Physical and chemical characteristics of the Tanzanian inshore and offshore waters of Lake Victoria in 2005–2008

Abstract

Assuming that the inshore and offshore waters of Lake Victoria are impacted differently by human activities in its catchment, this study investigated the water quality dynamics of the lake. A total of 29 stations were sampled in 2005–2008 for dissolved oxygen (DO), pH, Secchi transparencies, temperature, turbidity, chlorophyll a, NO₃, SRSi, TN and TP. There was a decreasing trend of the measured parameters towards offshore sites, except for Secchi transparency and NO₃, which increased towards the offshore waters. DO concentrations (mean ± SD) varied between 6.97 ± 0.57 mg O₂ l^–1 and 5.80 ± 0.72 mg O₂ l^–1 in the inshore and offshore waters, respectively. Turbidity values were comparatively higher in the inshore (3.73 ± 2.21 NTU) than the offshore waters (2.19 ± 1.81 NTU). Chlorophyll a concentrations varied between 17.36 ± 6.13 µg l^–1 and 8.09 ± 4.38 µg l^–1 in the inshore and offshore waters, respectively. Increases of unsustainable human activities in the lake and its catchments, plus increased degradation of wetlands, are among the causes of the observed water quality changes. In order to be fruitful and sustainable, the management of Lake Victoria and its catchment needs to take an ecosystem approach, and to involve all key stakeholders.

Keywords:

• catchments
• chlorophyll a
• dissolved oxygen
• temperature
• turbidity