Euro-limpacs Deliverables

ABSTRACT - DELIVERABLE 42

Report on first results from the short-term solute additions along the Mediterranean aridity gradient. Comparison of sites with differing degrees of aridity

Climate change in the Mediterranean region is expected to result in an increase in temperature. Precipitation will probably decrease but, most importantly, the seasonality of precipitation will be complicated by more rain and more episodic events during the rainy seasons and more intense droughts in the summer. These changes in climate will have clear effects on stream hydrology, altering the flooding regime (probably with more spiky hydrographs) and increasing the number of intermittent streams associated with increases in water deficit in the catchment. In the Mediterranean region, fluvial ecosystems are prominent among aquatic ecosystems and most of them are currently subjected to intermittency, which provides a good opportunity to explore stream biogeochemical responses to future climate change scenarios of more humid regions in Europe.
Even though impacts of climate change on stream community structure are relatively well understood, our knowledge about impacts on stream ecosystem function is much poorer. Specifically, it is important to increase our knowledge of how environmental factors, such as hydrology and water temperature, influence stream biogeochemistry (e.g., nutrient retention, organic matter processing, metabolism) to be able to predict the effects of climate change on ecosystem function. Our hypothesis is that the relevance of these factors controlling ecosystem function may vary depending on the local climate conditions.
The overall aim of our study is to assess the variability in stream response in terms of nutrient retention and examine the role of stream hydrology and water temperature on this variability. For this purpose we have selected several streams within the Mediterranean region that cover a temperature and aridity gradient. In these streams, we will examine spatial variability in nutrient retention across streams for a given period of the year and temporal variability (i.e., over more than a year) in nutrient retention in streams located at different altitudes. Here we report the first results on the temporal variation in stream nutrient retention efficiency for ammonium and phosphate from two Mediterranean streams located at different altitudes within the same catchment. With these results we examined the temporal variation of hydrological and chemical parameters and compared it to that observed for nutrient retention parameters for each stream and between streams.

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