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Metacommunity studies on lake bacterioplankton indicate the importance of environmental factors in structuring communities. Yet most of these studies cover relatively small spatial scales. We assessed the relative importance of environmental and spatial factors in shaping bacterioplankton communities across a > 6000 km latitudinal range, studying 48 shallow lowland lakes in the tropical, tropicali (isothermal subzone of the tropics) and tundra climate regions of South America using denaturing gradient gel electrophoresis. Bacterioplankton community composition (BCC) differed significantly across regions. Although a large fraction of the variation in BCC remained unexplained, the results supported a consistent significant contribution of local environmental variables and to a lesser extent spatial variables, irrespective of spatial scale. Upon correction for space, mainly biotic environmental factors significantly explained the variation in BCC. The abundance of pelagic cladocerans remained particularly significant, suggesting grazer effects on bacterioplankton communities in the studied lakes. These results confirm that bacterioplankton communities are predominantly structured by environmental factors, even over a large-scale latitudinal gradient (6026 km), and stress the importance of including biotic variables in studies that aim to understand patterns in BCC. ispartof: Environmental Microbiology vol:17 issue:7 pages:2336-2351 ispartof: location:England status: published

1.The hypothesis that cyanobacteria have higher optimum growth temperatures and higher growth rates at the optimum as compared to chlorophytes was tested by running a controlled experiment with eight cyanobacteria species and eight chlorophyte species at six different temperatures (20-35°C) and by performing a literature survey. 2.In the experiment, all organisms except the chlorophyte Monoraphidium minutum grew well up to 35°C. The chlorophyte Chlamydomonas reinhardtii was the fastest-growing organism over the entire temperature range (20-35°C). 3.Mean optimum growth temperatures were similar for cyanobacteria (29.2°C) and chlorophytes (29.2°C). These results are concordant with published data, yielding slightly higher mean optimum growth temperatures for cyanobacteria (27.2°C) than for chlorophytes (26.3°C). 4.Mean growth rates of cyanobacteria at 20°C (0.42day-1) were significantly lower than those of chlorophytes at 20°C (0.62day-1). However, at all other temperatures, there were no differences between mean growth rates of cyanobacteria and chlorophytes. 5.Mean growth rates at the optimum temperature were similar for cyanobacteria (0.92day-1) and chlorophytes (0.96day-1). However, analysis of published data revealed that growth rates of cyanobacteria (0.65day-1) were significantly lower than those of chlorophytes (0.93day-1) at their optimum temperatures. 6.Although climate warming will probably lead to an intensification of cyanobacterial blooms, our results indicate that this might not be as a result of higher growth rates of cyanobacteria compared with their chlorophyte competitors. The competitive advantage of cyanobacteria can more likely be attributed to their ability to migrate vertically and prevent sedimentation in warmer and more strongly stratified waters and to their resistance to grazing, especially when warming reduces zooplankton body size. © 2012 Blackwell Publishing Ltd.

Er bestaat onduidelijkheid over de effecten van sulfaat op de waterkwaliteit en over het relatieve belang van verschillende bronnen van sulfaat in het Hollands-Utrechtse veenlandschap. Deze studie laat zien dat de oxidatie van het gebiedseigen veen meestal de belangrijkste bron is en dat de veenpolders netto exporteurs zijn van sulfaat. Over het algemeen zijn de sulfaatconcentraties in het oppervlaktewater van het laagveengebied vrij hoog. Dit heeft een verarmende invloed op de watervegetatie. _ Annual sulfate mass balances have been constructed for low-lying peat polders in the Netherlands. These peat polders are generally used for dairy farming or nature conservation, and can have large areas of shallow ditches and ponds (mean 16%, range 6-43%). As a consequence of continuous drainage, the peat (organic matter and sulfides) in these polders mineralizes and the soil subsides at rates between 2 and 10 mm y". This mineralization is generally the most important internal source of sulfate, providing some 96 kg SO 4 ha-1 mm-1 subsidence y1. During summer, when evapotranspiration exceeds rainfall, sulfate accumulates in the unsaturated zone, to be washed away and drained off during the wet autumn and winter. In some polders, upward seepage of early Holocene, brackish water can be a source of sulfate. Aquatic sediments are an important temporary sulfate sink, which is emptied every 6 to 10 years when the ditches are dredged and these sediments are put back on the fields. External sources are precipitation and water supplied during summer to compensate for water shortage, but these are minor compared to internal release. Peat polders export sulfate to the regional water system and the sea during winter drainage. Most surface waters have high sulfate concentrations; 76% exceed a threshold of 0.3-0.5 mmol SO s41-1 which may lead to impoverished aquatic communities.

