Lake Vegetation Research Articles

Spatial and Seasonal Dynamics of Water Quality, Sediment Properties and Submerged Vegetation in a Eutrophic Lake after Ten Years of Ecological Restoration

Eutrophication has caused many serious environmental issues in lakes. Submerged vegetation, which plays a key role in maintaining the clear water state of shallow lakes, is strongly influenced by water quality and sediment properties. In this study, we seasonally investigated the water quality, sediment properties and submerged plant communities in 18 sites in Lake Honghu of China, an internationally important wetland under the Ramsar Convention. Results indicated that most of the water quality parameters and sediment properties showed no significant difference among the three site types (i.e., perennially vegetated, seasonally vegetated and unvegetated). However, the Secchi depth in perennially and seasonally vegetated sites was significantly higher that in unvegetated sites. By contrast, season had a strong effect on most of the water quality parameters and sediment properties (e.g., water chlorophyll-a concentration). For submerged vegetation, species richness and biomass showed significant spatial but not seasonal differences, with higher richness and biomass in perennially vegetated sites. Canonical correspondence analysis indicated that the distribution of submerged plants was mainly determined by water NH4+ concentration and water depth. Our findings suggest that restoration of submerged vegetation in Chinese eutrophic lakes may be a feasible method for improving water environments and enhancing ecological functions.

Первая экспедиция Л. Г. Раменского и ее значение в его творческой биографии

Первая экспедиция Л. Г. Раменского и ее значение в его творческой биографии

Response of vegetation to growing recreational pressure in the shallow Raczyńskie Lake

Strong human impact accelerates eutrophication which deteriorates water quality and consequently prevents recreational use. Increasing trophy and low transparency induce macrophyte rebuilding. A gradual transformation of the land use of the direct catchment area of Raczyńskie Lake from agricultural to recreational has been observed over the last 45 years. In built-up areas sewage facilities were inadequate and septic tanks did not work properly and as a consequence most wastewater was able to infiltrate through the ground into the lake. The lake ecosystem became unstable and water blooms intensified. The aim of the study was to assess the changes in the composition of the lake vegetation over the last 45 years, during which the use of the direct catchment has changed and recreational pressure increased. A reduction of the number of plant communities from 24 to 15 and the disappearance of almost all the submerged vegetation was observed. The dominant reed beds (Phragmitetum communis,Typhetum angustifoliae) were unable to provide a sufficient barrier to the flow of pollution from the catchment because of the numerous gaps made for angling piers, bathing sites, jetties, etc. The macrophyte index indicated a bad ecological status. To improve the ecological status of Raczyńskie Lake it is necessary to introduce intensive protection and restoration treatments.

Influence of littoral periphyton on whole-lake metabolism relates to littoral vegetation in humic lakes.

The role of littoral habitats in lake metabolism has been underrated, especially in humic lakes, based on an assumption of low benthic primary production (PP) due to low light penetration into water. This assumption has been challenged by recent recognition of littoral epiphyton dominance of whole-lake PP in a small highly humic lake and of epiphyton as an important basal food source for humic lake biota. However, as these studies have mostly concerned single lakes, there is a need to test their wider generality. We studied the whole-lake PP and community respiration (CR) in eight small humic lakes in southern Finland during July 2015 using 14 C incorporation to measure pelagic PP and the changes in dissolved inorganic carbon in light and dark insitu incubations to measure CR and littoral PP by epiphyton. Changes in O2 concentration in both pelagic and littoral surface water were measured periodically from each lake and, additionally, continuously with a data logger from one lake during the study period. The results revealed that the littoral dominated whole-lake net primary production (NPP) in five of the eight lakes, which was supported by observed O2 supersaturation in the littoral surface water in most of the lakes. Calculated pelagic:littoral ratios by area correlated negatively with both littoral NPP and littoral contribution to whole-lake NPP. Moreover, there was a significant positive relationship between littoral proportion of whole-lake NPP and the fraction of lake surface area covered by littoral aquatic vegetation. This demonstrates that increased aquatic littoral vegetation cover increases the overall importance of the littoral to whole-lake PP in highly humic lakes. Littoral NPP also correlated strongly with littoral O2 saturation, and the continuously measured O2 revealed substantial temporal variation in O2 saturation, particularly in the littoral zone. Whole-lake gross primary production:community respiration (GPP:CR) ratios revealed that accounting for littoral metabolism produced a marked shift towards lake metabolic balance, although all the eight lakes remained net heterotrophic. This study emphasizes that littoral metabolism needs to be accounted for when estimating whole-lake C fluxes in all lakes, even in highly colored humic waters.

