The fish biodiversity in the Congo River and its tributaries is extremely rich but the information on fish communities in the headwaters in terms of catch and biomass estimates is rare. Fishes in the running and stagnant waters in this region are of vital importance as a food resource for local residents. This study aimed to describe the fish community, catch, and biomass in the three headwater streams Bambou, Lebomo, and Bongo in the Lake Tumba Landscape (LTL) of the Democratic Republic of the Congo. Such information is of vital importance as a benchmark to understand the sustainability of the fish population for future generations of residents of the LTL. The field data were collected from 2007 through 2011, including dry and wet seasons. Here we present the results of this systematic, multi-annual study which was the first for fishes in streams of this region. In total, 50 species of 15 families were found in the nutrient-poor brown waters of these streams where high concentrations of humic acids cause a low pH. Among abundant species occurring in all three streams were the cyprinid Enteromius holotaenia (Boulenger, 1904), the mormyrid Marcusenius moorii (Günther, 1867), the alestids Clupeocharax schoutedeni Pellegrin, 1926 and Bryconaethiops boulengeri Pellegrin, 1900, and the clariid Clarias angolensis Steindachner, 1866. Bongo Stream was distinguished from the others by a rich abundance of Alestopetersius compressus (Poll et Gosse, 1963). The presence of several species at low pH (between 5.0 and 5.5) is new information that lowers the bottom of the pH interval for these species compared to earlier reports. The maximum total length (TL) of some other species was by 5–20 percentage points higher than those reported earlier. The median weight per unit effort (WPUE) in the streams varied between 30 and 115 g per hour during the dry seasons and between 18 and 86 g per hour during the wet seasons. The fish biomass in the streams varied between 0.05 and 0.7 g ⸱ m–2 with a median 0.14 g ⸱ m–2. This relatively low value compared to other tropical headwaters may be a result of the low pH and dark color of these headwaters. The results of the study serve as a reference point to which future monitoring of fish fauna can be compared for sustainable management of the LTL.

The transfer of microcystins (MC) up the food chain was measured in 4 lakes in central Sweden; Ekoln, Lilla Ullfjärden, Valloxen, and Storsjön. In lakes Ekoln and Valloxen, Microcystis aeruginosa was the dominant cyanobacterium, while the oscillatorian species Planktothrix prolifica form dense blooms in Lake Lilla Ullfjärden. The cyanobacterial composition in Lake Storsjön was more diverse with several Microcystis and Dolichospermum species. All dominant taxa are well-known producers of hepatotoxic MC. The highest recorded MC in the water samples from Lake Lilla Ullfjärden was measured in the bloom of P. prolifica (35 μg L−1). The highest MC content was measured in invertebrates; however, the MC concentration was usually low in fish. Maximum levels were 9 μg g−1 dry weight (dw) in zooplankton, 10 μg g−1 dw in benthos, and 2.7 μg g−1 dw in fish (smelt) liver. In fish muscle the highest recorded levels were 0.10–0.18 μg g−1 dw in bleak and smelt from Lake Lilla Ullfjärden and in pike-perch and roach from Lake Storsjön. Based on the World Health Organization's tolerable daily intake value of 0.04 μg kg–1 body weight, we conclude that any risk related to MC from human consumption of fish from these lakes is minimal.

Species distribution models are used for a wide range of ecological applications, such as assessment of ecological status. For many such assessments, predictions of entire communities are preferred. When entire community compositions are modelled, two options are available: (1) to model all of the communities' species individually and (2) to incorporate community information into the models. Here, we compared the accuracy of these two modelling approaches for predicting boreal lake phytoplankton assemblages and their ability to detect human impact. The modelling approaches tested were specifically classification-then-modelling (here a RIVPACS-type model, using random forest to predict biological group membership) and species-by-species modelling, using a random forest model for each species.The species-by-species models performed better than the RIVPACS model according to the dissimilarity measure BC, the area under curve (AUC) and proportion of true positives. In contrast, the taxonomic completeness index (O/E), commonly used for freshwater assessments, indicated that the RIVPACS model performed better. However, we believe that O/E overestimates model performance, due to the index omitting false negative errors (i.e. errors where species are wrongly predicting as absent).No support was found for our hypothesis that rare species would be better modelled by the RIVPACS model. Indeed, the RIVPACS model predicted common species significantly better than the species-by-species models, whilst the species-by-species models predicted rare species better than the RIVPACS model.Both modelling methods were able to separate impaired sites (acidified and eutrophic) from reference sites.We suggest that classification-then-modelling is evaluated using data-set containing more possible biological interactions, e.g. phytoplankton, zooplankton and fish. We also suggest that AUC is used as a complement to taxonomic completeness when evaluating models for reference condition taxa composition. (C) 2012 Elsevier B.V. All rights reserved.

