H.-G. Frede

Modeling pesticide losses with surface runoff in Germany

Abstract A model has been developed which estimates relative pesticide losses with surface runoff for all of Germany. The 42 active ingredients considered in this study were chosen according to their annual sales in 1993 (herbicides, fungicides >100 t year −1 , insecticides >50 t year −1 ). After the construction of a nationwide data base on pesticide application rates, the runoff losses of pesticides were calculated by incorporating various spatial data sets on climate, soil, land use and other topics that have significant effects on pesticide runoff from fields. Results for the cumulative loss of 42 active ingredients applied in 11 field crops, orchards and vineyards are presented in digital raster maps (100×100 m). The model enables both a visualization of the spatial distribution of runoff risk and an assessment of the potential pollution levels originating from certain crops in specified application periods. Due to the scale of the studied area studied, the model development had to follow a strictly stochastic approach which contains some notable uncertainties. The lack of reliable information on the behaviour of the pesticides under site specific conditions constitutes the most important limitation.

Deforestation and benthic indicators: how much vegetation cover is needed to sustain healthy Andean streams?

Deforestation in the tropical Andes is affecting ecological conditions of streams, and determination of how much forest should be retained is a pressing task for conservation, restoration and management strategies. We calculated and analyzed eight benthic metrics (structural, compositional and water quality indices) and a physical-chemical composite index with gradients of vegetation cover to assess the effects of deforestation on macroinvertebrate communities and water quality of 23 streams in southern Ecuadorian Andes. Using a geographical information system (GIS), we quantified vegetation cover at three spatial scales: the entire catchment, the riparian buffer of 30 m width extending the entire stream length, and the local scale defined for a stream reach of 100 m in length and similar buffer width. Macroinvertebrate and water quality metrics had the strongest relationships with vegetation cover at catchment and riparian scales, while vegetation cover did not show any association with the macroinvertebrate metrics at local scale. At catchment scale, the water quality metrics indicate that ecological condition of Andean streams is good when vegetation cover is over 70%. Further, macroinvertebrate community assemblages were more diverse and related in catchments largely covered by native vegetation (>70%). Our results suggest that retaining an important quantity of native vegetation cover within the catchments and a linkage between headwater and riparian forests help to maintain and improve stream biodiversity and water quality in Andean streams affected by deforestation. This research proposes that a strong regulation focused to the management of riparian buffers can be successful when decision making is addressed to conservation/restoration of Andean catchments.

Solute behaviour and export rates in neotropical montane catchments under different land-uses

To improve our knowledge of the influence of land-use on solute behaviour and export rates in neotropical montane catchments we investigated total organic carbon (TOC), Ca, Mg, Na, K, NO3 and SO4 concentrations during April 2007-May 2008 at different flow conditions and over time in six forested and pasture-dominated headwaters (0.7-76 km²) in Ecuador. NO3 and SO4 concentrations decreased during the study period, with a continual decrease in NO3 and an abrupt decrease in February 2008 for SO4. We attribute this to changing weather regimes connected to a weakening La Nina event. Stream Na concentration decreased in all catchments, and Mg and Ca concentration decreased in all but the forested catchments during storm flow. Under all land-uses TOC increased at high flows. The differences in solute behaviour during storm flow might be attributed to largely shallow subsurface and surface flow paths in pasture streams on the one hand, and a predominant origin of storm flow from the organic layer in the forested streams on the other hand. Nutrient export rates in the forested streams were comparable to the values found in literature for tropical streams. They amounted to 68 kg/ha*y for Ca, 78 kg/ha*y for K, 45 kg/ha*y for Mg, 11-14 kg/ha*y for Na, 19-22 kg/ha*y for NO3 and 17 kg/ha*y for SO4. Our data contradict the assumption that nutrient export increases with the loss of forest cover. For NO3 we observed a positive correlation of export value and percentage forest cover.