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Biological purification of streams


How do we optimize natural water purification in streams?

Streams are connecting land to coastal areas and transport dissolved and particulate nutrient and carbon downstream. Downstream export of excess nutrient and organic matter is a well-known problem to coastal waters causing eutrophication, harmful algal blooms, oxygen depletion, loss of benthic plants and consequently impairment of fisheries.

Stream processes such as primary production, decomposition and nutrient uptake is important for the downstream export of nutrient and organic matter, and these processes are strongly mediated by habitat conditions and biological communities. In particular, aquatic plants have shown to enhance nutrient and organic matter removal in stream ecosystems via an array of factors (see figure below). We believe that the large potential that aquatic plants provide to a large extent remains unexploited, particularly because current stream management practices jeopardize retention processes by removing aquatic plant biomass in critical periods during summer.

The objective of this project is therefore to address societal concerns about the ongoing eutrophication of coastal areas by providing the knowledge to optimize management in streams to reduce nutrient and organic matter export downstream. We will measure in-stream processes under different stream management practices to gain knowledge on how and to what extent streams can provide cleaner water to coastal areas. This knowledge can be used for optimizing management with the aim to support inherent physical and biological conditions and thus boost natural purification of stream water. VELUX Foundation has supported this research with 1.8 mill DKK.