Temporal variability in groundwater and surface water quality in humid agricultural catchments; driving processes and consequences for regional water quality monitoring

Abstract

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.