Okavango Delta Under Threat

FEW images invoke the feeling of Africa＇s natural beauty more than the Okavango Delta.Yet this environmentally sensitive and economically significant area of Botswana is under threat due to climate change. The Okavango Delta is the world＇s largest inland delta, a permanent swamp that covers over 15,000 square km. The Delta floods yearly, between January and February, but the water, originating in the Angola highlands, evaporates and never reaches the major body of water.

Soil Factors That Influence the Abundance and Distribution of Threatened and Endangered Species in the Okavango Delta;with Particular Emphasis on <i>Eulophia angolensis</i>

Eulophia angolensis is an endangered plant species found in the Okavango Delta. Generally, there is lack of botanical information on this species in Botswana, which is necessary for its in-situ and ex-situ conservation. The objectives of this research are to map areas where E. angolensis occurs, determine the species that co-exist with it, and establish soil factors that influence its abundance and distribution in the Okavango Delta. A survey of the area where the plant was sighted in 2004 was carried out using recorded GPS points. Soil samples were collected at 0 - 20 cm depth from the floodplain where the species occurred to determine the macronutrients: total nitrogen, phosphorus, potassium (N, P, and K) and soil organic carbon (SOC) contents. The researchers could not find the plant at all GPS locations where the plant was sighted in 2004, but discovered a new unrecorded site for the species. The species was very close to the water channel;approximately 40 cm away, with only one plant about 60 cm away. The mean macronutrients concentrations in the site that contained E. angolensis were total N = 2.61 ± 0.61 mg/L, P = 7.02 ± 0.8 mg/L and K = 14.41 ± 4.28 mg/L. SOC concentration was 40.1 ± 10.28 mg/L. Furthermore, there was K biogeochemical gradient within the E. angolensis habitat, with more concentrations directly around the plant. Therefore, E. angolensis needs critical amounts of N, P, K and SOC, with K, SOC and water requirement being the crucial factors. Frequent monitoring of the endangered species found in the Okavango Delta is required, and ex-situ conservation of the species in the country in the form of a botanical garden should be established for future generations.

Spatial variation of the influence of distance from surface water on riparian plant communities in the Okavango Delta,Botswana

Introduction:Understanding the environmental factors that influence riparian vegetation community composition and distribution is important for understanding wetland ecosystem functioning.This understanding can further serve to inform policy aimed at conserving wetlands such as the Okavango Delta.In the Okavango Delta,information on the influence of distance from surface water on vegetation community composition and structure is limited.The objective of this study was to determine the relationship between distance from surface water and riparian plant communities at different sites in the Okavango Delta.Methods:Vegetation sampling was conducted in four sites in 20 m×10 m belted plots placed perpendicular to the river bank at 0–10 m,10–20 m,20–30 m,30–40 m,and 40–50 m distance classes.At each site,10–15 plots were sampled at each distance class.Basal area,species richness,cover,and plant diversity were determined for each plot.Indicator species analysis was used to determine the characteristic species at each distance class.One-way analysis of variance and Tukey post hoc analyses were used to compare species diversity,richness,cover,and basal area between distance classes.Generalized linear mixed(GLM)model was used to test for the overall impact of site and distance on each plant parameter.Results:Mean species richness was significantly(p<0.05)higher at 0–10 m than at 20–30 m,30–40 m,and 40–50 m in Boro.There was no significant difference within other sites.Mean species diversity also varied significantly(p<0.05)in Boro where it was higher at 0–10 m and 10–20 m than at 30–40 m.Mean basal area differed significantly within Jao and Upper Panhandle.In Jao,it was higher(p<0.05)at 0–10 m than at other distance classes.Mean percentage canopy cover differed significantly within all sites.In addition to this,plant species composition also changed along distance from surface water within each site.From GLM analysis,both distance and site significantly(p<0.05)influenced diversity and basal area.Species richness and cover were significantly(p<0.05)influenced by site only.Conclusion:Distance from surface water and site are important determinants of riparian plant dynamics in the Okavango Delta.

