Kunnen wateren met veel ondergedoken waterplanten CO2 uit de atmosfeer vastleggen?

Aquatische ecosystemen met veel ondergedoken waterplanten zijn potentiëlehotspots voor de invang van organisch materiaal. Waterplanten slaan koolstofen nutriënten op in hun biomassa, afgestorven planten en andere detritusvormen een organische laag op de bodem. Kunnen dergelijke systemen misschien de hoeveelheid CO2 in de atmosfeer omlaag brengen? En hoe verlooptdie vastlegging als het water door klimaatverandering opwarmt

Differential effects of elevated <scp> <i>p</i> CO ₂ </scp> and warming on marine phytoplankton stoichiometry

Phytoplankton stand at the base of the marine food-web, and play a major role in global carbon cycling. Rising CO2 levels and temperatures are expected to enhance growth and alter carbon:nutrient stoichiometry of marine phytoplankton, with possible consequences for the functioning of marine food-webs and the oceanic carbon pump. To date, however, the consistency of phytoplankton stoichiometric responses remains unclear. We therefore performed a meta-analysis on data from experimental studies on stoichiometric responses of marine phytoplankton to elevated pCO2 and 3–5° warming under nutrient replete and limited conditions. Our results demonstrate that elevated pCO2 increased overall phytoplankton C:N (by 4%) and C:P (by 9%) molar ratios under nutrient replete conditions, as well as phytoplankton growth rates (by 6%). Nutrient limitation amplified the CO2 effect on C:N and C:P ratios, with increases to 27% and 17%, respectively. In contrast to elevated pCO2, warming did not consistently alter phytoplankton elemental composition. This could be attributed to species- and study-specific increases and decreases in stoichiometry in response to warming. While our observed moderate CO2-driven changes in stoichiometry are not likely to drive marked changes in food web functioning, they are in the same order of magnitude as current and projected estimations of oceanic carbon export. Therefore, our results may indicate a stoichiometric compensation mechanism for reduced oceanic carbon export due to declining primary production in the near future

Factors influencing submerged macrophyte presence in fresh and brackish eutrophic waters and their impact on carbon emissions

In agricultural landscapes of North-Western Europe, the majority of water bodies do not meet the targets set by the European Water Framework Directive due to a lack of submerged macrophytes and associated biodiversity. These eutrophic waters can also be a substantial source of methane (CH4) and carbon dioxide (CO2) to the atmosphere. Here we present a two-year field experiment on the island of Goeree-Overflakkee (southwest Netherlands), conducted in six drainage ditches varying in salinity, where we monitored four permanent plots per ditch and varied the presence of both fish and macrophytes. We aimed to: 1) investigate factors limiting submerged macrophyte growth, focussing on exclusion of grazing pressure and bioturbation by fish; and 2) quantify the CO2 and CH4 emission under these conditions. Even in highly eutrophic, semi turbid ditches with fluctuating salinity levels and sulphide presence in the root zone, submerged macrophytes established successfully after introduction when the influence of grazing and bioturbation by fish was excluded. In the exclosures, diffusive CH4 and CO2 emissions, but not ebullitive CH4 emissions were significantly reduced. The spontaneous development of submerged macrophytes in the exclosures without macrophyte introduction underlined the effect of grazing and bioturbation by fish and suggest that abiotic conditions did not hamper submerged macrophyte development. Our results provide important insights into the influential factors for submerged macrophyte development and potential for future management practices. Large-scale fish removal may stimulate submerged macrophyte growth and reduce methane emissions, albeit that the macrophyte diversity will likely stay low in our study region due to fluctuating salinity and eutrophic conditions.</p

De ecologische meerwaarde van het aanbrengen van grindbedden in de Tongelreep

Beekfauna kan profiteren van het aanbrengen van grindbedden in beken. Eén van de weinige beken in Nederland waarin grind is aangebracht is de Tongelreep in Noord-Brabant. Dit artikel beschrijft de ervaringen met deze maatregel, waarbij is gekeken naar de stabiliteit van de grindbedden en de aanwezigheid van macrofauna. De grindbedden bleken zich niet te verplaatsen, maar varieerden wel in grootte door tijdelijke sedimentbedekking. Het aantal op het ingebrachte grind aanwezige kenmerkende taxa was opvallend hoog. Het stimuleren van het ontstaan van grindbedden verdient daarom meer aandacht bij het ontwerp van beekherstelmaatregelen

Differential effects of elevated pCO2 and warming on marine phytoplankton stoichiometry

Phytoplankton stand at the base of the marine food-web, and play a major role in global carbon cycling. Rising CO2 levels and temperatures are expected to enhance growth and alter carbon:nutrient stoichiometry of marine phytoplankton, with possible consequences for the functioning of marine food-webs and the oceanic carbon pump. To date, however, the consistency of phytoplankton stoichiometric responses remains unclear. We therefore performed a meta-analysis on data from experimental studies on stoichiometric responses of marine phytoplankton to elevated pCO2 and 3–5° warming under nutrient replete and limited conditions. Our results demonstrate that elevated pCO2 increased overall phytoplankton C:N (by 4%) and C:P (by 9%) molar ratios under nutrient replete conditions, as well as phytoplankton growth rates (by 6%). Nutrient limitation amplified the CO2 effect on C:N and C:P ratios, with increases to 27% and 17%, respectively. In contrast to elevated pCO2, warming did not consistently alter phytoplankton elemental composition. This could be attributed to species- and study-specific increases and decreases in stoichiometry in response to warming. While our observed moderate CO2-driven changes in stoichiometry are not likely to drive marked changes in food web functioning, they are in the same order of magnitude as current and projected estimations of oceanic carbon export. Therefore, our results may indicate a stoichiometric compensation mechanism for reduced oceanic carbon export due to declining primary production in the near future

