African Wetlands Research Articles

Predicting changes in the abundance of African wetland birds by incorporating abundance–occupancy relationships into habitat association models

AbstractAim To map changes in the abundance of African wetland birds using remotely derived habitat data. We show that abundance–occupancy relationships can be coupled with habitat association models to map changes in abundance. As conservation resources are more easily allocated when spatial and temporal patterns of abundance are known, our method provides guidance for conservation planning.Location Papyrus, Cyperus papyrus, swamps in east central Africa.Methods Presence/absence surveys of six bird species in 93 wetlands were used to construct models predicting probability of occurrence from habitat characteristics. Densities were then determined from surveys in 23 additional wetlands and modelled as functions of occurrence probability. We then used satellite imagery to derive habitat characteristics remotely in two time periods (1984–87 and 2000–03) and used the modelled relationships between (1) habitat and occupancy and (2) occupancy and density, to infer changes in abundance in all c. 30,000 wetlands within the study area.Results Wetlands within the region declined by 8.6% between the two time periods, but by > 75% in regions of high human population density. Bird densities were also highest in these regions, which comprised wetlands subject to high levels of disturbance. The geographical coincidence of high densities and habitat loss and the existence of positive associations between bird density and occurrence meant that birds declined by much more than the average rate of their habitat.Main conclusions Targeting conservation efforts in areas with high drainage would protect a high proportion of the bird populations. Encouraging people to derive income from disturbance to which the birds are tolerant, rather than drainage, is likely to be an effective strategy. Because habitat characteristics are a key driver of abundance–occupancy relationships, we conclude that there is wide‐scale scope to couple abundance–occupancy relationships with remote habitat mapping to efficiently inform conservation planning.

Status of migrant and resident waders, and moult strategies of migrant waders using African inland wetland habitats, at Barberspan Bird Sanctuary in South Africa

Status of migrant and resident waders, and moult strategies of migrant waders using African inland wetland habitats, at Barberspan Bird Sanctuary in South Africa MAGDALENA REMISIEWICZ* & JOEL AVNI Animal Demography Unit, Department of Zoology, University of Cape Town, Rondebosch 7701, South Africa Avian Ecophysiology Unit, Department of Vertebrate Ecology and Zoology, University of Gdansk, al. Legionow 9, 80-441 Gdansk, Poland Ecotone Africa, 16 Kimberley Rd, Observatory 7925, Cape Town, South Africa

Water chemistry and effect of evapotranspiration on chemical sedimentation on the Mkuze River floodplain, South Africa

The Mkuze Wetland System, forming part of the iSimangaliso World Heritage Site, is South Africa’s largest freshwater wetland area and is known to act as a sink for naturally occurring solutes within the landscape. The chemistry of groundwater and porewater samples, collected from two transects on the Mkuze River floodplain, was investigated to identify processes involved in the control of solute concentrations. Results show that solutes in the groundwater become increasingly concentrated under the influence of evapotranspiration, resulting in the saturation, precipitation, and accumulation of less soluble compounds. Trends in porewater chemistry and calculated saturation indices support previously documented mineralogical and sediment geochemical investigations, with CaCO 3 and silica precipitation, and Fe-rich smectite neoformation identified as the major controls on solute concentration. The association of these mineral phases with zones of high salinity suggests that mineral precipitation is an active process on the floodplain which results in the progressive development of salinity, particularly in areas dominated by deep-rooted trees. Similarities between geochemical processes documented in the Okavango Delta (Botswana) and those identified in this study suggest that evapotranspiration-induced chemical sedimentation is an important process in southern African wetlands, which has the potential to influence vegetation distribution, hydrological flows, and local topography.

