Abstract
Phosphorus (P) impairment of surface waters still represents a major concern worldwide, despite decades of awareness and implementation of remedial measures. In view of this situation, it is all the more necessary to provide decision makers with reliable modelling tools, which can correctly estimate the effect of alternative management strategies. This work tests the performance of the semi-empirical model MONERIS (Modelling of Nutrient Emissions in River Systems) in depicting and quantifying trends of instream total phosphorus (TP) concentration in three catchments located in Upper Austria, a region affected by high agricultural nutrients emissions. The model correctly depicts both the existence of increasing trends (4–µ g TP L − 1 year − 1 ) and the lack thereof (<0.1 µ g TP L − 1 year − 1 ) in different sub-catchments within the period 2001–2014, although it systematically underestimates the trends magnitude. Furthermore, MONERIS together with an optimized data management system has allowed identifying the probable cause of such trends. The results suggest that, despite considerable improvements achieved through enhanced P removal from wastewater and through the implementation of an agri-environmental programme, changes in land use and in cultivated crop types have led to an offsetting increase of erosion-driven emissions. This methodology offers high potential to predict the effect of different management scenarios, but further model fine-tuning concerning erosion and retention processes is required to improve the model accuracy.
Highlights
After decades of awareness of the crucial role played by phosphorus (P) emissions in triggering eutrophication, and despite the implementation of diverse remedial strategies, P impairment of surface waters still represents a worldwide concern [1,2,3,4]
Austrian municipal wastewater treatment plants (WWTPs) gradually enhanced their P removal rate from less than 50% at the end of the 1980s to 82% in 2001 [37,38]. This explanation is supported by the similar results obtained for soluble reactive phosphorus (SRP) concentrations (32 out of 63 stations show significant trends, out of which 28 were declining; Figure 2a), given that SRP, as the typically prevalent phosphorus species in WWTP effluents, is a good indicator for point emissions [39]
The performance of the MONERIS model for the assessment of changes of phosphorus concentrations in surface waters driven by environmental measures was tested on selected Austrian catchments and sub-catchments
Summary
After decades of awareness of the crucial role played by phosphorus (P) emissions in triggering eutrophication, and despite the implementation of diverse remedial strategies, P impairment of surface waters still represents a worldwide concern [1,2,3,4]. Europe has made substantial progress, but a considerable number of water bodies still fail to meet the levels of P concentrations required to achieve the good ecological status defined by the Water Framework Directive (WFD) [5,6,7] This can be primarily attributed to legacy P inputs, to inadequate soil conservation and nutrients management strategies in agriculture and partially to climate fluctuations [8]. In this context, reliable modelling tools are necessary to identify and quantify the sources and pathways of phosphorus emissions into surface waters and to support policy makers in the design of management strategies and in the assessment of their performance. In light of MONERIS’s role as a policy-support tool, it is imperative that its performance in predicting the effect of distinct management strategies and the reliability of its scenarios are thoroughly investigated at different scales, in different river systems and under different contexts of data availability
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