| Along with climate warming, many freshwater and coastal ecosystems have become greener and browner due to increased concentrations of nutrients, iron and dissolved organic matter from run-off entering water bodies. Water temperatures, nutrient and light conditions are thus undergoing rapid change. Although we know quite a lot about how these factors in isolation affect organisms living in water, we currently largely lack knowledge to predict consequences of combined changes of these factors. At the same time as the supply of light and nutrients is changing the living conditions for aquatic primary producers, climate warming is altering body size distributions in aquatic food webs. These changes are all likely to affect how aquatic food webs function. This project therefore aims to resolve how simultaneous greening, browning and warming of water bodies change the efficiency of energy transfer from primary producers to fish (i.e. food web efficiency, FWE), taking size variation among individuals both within and between species into account. Understanding how energy flows from primary producers up the food web is important for predicting both biomass distributions in food webs and ecosystem services at the base (e.g. carbon sequestration) and the top (e.g. fishery yields) of aquatic food webs.
To provide this new knowledge, we will in a PhD-project use a combination of comparative lake data, collection and analyses of data from a whole-ecosystem warming experiment, manipulative experiments and analyses of dynamic stage-structured bio-energetic food web models to produce knowledge about: (1) How warming-induced shifts in FWE vary with light and nutrients, (2) How food web configuration and (3) Size variation within and between species modify FWE in different climate change scenarios.
Management of waters is often concerned with how to assess and take actions to mitigate negative effects of one environmental stressor at a time, such as eutrophication. The problem with this approach is that water bodies are not only becoming greener (i.e. affected by increased nutrient supply), but at the same time becoming warmer and browner. With the proposed research program we will generate knowledge needed to evaluate strategies to minimize negative consequences of several simultaneously changing environmental conditions in Swedish water bodies, with specific relevance to loss of food web efficiency under ongoing climate change. Our research will also be of relevance for long-term goals concerning the capacity of aquatic environments to maintain biodiversity, produce seafood and act as carbon sinks in face of eutrophication and climate change.
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