Impact of Filters to Reduce Phosphorus Losses: Field Observations and Modelling Tests in Tile-Drained Lowland Catchments

Abstract

In this study, we analyzed Dissolved Reactive Phosphorus (DRP) and Total Phosphorus (TP) concentration dynamics over two years in surface waters of five nested catchments in northeastern Germany. Based on this, we constructed a filter box filled with iron-coated sand for Phosphorus (P) removal at the edge of a tile-drained field. Results of the filter box experiment were used for a model scenario analysis aiming at evaluating the P removal potential at catchment scale. DRP and TP concentrations were generally low but they exceeded occasionally target values. Results of the filter box experiment indicated that 28% of the TP load could be retained but the DRP load reduction was negligible. We assume that DRP could not be reduced due to short residence times and high flow dynamics. Instead, particulate P fractions were probably retained mechanically by the filter material. The scenario analysis revealed that the P removal potential of such filters are highest in areas, in which tile drainage water is the dominant P source. At a larger spatial scale, in which other P (point) sources are likewise important, edge-of-field P filters can only be one part of an integrated catchment strategy involving a variety of measures to reduce P losses.

Examining characteristics and sampling methods of phosphor dynamics in lowland catchments

“…This seasonal pattern, with higher concentrations in summer than in winter, in the Kielstau was also found by Wagner et al ( 2018 ). Other researchers also documented similar seasonal effects in comparable lowland catchments in north Germany (Bauwe et al 2019 ; Bitschofsky and Nausch 2019 ) and elsewhere (Ballantine et al 2008 , May et al 2001 , Schmalz et al 2016 2015, Yates and Johnes 2013 , Zieliński and Jekatierynczuk-Rudczyk 2015 ). These effects are frequently linked at least partially to point sources, which experience more dilution during periods of high flow than during periods of low flow (Abbott et al 2018 ; Bowes et al 2003 ; Yates and Johnes 2013 ).…”

“…Agricultural drainage, in otherwise relatively flat areas, greatly accelerates the movement of sediments and nutrients from these fields to receiving surface waters (Blann et al 2009 ; Brendel et al 2019 ; Skaggs et al 1994 ) and plays a significant role in causing algal blooms and eutrophication problems in major surface water bodies worldwide (Bauwe et al 2019 ; Rabalais and Turner 2019 ; Tiemeyer et al 2009 ). Due to phosphorus being one of the most immobilized macronutrients in soil and its strong binding to soil particles (Arai and Livi 2013 ; Tian et al 2016 ), heavy precipitation events have a major impact on the amount of phosphorus introduced into surface waters (Waller et al 2021 ).…”