Groundwater quality

Much of the literature on groundwater in Africa is focused on quantity rather than quality. However, we must remember that sufficient water quality is needed for it to be used effectively in agricultural irrigation, and therefore it is a worthy topic to be discussed. There is limited research on this subject, so much of the impacts of climate change on groundwater quality remain uncertain and should therefore be treated cautiously. It is not the intention of this blog post to provide a comprehensive audit of the effects of climate change on groundwater quality, merely to highlight that it is something that must be considered when assessing groundwater’s potential by discussing some of its impacts.

Water quality, affected by the chemical, physical and biological changes of water, is value specific, in that its value relates to the specific activity it is needed for (Green et al. 2011, FAO 2016). For example, for agricultural irrigation, the FAO outlines a number of issues regarding water quality that can result in decreased yields or lack of effectiveness (see my summary in Table 2).

Table 2: Water quality issues, information summarised from FAO (2016)

Issue	Anticipated Result
Salinity	If salts are present in soil or water, this can reduce the water availability to the crop, potentially affecting yields.
Water Infiltration Rate	High sodium or low calcium levels in soil or water can reduce rate of entry of irrigation water. This can result in insufficient water quantities being infiltrated to supply crops between irrigations.
Specific Ion Toxicity	Ions (such as sodium, chloride or boron) can damage crops and reduce yields if they appear in sufficient concentrations.
Miscellaneous	Too high levels of nutrients can decrease yields and/or quality. Unattractive deposits on crops can reduce market potential. “Excessive corrosion of equipment increases maintenance and repairs.”

So we can see that changes in the make-up and quality of groundwater could lead it to be unsuitable for irrigation. So how is it thought that climate change will affect it? Green at al. (2011) provide a fairly comprehensive list of the possible impacts, as summarized below:

1.     Recharge during prolonged dry and wet periods may have greater and lower concentrations of salts and total dissolved solids respectively.

2.     High intensity precipitation events may cause high levels of infiltration, potentially resulting in the mobilization of “large pore-water chloride and nitrate reservoirs” in the unsaturated zone of aquifers in semi-arid/arid regions. If these reach the water table, groundwater quality may decline (544).

3.     Sea level rise, spatial and temporal variability in precipitation and evapotranspiration and increased abstraction of groundwater may lead to increased groundwater salinization in coastal regions.

4.     Increases in recharge rates could lead to growth of contaminant transport, and thus groundwater exposure to contamination.

5.     Temperature rises may alter subsurface biogeochemical reactions, potentially altering groundwater properties and quality.

6.     Increases in flood events may cause urban contaminant levels to rise in groundwater such as oil, solvents and sewage.

7.     Sea level rise, and subsequent seawater intrusion, may decrease the depth of the freshwater lens (a layer of fresh groundwater that sits on top of the denser saltwater) in coastal aquifers such as the Niger delta (Taylor et al. 2009).

It is clear that adequate water quality is important to agricultural irrigation and that the quality of groundwater is likely to change in the face of anthropological climate change. However, studies are extremely limited, and the magnitude of such predicted changes remains unclear. In addition to this, the relationship between water quality and most climatic variables in one that is non-linear, making it even more difficult to predict (IPCC 2014a). My purpose in writing this blog post is to highlight that groundwater quality should not be assumed as a constant or as suitable for irrigation. Further research is needed, and is greatly encouraged on my part, into how groundwater quality will be affected by climate change so that we are able to ascertain whether its quality allows it to remain a suitable option for agricultural irrigation.