Optimizing placement of constructed wetlands at landscape scale in order to reduce phosphorus losses

Faruk Djodjic,Pia Geranmayeh,Hampus Markensten

doi:10.1007/s13280-020-01349-1

Faruk Djodjic, Pia Geranmayeh + Show 1 more

Open Access

https://doi.org/10.1007/s13280-020-01349-1

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Abstract

Constructed wetlands (CWs) are one of the main countermeasures to reduce diffuse phosphorus (P) losses, but there is still a lack of systematic guidance accounting for spatially variable effects of hydraulic and P load on P retention. We present a three-step modelling approach for determining suitable placement of CWs in four different size groups (0.1–1.0 ha), based on incoming hydraulic and P load. The modelled hypothetical CW area was only 17% of that previously estimated and area of efficient CWs is even lower. The mean area-specific P retention increased with CW size. However, the spatial variation in retention was large for all size groups and largest (6–155 kg ha−1 year−1) for the smallest CWs due to highly variable incoming P loads, showing the possible benefits of targeted placement of CWs. The presented modelling approach has also flexibility to include and account for possible future changes in land cover and management.

Highlights

Following successful reductions in nutrient loads from point sources such as wastewater treatment plants, agriculture is considered to be the main non-point source of eutrophying nutrients in many parts of the world (Carpenter et al 1998; Sharpley et al 2015)
This study showed that the potential area for Constructed wetlands (CWs) is much lower than estimated previously in a specific catchment
It showed that P retention in CWs will differ based on the incoming P loads, which in turn are the result of land use and soil distribution in the upstream area of each CW

Summary

Introduction

Following successful reductions in nutrient loads from point sources such as wastewater treatment plants, agriculture is considered to be the main non-point source of eutrophying nutrients in many parts of the world (Carpenter et al 1998; Sharpley et al 2015). In Sweden, agriculture is estimated to be the largest anthropogenic source of both nitrogen (N, 23 300 t) and phosphorus (P, 460 t) (Ejhed et al 2016). Construction or restoration of wetlands is an important countermeasure to reduce nutrient delivery to aquatic ecosystems (Fisher and Acreman 2004; O’Geen et al 2010). Since 2010, approximately 4500 hectares of new wetlands have been constructed or restored in Sweden, with on average of more than 500 ha of new wetlands constructed annually, at a cost of approximately 30 million SEK per year (Swedish Environment Protection Agency 2019). As intensification of mitigation efforts to reduce nutrient losses from agriculture is required, further increases in the number and area of wetlands can be expected. The Swedish government will invest * 200 million SEK in the construction/restoration of wetlands in the period 2018–2021

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