Fine sediment sources, sedimentation risk and siltation of salmonid spawning gravels in the Herefordshire Lugg, UK

Abstract

This paper presents initial results of a three-year fine sediment research monitoring programme funded through the SITA Trust’s ‘Enriching Nature’ programme, the Environment Agency and Arup. This research has been evaluating a catchment-wide, monitoring approach to establish spatial and temporal patterns, and sources of fine sediment in the Herefordshire Lugg catchment, UK. The project aims to provide the underpinning science for the implementation of DEFRA’s Catchment Sensitive Farming initiative, promoting fine sediment management in the Lugg catchment. Delivery of suspended sediments to five sink sites was monitored between April 2009 and April 2012, using time-integrated samplers. Additional flood deposits were also sampled following the larger events. Gravel quality of the bed substrate was also established at each of the sites using freeze core sampling. Geochemical analysis, using ICP-IES, was conducted on all the sink samples (130+) and on 270+ potential source samples taken from tributaries upstream of the sink sites. A two-stage statistical procedure involving a Kruskal-Wallis H test, and Discriminant Function Analysis was undertaken to identify the optimum geochemical fingerprint. This fingerprint was then used to identify sediment sources using a multivariate mixing model. Initial findings are presented for temporal variations in sources for the River Arrow catchment, a key tributary. The approach appears successful at identifying problem sub-catchments (e.g. Honeylake Brook and Curl Brook). Further analysis will investigate fine sediment sources within these problem sub-catchments.