B.W. Ibelings

The impact of climate change on lakes in the Netherlands: a review

Climate change will alter freshwater ecosystems but specific effects will vary among regions and the type of water body. Here, we give an integrative review of the observed and predicted impacts of climate change on shallow lakes in the Netherlands and put these impacts in an international perspective. Most of these lakes are man-made and have preset water levels and poorly developed littoral zones. Relevant climatic factors for these ecosystems are temperature, ice-cover and wind. Secondary factors affected by climate include nutrient loading, residence time and water levels. We reviewed the relevant literature in order to assess the impact of climate change on these lakes. We focussed on six management objectives as bioindicators for the functioning of these ecosystems: target species, nuisance species, invading species, transparency, carrying capacity and biodiversity. We conclude that climate change will likely (i) reduce the numbers of several target species of birds; (ii) favour and stabilize cyanobacterial dominance in phytoplankton communities; (iii) cause more serious incidents of botulism among waterfowl and enhance the spreading of mosquito borne diseases; (iv) benefit invaders originating from the Ponto-Caspian region; (v) stabilize turbid, phytoplankton-dominated systems, thus counteracting restoration measures; (vi) destabilize macrophyte-dominated clear-water lakes; (vii) increase the carrying capacity of primary producers, especially phytoplankton, thus mimicking eutrophication; (viii) affect higher trophic levels as a result of enhanced primary production; (ix) have a negative impact on biodiversity which is linked to the clear water state; (x) affect biodiversity by changing the disturbance regime. Water managers can counteract these developments by reduction of nutrient loading, development of the littoral zone, compartmentalization of lakes and fisheries management.

Recruitment of benthic Microcystis (Cyanophyceae) to the water column: internal buoyancy changes or resuspension?

In some lakes, large amounts of the potentially toxic cyanobacterium Microcystis overwinter in the sediment. This overwintering population might inoculate the water column in spring and promote the development of dense surface blooms of Microcystis during summer. In the Dutch Lake Volkerak, we found photochemically active Microcystis colonies in the sediment throughout the year. The most vital colonies originated from shallow sediments within the euphotic zone. We investigated whether recruitment of Microcystis colonies from the sediment to the water column was an active process, through production of gas vesicles or respiration of carbohydrate ballast. We calculated net buoyancy, as an indication of relative density, using the amounts and densities of the major cell constituents (carbohydrates, proteins, and gas vesicles). Carbohydrate content of benthic Microcystis cells was very low throughout the year. Buoyancy changes of benthic Microcystis were mostly a result of changes in gas vesicle volume. Before the summer bloom, net buoyancy and the amount of buoyant colonies in the sediment did not change. Therefore, recruitment of Microcystis from the sediment does not seem to be an active process regulated by internal buoyancy changes. Instead, our observations indicate that attachment of sediment particles to colonies plays an important part in the buoyancy state of benthic colonies. Therefore, we suggest that recruitment of Microcystis is more likely a passive process resulting from resuspension by wind‐induced mixing or bioturbation. Consequently, shallow areas of the lake probably play a more important role in recruitment of benthic Microcystis than deep areas.

FUZZY MODELING OF CYANOBACTERIAL SURFACE WATERBLOOMS: VALIDATION WITH NOAA‐AVHRR SATELLITE IMAGES

Surface waterblooms of toxic cyanobacteria (scums) interfere with the use of lakes, for instance in the production of drinking water or for recreation. Routine monitoring data are not sufficient for early warning due to the large temporal and spatial variability in the occurrence of surface waterblooms, and the time lag between the formation of the scum and the availability of relevant information for risk management. We combined a “traditional” dynamic simulation model based upon differential equations with fuzzy logic to describe the three main conditions governing surface waterbloom formation: (1) a preexisting population of cyanobacteria, (2) buoyancy of the cells, and (3) stability of the water column. The attributes and membership functions of the fuzzy model were based on earlier field studies of diel changes in buoyancy and vertical distribution of cyanobacteria. The model was applied without further calibration to the large lake IJsselmeer (1200 km2) in the Netherlands, and we validated the model...

A Global Lake Ecological Observatory Network (GLEON) for synthesising high–frequency sensor data for validation of deterministic ecological models

Abstract A Global Lake Ecological Observatory Network (GLEON; www.gleon.org) has formed to provide a coordinated response to the need for scientific understanding of lake processes, utilising technological advances available from autonomous sensors. The organisation embraces a grassroots approach to engage researchers from varying disciplines, sites spanning geographic and ecological gradients, and novel sensor and cyberinfrastructure to synthesise high-frequency lake data at scales ranging from local to global. The high-frequency data provide a platform to rigorously validate process-based ecological models because model simulation time steps are better aligned with sensor measurements than with lower-frequency, manual samples. Two case studies from Trout Bog, Wisconsin, USA, and Lake Rotoehu, North Island, New Zealand, are presented to demonstrate that in the past, ecological model outputs (e.g., temperature, chlorophyll) have been relatively poorly validated based on a limited number of directly comparable measurements, both in time and space. The case studies demonstrate some of the difficulties of mapping sensor measurements directly to model state variable outputs as well as the opportunities to use deviations between sensor measurements and model simulations to better inform process understanding. Well-validated ecological models provide a mechanism to extrapolate high-frequency sensor data in space and time, thereby potentially creating a fully 3-dimensional simulation of key variables of interest.

