The species diversity data of seven globally important wetlands (Canadian peatlands, Florida Everglades, Pantanal, Okavango Delta, Sundarban, Tonle Sap, and Kakadu National Park) were compared. The available data for most groups of lower plants and animals are insufficient for a comparative analysis. Data on vertebrates and higher plants are more complete and show high species diversity. The large habitat diversity allows the coexistence of amphibious species with many immigrants from connected deepwater and terrestrial habitats. Several of these immigrant species find an important permanent refuge in the wetlands; some use the wetlands as periodic habitats. All wetlands are important habitats for long-distance migratory bird species. The species composition reflects the biogeography of the respective regions, e.g. the high diversity of large ungulates characteristic for Africa is also found in the Okavango Delta in Botswana, and the high fish species diversity typical for South America is also reflected in the Pantanal in Brazil. The number of endemic species in most wetlands is low, except in the Everglades. The low numbers are explained to some extent by the dramatically changing paleo-climatic conditions that increased extinction rates, but also by the connection with large river systems that act as migratory and transport routes for species from large catchment areas and hinder the genetic isolation of wetland populations. The high number of endemic species in the Everglades is explained in part by its isolation on a peninsula. The relatively low nutrient status of most wetlands does not negatively affect species diversity and often leads to high animal densities. Large populations of endangered or rare species in all wetlands contribute to the great value of these areas for biodiversity protection. All wetlands are subjected to an increasing degree to human pressure through, e.g. water abstraction, changes in the natural flood regime, land reclamation, pollution, over-utilization of natural resources, and poaching. High habitat diversity and a pronounced natural disturbance regime make some of the wetlands vulnerable to invasion by exotic species, as shown for the Everglades. All studied wetlands are at least in part protected by national and international conventions. This provides perspectives for long-term protection only to a limited extent because of major environmental changes in their surroundings. Further strong efforts are required to match protection and sustainable use of the wetlands proper with management activities in their catchments

In the Okavango Delta (about 28,000 km 2 ) the number of identifi ed species is 1,300 for plants, 71 for fi sh, 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 fl oodplains, 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 signifi cant 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 Southcentral 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 fl ooding patterns that in turn force constant changes in patterns of plant succession and dependent animals. Temporal variations in fl ooding 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.

This paper summarizes the importance of climate on tropical wetlands. Regional hydrology and carbon dynamics in many of these wetlands could shift with dramatic changes in these major carbon storages if the inter-tropical convergence zone (ITCZ) were to change in its annual patterns. The importance of seasonal pulsing hydrology on many tropical wetlands, which can be caused by watershed activities, orographic features, or monsoonal pulses from the ITCZ, is illustrated by both annual and 30-year patterns of hydrology in the Okavango Delta in southern Africa. Current studies on carbon biogeochemistry in Central America are attempting to determine the rates of carbon sequestration in tropical wetlands compared to temperate wetlands and the effects of hydrologic conditions on methane generation in these wetlands. Using the same field and lab techniques, we estimated that a humid tropical wetland in Costa Rica accumulated 255 g C m -2 year -1 in the past 42 years, 80% more than a similar temperate wetland in Ohio that accumulated 142 g C m -2 year -1 over the same period. Methane emissions averaged 1,080 mg-C m -2 day -1 in a seasonally pulsed wetland in western Costa Rica, a rate higher than methane emission rates measured over the same period from humid tropic wetlands in eastern Costa Rica (120-278 mg-C m -2 day -1 ). Tropical wetlands are often tuned to seasonal pulses of water caused by the seasonal movement of the ITCZ and are the most likely to be have higher fire frequency and changed methane emissions and carbon oxidation if the ITCZ were to change even slightly.

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The succession. biomass and production of phytoplanktm was studied during 7 years in two Swedish forest lakes in relation t o nutrients. temperature and light climate . The succession of species and taxonomic groups can be described by their different demands concerning temperaturo and light climate while the total biomass is correlated to light climate and total phosphorus concentration . Differences in production between the two lakes can be explained by different taxonomic groups having different efficiencies .