| 1. |
- Rozemeijer, Joachim C., et al.
(författare)
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Improving Load Estimates for NO(3) and P in Surface Waters by Characterizing the Concentration Response to Rainfall Events
- 2010
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 44, s. 6305-6312
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Tidskriftsartikel (refereegranskat)abstract
- For the evaluation of action programs to reduce surface water pollution, water authorities invest heavily in water quality monitoring. However, sampling frequencies are generally insufficient to capture the dynamical behavior of solute concentrations For this study, we used on-site equipment that performed semicontinuous (15 min interval) NO(3) and P concentration measurements from June 2007 to July 2008 We recorded the concentration responses to rainfall events with a wide range in antecedent conditions and rainfall durations and intensities. Through sequential linear multiple regression analysis, we successfully related the NO(3) and P event responses to high-frequency records of precipitation, discharge, and groundwater levels We applied the regression models to reconstruct concentration patterns between low-frequency water quality measurements. This new approach significantly improved load estimates from a 20% to a 1% bias for NO(3) and from a 63% to a 5% bias for P. These results demonstrate the value of commonly available precipitation, discharge, and groundwater level data for the interpretation of water quality measurements. Improving load estimates from low-frequency concentration data Just requires a period of high-frequency concentration measurements and a conceptual, statistical, or physical model for relating the rainfall event response of solute concentrations to quantitative hydrological changes.
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| 2. |
- van der Velde, Ype, et al.
(författare)
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Field-Scale Measurements for Separation of Catchment Discharge into Flow Route Contributions
- 2010
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 9:1, s. 25-35
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Tidskriftsartikel (refereegranskat)abstract
- Agricultural pollutants in catchments are transported toward the discharging stream through various flow routes such as tube drain flow, groundwater flow, interflow, and overland flow. Direct measurements of flow route contributions are difficult and often impossible. We developed a field-scale setup that can measure the contribution of the tube drain flow route to the total discharge toward the surface water system. We then embedded these field-scale measurements in a nested measurement setup to asses the value of field-scale measurements for interpretation of catchment-scale discharge and nitrate concentrations using a linear flow route mixing model. In a lowland catchment, we physically separated the tube drain effluent from the discharge of all other flow routes. Upscaling the field-scale flow route discharge contributions to the subcatchment and the catchment scale with a linear flow route mixing model gave a good prediction of the catchment discharge. Catchment-scale nitrate concentrations were simulated well for a heavy rainfall event but poorly for a small rainfall event. The nested measurement setup revealed that the fluxes at a single field site cannot be representative for the entire catchment at all times. However, the distinctly different hydrograph reaction of the individual flow routes on rainfall events at the field site made it possible to interpret the catchment-scale hydrograph and nitrate concentrations. This study showed that physical separation of flow route contributions at the field scale is feasible and essential for understanding catchment-scale discharge generation and solute transport processes.
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