Matthew Saunders

Functioning and dynamics of wetland vegetation of Lake Victoria: an overview

The aquatic macrophytic vegetation constituting the wetlands situated along the coast of Lake Victoria provides valuable services to both local and regional communities as well as an important ecological function through the transition between terrestrial and aquatic ecosystems. The wetland vegetation is typically rooted in the substrate on the landward side of the lake, but forms a floating mat towards the middle of the wetland and at the wetland/lake interface. Cyperus papyrus and Miscanthidium violaceum vegetation typically dominate the permanently inundated wetland areas along most of the shores of Lake Victoria. Due to the prevailing climatic and hydrological catchment conditions, these macrophytic plants (papyrus in particular) tend to exhibit high net productivity and nutrient uptake which strongly influences both wetland status and lake water quality. In addition, these wetlands provide important economic livelihoods for the local populations. The integrity and physical structure of these wetlands strongly influences their associated mass transport mechanisms (water, nutrients and carbon) and ecosystem processes. Wetland degradation in Africa is an increasing problem, as these ecosystems are relied upon to attenuate industrial, urban and agricultural pollution and supply numerous services and resources. In an integrated project focused on the wetlands of Lake Victoria, the ecological and economic aspects of littoral wetlands were examined and new instruments developed for their sustainable management.

Toward a consistency cross-check of eddy covariance flux-based and biometric estimates of ecosystem carbon balance,.

Quantification of an ecosystems carbon balance and its components is pivotal for understanding both ecosystem functioning and global cycling. Several methods are being applied in parallel to estimate the different components of the CO2 balance. However, different methods are subject to different sources of error. Therefore, it is necessary that site level component estimates are cross-checked against each other before being reported. Here we present a two-step approach for testing the accuracy and consistency of eddy covariance–based gross primary production (GPP) and ecosystem respiration (Re) estimates with biometric measurements of net primary production (NPP), autotrophic (Ra) and heterotrophic (Rh) respiration. The test starts with closing the CO2 balance to account for reasonable errors in each of the component fluxes. Failure to do so within the constraints will classify the flux estimates on the site level as inconsistent. If the CO2 balance can be closed, the test continues by comparing the closed site level Ra/GPP with the Rh/GPP ratio. The consistency of these ratios is then judged against expert knowledge. Flux estimates of sites that pass both steps are considered consistent. An inconsistent ratio is not necessarily incorrect but provides a signal for careful data screening that may require further analysis to identify the possible biological reasons of the unexpected ratios. We reviewed the literature and found 16 sites, out of a total of 529 research forest sites, that met the data requirements for the consistency test. Thirteen of these sites passed both steps of the consistency cross-check. Subsequently, flux ratios (NPP/GPP, Rh/NPP, Rh/Re, and Re/GPP) were calculated for the consistent sites. Similar ratios were observed at sites which lacked information to check consistency, indicating that the flux data that are currently used for validating models and testing ecological hypotheses are largely consistent across a wide range of site productivities. Confidence in the output of flux networks could be further enhanced if the required fluxes are independently estimated at all sites for multiple years and harmonized methods are used.

Simulating the impacts of land use in Northwest Europe on Net Ecosystem Exchange (NEE): The role of arable ecosystems, grasslands and forest plantations in climate change mitigation

In this study, we compared measured and simulated Net Ecosystem Exchange (NEE) values from three wide spread ecosystems in the southeast of Ireland (forest, arable and grassland), and investigated the suitability of the DNDC (the DeNitrification-DeComposition) model to estimate present and future NEE. Although, the field-DNDC version overestimated NEE at temperatures >5 °C, forest-DNDC under-estimated NEE at temperatures >5 °C. The results suggest that the field/forest DNDC models can successfully estimate changes in seasonal and annual NEE from these ecosystems. Differences in NEE were found to be primarily land cover specific. The annual NEE was similar for the grassland and arable sites, but due to the contribution of exported carbon, the soil carbon increased at the grassland site and decreased at the arable site. The NEE of the forest site was an order of magnitude larger than that of the grassland or arable ecosystems, with large amounts of carbon stored in woody biomass and the soil. The average annual NEE, GPP and Reco values over the measurement period were -904, 2379 and 1475 g C m(-2) (forest plantations), -189, 906 and 715 g C m(-2) (arable systems) and -212, 1653 and 1444 g C m(-2) (grasslands), respectively. The average RMSE values were 3.8 g C m(-2) (forest plantations), 0.12 g C m(-2) (arable systems) and 0.21 g C m(-2) (grasslands). When these models were run with climate change scenarios to 2060, predictions show that all three ecosystems will continue to operate as carbon sinks. Further, climate change may decrease the carbon sink strength in the forest plantations by up to 50%. This study supports the use of the DNDC model as a valid tool to predict the consequences of climate change on NEE from different ecosystems.

