microcystis aeruginisa Kütz. demonstrated the greatest 15N accumulation capacity, with the natural variation in isotopic ratio (δ 15N) and the isotope fractionation factor (ɛ, ‰) being the highest among the species investigated. The transformation and utilization of 15N by snails differed depending on the specific algae consumed (highest for Chlorella pyrenoidosa Chick., lowest for M. aeruginisa). When snails was seeded in the experimental pond, the algae population structure changed significantly, and total algal biomass as well as the concentration of all nitrogen species decreased, causing an increase in water transparency. A model, incorporating several chemical and biological parameters, was developed to predict algal biomass in an aquatic system when snails was present. The data collected during this investigation indicated that the gastropods such as snails could significantly impact biological community and water quality of small water bodies, suggesting a role for biological control of noxious algal blooms associated with eutrophication.

Approaching storm: Disappearing winter bloom in Lake Michigan

Between 1990 and 2001, late-winter phytoplankton blooms were common in parts of the lower Great Lakes (southern Lake Michigan, Saginaw Bay and southern Lake Huron, and western Lake Erie), providing resources for over-wintering zooplankton. In Lake Michigan up to 2001, detailed remote sensing and ship studies documented well-developed late-winter blooms in the southern gyre (circular bloom termed the ‘doughnut’). However, from 2001 to 2008, the winter blooms in Lake Michigan also supported early season veliger larvae from the introduced, cold-water adapted “profunda” morph of quagga mussels ( Dreissena rostriformis bugensis). Remote sensing and ship studies revealed that settled mussels caused an extraordinary increase in water transparency and a simultaneous decrease of Chl a in the late-winter bloom. Before quagga mussels in 2001, water transparency was 74–85% at deep-water sites, whereas it increased progressively to 89% by 2006 and 94–96% by 2008. Chlorophyll a concentrations in the gyre rings were 1.1–2.6 µg/L in 2001, declining to 0.5–1.7 µg/L by 2006 and 0.4–1.5 µg/L by 2008. The reduction of Chl a in the winter bloom rings from 2001 to 2008 was 56–78% for the western limb and 74–75% for the eastern limb. Zooplankton species abundance, composition and abundance also changed, as cyclopoid copepods became very scarce and over-wintering omnivorous calanoid copepods declined. Reduction in late-winter phytoplankton and zooplankton poses a serious threat to open-water food webs.

Factors contributing to cucumber odor in a northern USA reservoir

Episodic occurrences of cucumber odor caused by the alga Synura petersenii in Meander Creek Reservoir (MCR), northeastern Ohio, USA, are partly attributed to increased water transparency resulting from decreased phosphorus and suspended solids loading from the watershed. The first documented occurrence of nuisance odor levels was in 1984, 52 years after the reservoir was filled. This indicates that previous environmental factors constraining the growth of S. petersenii have been relaxed, probably from changes in the physical–chemical environment in the reservoir caused by changes in land use in the catchment. Reduction in farming since 1950, and diversion of sewage around the reservoir in 1977, reduced suspended solids and total phosphorus loading into the reservoir during the time that the cucumber odors occurred. These observations support the hypothesis that increased transparency of the reservoir, resulting from decreased sediment loading and reduced productivity, has permitted the occasional occurrence of nuisance densities of S. petersenii. Based on available data, pH, iron, and silica do not appear to be key factors regulating growth of S. petersenii in MCR. The transition to lower turbidity and total phosphorus concentrations from catchment restoration actions may increases the risk of S. petersenii blooms and cucumber odor episodes. While the overall benefits of cleaner raw water for water supply may outweigh this risk, it is desirable to understand the factors that promote nuisance growths and take actions to control them.

