The water quality of the River Enborne, UK: observations from high-frequency monitoring in a rural, lowland river system

This paper reports the results of a 2-year study of water quality in the River
Enborne, a rural river in lowland England. Concentrations of nitrogen and phosphorus
species and other chemical determinands were monitored both at high-frequency (hourly),
using automated in situ instrumentation, and by manual weekly sampling and laboratory
analysis. The catchment land use is largely agricultural, with a population density of
123 persons km−2. The river water is largely derived from calcareous groundwater, and
there are high nitrogen and phosphorus concentrations. Agricultural fertiliser is the
dominant source of annual loads of both nitrogen and phosphorus. However, the data show
that sewage effluent discharges have a disproportionate effect on the river nitrogen and
phosphorus dynamics. At least 38% of the catchment population use septic tank systems,
but the effects are hard to quantify as only 6% are officially registered, and the
characteristics of the others are unknown. Only 4% of the phosphorus input and 9% of the
nitrogen input is exported from the catchment by the river, highlighting the importance of
catchment process understanding in predicting nutrient concentrations. High-frequency
monitoring will be a key to developing this vital process understanding.