African Wetlands Research Articles

Migration of humans fleeing conflict in the Lake Chad region may increase pressures on natural resources in Lake Fitri (Chad): A case study on waterbirds

Abstract Sustainable harvest of wildlife is a major food security and conservation issue. In Africa, where wildlife is harvested mainly for subsistence, this remains a challenge. In this study, using waterbirds as model for natural resources, we assessed the sustainability of harvest through fishing bycatch on Lake Fitri (Chad). We estimated the abundance of 24 target taxa through aerial distance sampling over four consecutive years (2018–2021) and in parallel estimated the number of birds harvested through interviews of a sample of 105 out of approximately 5500 fishermen. By modelling their potential excess growth, we found a high risk of overexploitation for four species, including the world‐threatened Black Crowned Crane Balearica pavonina, likely due to an influx of fishermen to Lake Fitri fleeing the Boko Haram security crisis. Synthesis and applications: This work is likely the first quantitative approach of bird harvest sustainability in Africa. It should contribute to fill a methodological and an information gap in the strategic planification of several multilateral environmental agreements like the African‐Eurasian Waterbird Agreement and the Ramsar Convention. In particular, this work could help implementing adaptive management of natural resources (including birds) in Ramsar site management plans. African wetlands such as Lake Fitri may not be able to provide enough natural resources in the medium term for movements of displaced civilians forced by armed conflict into such biodiversity strongholds.

EcoSonicML: Harnessing Machine Learning for Biodiversity Monitoring in South African Wetlands

Biodiversity monitoring, particularly in a country as diverse as South Africa with its extensive migratory bird population, presents significant challenges. This challenge becomes even more pronounced in environments with a multitude of coexisting bird species, notably wetlands, which serve as crucial breeding and feeding grounds for various avian species. This research will address this challenge by designing a cost-effective sound-based sensor system capable of deployment in diverse wetland ecosystems. The primary aim is to aid in the monitoring of bird species by detecting their presence and distribution and then transmitting this valuable data to a central base station. To assess the system’s feasibility and performance, a series of experiments were conducted at the Rondevlei Nature Reserve in Cape Town, South Africa. These experiments focused on the sensor’s capacity to accurately identify avian species while maintaining robustness in varying environmental conditions. The results yielded promising outcomes, demonstrating the successful identification of bird species. Furthermore, the system exhibited reliability across different weather conditions, positioning it as a viable choice for long-term deployment in wetland environments. Beyond species detection, this project also delved into practical aspects of data transfer and storage efficiency, ensuring the system’s suitability for real-world applications. Modularity was another crucial consideration, simplifying maintenance and upgrades. Moreover, a preliminary cost analysis indicated the cost-effectiveness of the system compared to commercial alternatives. The integration of climate sensors into the monitoring system was explored as a future direction. This addition holds the potential to provide a more comprehensive approach to environmental monitoring by incorporating climate data into the analysis. Such a holistic approach can further enrich our understanding of bird behaviour in relation to changing environmental conditions. The findings of this research have significant implications for avian conservation and ecological studies, particularly in the unique context of South Africa. This project introduces an affordable and practical tool for monitoring bird species in wetland habitats, offering valuable insights into the preservation and management of these critical ecosystems.

Low-Cost Sensors and Multitemporal Remote Sensing for Operational Turbidity Monitoring in an East African Wetland Environment

Low-Cost Sensors and Multitemporal Remote Sensing for Operational Turbidity Monitoring in an East African Wetland Environment

Mapping Wetlands of Kenya Using Geographic Resources Analysis Support System (GRASS GIS) with Remote Sensing Data

Abstract Monitoring wetlands of Kenya is critical for analysis of environmental changes since they present unique ecosystems with special hydrological balance and biodiversity. In this study, the Landsat 8-9 OLI/TIRS satellite images for 2015-2022 were classified using GRASS GIS scripts to evaluate changes in the Lorian Swamp wetland, north-eastern Kenya. The results of the image analysis presented maps of land cover changes including wetlands. The study demonstrated technical effectiveness of the GRASS GIS for image analysis, and contributed to the environmental monitoring of African wetlands.

