Canga, Eriona4; Kjærgaard, Charlotte6; Iversen, Bo Vangsø6; Heckrath, Goswin Johann6
1 Department of Agroecology and Environment, Faculty of Agricultural Sciences, Aarhus University, Aarhus University2 Agrohydrology and Water Quality, Faculty of Agricultural Sciences, Aarhus University, Aarhus University3 Soil physics and Soil resources, Faculty of Agricultural Sciences, Aarhus University, Aarhus University4 unknown5 Department of Agroecology - Soil Physics and Hydropedology, Department of Agroecology, Science and Technology, Aarhus University6 Department of Agroecology - Soil Physics and Hydropedology, Department of Agroecology, Science and Technology, Aarhus University
Despite substantial efforts, the leaching of nutrients from agricultural land is still a serious and costly environmental problem in Denmark and elsewhere. The quality goals of the European Water Framework Directive (WFD) for the aquatic environment require a substantial reduction of diffuse nutrient loads from farmland in Denmark. Tile drains and ditches connect fields to receiving waters and act as subsurface highways for both soluble and particulate phosphorus (P), nitrogen (N) as well as other agricultural contaminants. Drainage losses of nutrients contribute to estimated 33% of total P losses and 45-60% of total N losses. Hence, for a large number of recipients, drainage water nutrient loads has a major impact on water quality, however, mitigation options targeting subsurface drainage are lacking. An end-of-pipe drainage filter solution offers the benefits of a targeted measure typically applied to point sources. This calls for a shift of paradigm towards the development of new, cost-efficient technologies to mitigate site-specific nutrient losses in drainage. A newly launched Danish research project “SUPREME-TECH” (2010-2015) (www.supreme-tech.dk) funded by the Danish Strategic Research Council, aims at providing the scientific basis for developing cost-effective filter technologies targeting P-retention and N-removal in agricultural subsurface drainage. The project studies different approaches of implementing the filter technologies including drainage well filters as well as surface-flow and subsurface flow constructed wetlands. Various natural and industrial P filter substrates are tested towards P sorption properties, as well as hydraulic efficiency and P retention efficiency during variable flow regimes. A major challenge is to reduce comparatively low P concentrations in drainage water to below environmental threshold values (<0.05 mg P l-1) under transient flow conditions and at the same time ensure sufficient hydraulic capacity of filters. The retention of other agricultural pollutants as well as the potential for recycling P saturated filters is also investigated. The project further explores the denitrification capacity and potential green house gas emissions in different types of constructed wetlands and filter solutions. Sensitivity analyses using integrated models will provide filter design parameters for optimized filter performance and allow analysis of cost effectiveness of the drainage filter technologies.