title: Causes of low oxygen in a lowland, regulated eutrophic river in Eastern England.
abstract: In the River Brett, Eastern England, over the period 1955-1998 there was a significant long-term decline in dissolved oxygen (DO), as well as increases in TON (total oxidised nitrogen) and SRP (soluble reactive phosphorus). Flow decreased from 1963 to 1998. Field studies in 1998-2000 showed increased pH and a gradient of DO beneath the filamentous alga Cladophora glomerata. DO decreased through the summer. Macrophytes accounted for 45% of community respiration at the study site, while sediment accounted for 36%. In container studies, muddy sediments had the highest maximum sediment oxygen demand (SOD), but canopies of C. glomerata and Lemna minor together increased the SOD by up to 90% over control samples. During periods of high temperature, abundant growths of C. glomerata and/or L. minor would increase the SOD of organic mud in river areas with shallow, ponded water, eventually leading to anoxic conditions and the release of nutrients from the sediment. If a river had large areas of mud, these processes could dramatically affect the river's oxygen budget, and hence its ecology.
authors.affiliation: Department of Biological Sciences, University of Essex, Wivenhoe Park, Essex, Colchester CO4 3SQ, UK.
authors.forename: Lynn B
authors.initials: LB
authors.lastname: Parr
authors.forename: Christopher F
authors.initials: CF
authors.lastname: Mason
mesh_terms: D029064:Araceae / Q000502:physiology; D002734:Chlorophyll / Q000032:analysis; D000077194:Chlorophyll A; D000460:Chlorophyta / Q000502:physiology; D004739:England; D004784:Environmental Monitoring; D005068:Eutrophication; D019015:Geologic Sediments / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009584:Nitrogen / Q000032:analysis; D010100:Oxygen / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis; D045483:Rivers / Q000737:chemistry*; D013696:Temperature
chemical_list: D002734:Chlorophyll; D010758:Phosphorus; D009584:Nitrogen; D010100:Oxygen; D000077194:Chlorophyll A