Evaluation of wetland CH4in the Joint UK Land Environment Simulator (JULES) land surface model using satellite observations

Abstract. Wetlands are the largest natural source of methane. The ability to model the emissions of methane from natural wetlands accurately is critical to our understanding of the global methane budget and how it may change under future climate scenarios. The simulation of wetland methane emissions involves a complicated system of meteorological drivers coupled to hydrological and biogeochemical processes. The Joint UK Land Environment Simulator (JULES) is a process-based land surface model that underpins the UK Earth System Model (UKESM) and is capable of generating estimates of wetland methane emissions. In this study, we use GOSAT satellite observations of atmospheric methane along with the TOMCAT global 3-D chemistry transport model to evaluate the performance of JULES in reproducing the seasonal cycle of methane over a wide range of tropical wetlands. By using an ensemble of JULES simulations with differing input data and process configurations, we investigate the relative importance of the meteorological driving data, the vegetation, the temperature dependency of wetland methane production and the wetland extent. We find that JULES typically performs well in replicating the observed methane seasonal cycle. We calculate correlation coefficients to the observed seasonal cycle of between 0.58 and 0.88 for most regions; however, the seasonal cycle amplitude is typically underestimated (by between 1.8 and 19.5 ppb). This level of performance is comparable to that typically provided by state-of-the-art data-driven wetland CH4 emission inventories. The meteorological driving data are found to be the most significant factor in determining the ensemble performance, with temperature dependency and vegetation having moderate effects. We find that neither wetland extent configuration outperforms the other, but this does lead to poor performance in some regions. We focus in detail on three African wetland regions (Sudd, Southern Africa and Congo) where we find the performance of JULES to be poor and explore the reasons for this in detail. We find that neither wetland extent configuration used is sufficient in representing the wetland distribution in these regions (underestimating the wetland seasonal cycle amplitude by 11.1, 19.5 and 10.1 ppb respectively, with correlation coefficients of 0.23, 0.01 and 0.31). We employ the Catchment-based Macro-scale Floodplain (CaMa-Flood) model to explicitly represent river and floodplain water dynamics and find that these JULES-CaMa-Flood simulations are capable of providing a wetland extent that is more consistent with observations in this regions, highlighting this as an important area for future model development.

Vegetation diversity in East African wetlands: Cocktail algorithms supported by a vegetation-plot database

Vegetation diversity in East African wetlands: Cocktail algorithms supported by a vegetation-plot database

Preliminary biological data of Sahel wetland ecosystems in Burkina Faso: Implications for ecological health assessment

Birds, amphibians, fish, and macroinvertebrates are useful indicators of ecological conditions and ensure considerable conservation value and tools for decision making in management of wetland ecosystems. However, the use of these organisms to monitor wetland ecosystems has rarely been explored in Western Africa. Whereas, we are currently facing to growing multiple anthropogenic pressures and climate warming that impact negatively our wetlands and the biodiversity. Notably, there is an urgent need of cost-effective tools for wetland ecosystems health assessment in Burkina Faso. In this study, we examined the taxonomic composition of birds, amphibians, fish, and macroinvertebrates and explored their potential use for monitoring wetland ecosystems. From our findings, measures of taxa composition and diversity respond to the gradients of anthropogenic alterations. Our results revealed that the highest diversity of fish and macroinvertebrates taxa was recorded in protected sites, whereas the lowest diversity was obtained in degraded sites. Additionally, the findings showed a strong and positive correlation between macroinvertebrates taxa and key water variables, whereas fish taxa were strongly correlated to xylal (deadwood) substrates. Most of bird’s species were recorded in tree-shrubs, and amphibians of protected wetlands were distinguished by identifying indicator taxa through indicator value index. African wetland ecosystems and biodiversity may be sustainably preserved through responsive monitoring programs of wetlands by limnologists.