Summary1. Analysing phytoplankton community data from 205 small, mainly oligotrophic Swedish lakes along a 13° latitudinal gradient, we found that the duration of the open‐water season (DT > 0) was best related to phytoplankton species richness and biomass, probably because DT > 0 can be used as a proxy for nutrient concentrations, as well as for light and temperature conditions in lakes.2. The relationships between DT > 0 and phytoplankton species richness and biomass were not linear but showed significant shifts, that is, richness suddenly doubled at DT > 0 = 170 days and phytoplankton biomass began to strongly increase at DT > 0 around 220 days.3. The doubling in species richness corresponded to a change in the seasonal plankton succession from one to two peaks per year, and the shift in biomass corresponded to a shift in nutrient concentrations.4. The geographical differences in richness and biomass shifts resulted in an exponential biodiversity–ecosystem functioning relationship along a DT > 0 gradient.5. We conclude that phytoplankton species richness and biomass are driven by different environmental factors, resulting in a nonlinear biodiversity–ecosystem functioning relationship. The shape of the diversity–functioning relationship varies along with variations in environmental drivers, which is of highest importance for ongoing discussions about impacts of global change on biodiversity and ecosystem functioning.

We hypothesized that unusual deaths and illnesses in wild and domestic animals in lake areas of the Rift Valley south of Addis Ababa were caused by toxic cyanobacteria. In the first cyanotoxic analyses conducted in samples from Ethiopia, we found lakes Chamo, Abaya, Awassa, Chitu, Langano, Ziway, and Koka all had concentrations of microcystins (MC) ranging from trace to hazardous, whereas only traces less than limits of detection (LOD) of cylindrospermopsin (CYN) were found. In the December 2006 dry season we sampled the lakes for analyses of MC, CYN, species structures, and calculations of cyanobacteria biomass. We used the Utermol technique to analyse cyanobacterial biomass and monitored MC toxins using HPLC-DAD, LC-ESI-MS-MRM, and ELISA-test and CYN with HPLC-DAD and ELISA. The various toxicity tests coincided well. In 4 of the lakes (Chamo, Langano, Ziway, and Koka), the inter-lake range of total MC concentration was 1.3-48 mu g L-1; in 3 (Abaya, Awassa, and Chitu), we found only traces of MC. Microcystis aeruginosa was the dominant species, with Microcystis panniformis, Anabaena spiroides, and Cylindrospermopsis spp. as subdominants. The MC concentration, especially in Lake Koka, exceeded levels for serious health hazards for humans, cattle, and wildlife.

Recent research has highlighted that positive biodiversity–ecosystem functioning relationships hold for all groups of organisms, including microbes. Yet, we still lack understanding regarding the drivers of microbial diversity, in particular, whether diversity of microbial communities is a matter of local factors, or whether metacommunities are of similar importance to what is known from higher organisms. Here, we explore the driving forces behind spatial variability in lake phytoplankton diversity in Fennoscandia. While phytoplankton biovolume is best predicted by local phosphorus concentrations, phytoplankton diversity (measured as genus richness, G ) only showed weak correlations with local concentrations of total phosphorus. By estimating spatial averages of total phosphorus concentrations on various scales from an independent, spatially representative lake survey, we found that close to 70 per cent of the variability in local phytoplankton diversity can be explained by regionally averaged phosphorus concentrations on a scale between 100 and 400 km. Thus, the data strongly indicate the existence of metacommunities on this scale. Furthermore, we show a strong dependency between lake productivity and spatial community turnover. Thus, regional productivity affects beta-diversity by controlling spatial community turnover, resulting in scale-dependent productivity-diversity relationships. As an illustration of the interaction between local and regional processes in shaping microbial diversity, our results offer both empirical support and a plausible mechanism for the existence of common scaling rules in both the macrobial and the microbial worlds. We argue that awareness of regional species pools in phytoplankton and other unicellular organisms may critically improve our understanding of ecosystems and their susceptibility to anthropogenic stressors.

