Nutrient contents and export from streams in semiarid catchments of central Spain

Thirty five catchments in semiarid Central Spain were monitored monthly in late winter and spring to search for relationships between environmental variables (sedimentary nutrients and hydrological topographical, geological, pedological, land use factors) and nutrient concentrations and exports. Results enabled to outline differences between semiarid and moist catchments, the latter drawn from other studies. While land use, topography and ecotone features explained an important fraction of overall variance of nutrients in moist areas, geological and pedological features were much better descriptors in semiarid catchments. Runoff explained most variability of total carbon, organic carbon and nitrogen export, and soil types and carbon and phosphorus contents stored in stream sediments best explained total phosphorus, dissolved- and particulate organic carbon export in semiarid catchments. In moist catchments geology, climate, pedology and land use were shown to influence nutrient export. Hydrology potentially swamped effects related to land use and landscape structure (i.e. topographical, geological and soil factors). Thus nutrient concentration and export in semiarid catchments deviate from those in moist catchments which is due to the overriding effects of hydrological features, geology and pedology. Further research, including the application of combined GIS techniques and modeling approaches, is needed to generalize our findings over other semiarid areas.