Mapping African wetlands for 2020 using multiple spectral, geo-ecological features and Google Earth Engine

Wetlands provide numerous ecosystem services essential for biodiversity conservation, climate change mitigation, and human well-being. Nevertheless, there are still no complete and uniform wetland maps providing information on the location, distribution, size, and changing status of wetlands in Africa. In this study, we used 130,000 Landsat satellite images and 270,000 sampling points evenly distributed across Africa to classify wetlands with a random forest classifier based on the Google Earth Engine (GEE) cloud platform. This resulted in the first systematic and comprehensive map of existing wetlands in Africa that quantified the area and distribution of these wetlands at a spatial resolution of 30 m, with an overall wetland producer accuracy of 90.22 % and user accuracy of 95.74 %. To address the seasonal variation in African wetlands, we used a dynamic threshold segmentation method based on the Otsu method, which can extract the extent of wetlands under different periods more accurately based on Landsat time series and African phenology data. Our results show that the total African existing wetlands extent from 2019 to 2021 (here in 2020), was approximately 1,341,500 km2, excluding shallow marine waters, comprises 3.98 % of Africa's total land area. Of these wetlands, inland wetlands account for 81 %, and coastal wetlands account for 19 %. The wetlands in Africa were symmetrically distributed around the equator and decreased with increasing latitude, accounting for 97 % of the total wetland area being within the 20°N and 20°S latitudes. African marshes were highly dynamic, expanding by 92.22 % from the dry to wet season. Our study demonstrates the substantial potential of large data samples, multiple wetland classification features (spectral-temporal, topographic, and hydrological features), and random forest classification in GEE for large-scale wetland mapping. The resulting wetland maps provide new baseline data for large-scale monitoring of seasonal dynamics and long-term trends in African wetlands.

Using cloud computing techniques to monitor long-term variations in ecohydrological dynamics of small seasonally-flooded wetlands in semi-arid South Africa

• Semi-arid Southern African wetlands are lost due to unsustainable use and poor management. • Ramsar Convention on wetlands encourages development of frameworks for wetlands conservation. • The implementation of these frameworks is hindered by a dearth of high-resolution data. • Google Earth Engine (GEE) offers opportunities to address data challenges. • Findings underscores the relevance of GEE in evaluating wetland ecohydrological dynamics. Wetlands in drylands have high inter- and intra-annual ecohydrological variations that are driven to a great extent by climate variability and anthropogenic influences. The Ramsar Convention on Wetlands encourages the development of frameworks for national action and international cooperation for ensuring conservation and wise use of wetlands and their resources at local, national and regional scales. However, the implementation of these frameworks remains a challenge. This is mainly due to limited availability of high-resolution data and suitable big data processing techniques for assessing and monitoring wetland ecohydrological dynamics at large spatial scales, particularly in the sub-Saharan African region. The availability of cloud computing platforms such as Google Earth Engine (GEE) offers unique big data handling and processing opportunities to address some of these challenges. In this study, we applied the GEE cloud computing platform to monitor the long-term ecohydrological dynamics of a seasonally flooded part of the Nylsvley floodplain wetland complex in north-eastern South Africa over a 20-year period (2000–2020). The specific objectives of the study were 1) to evaluate wetland ecohydrological dynamics using the 20-year multi-date Landsat composite data coupled with the Random Forest machine learning algorithm, and 2) to establish the major drivers of wetland ecohydrological changes, using selected spectral indices (i.e. Normalised Difference Vegetation Index (NDVI), Normalised Difference Water Index (NDWI) and Normalised Difference Phenology Index (NDPI)) coupled with climate data. The ecohydrology of the wetland changed over time, with some classes increasing twice when compared to the previous measurement, while others decreasing significantly during the study period. Notably, the bare surface class increased at rates of 230% and 350% between 2006–2010 and 2016–2020, respectively. Moreover, the indices showed similar trends throughout the 20-year period, with NDWI having minimum values less than zero in all cases. This implied no surface inundation, although the presence of some wetland vegetation indicated seasonal to semi-permanent soil saturation conditions. A comparative analysis of climate data and remotely sensed indices showed that annual changes of precipitation and evapotranspiration were the main drivers of wetland ecohydrological variations. The findings of the study underscore the relevance of cloud computing artificial intelligence techniques, and particularly the GEE platform, in evaluating wetland ecohydrological dynamics for semi-arid southern African systems which are deteriorating due to the unsustainable use and poor management resulting from limited knowledge about their changes over time.

