Assessing the Integration of Wetlands along Small European Waterways to Address Diffuse Nitrate Pollution

Natalia Donoso,Denis De Wilde,Sacha Gobeyn,Peter L M Goethals,Erik Meers,Pieter Boets

doi:10.3390/w9060369

Abstract

Nitrate concentrations in numerous European fresh watercourses have decreased due to end-of-pipe measures towards manure and fertilization management, but fail to meet the environmental objectives. The implementation of complementary measures to attenuate diffuse nitrate pollution in densely populated regions characterised by limited available area has been barely studied. To tackle this issue, this study evaluates the feasibility of integrating Constructed Wetlands (CWs) along waterways as a promising tool to facilitate compliance with the nitrate regulations. The aim is to calculate the required area of land alongside a specific watercourse to integrate CWs to reduce nitrate concentrations consistently below the 11.3 and 5.65 mgNO3-N/L levels, according to the Nitrates Directive and the Flemish Environmental Regulations. Nitrate-nitrogen removal efficiencies achieved at case study CWs were compared and validated with reported values to estimate the needed wetland areas. In addition, the removal efficiencies and areas needed to meet the standards were calculated via the kinetic model by Kadlec and Knight. The predicted areas by both methods indicated that CWs of 1.4–3.4 ha could be implemented in certain regions, such as Flanders (Belgium), with restricted available land. To conclude, three designs for ICWs (Integrated Constructed Wetlands) are proposed and evaluated, assessing the feasibility of their implementation.

Highlights

Agricultural activities and livestock production are responsible for increased nutrient levels in surface water [1]
Total nitrogen concentrations measured downstream of the Broenbeek (Figure 1 points 5a and 5b) receiving the discharged effluent from the Constructed Wetlands (CWs) located in Langemark–Poelkapelle and the runoff, were compared to the Flemish Environmental Regulations (VLAREM) environmental standard limit of 6 mgTN/L, whereas the nitrate-nitrogen concentrations reported by the VMM at their measuring station (Figure 1 point 3a) were evaluated with the 5.65 mgNO3 -N/L and 11.3 mgNO3 -N/L legislative limits
The NO3 -N concentrations reported by the VMM showed that seven out of ten measurements, registered in the same period, exceeded the VLAREM environmental standard limit and in one instance, the limit imposed by the Nitrates Directive

Summary

Introduction

Agricultural activities and livestock production are responsible for increased nutrient levels in surface water [1]. Several end-of-pipe measurements have been implemented to mitigate the effects of agriculture on the environment, nutrient concentrations in waterways remain elevated due to non-point (diffuse) sources. Excessive amounts of nitrogen in water lead to oxygen depletion affecting aquatic life and organisms. Nitrogen could be present in surface water in different forms, but total nitrogen (TN), ammonium nitrogen (NH4 -N), organic nitrogen, nitrite (NO2 ), and nitrate (NO3 ) are the main forms that end up in the surface water [2,3]. Several studies have reported that nitrate and nitrite concentrations in rivers greatly differ from each other, with nitrite concentrations being negligible in most cases. Nitrate and ammonium are highly soluble and directly end up in the surface

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Conclusion