Differential response to climatic variation of free-floating and submerged macrophytes in ditches

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

Differential response to climatic variation of free-floating and submerged macrophytes in ditches

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

Changing weather conditions and floating plants in temperate drainage ditches

Dominance of free-floating plants such as duckweed is undesirable as it indicates eutrophication. The objectives of this study are to investigate whether the onset of duckweed dominance is related to weather conditions by analysing field observations, to evaluate the effect of different climate scenarios on the timing of duckweed dominance using a model and to evaluate to what extent nutrient levels should be lowered to counteract effects of global warming. To analyse the onset of duckweed dominance in relation to weather conditions, duckweed cover in Dutch ditches was correlated with weather conditions for the period 1980-2005. Furthermore, a model was developed that describes biomass development over time as a function of temperature, light and nutrient availability, crowding and mortality. This model was used to evaluate the effects of climate change scenarios and the effects of lowering nutrients. The onset of duckweed dominance in the field advanced by approximately 14 days with an increase of 1 °C in the average maximum daily winter temperature. The modelled biomass development correlated well with the field observations. Scenarios showed that expected climate change will affect onset and duration of duckweed dominance in temperate ditches. Reducing nutrient levels may counteract the effect of warming. Synthesis and applications. Global warming may lead to an increase in the dominance of free-floating plants in drainage ditches in the Netherlands. The expected reductions in nutrient-loading to surface waters as a result of different measures taken so far are likely not sufficient to counteract these effects of warming. Therefore, additional measures should be taken to avoid a further deterioration of the ecological water quality in ditches. © 2013 The Authors. Journal of Applied Ecology © 2013 British Ecological Society

Changing weather conditions and floating plants in temperate drainage ditches

Dominance of free-floating plants such as duckweed is undesirable as it indicates eutrophication. The objectives of this study are to investigate whether the onset of duckweed dominance is related to weather conditions by analysing field observations, to evaluate the effect of different climate scenarios on the timing of duckweed dominance using a model and to evaluate to what extent nutrient levels should be lowered to counteract effects of global warming. To analyse the onset of duckweed dominance in relation to weather conditions, duckweed cover in Dutch ditches was correlated with weather conditions for the period 1980-2005. Furthermore, a model was developed that describes biomass development over time as a function of temperature, light and nutrient availability, crowding and mortality. This model was used to evaluate the effects of climate change scenarios and the effects of lowering nutrients. The onset of duckweed dominance in the field advanced by approximately 14 days with an increase of 1 °C in the average maximum daily winter temperature. The modelled biomass development correlated well with the field observations. Scenarios showed that expected climate change will affect onset and duration of duckweed dominance in temperate ditches. Reducing nutrient levels may counteract the effect of warming. Synthesis and applications. Global warming may lead to an increase in the dominance of free-floating plants in drainage ditches in the Netherlands. The expected reductions in nutrient-loading to surface waters as a result of different measures taken so far are likely not sufficient to counteract these effects of warming. Therefore, additional measures should be taken to avoid a further deterioration of the ecological water quality in ditches. © 2013 The Authors. Journal of Applied Ecology © 2013 British Ecological Society

Factors affecting the global distribution of Hydrilla verticillata

Hydrilla verticillata (Hydrocharitaceae) is a submerged freshwater flowering plant within the monotypic genus. Over the geological periods, fossils of this family and genus have shown distinct diversifications between warm and cool fluctuations with more adaptations occurring in warmer periods and suppressions during severely cold paleoclimate changes. Recently, H. verticillata has shown a wide range of adaptive plasticity, allowing successful proliferation into non-native regions, whilst also undergoing unexplained disappearance from its native localities, and this phenomenon has stimulated this inquiry. Against this somewhat complex background, particular interest for this investigation has been focussed on an understanding of which aspects of climate change have contributed towards global adaptations and distribution patterns of H. verticillata. Whilst it is recognised that some of these changes are natural, other aggravating impacts are due to anthropogenic influences. Identifying the appropriate combinations of these climatic factors (temperature, rainfall, photoperiod), in concert with environmental (water level, CO2, salinity, eutrophication), geographical (altitude, latitude) and other factors (UV-B) are necessary precursors for instituting appropriate management strategies. In this respect, control measures are needed in non-native regions and restoration of this plant in native habitats are essential for its ecologically balanced global distribution. © 2021 European Weed Research Societ