Abstract
Diffusive losses of nitrogen and phosphorus from agricultural areas have detrimental effects on freshwater and marine ecosystems. Mitigation measures treating drainage water before it enters streams hold a high potential for reducing nitrogen and phosphorus losses from agricultural areas. To achieve a better understanding of the opportunities and challenges characterising current and new drainage mitigation measures in oceanic and continental climates, we reviewed the nitrate and total phosphorus removal efficiency of: (i) free water surface constructed wetlands, (ii) denitrifying bioreactors, (iii) controlled drainage, (iv) saturated buffer zones and (v) integrated buffer zones. Our data analysis showed that the load of nitrate was substantially reduced by all five drainage mitigation measures, while they mainly acted as sinks of total phosphorus, but occasionally, also as sources. The various factors influencing performance, such as design, runoff characteristics and hydrology, differed in the studies, resulting in large variation in the reported removal efficiencies.
Highlights
The high intensive agricultural production dominating parts of the world, such as Western Europe and North America, is one of the main causes of eutrophicationElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.resulting in water quality problems and ecosystem degradation worldwide (Kronvang et al 2005; Diaz and Rosenberg 2008; Steffen et al 2015)
To obtain a better understanding of the opportunities and challenges of current and new drainage mitigation measures targeting the transport of nutrients from agricultural areas in oceanic and continental climates, we examined nitrate and total P (TP) removal efficiencies at 82 drainage sites established between 1991 and 2018 in eleven countries
Care should be taken when comparing values from different sites, as the absolute removal efficiency depended heavily on the nutrient loading to the system (Fig. S1)
Summary
Engineered ecotechnologies designed to intercept and reduce nitrogen (N) and phosphorus (P) losses from agricultural drainage systems have emerged over the last decades with the aim to improve water quality (Mitsch and Jørgensen 1989). Substantial changes in land use can be expected in the future when addressing energy and food security such as transformation of the society to a bio-economy (Marttila et al 2020; Rakovic et al 2020). Water quality and quantity are key elements in such a transformation, the development and implementation of drainage mitigation provide valuable opportunities for innovation in future bio-economies. Besides reducing nutrient losses to surface water, these measures can be designed to provide multiple ecosystem services, such as water storage and biomass production, as well as recycling of nutrients
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