Hydrological connectivity in small wetlands in tropical dryland areas

Wetlands are complex systems and understanding them through hydrological connectivity is necessary to uncover their interrelation with other environmental systems, such as rivers and streams. This study aims to understand the dynamics of hydrological connectivity in headwater wetlands and their influence on associated fluvial environments in the Araripe Sedimentary Plateau, located in the Brazilian northeast dryland. Fieldwork was conducted in two different areas (six analysed points), and surveys using a UAV were carried out during dry and rainy seasons to compare the hydrological dynamics of the systems across these periods. In the geoprocessing phase, drainage extraction was performed to identify and analyse water flow continuity using buffer zones (0–2 km, 3–5 km, and 5–10 km) from the base of the Araripe Sedimentary Plateau, where the headwater wetlands are located, to downstream points. Additionally, the NDVI was applied to analyse ecohydrological seasonality during the same distinct periods, and accumulated rainfall levels were calculated for each buffer zone to assess the ecohydrological context and its influence on the connectivity between wetlands and watercourses. The results showed that the highest NDVI values were obtained during the rainiest months when rainfall peaked. Among the analysed distances, segments within the 0–2 km range exhibited higher NDVI averages, whereas other segments had lower averages, except for a few instances where this trend was reversed. Another noteworthy finding is the influence of land use on the continuity of water flows between wetlands and fluvial channels. UAV-captured images revealed elements that could hinder connectivity, such as land-use-modified areas, altered river channels, and constructing barriers, such as low-water crossings. These alterations occurred particularly in downstream sections between 3–5 km and 5–10 km. Preliminary conclusions indicate that most analysed areas demonstrated connectivity, especially in the 0–2 km segments during periods of higher rainfall accumulation. In these environments, vegetation, slope, and the surface and subsurface water flow of wetlands favoured water flow continuity. Conversely, some wetlands did not maintain connectivity with other fluvial environments. Initial investigations suggest that this disconnection may have been caused by land use and other human interferences in fluvial channels.

Keywords: NDVI; Araripe Sedimentary Plateau; ecohydrology interactions; hydrological connectivity; wetland in drylands.