The potential distributions of African Azolla species and their implications for African wetland ecosystems for the future

AbstractClimate change is predicted to affect species in aquatic ecosystems. In Africa, factors that may influence the responses of aquatic species are poorly studied and challenging to predict. In this study, we examined the potential distribution of three aquatic fern species in the genus Azolla in Africa under projected climate change scenarios. MaxEnt was used to create ecological niche models of the three species using occurrence data and environmental variables. All models had satisfactory AUC and TSS values, indicating high prediction precision (AUC and TSS > 0.801). Results showed that elevation and precipitation were the most important variables limiting the species' expansion in the future. In addition, we observed significant variations in the climatic niches of the three species and their distinct climatically appropriate regions. The current potential distribution ranges for the species varied between 2,328,726 km2 and 4,026,363 km2. According to the model predictions for the current period, the potential range of Azolla species extended outside the known and recorded locations; however, under future climate conditions, the species were projected to lose between 8.1% and 48% of their suitable habitats due to climate change. Our findings can be used to develop sustainable conservation measures for aquatic species and raise awareness about the effects of climate change.

The alignment of projects dealing with wetland restoration and alien control: A challenge for conservation management in South Africa (with corrigendum)

An inventory of wetland vegetation across the country generated a list of the most common invasive alien plants across South Africa. Many of the plants on that list do not correspond with the priorities in the programmes for alien control across the country, as they are not listed on a government produced list that guides the priorities for alien control. We explore the reasons for this situation. We argue that because wetlands are such important parts of the landscape, invasive aliens in wetlands are of special concern, and there should be more alignment between alien control programmes and wetland rehabilitation programmes. This alignment starts by considering the full number of species that form a threat to wetland habitats, but also considers which pesticides to use, erosion and recolonisation in wetlands, planting indigenous vegetation after aliens have been removed, and strategising by working from upstream to downstream. Existing alien control programmes for specific grasses (some relatively new to the country and in the phase of early detection) and floating aquatic plants may guide how to tackle the invasions of grasses and forbs that have been established in South African wetlands for an extended period of time.Significance: Wetlands have a distinct set of alien invasive plants that affect their ecology and functioning and many of these plants are not listed as priorities in alien control programmes. Many restoration projects have an element of removing invasive plants and revegetating. Wetland restoration and alien control need to be integrated to preserve water resources.

A New Feature of Nesting Ecology in the Vulnerable European Turtle Dove: Nest Site and Nesting Tree Sharing with Coexisting Species at Three North African Wetlands

Investigations of niche splitting in the European turtle dove (Streptopelia turtur) have primarily addressed feeding habitats and foraging features and been limited to conspecific species, counting laughing dove and wood pigeon. The recent degradation of natural and suitable habitats for turtle doves, particularly in North Africa, would push this species to refuge in wetlands with a variety of other bird species. The understanding of potential cohabitation between doves and other species in these less disturbed ecosystems would help in the conservation measures of this declining game. This study, conducted from early March to September between 2015 and 2017, attempted to determine which species cohabit with turtle doves in three Northwest African wetlands in Morocco and how these species select nesting sites and trees. We used detrended corresponding analysis (DCA) to test the relevance of nest site and nesting tree variables in the nest distribution of the breeding species. The obtained results show a wide sharing of nest-niche between turtle doves and 7 breeding species, especially at the intermediate zone and downstream of the rivers. The lack of competition for food resources with neighbouring species may help in this harmonious sharing of both nesting sites and nesting trees. We further suggest guidelines for future research that seek to understand the spatiotemporal dynamics of species coexisting with turtle dove in the same habitats.

Monitoring human disturbance: Factors affecting escape behaviour of waterbirds in North African wetlands

AbstractUnderstanding the factors affecting escape behaviour in waterbirds can be useful in the management of human disturbances. A common measure of escape response is flight initiation distance (FID), the distance at which an approaching intruder disturbs an individual bird enough to make it move away. Here, we analyse the escape behaviour of a set of waterbirds for the first time within a North African context. We tested (one‐way ANOVA and general linear model) how FID varied with the area where waterbirds were temporal scale, distance at which the observer start approaching to the sampled birds, body size, flock size, species composition of the flock and foraging activity of the sampled birds. We collected 866 individual FIDs for 19 waterbird species wintering at two north Algerian wetlands (the Mekhada marsh, RAMSAR site, El‐taref District and the Sebkhet El‐Mahmel, unprotected wetland, Khenchela District). The obtained FIDs ranged from 32.6 m in smaller species as the Kentish plover Charadrius alexandrines to 167 m in larger ones as the ruddy shelduck Tadorna ferruginea. The obtained models stated that differences in the absolute levels of FIDs were mostly related to starting distance (Effect size = 0.62), to which is added a relatively little effect of wetland status, taxonomic differences, temporal scale, body size, flock size, species composition of the flock and bird activity. More specifically, FID was lower in smaller and homospecific groups at early winter in the protected wetland. Reserve managers in North Africa could use species and context‐specific FIDs in delineating appropriate buffer areas and in the design of management initiatives aimed at minimising eventual potential threat due to human disturbance and guaranteeing animal welfare and wildlife.