1.Different components of the climate system have been shown to affect temporal dynamics in natural plankton communities on scales varying from days to years. The seasonal dynamics in temperate lake plankton communities, with emphasis on both physical and biological forcing factors, were captured in the 1980s in a conceptual framework, the Plankton Ecology Group (PEG) model. 2.Taking the PEG model as our starting point, we discuss anticipated changes in seasonal and long-term plankton dynamics and extend this model to other climate regions, particularly polar and tropical latitudes. Based on our improved post-PEG understanding of plankton dynamics, we also evaluate the role of microbial plankton, parasites and fish in governing plankton dynamics and distribution. 3.In polar lakes, there is usually just a single peak in plankton biomass in summer. Lengthening of the growing season under warmer conditions may lead to higher and more prolonged phytoplankton productivity. Climate-induced increases in nutrient loading in these oligotrophic waters may contribute to higher phytoplankton biomass and subsequent higher zooplankton and fish productivity. 4.In temperate lakes, a seasonal pattern with two plankton biomass peaks - in spring and summer - can shift to one with a single but longer and larger biomass peak as nutrient loading increases, with associated higher populations of zooplanktivorous fish. Climate change will exacerbate these trends by increasing nutrient loading through increased internal nutrient inputs (due to warming) and increased catchment inputs (in the case of more precipitation). 5.In tropical systems, temporal variability in precipitation can be an important driver of the seasonal development of plankton. Increases in precipitation intensity may reset the seasonal dynamics of plankton communities and favour species adapted to highly variable environments. The existing intense predation by fish on larger zooplankters may increase further, resulting in a perennially low zooplankton biomass. 6.Bacteria were not included in the original PEG model. Seasonally, bacteria vary less than the phytoplankton but often follow its patterns, particularly in colder lakes. In warmer lakes, and with future warming, a greater influx of allochthonous carbon may obscure this pattern. 7.Our analyses indicate that the consequences of climate change for plankton dynamics are, to a large extent, system specific, depending on characteristics such as food-web structure and nutrient loading. Indirect effects through nutrient loading may be more important than direct effects of temperature increase, especially for phytoplankton. However, with warming a general picture emerges of increases in bacterivory, greater cyanobacterial dominance and smaller-bodied zooplankton that are more heavily impacted by fish predation. © 2012 Blackwell Publishing Ltd.

1. The alternative state theory claims that shallow lakes may have either clear water, and be dominated by submerged macrophytes, or turbid water and be dominated by phytoplankton. Most evidence for this theory comes from studies in temperate or boreal regions of Europe. Because of differences in the strength of trophic interactions, such as in the pressure of zooplankton grazing on phytoplankton, this influential theory might not apply elsewhere. 2. Here, we test the theory for South American lakes, combining field data and Landsat satellite data. We studied the frequency distribution of primary producers and water transparency, looking for potential bimodality separating clear and turbid lakes. A bimodal distribution might be observed if there are indeed alternative states, although would not itself be sufficient evidence for the theory. Possible shifts between alternative states were analysed by comparing satellite data from 1987 to 2005. 3. In our field data, there was a bimodal pattern in phytoplankton abundance and possibly in the abundance of submerged macrophytes, but not in water transparency. Analyses of the larger satellite data set revealed bimodality in lake transparency in 2005, but less so in 1987. In 1987, the lakes were generally clearer, and the transition to higher turbidity was more gradual than in 2005. The stronger bimodality in the more recent data, and the overall lower transparency, could have been caused by an increase in fertiliser use and subsequent eutrophication but also by differences in hydrology. Further, 1987 was much wetter than 2005, which could have caused dilution of suspended particles, leading to clearer water. 4. While a bimodal distribution in the abundance of primary producers and water clarity is not decisive evidence for or against the theory of alternative states, our data clearly fail to refute it

