Culterra 37

Aufbau eines Landschafts- Informationssystems und landwirtschaftliche Gewässerschutzberatung im Einzugsgebiet der Seefelder Aach

von ELMAR SCHLECKER (2004)

Summary

As a result of the EU Water Framework Directive (WFD) first steps are taken away from the sectoral approaches to-wards a holistic approach. New aspects of the river basin plans are the con-sideration of the whole catchment area, as well as the differentiation between point source and diffuse source pollu-tion. Nitrogen and phosphorus play an important role in water ecology. The main input into the water comes from diffuse sources, primarily agriculture. Nitrogen leaches into the groundwater in form of nitrate. Due to soil erosion phosphorus mostly reaches surface waters.

In the 'Seefelder Aach' catchment area the Ministry for Environment and Traffic launched a pilot project to im-plement the WFD. The Tübingen regional council was in charge of the project. Compared with other tributaries of Lake Constance the Seefelder Aach contains an exceptionally high content of nutrients, which are mostly outputs of agriculture. Reasons for the water pollution are site conditions and land use practices. An important task of the project 'Integrated Water Protection in the Seefelder Aach Catchment Area' was to reduce the diffuse nutrient pollu-tion coming from agriculture. The dissertation focuses on the development of the 'Landscape Information System Seefelder Aach' (LISA) and the agricultural water protection extension in order to implement practices that protect water.

The 'Landscape Information System Seefelder Aach' (LISA) serves as a GIS-based landscape and impact assessment tool, which locates areas vulnerable to erosion, also known as hot spots. The water protection extension makes these hot spots target issues. The LISA is to be transferable on a national scale. Based on the experience gathered in the course of this study, it can be concluded that it is possible to transfer the model to other catchment areas. More research is needed in this matter though. To ensure the transferability solely generally accessible data, which is available nationwide, was used. For the landscape and impact assessment climate and soil data, an elevation model, as well as land use data were integrated into the LISA. The factors of the models were derived from the various data sources through non-graphic data processed in a data-base, internal GIS algorithms, and with the help of translation keys.

The LISA made use of the Universal Soil Loss Equation (USLE) in order to estimate the soil erosion. The risk of nitrate leaching was quantified by analysing the relative exchange capacity of the soil water and the nitrogen balances. These empirically developed estimation methods for soil and nitrate leaching can be calculated with the help of commonly accessible data. Another advantage of the models is the consider-ation of influential factors related to site conditions and management practices.

Through the GIS-based calculation applied by the USLE the average soil erosion per annum, the site induced risk of erosion and the risk of soil erosion were calculated for the arable land of the Seefelder Aach catchment area. By employing this method it was possible to locate specific fields of arable land, which are susceptible to erosion.
These fields are then the focus of the water protection extension. A scenario was developed to illustrate how soil preparation practices reduce erosion.

By calculating the relative exchange capacity of the soil water, the site related risk of nitrate leaching from agri-culturally used land could be derived. The calculation of the potential nitrate concentration in the seepage was based on data about excessive fertilisation, which was collected in the Seefelder Aach catchment area. The results showed that it is a suitable method to determine the risk of erosion for agri-cultural and open land. Fertilisation of these so called hot spots was to be adapted in order to lessen the overall nitrate leaching. On account of the water protection extension for farmers, surplus nitrogen could be reduced. The positive effect of fertilisation which conforms with the practices of 'good workmanship in agriculture', on the risk potential, was calculated for a scenario and visualised by the LISA.

The essential task of the agricultural water protection extension in the Seefelder Aach catchment area was to implement production techniques, which contribute to water protection. To achieve this, a transdisciplinary approach to research was taken. The methodology is influenced by the focus of the research on the implementation and the participation of the actors. Farmers participated within the organi-sational framework of a working group dealing with cultivation practices that protect water. In cooperation with the participants problems with respect to water protection in agriculture were dis-cussed and suggestions for possible solutions were made. Behavioural models formed the basis of this specific method of extension. The abstract factors of these models were put into concrete terms to develop the water protection extension for the Seefelder Aach catchment area. Through questioning the participants of the working group the supportive as well as restrictive influences on the environ-mental behaviour of farmers were identified.

The effects of the extension, i.e. the degree to which the farmers adopted proposed practices, were also examined by questioning the working group members. Additionally, a quantitative comparison of the situation before and after the extension was undertaken.

Especially working group meetings, field trips and individual advice proved to be worthwhile tools of the water protection extension in the Seefelder Aach catchment area. Intensive assistance, as well as the participation achieved changes of the farmers' behaviour and the implementation of water protection measures.

Analysing the nitrogen crop balances made clear that current fertilisation practices of farms in the Seefelder Aach catchment area partly disagree with the principles of 'good workmanship in agriculture'. Problems with regard to fertilisation are mostly related to the calculation of the right amount of fertiliser according to 'good work-manship in agriculture' and the appli-cation of organic fertiliser.

On the basis of the calculated fertili-sation balance, cultivated species could be put in order according to their risk of nitrate leaching.
In conclusion, it can be stressed that the Landscape Information System (LISA) - developed to put the regulations of the EU Water Framework Directive into practice - is an important contribution to the implementation of water protection, which considers the causal relationships and site conditions. The water protection extension, as presented in this study, also showed that 'good workmanship in agriculture' contributes to a reduction of diffuse nutrient inputs into the water and therefore, supports water protection.