Convergence of potential net ecosystem production among contrasting C3 grasslands

Metabolic theory and body size constraints on biomass production and decomposition suggest that differences in the intrinsic potential net ecosystem production (NEPPOT ) should be small among contrasting C3 grasslands and therefore unable to explain the wide range in the annual apparent net ecosystem production (NEPAPP ) reported by previous studies. We estimated NEPPOT for nine C3 grasslands under contrasting climate and management regimes using multiyear eddy covariance data. NEPPOT converged within a narrow range, suggesting little difference in the net carbon dioxide uptake capacity among C3 grasslands. Our results indicate a unique feature of C3 grasslands compared with other terrestrial ecosystems and suggest a state of stability in NEPPOT due to tightly coupled production and respiration processes. Consequently, the annual NEPAPP of C3 grasslands is primarily a function of seasonal and short-term environmental and management constraints, and therefore especially susceptible to changes in future climate patterns and associated adaptation of management practices.

Tools for Wetland Ecosystem Resource Management in East Africa: Focus on the Lake Victoria Papyrus Wetlands

Lake Victoria is an ecological and economic resource of primary value. The wetlands that cover much of the lake shoreline provide a fundamental service in maintaining water quality, fisheries productivity and local meteorology. The management and maintenance of these papyrus wetlands are basic for any hope of controlling or reversing the eutrophication of the lake waters, in particular in the vital inshore area where fisheries are most important. In these areas, the presence of coastal wetlands strongly influences the optical and trophic characteristics of the inshore waters. Local water and energy exchanges are also strongly influenced by wetland conditions. The role of latent heat exchange in maintaining the micro-meteorological of the local watershed is influenced by the wetland vegetation and extension.

The socioeconomic and environmental impacts of wood energy value chains in Sub-Saharan Africa: a systematic map protocol

BackgroundThe vast majority of households in Sub-Saharan Africa (SSA) depend on wood energy—comprising firewood and charcoal—for their daily energetic needs. Such consumption trends are expected to remain a common feature of SSA’s wood energy production and supply chains, at least in the short- to medium-terms. Notwithstanding its importance, wood energy generally has low priority in SSA national policies. However, the use of wood energy is often considered a key driver of unsustainable management and negative environmental consequences in the humid and dry forests.To date, unsystematic assessments of the socio-economic and environmental consequences of wood energy use have underplayed its significance, thus further hampering policy debates. Therefore, a more balanced approach which considers both demand and supply dynamics is needed. This systematic map aims at providing a comprehensive approach to understanding the role and impacts of wood energy across all regions and aspects in SSA.MethodsThe objective of this systematic map is to collate evidence from studies of environmental and socio-economic impacts of wood energy value chains, by considering both demand and supply within SSA. The map questions are framed using a Populations, Exposure, Comparators and Outcomes (PECO) approach. We name the supply and demand of wood energy as the “exposure,” composed of wood energy production, harvesting, processing, and consumption. The populations of interest include both the actors involved in these activities and the forest sites where these activities occur. The comparator is defined as those cases where the same wood energy activities occur with i) available/accessible alternative energy sources, ii) regulatory frameworks that govern the sector and iii) alternative technologies for efficient use. The outcomes of interest encompass both socioeconomic and environmental impacts that can affect more than the populations named above. For instance, in addition to the direct socioeconomic impacts felt by participants in the wood energy value chain, forest dwellers may experience livelihood changes due to forest degradation caused by external harvesters. Moreover, intensified deforestation in one area may concurrently lead to forest regeneration in another.

