Evaluating the effects of hydrologic change in the Okavango Delta of Botswana: Analyses of aquatic organic matter transport and ecosystem economics.

摘要

Changes to the hydrology of Okavango Delta, a large pristine wetland in Botswana, can affect the basic ecosystem structure and function. This study specifically examined how hydrologic change will affect the amount of organic matter (OM) that is available for aquatic food web functioning. In order to understand this hydrology-biogeochemistry linkage, the relationship between the annual flooding of the Delta and the chemical quality of dissolved organic carbon (DOC) was determined. Changes to food web dynamics also affect wetland values that are aesthetically and economically important to humans, such as the values of wildlife-viewing and biodiversity. Because wildlife-viewing tourism in the Delta contributes to the economy of Botswana, this study also investigated the effects of diminished wildlife-viewing opportunities on wetland values from the tourism sector.; Results of chemical and spectroscopic analyses showed that the annual flood mobilized plant-derived DOC from floodplain soils and plant litter in seasonally-flooded areas. After the initial DOC pulse, the decline in DOC concentrations coincided with increased algal and bacterial sources of DOC, indicating that microbial degradation of DOC was occurring. Along spatial gradients, evapoconcentration and the flushing of DOC from terrestrial source areas were found to be important controls on the observed rise in DOC concentrations. Computations of mass flow in an experimental floodplain demonstrated that diminished flood volumes decreased the mass of DOC mobilized. In order to scale this relationship to the entire Delta, DOC leaching and decay rates were determined and a large-scale chemical transport model was evaluated. Due to the course spatial resolution of the model, temporal changes in DOC concentration could not be captured. The results of this study indicated that the coupled Delta-scale model is useful for examining water supply scenarios, but inappropriate for simulating organic solute transport.; Results of travel cost and contingent valuation analyses demonstrated that the tourists who visit the Delta annually value it at approximately US{dollar} 24 million/annum and were willing to directly contribute approximately US{dollar} 3.2 million for its preservation. The quality of wildlife-viewing correlated positively with willingness-to-pay for preservation and consumer surplus, indicating that diminished wildlife-viewing opportunities lowered the value of the Delta.