| PROJECT AIM
This project aims at evaluating the controls of sediment erosion in agricultural ditches. Erosion from unstable ditches together with eutrophication from excess nutrients is the main reason of failing Water Framework Directive’s goals and a threat not only to water quality but also biodiversity and health of aquatic biota. In Sweden out of 90 000 km of agricultural ditches, half is in poor ecological status. Remediation of agricultural ditches can reduce erosion and eutrophication pressures, however, recent findings repoort a large variation in effectiveness of remediated ditches (RDs) in reducing erosion and eutrophication, that is hypothesised to be driven by variation in structural properties of ditches: channel geometry, vegetation cover and maintenance practices. Therefore, in this project we evaluate the potential of RDs in reducing erosion compared to traditional ditches, test if RDs with net erosion are in poorer ecological and chemical status, and test the role of structural properties on erosion in a modelling study. The overall aim of this work is to understand controls of erosion in RDs to form guidelines on their optimal design and maintenance.
METHODOLOGY
The project is divided into 2 work packages running consecutively during one year. In WP1 we will use existing data (through LEVA catchments and our ongoing Formas projects) on chemical status of 50 Swedish RDs and evaluate long-term indicators of ecological status and erosion. This will be conducted through surveying macroinvertebrates in RDs and traditional ditches, measuring ditch channel geometry, measuring vegetation, flow and chemical parameters. This dataset will be used in WP2 to calibrate and validate HEC-RAS models which will test different types of RDs, the effect of ditch length, vegetation cover, presence of terraces and maintenance practices on erosion. The goal is to identify optimal designs of RDs that help to reduce erosion. The work will be carried out by a post-doc researcher supported by hydrochemist, stream ecologist, HEC-RAS modeller and drainage/ditch maintenance expert.
PRELIMINARY RESULTS
This project builds on our ongoing work (FORMAS 2018-00890) evaluating the effectiveness of two-stage ditches in Sweden, which shows that RDs show varied effectiveness in reducing erosion. We have also contacted LEVA catchments representatives in Sweden and collated information on available water and chemistry data and interest in RDs and their design and maintenance.
IMPORTANCE
Reducing erosion and eutrophication is critical to address many environmental objectives stipulated in e.g. Water Framework Directive, Sweden’s Zero Eutrophication but also newly adopted EU Green Deal. Traditional approaches to reduce erosion and eutrophication focus on targeting soils sources. However, this might not be enough to achieve significant reductions in erosion and eutrophication due to accumulation and transformation of pollution in stream networks. Therefore, in this project we evaluate what controls erosion in RDs and how it can be reduced through optimal design and maintenance. These results are important to reaching water conservation and management goals in Sweden and Europe, and important focus area of Stiftelsen Oscar och Lili Lamms Minne. |