Evolving interpolating models of net ecosystem CO 2 exchange using grammatical evolution

Accurate measurements of Net Ecosystem Exchange of CO2 between atmosphere and biosphere are required in order to estimate annual carbon budgets. These are typically obtained with Eddy Covariance techniques. Unfortunately, these techniques are often both noisy and incomplete, due to data loss through equipment failure and routine maintenance, and require gap-filling techniques in order to provide accurate annual budgets. In this study, a grammar-based version of Genetic Programming is employed to generate interpolating models for flux data. The evolved models are robust, and their symbolic nature provides further understanding of the environmental variables involved.

The potential use of papyrus (Cyperus papyrus L.) wetlands as a source of biomass energy for sub-Saharan Africa

Four of five people in sub‐Saharan Africa rely on the traditional use of solid biomass, mainly fuelwood, for cooking. In some areas, the current rate of fuelwood consumption will exhaust biomass reserves within the next decade or two. A largely unrecognized source of biomass are tropical wetland ecosystems which have been shown to be some of the most productive ecosystems globally, exhibiting rates of net primary productivity comparable with high‐input, intensively managed agricultural systems. Papyrus (Cyperus papyrus L.) is an emergent sedge with C4 photosynthesis which is native to the wetlands, river valleys and lakes of central, eastern and southern Africa. The mean standing dry matter of culms and umbels measured at a number of locations throughout East Africa is 38.3 ± 21.6 tDM ha−1, and the aerial net primary productivity ranges between 25.9 and 136.4 tDM ha−1 yr−1. Papyrus vegetation can be harvested by hand and stacked on the rhizome mat for partial air‐drying, and it has been demonstrated that an annual harvesting regime has no negative impacts on long‐term productivity. The use of papyrus as a biofuel for cooking and heating depends on converting it to a suitably combustible form, such as compressed or carbonized briquettes with a calorific value approximately one‐third less than wood charcoal. While papyrus has significant potential as a biofuel, we argue that an integrated management and decision‐making framework for the sustainable utilization of papyrus wetlands is required, in which all ecosystem services including the provision of biomass energy need to be assessed. Sustainability of papyrus wetlands requires management which combines the strength of traditional communal governance and modern legislation to promote its utilization. In this way, local communities can benefit from the inherent advantages of tropical wetlands as very productive ecosystems.

Estimating terrestrial gross primary productivity in water limited ecosystems across Africa using the Southampton Carbon Flux (SCARF) model

The amount of carbon uptake by vegetation is an important component to understand the functioning of ecosystem processes and their response/feedback to climate. Recently, a new diagnostic model called the Southampton Carbon Flux (SCARF) Model driven by remote sensing data was developed to predict terrestrial gross primary productivity (GPP) and successfully applied in temperate regions. The model is based on the concept of quantum yield of plants and improves on the previous diagnostic models by (i) using the fraction of photosynthetic active radiation absorbed by the photosynthetic pigment (FAPARps) and (ii) using direct quantum yield by classifying the vegetation into C3 or C4 classes. In this paper, we calibrated and applied the model to evaluate GPP across various ecosystems in Africa. The performance of the model was evaluated using data from seven eddy covariance flux tower sites. Overall, the modelled GPP values showed good correlation (R>0.59, p<0.0001) with estimated flux tower GPP at most sites (except at a tropical rainforest site, R=0.38, p=0.02) in terms of their seasonality and absolute values. Mean daily GPP across the investigated period varied significantly across sites depending on the vegetation types from a minimum of 0.44gCm-2day-1 at the semi-arid and sub-humid savanna grassland sites to a maximum of 9.86gCm-2day-1 at the woodland and tropical rain forest sites. Generally, strong correlation is observed in savanna woodlands and grasslands where vegetation follows a prescribed seasonal cycle as determined by changes in canopy chlorophyll content and leaf area index. Finally, the mean annual GPP value for Africa predicted by the model was 35.25PgCyr-1. The good performance of the SCARF model in water-limited ecosystems across Africa extends its potential for global application.

Replication Data for: Evidence Based Forestry on socio-economic and environmental consequences of wood energy

This systematic map aims at providing a comprehensive approach to understanding the role and impacts of wood energy across all regions and aspects in Sub-Saharan Africa.