Elephant space use in relation to ephemeral surface water availability in the eastern Okavango Panhandle, Botswana

The movement and distribution of elephants can be influenced by environmental factors over time (Foley, 2002). Examining how features in the landscape such as vegetation productivity, water sources and anthropogenic activities drive the movement of elephants can help in understanding patterns of movement. It can also help to inform the establishment and alignment of protected areas, wildlife corridors and identification of tourism hotspots as well as policy interventions to manage Human-Elephant Conflict (HEC). The Okavango Panhandle in Botswana is a HEC hotspot and the focus of My study. A number of strategies to address HEC are underway in the area, however one longer term strategy that has been proposed in this area involves provision of artificial water sources to influence elephant movements and keep animals away from fields during the cropping season. However, an improved understanding of how elephants utilize their habitats in relation to natural ephemeral surface water and other factors that influence their movements from dryland habitats to the Okavango Delta resources is needed to inform such management decisions. My study seeks to establish the role of ephemeral surface water on elephant distribution in the eastern Okavango Panhandle, Botswana as well as assess the movement distribution of elephants in relation to the seasonality, proximity and spatial extent of water presence represented by ephemeral surface water. Time series analysis of water extent on ephemeral surface water of the eastern Okavango panhandle will be developed and overlaid with elephant movement datasets. Elephant collar data from 15 elephants (5 males and 10 females) in the eastern Okavango Panhandle, Botswana have been analysed and Home Range (HR) sizes estimated using Kernel Density Estimation (KDE). The relative importance/probability of environmental variables in determining elephants' movement based on the Utilization Distribution (UD) were computed using Generalized Linear Mixed Models (GLMMs). I utilized a remote sensing spectral index, namely the Automated Water Extraction Index (AWEI) to delineate ephemeral surface water in dryland (excluding permanent waters) of the study area. The results reveal that during the wet season, elephants were evenly spread out all over the study area until the early dry season (April-June) when the ephemeral waterholes dried up. Elephants moved southwards towards the permanent waters of the Okavango River, where there are many human settlements and farms. Male HR sizes were found to be bigger than those of female elephants. Wet season (early and late) home range sizes were also bigger when compared to dry season (early and late) HR size. Mean daily distances were computed to investigate the effect of season on elephant daily distances and the distances ranged between 5km and 6.8km in the late wet and in the early wet and late dry season respectively. The Resource Selection Function (RSF) analysis shows that water adjacent sites are preferred over distant ones and both sexes prefer areas with high NDVI, with this preference being more pronounced in males. The seasonal variation of water use is notable in that it affirms the importance of proximity to water for elephants and has implications for their management and HEC. For example, I found that ephemeral surface water has a significant role in influencing elephant spatial use in the area, particularly during the early and late wet season. As ephemeral pans dried and NDVI (vegetation greenness) decreased, elephants started to move closer to the Okavango Delta and consequently human settlements and fields. However, further investigations into the timing of movements away from ephemeral waterholes and the influence of other environmental factors on elephant movements in the area would be needed before any recommendations can be made regarding artificial water provision in this area

From sink to source: high inter-annual variability in the carbon budget of a southern African wetland

We report on three years of continuous monitoring of carbon dioxide (CO2) and methane (CH4) emissions in two contrasting wetland areas of the Okavango Delta, Botswana: a perennial swamp and a seasonal floodplain. The hydrographic zones of the Okavango Delta possess distinct attributes (e.g. vegetation zonation, hydrology) which dictate their respective greenhouse gas (GHG) temporal emission patterns and magnitude. The perennial swamp was a net source of carbon (expressed in CO2-eq units), while the seasonal swamp was a sink in 2018. Despite differences in vegetation types and lifecycles, the net CO2 uptake was comparable at the two sites studied in 2018/2020 (−894.2 ± 127.4 g m−2 yr−1 at the perennial swamp, average of the 2018 and 2020 budgets, and −1024.5 ± 134.7 g m−2 yr−1 at the seasonal floodplain). The annual budgets of CH4 were however a factor of three larger at the permanent swamp in 2018 compared to the seasonal floodplain. Both ecosystems were sensitive to drought, which switched these sinks of atmospheric CO2 into sources in 2019. This phenomenon was particularly strong at the seasonal floodplain (net annual loss of CO2 of 1572.4 ± 158.1 g m−2), due to a sharp decrease in gross primary productivity. Similarly, drought caused CH4 emissions at the seasonal floodplain to decrease by a factor of 4 in 2019 compared to the previous year, but emissions from the perennial swamp were unaffected. Our study demonstrates that complex and divergent processes can coexist within the same landscape, and that meteorological anomalies can significantly perturb the balance of the individual terms of the GHG budget. Seasonal floodplains are particularly sensitive to drought, which exacerbate carbon losses to the atmosphere, and it is crucial to improve our understanding of the role played by such wetlands in order to better forecast how their emissions might evolve in a changing climate. Studying such hydro-ecosystems, particularly in the data-poor tropics, and how natural stressors such as drought affect them, can also inform on the potential impacts of man-made perturbations (e.g. construction of hydro-electric dams) and how these might be mitigated. Given the contrasting effects of drought on the CO2 and CH4 flux terms, it is crucial to evaluate an ecosystem's complete carbon budget instead of treating these GHGs in isolation

Phenology is the dominant control of methane emissions in a tropical non-forested wetland

Tropical wetlands are a significant source of atmospheric methane (CH4), but their importance to the global CH4 budget is uncertain due to a paucity of direct observations. Net wetland emissions result from complex interactions and co-variation between microbial production and oxidation in the soil, and transport to the atmosphere. Here we show that phenology is the overarching control of net CH4 emissions to the atmosphere from a permanent, vegetated tropical swamp in the Okavango Delta, Botswana, and we find that vegetative processes modulate net CH4 emissions at sub-daily to inter-annual timescales. Without considering the role played by papyrus on regulating the efflux of CH4 to the atmosphere, the annual budget for the entire Okavango Delta, would be under- or over-estimated by a factor of two. Our measurements demonstrate the importance of including vegetative processes such as phenological cycles into wetlands emission budgets of CH4

Water, Ecosystem Dynamics and Human Livelihoods in the Okavango River Basin (ORB): Competing Needs or Balanced Use? A Review

Freshwater is essential to life, and its availability poses a significant challenge to developmental needs and environmental sustainability globally. Due to increasing populations, global water requirements have increased in the twentieth century, and the trend is similar in the Okavango River Basin (ORB). With a total annual flow of 11 km3, the ORB is characterised by a flood pulse regime that drives and supports a diverse eco-sociological system. The Okavango River is a potential water source for the development of the semi-arid nation states of Botswana and Namibia. Therefore, there is a need to ensure that the water resource of this system is managed effectively to ensure water sustainability in the basin. Current water demand in the basin is less than 1% of the current total discharge, while projected demand over the next 10 years also falls below the total discharge. Moreover, the ORB is characterised by multi-functional use, where riparian communities have adapted to change hydrological conditions. While the ORB is relatively pristine, there are potential threats in this system, which can affect its water resources. We conclude that there is a need for a harmonised legislative framework in the basin to ensure that the ethos of water sustainability is maintained