A Preliminary Assessment of the Wetland Biological Integrity in Relation to Land Use: A Case of the Intunjambili Wetland, Matobo District, Zimbabwe.

Abstract

Research done in Zimbabwe on wetlands has tended to concentrate on hydrological aspects, agronomic practices, institutional arrangements, resource mapping, soil types, water quality and general conservation status. There is a dearth of knowledge regarding the nature, management and response of wetland biological integrity or health to agriculturally related activities and other land uses. The objective of the study was to assess and evaluate the impacts of land use practices on wetland health. This was done in Intunjambili wetland, in Matobo District, Zimbabwe. The wetland is approximately 30 ha in size, and is mainly used for cultivation, water abstraction, vegetable gardening, grazing, settlements, eucalyptus plantations, dam, brick making and sand abstraction. The study evaluated impacts of land use on wetland health, defined in the study as land cover changes, vegetation composition and NDVI, and macroinvertebrates abundance and diversity. Field visits and sampling were done in January and March 2009. There was a 57.9% increase in cultivated areas, a 48.5% decline in woodland, and a 50% decline in permanently wet areas, which indicated that the wetland was drying up from 1990 to 2008. There was a significant (p=0.00) decline in vegetation health with NDVI values as high as 0.64 in 1990 decreasing to values as low as 0.07 in 2008. Alien invasive species like Lantana camara, dry land plants like Euphorbia sp commonly known as Cactus and ruderal species like Eragrostis enamoena were found to replace wetland vegetation in some areas of the wetland. The macroinvertebrates habitat quality, characterised by pH, temperature, conductivity and dissolved oxygen and chemical parameters, BOD, ammonia, turbidity, nitrates, phosphates, total nitrates, total phosphates and total suspended solids, was found to be generally unpolluted, which determined the macroinvertebrates that were found. The 23 macroinvertebrates families that were identified demonstrated low taxa abundance and richness. Shannon Diversity Index that was calculated for the sites had values that were all below 1, indicating a poor diversity. The sensitivity of taxa calculated using the Biological Monitoring Working Party had values below 100 indicating some form of organic pollution. Chironomids and Oligochaetes, which are known to be the least sensitive taxa, dominated the communities. In conclusion it can be said that land use activities in Intunjambili wetland have had moderate impacts on wetland biological integrity. The impacts were mainly on vegetation, which has deviated from its perceived natural wetland vegetation and reduction of water. The impacts on macroinvertebrates communities are minimal.