Sigma factor SigC is required for heat acclimation of the cyanobacterium Synechocystis sp. strain PCC 6803

The role of the primary‐like sigma factor SigC was studied in Synechocystis. Under high temperature stress (48 °C) the ΔsigC inactivation strain showed a lower survival rate than the control strain. The ΔsigC strain grew poorly at 43 °C in liquid cultures under normal air. However, change to 3% CO2 enhanced growth of ΔsigC at 43 °C. Differences in expression of many genes related to the carbon concentrating mechanisms between the control and the ΔsigC strain were recorded with a genome‐wide DNA microarray. We suggest that low solubility of CO2 at high temperature is one of the factors contributing to the poor thermotolerance of the ΔsigC strain.

Potential synergistic effects of microcystins and bacterial lipopolysaccharides on life history traits of Daphnia galeata raised on low and high food levels

Metastudies have found no consistent effects of the cyanobacterial toxin microcystin on Daphnia, and there are discrepancies between field observations and experiments. Confounding factors include absence or presence of alternative high quality food or the presence of bioactive compounds, other than microcystins in cyanobacteria. Of specific interest are lipopolysaccharides (LPS) on the outer cell wall. LPS may have a number of biological effects, including reduced detoxication of microcystins in plants and animals. When grazing seston in the field, filterfeeders take up heterotrophic bacteria attached to cyanobacteria, as well as free-living bacteria. The LPS produced by heterotrophic bacteria have been shown to be much more harmful than cyanobacterial LPS. We performed two experiments in which we tested for potential synergistic effects between bacterial LPS and microcystins. Full-factorial experiments separated the main effects and interactions between (i) food quantity as well as food quality (addition of the green alga Scenedesmus), (ii) presence or absence of strains that vary in amount and composition of microcystins (microcystin free strain NIVA-CYA43, moderate microcystin producing strain NIVA-CYA140 and high microcystin producing strain PCC7820), and (iii) presence or absence of bacterial LPS on different life history traits of Daphnia galeata. We measured juvenile growth rate, age and size at first reproduction, death before first reproduction and standard carbon content of Daphnia. From the experiments we conclude that microcystin-producing Microcystis had deleterious effects on the life history of D. galeata, but especially when the availability of high quality green algal food was limited in comparison to the supply of microcystin producing strain PCC7820. In the experiment in which PCC7820 was used as microcystin-producing strain, addition of LPS lowered SCC of Daphnia, but had no effects on other life history parameters. The interaction between Microcystis strain, Microcystis concentration and LPS was highly significant in case of PCC7820, but not in case of CYA-140, indicating that the effects of LPS and its interactions with microcystin on Daphnia life history were strongly context dependent.

Transcript profiling indicates that the absence of PsbO affects the coordination of C and N metabolism in Synechocystis sp. PCC 6803

Transcript profiling of nitrate-grown Synechocystis sp. PCC 6803 PsbO-free mutant cells in comparison to wild-type (WT) detected substantial deviations. Because we had previously observed phenotypical differences between Synechocystis sp. PCC 6803 WT and its corresponding PsbO-free mutant when cultivated with l-arginine as sole N source and a light intensity of 200 mumol photons m(-2) s(-1), we also performed transcript profiling for both strains grown either with nitrate or with l-arginine as sole N source. We observed a total number of 520 differentially regulated transcripts in Synechocystis WT because of a shift from nitrate- to l-arginine-containing BG11 medium, while we detected only 13 differentially regulated transcripts for the PsbO-free mutant. Thus, the PsbO-free Synechocystis mutant had already undergone a preconditioning process for growth with l-arginine in comparison to WT. While Synechocystis WT suffered from growth with l-arginine at a light intensity of 200 mumol photons m(-2) s(-1), the PsbO-free mutant developed only a minor stress phenotype. In summary, our results suggest that the absence of PsbO in Synechocystis affects the coordination of photosynthesis/respiration and l-arginine metabolism through complex probably redox-mediated regulatory pathways. In addition, we show that a comparison of the transcriptomes of nitrate-grown Synechococcus elongatus PCC 7942 WT cells and its corresponding PsbO-free mutant cells resulted in only a few differentially regulated transcripts between both strains. The absence of the manganese/calcium-stabilizing PsbO protein of PSII with an assigned regulatory function for photosynthetic water oxidation causes bigger changes in the transcriptome of the permissive photoheterotrophically growing Synechocystis sp. PCC 6803 than in the transcriptome of the obligate photoautotrophically growing S. elongatus PCC 7942.