Papers by Mike Murray-Hudson
AGU Fall Meeting Abstracts, Dec 1, 2018
We present one year of continuous monitoring of methane emissions at two contrasting sites in the... more 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
IPBES, 2019
This document contains the draft Chapter 5 of the IPBES Global Assessment on Biodiversity and Eco... more This document contains the draft Chapter 5 of the IPBES Global Assessment on Biodiversity and Ecosystem Services. Governments and all observers at IPBES-7 had access to these draft chapters eight weeks prior to IPBES-7. Governments accepted the Chapters at IPBES-7 based on the understanding that revisions made to the SPM during the Plenary, as a result of the dialogue between Governments and scientists, would be reflected in the final Chapters. IPBES typically releases its Chapters publicly only in their final form, which implies a delay of several months post Plenary. However, in light of the high interest for the Chapters, IPBES is releasing the six Chapters early (31 May 2019) in a draft form. Authors of the reports are currently working to reflect all the changes made to the Summary for Policymakers during the Plenary to the Chapters, and to perform final copyediting.
Wetland goods and services provide a means of survival for many riparian rural communities in dev... more Wetland goods and services provide a means of survival for many riparian rural communities in developing countries, particularly in the Sub-Saharan Africa. To sustain the provision of goods and services for human use, spatial and temporal variations in the quantity and quality of water in a given wetland should be adequately understood and managed. In this study we monitored the quantity and quality of surface water through the Okavango Delta for 2 years, from June 2008 to June 2010. Specifically we monitored precipitation over the Delta and surface inflow and outflow (via the Okavango and Thamalakane Rivers respectively) for water quantity, nutrients, cation and anion levels in the surface water along a river transect from Mohembo through the Delta to Lake Ngami. The study revealed that the water balance during the study period was similar to earlier reports. Most of the water inflow was via the Okavango River while surface outflow via the Boro River accounted for about 2% of total...
People and Nature, 2020
Humanity is on a deeply unsustainable trajectory. We are exceeding planetary boundaries and unlik... more Humanity is on a deeply unsustainable trajectory. We are exceeding planetary boundaries and unlikely to meet many international sustainable development goals and global environmental targets. Until recently, there was no broadly accepted framework of interventions that could ignite the transformations needed to achieve these desired targets and goals. As a component of the IPBES Global Assessment, we conducted an iterative expert deliberation process with an extensive review of scenarios and pathways to sustainability, including the broader literature on indirect drivers, social change and sustainability transformation. We asked, what are the most important elements of pathways to sustainability? Applying a social–ecological systems lens, we identified eight priority points for intervention (leverage points) and five overarching strategic actions and priority interventions (levers), which appear to be key to societal transformation. The eight leverage points are: (1) Visions of a go...
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<p&amp... more <p><span>The southwestward propagation of the East African Rift System inside the southern African plateau generated the Okavango basin in a strike-slip context. This setup generates one of the largest endoreic ecosystem in Africa: the Okavango Delta alluvial fan. The sedimentary and topography dynamics of that system are driven by both annual flooding and strike-slip geodynamics. To evaluate the impact of ground deformation on the long-term evolution of the Okavango ecosystem, we estimated the 3D strain field from the deformation of a geodetic network composed of 7 dual-frequency GPS semi-permanent stations measured during 4 years. The Okavango basin is a half-graben: its SE edge being limited by a set of normal faults, while the NW limit is bounded by a right-lateral fault. This fault pattern generates strain partitioning with a stretching direction that changes from oblique to parallel to the graben trend and with the highest dilation to the NE and shortening to the SW. Integrating geophysical data, we propose a crustal model describing a strike-slip basin with a normal detachment zone connected to a steep strike-slip shear zone in the lower crust. We show that strain partitioning lead to dilating and shortening domains, which favors water flow toward the NE and progressively restricts water discharge into Lake Ngami, SW of the Delta.</span></p><p><span>At regional scale, the vertical component of the ground deformation recorded over 10 years reveals annual variations generated by the cyclic flooding, this process acting in addition to the ground deformation induced by the regional geodynamics. A preliminary numerical modeling of the ground flexure induced by the floods constrains the rheological properties of the crust. It highlights two domains with high subsidence limiting a domain with lower subsidence allowing differential water storage.</span></p><p><span>We conclude that the geodynamic deformation linked to the propagation of the East African Rift into the Okavango half-graben is a key factor controlling the hydrodynamics and ecosystem evolution of the Okavango Delta fan. This control is super-imposed to the effects of variations in sediment and water supply linked to regional climate change. More generally, we show that intra-continental endoreic systems can be highly sensible to low amplitude tectonic deformation.</span></p><p> </p>
Journal of Forestry Research, 2017
In sub-Saharan Africa (SSA), the main goals behind the development of a biofuel industry are empl... more In sub-Saharan Africa (SSA), the main goals behind the development of a biofuel industry are employment creation and income generation. Jatropha (Jatropha curcas L.) has emerged as a candidate for biodiesel production. It is a non-edible oil producing, drought-resistant plant that can be grown on marginal land with limited water and low soil fertility. However, these are also attributes that typify weedy and invasive plant species. Adding to these concerns are the general questioning of whether biofuel production will reduce Greenhouse gas (GHG) emissions globally. Currently, there is limited information on the potential invasiveness of many biofuel crops, and in particular, the potential risks of cultivating Jatropha. This paper aims to assess the benefits and risks, especially risks, of growing Jatropha for biodiesel production. Jatropha should be screened through a science-based risk-assessment procedure to predict the risk of becoming invasive before it is released for large-scale commercial cultivation. The net GHG savings can be achieved through the cultivation of Jatropha, considering two main factors: no landuse change and crop management without chemical fertilization.