Inference of Fish Community Assembly in Intermittent Rivers Using Joint Species Distribution Models and Trophic Guilds

Mechanisms that drive species co-occurrence are poorly documented for intermittent rivers of semiarid regions. Here, we investigated fish community assembly in response to habitat types and physicochemical conditions in intermittent rivers of the lower Okavango Delta, Botswana. Using Joint Species Distribution Models, we inferred relative influences of environmental filtering and species interactions on patterns of species co-occurrence. Fishes were surveyed from multiple locations during drought and flood phases of the annual hydrological cycle. Species were classified into trophic guilds to facilitate inference about the types of species interactions that influence community structure. Water physicochemistry (depth, temperature, and dissolved oxygen concentration) was significantly associated with species distributions, whereas habitat type (ephemeral vs. permanent) was not significantly associated with species distribution. Controlling for the influence of environmental covariates resulted in three negative residual correlations, of which two involved non-predatory fishes from different trophic guilds, suggesting a behavioral selection of, or enhanced survival within, habitats with different environmental conditions. There was a negative residual correlation between a predator and a potential prey species, suggesting a role for predation mortality or threat in species segregation. Our results demonstrate that using trophic guilds in conjunction with JSDMs can enhance inferences about mechanisms of community assembly.

Seismicity Study of Botswana from 1966 to 2012

The history of Botswana’s major seismic events has been initiated by two earthquakes that occurred on the 11th of September and 11th of October 1952 with ML Richter magnitudes of 6.1 and 6.7, respectively, in the Okavango Delta Region (ODR). Not much is known and well documented about the seismicity of a larger coverage of Botswana primarily because over the years, local seismic stations were biased to the north-western part of Botswana, to monitor the more seismogenic ODR. The objective of this study is to use data from the International Seismological Centre (ISC) bulletin for the period 1966-2012 to estimate the relative size distribution of seismic events (b-value), the rate of seismic activity (a-value), and associated stress condition prevailing in Botswana to assist in the quest of hazard mitigation. This study shows that micro-seismic activities of magnitude ranging from 1.3 to 5.7 are distributed not only on the northern part of Botswana, but also in other parts of the country such as the Southern (including Kweneng East and West), Central and Eastern Botswana. Based on 327 events extracted from data compiled by the ISC, the frequency-magnitude distribution (FMD) of earthquakes in Botswana from 1966 to 2012 was estimated with b-value and a-value for the entire catalogue found to be 1.2 and 6.3, respectively, implying a region of low stress dominated by small to moderate events. The minimum completeness magnitude (MC), a value that indicates the lowest magnitude above which all seismic events are reliably recorded was found to be 3.8. From this analysis, annual probabilities of occurrence for M4 and M5 events were found to be 67.2% and 4.3%, respectively, while M6 or larger event has an annual probability of 0.3%.

利用ICA方法提取奥卡万戈三角洲水储量变化信号

利用重力恢复与气候实验(gravity recovery and climate experiment, GRACE)时变地球重力场模型计算得到非洲奥卡万戈三角洲地区2003-01—2014-12的陆地水储量变化信息,分别采用主成分分析(principal component analysis, PCA)和独立成分分析(independent component analysis, ICA)提取质量变化信号,并与全球陆地数据同化系统(global land data assimilation system, GLDAS)的水文模型进行对比。结果显示,在奥卡万戈河流域东北部,水储量表现出很强的周期性变化,两种数据空间特征分布的信号出现在相同位置的成分GRACE-IC1和GLDAS-IC1对应的时间序列的相关系数达到0.85。奥卡万戈三角洲地区水储量从2003-01—2011-10呈现上升趋势,两种数据空间特征分布的信号出现在相同位置的成分GRACE-IC2和GLDAS-IC3对应的时间序列的相关系数达到0.81,说明GRACE反演结果与GLDAS水文模型反演结果在研究区域内具有很强的一致性。引入全球降水气候中心降水数据和Water GAP全球水文模型数据对研究区域陆地水储量变化的原因进行分析。实验结果表明,相对于传统的多项式拟合方法,ICA可以在较大区域内直接对特定位置质量变化信号的时空特征进行提取;对比GRACE数据两种方法分解结果的第3成分可以看出,在空间尺度和时间尺度上,ICA方法对信号的分解能力要优于主成分分析方法。

非洲高端旅游与少数族群文化变迁——以博茨瓦纳奥卡万戈三角洲为例

壮丽的自然景观、多样的野生动物和丰富的历史文化,让每个非洲国家都与众不同。奥卡万戈三角洲地处博茨瓦纳西北部卡拉哈里沙漠边缘,是世界上风景最美的内陆三角洲,也是非洲高端旅游的胜地。本文基于对居住在奥卡万戈三角洲下游的族群进行长期深入的田野调查,探讨族群与奥卡万戈三角洲之间的共生关系,现代化的高端旅游给少数族群带来的改变以及如何保护和传承传统文化、人与自然的和谐共生、可持续发展等问题。