Quantifying spatiotemporal rhythm of stream metabolism along human disturbance gradients

This study aimed at investigating the effects of the urban wastewater treatment plant (WTP) discharges on the metabolism of Buyuksu Stream (Bolu, Turkey), and modelling the metabolism components as a function of measured environmental variables. Dissolved oxygen (DO) and water temperatures (Tw ) were measured to estimate montly stream metabolism in the four reaches: Before and after discharges of the WTP, and the headwaters of Abant Creek and Mudurnu Creek feeding Buyuksu Stream. The DO and Tw measurements were performed for 17 months between August 2015 and December 2016. Metabolism components of community respiration (Rc ), gross primary production (GPP) and net ecosystem metabolism (NEM) were estimated by using the two-station method. According to naturality gradient (reach disturbance gradients: before and after discharges, and headwaters of the creeks), mean metabolism components were compared by performing the one-way analysis of variance. The comparison results showed that the WTP discharges increased the average Rc from −30.6 g O2 m−2 day−1 to −130.9 g O2 m−2 day−1 , and had no significant impact on the average GPP, statistically (15.6 and 9.1 g O2 m−2 day−1 before and after discharges, respectively). Validations of the multiple non-linear regression models of NEM and Rc gave coefficients of determination of 74.9% and 66.6%, respectively.