Soil physicochemical gradient from headwaters to flooded riparian zones in the Falsino River, Eastern Amazonia

This study investigates the edaphic-hydrological gradients of riparian zones in the Falsino River basin, Eastern Amazon. We defined 21 sampling units based on water body order (2nd to 4th) to capture edaphic and hydrological variation. Maximum river level values (MRL) were represented using limnimetric rulers as proxy of flood pulse intensity, and physicochemical analysis was performed on 378 soil samples. The topographic measurements by Global Positioning System (GPS) and Shuttle Radar Topography Mission (SRTM) quantified basin levels and the results were compared. Results reveal a clear spatial pattern, with MRL increasing with tributary order and decreasing elevation. Flood pulse intensity strongly influenced soil texture and acidity, while variables such as organic matter and phosphorus were weakly associated. The inverse relationship between elevation and MRL highlights the topographic control on hydrological dynamics, although elevation alone did not explain most soil variations. Both GPS and SRTM showed strong agreement, validating their use in low-relief Amazonian landscapes. Sample plot delimitation along the basin's longitudinal profile facilitated the evaluation of abiotic attribute relationships. This research provides novel insights into how hydro-topographic interactions shape riparian soil properties, offering a practical framework for hydropedological assessments in remote tropical basins.