Changes of phytoplankton communities in Lakes Naivasha and Oloidien, examples of degradation and salinization of lakes in the Kenyan Rift Valley

Abstract

Increasing degradation of the water quality, caused by overuse and salinization, leads to considerable changes of the phytoplankton composition in Kenyan Rift Valley lakes. Exemplarily, the phytoplankton communities and biomasses of deteriorating freshwater Lake Naivasha and salinizing Lake Oloidien were studied between 2001 and 2005, accompanied by physico-chemical measurements (pH, total phosphorus and nitrogen, alkalinity, conductivity). Over the last three decades, the ecology of these two water basins has been subjected to dramatic changes, caused by excessive use of water and catchment area by man. In L. Naivasha a shift in the dominance of coccoid cyanobacteria towards dominance of Chlorophyceae (Botryococcus terribilis) was observed. Lake Oloidien exhibited a shift in the dominance of coccoid Chlorophyceae towards dominance of cyanobacteria (Arthrospira fusiformis, Anabaenopsis elenkinii). Phytoplankton findings and chemical data demonstrate that L. Naivasha has developed towards a eutrophic freshwater lake while L. Oloidien has progressed towards a hypereutrophic alkaline-saline lake.

An Overview of the Current Status of Lake Naivasha Fishery: Challenges and Management Strategies

“…There has been a dramatic elevation in chlorophyll-a concentration in the lake attributed to increased nutrients loading into the lake [30]. Recent studies found algal biomass, measured as chlorophyll-a concentration ranged between 16, 850 μg l −1 and 37, 730 μg l −1 with a mean concentration of 2,455 ± 7,170 μg l −1 (KMFRI unpublished data) compared to 40 -50 μg l −1 in the 1980s [13].…”

“…For sustainability of Lake Naivasha and its resources, wetland restoration holds a key role [30]. Major interventions for restoration would involve considering ecohydrology at the site where River Malewa enters the lake or use of ecological manipulation around Gilgil River.…”

Assessing water quality in lake Naivasha

“…The pH at Mouth of Malewa and Northeast is somewhat lower in comparison to the other sites which can be attributed to the high influx of fresh water from the Malewa, Gilgil and Karati Rivers (Gaudet, 1979;Stoof-Leichsenring et al, 2011). The range of conductivity in lake Naivasha seems to have widened from 282-374 μS cm -1 as measured by Ballot, Kotut et al (2009) in 2001 years to 74-526 μS cm -1 in the present study. Turbidity and TSS were generally high at Mouth of Malewa due to the effect of surface runoff from the agriculturally rich catchment area.…”

“…The average TSI-TP and TSI-CHL values of just below 60 (eutrophic) increased to 65 and 76, respectively, while the TSI-SD value increased from 66 to 82. Although other studies (Ballot et al, 2009;Kalff, 1983) did not provide specific details regarding the time or location of sample collections, the TP values compared favourably. These changes are probably attributable to the ever-increasing multiple stressors, such as increased agricultural activities, urbanization and climate change (Becht et al, 2005;Harper et al, 2011a).…”

“…Changes in land use upstream have resulted in fluctuations in the inflow and increase in agrochemicals leading to pollution and therefore exerting more pressure on the ecosystem and society (Ballot et al, 2009). A series of environmental tragedies, with the most recent being the death of over 1000 fish due to lack of oxygen in February 2010 (Morara, 2010), continue to deteriorate the health of lake Naivasha.…”