Exotic species of zooplankton in the Upper Paraná River floodplain, Daphnia lumholtzi Sars, 1885 (Crustacea: Branchiopoda)

The integrity of aquatic ecosystems is being challenged worldwide by invading species, which has been one of the frequent causes of biodiversity loss. The invader may cause extinctions of vulnerable native species through predation, grazing, competition and habitat alteration. Daphnia lumholtzi G. O. Sars, 1885, a native cladoceran from Australia, Southwestern Asia and North Africa, has recently been found in the Neotropical region. The D. lumholtzi records from the Upper Paraná River floodplain were restricted to the Pombas floodplain lake (22 degrees 47' 55.92" S and 53 degrees 21' 32.58" W) and Pau Véio Backwater (22 degrees 44' 50.76' S and 53 degrees 15' 11.16' W), in 2003 and 2008, respectively. This species can be distinguished from the other Daphnia species registered in Brazil by the conspicuous pointed fornix, the sizes of the tail spine and helmet, and a carapace ventral margin with strong spines. The high temperatures in the tropical region, as well as the increase in water transparency and the decrease in nutrient concentration observed in the environments of the Upper Paraná River floodplain due to the upstream retention by dams, may favor the development of D. lumholtzi populations. The development of populations of D. lumholtzi in natural environments of the Upper Paraná River floodplain may suggest that this species is establishing in the Neotropical region.

Limnology in the Upper Paraná River floodplain: large-scale spatial and temporal patterns, and the influence of reservoirs

Knowledge of abiotic limnological factors is important to monitor changes caused by humans, and to explain the structure and dynamics of populations and communities in a variety of inland water ecosystems. In this study, we used a long term data-set (eight years) collected in 10 habitats with different features (river channels, and connected and isolated lakes) to describe the spatial and temporal patterns of some of the principal limnological factors. In general, the degree of connectivity of the lakes, together with the rivers to which the lakes are connected, were important determinants of their limnological characteristics. These differences are expected, because rivers entering the floodplain come from different geological regions and are subject to different human impacts. At large spatial scales, these differences contribute to the increased habitat diversity of the floodplain and thus to its high biodiversity. With regard to temporal variation, Secchi-disk transparency increased, and total phosphorus decreased in the Paraná River main channel during the last 20 years. Although these changes are directly attributed to the several reservoir cascades located upstream, the closing of the Porto Primavera dam in 1998 enhanced this effect. The increase in water transparency explains biotic changes within the floodplain. The lower-phosphorus Paraná River water probably dilutes concentrations of this element in the floodplain waterbodies during major floods, with future consequences for their productivity.

Multi‐decadal shoaling of the euphotic zone in the southern sector of the California Current System

We document a long‐term reduction in Secchi depth of 0.06–0.13 m yr−1 in the southern California Current System (CCS) over the period 1969–2007, reflecting a long‐term shoaling of the euphotic zone. Calibrated water clarity observations from 1949 to 1954 reinforce the results indicating a progressive shoaling. For the inshore area, 150 km off the coast, Secchi disk has shoaled 8.4 ± 1.2 m since 1949. This change has been accompanied by a nitracline shoaling of 18.2 ± 6.4 m since 1969 and an increase in chlorophyll a since 1978. These changes have occurred despite an increase in density stratification in the CCS. Increased stratification has been linked by others to decreased nutrient fluxes, reduced primary production, increased water transparency, and a deepening of the euphotic zone, contrary to our findings. We explore this apparent paradox with a simple steady‐state model of the thickness of the euphotic zone. A sensitivity analysis suggests that the observed shoaling of the euphotic zone is consistent with a doubling in nutrient upwelling, but in this analysis we also consider alternative causes for such shoaling: water‐column darkening caused by freshening, increased residence time of the phototrophic biomass in the euphotic zone, and supply of nutrients of anthropogenic origin.

Diurnal dynamics of the vertical distribution of zooplankton in an oligotrophic lake

The diurnal dynamics of the vertical distribution of zooplankton was studied in an oligotrophic lake with a high water transparency. Those sedentary species which occupy the upper water layers in waterbodies with low water transparency shift to a border between epy- and metalimnion and stay there during most of the day in Koskovskoye Lake, which has a high water transparency. Active diurnal vertical migrations are characteristic of large organisms. Increased water transparency weakly affects large zooplankters that occupy metalimnial layers in mesotrophic waterbodies. The relationship between the zooplankton’s vertical distribution and the distribution of phytoplankton and fish is analyzed.

