Stream Ecology

Ecosystem metabolism and nutrient spiraling in macrophyte-rich streams

Primary production and respiration are important controllers of ecosystem biomass and energy flow. Besides stream metabolism another key process in stream ecosystem function is nutrient cycling. In streams nutrients (phosphorus and nitrogen) undergo transformations from dissolved available form in the water column to uptake by organisms or by physical retention. The nutrient spiral is complete when the nutrients return to the water column. The project will identify how stream ecosystem function in terms of spatial and temporal variability of stream metabolism and nutrient spiraling relates to the abundance, distribution and community composition of macrophytes in temperate lowland streams.  The aims are (1) to understand spatial and temporal changes in stream metabolism and nutrient spiraling in relation to macrophyte biomass and biomass distribution; (2) to understand how morphology and biomass-specific rates of macrophyte species affect stream metabolism and nutrient spiraling, (3) to identify how stream management (weed-cutting and dredging) as well as restauration affect nutrient dynamic and stream metabolism in macrophyte-rich streams.

Participants: Tenna Riis og Annette Baattrup-Pedersen

Nutrient uptake in big rivers across seasons

River networks regulate the export of nutrients from the terrestrial landscape, and thus play an important role in mitigating eutrophication of downstream ecosystems. To protect our freshwater resources, we must understand how river networks, from headwaters to outlets contribute to watershed nutrient export. Unfortunately, we know little about the ability of rivers to retain and transform inorganic nutrients as the majority of nutrient uptake measurements have been made in headwater streams with discharge

Participants: Tenna Riis, Jennifer Tank, Annette Baattrup-Pedersen

Effect of increased nutrient run-off to High Arctic streams following climate change

In Arctic higher run-off of dissolved organic matter (DOM), inorganic nitrogen (N) and phosphorus (P) is expected in the future, because more organic matter is decomposed in warmer systems and in systems with higher summer precipitation. Higher mineralization rate and run-off of DOM and N and P to streams can increase stream ecosystem primary production and respiration, increase bacterial biomass, and cause effects on higher trophic levels and ultimately on the whole ecosystem structure and function. The objectives of this study are 1) to determine the amount of DOM and inorganic N and P run-off to two High Arctic streams with stable ground water flow, and 2) clarify the fate of in-stream DOM  and inorganic nutrients, and how a future increase will change the biological structure and function in the streams. The study will provide a mechanistic understanding of the effect on a future increase in DOM and inorganic nutrient in high-arctic streams.

Participants: Tenna Riis, Annette Baattrup-Pedersen

Choosing the best plants for wetlands

Currently small wetlands are established in order to reduce nitrogen (N) and phosphorus (P) run-off from the landscape to down-stream estuaries. The role of the wetlands is to enhance N and P retention and removal through assimilatory uptake, sedimentation, and denitrificaition. Morover, the wetlands offer an opportunity to increase overall biodiversity in an area by increasing the habitat variability in agricultural landscapes. In this project we will test the nutrient retention and removal efficiency offered by a range of wetlands plants, and their ability to support biodiversity (e.g. terrestrial and aquatic fauna). This project is part of a larger GUDP project (PLANTNAT, see bios.au.dk/om-instituttet/organisation/soe-oekologi/forvaltning/plantnat/)

Participants: Tenna Riis, Torben L. Lauridsen, Beate Strandberg, Carl-Christian Hoffmann.