Predicting biochemical oxygen demand in European freshwater bodies

Olga Vigiak,Bruna Grizzetti,Angel Udias-Moinelo,Michela Zanni,Chiara Dorati,Fayçal Bouraoui,Alberto Pistocchi

doi:10.1016/j.scitotenv.2019.02.252

Abstract

Biochemical Oxygen Demand (BOD) is an indicator of organic pollution in freshwater bodies correlated to microbiological contamination. High BOD concentrations reduce oxygen availability, degrade aquatic habitats and biodiversity, and impair water use. High BOD loadings to freshwater systems are mainly coming from anthropogenic sources, comprising domestic and livestock waste, industrial emissions, and combined sewer overflows. We developed a conceptual model (GREEN+BOD) to assess mean annual current organic pollution (BOD fluxes) across Europe. The model was informed with the latest available European datasets of domestic and industrial emissions, population and livestock densities. Model parameters were calibrated using 2008–2012 mean annual BOD concentrations measured in 2157 European monitoring stations, and validated with other 1134 stations. The most sensitive model parameters were abatement of BOD by secondary treatment and the BOD decay exponent of travel time. The mean BOD concentrations measured in monitored stations was 2.10 mg O2/L and predicted concentrations were 2.54 mg O2/L; the 90th percentile of monitored BOD concentration was 3.51 mg O2/L while the predicted one was 4.76 mg O2/L. The model could correctly classify reaches for BOD concentrations classes, from high to poor quality, in 69% of cases. High overestimations (incorrect classification by 2 or more classes) were 2% and large underestimations were 5% of cases. Across Europe about 12% of freshwater network was estimated to be failing good quality due to excessive BOD concentrations (>5 mg O2/L). Dominant sources of BOD to freshwaters and seas were point sources and emissions from intensive livestock systems. Comparison with previous assessments confirms a decline of BOD pollution since the introduction of EU legislation regulating water pollution.

Highlights

Biochemical Oxygen Demand (BOD) is the amount of oxygen used by organisms to consume oxidisable organic matter in a given time (EEA, 2015)
This projection partly contrasts with the Europeanwide assessment of Voß et al (2012), which indicated that the Eastern part of Europe and the Black Sea were to be more affected by reduced dilution capacity of rivers and potential degradation of water quality
Within the 1500 simulations, we identified a subset of best parameter sets (‘behavioral’ using the terminology of Beven and Freer, 2001), i.e. parameter sets that would best fit the observations while remaining in an acceptable physical ranges, as those that scored in the upper quartile of Kling-Gupta efficiency (KGE) and R2

Summary

Introduction

Biochemical Oxygen Demand (BOD) is the amount of oxygen used by organisms to consume oxidisable organic matter in a given time (EEA, 2015). Projections of demographic growth coupled with increased demand and consumption of meat and dairy products prompted concerns for worsening of global ‘sanitation crisis’ (Vörösmarty et al, 2010), especially in rivers where discharge flows and dilution capacity are predicted to decrease as a consequence of climate changes. For Europe, the study projected an increase in organic pollution especially in the Southern Countries due to loss of dilution capacity for rivers in water scarce areas. This projection partly contrasts with the Europeanwide assessment of Voß et al (2012), which indicated that the Eastern part of Europe and the Black Sea were to be more affected by reduced dilution capacity of rivers and potential degradation of water quality

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Discussion

Conclusion