Definitions and Mapping of East African Wetlands: A Review <s> Review of Wetlands Definitions <s> From foreword: "This report represents the most current methodology available for wetland classification and culminates a long-term effort involving many wetland scientists." <s> BIB001 </s> Definitions and Mapping of East African Wetlands: A Review <s> Review of Wetlands Definitions <s> A global data base of wetlands at 1° resolution has been developed from the integration of three independent global, digital sources: (1) vegetation, (2) soil properties and (3) fractional inundation in each 1° cell. The integration yielded a global distribution of wetland sites identified with in situ ecological and environmental characteristics. The wetland sites have been classed into five major wetland groups on the basis of environmental characteristics governing methane emissions. The global wetland area derived in this study is ∼5.3 × 1012m2, approximately twice the wetland area previously used in methane-emission studies. Methane emission was calculated using methane fluxes for the major wetland groups, and simple assumptions about the duration of the methane production season. The annual methane emission from wetlands is ∼110 Tg, well within the range of previous estimates (11-300 Tg). Tropical/subtropical peat-poor swamps from 20°N-30°S account from ∼30% of the global wetland area and ∼25% of the total methane emission. About 60% of the total emission comes from peat-rich bogs concentrated from 50°-7O°N, suggesting that the highly seasonal emission from these ecosystems is the major contributor to the large annual oscillations observed in atmospheric methane concentrations at these latitudes. <s> BIB002 </s> Definitions and Mapping of East African Wetlands: A Review <s> Review of Wetlands Definitions <s> A global data set on the geographic distribution and seasonality of freshwater wetlands and rice paddies has been compiled, comprising information at a spatial resolution of 2.5° by latitude and 5° by longitude. Global coverage of these wetlands total 5.7×106 km2 and 1.3×106 km2, respectively. Natural wetlands have been grouped into six categories following common terminology, i.e. bog, fen, swamp, marsh, floodplain, and shallow lake. Net primary productivity (NPP) of natural wetlands is estimated to be in the range of 4–9×1015 g dry matter per year. Rice paddies have an NPP of about 1.4×1015 g y−1. Extrapolation of measured CH4 emissions in individual ecosystems lead to global methane emission estimates of 40–160 Teragram (1 Tg=1012 g) from natural wetlands and 60–140 Tg from rice paddies per year. The mean emission of 170–200 Tg may come in about equal proportions from natural wetlands and paddies. Major source regions are located in the subtropics between 20 and 30° N, the tropics between 0 and 10° S, and the temperate-boreal region between 50 and 70° N. Emissions are highly seasonal, maximizing during summer in both hemispheres. The wide range of possible CH4 emissions shows the large uncertainties associated with the extrapolation of measured flux rates to global scale. More investigations into ecophysiological principals of methane emissions is warranted to arrive at better source estimates. <s> BIB003 </s> Definitions and Mapping of East African Wetlands: A Review <s> Review of Wetlands Definitions <s> Review: Wetlands In Danger: A World Conservation Atlas Edited by Patrick Dugan Reviewed by Daniel L. Tufford University of South Carolina Dugan, Patrick , editor. Wetlands In Danger: A World Conservation Atlas. New York: Oxford University Press, 1993. 192 pp. US $35.00 cloth ISBN:0-19-520942-7. For sheer excellence of presentation, Wetlands In Danger exceeds the value of its sale price. The work is well-organized and illustrated with high-quality photography. Anyone interested in wetland issues will find useful information here. In addition to physical geography, the authors discuss wetland biology and ecology, anthropogenic pressures on wetlands, and the political, economic, and cultural geography of wetlands. The first four chapters are an introduction to the atlas itself. The first chapter defines wetlands and gives an overview of each type. The authors use the wetland definition agreed to at the 1971 Ramsar convention sponsored by the International Union for Conservation of Nature and Natural Resources (IUCN). Many readers will be unfamiliar with the inclusion of lakes as wetlands, but the Ramsar definition includes water up to 6 meters deep. The second chapter introduces wetland ecology, a science still viewed as fundamentally biological. This chapter effectively shows that landscape- scale hydrologic and geochemical processes are essential elements of the role of wetlands in both local and regional ecology. However, the biological ecology of wetlands remains the most obvious and most easily explained to a diverse audience. Thus, the third chapter discusses the unique life in wetlands and the unique role wetlands play in the life cycle of animals not confined to a wetland habitat. The fourth chapter discusses the historical causes and extent of wetland loss worldwide, including the once prevailing notion that wetland use for agriculture was a positive expression of human control over nature. Here, the theme of the book is clarified. Wetland loss is occurring in devastating