A Review of the Relative Merits of Conserving, Using, or Draining Papyrus Swamps

Wetlands are a vital resource, particularly in Africa where livelihoods are closely linked to natural capital. In recent years, extensive drainage has occurred to make way for agriculture. To gain insight into whether drainage is justified, we review the value of African wetlands dominated by Cyperus papyrus in relation to use, conservation and conversion. Evidence suggests that the value derived from low-intensity, multifunctional wetland use far exceeds the value derived from swamp reclamation and generally exceeds that of conservation. At a local level, the main driver of wetland misuse appear to be a breakdown in collaborative management regimes and the main constraint on wetland use, the value of labor and selling-times. Local drivers are linked to regional factors such as the lack of coordinated wetland policies and difficulties in ensuring that legislation is absorbed by all sectors of society. We highlight opportunities for ensuring more effective collaborative management and legislation communication, which capitalize on existing governance structures. In contrast to predictions by Hardin's Tragedy of the Commons model, we argue that effective wetland management is best achieved by preventing privatization and promoting common property management regimes. We also argue that poverty and income inequity are more important drivers of unsustainable resource use than environmental managers commonly acknowledge.

Ecological Modeling of the Spatial Distribution of Wild Waterbirds to Identify the Main Areas Where Avian Influenza Viruses are Circulating in the Inner Niger Delta, Mali

Predicting areas of disease emergence when no epidemiological data is available is essential for the implementation of efficient surveillance programs. The Inner Niger Delta (IND) in Mali is a major African wetland where >1 million Palearctic and African waterbirds congregate. Waterbirds are the main reservoir of Avian Influenza Viruses (AIV). Our objective was to model their spatial distribution in order to predict where these viruses would be more likely to circulate. We developed a generalized linear model (GLM) and a boosted regression trees (BRT) model based on total aerial bird counts taken in winter over 6 years. We used remotely sensed environmental variables with a high temporal resolution (10 days) to predict the spatial distribution of four waterbird groups. The predicted waterbird abundances were weighted with an epidemiological indicator based on the prevalence of low pathogenic AIV reported in the literature. The BRT model had the best predictive power and allowed prediction of the high variability of waterbird distribution. Years with low flood levels showed areas with a higher risk of circulation and had better spatial distribution predictions. Each year, the model identified a few areas with a higher risk of AIV circulation. This model can be applied every 10 days to evaluate the risk of AIV emergence in wild waterbirds. By taking into account the IND's ecological variability, it allows better targeting of areas considered for surveillance. This could enhance the control of emerging diseases at a local and regional scale, especially when resources available for surveillance programs are scarce.

Wide Area Wetland Mapping in Semi-Arid Africa Using 250-Meter MODIS Metrics and Topographic Variables

Wetlands in West Africa are among the most vulnerable ecosystems to climate change. West African wetlands are often freshwater transfer mechanisms from wetter climate regions to dryer areas, providing an array of ecosystem services and functions. Often wetland-specific data in Africa is only available on a per country basis or as point data. Since wetlands are challenging to map, their accuracies are not well considered in global land cover products. In this paper we describe a methodology to map wetlands using well-corrected 250-meter MODIS time-series data for the year 2002 and over a 360,000 km2 large study area in western Burkina Faso and southern Mali (West Africa). A MODIS-based spectral index table is used to map basic wetland morphology classes. The index uses the wet season near infrared (NIR) metrics as a surrogate for flooding, as a function of the dry season chlorophyll activity metrics (as NDVI). Topographic features such as sinks and streamline areas were used to mask areas where wetlands can potentially occur, and minimize spectral confusion. 30-m Landsat trajectories from the same year, over two reference sites, were used for accuracy assessment, which considered the area-proportion of each class mapped in Landsat for every MODIS cell. We were able to map a total of five wetland categories. Aerial extend of all mapped wetlands (class “Wetland”) is 9,350 km2, corresponding to 4.3% of the total study area size. The classes “No wetland”/“Wetland” could be separated with very high certainty; the overall agreement (KHAT) was 84.2% (0.67) and 97.9% (0.59) for the two reference sites, respectively. The methodology described herein can be employed to render wide area base line information on wetland distributions in semi-arid West Africa, as a data-scarce region. The results can provide (spatially) interoperable information feeds for inter-zonal as well as local scale water assessments.