Recovery of lake vegetation following reduced eutrophication and acidification

Abstract In recent decades, many aquatic ecosystems in Europe and North America have experienced reduced inputs of nutrients and acidifying substances because of improved sewage treatment and reduced emission of sulphur oxides. We evaluated the consequences of these efforts to changes in water chemistry, species richness and community composition of aquatic macrophytes in 56 lakes in Denmark around 1990 and again around 2010. Reductions in lake water concentrations of phosphorus and nitrogen were strongest in eutrophic and hypertrophic lakes, for example, lakes which had been heavily affected by domestic sewage. These changes translated into decreased algal biomass in the most eutrophied lakes. Oligo‐ and mesotrophic lakes did not change significantly in terms of nutrients or algal biomass. Water clarity increased across all lakes but not significantly in specific trophic lake groups. Alkalinity and pH increased significantly (up to 2 pH‐units) in low‐alkaline lakes, while well‐buffered high‐alkaline lakes (>0.5 meq/L) did not show any change. Macrophyte species richness per lake increased, on average, by 13% during the 20‐year study period. The increase was strongest in species preferring nutrient‐rich conditions and could be directly attributed to reductions in phytoplankton biomass in lakes of medium water clarity. The similarity among all lakes in terms of species composition increased over the study period. This development was closely related to higher average species richness and was mainly caused by recolonisation of lakes, recovering from past eutrophication, by relatively common species (e.g., Lemna trisulca, Sparganium emersum and Potamogeton berchtoldii). Higher pH in low‐alkaline lakes was accompanied by a shift from acid‐tolerant to more acid‐sensitive species. Our results demonstrate that investment in pollution control has been successful in terms of markedly improving water quality of lakes and, with a time lag, macrophyte species richness. Although relatively common species have spread across lakes and resulted in homogenised macrophyte communities, continued efforts to reduce pollution could ensure the survival of rare specialist species and perhaps even increase their abundance in the future.

Ant fauna associated with areas under the direct impact of small hydropower plants in the state of Paraná, Brazil

Ants can be important tools to assess the conditions of a given environment, as well as to monitor restoration of degraded areas. This study evaluated the richness and abundance of ant assemblages associated with areas directly impacted by the construction of small hydropower plants in the State of Paraná. To survey the ant fauna, samples were collected in September 2014 and January 2015 using pitfall and malaise traps. The association of the ant fauna composition with fragments and seasonality was analyzed by detrended correspondence. Fifty-eight species of ants were registered. The subfamily Myrmicine and the genus Camponotus were the most abundant (S= 25, S = 10, respectively). The removal of vegetation and formation of lakes in the directly affected area cause impacts that can be monitored based on the results of this study.

Is the flora of oxbow lakes different from that of fishponds? A comparison of two types of water reservoirs in the Noteć River valley and Bydgoszcz Canal valley (NW Poland)