proportions, and we are only beginning to understand the <s> BIB004 </s> Definitions and Mapping of East African Wetlands: A Review <s> Review of Wetlands Definitions <s> The global distribution of potential wetlands and their methane (CH4) emissions at the present-day and the Last Glacial Maximum (LGM) are estimated using a GCM simulation of LGM climate, a vegetation model, and simple algorithms for determining wetland area based on topography and soil moisture, and CH4 emissions based on ecosystem carbon turnover in wet soils. LGM wetland area was 15% larger than present, but CH4 emissions were 24% less. Extensive wetlands were simulated on the exposed continental shelves. The soil CH4 sink was simulated as 14 Tg now but <0.5 Tg at the LGM. CH4 emissions at LGM were limited by substrate availability, in turn due to low atmospheric CO2. The glacial-interglacial change in atmospheric CH4 concentration cannot be completely attributed to changes in the wetland source. <s> BIB005 </s> Definitions and Mapping of East African Wetlands: A Review <s> Review of Wetlands Definitions <s> Studies of wetlands in Australia, as in other countries, have taken a wide variety of approaches to defining, surveying and classifying these environments. Past and current approaches in Australia are reviewed for each of the States and Territories which provide the context for much of the natural resource investigation in the country. While there are obvious advantages of national, and perhaps international, agreement on definition and types of wetlands, a variety of approaches to inventory and classification will always be necessary for particular purposes. More fundamental than general agreement on approaches is the need for wetland scientists and managers to maximise the accuracy of survey information, to test the assumptions involved in the use of classifications, and to ensure that the classifications they use are the most appropriate for their purposes. The issue of a global wetland classification scheme is discussed on the basis of a representative range of views by Australian wetland workers. <s> BIB006 </s> Definitions and Mapping of East African Wetlands: A Review <s> Review of Wetlands Definitions <s> A geomorphic classification of inland wetlands on criteria other than vegetation is proposed, based on their host landform and degree of wetness. Thus, the classification addresses the underlying structure of most inland wetlands, i.e. their landform setting and their various types of hydroperiod. Landforms host to wetlands include: basins, channels, flats, slopes and hills/highlands. Degrees of wetness include: permanent, seasonal or intermittent inundation, and seasonal waterlogging. From combining the landform type with hydroperiod, thirteen primary types of common wetlands are recognized: 1. permanently inundated basin = lake; 2. seasonally inundated basin = sumpland; 3. intermittently inundated basin = playa; 4. seasonally waterlogged basin = dampland; 5. permanently inundated channel = river; 6. seasonally inundated channel = creek; 7. intermittently inundated channel = wadi; 8. seasonally waterlogged channel = trough; 9. seasonally inundated flat = floodplain; 10. intermittently inundated flat = barlkarra; 11. seasonally waterlogged flat = palusplain; 12. seasonally waterlogged slope = paluslope; and 13. seasonally waterlogged highlands = palusmont. Water, landform and vegetation descriptors can augment the nomenclature of the primary units: e.g. salinity of water; size and shape of landform; and organisation, structure and floristics of vegetation. The classification can be used in many settings, regardless of climate and vegetation types. Using the approach adopted in this classification, in principle, more landform types and degrees of wetness, if necessary, can be added to the system to define additional wetland types. <s> BIB007 </s> Definitions and Mapping of East African Wetlands: A Review <s> Review of Wetlands Definitions <s> Abstract Drawing upon a variety of existing maps, data and information, a new Global Lakes and Wetlands Database (GLWD) has been created. The combination of best available sources for lakes and wetlands on a global scale (1:1 to 1:3 million resolution), and the application of Geographic Information System (GIS) functionality enabled the generation of a database which focuses in three coordinated levels on (1) large lakes and reservoirs, (2) smaller water bodies, and (3) wetlands. Level 1 comprises the shoreline polygons of the 3067 largest lakes (surface area ≥50 km2) and 654 largest reservoirs (storage capacity ≥0.5 km3) worldwide, and offers extensive attribute data. Level 2 contains the shoreline polygons of approx. 