Project title: Biodiversity and ecological function in streams
Period: 2011 – 2014
Funding: The Danish National Research Foundation
Objective
The overall objective with this project is to analyse plants roles in nitrogen turn over in streams.
Background
Nutrient cycling is an important ecological function in streams. Streams receive extensive amount of
nitrogen and phosphorus from human activities such as agricultural production and industry, and a better
understanding for nutrient cycling is important to be able to predict the consequences of changed nutrient
conditions in the future. It is therefore important to know the velocity by which inorganic nitrogen is
immobilized and how various components in the ecosystem is acting in uptake and long-term retention.
In this project we will use stable isotope (15N) as a marker in field experiments (Fry et al.
1995). Release of small amounts of 15N will not result in any important increase in nitrogen concentration
and will therefore not stimulate production. By release of 15N as a marker we can therefore determine
nitrogen uptake, transformation and turn-over rates, as well as relationships between consumers and food
resources in streams. The movement of 15N- ammonium is followed in various organism types from primary
producers and microorganism’ assimilation to primary consumers and predators. Moreover we can
determine nitrification rates by measuring 15N in the two nitrogen species (Mulholland et al. 2000, Dodds et
al. 2000).
Subsequently comparison of nutrient cycling in a range of streams with various biodiversity, we can
quantify the effect of diversity on ecosystem function expressed by nitrogen cycling. Results from this
project will therefore be used in a meta-analysis on comparison of parameters describing nitrogen cycling
(uptake and turn-over rates) and parameters describing biodiversity in streams (number of taxa within
different components, trophic structure).
Referencer
1. Dodds, W.K., Evans-White, M.A., Gerlanc, N.M. 2000. Quantification of the nitrogen cycle in a prairie stream.
Ecosystems, 3, 574-589
2. Mulholland, P.J., Tank, J.L., Sanzone, D.M. 2000. Nitrogen cycling in a forest stream determined by a 15N tracer
addition. Ecological Monographs, 70, 471-493.