Sulfaatconcentraties in het oppervlaktewater van het West-Nederlandse laagveengebied kunnen bijzonder hoog zijn. Er bestaat onduidelijkheid over de bronnen en de effecten van dit sulfaat. De huidige studie combineert jaarbalansen op perceel-, polder- en stroomgebiedsschaal met een analyse van de ruimtelijke variatie in sulfaatconcentraties, en met een literatuurstudie naar kritische drempelconcentraties voor eutrofiëring, toxiciteit, en de ontwikkeling van gewenste laagveennatuur. De bevindingen worden gecombineerd met KNMI klimaatscenario’s zodat de effecten van klimaatsveranderingen kunnen worden ingeschat.

Dit rapport bundelt de belangrijkste kennis over mogelijke invloeden van klimaatverandering op zoete aquatische ecosystemen en geeft waterbeheerders handvatten hoe ze rekening kunnen houden met de effecten van klimaatverandering bij het uitvoeren van hun taken. Met de kennis uit dit rappport kunnen waterbeheerders een optimaal (effectief) pakket aan maatregelen samenstellen om de waterkwaliteit te verbeteren. Daarnaast kunnen ze bij inrichting en beheer goed rekening houden met de effecten van klimaatverandering. Het rapport ondersteunt daarmee het opstellen van de tweede generatie stroomgebiedbeheersplannen, die in 2015 gereed moeten zijn.

Zowel de fysische als de chemische en biologische toestand van oppervlaktewateren worden door klimaatverandering beïnvloed. Doordat verschillende klimaatfactoren verschillende effecten hebben, is de invloed van klimaatverandering op aquatische ecosystemen niet altijd eenduidig. Wat echter wel duidelijk is, is dat klimaatverandering eutrofiëring versterkt. Om deze negatieve effecten van klimaatverandering tegen te gaan zijn extra reducties in nutriëntenbelasting nodig. Ook is duidelijk dat hogere temperaturen leiden tot meer cyanobacteriën, met name in eutrofe wateren. Cyanobacteriën kunnen toxische stoffen produceren. De resultaten van onze studie bevestigen de aanwezigheid van een groot aantal eerder aangetroffen cyanobacteriële toxines in Nederlandse oppervlaktewateren.

1. Shallow lakes may switch from a state dominated by submerged macrophytes to a phytoplankton-dominated state when a critical nutrient concentration is exceeded. We explore how climate change may affect this critical nutrient concentration by linking a graphical model to data from 83 lakes along a large climate gradient in South America. 2. The data indicate that in warmer climates, submerged macrophytes may tolerate more underwater shade than in cooler lakes. By contrast, the relationship between phytoplankton biomass [approximated by chlorophyll-a (chl-a) or biovolume] and nutrient concentrations did not change consistently along the climate gradient. In warmer climates, the correlation between phytoplankton biomass and nutrient concentrations was overall weak, especially at low total phosphorus (TP) concentrations where the chl-a/¿TP ratio could be either low or high. 3. Although the enhanced shade tolerance of submerged plants in warmer lakes might promote the stability of their dominance, the potentially high phytoplankton biomass at low nutrient concentrations suggests an overall low predictability of climate effects. 4. We found that near-bottom oxygen concentrations are lower in warm lakes than in cooler lakes, implying that anoxic P release from eutrophic sediment in warm lakes likely causes higher TP concentrations in the water column. Subsequently, this may lead to a higher phytoplankton biomass in warmer lakes than in cooler lakes with similar external nutrient loadings. 5. Our results indicate that climate effects on the competitive balance between submerged macrophytes and phytoplankton are not straightforward