250,000 smaller lakes, reservoirs and rivers (surface area ≥0.1 km2), excluding all water bodies of level 1. Finally, level 3 represents lakes, reservoirs, rivers, and different wetland types in the form of a global raster map at 30-second resolution, including all water bodies of levels 1 and 2. In a validation against documented data, GLWD proved to represent a comprehensive database of global lakes ≥1 km2 and to provide a good representation of the maximum global wetland extent. GLWD-1 and GLWD-2 establish two global polygon maps to which existing lake registers, compilations or remote sensing data can be linked in order to allow for further analyses in a GIS environment. GLWD-3 may serve as an estimate of wetland extents for global hydrology and climatology models, or to identify large-scale wetland distributions and important wetland complexes. <s> BIB008 </s> Definitions and Mapping of East African Wetlands: A Review <s> Review of Wetlands Definitions <s> We describe a robust methodology to detect and estimate the size of temporary wetlands using AVHRR satellite data within large areas (106 km2) of the arid zone. The methodology uses spectral matching and exclusion of salt surfaces to discriminate between water and non-water surfaces. The status of 115 lakes was used to evaluate the methodology. A classification accuracy of 98% was achieved for wetlands >120 ha, with accuracy of area estimates varying with the size and shape of individual lakes. Spectral matching of AVHRR data has methodological and cost advantages over the use of higher spatial resolution data for understanding changes in the distribution of water at broad scales. <s> BIB009 </s> Definitions and Mapping of East African Wetlands: A Review <s> Review of Wetlands Definitions <s> article i nfo This study reports results of a classification tree approach to mapping the wetlands of the Congo Basin, focusing on the Cuvette Centrale of the Congo River watershed, an area of 1,176,000 km 2 . Regional expert knowledge was used to train passive optical remotely sensed imagery of the Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) sensors, JERS-1 active radar L-band imagery, and topographical indices derived from 3 arc sec elevation data of the Shuttle Radar Topography Mission (SRTM). All data inputs were resampled to a common 57 m resolution grid. A classification tree bagging procedure was employed to produce a final map of per-grid cell wetland probability. Thirty bagged trees were ranked and the median result was selected to produce the final wetland probability map. Thresholding the probability map at < 0.5 yielded a proportion of wetland cover for the study area of 32%, equivalent to 360,000 km 2 . Wetlands predominate in the CARPE Lake Tele-Lake Tumba landscape located in the western part of the Democratic Republic of the Congo and the south-eastern Republic of Congo, where they constitute 56% of the landscape. Local topography depicting relative elevation for sub-catchments proved to be the most valuable discriminator of wetland cover. However, all sources of information (i.e. optical, radar and topography) featured prominently in contributing to the classification tree procedure, reinforcing the idea that multi-source data are useful in the characterization of wetland land cover. The method employed freely available data and a fully automated process, except for training data collection. Comparisons to existing maps and in situ field observations indicate improvements compared to previous efforts. <s> BIB010
The term wetlands groups several types of moist environments that manifest in a wide range of landscape units BIB001 . According to the majority of the references examined, wetlands can be described as having conditions of soil or bedrock formation and hydrology in common that, together, cause and reflect the abundance of water over a time span sufficient to support internally diverse natural (riparian) vegetation that differs from the surrounding uplands. This definition reflects the three core components of wetland formation: hydrology, soils and vegetation [24] . Aside from these fundamental elements, wetland environments display immense variation over the globe and many "…have more in common with non-wetland habitats than with each other" BIB006 . In addition, wetland surface covers may be internally spatially fragmented and temporally variable  . Wetlands are azonal ecosystems present throughout the world, and their formation is not primarily conditioned by climate BIB004 . At a global level, however, wetland surface area and expression are dependent on climatic zones [24, BIB004 BIB007 BIB008 BIB002 BIB003 , and wetland nomenclature and descriptors differ according to region and language [32] . A comprehensive understanding of wetlands must be established along with a common, uniformly applicable definition of wetlands if these environments are to be protected and conserved throughout the world. Great regional variation is seen throughout the world in perception, understanding and description of different wetland environments, and linguistic barriers are a hindrance in wetland research. Table 1 provides an excerpt and an exemplary grouping of different wetland terms as given by Mitsch and Gosselink [24] . The diversity in wetland terminology is described as useful in understanding subtle differences among the diverse wetlands ecosystems found in different locales by Mitsch and Gosselink [24] , although the authors also emphasize that the diversity of terms and the lack in standardization can be confusing for the international scientific community [24] . The need to harmonize knowledge about and understanding of wetlands is critical for large-scale, cross-border inventories. In his discussion of wetland definitions, Lewis states that "…some critical words can be interpreted by the application of common sense"  . This is questionable in the case of cross-boundary consistent maps, as notions of common sense may