Population density controls on microbial pollution across the Ganga catchment

• Published in: Water research (Oxford) 2018-01, Vol.128, p.82-91
• Main Authors: Milledge, D.G., Gurjar, S.K., Bunce, J.T., Tare, V., Sinha, R., Carbonneau, P.E.
• Format: Article
• Language: English
• Subjects: Catchment-scale; Faecal coliform; Population density; River network
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2017.10.033

For millions of people worldwide, sewage-polluted surface waters threaten water security, food security and human health. Yet the extent of the problem and its causes are poorly understood. Given rapid widespread global urbanisation, the impact of urban versus rural populations is particularly important but unknown. Exploiting previously unpublished archival data for the Ganga (Ganges) catchment, we find a strong non-linear relationship between upstream population density and microbial pollution, and predict that these river systems would fail faecal coliform standards for irrigation waters available to 79% of the catchment's 500 million inhabitants. Overall, this work shows that microbial pollution is conditioned by the continental-scale network structure of rivers, compounded by the location of cities whose growing populations contribute c. 100 times more microbial pollutants per capita than their rural counterparts. •Faecal coliform concentration is strongly related to upstream population density [80].•Local rivers predicted to fail WHO irrigation standards for 79% of the population [83].•Rivers receive c. 100 times more sewage per capita from urban than rural populations [84].•Microbial pollution is conditioned by river network structure and settlement pattern [84].•Himalayan headwaters continue to dilute microbial pollution far downstream [74].