137Cs and 210Pb derived sediment accumulation rates and their role in the long-term development of the Mkuze River floodplain, South Africa

Wetlands are well known to act as sinks for sediment and chemicals in the landscape. Within the Mkuze River floodplain in northern KwaZulu-Natal, South Africa, deposition of clastic sediment occurs predominantly in close proximity to the river channel, resulting in the formation of levees. Over time, this leads to channel avulsion, a process that may be accelerated by the activities of hippopotami whose trails create hydraulically favourable pathways. Sedimentation rates, determined using the isotopes 210Pb and 137Cs, indicate that the Mkuze River floodplain is a relatively rapidly aggrading system that should experience frequent avulsion, with average short-term rates in the order of 0.25 to 0.50 cm/y. Sediments on the floodplain are also an important sink for solutes, which concentrate in the groundwater and precipitate out because of evapotranspiration. Over long timescales, chemical sedimentation affects the landscape by influencing salinity, vegetation distribution, hydrological flows, and local topography. The Mkuze River floodplain is an actively evolving system, which continues to aggrade as a result of the combination of clastic and chemical sedimentation. In a region characterised by a strong annual water deficit, temporal patterns of clastic and chemical sedimentation are likely to exert influence on the long-term development of wetland systems elsewhere in southern Africa. This study, the first on sediment accretion rates using 210Pb and 137Cs dating for a southern African wetland, demonstrates that radioisotopic methods are an important tool that can be applied toward fully understanding wetland formation, evolution, and functioning in the region.

Feedbacks on convection from an African wetland

The Niger Inland Delta in Mali floods every year in response to rain falling hundreds of kilometers upstream. This study examines the remote hydrological feedback between rainfall, fluvial inundation, and new convective storms. A satellite thermal infra‐red dataset spanning 24 years is used to quantify both temporal variability in wetland extent, and the response of cloud cover to the wetland during August and September. The daytime initiation of convective storms is found to double during periods of inundation, consistent with a hypothesised “wetland breeze” effect. A signal of enhanced cloud cover propagates hundreds of kilometers westwards, linked to increased numbers of long‐lived Mesoscale Convective Systems emanating from the wetland region. This effect raises the possibility that changes in upstream water use could have a climatic impact over a wide area.

The language of intervention: A review of concepts and terminology in wetland ecosystem repair

As programmes and projects aimed at addressing wetland degradation gain momentum in South Africa, it is critical that related ideas are communicated among and between researchers, practitioners, management agencies, land-owners and the general public in a common language. This paper explores the meaning of ‘restoration’ and ‘rehabilitation’; terms that we suggest are key to understanding and advancing South Africa’s efforts to address wetland degradation. In its essence, the paper is a critical review of wetland ecosystem repair concepts and terminology from local and international literature. The major products of the paper are proposed definitions of the terms ‘restoration’ and ‘rehabilitation’ in a South African wetland science and management context. Although the terms are often used interchangeably, we argue that their absolute distinction will allow scientists and practitioners to better understand what it is that ecosystem repair interventions aim to achieve. We suggest that the terms be distinguished on the basis of what could be considered their respective ecological starting points, where ‘restoration’ applies to part of a system or a system in its entirety that has been completely and permanently, but not irreparably altered, and essentially removed from the landscape, and ‘rehabilitation’ applies to part of a system or a system in its entirety that has not been removed from the landscape through complete and permanent alteration, but is in a degraded state. Thus, ‘wetland restoration’ is defined as the process of reinstating natural ecological driving forces within part or the whole of a completely and permanently altered wetland to recover former or desired ecosystem structure, function, biotic composition and ecosystem services, while ‘wetland rehabilitation’ is defined as the process of reinstating natural ecological driving forces within part or the whole of a degraded wetland to recover former or desired ecosystem structure, function, biotic composition and ecosystem services.