Wading into the debate on section 2(4)(r) of the National Environmental Management Act 107/1998 and its impact on policy formulation for the protection of South African wetlands

The loss and degradation of wetlands is an international dilemma and measures are put in place to ensure their conservation. In South Africa, the Department of Water and Sanitation’s Revised Strategic Plan 2015/2016 to 2019/2020 submitted that, of the 792 wetland ecosystems, 65 per cent have been identified as threatened and 48 per cent as critically endangered. A later revised plan provides that 50 per cent of South Africa’s wetlands have been lost.3 This is worrisome considering the all-important functions they fulfil and the benefits they provide.

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.This article is part of a discussion meeting issue ‘Rising methane: is warming feeding warming? (part 2)’.

Chronostratigraphic palaeo-climate phasing based on southern African wetlands: From the escarpment to the eastern seaboard

AbstractThis paper aims to identify chronostratigraphic palaeo-climatic boundaries based on proxy indications from mountain- and coastal wetlands in eastern South Africa and Lesotho. Phase boundaries were identified from timing of climate change inferred by proxies, as well as regime shifts in climate variability. Sometimes magnitude and/or frequency of change was also considered. Summarizing the common palaeo-climatic indications suggest the following chronostratigraphic climate phases: 25 to 18 ka, 18 to 15 ka, 15 to 11.5, 11.5 to 8 ka, 8 to 5.5 ka, 5.5 to 2 ka and 2 to 0 ka. The most robust boundaries were identified at 18 ka, 15 ka and 2 ka, i.e. these boundaries were supported by several proxies/sites. The other boundaries were less clearly detected from available proxies/sites and should be regarded tentative. The timing of a climate shift often coincides at coast and mountain sites. However, the climate conditions within each chronostratigraphic phase sometimes vary between coast and inland sites. The 25 to 18 ka phase was cool and dry with strong and frequent storms, followed by the ca. 18 to 15 ka period when conditions were less severe but still generally cool and dry. At ca. 15 to 11.5 ka several proxies infer warmer climate, with less winter rains. During 11.5 to 8 ka a general increase in wetness is inferred, followed by warming over the 8 to 5.5 ka phase. Between 5.5 and 2 ka a successive change towards wetter is indicated, although timing differ between sites. After 2 ka generally a more variable climate is seen, often with high magnitude shifts between dry and wet. The data resolution, i.e. the number of available wetland records, increases with time from very low during glacial times, to highest resolution during late Holocene. Geographically, sites in the mountain region are overrepresented compared to coastal sites.A comparison with coastal lake records suggests a more variable climate at coastal sites compared to mountain sites during mid- and late Holocene, although different proxy resolution and methodology cannot be ruled out as an explanation. A case study compares multiproxy records from Drakensberg (Sekhokong, Ntsikeni) and the coast (Mfabeni), discussing advantages and problems associated with proxy-comparisons within and between sites.

Assessing the effects of management and hydro-edaphic conditions on rice in contrasting East African wetlands using experimental and modelling approaches

