Developing prospects for wet arable land in Switzerland

Dry up the swamps! In some cases, the melioration failed and parts of the wetlands became conservation areas. For a large extent of drained land, agriculture again faces similar challenges decades later. Large investments are needed as one third of Switzerland’s drainage systems are in poor or unknown conditions (Béguin & Smola 2010). Whilst, in earlier times, no other ecosystem values were considered outside of agricultural productivity, the loss of wetlands is now recognised as a major threat to biodiversity (Lachat et al. 2010) and, in the case of organic soils, as a contributor to climate change via CO2 emissions (Wüst et al. 2016). Wetlands have now been declared as key habitats of Switzerland’s Environmental Targets for Agriculture (Walter et al. 2013). In a nationwide project mandated by the Swiss Federal Office for Agriculture and the Swiss Federal Office for the Environment, agricultural land affected by water is mapped and typified and new prospects for wet arable land are developed.

The relief induced risk of water logging in planes and geomorphologic depressions was modelled for Switzerland using swissALTI3d elevation data at a two metre resolution (swisstopo 2016). As the road network is directly connected to the drainage system, the analysis was computed for micro watersheds by means of field blocks, delimited by water bodies, forests, road networks, and developed areas. Slope was calculated on a 2 x 2 m grid and combined with the maximum elevational decline within a 25 metres radius to identify planes and medium sized depressions. The difference between the elevation of each single cell and the minimum elevation inside the field block was integrated as a simple measure for water accumulation in the micro watershed. The mean annual precipitation was used to adjust the results to the climatic gradient. Soil and geological maps were classified in terms of soil-water characteristics, and into organic and mineral soils. In addition, biodiversity hotspots were identified based on distribution data of target species relying on wet arable land (Info Species 2017).

The synthesis of relief and soil information allows the prediction of potential water-induced yield losses. The biodiversity hot spots indicate field blocks with special importance to the habitat connectivity of target species on wet arable land. Land use data, maps of artificial drainage systems, and a connectivity map of agricultural land to surface waters (Alder et al. 2015) indicate the level of human impact and help to localise conflict areas.

The aim of the project is to provide policy support and to develop sustainable management options for wet arable land. The primary focus is on biodiversity promotion, but we also intend to explore possible synergy effects which limit CO2 emissions and reduce nutrient and pesticide losses to ground and surface waters. In case studies, we will evaluate alternatives for the future use of wet arable land.