Working Wetland Potential: An index to guide the sustainable development of African wetlands

AbstractPast experience shows that inappropriate agricultural development in wetlands can undermine sustainability and may have profound social and economic repercussions for people dependent on the range of ecosystem services provided by those wetlands. Nonetheless, there is escalating pressure to expand agriculture within wetlands due to increasing population, in conjunction with efforts to increase food security. This paper describes the development of a semi‐analytical framework for identifying, organizing and analyzing the complex factors that link people, agriculture and wetland ecosystems — an index of Working Wetland Potential (WWP). The method is based on a form of multi‐criteria analysis that integrates biophysical and socio‐economic aspects of wetland utilization. The WWP index emerges from the aggregation of two values: the first arising from an appraisal of both the biophysical and socio‐economic suitability of using the wetland for agriculture; and the second resulting from an assessment of the possible hazards, in relation to both social welfare and the ecological character of the wetland. Hence, the approach provides a way to explicitly integrate biophysical and social aspects of wetland utilization in a single index to enable an initial assessment of the suitability of using a wetland for agriculture. Results from three contrasting wetlands in sub‐Saharan Africa are presented.

Valuing the Provisioning Services of Wetlands: Contrasting a Rural Wetland in Lesotho with a Peri-Urban Wetland in South Africa

Given that few studies have valued the provisioning services of temperate southern African wetlands, research on this topic was undertaken in a remote rural wetland, Letseng-la-Letsie, in Lesotho and a peri-urban wetland in Mfuleni, Cape Town. The objectives were to quantify incomes from wetland resources, assess the relative dependency of communities on wetland provisioning services, and estimate the total provisioning value of the wetlands. Data were collected from informal interviews and structured household surveys. Despite the different settings, both wetlands were used mainly for grazing livestock. The estimated total value added during 2007 from grazing was U.S. $180,078 for Letseng-la-Letsie and U.S. $540,286 for Mfuleni. Letseng-la-Letsie and Mfuleni were also used for hunting, and Mfuleni was partially cultivated. Even though the local wetlands were easier to access from Mfuleni, only 13% of households used them, compared with 65% in Letseng-la-Letsie. However, the households around Letsengla-Letsie derived less of their income (6%) from the wetlands, compared with 82% in Mfuleni. This reflects the more specialized livelihood strategies in the urban compared with the rural setting, in which riskspreading household production strategies were more prevalent. The loss of the wetland in Letseng-laLetsie would therefore potentially affect more people but have less of an effect on the finances of individual households than in Mfuleni. It is estimated that U.S. $220/ha and U.S.$1765/ha is derived annually from wetland provisioning services in Letseng-la-Letsie and Mfuleni, respectively. A standard protocol is needed for valuing wetlands in southern Africa.

Movements of waterbirds within Africa and their conservation implications

Waterbirds in Africa have developed diverse strategies to exploit the wide variety of African wetlands. Whilst some species are largely sedentary, especially those in relatively static tropical climates, most demonstrate movements in response to changing seasons and environmental conditions. The onset of rain is an important trigger for migration: some waterbirds are harbingers of the rainy season, whilst others follow in the wake of rain. However, levels and timing of rain can be unpredictable and rain may not fall at all some years. When rain falls in arid and semi-arid areas, productive temporary wetlands can appear rapidly and attract large numbers of waterbirds, many of which are partially nomadic. This unpredictability presents difficult management scenarios. Overall, waterbird movements within Africa are poorly understood, which limits our abilities to conserve waterbirds in Africa and to implement the African-Eurasian Migratory Waterbird Agreement. It will take major resources and many years before we have clear pictures of waterbird movements within Africa. Influencing factors such as climate change and wetland degradation may well lead to further changes in migratory patterns. Nevertheless, conservation measures are required immediately, especially for declining species.