The study was conducted in the growing seasons of 2011–2013 and involved 10 oxbow lakes located in the vicinity of Chobielin and 10 fishponds near Ślesin (north-western Poland). The oxbow lakes were characterized by a greater floristic diversity (212 species) compared with the ponds (131 species). Their flora has a more natural character, which is manifested in a higher pro- portion of native species, including non-synanthropic spontaneophytes (45.3%) as well as some legally protected species. In the ar- tificial reservoirs, non-native species represented 12.2% of the total number of species, in natural reservoirs – only 8.5%. The main differences in the spectrum of life forms were manifested in a higher relative abundance of phanerophytes in the vegetation of the oxbow lakes (10.8%), and a higher abundance of hydrophytes along with helophytes (17.6%), therophytes (18.3%), and geophytes (16.3%) in the ponds. The flora of the oxbow lakes was represented by species belonging to 20 phytosociological classes, while the flora of the ponds – 14 classes. Molinio-Arrhenatheretea and Phragmitetea australis accounted for the highest relative species abun- dance in both types of water bodies. Oxbow lakes are characterized by a much greater proportion of species from Querco-Fagetea, almost exclusively non-synanthropic spontaneophytes. Management practices associated with the maintenance of the ponds translate into a higher proportion of ruderal species, by nearly 6%. As a result, taxa from Artemisietea vulgaris were more numerous in the ponds. Edificators from Lemnetea minoris and Potametea were also abundant there. The differences in the analysed flora, resulting primarily from different origins of the reservoirs and their surroundings (mainly forests in the case of the oxbow lakes and meadows around the ponds), was confirmed by statistical analysis and synanthropization indices. Despite their different origin and management methods, both types of reservoirs are valuable refuges for native flora and are characterized by high and similar values of floristic diversity indices. While the oxbow lakes are protected from degradation as protected habitats, the existence and condition of vegeta- tion in fishponds are entirely dependent on the economic regime of fish farms.

Aquatic vegetation in deep lakes: Macrophyte co-occurrence patterns and environmental determinants

Our aims were to test the hypothesis that in deep lakes the co-occurrence patterns of macrophytes are not random, and to compare the relative contribution of the main environmental determinants (light, water and sediment parameters, phytoplankton) in structuring aquatic vegetation. We collected data from five deep Chara-dominated lakes in Central Italy along gradients of depth (33 to 165 m), dimension (1.7 to 114.5 km2) and water trophic conditions (12.4 to 41.3 μg L-1 of total phosphorous). Twenty-five sampling plots per lake were randomly selected at five predetermined depths (1.5, 3.0, 6.0, 12.0 and 20.0 m; n=5) within homogenous littoral sectors. Data were explored by a null model analysis using the checkerboard score (C-score) index, and Canonical Correspondence Analysis. Our data verify the not random co-occurrence patterns of macrophyte’ communities in deep lakes. However, present data suggested that C-scores are strictly dependent on lake’ trophic status: low nutrient loads, in both water and sediments, seemed to be reflected in a not random co-occurrence zonation of macrophytes. Summarizing, it is fundamental evaluate the local effects of lake trophy on the macrophyte community dynamics both in time and space before inquiring about mutual links. If it fails to assess macrophyte co-occurrence patterns, it may be not possible to identify the determinants of the spatial arrangement of macrophytes and, in turn, the conservation status or the ongoing dynamics of lakes.

Impact of acid precipitation on historical monuments and statues

Abstract A host of deleterious factors can impact the aging and integrity of historical monuments and statues. These may include natural causes such as water, wind, and temperature variation as well as the even more detrimental human causes of industrial pollution, urban warming, and fossil fuel emissions from vehicles all of which contribute to the development of acid precipitation. In addition, where the use of fossil fuels is wide-spread the occurrence of acid precipitation tends to be more prevalent and as a result serious damage can occur to the natural environment. Acid precipitation causes irreparable damage to vegetation, wildlife, and fish populations in lakes, streams, and rivers. Also, damage caused by acid precipitation can be quite recognizable on historical monuments and statues constructed from carbonate-based stone. The stone derived from carbonate sources such as limestone, dolomite, and marble have been widely used for thousands of years in the construction of monuments and statues. Carbonate-based stone was often chosen because of its abundance, suitability for shaping, and robust quality. Many historic works of art which not only characterize a period of art but also create powerful images of the artist and artwork have survived for thousands of years. The emergence of acid precipitation though has caused irreparable damage and destruction to many of these irreplaceable works of art, monuments, and statues. In this study, the research focuses on better understanding of acid precipitation and its impact on items of cultural heritage such as historical monuments and statues. Sample cases were chosen to emphasize and evaluate deleterious impact which may have occurred to these items of cultural heritage. According to research evaluation results from this study the researcher has provided recommendations for resolving the impacts of acid precipitation on these historical monuments and statues. Keywords: fossil fuels, acid precipitation, historical artefacts, marble statues.
 Keywords: fossil fuels, acid precipitation, historical artefacts, marble statues.

