A reconnaissance survey of channel bank particulate phosphorus
concentrations, controls and estimated contributions to riverine loads
across England
Abstract
Channel banks can contribute a significant proportion of fine-grained
(<63 µm) sediment to rivers, thereby also contributing to
riverine total particulate phosphorus loads. Improving water quality
through better agricultural practices alone can be difficult since the
contributions from non-agricultural sources, including channel banks,
can generate a ‘spatial mismatch’ between the efficacy of best
management applied on farms and the likelihood of meeting environmental
objectives. Our study undertook a reconnaissance survey (n=76 sites each
with 3 profiles sampled) to determine the total phosphorus (TP)
concentrations of channel banks across England and to determine if TP
content can be predicted using readily accessible secondary data. TP
concentrations adjacent field topsoils and local soil soil type/texture
and geological parent material were examined as potential predictors of
bank TP. Carbon and nitrogen content were also analysed to explore the
impacts of organic matter content on measured TP concentrations. The
results suggest that channel bank TP concentrations are primarily
controlled by parent material rather than adjacent topsoils, but
significant local variability in concentrations prevents the prediction
of bank TP content using mapped soil type or geology. A median TP
concentration of 873 mg kg -1 was calculated for the
middle section of the sampled channel bank profiles, with a 25
th percentile of 675 mg kg -1, and
75 th percentile of 1159 mg kg -1.
Using these concentrations and, in comparison with previously published
estimates, the estimated number of inland WFD waterbodies in England for
which channel bank erosion contributes >20% of the
riverine total PP load increased from 15 to 25 (corresponding range of
17 to 35 using the 25 th and 75 th
percentiles of measured TP concentrations). Collectively, these 25
waterbodies account for 0.2% of the total inland WFD waterbody area
comprising England.