Functional properties of DOM in a stream draining blanket peat

The functional properties of dissolved organic matter (DOM) from Rough Sike, a stream draining blanket peat in the northern Pennines, UK, were investigated using a series of 12 standardised assays. Nine stream samples were collected at different discharges during 2003–2006, and DOM concentrates obtained by low temperature rotary evaporation. Suwannee River Fulvic Acid was used as a quality control standard in the assays. Dissolved organic matter in high-discharge samples was more light-absorbing at 280 and 340 nm and adsorbed more strongly to alumina, than DOM characteristic of low streamflow, but was less fluorescent and hydrophilic, and poorer in proton-dissociating groups. No significant differences were found in light absorption at 254 nm, copper- or benzo(a)pyrene binding, or photochemical fading. Combination of the Rough Sike data with previously-published results for other streams and a lake yields totals of 20–23 values per assay, for a range of DOM types. For the combined data, variability in all the assays is significant (p < 0.001), as judged by comparison with variations in repeat measurements on the quality control standard. Analysis of the combined data shows that DOM hydrophilicity and adsorption are well-predicted by linear relationships with the extinction coefficient at 340 nm (E340), while good quadratic relationships exist between E340 and both buffering capacity and fluorescence.