The spatiotemporal distribution and potential for export of the organic and inorganic fractions of the major dissolved nutrients, carbon, nitrogen and phosphorous, in the catchment of the river Conwy, North Wales, were observed for two full years from May 2001 to May 2004. Distinct and seasonally consistent peaks were documented for dissolved organic carbon and chromophoric dissolved organic matter. Specific and consistent point sources were established for dissolved organic carbon and nitrogen, chromophoric dissolved organic matter, nitrate, and silicate. These sources were shown to be attributable to a combination of land use, geography, and geology.
A strong, functional, catchment scale relationship between dissolved organic carbon, and chromophoric dissolved organic matter was established. This correspondence was found to have no consistent seasonal component.
Through examination of the estuarine cycling of the major nutrients, evidence is
presented for the net seaward flux of inorganic forns of the major nutrients,
chromophoric dissolved organic matter was the only organic solute found to behave consistently conservatively within the estuary. The seasonality of estuarine cycling was not established.
Experimental irradiation of waters from several sites along a gradient of organic content, revealed a higher lability for optical remineralisation of chromophoric dissolved organic matter, relative to dissolved organic carbon. Also a gradient of increasing lability was observed with greater distance from the source. In every instance quartz incubations resulted in greater change than either exposure in glass, or purely biological dark incubations.