differ among interpreters from different cultures speaking different languages. Ideally, a definition should be precise and avoid vague terms, like normally or many times, which lead to broad interpretation. Where a definition may form the basis for legally-binding decisions (e.g., the protected area of a wetland, which carries use restrictions), imprecise formulations should be avoided. Concise definitions are also vital in the application of remote sensing for large-scale land use/land cover inventories. Automated decision-rule classifiers require unambiguous definitions and descriptors to allow accurate identification and unequivocal partitioning of landscape units. The process of delineating wetlands from uplands is also inherently linked to a wetland's definition. Semeniuk and Semeniuk BIB007 show that wetlands need to be demarcated relative to the environments in which they are manifest. Here, the question of scale is of interest. A regional or worldwide map that includes climatic gradients and diverse wetland types and formations must incorporate a definition that is valid in all relevant environmental settings. In contrast, a local wetland may be separated from the neighbouring upland by a less complicated interpretation of land surface data (particularly relative to wetland/upland surface moisture condition). Soil water moves along hydrostatic pressure gradients  ; this is reflected in wetlands' dynamic surface gradients and complicates the question of wetland boundaries. Wetlands typically develop in shallow ground BIB005 BIB010 , and slight changes in soil water availability can cause substantial changes in wetland extent. Many parts of wetlands undergo seasonal saturation and desiccation, as they are located in transition zones between permanently dry uplands and the permanent aquatic surfaces of lakes, ponds or rivers. Some authors define wetlands exclusively by the feature of the dynamic change in water availability (e.g.,   BIB009 ). Semeniuk and Semeniuk BIB007 proposed that the "…boundary of a wetland should encompass all that terrain that conforms to the definition of a 'wet land'", including seasonally-inundated and seasonally-waterlogged zones. However, it should be understood that concise wetland boundaries, "…immovable (and) sharply defined on paper and on the ground…" are a "…legal fiction" BIB006 . For this reason, legally-binding, jurisdictional wetland boundary delineations will continue to require case-specific, high-resolution in situ ancillary data that cannot be provided by mapping efforts conducted solely using remote sensing techniques [40] . The definition and delineation of wetlands are controversial issues, and this is reflected in the scientific literature on the topic. Figure 1 summarizes our examination of the wetland literature regarding the 'applied' definitions of wetlands. Figure 1a groups literature as publications on wetlands in general and consists mainly of monographs on wetlands and global-scale wetland studies. Figure 1b includes literature that documents studies of wetland analysis methodologies or those that are focused on applications smaller than the global scale, designating these works as wetland case studies. This quantitative analysis confirms that a high proportion of literature related to wetlands, especially remote sensing-based case studies, includes no, or only an indirect, definition of the land cover class of interest. This supports Finlayson and Spiers  , who critically observed that "…only 30% of (wetland inventory) sources defined the wetlands they covered, and for over one-third (34%) , no definition could even be inferred from the material presented."  . ** Wetland definition of the United States Fish and Wildlife Service BIB001 . *** Wetland definition of the 'Small Wetlands in East Africa' Project  . We used 245 references for the analysis discussed above. To better understand how these existing definitions of wetlands relate to specific applications, a classified matrix of definitions was compiled (Figure 2 ). From the 245 references, 103 different definitions of wetlands were identified and classified. These definitions are plotted by theme and study spatial scale. Case examples are shown in Table 2 . Definitions A, B and C are considered as concise definitions for specific surfaces under study. These three groups include over 60% (64/103) of all identified definitions. A definitions are not comprehensive, as only a wetland subtype (e.g., mires, floodplains, etc.) is defined. B and C are considered as definitions appropriate for wetlands mapping. One of the most important wetland definitions was formulated at the Ramsar Convention: "(W)etlands are areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres."  . This definition is applied internationally and at all spatial scales (X, Y and Z in Figure 2 ). D and E comprise cases where surface properties, typically vegetation or land cover groups of wetlands or analytical identification of wetlands are applied. These cannot be regarded as valid definitions of wetlands, but rather serve as surrogates. The inductive approach of these studies presents a delineation of wetlands based on analytical results, but does not provide a holistic understanding of what wetlands are. As shown in Figure 2 , such cases appear frequently in remote sensing case studies. 