COD BE OUT OF FOOD SOON!

 

Previously, I introduced the Gibe III dam and overviewed the effects that the dam’s construction will have on the ecology and hydrological cycles of the Omo-Turkana basin.

Here I will delve deeper into the impacts of the construction of the Gibe III dam on the ecology and hydrology.

VITAL NUTRIENT DEFICIT

Lake Turkana is the world’s largest desert lake whose flows from the Omo river have transformed since the construction of the Gibe III dam in 2015. A study into the impacts of dam-associated hydrological changes on chlorophyll-a was undertaken in Turkana. Using satellite remote sensing, the study evaluated the influence of these modified hydrological patterns on large-scale phytoplankton concentrations (Tebbs et al. 2020). It was estimated that chlorophyll mean annual concentrations declined by 30% during the filling of the dam. Prior to the dam’s construction, seasonal cycles in chlorophyll were observed as seasonal phytoplankton blooms correspond with annual flooding from the river Omo, denoting a strong correlation between river inflows and lake levels on the amount of chlorophyll found. This illustrates the influences that infrastructure development can have on primary production in lakes. Reductions in nutrients levels from the reduced inflows also result in the decline of commercially important species for Turkana like Tilapia zillii, which have specialist diets that are not resilient to changes in nutrients levels (Gownaris et al. 2015).

Stratification – ‘the separation of reservoir waters into stable layers of differing densities’- has critical consequences for water quality downstream of dams (Calamita et al. 2018:4). Deeper waters are often hypoxic, leading to the discharge of sediment-bound nutrients. Stratification has a predisposition to cause deoxygenation of reservoir waters due to heterotrophic consumption which produces considerable ecological harm downstream in lake Turkana(ibid). Dissolved oxygen is crucial to sustaining most aquatic life and in supporting oxidative self-purification processes within rivers (Petts 1986).

 IT’S KRILLING THE FISH!

Source: View of cyanobacteria in Lake Turkana 

Lake Turkana is home to more than 60 different fish species of which 10 are endemic to the desert lake (Kolding 1995). These fish species and those who rely on them are in danger of complete depletion of fish stocks because of the Gibe III dam construction. The characteristic colour of Lake Turkana is produced by high concentrations of cyanobacteria which is vital for maintaining the productive fisheries of the lake (Kolding 1993).  This bacterium is found less and less within Turkana’s waters with the declining lake levels. Turkana’s fish rely on the seasonality of fluctuating flows and flood pulses to breed, the building of the Gibe III has reduced variability, not signalling fish to breed, diminishing fish populations (Gownaris et al. 2015).

It has been predicted that the changes of infrastructure development upstream may reduce the lake’s biomass by up to 50%, declining the productivity of lake Turkana’s fisheries by more than two-thirds (Avery 2012; Gownaris et al. 2015). Turkana’s fish populations are very sensitive to the changes occurring at the Omo river upstream. The changes in nutrients, lake level, seasonal flows, flood pulses and ecology are dramatically altering the water’s composition. Diminished inflows from Omo is likely to increase the salinity of lake Turkana, considering it is a closed basin, further forming an environment to decrease fisheries (Avery 2012). This is particularly damaging considering there are 10 species of fish that are endemic to the desert lake and their tolerance to increasing salinity is unknown. All of this is exacerbated by climate change that is increasing rates of desertification and evaporation, further making it difficult to have sufficient water levels for food.

The Omo-Turkana basin is exemplifying the realities of transboundary water management and the knock-on effects of changes upstream for the hydrology and ecology of water resources downstream. The construction of the Gibe III is having critical consequences for lake Turkana and reducing nutrients, resulting in declining fish populations which has wider consequences to the food web.

What effect is this all having on the indigenous people?