Dissolved organic matter (DOM) plays an important role in freshwater biogeochemistry. To investigate the influence of catchment character on the quality and quantity of DOM in freshwaters, forty-five sampling sites draining subcatchments of contrasting soil type, hydrology and land cover within one large upland-dominated and one large lowland-dominated catchment, were sampled over a one-year period. Dominant land cover in each subcatchment included: arable and horticultural, blanket peatland, coniferous woodland, improved-, unimproved-, acid- and calcareous-grasslands. The composition of the C, N, and P pool was determined as a function of the inorganic nutrient species (NO3-, NO2-, NH4+, PO43-) and dissolved organic nutrient (DOC, DON and DOP) concentrations. DOM quality was assessed by calculation of the molar DOC:DON and DOC:DOP ratios and specific ultraviolet absorbance (SUVA254). In catchments with little anthropogenic nutrient inputs, DON and DOP typically comprised >80% of the TDN and TDP concentrations. By contrast, in heavily impacted agricultural catchments DON and DOP typically comprised 5-15% of TDN and 10-25% of TDP concentrations. Significant differences in DOC:DON and DOC:DOP ratios were observed between land cover class with significant correlations observed between both the DOC:DON and DOC:DOP molar ratios and SUVA254 (rs = 0.88 and 0.84, respectively). Analysis also demonstrated a significant correlation between soil C:N ratio and instream DOC:DON/DOP (rs = 0.79 and 0.71 respectively). We infer from this that soil properties, specifically the C:N ratio of the soil organic matter pool, has a significant influence on the composition of DOM in streams draining through these landscapes.
- Biogeochemical cycling
- Nutrient stoichiometry