Estimating the biomass of unevenly distributed aquatic vegetation in a lake using the normalized water-adjusted vegetation index and scale transformation method

Satellite remote sensing is advantageous for the mapping and monitoring of aquatic vegetation biomass at large spatial scales. We proposed a scale transformation (CT) method of converting the field sampling-site biomass from the quadrat to pixel scale and a new normalized water-adjusted vegetation index (NWAVI) based on remotely sensed imagery for the biomass estimation of aquatic vegetation (excluding emergent vegetation). We used a modeling approach based on the proposed CT method and NWAVI as well as statistical analyses including linear, quadratic, logarithmic, cubic, exponential, inverse and power regression to estimate the aquatic vegetation biomass, and we evaluated the performance of the biomass estimation. We mapped the spatial distribution and temporal change of the aquatic vegetation biomass using a geographic information system in a test lake in different months.The exponential regression models based on CT and the NWAVI had optimal adjusted R2, F and Sig. values in both May and August 2013. The scatter plots of the observed versus the predicted biomass showed that most of the validated field sites were near the 1:1 line. The RMSE, ARE and RE values were small. The spatial distribution and change of the aquatic vegetation biomass in the study area showed clear variability.Among the NWAVI-based and other vegetation index-based models, the CT and NWAVI-based models had the largest adjusted R2, F and the smallest ARE values in both tests. The proposed modeling scheme is effective for the biomass estimation of aquatic vegetation in lakes. It indicated that the proposed method can provide a most accurate spatial distribution map of aquatic vegetation biomass for lake ecological management. More accurate biomass maps of aquatic vegetation are essential for implementing conservation policy and for reducing uncertainties in our understanding of the lake carbon cycle.

Растительность акватории и побережий озера Таловское и его окрестностей (Корякский округ, Камчатский край)

Растительность акватории и побережий озера Таловское и его окрестностей (Корякский округ, Камчатский край)

Remarkable richness of aquatic macrophytes in 3-years old re-established Lake Fil, Denmark

In August 2014, we discovered a surprisingly high species richness of aquatic macrophytes (33 species) in Lake Fil only two years after the large, shallow lake had been re-established following land reclamation and 60 years of intense agricultural use. In 2015, plant richness had increased even further (to 40 species). Some rare, oligotrophic species, which formerly were common in the historical lake, have re-established populations (e.g. Elatine hydropiper and Lythrum portula). However, a larger number of meso- and eutrophic species have colonized the re-established lake, changing the character of aquatic macrophyte flora as compared to the historical lake. The very rare Baldellia repens, considered extinct species in Denmark, has become re-established with at least 13 subpopulations in the new Lake Fil. Also two species recently discovered in Denmark (Callitriche obtusangula and Lemna turionifera) were found. Half of the species may have colonized the re-established lake from now submerged drainage canals and from an upstream lake, while the other half presumably have colonized from more distant lakes. The high richness of aquatic macrophytes in the re-established Lake Fil is matched by only a few natural lakes in Denmark. According to predictions of species richness from environmental conditions and colonized area in 56 natural Danish lakes, the observed richness in Lake Fil is two-fold the expected. We attribute the high plant richness to: shallow waters, large open areas on grazed or physically exposed lake shores and high likelihood of species recruitment from neighboring lakes via dense populations of migratory waterfowl. High plant richness was established despite low transparency due to high release of dissolved organic matter and particles from flooded soils. We conclude that suitable bathymetry, physical disturbance, grazing by cattle and waterfowl in the littoral zone and high dispersal capacity of propagules may ensure rapid establishment of a rich aquatic vegetation in new lakes, even when nutrient-rich farmland is the starting point.

