Water quality status and trends in agriculture-dominated headwaters; a national monitoring network for assessing the effectiveness of national and European manure legislation in The Netherlands
Rozemeijer, J.C. ; Klein, J. ; Broers, H.P. ; Tol-Leenders, T.P. van; Grift, B. van der - \ 2014
Environmental Monitoring and Assessment 186 (2014)12. - ISSN 0167-6369 - p. 8981 - 8995.
flow route contributions - long-term change - surface-water - nutrient concentrations - temporal variability - groundwater quality - catchment discharge - fresh-water - land-use - phosphorus
Large nutrient losses to groundwater and surface waters are a major drawback of the highly productive agricultural sector in The Netherlands. The resulting high nutrient concentrations in water resources threaten their ecological, industrial, and recreational functions. To mitigate eutrophication problems, legislation on nutrient application in agriculture was enforced in 1986 in The Netherlands. The objective of this study was to evaluate this manure policy by assessing the water quality status and trends in agriculture-dominated headwaters. We used datasets from 5 agricultural test catchments and from 167 existing monitoring locations in agricultural headwaters. Trend analysis for these locations showed a fast reduction of nutrient concentrations after the enforcement of the manure legislation (median slopes of -0.55 mg/l per decade for total nitrogen (N-tot) and -0.020 mg/l per decade for total phosphorus (P-tot)). Still, up to 76 % of the selected locations currently do not comply with either the environmental quality standards (EQSs) for nitrogen (N-tot) or phosphorus (P-tot). This indicates that further improvement of agricultural water quality is needed. We observed that weather-related variations in nutrient concentrations strongly influence the compliance testing results, both for individual locations and for the aggregated results at the national scale. Another important finding is that testing compliance for nutrients based on summer average concentrations may underestimate the agricultural impact on ecosystem health. The focus on summer concentrations does not account for the environmental impact of high winter loads from agricultural headwaters towards downstream water bodies.
Iron oxidation kinetics and phosphate immobilization along the flow-path from groundwater into surface water
Grift, B. van der; Rozemeijer, J.C. ; Griffioen, J. ; Velde, Y. van der - \ 2014
Hydrology and Earth System Sciences 18 (2014)11. - ISSN 1027-5606 - p. 4687 - 4702.
suspended sediment - ferrous iron - fresh-water - phosphorus limitation - nutrient dynamics - fe(ii) oxidation - arsenic removal - natural-waters - riparian zone - river
The retention of phosphorus in surface waters through co-precipitation of phosphate with Fe-oxyhydroxides during exfiltration of anaerobic Fe(II) rich groundwater is not well understood. We developed an experimental field set-up to study Fe(II) oxidation and P immobilization along the flow-path from groundwater into surface water in an agricultural experimental catchment of a small lowland river. We physically separated tube drain effluent from groundwater discharge before it entered a ditch in an agricultural field. Through continuous discharge measurements and weekly water quality sampling of groundwater, tube drain water, exfiltrated groundwater, and surface water, we investigated Fe(II) oxidation kinetics and P immobilization processes. The oxidation rate inferred from our field measurements closely agreed with the general rate law for abiotic oxidation of Fe(II) by O-2. Seasonal changes in climatic conditions affected the Fe(II) oxidation process. Lower pH and lower temperatures in winter (compared to summer) resulted in low Fe oxidation rates. After exfiltration to the surface water, it took a couple of days to more than a week before complete oxidation of Fe(II) is reached. In summer time, Fe oxidation rates were much higher. The Fe concentrations in the exfiltrated groundwater were low, indicating that dissolved Fe(II) is completely oxidized prior to inflow into a ditch. While the Fe oxidation rates reduce drastically from summer to winter, P concentrations remained high in the groundwater and an order of magnitude lower in the surface water throughout the year. This study shows very fast immobilization of dissolved P during the initial stage of the Fe(II) oxidation process which results in P-depleted water before Fe(II) is completely depleted. This cannot be explained by surface complexation of phosphate to freshly formed Fe-oxyhydroxides but indicates the formation of Fe(III)-phosphate precipitates. The formation of Fe(III)-phosphates at redox gradients seems an important geochemical mechanism in the transformation of dissolved phosphate to structural phosphate and, therefore, a major control on the P retention in natural waters that drain anaerobic aquifers.
Improving catchment discharge predictions by inferring flow route contributions from a nested-scale monitoring and model setup
Velde, Y. van der; Rozemeijer, J.C. ; Rooij, G.H. de; Geer, F.C. van; Torfs, P.J.J.F. ; Louw, P.G.B. de - \ 2011
Hydrology and Earth System Sciences 15 (2011)3. - ISSN 1027-5606 - p. 913 - 930.
mesoscale catchment - hillslope scale - watershed scale - soil - groundwater - complex - quality - losses - paths - sum
Identifying effective measures to reduce nutrient loads of headwaters in lowland catchments requires a thorough understanding of flow routes of water and nutrients. In this paper we assess the value of nested-scale discharge and groundwater level measurements for the estimation of flow route volumes and for predictions of catchment discharge. In order to relate field-site measurements to the catchment-scale an upscaling approach is introduced that assumes that scale differences in flow route fluxes originate from differences in the relationship between groundwater storage and the spatial structure of the groundwater table. This relationship is characterized by the Groundwater Depth Distribution (GDD) curve that relates spatial variation in groundwater depths to the average groundwater depth. The GDD-curve was measured for a single field site (0.009 km(2)) and simple process descriptions were applied to relate groundwater levels to flow route discharges. This parsimonious model could accurately describe observed storage, tube drain discharge, overland flow and groundwater flow simultaneously with Nash-Sutcliff coefficients exceeding 0.8. A probabilistic Monte Carlo approach was applied to upscale field-site measurements to catchment scales by inferring scale-specific GDD-curves from the hydrographs of two nested catchments (0.4 and 6.5 km(2)). The estimated contribution of tube drain effluent (a dominant source for nitrates) decreased with increasing scale from 76-79% at the field-site to 34-61% and 25-50% for both catchment scales. These results were validated by demonstrating that a model conditioned on nested-scale measurements improves simulations of nitrate loads and predictions of extreme discharges during validation periods compared to a model that was conditioned on catchment discharge only.
