Assessing macroinvertebrate diversity and temporal changes in groundwater-dependent pan wetland at Khakhea–Bray transboundary aquifer.

Abstract

Wetlands are productive ecosystems that provide important ecological, hydrological, andsocio–economic services. However, they are also one of the ecosystems that are most at risk around the world, especially in semi–arid areas. In southern Africa, pan wetlands primarily rely on groundwater and are becoming more susceptible to changes in land use, groundwater extraction, and climate variability. This research examined the impact of environmental gradients, elevation, and spatial positioning on physicochemical conditions and the macroinvertebrate community structure in pan wetlands located within the Khakhea–Bray Transboundary Aquifer (KBTA), a semi–arid aquifer jointly managed by South Africa and Botswana. A total of 221 pan wetlands were sampled, which were divided into four elevation groups: <1100 m, 1100–1149 m, 1150–1199 m, and >1200 m. We used standard field and lab methods to measure the physicochemical properties of water, the concentrations of nutrients, and the types of macroinvertebrates. To find out how community composition changed across elevation classes, we used multivariate statistical tests such as permutational analysis of variance (PERMANOVA), analysis of similarities (ANOSIM), similarity percentages (SIMPER), and non–metric multidimensional scaling (nMDS). Correlation analyses and boosted regression tree (BRT) models were used to invesatigate the relationships between environmental variables, spatial gradients, and macroinvertebrate communities. Spatial analyses demonstrated that longitude served as the most significant predictor of macroinvertebrate richness and diversity, accounting for the majority of the variation in taxa richness based on the boosted regression trees model. Diversity increased along a longitudinal gradient, suggesting that landscape–scale processes have a more significant impact on community assembly than local water chemistry or short–range elevation variations. Longitudinal gradients show differences in how well groundwater connects, how the basin is shaped, the weather, and the effects of all the land use on the aquifer system. These factors together determine how long water stays, the availabity of nutrients and how different habitats are, which has a big effect on biodiversity patterns. Local physicochemical variables only had a small effect on diversity patterns. This suggests that the water quality conditions were generally acceptable for the regional species pool. ii The ecological patterns identified have significant implications for the conservation and management of groundwater–dependent pan wetlands within the Khakhea–Bray Transboundary Aquifer region. Mid–elevation pans are biodiversity hotspots because they have the most macroinvertebrates and the most diverse communities. They are also very sensitive to changes in hydroperiod, nutrient inputs, and groundwater abstraction. Low– and high–elevation pans also add to regional beta diversity by providing habitats for specialised taxa that can live in very extreme or very stable conditions. The Khakhea–Bray Transboundary Aquifer pan systems are a major water source for the people living in these areas. More studies evaluating ecosystem integrity, functionality, and service dynamics are necessary to comprehend the importance of these systems to landscape and human community dynamics.