Euro-limpacs Deliverables

ABSTRACT - DELIVERABLE 57

Report detailing plans and protocols for experimental fertilisation experiments and paired site analyses in Iceland

The aim of the study was to investigate community structure and trophic relationships along a gradient in geothermal influenced streams. Fifteen streams were examined in August 2004. They were selected due to their proximity to each other and the differences in temperature between them (4.5 to 40 oC). Water chemistry, algal biomass, macro−invertebrates and fish were sampled in each stream. In addition, hydro−morphological features and macrophyte coverage were assessed. Samples were taken from all trophic levels for stable isotope analysis. In addition to the survey, nutrient diffusion substrates (N, P, N+P and control) and leaf packs (mesh size 0.2 and 10 mm) containing birch (Betula pubescens) leaves were introduced to 10 replicate stream reaches and retrieved after 25 days. The 10 streams, which were a subset of the 15 streams surveyed, could roughly be grouped into two distinct temperature regimes, 8 ? 14 oC and 19 ? 23 oC, respectively. Physically the streams varied to a great extent, particularly in terms of slope and substrate composition. Macrophytes were unevenly distributed among sites with the low slope and fine sediment streams having a dense cover. Temperature seems to have a significant influence on the macroinvertebrate community structure, with cold streams primarily characterized by Chironomidae−Plecoptera−Trichoptera communities, whereas the warmer streams were primarily dominated by high densities of blackflies (Simulium vittatum) and the snails (Lymnaea peregra). Most streams contained brown trout (Salmo trutta) with the exception of the steep streams with step−pools and streams with temperatures above 23 oC. Results from the diffusion substrate experiment indicate nitrogen as being limiting for primary production in the streams across the temperature gradient. Leaf litter decomposition was highest in the coarse leaf packs to which macroinvertebrates had access. The results suggest that macro−invertebrate community structure is primarily driven by the differences in temperature while the different hydromorphological features of the streams investigated also affected other biotic elements.

One of the main aims of the survey undertaken in 2004 was to gather sufficient information about streams with differences in geothermal influence to select sites for future experiments in 2005 and 2006. The overall aim of these experiments carried out 2005 and 2006 is to investigate how nutrient additions (i.e. eutrophication) will impact on the structure and function in streams with different temperatures. This can be broken up into a number of more specific sub−aims:
i) Will nutrient additions change a part or the entire structure (number of species, dominating species etc,) of the stream ecosystems differently with temperature? (Hypothesis: that the change in structural components will be most pronounced with highest temperature).

ii) How will life cycles of individual macro−invertebrate species (maybe also plants (e.g. diatoms) and fish if we can include it) be affected by increased nutrient levels? This will include growth rates, production, emergence success and timing, and maybe dispersal abilities (Hypothesis: growth rates, production and emergence timing will increase with increased nutrient levels; individual size will decrease).

iii) How will the food web structure change with increased levels of nutrients ? including changes in biotic interactions? (Hypothesis: fewer linkages in the food web with higher levels of nutrients, more specialisation and more biotic interactions (predation?)).

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