The Impact of Sediment Pollution on Biodiversity in Lake Tanganyika

Abstract

We investigated the impact of excess sediment pollution on the biodiversity of Lake Tanganyika, Africa. The lake’s basin is undergoing deforestation at an alarming rate; rapid erosion as a consequence of this deforestation is resulting in the discharge of large volumes of sediment into normally clear‐water littoral and sublittoral environments. We determined species richness patterns among ostracodes, fish, and diatoms for undisturbed, moderately disturbed, and highly disturbed areas to see if there is a consistent pattern of lower species richness in disturbed areas. Ostracodes are significantly less diverse in highly disturbed sites than in less disturbed ones for both soft and hard substrate littoral environments, with reductions in species richness ranging from 40% to 62%. Species richness patterns for profundal ostracodes show smaller differences between low‐ and high disturbance environments (7–32%) that are not statistically significant. Fish census data show a similar pattern to ostracodes, although the sample sizes are too small to be analyzed statistically. For the four water depths where comparative transects were made, species richness was between 35% and 65% lower at high disturbance sites than at low disturbance sites. Diatoms showed only minor and statistically insignificant reductions in species richness between low and high disturbance sites (15–20%). Ostracodes and fish may be more affected by sedimentation because they are mostly endemic and may require clearwater habitats, whereas the benthic diatom species in the lake are largely cosmopolitan and in many cases also occur in turbid affluent rivers (such as the Ruzizi). Fossil and sedimentological 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 implications for establishing and managing underwater reserves in Lake Tanganyika. They suggest that lake margins adjacent to small, erosion‐resistant watersheds will be most easily protected in the event of deforestation. Conversely, lake reserves established adjacent to large and/or easily eroded watersheds should incorporate those adjacent areas as part of the reserve to prevent subsequent sedimentation damage to the reserve ecosystems.