The significance of climate change in streams utilised by humans

To better understand the role of climate change in catchments that are already under pressure of human activities one needs to study past, current and future conditions. Therefore, the catchment of the river Vecht (The Netherlands), representative for many human utilised, medium-sized lowland river catchments in this ecoregion, was chosen as case example. Canalisation of the river Vecht went along with changes in land-use and took place during three major time-intervals: ±1895-1905, 1925-1935, and 1955-1965. As elsewhere in Europe, the agricultural, urban and other human uses increased and the morphological features of the streams showed degradation over the last 100 years. Most streams were straightened, total stream length was shortened (20 %), many connected side-arms got lost (40 %), and the number of oxbows decreased (38 %). There was a positive trend in temperature and precipitation observed over the last hundred years. But land-use and hydromorphology changes were independent from climate change. Six climate scenarios (two current and four for the years 2070-2100; SIMGRO model) showed that discharge will become somewhat more dynamic. The future low flow conditions predicted (MLR-EKOO model) macroinvertebrate assemblages that are more often found in temporary, -mesosaprobic, natural upper courses and polysaprobic, natural and canalised upper- and middle courses. This indicates slight quality deterioration. But comparing the major changes in land-use in the past that dramatically affected the stream ecosystems with these predicted small climate change induced changes justifies the conclusion that future land-use change will be of much greater importance than the effect of climate change