Hydrological and lateral spatial gradients affect water quality, nutrient, carbon and algae dynamics in a large...

Meandering river corridors are spatially complex, with floodplains and oxbow lakes contributing to a large portion of the river network, especially in low gradient systems. Surface hydrological connectivity drives the abiotic processes within these habitats, but hydrological cycling is changing due to climate change. We collected physiochemical parameters [temperature, conductivity (EC), pH, dissolved oxygen (DO) and total dissolved solids (TDS)], nutrients [total nitrogen (TN), nitrite + nitrate (NO_X), ammonium (NH₄) and orthophosphate (PO₄)], total (TOC) and dissolved (DOC) organic carbon, and chlorophyll measures during an early, and late hydrological stage for three habitats (floodplain, oxbow lake and river channel) at six sites along the lower Savannah River (Georgia, U.S.). We found that the mid hydrological stage (July-August 2022) had lowest levels of EC, pH, TN, NO_X, NH₄, PO₄, TOC and DOC. We also found that floodplains were highly nutrient rich and acidic, oxbow lakes mostly exhibited intermediate nutrient, carbon and algae levels, and rivers channel habitats had the lowest levels for most measures despite lateral connection. However, some measures (TN and PO₄) were idiosyncratic and did not follow a lateral gradient. Although our results were complex and drivers the water quality and nutrient measures were difficult to isolate, our study demonstrates the importance of hydrology as a key driver of water quality and nutrient dynamics and emphasizes the critical role of lateral connectivity for the mobilization, transformation and storage of pollutants.