Comparing nutrient reference concentrations in Nordic countries with focus on lowland rivers
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ENVIRONMENTAL EFFECTS OF A GREEN BIO-ECONOMY
Comparing nutrient reference concentrations in Nordic countries with focus on lowland rivers Eva Skarbøvik , Jukka Aroviita, Jens Fo¨lster, Anne Lyche Solheim, Katarina Kyllmar, Katri Rankinen, Brian Kronvang
Received: 15 December 2019 / Revised: 14 May 2020 / Accepted: 14 July 2020 / Published online: 15 September 2020
Abstract Reference conditions of water bodies are defined as the natural or minimal anthropogenically disturbed state. We compared the methods for determining total phosphorus and total nitrogen reference concentrations in rivers in Finland, Norway and Sweden as well as the established reference conditions and evaluated the possibility for transfer and harmonisation of methods. We found that both methods and values differed, especially for lowland rivers with a high proportion of agriculture in the catchment. Since Denmark has not yet set reference conditions for rivers, two of the Nordic methods were tested for Danish conditions. We conclude that some of the established methods are promising but that further development is required. We moreover argue that harmonisation of reference conditions is needed to obtain common benchmarks for assessing the impacts of current and future land use changes on water quality. Keywords Nordic Nutrients Reference conditions Rivers EU Water Framework Directive
INTRODUCTION Reference conditions (RC) represent a baseline for assessing the current ecological status of water bodies and can be quantified by, for instance, biological indicators and nutrient concentrations. The EU Water Framework Directive (WFD; EC 2000) defines RC as ‘‘no, or only very minor, anthropogenic alterations (…) for the surface water body types from those normally associated with that type Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13280-020-01370-4) contains supplementary material, which is available to authorised users.
under undisturbed conditions’’. This definition leaves space for interpretation, especially in terms of the ‘‘very minor’’ deviation from undisturbed conditions (CIS Guidance 2003a). Stoddard et al. (2006) advocated that RCs in rivers should reflect minimally disturbed conditions or ‘the condition of streams in the absence of significant human disturbance’, but in lowland rivers such conditions are rarely found. In consequence, several methods have been advocated for establishing nutrient RCs (CIS Guidance 2003a; Stoddard et al. 2006; Poikane et al. 2019). In the presence of pristine water bodies, the preferred method to determine nutrient RCs is use of monitoring data on nutrients and nutrient-sensitive biological indicators. In the absence of pristine water bodies, a variety of other methods can be used, including models, data and information derived from historical records, expert judgement or a combination of these. Determination of RCs is important since the RC concept serves different purposes (Stoddard et al. 2006; Carvalho et al. 2019; Fig. 1). Hawkins et al. (201
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