Drivers of impaired ecological functioning in constructed delta lakes: a case study on lake Markermeer (Rhine delta).
In natural deltas, the exchange between marine, freshwater and terrestrial ecosystems created large and dynamic gradients with productive and diverse biological communities. Their abundance of natural resources has attracted human populations, with currently growing cities in delta areas around the globe. In densely populated deltas, year-round access to sufficient freshwater and protection against flood events from the river or sea is regulated by dams and dykes. This resulted in compartmentalisation of deltas and the creation of artificial lakes. While these lakes still provide a wide range of ecosystem services, ecological functioning in constructed delta lakes is often impaired, with a multitude of potential drivers responsible for the low diversity and altered productivity of aquatic communities.
In this presentation, I will focus on lake Markermeer, a large (700 km2) and shallow (average depth 3.6 m) reservoir created in 1975 in the Rhine delta in the central part of the Netherlands. In this lake, an ecological collapse was observed during the past decades, i.e. strong decline in flagship bird and fish species. Important drivers for ecological functioning include altered nutrient dynamics, resuspension of fine sediments and formation of limnetic aggregates, development of submerged vegetation, and shifts in aquatic consumer communities. I will present results of experiments and field monitoring, studying the influence of biotic and a-biotic benthic processes on productivity and food-web structure in lake Markermeer. By analysing the main drivers underlying observed changes in relation to the negative ecological impacts, essential insight is generated to effectively restore the ecological functioning of important wetland habitats in densely populated delta regions.
Host: Sabine Hilt