Short‐term dynamics of submerged aquatic vegetation diversity and abundance in deep lakes

AbstractQuestionWhat are the short‐term trends of submerged aquatic vegetation (SAV) in deep lakes? Is it possible to measure significant changes in SAV distribution in deep lakes characterized by different trophic states and stable water physico‐chemical conditions using standard procedures over a 3‐yr period (2010–2013), as defined by the Water Framework Directive?LocationWe collected data from four deep lakes belonging to the Italian volcanic lake system (central Italy), which is one of the most important reserves of freshwater in Mediterranean Italy as well as one of the main hotspots of stonewort diversity in the Mediterranean area.MethodsMacrophytes were sampled along five transects in each lake in 2010 and 2013. Data on aquatic plant diversity, composition and abundance were collected from each 1‐m depth intervals down to the maximum colonization depth. Simultaneously, the water quality and climate were assessed by standard procedures. Data were analysed with PCA, ANOVA, PROTEST and rank abundance curves.ResultsThe sampling revealed a significant rearrangement of SAV. Increased species diversity in the first meters of depth (0–5 m) was due to the migration of mid‐depth species to lower depths. A reduction in the maximum growing depth of macrophytes was observed within the deepest stonewort communities (below 5 m). No significant changes emerged in water quality or climate.ConclusionsOver 3 yr, SAV displayed significant changes that appear to be independent of summer nutrient conditions and climate drivers. In particular, vascular and stonewort species underwent a distinct spatial rearrangement according to specific behaviours. The present data point to the need for more rigorous analyses of the intra‐annual dynamics of macrophytes in deep lakes. An influence of the significant increase in spring precipitation (which is in keeping with local climate variability) recorded in central Italy in the last decade cannot be ruled out a priori, nor can the possibility of stochastic fluctuations be excluded. All these considerations further highlight the critical role of aquatic plants as bioindicators.

Xingu State Park vascular plant survey: filling the gaps

Located in the southeastern limit of the Amazon biome, the Xingu State Park (PEX) was identified as a knowledge gap, leading to a floristic and vegetation survey of the area. During this work, 463 species distributed in 295 genera and 111 families of vascular plants were recorded, including dozens of new records for the state of Mato Grosso and at least five species new to science. Seven vegetation types were found, among which the Open Ombrophilous forest and the “Varzea” (floodplain) and lake vegetation showed the highest species richness. The vegetation of the Alto Xingu River was hitherto undocumented although this area is subject to strong deforestation pressure for cattle ranching from the southwest and soybean cultivation from the southeast, and is currently a focus of international attention due to the plans for the Belo Monte hydroelectric plant downriver in the state of Para. When compared with a survey of the neighbouring Cristalino State Park, there was remarkably little overlap in vegetation types and plant species, highlighting the importance of increasing the intensity of plant surveys and collections in the Amazon including protected areas, so as to address the many, vast lacunae in our understanding of this biodiverse and threatened biome. Historic and geographic factors have polarized research in Brazil such that the Amazonian biome lags behind the eastern part of the country in terms of plant knowledge, and this type of initiative helps in providing much needed data to address this situation.

Long‐term effects of liming in Norwegian softwater lakes: the rise and fall of bulbous rush (Juncus bulbosus) and decline of isoetid vegetation

Summary Acidification has been recognised as a serious environmental problem in Scandinavia since the 1970s, and liming has been the main strategy to counteract negative effects on biota by improving water quality. We studied the short‐ and long‐term effects of liming on sediment and water quality, as well as macrophyte development, by comparing five limed with five unlimed lakes during the period 1993–2013. In the limed lakes, massive development of bulbous rush (Juncus bulbosus: Juncaceae) occurred during the first 6–9 years after the start of liming (1984–1993). Juncus bulbosus then started to decline around 1999 and eventually reached its original abundance in 2010. In addition, the cover of the original isoetid vegetation declined by around 60% between 1995 and 2010. In contrast, changes in submerged aquatic vegetation in the unlimed lakes were minor. Liming initially stimulated anaerobic breakdown of sediment organic matter with Fe as the electron acceptor. Juncus bulbosus probably benefitted from the higher CO2 fluxes from the sediment to the water layer in combination with a high NH4+ concentration in the limed sediment. However, the organic matter became less reactive over time, thus eventually providing less CO2. Together with the significant increase in water pH over time, this would have led to a decline in C availability in sediment and water, thus discouraging excessive growth of J. bulbosus. This may explain why J. bulbosus thrived only during the first years after liming. The decline of isoetids in limed lakes was probably caused by a combination of uprooting and sediment anoxia. In limed lakes, isoetids developed a shoot : root ratio that was above the threshold known to promote uprooting of these high buoyancy species on organic sediment. In addition, isoetids eventually became covered by algae and dead J. bulbosus, affecting light conditions and suffocating the remaining isoetid vegetation on limed reductive sediments. In the future, renewed excessive growth of J. bulbosus seems unlikely due to the lack of sufficient carbon sources. It remains, however, unclear whether the original isoetids vegetation can recover. We hypothesise that the isoetid Littorella uniflora may eventually recolonise the lake from the shore and improve the oxygen content of limed sediments; this, in turn will facilitate the germination of other plant species, through high radial oxygen loss in combination with asexual reproduction.