Elements of carbon cycling : primary producers in aquatic systems under global change

It is of crucial importance to understand the consequences of climatic changes (e.g. elevated pCO2, warming and eutrophication) on aquatic primary producers, as they play a vital role in the global carbon cycle. Therefore, the main aims of the thesis were (1) to assess the role of primary producer identity (i.e. phytoplankton vs submerged aquatic plants) in aquatic carbon cycling, and (2) to assess the effects of elevated pCO2, warming and eutrophication on aquatic carbon cycling (with the focus on primary producers). The results of this thesis show that global change can significantly alter the role of primary producers in the carbon cycle, but that the direction of this change may depend on the prominent global change stressor. Producer carbon:nutrient stoichiometry can be enhanced by elevated pCO2, but reduced by eutrophication. The effect of warming on carbon:nutrient stoichiometry is context-dependent and may be influenced by abiotic conditions such as nutrient availability. Systems dominated by aquatic plants can have significantly higher sedimentation fluxes of carbon than those dominated by phytoplankton. This difference can be attributed to standing stocks of producer biomass related to producer identity. Additionally, the results of this thesis show that consumer biomass can advance in response to climatic warming, thereby imposing top-down control on primary producers. Thus, processes hampering the build-up of producer biomass may alter the flux of carbon to the sediment. To integratively assess the effect of warming on freshwater carbon cycling, producer biomass, sedimentation and decomposition were measured in a mesocosm experiment. The results of this experiment show that warming can significantly enhance the standing stock of plant biomass, sedimentation and decomposition. When combined into a carbon budget model, these similarly enhanced carbon fluxes cancelled each other out resulting in no net change in carbon burial between temperature treatments. All in all, I conclude that global change can affect the balance of aquatic carbon cycling by altering the biomass and carbon:nutrient stoichiometry of aquatic primary producers as well as their interactions with higher trophic levels. These changes in turn can have potential consequences for our future climate

Meta‐analysis reveals enhanced growth of marine harmful algae from temperate regions with warming and elevated CO2 levels

Elevated pCO2 and warming may promote algal growth and toxin production, and thereby possibly support the proliferation and toxicity of harmful algal blooms (HABs). Here, we tested whether empirical data support this hypothesis using a meta‐analytic approach and investigated the responses of growth rate and toxin content or toxicity of numerous marine and estuarine HAB species to elevated pCO2 and warming. Most of the available data on HAB responses towards the two tested climate change variables concern dinoflagellates, as many members of this phytoplankton group are known to cause HAB outbreaks. Toxin content and toxicity did not reveal a consistent response towards both tested climate change variables, while growth rate increased consistently with elevated pCO2. Warming also led to higher growth rates, but only for species isolated at higher latitudes. The observed gradient in temperature growth responses shows the potential for enhanced development of HABs at higher latitudes. Increases in growth rates with more CO2 may present an additional competitive advantage for HAB species, particularly as CO2 was not shown to enhance growth rate of other non‐HAB phytoplankton species. However, this may also be related to the difference in representation of dinoflagellate and diatom species in the respective HAB and non‐HAB phytoplankton groups. Since the proliferation of HAB species may strongly depend on their growth rates, our results warn for a greater potential of dinoflagellate HAB development in future coastal waters, particularly in temperate regions

Data from: Meta-analysis reveals enhanced growth of marine harmful algae from temperate regions with warming and elevated CO2 levels

Elevated pCO2 and warming may promote algal growth and toxin production, and thereby possibly support the proliferation and toxicity of HABs. Here, we tested whether empirical data supports this hypothesis using a meta-analytic approach and investigated the responses of growth rate and toxin content or toxicity of numerous marine and estuarine HAB species to elevated pCO2 and warming. Most of the available data on HAB responses towards the two tested climate change variables concerns dinoflagellates, as many members of this phytoplankton group are known to cause HAB outbreaks. Toxin content and toxicity did not reveal a consistent response towards both tested climate change variables, while growth rate increased consistently with elevated pCO2 . Warming also led to higher growth rates, but only for species isolated at higher latitudes. The observed gradient in temperature growth responses shows the potential for enhanced development of HABs at higher latitudes. Increases in growth rates with more CO2 may present an additional competitive advantage for HAB species, particularly as CO2 was not shown to enhance growth rate of other non-HAB phytoplankton species. However, this may also be related to the difference in representation of dinoflagellate and diatom species in the respective HAB and non-HAB phytoplankton groups. Since the proliferation of HAB species may strongly depend on their growth rates, our results warn for a greater potential of dinoflagellate HAB development in future coastal waters, particularly in temperate regions

Kunnen wateren met veel ondergedoken waterplanten CO2 uit de atmosfeer vastleggen?

Aquatische ecosystemen met veel ondergedoken waterplanten zijn potentiëlehotspots voor de invang van organisch materiaal. Waterplanten slaan koolstofen nutriënten op in hun biomassa, afgestorven planten en andere detritusvormen een organische laag op de bodem. Kunnen dergelijke systemen misschien de hoeveelheid CO2 in de atmosfeer omlaag brengen? En hoe verlooptdie vastlegging als het water door klimaatverandering opwarmt