OR/17/056 Current knowledge gaps and future research

Lapworth, D J, Stuart, M E, Pedley, S, Nkhuwa, D C W, and Tijani, M N. 2017. A review of urban groundwater use and water quality challenges in Sub-Saharan Africa. British Geological Survey Internal Report, OR/17/056.

Knowledge gaps reflect the complexity of the urban groundwater system and the associated large costs of characterising the system fully. They also reflect the lack of research that has been undertaken in SSA compared to other more developed parts of the world. Systematic groundwater quality surveys with rigorous methods and large sample sizes are lacking for SSA and it would be fair to say that the research effort to date has largely focussed on water availability in SSA rather than water quality. The focus of future research should be targeted at understanding the sources, pathways and survival of pathogens in groundwater, particularly in vulnerable settings with rapid horizontal and vertical pathways.

Quantifying and fingerprinting source terms
There are a wide range of different industries across SSA which will have a correspondingly broad range of effluent quality and method of disposal. Detailed information on the groundwater impact of many of these is completely lacking. Within the literature there has been a focus on understanding faecal sources from pit latrines, and a notable paucity of studies that have investigated the impact of multi-point faecal contamination due to limited sanitation coverage in many urban and peri-urban centres in SSA.

Understanding rapid pathways in the subsurface
Important knowledge gaps remain in the characterisation of the aquifer pathway term. It is unlikely that for many urban areas of SSA there will be a wealth on detail on the characteristics of the local aquifer particularly in terms of permeability and local flow direction. Given the important role rapid horizontal (and vertical) pathways in tropical soils have in the migration of contaminants in the subsurface, and their widespread occurrence in this region, and Africa more generally, this is a key topic that warrants further investigation. Research focused on understanding the factors controlling the high failure rates (hydrogeological or otherwise) of shallow groundwater sources in the dry season would be beneficial.

There is a need to understand the resilience of groundwater quality to changes in rainfall patterns and recharge processes, including flooding, due to regional and seasonal changes in climate patterns as well as the risk of water point failure due to limited waste management in this region and their implications long-term for water resource policy and management. Tracing and quantifying residence times and pathogen occurrence in the subsurface, including in shallow groundwater systems as well as deeper systems is key to making a robust assessment of the vertical separation required between sources of pollution and groundwater points.

Microbial source tracking and anti-microbial resistance (AMR) in the environment
New techniques such as molecular marker methods (e.g. Mattioli et al., 2012; Sorensen et al 2015c) for fingerprinting pathogens, fluorescence sensors for rapidly mapping microbiological contamination of water sources (e.g. Sorensen et al., 2015a), and attention on type/depth of water point may help resolve key sources and pathways for contamination of groundwater points in this region. Very few studies using molecular tracking techniques have been undertaken in SSA to look at different sources of faecal contamination. AMR is a growing concern and very few studies have assessed anti-microbial resistance and anti-microbial residue occurrence in the environment in Africa.

Pathogen survival
There is still relatively little known about pathogen survival in the subsurface and much of the literature does not consider environmental conditions that are relevant for SSA. Much more work, including laboratory and field based studies are needed to quantify pathogen survival in the subsurface. Relatively little is known about the occurrence and mobility of enteric viruses in shallow groundwater systems in SSA compared to bacterial pathogens.