Water body and riparian buffer strip characteristics in a vineyard area to support aquatic pesticide exposure assessment.

The implementation of a geodata-based probabilistic pesticide exposure assessment for surface waters in Germany offers the opportunity to base the exposure estimation on more differentiated assumptions including detailed landscape characteristics. Since these characteristics can only be estimated using field surveys, water body width and depth, hydrology, riparian buffer strip width, ground vegetation cover, existence of concentrated flow paths, and riparian vegetation were characterised at 104 water body segments in the vineyard region Palatinate (south-west Germany). Water body segments classified as permanent (n=43) had median values of water body width and depth of 0.9m and 0.06m, respectively, and the determined median width:depth ratio was 15. Thus, the deterministic water body model (width=1m; depth=0.3m) assumed in regulatory exposure assessment seems unsuitable for small water bodies in the study area. Only 25% of investigated buffer strips had a dense vegetation cover (>70%) and allow a laminar sheet flow as required to include them as an effective pesticide runoff reduction landscape characteristic. At 77 buffer strips, bordering field paths and erosion rills leading into the water body were present, concentrating pesticide runoff and consequently decreasing buffer strip efficiency. The vegetation type shrubbery (height>1.5m) was present at 57 (29%) investigated riparian buffer strips. According to their median optical vegetation density of 75%, shrubberies may provide a spray drift reduction of 72±29%. Implementing detailed knowledge in an overall assessment revealed that exposure via drift might be 2.4 and via runoff up to 1.6 fold higher than assumed by the deterministic approach. Furthermore, considering vegetated buffer strips only by their width leads to an underestimation of exposure by a factor of as much as four. Our data highlight that the deterministic model assumptions neither represent worst-case nor median values and therefore cannot simply be adopted in a probabilistic approach.

Geodata-based probabilistic risk assessment and management of pesticides in Germany: a conceptual framework.

The procedure for the risk assessment of pesticides in Germany is currently further developed from a deterministic to a geodata-based probabilistic risk assessment (GeoPRA) approach. As the initial step, the exposure assessment for spray drift in permanent crops, such as vineyards, fruit orchards, and hops, is considered. In our concept, geoinformation tools are used to predict distribution functions for exposure concentrations based mainly on spatial information regarding the neighbourhood of crops and surface waters. A total number of 23 factors affecting the drift into surface waters were assessed and suggestions for their inclusion into the approach developed. The main objectives are to base the exposure estimation on a realistic representation of local landscape characteristics and on empirical results for the impact of each feature on the drift deposition. A framework for the identification of high-risk sites (active management areas [AMAs]) based on protection goals and ecological considerations was developed in order to implement suitable risk mitigation measures. The inclusion of active mitigation measures at sites with identified and verified risk is considered a central and important part of the overall assessment strategy. The suggested GeoPRA procedure itself is comprised of the following 4 steps, including elements of the extensive preliminary work conducted so far: 1) nationwide risk assessment, preferably based only on geodata-based factors; 2) identification of AMAs, including the spatial extension of contamination, the level of contamination, and the tolerable effect levels; 3) refined exposure assessment, using aerial photographs and field surveys; and 4) mitigation measures, with a focus on landscape-level active mitigation measures leading to effective risk reductions. The suggested GeoPRA procedure offers the possibility to actively involve the farming community in the process of pesticide management. Overall, the new procedure will aim at increased flexibility of pesticide application regulations and a high level of protection of surface waters.