LAUSR

Concentrations determined using Diffusive Gradients in Thin-Films (DGT) have been used to derive time-averaged loads in streams and rivers. DGT, however, provide time-weighted average concentrations that assume the independence of concentration and flow. Additionally, dynamic and coordinated changes in temperature, flow, and concentration, are potential sources of bias in concentration and load calculations. We modelled scenarios in which temperature and flow were correlated to varying degrees with concentration, and evaluated the consequences for DGT concentration and load calculations. As the correlation between solution flow and concentration moved towards 1 and -1, the load determined by DGT either over or underestimated the actual load by as much as 30%. In DGT-based load estimates, the degree of potential bias should be assessed, and the concentration-flow relation characterised. As the correlation of analyte concentration and temperature approached 1 and -1, the deviation of the concentration determined by DGT (CDGT ) from the actual concentration increased. In most cases, this bias was less than 2%, however, if the changes in concentration and temperature were large (∼10 mg L-1 and ∼10°C) the bias exceeded 5%. Concentration and temperature are unlikely to be perfectly or strongly correlated or anti-correlated in natural systems and thus should not affect the accuracy of DGT concentration calculations in most circumstances. The more uncorrelated solution temperature, flow and concentration, the closer DGT derived concentration and load were to the actual solution concentration and load. This article is protected by copyright. All rights reserved.