THE IMPACT OF SEDIMENT POLLUTION ON BIODIVERSITY IN LAKE TANGANYIKA

We investigated the impact of excess sediment pollution on the biodive rsity of Lake Tanganyika, Africa The lake's basin is undergoing defore station at an alarming rate, rapid erosion as a consequence of this de forestation is resulting in the discharge of large volumes of sediment into normally clear-water littoral and sublittoral environments. We d etermined species richness patterns among ostracodes, fish, and diatom s for undisturbed, moderately disturbed, and highly disturbed areas to see if there is a consistent pattern of lower species richness in dis turbed areas. Ostracodes are significantly less diverse in highly dist urbed sites than in less disturbed ones for both soft and hard substra te littoral environments, with reductions in species richness ranging from 40% to 62%. Species richness patterns for profundal ostracodes sh ow smaller differences between low- and high disturbance environments (7-32%) that are not statistically significant Fish cen-sus data show a similar pattern to ostracodes, although the sample sizes are too sma ll to be analyzed statistically. For the four water depths where compa rative transects were made, species richness was between 35% and 65% l ower at high disturbance sites than at low disturbance sites. Diatoms showed only minor and statistically insignificant reductions in specie s richness between low and high disturbance sites ( 15-20% ). Ostracod es and fish may be more affected by sedimentation because they are mos tly endemic and may require clearwater habitats, whereas the benthic d iatom species in the lake are largely cosmopolitan and in many cases a lso occur in turbid affluent rivers (such as the Ruzizi). Fossil and s edimentological data from short cores are required to confirm whether the low diversity observed at high disturbance sites is a consequence of increasing sedimentation rates through time Our results have implic ations for establishing and managing underwater reserves in Lake Tanga nyika They suggest that lake margins adjacent to small erosion-resista nt watersheds will be most easily protected in the event of deforestat ion. Conversely, lake reserves established adjacent to large and/or ea sily eroded watersheds should incorporate, those adjacent areas as par t of the reserve to prevent subsequent sedimentation damage to the res erve ecosystems.