Abstract
The contribution of groundwater (GW) to the nitrate loads in surface waters (SW) was exemplarily studied for the river Augraben with a catchment area of 89.9 km2, located in north eastern Germany. The study uses available GW and SW quality data in order to develop a relationship between SW and GW in the Augraben catchment. The calculated ratio of base flow varies from 40% to 80% using various filtering methods of hydrograph separation methods (without taking into account the drainage) in comparison to a calculated GW infiltration of 5% - 7% applying Darcy’s law (upper unconfined aquifer). Drainage was estimated as the difference in base flow obtained through filtering methods of hydrograph separation and the Darcy’s law. Results on the basis of monitoring data and hydrograph separation in quick flow and base flow showed that during winter periods, high concentration in SW has been found parallel to periods of higher GW flow with a strong correlation between SW and GW concentrations. These findings also coincided with the non-vegetation period, i.e. low nitrogen uptake by plants. Overall, nitrate-nitrogen loads at the SW monitoring point (Bei Lindenberg represents the 85% area of the catchment) were 193.5, 97.72, and 122 tons for the year 2010, 2011 and 2012 respectively. Measured GW concentrations in the catchment differ strongly, depending on land use, with elevated concentrations in agricultural areas compared to monitoring points in grass land and in forest areas. In one GW monitoring station, NO3 concentrations exceed the maximum permissible limits (MPL) according to EU water quality standards (MPL = 50 mg/l NO3), up to factor two. High ammonia concentrations at another station may be due to excessive application of manure. The contribution of the different sub-catchments to nitrate load in SW can be ranked in decreasing order in Zone B, D, A and C. Drainage and interflow proved to be a major contributor with 55% - 65% of total load in SW. With the applied method a robust estimation of GW contribution to nitrate loads is feasible using typically available monitoring data of German environmental authorities.
Highlights
Agriculture related pollution has attracted increased attention worldwide over the past 40 years due to its important consequences on water quality [1] [2]
Test catchment analysis found a strong relationship between surface waters (SW) and GW quality
This means that GW improvement will result in improved standards of SW quality
Summary
Agriculture related pollution has attracted increased attention worldwide over the past 40 years due to its important consequences on water quality [1] [2]. Nitrogen inputs in intensive-agricultural catchments have been identified as the major causal factors in the trends of increased nutrient concentrations in surface, ground and coastal waters [3], though inputs from effluents and atmospheric deposition are important. Due to its main input source, ammonia toxicity in aquatic systems is of special concern in regions of high human habitation and deficient wastewater treatment and/or large numbers of farm animals [9]. Nitrogen losses from the upper soil are generally increasing nitrate concentration in GW and its discharge towards the SW system may cause exceedance of SW quality standards as well [10] [11] [12]
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