Direct measurements of the tile drain and groundwater flow route contributions to surface water contamination: from field-scale concentration patterns in groundwater to catchment-scale surface water quality
Rozemeijer, J.C. ; Velde, Y. van der; Geer, F.C. van; Broers, H.P. ; Bierkens, M.F.P. - \ 2010
Environmental Pollution 158 (2010)12. - ISSN 0269-7491 - p. 3571 - 3579.
nitrate concentrations - hydrological pathways - agricultural soils - transport - phosphorus
Enhanced knowledge of water and solute pathways in catchments would improve the understanding of dynamics in water quality and would support the selection of appropriate water pollution mitigation options. For this study, we physically separated tile drain effluent and groundwater discharge from an agricultural field before it entered a 43.5-m ditch transect. Through continuous discharge measurements and weekly water quality sampling, we directly quantified the flow route contributions to surface water discharge and solute loading. Our multi-scale experimental approach allowed us to relate these measurements to field-scale NO3 concentration patterns in shallow groundwater and to continuous NO3 records at the catchment outlet. Our results show that the tile drains contributed 90–92% of the annual NO3 and heavy metal loads. Considering their crucial role in water and solute transport, enhanced monitoring and modeling of tile drainage are important for adequate water quality management
Application and evaluation of a new passive sampler for measuring average solute concentrations in a catchment-scale water quality monitoring study
Rozemeijer, J.C. ; Velde, Y. van der; Jonge, H. de; Geer, F.C. van; Broers, H.P. ; Bierkens, M.F.P. - \ 2010
Environmental Science and Technology 44 (2010)4. - ISSN 0013-936X - p. 1353 - 1359.
aromatic-hydrocarbons pahs - membrane devices spmds - groundwater - loads - contaminants - pollutants
We present a field based testing, optimization, and evaluation study of the SorbiCell sampler (SC-sampler); a new passive sampling technique that measures average concentrations over longer periods of time (days to months) for various substances. We tested the SC-sampler within a catchment-scale monitoring study of NO(3) and P concentrations in surface water and tile drain effluent. Based on our field experiences, we optimized the flow velocity control and the sample volume capacity of the SC-samplers. The SC-samplers were capable of reproducing the NO(3) concentration levels and the seasonal patterns that were observed with weekly conventional grab sampling and continuous water quality measurements. Furthermore, we demonstrated that average measurements produce more consistent load estimates than "snapshot" concentrations from grab sampling. Therefore, when the purpose of a monitoring program is to estimate reliable (trends in) average concentrations or loads, the SC-samplers are a cost-effective alternative for grab sampling
Improving load estimates for NO3 and P in surface waters by characterizing the concentration response to rainfall events
Rozemeijer, J.C. ; Velde, Y. van der; Geer, F.C. van; Rooij, G.H. de; Torfs, P.J.J.F. ; Broers, H.P. - \ 2010
Environmental Science and Technology 44 (2010)16. - ISSN 0013-936X - p. 6305 - 6312.
field-scale - land-use - phosphorus - catchments - dynamics - management - separation - frequency - transport - nutrient
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) NO3 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 NO3 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 NO3 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
The nitrate response of a lowland catchment: on the relation between stream concentration and travel time distribution dynamics
Velde, Y. van der; Rooij, G.H. de; Rozemeijer, J.C. ; Geer, F.C. van; Broers, H.P. - \ 2010
Water Resources Research 46 (2010). - ISSN 0043-1397 - 17 p.
nitrogen mineralization - grassland soils - organic-matter - groundwater - transport - scale - model - texture - uncertainty - netherlands
Nitrate pollution of surface waters is widespread in lowland catchments with intensive agriculture. For identification of effective nitrate concentration reducing measures the nitrate fluxes within catchments need to be quantified. In this paper we applied a mass transfer function approach to simulate catchment-scale nitrate transport. This approach was extended with time-varying travel time distributions and removal of nitrate along flow paths by denitrification to be applicable for lowland catchments. Numerical particle tracking simulations revealed that transient travel time distributions are highly irregular and rapidly changing, reflecting the dynamics of rainfall and evapotranspiration. The solute transport model was able to describe 26 years of frequently measured chloride and nitrate concentrations in the Hupsel Brook catchment (6.6 km2 lowland catchment in the Netherlands) with an R2 value of 0.86. Most of the seasonal and daily variations in concentrations could be attributed to temporal changes of the travel time distributions. A full sensitivity analysis revealed that measurements other than just surface water nitrate and chloride concentrations are needed to constrain the uncertainty in denitrification, plant uptake, and mineralization of organic matter. Despite this large uncertainty, our results revealed that denitrification removes more nitrate from the Hupsel Brook catchment than stream discharge. This study demonstrates that a catchment-scale lumped approach to model chloride and nitrate transport processes suffices to accurately capture the dynamics of catchment-scale surface water concentration as long as the model includes detailed transient travel time distributions