Abstract
Gipuzkoa (Basque Country, North Spain) is an industrial region where investments in sanitation and wastewater treatment have improved water quality and partially recovered river biological communities. However, further technological improvements are unlikely. Our objective was to assess whether in-stream self-purification may contribute to improvement of the trophic state of rivers. We propose an integrative approach to assessing river water quality, which diagnoses problems, identifies likely causes and prescribes solutions. We first analysed the loads of nutrients transported by Gipuzkoa rivers and compared them with the potential nutrient uptake rates (estimated from published empirical regressions). In reaches where both of them were within one order of magnitude, we considered that the self-purification capacity of river channels may influence nutrient concentrations. Then, we selected some river reaches where no other water quality problems beyond nutrient concentrations occurred and ran the expert system STREAMES 1.0 to diagnose the problems and detect their causes. The studied reaches differed in their problems and in their potential solutions. We empirically determined nutrient retention in two streams by means of mass balances and slug nutrient additions. We detected large differences in retention capacity between reaches and siltation as one of the main problems affecting the self-purification capacity of the study streams. Finally, we used STREAMES 1.0 to identify potential solutions to specific river sections. The results obtained so far point towards an important potential of in-stream bioreactive capacity to reduce nutrient loads and to specific restoration activities that may improve the functionality and trophic status of the streams in Gipuzkoa.
Highlights
Rivers are among the ecosystems most threatened by human activities [1,2,3], including dam building [4], alteration of flow regimes [5], water abstraction [6], pollution [7], channel modification [8] and climate change [9]
We propose an integrative approach to assess water quality associated with river networks, which diagnoses problems, identifies the likely causes and prescribes potential solutions for nutrient status
This approach was applied to a remarkable number of river sections (77), which covered a large range of nutrient concentrations reflecting the wide diversity of environmental pressures in the drainage basins of the region [43]
Summary
Rivers are among the ecosystems most threatened by human activities [1,2,3], including dam building [4], alteration of flow regimes [5], water abstraction [6], pollution [7], channel modification [8] and climate change [9]. The most common management approaches focus on the source of nutrients and include measures to reduce nutrient loading, such as improved sewage systems [23], advanced wastewater treatment plants (WWTP) [18] and improving fertilization practices in agricultural fields [24] Despite these efforts, nutrient problems are still common in freshwaters [22] and significant reductions in nutrient inputs often involve expensive technologies, such as tertiary wastewater treatment, with reduced benefits [18]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call