Organic carbon in the Humber rivers
Authors: Tipping, E., Marker, A.F.H., Butterwick, C., Collet, G.D., Cranwell, P.A., Ingram, J.K.G., Leach, D., Pinder, A.C. and Rigg, E.
Journal: Science of the Total Environment
Dissolved organic carbon (DOC), particulate organic carbon (POC), particulate organic nitrogen (PON), chlorophyll-a, and alkalinity were determined weekly or more frequently in samples from 11 rivers in the Humber catchment, between September 1993 and February 1995. [DOC] varied overall from 1 to 15 mg l−1, [POC] from 0.2 to 67 mg l−1, [LOC] from 0.01 to 7.6 mg l−1 and [DIC] from 1 to 52 mg l−1. For the rivers with predominantly rural catchments, the complex dependence of [DOC] on season and discharge can be interpreted in terms of soil humification and hydrological processes, whereas the inverse dependence of [DOC] on discharge in the more polluted industrial rivers indicates the dominance of point-source effluents. Concentrations of POC depend significantly upon discharge and on concentrations of suspended particulate matter, suggestive of particle mobilisation when physical thresholds are exceeded. During summer months, the ‘living organic carbon’ of algae accounts for much of the POC in all but the most polluted rivers. Fluxes of organic carbon were estimated by combining daily concentrations (measured or interpolated) with discharge data. The contribution of DOC to the annual flux of organic carbon in the different rivers varies from 51 to 80%, the overall contribution being 63%. For both DOC and POC, the main transport to the estuary takes place during the autumn-winter period. For the study rivers, the total flux of organic carbon during the period September 1993 to September 1994 was 73 × 109 g a−1. However, these rivers represent only about two-thirds of the total catchment area of the Humber estuary, and so the true total flux is probably closer to 100 × 109 g a−1.
Preferred by: Adrian Pinder