Estimating Abundance from Occurrence: An Underdetermined Problem

Estimating Abundance from Occurrence: An Underdetermined Problem

Pollutant transformation performance in a peri-urban African wetland system receiving point source effluent and diffuse source pollutant inputs

Water quality investigations were undertaken in the Dionosoyiet wetland (Lake Victoria basin, Kenya) from June 2004 to April 2005 for nutrients and suspended solids. Hydrology and Water Quality modelling were performed based on the CRC FE POND model. The model was adapted to incorporate a rainfall runoff module based on the isochronal histogram technique and a partially stochastic prediction of water quality (TSS, TN and TP) based on incoming flow rates. Using the data gathered from June 2004 to April 2005 for calibration and earlier climatic data, modelling was performed to cover an 11 year period, from January 1994 to December 2004, and indicated that the wetland removed 43% TSS, 41% TP and 20% TN with average areal removal rates of 21.3 TSS, 0.038 TP and 1.03 TN (kg ha−1 day−1).The findings show that, in addition to being a central community activity feature of the town, the wetland performs significant functions of water quality improvement. The preservation of this wetland and other similar wetlands is important in ensuring sustainable utilisation of water resources in the Lake Victoria Basin.

Species diversity of the Okavango Delta, Botswana

In the Okavango Delta (about 28,000 km2) the number of identified species is 1,300 for plants, 71 for fish, 33 for amphibians, 64 for reptiles, 444 for birds, and 122 for mammals. The local occurrence of different species of these taxonomic groups in the Okavango Delta is mainly due to a hydrological gradient from permanent streams and swamps to seasonal floodplains, riparian woodlands, and dry woodlands. This level of species diversity is normal for the southern African region, and all analyzed aquatic groups are composed of ubiquitous species with an additional significant proportion of species originating from northern, more tropical systems. Cyclical variations in climate over thousands of years have created a huge wetland complex in the upper Zambezi and Okavango Rivers during wet phases. This wetland complex has fragmented into the Okavango Delta and other large wetlands in Zambia during dry phases. There are no endemic species in the Okavango Delta while the South-central African wetland complex is a centre of endemism. Species diversity of the Okavango Delta is a consequence of this unique environment, with dynamic shifts in flooding patterns that in turn force constant changes in patterns of plant succession and dependent animals. Temporal variations in flooding also cause accumulation and sudden mobilization of nutrients which are readily used by well adapted plant species. As a consequence, locally high biological productivity occurs, which in turn results in high numbers of grazing mammals.

Use of the Nile Monitor, Varanus niloticus L (Reptilia: Varanidae), as a Bioindicator of Organochlorine Pollution in African Wetlands

Use of the Nile Monitor, Varanus niloticus L (Reptilia: Varanidae), as a Bioindicator of Organochlorine Pollution in African Wetlands

Towards the development of a macroinvertebrate sampling technique for palustrine wetlands in South Africa: a pilot investigation in the KwaZuluNatal midlands

A study was undertaken in November 2003 to derive a suitable sampling technique for collecting a representative sample of aquatic macroinvertebrates from a selected emergent vegetation biotope in a palustrine wetland, Melmoth Vlei, KwaZulu-Natal, South Africa. The aim was to undertake a preliminary investigation on the development and testing of a macroinvertebrate sampling technique for use in emergent sedge-dominated palustrine wetlands (sensu Cowardin et al. 1979), which could contribute to the development of a South African wetland health biomonitoring programme. Sweep nets and activity traps were evaluated for their effectiveness in terms of macroinvertebrate collection. Sweep net sampling was tested over a range of sweep intensities to determine the minimum number of sweeps required to collect a representative sample. Sampling efficiency of activity traps placed at four depths was tested, and taxon diversity and composition of sweep net and activity trap samples were compared to determine whether activity traps are required to supplement sweep net data. A total of 32 taxa (identified mainly to family level) were identified in the samples collected. Taxon diversity and composition did not differ in the activity traps placed at the four depth locations. Taxon diversity did not differ significantly between different sweep intensities. This may be a result of high variability of macroinvertebrate distribution within a wetland. There is evidence, however, to suggest that this result is due to an inadequate sample size. There was a significant difference in taxon composition between the different sweep intensities (P < 0.05) and between activity trap and sweep net samples (P < 0.05). Sixty-eight percent of taxa appeared more frequently in sweep net sampling than in activity trap sampling. Two taxa were found exclusively in activity traps, although the numbers of these taxa collected were not significant, and they do not represent any unique trophic group. Based on these findings, it was concluded that activity traps are not required to supplement sweep net data, and a technique using a sweep net with a sweep intensity of five would be suitable for collecting a representative sample of macroinvertebrates from a palustrine wetland.

