Streams interact closely with their drainage areas in a way that anthropogenic-induced shifts in the respective watersheds can dramatically impair their structure and functioning. This study aimed to assess metabolic rates (ecosystem respiration [ER] and gross primary production [GPP]) and soluble reactive phosphorus (SRP) ambient uptake metrics (length [S_w], velocity [V_f], and rate [U]) in two contiguous reaches (~ 500 m each) of a tropical urban stream (< 200 L s^-1) under different typologies of anthropogenic impacts (R1 [natural substrate, preserved riparian vegetation, signs of erosion, and a meandering channel] and R2 [altered substrate, degraded riparian vegetation, erosive features, and wastewater inputs]). SRP uptake metrics and metabolic rates were obtained with tracer addition and whole-stream single-station methods, respectively, in six campaigns in 2022 (one every two months). S_w (65.3 [min.] - 985.1 [max.] [R1] and 779.5 – 2963.4 m [R2]) and V_f (1.9 – 41.6 and 0.8 – 4.7 mm min^-1) were significantly different between reaches (p < 0.05, Wilcoxon test), while U (23.6 – 795.5 and 38.5 – 109.1 µg m^-2 min^-1), ER (0.45 – 10.35 and 5.82 – 14.04 g O₂ m^-2 d^-1), and GPP (0.10 – 0.35 and 0.05 – 0.26 g O₂ m^-2 d^-1) were not (p > 0.05). In conclusion, contiguous reaches can have great variability concerning nutrient uptake despite having similar metabolic rates. Although highly impacted urban reaches may retain some nutrient uptake ability, those better preserved will have more. Such spatial heterogeneity must be considered in further studies and monitoring of urban streams.

Primary Presenter: João Miguel Merces Bega, Universidade de São Paulo - USP (joaobega@usp.br)

Authors:

João Bega, Universidade de São Paulo (USP)  (joaobega@usp.br)

Daniel von Schiller, Universitat de Barcelona (UB)  (d.vonschiller@ub.edu)

Davi Cunha, Universidade de São Paulo (USP)  (davig@sc.usp.br)