Scenario-based simulation of runoff-related pesticide entries into small streams on a landscape level.

The prediction of runoff-related pesticide entry into surface waters on a landscape level usually requires considerable efforts with regard to input data, time, and personnel. Therefore, the need for an easy to use simulation tool with easily accessible input data, for example from already existing public sources, is obvious. In this paper, we present a simulation tool for the simulation of pesticide entry from arable land into adjacent streams. Our aim was to develop a tool applicable on the landscape level using "real world data" from numerous sites and for the simulation of parameter case studies concerning particular parameters at single sites. We used the ratio of exposure to toxicity (REXTOX) model proposed by the OECD, which had been successfully validated in the study area as part of a previous study and which was extended to calculate pesticide concentrations in adjacent streams. We simulated the pesticide entry on the landscape level at 737 sites in small streams situated in the central lowland of Germany with winter wheat, barley, and sugar beat as the main agricultural crops. A sensitivity analysis indicated that the most significant model parameters were the width of the no-application zone and the degree of plant interception. The simulation was carried out for the 15 most frequently detected substances found in the study area using eight different environmental scenarios, covering variation of the width of the no-application zone, climate, and seasonal scenarios. The highest in-stream concentrations were predicted for a scenario using no (0m) buffer zone in conjunction with increased precipitation. According to the predicted concentrations, the risk for the aquatic communities was estimated based on standard toxicity tests and the application of a safety factor. The simulation results are presented both by means of risk maps for the study area showing the simulated pesticide concentration and the resulting ecological risk for numerous sites under varying scenarios and by case study diagrams with focus on the model behavior under the influence of single parameters. Risk maps confirmed the importance of no-application (buffer) zones for the levels of pesticide input. They also indicated the importance of the existing no-application zones for certain compounds and in some cases the need for a further evaluation of these regulations. The simulation tool was implemented as a standard PC software combining the REXTOX model with a geographical information system and can be used on any current personal computer. All input data was taken from public sources of German authorities. With little effort the tool should be applicable for other areas with similar data quality.

Test-plot studies on runoff of sulfonamides from manured soils after sprinkler irrigation.

Three test-plot series have been performed to gather information on runoff of sulfonamides from manured arable and grassland after sprinkler irrigation. To prepare test slurries with defined aged residues, liquid bovine manure was fortified with sulfadiazine, sulfadimidine, and sulfamethoxazole and stored short-term. After test-slurry application, the arable land was treated by soil cultivation before irrigation, and the manured grassland was irrigated directly with 50 mm h(-1) for 2 h. The runoff suspensions were sampled at 5- to 10-min intervals, separated into aqueous phase and suspended matter and residue analyzed. Higher runoff emissions were found from manured grassland plots. The discharge volumes ranged from 106 to 252 L and the total runoff emissions ranged from 13 to 28% of sulfonamides applied initially. Within the first 20 min of the irrigation period that represented a rainfall of 17 mm, emissions, on average, were 4%. The loads of sulfonamides predominantly occurred in the runoff water. The only emissions via suspended matter, on average, were 0.02%. On arable land, however, the runoff was reduced by soil cultivation. Discharge volumes and sulfonamide emissions were 36 to 128 L and 0.1 to 2.5%, respectively. Despite the high-intensity sprinkler irrigation, major emissions did not occur until a 60-min delay.

Macroinvertebrate community structure in agricultural streams: impact of runoff-related pesticide contamination.

This study aims to assess the runoff-related pesticide contamination, among other environmental factors, that contributes to differentiation in the macroinvertebrate communities inhabiting six streams in northern Germany (Braunschweig, Lower Saxony). A total of 91 macroinvertebrate taxa were sampled three times (April, May and June 2000) during the main period of pesticide application to cereals and sugar beets in the catchment. Thirteen environmental variables (e.g., nutrients, discharge, in-stream structure), including runoff-related pesticide concentrations expressed as a sum parameter based on toxicity units (TU(SUM)), were analyzed using canonical correspondence analysis (CCA) and redundancy analysis. CCA based on species-level data and environmental variables explained 48% of the variance, with TU(SUM), stream width, percentage of detritus in the stream bed, and temperature being the most important variables. The sampling dates were of minor importance for the classification. The community composition in three streams exposed to maximum total pesticide levels between 0.2 x and 0.01 x acute toxicity to Daphnia (48-h LC(50)) was clearly distinct from that at three control sites. Redundancy analysis using average values of the environmental variables and taxonomic orders explained 95% of the variance, with TU(SUM) being the only significant variable. The results show that the present pesticide levels affect the invertebrate community structure in the field. Furthermore, they underline the potential for effects in the field at pesticide concentrations greater than 0.01 x acute toxicity to Daphnia and are thus in agreement with the assumptions underlying the standards set by the European Union uniform principle.

A comparison of predicted and measured levels of runoff-related pesticide concentrations in small lowland streams on a landscape level.

Short-term pollution events via runoff are typical of streams in agricultural areas. Existing runoff models that simulate pesticide loss from agricultural fields require extensive input of information. There is thus a need for a simple model that can predict runoff-related pesticide concentrations in many streams on a landscape level when only limited data are available. To validate such a model, the runoff-related pesticide load of 18 small lowland streams was predicted with an extended version of the model "simplified formula for indirect loadings caused by runoff" (available from the Organisation for Economic Cooperation and Development, OECD). The authors suggest that the model presented here is suitable for use in routine exposure assessment of pesticides on a landscape level, as all input data (soil, slope, precipitation, pesticide application) are readily available from public authorities or could be generated by simple regional flood hydrograph curves. The predicted concentrations were compared with measured concentrations obtained by runoff-triggered sampling. Fungicides, insecticides and herbicides were detected in 17 streams, with max. concentrations measuring up to 29.7 microg/l for the fungicide azoxystrobin and 0.3 microg/l for the insecticide parathion-ethyl. Herbicides were detected in 16 streams, with max. concentrations between 13.7 and 1.2 microg/l. The linear regression between the predicted and measured concentrations (log-values) shows significant correlations for the following pesticides: azoxystrobin: r2=0.43; p=0.03; epoxiconazole: r2=0.71; por=0.5 microg/l).

Linking land use variables and invertebrate taxon richness in small and medium-sized agricultural streams on a landscape level.

In this study the average numbers of invertebrate species across an arable landscape in central Germany (surveys from 15 years in 90 streams at 202 sites) were assessed for their correlation with environmental factors such as stream width, land use (arable land, forest, pasture, settlement), soil type, and agriculture-derived stressors. The stress originating from arable land was estimated by the factor "risk of runoff," which was derived from a runoff model (rainfall-induced surface runoff). Multivariate analysis explained 39.9% of the variance in species number, revealing stream width as the most important factor (25.3%), followed by risk of runoff (9.7%). The results showed that wider streams--with or without agricultural stressors--contained significantly higher species numbers than narrower streams. This can be explained by potentially more diverse in-stream structures leading to more habitats and niches. However, negative effects on species number owing to runoff from arable land could be distinguished from the effect of stream width: the number of species within each stream width class significantly decreased with increasing risk of runoff. Therefore the factor "risk of runoff" is considered to express a significant proportion of the variability in macroinvertebrate communities caused by stressors of agricultural origin.