Land use and cover change impacts on quality of African water
Last post explored about the impacts of land use/cover change on African water supplies. This time, the impacts on the quality of African water will be investigated.
As mentioned at the end of the last post, the quality of water is crucial for both human socioeconomic development and conditions of environment; and land use/cover changes could lead to significant changes in water quality.
Many scholars examined the effects of land use change on water quality, mostly suggesting strong relationship between them in the concluding remarks (i.e. Gburek & Folmar, 1999). For example, Bolstad and Swank (1997) suggested that consistent changes in water quality variables were accompanied by the changes in land-use and Tong (1990) also implied that the urban development in the watershed of study area (Little Miami River basin) caused substantial modification of flood runoff and water quality. To investigate further of such relationship, I would like to look closer on the study from Tong and Chen (2002) examining the hydrologic effects of land use at both regional and local scale of the study area:
Tong and Chen (2002) conducted statistical and spatial analyses to examine the relationships of land use, flow and water quality in receiving waters on regional scale (the State of Ohio). Also, in local scale (local watershed in the East Fork Little Miami River Basin) as well, by modelling effects of land use on water quality using BASINS method. The results in regional scale indicated that land use was related to many water quality parameters; correlation between different land-use types and water quality variables in the watersheds in the State of Ohio was statistically significant, with a probability level of <0.0001 (See Table below).
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Table of results of the Spearman's rank correlation analysis on land-use types and water quality variables in all sub-watersheds in the State of Ohio, from Tong & Chen (2002). |
Moreover, the results of modelling impacts of land-use change on water quality of the smaller local watershed revealed that runoff from agricultural and impervious urban land-use had much more phosphorus and nitrogen. This may be related to the enrichment of nutrients and/or sediments from agricultural land and rubber fragments, heavy metals and sodium from road deicers (Tong & Chen, 2002).
Thus, the study signified that the changes in land use have resulted in altering the parameters of water quality in the study area. This could be helpful in understanding the land-use change impacts on African water quality since the region is experiencing rapid urbanisation and expansion in agriculture, which affects the water quality the most - as elaborated previously by other studies as well.
As an applied case study in African region, a study by Du Plessis et al. (2014) - quantifying and predicting the relationship between water quality and land-cover change - can be an example.
The study aims to quantify relationships between selected water quality parameters and land cover change in the Blesbok Spruit Catchment in South Africa, with application of Partial Least Squares (PLS) Regression model to come up with model equations for predicting water quality.
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| Map of South Africa showing the location of Blesbok Spruit catchment (dark orange shaded area), from Du Plessis et al., 2014. |
The results demonstrated that the Blesbok Spruit catchment has very poor water quality levels, heavily influenced by the densely populated characteristics with economic growth and development, cultivated land, and mining land cover within the catchment. Particularly, the whole catchment area has been affected by the discharge of mining effluent, sewage, and other pollution sourced from urbanisation, industrial and agricultural growth over the past decades. Furthermore, the efforts of retransforming the land cover into natural areas have caused undesirable side effects because of the degradation of the region's buffering capabilities and failure in decommissioning the mining operations. Du Plessis et al. (2014) concludes with emphasis on the urgency of addressing the water quality issues affected from the land cover changes since it not only disrupts the water quality of the area, but also can limit the future economic growth and development in the region.
There are already cases of water quality altered by the land-cover changes in Africa, especially from urbanisation and development, and it is expected to be faced by more regions as many of them are going through rapid development or yet to start.
After exploring the impacts of land use/cover change on water in Africa - in different aspects of quantity and quality of water system - it seems to me that demographic change happening in Africa is inseparable in current discussion about relationship between land use/cover change and water in Africa, since it is one of the most influential factors altering the landscapes of Africa. Hence, I would like to explore a bit further on the impacts of population growth on land use/cover change and availability of water in Africa in the next post.
