Land use and land cover changes along the Boteti-Thamalakane River system in Ngamiland District, Botswana

Analysis of the dynamics of land use and land cover change (LULCC) along rivers that supply water to settlements provides crucial information to decision-makers; it offers information for planners and water supply authorities on water management issues in general. The paper analyzed LULCC along Boteti and Thamalakane rivers and predicted the probable LULCC for the year 2050 using the artificial neural network (ANN) of the module for land use evaluation (MOLUCE) within the QGIS 2.9 software. Adopting a supervised classification method, the Maximum Likelihood Classification (MLC) algorithm was used to classify the study area into five LULC categories. Findings show an increase in a built-up area (46.5%), barren land (90.1%) and a decrease in shrubs/trees (67.4%), water/waterlogged area (48%) and hydrophytes (39.3%) between 1990 and 2020. Using 2020 as the baseline, the ANN modelling approach predicted an increase in the built-up area and a continued shrinking of water and shrubs/trees spatial coverage in the next 30 years. Findings also reveal the presence of building constructions within less than 500 m from the river channel and/or flood plains. While a strict monitoring of the construction works along the riverbank needs to be constantly carried out, the paper also recommends the creation of a buffer zone of 500 m along the rivers where construction activities are prohibited

Methane emissions from a pristine southern African wetland

We present one year of continuous monitoring of methane emissions at two contrasting sites in the Okavango Delta, a UNESCO World Heritage site located in North-Western Botswana. The wetlands of the Okavango Delta are in pristine condition and can be separated into three categories: permanently flooded, seasonally flooded (3-6 months per year) and occasionally flooded (typically once per decade). We set up two eddy-covariance systems in August 2017, one at Guma Lagoon (18°57'53.01" S; 22°22'16.20" E) at the edge of an extensive papyrus bed in the permanently-flooded section of the delta, and the second one at Nxaraga on the SW edge of Chief’s Island (19°32'53'' S; 23°10'45'' E) in the seasonal floodplain. We also conduct monthly measurements of methane and carbon dioxide fluxes by using a clear dynamic chamber at Nxaraga along transects chosen to span the natural soil moisture gradient (very dry to waterlogged soils). We observed contrasting spatial and temporal patterns of methane emissions between the sites as well as significant differences in emission intensities. Methane hotspots were observed in the Guma Lagoon papyrus swamp whereas fluxes at Nxaraga increased gradually with distance into the floodplain, which correlates with the spatial gradient of soil moisture in the seasonal floodplain. The differences observed at the two measurement sites suggest different controls, with soil moisture likely to be the dominant one at the seasonal floodplain. In contrast, we expect the emissions from the permanent wetland to be driven by a complex set of mechanisms, which could include plant-mediated transport, diffusion at the water-air interface, bubbling and convective flow within the water column