African Journal of Ecology, 2016
The objective of this study was to determine the influence of distance from surface water on ripa... more The objective of this study was to determine the influence of distance from surface water on riparian woodland communities in the Okavango Delta. Vegetation sampling was conducted in seven sites within the Okavango Delta in 20 m × 10 m belted plots placed perpendicular to the river bank. The plots were placed at 0–10 m, 10–20 m, 20–30 m, 30–40 m and 40–50 m distance classes increasing away from the river bank. Tree height, basal area, species richness, canopy cover and diversity were determined for each distance class. Indicator species analysis was used to determine the characteristic species at each distance class. Single‐factor ANOVA and Tukey post hoc analysis were used to compare species diversity, mean tree height, cover and basal area between distance classes. Correlation between distance from surface water and vegetation parameters was sought using Spearman regression analysis. All parameters except for species richness varied significantly (P < 0.05) along distance from ...
Tectonophysics, 2017
The Okavango Graben (OG) has been considered as the terminus of the southwestern branch of the Ea... more The Okavango Graben (OG) has been considered as the terminus of the southwestern branch of the East African Rift System (EARS) since the 1970's based on fault morphology and early seismic and geophysical data. Thus it is assumed to be an incipient rifting zone, analogous to the early stage of mature rifts in the EARS. Recent geodetic data and geophysical studies in the area bring new insights on the local crust and lithosphere, mantle activity and fault activity. In this study, we computed the velocities for three permanent GPS stations surrounding the graben and undertook a review of the new geophysical data available for the area. The northern and southern blocks of the graben show exclusively a low strike-slip displacement rate of about 1 mm/yr, revealing the transtensional nature of this basin. The seismic record of central and southern Africa is revealed to be instrumentally biased for the events recorded before 2004 and the OG may not represent the most seismically active area in Botswana anymore. Moreover, no significant lithosphere and crustal thinning is found in the tectonic structure as well as no strong negative Bouguer anomaly and surface heat flux. Thus the OG does not match the classical model for a rifting zone. We propose a new geodynamic model for the deformation observed west of the EARS based on accommodation of far-field deformation due to the differential extension rates of the EARS and the displacement of the Kalahari craton relative to the Nubian plate.