1. Experimental studies have indicated in freshwater ecosystems that a shift in dominance from submerged to free-floating macrophytes may occur with climate change because of increased water surface temperatures and eutrophication. Field evidence is, however, rare. 2. Here, we analysed long-term (26 years) dynamics of macrophyte cover in Dutch ditches in relation to Dutch weather variables and the North Atlantic Oscillation (NAO) winter index. The latter appears to be a good proxy for Dutch weather conditions. 3. Cover of both free-floating macrophytes and evergreen overwintering submerged macrophytes was positively related to mild winters (positive NAO winter index). On the other hand, high cover of submerged macrophytes that die back in winter coincided with cold winters (negative NAO winter index). Our results therefore suggest that the effect of weather on macrophyte species depends strongly on their overwintering strategy. 4. The positive relation of free-floating macrophytes with the NAO winter index was significantly stronger in ditches in organic soil than in those in inorganic soil. This may be because of increased nutrient loading associated with increased decomposition of organic matter and increased run-off to these ditches during mild wet winters. 5. Our results suggest that mild winters in a changing climate may cause submerged macrophytes with an evergreen overwintering strategy and free-floating macrophytes to outcompete submerged macrophytes that die back in winter.

Inland waters, just as the world's oceans, play an important role in the global carbon cycle. While lakes and reservoirs typically emit CO2, they also bury carbon in their sediment. The net CO2 emission is largely the result of the decomposition or preservation of terrestrially supplied carbon. What regulates the balance between CO2 emission and carbon burial is not known, but climate change and temperature have been hypothesized to influence both processes. We analyzed patterns in carbon dioxide partial pressure (pCO2) in 83 shallow lakes over a large climatic gradient in South America and found a strong, positive correlation with temperature. The higher pCO2 in warmer lakes may be caused by a higher, temperature-dependent mineralization of organic carbon. This pattern suggests that cool lakes may start to emit more CO2 when they warm up because of climate cha