Based on the currently largest available dataset of phytoplankton in lakes in northern Europe, we quantified the responses of three major phytoplankton classes to eutrophication. Responses were quantified by modelling the proportional biovolumes of a given group along the eutrophication gradient, using generalized additive models. Chlorophyll-a (Chl-a) was chosen as a proxy for eutrophication because all classes showed more consistent responses to Chl-a than to total phosphorus. Chrysophytes often dominate in (ultra-) oligotrophic lakes, and showed a clear decrease along the eutrophication gradient. Pennate diatoms were found to be most abundant at moderate eutrophication level (spring-samples). Cyanobacteria often dominate under eutrophic conditions, especially in clearwater lakes at Chl-a levels >10 μg l−1 (late summer samples). We compare the relationships among types of lakes, based on the lake typology of the northern geographic intercalibration group, and among countries sharing common lake types. Significant differences were found especially between humic and clearwater lakes, and between low- and moderately alkaline lakes, but we could not identify significant differences between shallow and deep lakes. Country-specific differences in response curves were especially pronounced between lakes in Norway and Finland, while Swedish lakes showed an intermediate pattern, indicating that country-specific differences reflect large-scale geographic and climatic differences in the study area.

Mean global air temperatures have steadily increased during recent decades, resulting in an earlier timing of lake ice breakup. In Sweden’s largest lakes, Vänern and Vättern, the breakup of ice has occurred considerably earlier since 1979 and ice-free winters have become more frequent. Comparison between the years when the lakes were ice covered with those when they remained ice-free in terms of 37 lake variables revealed significant differences in water temperatures, sulphate concentrations and the biomass of diatoms in May after ice breakup (P < 0.01). In particular, the biomass of the genus Aulacoseira increased significantly, which may explain increasing complaints about algae that clog fishing-nets, filter-beds and micro-strainers in waterworks in Vänern and Vättern. We assume that Aulacoseira is mainly affected by changes in climate-driven water circulation patterns. In contrast, other observed water quality changes such as changes in sulphate concentration might rather be attributed to changes in atmospheric deposition. To explain water quality changes in Sweden’s largest lakes it is important to consider changes in both climate and atmospheric deposition as well as catchment measures.

The relationship between species diversity and ecosystem functioning has been debated for decades, especially in relation to the “macroscopic” realm (higher plants and metazoans). Although there is emerging consensus that diversity enhances productivity and stability in communities of higher organisms; however, we still do not know whether these relationships apply also for communities of unicellular organisms, such as phytoplankton, which contribute ≈50% to the global primary production. We show here that phytoplankton resource use, and thus carbon fixation, is directly linked to the diversity of phytoplankton communities. Datasets from freshwater and brackish habitats show that diversity is the best predictor for resource use efficiency of phytoplankton communities across considerable environmental gradients. Furthermore, we show that the diversity requirement for stable ecosystem functioning scales with the nutrient level (total phosphorus), as evidenced by the opposing effects of diversity (negative) and resource level (positive) on the variability of both resource use and community composition. Our analyses of large-scale observational data are consistent with experimental and model studies demonstrating causal effects of microbial diversity on functional properties at the system level. Our findings point at potential linkages between eutrophication and pollution-mediated loss of phytoplankton diversity. Factors reducing phytoplankton diversity may have direct detrimental effects on the amount and predictability of aquatic primary production.

Freshwater BiologyVolume 53, Issue 1 p. 213-214 The Lakes Handbook, Volume II. Lake Restoration and Rehabilitation Eva Willén, Eva WillénSearch for more papers by this author Eva Willén, Eva WillénSearch for more papers by this author First published: 20 November 2007 https://doi.org/10.1111/j.1365-2427.2007.01879.xCitations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume53, Issue1January 2008Pages 213-214 RelatedInformation

About 20% o f Swedish lakes situated o n low weathering bedrock or in areas with lime-poor so iis have been impacted by atmospheric deposition o f strong acids, especially sulphur emissions. This has caused the acidification process to proceed m ue h quicker in comparison with that caused by reforestation o f agricultural lan d (RENBERG et al. 1993 ). In the most affected areas a decrease of 1-2 p H units is common. This acidification process i s accompanied by oligotrophication d ue to trapping of phosphorus in the catchment soi1s. Wide-spread bio1ogica1 damage with extensive losses within al! organism groups and displacements in the food-web to a few acid-tolerant species follows in the track of acidification, but the loss of attractive fish species especially draws public attention.

Effects of an extreme precipitation event on water chemistry and phytoplankton in the Swedish Lake Malaren