Plankton studies in Buzzards Bay, Massachusetts, USA. VI. Phytoplankton and water quality, 1987 to 1998

From October 1987 through September 1998, phytoplankton composition, inorganic nutrients, temperature, salinity, water clarity, and chlorophyll a (chl a) + phaeopigments were moni- tored during 141 monthly cruises in Buzzards Bay, Massachusetts, USA. There were large seasonal and interannual variations in nitrate, silicate and phytoplankton abundance and composition. There were no consistent interannual patterns of recurrent spring blooms, measured as either chl a or phytoplankton cell abundance. Rather, blooms of various taxa were sporadic, particularly diatom blooms in the late summer and fall. Other parameters were similar bay-wide on a given day, and over seasons and years for stations away from New Bedford Harbor, but concentrations of ammonium, phosphate, and chl a were elevated at the New Bedford sewage outfall, prior to its conversion to sec- ondary treatment in September 1996. After conversion, increased water transparency and decreased levels of ammonium indicated improved water quality at the outfall. Bay-wide chl a and nitrate had significant declines over time from the late 1980s to the late 1990s. There were no significant linear trends with time for annual means of temperature, but there was a significant trend of increased warming in spring. Phytoplankton abundance (0.012 to 26.0 × 10 6 cells l -1 , 1988 to 1998) was higher than reported in other coastal waters of New England, due to preservation that did not destroy the delicate microflagellates and phytoflagellates which dominated phytoplankton abundance. Poten- tially harmful algal species included diatoms of the genus Pseudo-nitzschia, and the dinoflagellate Alexandrium fundyense. Buzzards Bay is a favorable habitat for phytoplankton in that it is well- mixed and well-illuminated, and nutrient-replete.

Changes in depth distribution and biomass of sublittoral seaweeds at Helgoland (North Sea) between 1970 and 2005

Recent investigations of the intertidal macrophyto- and zoobenthos of the island of Helgo- land (North Sea) revealed that species composition and spatial extent of communities have changed within the last century. To evaluate the situation in the subtidal, a diving study from the late 1960s was repeated with comparable methods in 2005 and 2006. Along 2 vertical transects, the cover of dominant brown seaweeds, Fucus serratus, Laminaria digitata, L. hyperborea, Saccharina latissima (= Laminaria saccharina), Sargassum muticum and Desmarestia aculeata, was semi-quantitatively assessed to define vegetation zones. Within each zone, all macroalgal species were estimated quantitatively in 3 to 6 random 1 m 2 quadrats. Additionally, a replicated biomass survey was performed at 6 depths (0.5, 2, 4, 6, 8 and 10 m below mean low water spring tide (MLWS)). Comparison of recent and historical data showed some characteristic changes. The previously dominant brown seaweed S. latissima showed a decline in the northern part of the island, but is still present at other sites. S. muticum invaded the kelp forest, but is not dominant within this vegetation. The vertical distribution of L. hyperborea increased, and its lower depth limits as well as those of various understory seaweeds deepened by about 2 to 8 m. Biomass data followed this trend. The maximum biomass of L. hyperborea shifted from 2 m below MLWS in 1967 to 4 m below MLWS in 2005. The overall downward extension of the Laminaria forest is concordant with the increase in water transparency observed around Helgoland since 1975.

Impact of the zebra mussel invasion on the ecological integrity of Lough Sheelin, Ireland: distribution, population characteristics and water quality changes in the lake

The zebra mussel, Dreissena polymorpha (Pallas 1771), invaded Lough Sheelin in the midlands of Ireland in 2001. In order to assess the status of the mussel population in the lake, the distribution, extent of colonisation, abundance, biomass and size-frequency structure of post-settlement stages were studied in 2005 and 2006. In addition, changes to water quality parameters in the lake postestablishment were assessed with reference to the pre-invasion period. Zebra mussels were found throughout the lake at most sites on all main categories of substrates examined (stony and soft substrate; submerged vegetation: Characeae, Elodea spp., Cladophora spp., Potamogeton spp. and Myriophyllum spp., and emergent vegetation: Phragmites australis and Schoenoplectus lacustris). Overall, increases in density and biomass of mussels were recorded from 2005 to 2006. Analysis of physiochemical data show a reduction in chlorophyll a with an increase in water transparency, however the total phosphorus concentration remains high. This paper highlights the common misconception that zebra mussel introductions lead to overall improvements in water quality.