Lowland rice yields in East Africa remain low despite favourable hydro-edaphic conditions as benefits from improved cultural management vary between and within wetland types and interactions are poorly understood. Hence, multi-year agronomic field experiments were established to assess the differential responses of lowland rice to management (rainfed 0 and 60 kg N ha−1, and irrigated 120 kg N ha−1 + 60 kg PK ha−1) and field position within a floodplain in Tanzania (fringe and middle positions) and an inland valley in Uganda (valley-fringe, mid-valley and valley-bottom positions). We then calibrated and validated the Agricultural Production System Simulator (APSIM), evaluated the importance of external water table data as model input and assessed the relative effects of water and N stress on yield as affected by wetland type and field position. Yields of 3.2–9.2 Mg ha−1 were attained in the floodplain and of 1.9–6.3 Mg ha−1 in the inland valley, highlighting the substantial scope to boost yields beyond current regional means of around 2 Mg ha−1. The model estimated grain yields in both wetlands well within the experimental uncertainty during model validation (n = 12, r2 = 0.76, RMSEa= 0.92 Mg ha−1 in the floodplain; n = 18, r2 = 0.71, RMSEa= 0.72 Mg ha−1 in the inland valley). Results further emphasised the importance of external water table data for sound model performance as they evidently alleviated seasonal droughts. Simulated abiotic stress patterns additionally highlighted hydro-edaphic differences from field positioning within and between both wetlands. While low soil N was generally the main yield constraint, water stress was comparably more pronounced in the inland valley and supplemental irrigation thus more beneficial on yield. Hydro-edaphic field conditions favoured rice production in the floodplain’s fringe with comparably lower N stress, while large spatial-temporal variabilities prevented a distinct delineation based on toposequential field positions in the inland valley.

Editorial: Towards the Sustainable Use of African Wetlands

Editorial: Towards the Sustainable Use of African Wetlands

Economic valuation of the averted degradation of the Vyeboom Wetland in the Theewaterskloof Dam catchment, South Africa

Wetlands within the catchments of water supply dams have potential to make important contributions to water-related ecosystem services, particularly water quality enhancement. Wetlands are facing growing threats and continuing degradation. There have been limited attempts at evaluating the contribution of South African wetlands, and their rehabilitation, for water quality enhancement and other water-related ecosystem services. A comprehensive and integrated wetland services economic assessment determined the value of the Vyeboom Wetland in the catchment of the Theewaterskloof Dam. The water of this dam is a significant contributor to the City of Cape Town’s water supply. The economic valuation model integrates hydrological, catchment status and economic models, with a long-term (80-year monthly) wetland water balance from a calibrated hydrological model as a driver for the nutrient removal aspect. The economic valuation builds on a water quality enhancement model, based on the minimisation of indirect use replacement cost principle, supplemented by a sediment retention and carbon storage assessment. The capability of the economic valuation model is illustrated by assessing the rehabilitation of a 25-ha area in the Vyeboom Wetland, which is currently intact, but is under threat of being severely degraded by the advancing erosion headcut. It was assumed that the current state of the Vyeboom Wetland is almost pristine (only 1 ha degraded), but that a further 24 ha would degrade over a period of 50 years, following spatial changes over time. By balancing the total investment in offsetting the potential loss in benefits, it is evident that an amount of 2.5 million ZAR could be afforded for rehabilitation. If, instead of a logistic degradation profile, the wetland is assumed to already be in a state of accelerated deterioration, the rehabilitation project budget for Vyeboom Wetland will increase once the other intrinsic benefits described are considered in the analysis.

Water-use characteristics of Palmiet (Prionium serratum), an endemic South African wetland plant

Palmiet, Prionium serratum, is an endemic wetland plant which dominates oligotrophic wetlands throughout the Cape Floristic Region, South Africa. Palmiet is often perceived as undesirable by landowners, in part because it is thought to have high water-use, although little is known about the water-use of this important wetland species. We estimated the water-use dynamics of Palmiet at the leaf scale, using stomatal conductance measurements, and at the wetland scale, by modelling evapotranspiration using remote sensing and an energy-balance model. Factors that influenced Palmiet water-use were also considered, and seasonal variations were analysed. The aim was to estimate Palmiet wetland water-use, and to develop a set of crop factors (Kc) for use in hydrological modelling of catchments containing Palmiet wetlands. Results show that Palmiet has a comparatively low stomatal conductance (11–152 mmol∙m-2∙s-1), which was lower in summer than winter, and moderate evapotranspiration for a riparian species (1 220 mm∙a-1 compared to a local reference evapotranspiration of 1 302 mm∙a-1 and A-Pan evaporation of 2 809 mm∙a-1), which was higher in summer (more energy to drive evapotranspiration and higher vapour pressure deficits). Morphological and physiological adaptations to nutrient poverty or periodic drought are suggested theories which may explain the controls on transpiration for Palmiet.