Importance of spatial scale in structuring emergent lake vegetation across environmental gradients and scales: GIS-based approach

Geographical information systems (GIS)-based approaches support the traditional empirical assessment and monitoring measures to indicate large-scale environmental alterations caused by global change. We examined the relationship between cover patterns of emergent aquatic plants derived from the CORINE land cover database, and environmental gradients (i.e. lake, climate and land cover and soil variables) at four different buffer scales (50m, 100m, 300m and 500m) in 408 boreal lakes in Finland. Our main statistical methods were hierarchical partitioning (HP), generalized linear models (GLM) and variation partitioning (VP).Based on correlations and HP, the importance of different buffer zones varied between environmental variables in explaining the vegetation cover. Our study also demonstrated that landscape productivity variables (i.e. Normalized Difference Vegetation Index and Tasseled Cap Greenness) strongly structured the vegetation cover. These productivity variables proved to be proxies for agricultural land and nutrient leaching from terrestrial areas to water, but they were also associated with shading of riparian vegetation. In the VP, land cover and soil variable groups influenced emergent vegetation cover the most, followed by lake and, lastly, by climate variables.Our work emphasized the importance of spatial scale in structuring freshwater assemblages that should be taken into account in ecological research and bioassessment. The use of a single spatial scale may lead to flawed results on the relevance of various environmental gradients on freshwater assemblages. Moreover, our study showed that satellite-based productivity variables can be powerful proxies for the amount of nutrients eventually entering aquatic ecosystems from adjacent terrestrial areas. The GIS-based approach used here provided an ecologically sound and cost-efficient early-warning estimation of vegetation overgrowth in boreal lakes. This approach is applicable to other regions with similar land cover data sets.

The effect of ice phenology exerted on submerged macrophytes through physicochemical parameters and the phytoplankton abundance

<p>The physicochemical parameters of water, the concentration of chlorophyll-<em>a</em> and the submerged aquatic vegetation (SAV) were studied to evaluate the effects of different winter seasons on the biomass of macrophytes in shallow eutrophic lakes. We hypothesised that a lack of ice cover or early ice-out can influence the physicochemical parameters of water and thus change the conditions for the development of phytoplankton and SAV. The studies were conducted in four lakes of the Western Polesie region in mid-eastern Poland after mild winters with early ice-out (MW, 2011 and 2014) and after cold winters with late ice-out (CW, 2010, 2012 and 2013). The concentrations of soluble and total nitrogen, chlorophyll-<em>a</em> and the TN:TP ratio in the lakes were considerably higher, whereas the concentration of soluble and total phosphorus and water transparency were significantly lower after the MW compared with after the CW. No differences were found in water temperature, reaction and electrolytic conductivity. Low water turbidity linked with low concentration of chlorophyll-<em>a</em> after the CW resulted in increased water transparency and the total biomass of the SAV. The negative effect of the MW on the macrophyte species was stronger on more sensitive species (<em>Myriophyllum spicatum</em>,<em> Stratiotes aloides</em>) compared with shade tolerant <em>Ceratophyllum demersum</em>. Our findings show that the ice cover phenology affected by climate warming can change the balance between phytoplankton and benthic vegetation in shallow eutrophic lakes, acting as a shift between clear and turbid water states. We speculate that various responses of macrophyte species to changes in the water quality after two winter seasons (CW and MW) could cause alterations in the vegetation biomass, particularly the expansion of shade tolerance and the decline of light-demanding species after a series of mild winters.</p>

