Efficiency of mitigation measures targeting nutrient losses from agricultural drainage systems: A review

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.

Conceptual Mini-Catchment Typologies for Testing Dominant Controls of Nutrient Dynamics in Three Nordic Countries

“…However, using C-Q typologies to classify catchments based on their export behaviour could still be used as part of a decision support system for the improvement of monitoring design and for spatially targeting of catchment scale mitigation measures. For example, in the spatial targeting of measures, application of transport mitigation measures (e.g., constructed wetlands) may be appropriate for catchment/nutrient combinations showing enrichment export regimes [71], while source mitigation measures may be more useful for catchment/nutrient combinations characterised by dilution export regimes [72]. Further, for enrichment export regimes, a higher frequency of water chemistry sampling may be appropriate compared with constant (medium-frequency) and dilution-type catchment/nutrient combinations [73].…”

Land‐use dominates climate controls on nitrogen and phosphorus export from managed and natural Nordic headwater catchments

“…Hydrological conditions are changing in the Nordic region (Oygarden et al, 2014) and are expected to continue to do so in the future (Arheimer & Lindstrom, 2015; Huttunen et al, 2015). Nutrient‐runoff mitigation measures at the catchment scale (e.g., buffer zones, artificial wetlands) in a changed climate (Carstensen et al, 2020; Haygarth et al, 2012; Laudon et al, 2016) may not be sufficient for adequate protection of water quality.…”

Catchment effects of a future Nordic bioeconomy: From land use to water resources

“…Environmental goals determine the amount of mitigation measures needed, and as we move towards a future with both changed climate and land use, it is likely that a new generation of mitigation measures must be developed. This means that there is a need to improve the targeting, precision, cost-effect and cost-benefits of the measures, while at the same time enhancing multiple functions and reducing negative side effects (Blankenberg and Skarbøvik 2020;Carstensen et al 2020;Djodjic et al 2020;Hashemi and Kronvang 2020). Increased conflicts between mitigation measures and production of biomass are not unlikely in the future bioeconomy and this calls for studies that minimise the land needed for mitigation measures without compromising the ecological needs.…”

“…Skarbøvik et al 2020;Vermaat et al 2020) and informing the development of environmental impacts and mitigation measures (e.g. Carstensen et al 2020;Djodjic et al 2020;Sundnes et al 2020) is a requirement for bioeconomy data gathering in a changing climate.…”

“…The authors concluded that their method may be used for assessing possible effects of a bioeconomy and can be used to model effects of the Nordic Bioeconomy Pathways (cf., element # 1; Rakovic et al 2020). Carstensen et al (2020) also discussed the need to maximise the effects of mitigation measures, but they also stressed the importance of minimising undesirable byproducts. Thus, the management and design of mitigation measures should not solely focus on nutrient reduction, but also take into consideration potential negative by-products such as Green House Gas (GHG) emissions, phosphate releases or reduced biodiversity.…”