Anthropogenically induced changes in groundwater outflow and quality, and the functioning of Eastern African nearshore ecosystems (GROFLO) - INCO-DC: International Cooperation with Developing Countries (1994-1998) Contract number: ERBIC18CT960065 - Final report.

Abstract

The general conclusion of the GROFLO project is that the East African nearshore coastal ecosystem is affected by the amount of groundwater outflow and by its quality. The data collected showed a strong impact of groundwater outflow on a number of components of the back-reef lagoon ecosystem. Sites with high groundwater outflow displayed a lower seagrass species diversity than sites with low groundwater outflow. Seagrasses are “structuring species”, which means that they constitute an important component of the system. Changes in seagrass vegetation can affect the whole ecosystem. Results also indicate that anthropogenically induced elevated nutrient inputs caused enhanced phytoplankton cell abundance and reduced species diversity. Furthermore, certain groups or species in the lagoon ecosystem could be identified as indicators of groundwater outflow. The presence of mysids was indicative of groundwater discharge. And, a proliferation of green macroalgae was observed at the beach sites with groundwater influence. At present, information on the function of many of these species in the ecosystem of back-reef lagoons is absent, which impedes predictions of possible consequences of changes in groundwater outflow rates and groundwater quality. The socio-economic studies provided valuable baseline data on water usage patterns. Analysis of the water quality of the wells yielded results on levels of contamination with microoganisms, nutrients and pesticides that call for caution. The results will be conveyed to the local administrators. The groundwater model that was developed during the GROFLO project, proved to be an an indispensable tool for the field studies. The model is now available on CD-ROM, and can be obtained from VUB. It can be a valuable aid to coastal managers, e.g. for use in Environmental Impact Studies to predict effects of changes in groundwater use on the outflow rates into the coastal zone.