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.
Temporal variability in groundwater and surface water quality in humid agricultural catchments; driving processes and consequences for regional water quality monitoring
Rozemeijer, J. ; Velde, Y. van der - \ 2014
Fundamental and Applied Limnology 184 (2014)3. - ISSN 1863-9135 - p. 195 - 209.
flow route contributions - land-use - nutrient concentrations - nitrate concentrations - network design - storm events - phosphorus - dynamics - contamination - netherlands
Considering the large temporal variability in surface water quality is essential for adequate water quality policy and management. Neglecting these dynamics may easily lead to decreased effectiveness of measures to improve water quality and to inefficient water quality monitoring. The objective of this paper is to summarise our understanding of temporal variability in surface water and upper groundwater quality and to discuss the consequences and opportunities for regional water quality monitoring. In regional monitoring networks, measurement frequencies are typically too low to capture the short-term temporal variations in solute concentrations. This causes large uncertainty in the assessment of (trends in) average concentrations and contaminant loads. The most important driver for short-term variations in water quality in most catchments is the variability in meteorological conditions, which induces changes in the relative discharge contributions of water from different flow routes and different chemical compositions. Various options exist for dealing with the transient behavior of water quality in regional water quality monitoring. Estimates of average concentrations and loads from low-frequency concentration data can be improved by using the explanatory strength of commonly available measurements of quantitative hydrological data like precipitation, discharge, and groundwater levels. This paper provides examples of the relationship between water quality and explanatory variables in conceptual, statistical, or process-based models. Another strategy for dealing with short-term variability in water quality monitoring is to measure long-term average solute concentrations using passive samplers. Similarly, on-site auto analyzers and ion specific electrodes provide opportunities for continuous water quality measurements.
Diversity and species composition of West African ungulate assemblages: effects of fire, climate and soil
Klop, L.F. ; Prins, H.H.T. - \ 2008
Global Ecology and Biogeography 17 (2008)6. - ISSN 1466-822X - p. 778 - 787.
spatial autocorrelation - geographical ecology - red herrings - nutrient concentrations - postfire regrowth - mineral-nutrition - large herbivores - national-park - savanna - consequences
Aim Anthropogenic fires are a major component of the ecology of rangelands throughout the world. To assess the effects of these fires on the diversity patterns of herbivores, we related gradients in fire occurrence, climate and soil fertility to patterns in alpha and beta diversity of African ungulates. Location West Africa. Methods We used a survey-based approach for ungulates in 37 protected areas in desert, savanna and rain forest habitats throughout West Africa, combined with satellite images of fire occurrence and digital maps of actual evapotranspiration and soil fertility. Alpha diversity was related to the environmental variables using conventional and spatial regression models. We investigated beta diversity using partial Mantel tests and ordination techniques, and by partitioning the variance in assemblage composition into environmental and spatial components. Results The species richness of grazers showed a quadratic relationship with actual evapotranspiration, whereas that of browsers and frugivores showed a linear relationship. However, in the multiple regression models fire occurrence was the only variable that significantly correlated with the species richness of grazers. Soil fertility was weakly related to overall beta diversity and the species richness of browsers, but was non-significant in the multiple regression models. Fire occurrence was the most important variable explaining species composition of the overall species set and of grazers, whereas the assemblage composition of browsers and frugivores was explained mostly by actual evapotranspiration. Main conclusions In contrast to previous studies, our analyses show that moisture and nutrients alone fail to adequately predict the diversity patterns of grazing ungulates. Rather, the species richness and assemblage composition of grazers are largely governed by anthropogenic fires that modify the quality and structure of the grass sward. Diversity patterns of browsers and frugivores are markedly different from grazers and depend mainly on the availability of moisture, which is positively correlated with the availability of foliage and fruits. Our study highlights the importance of incorporating major human-induced disturbances or habitat alterations into analyses of diversity patterns.