The Biological Condition of Cox’s Creek and Cox’s Rivulet: November 2006. Report to Dorset Council

The condition of Cox’s Creek and Cox’s Rivulet downstream of the Scottsdale WWTP discharge was assessed by Davies and Cook (2002, 2004) conducting a biological survey of aquatic macroinvertebrates in early November in both 2002 and 2004. That survey was designed to provide an updated picture of the condition of the receiving streams for the Scottsdale WWTP discharges in comparison with its previous condition and state-wide standards derived from a large database of minimally polluted reference sites. Four other local reference stream sites were also sampled for comparison, in Hurst Creek and Tuckers Rivulet. The survey conducted in 2002 indicated that the upper reaches of Cox’s Creek and Rivulet downstream of the WWTP discharge were in very poor condition, with severely depleted macroinvertebrate assemblages dominated by forms tolerant of organic pollution (e.g. worms, chironomid midges). There was a gradual recovery in macroinvertebrate diversity and abundance downstream of the WWTP discharge point. However the influence of the WWTP was evident even in the lower reaches so Coxs Rivulet. The survey was repeated in November 2004, following substantial change to the nature of the Scottsdale WWTP discharge after the closure of the Simplot factory, whose wastewater was discharged via the WWTP. Fish populations were sampled at several sites for the first time. The survey found significant improvement in the diversity and community composition of macroinvertebrates had occurred since 2002, as well as a reduction in the extent of stream affected by the WWTP discharge. This document describes the result of a repeat of the survey for macroinvertebrates and fish, conducted at the same sites and with the same techniques, in November 2006