River water quality in the northern sugarcane-producing regions of South Africa and implications for irrigation: A scoping study

Abstract

Sustainable cultivation of crops under irrigation requires water of appropriate quality, especially with regards to salinity and sodicity. Agriculture can impact negatively on water quality, often through the export of nutrients (particularly nitrogen (N) and phosphorus (P)) from the root zone, resulting in eutrophication of surface water and pollution of groundwater. Sugarcane is the major irrigated crop with regards to area cultivated in the Crocodile, Komati-Lomati and Pongola River catchments. Increasing demand for and use of water resources in these catchments has led to concerns about deterioration in water quality. In this study, chemical water quality data obtained from the South African Department of Water Affairs was used to assess the quality of river water in the above catchments. Electrical conductivity (EC) data show an increase in salt concentration along the river course as a result of various anthropogenic activities in the catchment. Irrigators located further downstream will therefore generally have to pay more attention to the quality of their irrigation water and on-farm salinity management. For the lower parts of the Komati-Lomati and Pongola River catchments, hazards due to sodicity will also need attention. Interestingly, acidifying effects of mine water drainage are potentially being countered by high salt input from agricultural return flow. Nutrient enrichment was evident at many of the river sampling points. Increasing salt, sodicity, N and P over time for most of the rivers studied is also a concern that requires action to ensure the sustainability of irrigation activities in these catchments. More intensive monitoring, including measurement of organic N and P fractions, is recommended to improve understanding of the contribution of different anthropogenic activities to river water pollution and to develop effective mitigation strategies.

Long-Term Water Quality Patterns of a Flow Regulated Tropical Lowland River

“…South Africa has a well-developed commercial agricultural industry, as well as subsistence agricultural activities predominantly in rural areas [34], and many of these occur in close proximity to rivers and dams. The Phongolo River is a prime example of this, as the largest part of its catchment is covered by forestry plantations, commercial and subsistence farming [35] as well as pivot irrigation (water sprinkler irrigation with a central pivot system; [36]). The Phongolo River is also a cross-border river, as it is shared with Mozambique, and is important to both countries [35].…”

“…The Phongolo River is a prime example of this, as the largest part of its catchment is covered by forestry plantations, commercial and subsistence farming [35] as well as pivot irrigation (water sprinkler irrigation with a central pivot system; [36]). The Phongolo River is also a cross-border river, as it is shared with Mozambique, and is important to both countries [35]. Careful monitoring of water quality over long-and short-term periods of such cross-border systems is not only ecologically but also politically important [37].For efficient management, and to minimize impacts on downstream water quality and ecological functions and services (which may support both environmental and human health and wellbeing), it is important to maintain the ecological integrity of an ecosystem [4,8,38].…”

“…A substantial amount of analytical data are available for the for the Phongolo River in northern KwaZulu-Natal dating back to the early 1970s, due to regular assessments of monitoring stations and the completion of a water quality study on the system [62]. Possible impacts of the agricultural developments surrounding Pongolapoort Dam and the upper Phongolo River have been mentioned in previous assessments of the area (e.g., [35,[63][64][65]). However, these studies largely focused on the middle and upper reaches of the catchment and there is still a lack of summarizing studies considering long-term analysis of the river itself, particularly in its downstream region.…”

Environmental Benefits of Improved Water and Nitrogen Management in Irrigated Sugar Cane: A Combined Crop Modelling and Life Cycle Assessment Approach

“…According to Hoekstra et al (2011), impact on water quality also needs to be considered from a geographic perspective, including the effects on seasonal water flow and quality in the specific catchment. The deterioration of water quality observed for the Pongola River is a concern (Van der Laan et al, 2012), and improving irrigation scheduling and N management can potentially reduce irrigation's contribution to pollutant loads.…”

“…Of the total area under cultivation, 25% is irrigated and predominantly located in the Crocodile River, Komati-Lomati River and Pongola River catchments. Emerging water quality problems have been observed for the rivers in these catchments (Van der Laan et al, 2012), and rising competition for water from domestic and industrial sectors, and pressure to increase international and environmental flow obligations means that irrigation has a key role to play in the sustainable use of water resources in these catchments.…”