Environment and Water Resource Management / 837: Health Informatics / 838: Modelling and Simulation / 839: Power and Energy Systems, 2016
This study aimed to determine the influence of flooding frequency on the species composition and ... more This study aimed to determine the influence of flooding frequency on the species composition and distribution of riparian woodland vegetation in the Okavango Delta. Sampling was done in 20m × 50m plots in the Panhandle, Seronga, Jao, Moremi and Boro. Plant cover, seedling density, species richness and diversity were determined at each site. Plant cover was estimated using the modified Braun-Blanquet cover/abundance scale. Annual flooding frequency was also determined at each site. Plant species fell into two assemblages occurring at each site. There was spatial variation in mean cover, density, species diversity and richness in the Okavango Delta. ANOVA followed by Tukey post hoc analysis showed that in Seronga mean seedling density was significantly higher than in Boro and Moremi. In the Panhandle, seedling density was higher (p<0.05) than in Boro while in Jao it was higher (p<0.05) than in Moremi. Species richness was higher (p<0.05) in Seronga, Jao and Panhandle than in Moremi. Species diversity was higher (p<0.05) in Boro, Jao, Panhandle and Seronga than in Moremi. This study has shown that there is a potential to use riparian vegetation to reconstruct historical hydrological gradients
Environmental Monitoring and Assessment, 2016
Wetlands fed by rivers can be a sink for elements depending on elemental concentrations, wetland ... more Wetlands fed by rivers can be a sink for elements depending on elemental concentrations, wetland hydrology, geochemistry, vegetation and climate. In the case of the Okavango Delta, northern Botswana, the outflow discharge is a small fraction (2-5%) of the inflow. This has strong potential consequences for the Delta, as it strongly affects element cycling and storage within the Delta. We estimated the inputs, behaviour and distribution of multiple elements along a longitudinal transect within the Okavango Delta, to show potential effects of retention mechanisms of different elements. High annual element input is rather attributed to discharge than to the concentration within the water, which is generally extremely low. We observed minimal
African Journal of Agricultural Research, Apr 9, 2015
Flood recession farming locally known as molapo farming in the Okavango Delta is practiced along ... more Flood recession farming locally known as molapo farming in the Okavango Delta is practiced along the edges of the river channels or seasonally flooded depressions on its fringes. It relies on residual moisture and natural fertilization of the floodplains, and is promoted as being more productive than dryland farming. However, the productivity of this low-input farming system has not been extensively investigated. The objective of this study was to evaluate the yield potential of hybrid maize (Zea mays L.) in molapo farming. Two molapo field experiments and one dry-land experiment were conducted at Matsaudi and Lake Ngami, and Shorobe, respectively, in a randomized complete block design with four replications. Maize grain yield and plant height were measured from six consecutive plants from the centre row. The results showed that maize grain yield and plant height were significantly (P < 0.05) higher at Lake Ngami than at either Matsaudi or Shorobe. Late planting at Lake Ngami coincided with rainfall in November providing even and abundant soil moisture which contributed to better productivity of maize. Similarly, soil fertility was also better at Lake Ngami. Maize grain yield although lower (2.41 t ha -1 ) at Matsaudi and Shorobe (2.58 t ha -1 ) than at Lake Ngami (3.4 t ha -1 ), it is much higher than yields normally obtained by small-holder farmers in semi-arid zones in sub-Saharan Africa, where actual yields are often less than half of the potential yields. Similarly, plant height was significantly (P < 0.05) higher at Lake Ngami (235 cm) than either Matsaudi (194 cm) or Shorobe (192 cm). It could be concluded that timely planting of maize in molapo fields supplemented by rainfall is capable of producing better yields in semi-arid regions where water is the most limiting resource to crop production
Botswana notes and records
In data-poor regions, especially when they are large and remote, the measurement of biodiversity ... more In data-poor regions, especially when they are large and remote, the measurement of biodiversity presents considerable challenges. This paper explores a way of estimating regional patterns of biodiversity through a combination of land-cover field mapping, remote sensing and interpretative GIS techniques. The results show spatial variations of potential biodiversity in the remote Ngamiland region of Botswana, with areas of higher variability of land-cover classes indicative of higher degrees of biodiversity. The methodology is potentially replicable in other data-poor regions in developing countries.
Most work globally on Phragmites spp. has been done in temperate northern hemisphere localities, ... more Most work globally on Phragmites spp. has been done in temperate northern hemisphere localities, where winter low temperatures and short day lengths cause a seasonal decrease in growth. In this study, we report above-ground stem length-mass relationships, stem densities and daily growth rates in 3 Phragmites australis reedbeds in the flood-pulsed, subtropical Okavango Delta, with the aim of assessing the economic value of this plant, which is widely used throughout north-western Botswana for cladding house walls and fencing yards. Stem density averaged 77 m -2 in 32 plots. Length-mass relationships were best represented by a power function y = 8.05x 1.85 , where y is the dry mass in grams, and x is the length in metres (r 2 = 0.895). The mean daily growth rate was 0.015 m and did not appear to vary systematically with season. The maximum standing crop calculated from stem length was 2.89 kg m -2 , and occurred in May 2005. Annual above-ground production was conservatively estimated at 20-30 t ha -1 . Assuming that harvesting takes place not more than once annually, reed beds in the Okavango Delta are worth ~US$ 45,000 ha -1 at market. This land use value is over 90 times that of flood recession agriculture in the same area.
Biodiversity and Ecology, 2013
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Papers by Mike Murray-Hudson