The potential effect of wetland rehabilitation on wetland ecosystem goods and services : an investigation of three South African case studies.

Abstract

Wetlands supply very diverse and important goods and services to society. Goods are tangible resources, e.g. harvestable resources, cultivated foods, water for human use, cultural significance, tourism and recreation, and education. Services are less tangible and include: flood attenuation, streamflow regulation, sediment trapping, phosphate and nitrate assimilation, toxicant assimilation, erosion control, carbon storage and biodiversity maintenance. The literature reviewed confirms that these goods and services are dependent to varying degrees on the hydrology of a wetland. Dependence is due to the fact that hydrology is probably the single most important determinant of the establishment and maintenance of specific types of wetlands and process occurring in wetlands. Ecosystem goods and services are normally lost during degradation of a wetland and to restore them is a challenge. Causes of degradation could result from chemical, biological and physical processes. In South Africa physical processes such as gully erosion are one of the greatest causes of wetland degradation. Wetland rehabilitation generally seeks to retrieve the natural water regime or hydrology of a degraded wetland, with the aim of retrieving the ecosystem goods and services that were lost during degradation. The literature shows that there is a clear link between wetland rehabilitation, hydrology and ecosystem goods and services. To better understand this relationship, three selected South African wetlands were examined. The water tables and hydrological zonation of these wetlands were described and WET-EcoServices was used as a means of determining wetland functionality and assessing likely changes in function as the result of altered hydrology. The hydrological zonation of the Pelham wetland and portion 2 of the Craigieburn wetland were similar in terms of water table depth and hydrological zonation (the temporary, seasona.1 and permanent zones were represented), while portion 1 of the Craigieburn wetland had a much lower water table and degree of wetness (only the temporary zone was represented), which appears to be due to degradation. The general trend found in the second wetland is that the water table became lower towards the erosion head cut at the downstream end of the wetland. Applying a WET-EcoServices assessment shows that the first site (Pelham wetland) and portion 2 of Craigieburn wetland, which had similar hydrology, showed similarities in terms of hydrological services, such as nitrate and toxicant assimilation, that are dependent on a high degree of wetness. This dependence is due to hydrologic conditions that influence nutrient cycling, nutrient availability and rates of organic matter decomposition. In terms of goods, all three sites were important for research. Except for recreation, Pelham wetland provided little other direct benefits. In contrast, portion 1 and 2 of Craigieburn were very important for providing cultivated foods, which contribute significantly to the food security of the many poor households who use the wetland. However, portion 1 of Craigieburn was less important than portion 2 of Craigieburn for supplying natural resources (e.g. reeds for harvesting) and water for human use because of its drier condition. The Pelham wetland was found to be highly invaded by alien vegetation. The study shows that in a rehabilitated wetland and through effective management, ecosystem goods and services do increase. But, due to the high cost associated with the rehabilitation process, the study highlighted the value of assessing the potential benefits of rehabilitating degraded wetlands, particularly ecosystem goods and services that will be secured.