Dissolved oxygen dynamics of streams draining an urbanized and an agricultural catchment

The extreme value method (EVM), based on the maximum and minimum dissolved oxygen (DO) deficits, was derived to estimate metabolism rates (photosynthesis and respiration) in streams. The proposed method was applied to DO concentrations that were measured in two creeks located in urbanized and agricultural watersheds, respectively. The results obtained by the EVM agree with the delta method used for the estimation of metabolism rates in streams. Diurnal DO variations were explained using a DO mass balance equation with the estimated daily metabolism rates. A comparison between the metabolism rates obtained in two creeks indicates that the creek located in a non-urban watershed has higher metabolism rates than the creek located in an urban watershed. The non-urban creek was periodically autotrophic, and the urban creek was heterotrophic during the measurement period. Simulations conducted by using 1-day metabolism rates and augmenting the basic DO mass balance equation with the dimensionless relationships between the metabolism rate and discharge in creeks followed actual diurnal DO concentrations measured in the streams.