Title: Trace elements in water, sediments, hydropsychidae larvae and freshwater crab from Gura and Sagana Rivers, Kenya

Author: Doreen Kemunto Abuya

Supervising Institution: BOKU - University for Natural Ressources and Life Sciences, Vienna

Year: 2019

 

Abstract:

Trace elements, including heavy metals and other possible toxic elements, naturally occur in aquatic ecosystems, but their concentrations can be elevated due to natural and anthropogenic activities. High levels may lead to the accumulation in certain organisms and then become a threat to aquatic life. Hence, environmental monitoring of these trace elements is of great interest especially using aquatic organisms, which can bio-accumulate them. Therefore, this study focused on the upstream to downstream distribution of trace element concentrations in water, sediments, trichopteran larvae (Hydropsychidae) and freshwater crabs from Gura river and Sagana river in Kenya. Sampling was carried out at 11 sites that have different land uses, in October 2018 and November 2018. The following parameters were determined in the water: Temperature, dissolved oxygen, pH, electrical conductivity, turbidity, dissolved organic carbon (DOC), dissolved bound nitrogen (DN) and major cations. The data obtained for DOC and TN ranged from 0.99 mg L-1 to 4.35 mg L-1 and 0.16 mg L-1 to 0.87 mg L-1 respectively. In the sediments mean trace element concentrations exhibited a clear dominance of Zn>Cr>Pb>Ni>Cu>As>Cd>Ag at different sampling points in Gura and Sagana rivers. Trace element concentrations (μg g -1 dw) in pooled samples of Hydropsychidae larvae were; As (0.18 - 1.04), Cd (0.19 - 3.05), Cr (3 - 24), Cu (13 - 26), Ni (2 - 6), Pb (0.40 – 1.89), Ag (0.02 – 0.04) and Zn (100 - 152). Trace element concentrations (μg g -1 dw) in limbs of freshwater crabs were as follows; As (0.09 - 0.47), Cd (0.02 – 0.09), Cr (0.11 – 0.31), Cu (23 - 72), Ni (9 - 18), Pb (0.01 – 0.12), Ag (0.01 – 0.06) and Zn (45 - 155). Cadmium levels were remarkably high in Hydropsychidae larvae with a highest value of 3.05 μg g -1 dw compared to much lower levels in sediments (< 0.5 μg g -1 dw) and freshwater crabs. The freshwater crabs accumulated copper and silver compared to sediments and Hydropsychidae larvae.

 

Keywords: Trace elements, heavy metals, arsenic, cadmium, chromium, copper, lead, nickel, silver, zinc, sediments, Hydropsychidae larvae, freshwater crabs, Gura river, Sagana river, freshwater systems, pollution, bio-indication, dissolved organic carbon (DOC), dissolved bound nitrogen (DN)