Nutrient Dynamics in Wetlands of the Middle Paraná River Subjected to Rotational Cattle Management

The progressive degradation of wetlands has stressed the need of developing sustainable management strategies for maintaining their ecological character within the context of sustainable development. Rotational cattle grazing is a common grazing strategy in aquatic systems but its effect on nutrient dynamics in lakes is scarcely known. The objectives of this study were to evaluate if cattle produces a significant increase of TN and TP in wetlands, and if the value of these nutrients decrease after cattle are removed. Samples of water, sediment and macrophytes were collected for nutrient, organic matter and other chemical analyses. Results showed a significant increase in water nutrients during the presence of cattle, decreasing during their absence. These changes occurred surprisingly rapid, suggesting a high resilience of these systems to this impact. The presence of submerged vegetation in lakes ameliorated the effect of cattle on water nutrients, suggesting an important role of these plants in ecosystem management. Rotational management would minimize the increase of nutrients in water, maintaining the ecological integrity of wetlands.

Presence of riparian vegetation increases biotic condition of fish assemblages in two Brazilian reservoirs

Abstract The riparian vegetation in lakes and reservoirs is source of course wood structures such as trunks and branches and is used as sheltering, spawning and foraging habitats for fishes. The reduction of these submerged structures can thus, affect the composition and structure of fish assemblages in reservoirs. Aim To evaluate the influence of riparian vegetation on the biotic condition of fish assemblage by adapting the Reservoir Fish Assemblage Index (RFAI) to two reservoirs in the Upper Paranapanema river basin, São Paulo State, Brazil. Methods The RFAI was adapted from metrics related to the functional characteristics and composition of fish assemblages through a protocol of metric selection and validation, and to its response to the presence of riparian vegetation. Results The final RFAI was composed by nine metrics, been lower in sites without riparian vegetation as consequence of the predominance of larger individuals and the percent of piscivorous and detritivorous fishes. Conclusions These results suggest that increasing shore habitat complexity in reservoirs by maintaining riparian vegetation increases fish biotic integrity.

Mapping Aquatic Vegetation in a Large, Shallow Eutrophic Lake: A Frequency-Based Approach Using Multiple Years of MODIS Data

Aquatic vegetation serves many important ecological and socioeconomic functions in lake ecosystems. The presence of floating algae poses difficulties for accurately estimating the distribution of aquatic vegetation in eutrophic lakes. We present an approach to map the distribution of aquatic vegetation in Lake Taihu (a large, shallow eutrophic lake in China) and reduce the influence of floating algae on aquatic vegetation mapping. Our approach involved a frequency analysis over a 2003–2013 time series of the floating algal index (FAI) based on moderate-resolution imaging spectroradiometer (MODIS) data. Three phenological periods were defined based on the vegetation presence frequency (VPF) and the growth of algae and aquatic vegetation: December and January composed the period of wintering aquatic vegetation; February and March composed the period of prolonged coexistence of algal blooms and wintering aquatic vegetation; and June to October was the peak period of the coexistence of algal blooms and aquatic vegetation. By comparing and analyzing the satellite-derived aquatic vegetation distribution and 244 in situ measurements made in 2013, we established a FAI threshold of −0.025 and VPF thresholds of 0.55, 0.45 and 0.85 for the three phenological periods. We validated the accuracy of our approach by comparing the results between the satellite-derived maps and the in situ results obtained from 2008–2012. The overall classification accuracy was 87%, 81%, 77%, 88% and 73% in the five years from 2008–2012, respectively. We then applied the approach to the MODIS images from 2003–2013 and obtained the total area of the aquatic vegetation, which varied from 265.94 km2 in 2007 to 503.38 km2 in 2008, with an average area of 359.62 ± 69.20 km2 over the 11 years. Our findings suggest that (1) the proposed approach can be used to map the distribution of aquatic vegetation in eutrophic algae-rich waters and (2) dramatic changes occurred in the distribution of aquatic vegetation in Lake Taihu during the 11-year study.