CARBON RETENTION CAPACITY IN A TROPICAL STREAM (SÃO CARLOS, SP): COMPARISON BETWEEN RESTORED AND IMPACTED REACHES

Abstract

Urban streams provide several essential ecosystem services, including different direct and indirect water uses. However, these aquatic systems have been subjected to deterioration in their quality, hampering fundamental processes to the ecosystem balance, such as water purification. Still scarce in tropical regions, the study of retention capacity in small streams is relevant for the understanding of the transport of nitrogen, phosphorus and carbon forms throughout the watershed, contributing to revitalization projects of these environments and to the management of water resources in general. Small streams are especially active components in biogeochemical cycles, but there is still a gap in knowledge regarding the role of these environments in tropical zones for processing organic carbon and its retention or export to downstream streams. This research project aims at analyzing the retention of organic carbon in two reaches of the Tijuco Preto stream (São Carlos, SP) characterized by different environmental conditions: a more upstream revitalized reach (close to the spring), and a rectified and degraded reach, more downstream. For modeling and quantifying carbon retention metrics, the TASCC (Tracer Additions for Spiraling Curve Characterization) method will be employed, which is divided into field data collection and subsequent mathematical formulation. In the field, instantaneous addition experiments of dissolved organic carbon (in the form of acetate, readily bioavailable) combined with a conservative tracer (in the form of sodium chloride) will be carried out for both reaches of the studied stream. The variation of the added nutrient concentration over time will inform the mathematical formulation and subsequent modeling of the retention rates (Uamb), distances (Sw-amb), and velocities (Vf-amb) of carbon uptake. We expect our results will help actions for mitigating environmental impacts as well as aid in the implementation or continuity of projects that seek the restoration of impacted streams. Also, our results will contribute to the understanding of the dynamics of nutrient retention and energy flows in lotic tropical systems. This scholarship, if approved, will be part of the project RESTOLINK: Quantification of restoration success in different biomes by integrating biodiversity, multifunctionality and hydromorphological heterogeneity (currently funded by FAPESP, Process 2021/04399-1, and coordinated by Prof. Davi G. F. Cunha).