Changes in dissolved nutrients in the lower Ebro river: Causes and consequences

Changes in dissolved nutrients in the lower Ebro River: Causes and consequences Water quality time series data regarding nutrient concentration and chlorophyll in the lower Ebro River and its estuary were analyzed over an 18 year period (1987-2004). Causes and consequences of changes in nutrient concentration are discussed and some hypotheses about it are established. A very significant decrease in the concentration of the dissolved nutrients, especially phosphorus, was observed after the mid 90s. This decrease coincides with the improvement of urban sewage treatment in the most important cities of the Ebro basin. There was also a significant positive correlation between the concentration of dissolved phosphorus and the concentration of total chlorophyll. Data suggest that low flow conditions together with the lower dissolved phosphorous and, therefore, less phytoplankton were likely the main factors causing the increase of water transparency. These conditions propitiated the spread of macrophytes and the massive appearance of the black fly. In the lower river and its estuary, the water undewent a decrease in phytoplankton, which improved its eutrophy condition. Results of this study suggest that the decrease in phosphorus is the main cause of the recent changes in the lower Ebro ecosystem, but other factors can also play a role by causing a further increase in water transparency and macrophyte spreading (positive feed-back).

Reverse Evolution of Armor Plates in the Threespine Stickleback

Faced with sudden environmental changes, animals must either adapt to novel environments or go extinct. Thus, study of the mechanisms underlying rapid adaptation is crucial not only for the understanding of natural evolutionary processes but also for the understanding of human-induced evolutionary change, which is an increasingly important problem [1-8]. In the present study, we demonstrate that the frequency of completely plated threespine stickleback fish (Gasterosteus aculeatus) has increased in an urban freshwater lake (Lake Washington, Seattle, Washington) within the last 40 years. This is a dramatic example of "reverse evolution,"[9] because the general evolutionary trajectory is toward armor-plate reduction in freshwater sticklebacks [10]. On the basis of our genetic studies and simulations, we propose that the most likely cause of reverse evolution is increased selection for the completely plated morph, which we suggest could result from higher levels of trout predation after a sudden increase in water transparency during the early 1970s. Rapid evolution was facilitated by the existence of standing allelic variation in Ectodysplasin (Eda), the gene that underlies the major plate-morph locus [11]. The Lake Washington stickleback thus provides a novel example of reverse evolution, which is probably caused by a change in allele frequency at the major plate locus in response to a changing predation regime.

REGIME SHIFT IN A COASTAL MARINE ECOSYSTEM

We demonstrate changes in ecosystem stable states in a coastal lagoon that are consistent with what a regime shift would hypothesize. In the nutrient-stressed Ringkøbing Fjord, Denmark, a small change in one variable (salinity) facilitated by a change in sluice management, caused a sudden regime shift from a bottom-up controlled turbid state, into a top-down controlled clear-water state. The change in dominating pathway of organic matter production from pelagic turnover to benthic-pelagic coupling was facilitated by new recruitment and growth of existing suspension-feeding clams, Mya arenaria. With the invasion of clams, benthic grazing became the key feature of the biological structure. Phytoplankton composition and zooplankton abundance were also affected by the change in biological structure. The small, but sudden, increase in salinity caused by the change in sluice management led to a dramatic reduction in biomass and coverage of benthic vegetation and thus affected herbivorous waterbird populations. In recent years, plant coverage has been increasing, as can be expected with increased water transparency. The regime shift has some major implications for coastal water management and revealed some conflicts between different types of nature and environmental protection legislation.

Response of waterbirds to alternating clear and turbid water phases in two shallow Mediterranean lakes

Albufera de Adra (Southern Spain) constitutes an internationally-recognised marsh for waterbirds; important populations of some endangered species such as White-headed Duck and Red-crested Pochard overwinter and breed in its two shallow permanent lakes (Lake Honda and Lake Nueva). In a recently published article, we revealed the factors responsible for the irregular alternation between phytoplankton-dominated turbid phases and macrophyte-dominated clear water phases in Lake Honda and Lake Nueva. In this note, we try to clarify the impact of such an alternation of equilibrium states on the waterbird dynamics. Marked increments in abundance, and brood recruitment of dabbling and diving waterbirds were recorded during the clear water phases in contrast with the turbid water phases, as the increase of macrophytes associated with increased water transparency attract waterbirds for available food. Implications for ecosystem management, restoration and conservation are identified.