How to Constrain Multi‐Objective Calibrations of the SWAT Model Using Water Balance Components

Accurate discharge simulation is one of the most common objectives of hydrological modeling studies. However, a good simulation of discharge is not necessarily the result of a realistic simulation of hydrological processes within the catchment. We propose an evaluation framework that considers both discharge and water balance components as evaluation criteria for calibration of the Soil and Water Assessment Tool (SWAT). In this study, we integrated average annual values of surface runoff, groundwater flow, and evapotranspiration in the model evaluation procedure to constrain the selection of good model runs for the Little River Experimental Watershed in Georgia, United States. For evaluating water balance and discharge dynamics, the Nash‐Sutcliffe efficiency (NSE) and percent bias (PBIAS) were used. In addition, the ratio of root mean square error and standard deviation of measured data (RSR) was calculated for individual segments of the flow duration curve to identify the best model runs in terms of discharge magnitude. Our results indicate that good statistics for discharge do not guarantee realistic simulations of individual water balance components. Therefore, we recommend constraining the ranges of water balance components to achieve a more realistic simulation of the entire hydrological system, even if tradeoffs between good statistics for discharge simulations and reasonable amounts of the water balance components are unavoidable. Editor's note : This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.     

Monitoring plastic ingestion by the northern fulmar Fulmarus glacialis in the North Sea

The abundance of plastics in stomachs of northern fulmars from the North Sea is used in the OSPAR Ecological Quality Objective (EcoQO) for marine litter. The preliminary EcoQO defines acceptable ecological quality as the situation where no more than 10% of fulmars exceed a critical level of 0.1 g of plastic in the stomach. During 2003-2007, 95% of 1295 fulmars sampled in the North Sea had plastic in the stomach (on average 35 pieces weighing 0.31 g) and the critical level of 0.1 g of plastic was exceeded by 58% of birds, with regional variations ranging from 48 to 78%. Long term data for the Netherlands since the 1980s show a decrease of industrial, but an increase of user plastics, with shipping and fisheries as the main sources. The EcoQO is now also used as an indicator for Good Environmental Status in the European Marine Strategy Framework Directive.     

Schwermetalle und organische Umweltchemikalien in Rehwild (Capreolus capreolus L.) aus Forst- und Agrarstandorten

The roe deer indicates the contamination of ecosystems with environmental chemicals. The influence of land use on the contamination of five different forest and agricultural ecosystems in Rheinland Pfalz was proven. The cadmium and lead content was measured in renal tissue of the roe deer. The organic chemicals PCB, α-HCH, Lindan, DDT, and DDE were investigated in kidneys and liver and correlated to adipose tissue. The following results have been obtained: Lead: The Pb-contamination was generally low in all ecosystems investigated. Cadmium: The Cd-values showed an area-dependend contamination of the organs. The data of the test organs from the forest sites and the semi-agricultural area were 2–4 times higher than the ZEBS-limit. The contamination of the animals corresponded to the wet deposition of Cd in the regions. σPCB: The PCB-results indicated a relativly high contamination of the ecosystems. The PCB-ZEBS-limit for the interior organs was surpassed in all areas.α-HCH, γ-HCH (Lindan): The uniformly low values of the HCH-group indicated that these compounds were probably not of ecotoxicological significance in the agricultural and forest regions.DDT, DDE: The results obtained showed a low background contamination in all ecosystems investigated. Areas with former high DDT-applications revealed higher values of DDE in the tissues. ZEBS: Central institution for the evaluation of chemicals in the environment (Bundesgesundheitsamt)