Economic consequences of wetland degradation for local populations in Africa

Wetlands in Africa are an important source of water and nutrients necessary for biological productivity and often sheer survival of people. Sustainable management of wetlands is therefore critical to the long-term health, safety and welfare of many African communities. Despite their importance, wetlands are being modified or reclaimed, often driven by economic and financial motives. Wetlands, however, contain numerous goods and services that have an economic value not only to local populations but also to people living outside the periphery of the wetland. These values can be made more explicit through economic valuation studies. The goal of this paper is to highlight the importance of wetlands for local populations in Africa and the economic consequences for these people if wetlands are degraded. After explaining the characteristics, distribution and status of wetlands in Africa, the economic values of African wetlands will be highlighted through a discussion of several economic valuation studies carried out for different African wetlands. Recommendations are made as to how economic values may be used in decision-making on wetlands to allow more sustainable management of African wetlands.

Livelihoods in the wetlands of Kilombero Valley in Tanzania: Opportunities and challenges to integrated water resource management

Wetlands contribute in diverse ways to the livelihood of many people in Africa. One of the major constraints to the wise use of African wetlands is lack of knowledge by planners and natural resource managers on the benefits that they provide and techniques by which they can be utilised in a sustainable manner. This paper presents findings from a study undertaken in Kilombero Valley, Tanzania, on the dynamics and benefits of natural resource use in the wetlands. The paper specifically focuses on opportunities and challenges related to integrated water resource management. The study was conducted in two villages, Idete and Signali located in Kilombero District, Morogoro Region. Participatory assessment and household interviews were employed to obtain both qualitative and quantitative information, respectively, pertaining to biophysical, agronomic and socio-economic facts that influence community access to, and utilisation of the wetland resources. The findings show that Kilombero Valley has high potential for a diversity of livelihood activities. The wetland also serves as a source of water for farming, livestock, fishing and for domestic uses. Over the last two decades the use of wetlands for agriculture has increased because of increasing population of both pastoral and agro-pastoral communities, and hence the resultant need to produce more food. However, there are environmental concerns associated with increasing use of wetlands for agriculture and other livelihood activities, including deforestation and trampling of soils by increasing livestock numbers, increased demand on the water resources and lack of elaborate institutional framework to facilitate the integration of the various sectoral and cross-sectoral uses of the wetland resources and among stakeholders. The main conclusion is that sustainable livelihood development of wetland communities requires multidisciplinary and integrated efforts in addressing constraints in the various sectors such as agriculture, natural vegetation use, water resources and fishing.

The hydrology and hydrogeology of dambos: a review

Dambos are shallow, seasonally waterlogged, tropical and subtropical African wetlands. Their importance, through their role in agriculture and water supply to downstream river networks, has been widely acknowledged. As a result, much research has been conducted on the hydrological functions of dambos and their hydrogeological structures, in an attempt to better understand, utilize and manage this regionally ubiquitous landform. However, these studies have resulted in little consensus regarding the geomorphology of dambos, their hydrological regimes and the hydrogeological model that drives those regimes. This review paper, focusing on dambo hydrology, hydrogeology and their primary determinants, highlights the key issues of the debate and draws some overriding conclusions from the divergent literature. Five hypotheses are proposed based on these conclusions, in an attempt to focus future dambo research efforts.