Identifying the erosion risk areas and efficient targeting of erosion control measures

What is the best method to reduce erosion and sediment control measures?

CHALLENGE DESCRIPTION Soil erosion is a gradual process that occurs when the impact of water detaches and transports soil particles. Soil deterioration and water pollution due to erosion via runoff have become severe problems worldwide. Indeed, erosion is a serious problem both for productive agricultural land and for water quality concerns. Therefore, erosion control should be an integral part of agricultural management to maintain and improve the quality of both waters and soils. Eroded topsoil is finally transported into streams and other waterways. The subsequent sediment accumulation in the recipient waterbodies is a product of sheet and rill erosion from upland areas and, to a lesser extent, from cyclic erosion processes in drainageways. Soil erosion can occur in two stages: 1) detachment of soil particles by impacts of raindrop splash and flowing water; and 2) transport of the detached particles by flowing water. Thus, soil erosion is a physical process requiring energy, and its control requires certain measures to dissipate this energy. In addition to silting, erosion material also causes harm to the recipient waterbody by transporting nutrients, particularly phosphorus (P) which, in turn, accelerates eutrophication. Moreover, during the transport process part of the particle-bound P can be released into the form of dissolved reactive P, which is directly available to blue-green algae and thereby particularly harmful P-fraction in surface waters.

DESCRIPTION OF THE SOLUTION Key question in minimizing the sediment buildup in waterbodies is the stabilization of the sediment source by controlling erosion. Several conservation practices are usually needed to control erosion. In some situations, where the erosion is minimum, erosion control can be achieved by implementing a single practice, such as the establishment of grassed waterways. The single most effective way to control erosion is to maintain a permanent vegetation cover on the soil surface. Moreover, improving the soil infiltration rate by e.g. refurbishing the subsurface drainage, results in lower surface runoff and thus lesser erosion. Other measures that have proven effective in erosion control are no- or reduced tillage and direct sowing of annually cropped and harvested fields. Nevertheless, whatever the measure is to control erosion, the key issue is that the measures are effectively targeted. For this, modern map- and GIS-based tools offer invaluable assistance. A good example of such tool is RUSLE2015 (Panagos et al. 2015, that can estimate soil loss at 100 m resolution based on the best available data. In Finland, RUSLE2015 has been fine-tuned to local conditions by the Natural Resources Institute Finland (Luke 2017, In this work, the goal is to produce a nationwide system based on Lidar-mapped (laser-scaling technique) Digital Elevation Model (DEM) for accurate erosion sensitivity maps. The maps produced by RUSLE are a good base for discussions on targeting of the measures between farmers and agriculturalists.

POSSIBILITY OF ADAPTING THE SOLUTION Finnish farmers have in several occasions estimated the qualitative (the relative risk of occurrence of erosion) accuracy of the RUSLE maps to be good (Luke 2017). However, the quantitative accuracy (t/ha/y) has not been as good. This is partly related to the common experience that application of USLE type models (originally developed in the USA) in the boreal conditions has been difficult. Improvement work in this respect is, however, continuing in Luke (Räsänen 2020, pers. comm.). One of possible future improvements of RUSLE is so-called P-factor (P for “protection”), which takes into account erosion-reducing measures that are already implemented so that a field-block with no measures whatsoever gets value 1, and the more and more effective measures there are, the closer-to-zero value the field-block in question will get. The final map material will be made freely available through the Luke’s future WMS viewing service, but the property information related to the field plots can only be made available to farmers and agricultural advisors. The RUSLE maps are suitable for use on individual farms and in watersheds critical to water protection to target measures cost-effectively. In the future, also more accurate maps of soil type, P-status and farming practices will hopefully be available for further improvement of the targeting of the erosion-control measures. Here, developing use of satellite images may offer great new possibilities.

Authors of the solution description:SirkkaTattari, Jari Koskiaho
State of implementation of the solution:in progress

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