| Summary: | Dissolved organic matter (DOM) is a significant component of carbon (C), nitrogen (N) and phosphorus (P) flux from source to sea. This thesis presents the results of an investigation into the seasonal and spatial variability of DOM character, and flux of DOM relative to inorganic N and P, in two contrasting lowland UK catchments: the chalk-dominated River Wylye and peat-dominated Millersford Brook. Each catchment was sampled weekly at a total of 14 sampling locations, with daily sampling at three sites in each catchment. Dissolved organic carbon (DOC), all N species, P fractions, and both chromophoric and fluorescent dissolved organic matter were measured over a two year period (2010-2012). Contributing nutrient source areas varied between catchments. In the Wylye catchment nutrient fluxes were strongly influenced by groundwater and diffuse agricultural inputs. Point source discharges from sewage treatment facilities contributed significantly to instream loading in the lower reaches with inorganic fractions dominating the nutrient chemistry across the catchment. Chromophoric dissolved organic matter (CDOM) measurements related to aromaticity and molecular weight were low across the Wylye catchment, but significantly elevated during periods of high flow indicating the flushing of material with a greater aromatic content from the surrounding catchment. In contrast, Nand P data from Millersford Brook was dominated by organic Nand P respectively with DOC significantly elevated compared to the Wylye catchment. As a result of catchment geology and varying nutrient source areas CDOM measurements suggested both waters to differ significantly in their DOM aromatic content. No obvious temporal variation instream was observed during the monitoring period however, data from storm event sampling found high flow events responsible for the delivery of material with a low aromatic content when compared to CDOM under baseflow conditions. Results presented here give further insight into the compositional variations in the bulk chemistry within and between two contrasting lowland catchments, suggesting significant differences in DOM composition across study areas
|
|---|