cum laude graduation (with distinction) There is concern that a warmer climate may boost carbon emissions from lakes and promote the chance that they lose their vegetation and become dominated by phytoplankton or cyanobacteria. However, these hypotheses have been difficult to evaluate due to the scarcity of relevant field data. To explore potential climate effects we sampled 83 lakes along a latitudinal gradient of more than 6000 km ranging from Rio Grande do Norte in Brazil to the South of Argentina (5-55 oS). The lakes were selected so as to be as similar as possible in morphology and altitude while varying as much as possible in trophic state within regions. All lakes were sampled once during summer (subtropical, temperate and tundra lakes) or during the dry season (tropical lakes) between November 2004 and March 2006 by the same team. In the first chapters I address the question how climate might affect the chances for shallow lakes to be dominated by submerged plants. It has been shown that temperate lakes tend to have two contrasting states over a range of conditions: a clear state dominated by aquatic vegetation or a turbid state. The turbid state is typically dominated by phytoplankton and often characterized by poorer water quality than the clear state. The backbone of the theory explaining this pattern is a supposed positive feedback of submerged vegetation on water clarity: vegetation enhances water clarity and clearer water, in turn, promotes vegetation growth. The theory furthermore asserts that submerged vegetation coverage diminishes when nutrient concentrations increase until a critical point at which the entire vegetation disappears due to light limitation. Both aspects of the alternative state theory have been well studied in temperate shallow lakes, but the validity of the theory for warmer lakes has been questioned. In chapter 2 a graphical model is used to show how climate effects on different mechanisms assumed in the theory may affect the general predictions. An analysis of our data presented in chapter 4 reveals that submerged vegetation has similar overall effects on water clarity across our climatic gradient. Nonetheless, the results hint at differences in the underlying mechanisms between climate zones. For example, the data suggest that the positive effect of vegetation on top-down control of phytoplankton by zooplankton is lost at high densities of fish that are often found in warmer regions. The main factor explaining differences in the water clearing effect of vegetation among lakes in our data set was the concentration of humic substances. In lakes with a high concentration of humic substances vegetation did not enhance the water clarity. Het warmer worden van de aarde heeft mogelijk vergaande gevolgen voor meren. Om de mogelijke klimaatseffecten te onderzoeken hebben we 83 meren bemonsterd in verschillende klimaatzones in Zuid Amerika. De geselecteerde meren leken zoveel mogelijk op elkaar qua grootte en diepte, maar varieerden per klimaatzone zoveel mogelijk qua vervuiling met voedingsstoffen zoals fosfaat. De onderzoeksresultaten van Sarian Kosten geven aan dat de negatieve effecten van de vervuiling met voedingsstoffen waarschijnlijk sterker zijn in een warm klimaat dan in een kouder klimaat. "In gebieden met weinig vorstdagen veranderen meren waarschijnlijk al bij lagere concentraties fosfaat in een groene algensoep waarin onderwatervegetatie geen kans krijgt om te groeien dan in gebieden met langere vorstperioden. Dit geeft aan dat, wanneer we de ondergedoken vegetatie willen behouden, de fosfaat concentraties mogelijk verlaagd zullen moeten worden in regio’s waar klimaatverandering zal leiden tot minder vorstdagen. Tevens blijkt dat warmere meren een grotere kans hebben om gedomineerd te worden door blauwalgen ten opzichte van koude meren met hetzelfde gehalte aan voedingsstoffen. Tenslotte suggereren mijn onderzoeksresultaten dat koude meren mogelijk meer koolstof uit gaan stoten als ze opwarmen, wat de klimaatverandering verder kan versterken".

Een warmer en grilliger klimaat met meer neerslag in korte tijd verhevigt de eutrofiëringsproblemen en leidt tot grote gevolgen voor de interacties tussen algen, waterplanten, vissen en zoöplankton. Dit is kort samengevat de conclusie van een grote verscheidenheid aan onderzoeken die onlangs werden gepresenteerd in Uruguay. Dit kwam niet voor iedereen als een verrassing, maar wat betekent het voor het waterbeheer in Nederland

Korte beschrijving van de inventarisatie van cyanotoxines die binnen het Kennis voor Klimaat Programma uitgevoerd gaat worden in Nederlandse oppervlaktewateren, om een indruk te krijgen welke toxines waar en onder welke omstandigheden voorkomen.

Waternet is van plan om in het gebied Terra Nova een damwand aan te brengen tussen de delen Terra Nova Noord en Terra Nova Zuid om daarmee de overlast van blauwalgen in Terra Nova Noord tegen te gaan. Een groep bewoners van Terra Nova Zuid vreest echter voor negatieve gevolgen van deze maatregel op de waterkwaliteit van Terra Nova Zuid. Deze bewonersgroep heeft Wageningen UR gevraagd te beoordelen of de effecten van het aanbrengen van een dam op het watersysteem van Terra Nova Zuid goed zijn onderbouwd.

Stedenbouwkundigen hebben het water ontdekt als sierend en recreatief element in nieuwe woonwijken. Toch hoor je ook steeds vaker negatieve berichten over al dat nieuwe oppervlaktewater. Deze brochure gaat in op de vraag of deze veronderstellingen reëel zijn. Er komen verschillende plagen en ziekten aan bod, die in verband worden gebracht met de aanwezigheid van oppervlaktewater. Hierbij besteden we niet alleen aandacht aan de vraag of deze ziekten en plagen werkelijk kunnen ontstaan, maar ook aan de vraag hoe je ze kunt beperken of voorkomen.