Vol.:(0123456789) 1 3 Environmental Earth Sciences (2017) 76:790 https://doi.org/10.1007/s12665-017-7149-9 ORIGINAL ARTICLE Spatial and seasonal variations of surface and groundwater quality in a fast‑growing city: Lubango, Angola M. Manuela Vinha G. Silva 1,2  · Elsa M. C. Gomes 1,2  · Malaquias Isaías 3  · José Manuel M. Azevedo 4,2  · Benedito Zeferino 5 Received: 18 April 2017 / Accepted: 17 November 2017 © Springer-Verlag GmbH Germany, part of Springer Nature 2017 Abstract Lubango is a fast-growing city of Angola, with a very defcient water distribution public system. The majority of the popula- tion uses groundwater from shallow, rudimentary dug wells and also surface water from the Mapunda River, which crosses the city. The city has very poor systems for collecting domestic sewage and household wastes. The majority of domestic sewage is dumped directly into the Mapunda River or in pit latrines. In this study, the surface water quality and groundwater quality were assessed. In surface water, the low oxygen contents are related to the high temperature (T) in the warm rainy season and with high contents of oxygen-consuming organic pollution and nutrients, as shown by PCA, in both seasons. Anoxic conditions, with negative ORP values (− 55.7 mV), are caused by oxygen-consuming organic pollution, added with low fow regime during the dry, cold season. The very low ecological quality of the surface water is also indicated by the high contents of PO 4 and Cl t (up to 2.00 and 0.44 mg L −1 , respectively). The phosphate contamination is higher in the warm rainy season, due to higher run-of and higher T, as expressed by PCA, both in river water and groundwater. Most groundwater sampling points are contaminated with nitrate (contents up to 132 mg L −1 ). The pH, total dissolved solids (TDS), alkalinity, Cl t and K, determined in the surface water refect the anthropic contribution to the river water. The variations in water bulk parameters (T, TDS, alkalinity, ORP, DO) and chemical species are indicative of pollution by difuse sources (N-species, phosphates). The PCA shows that non-point sources such as the free discharge of household wastewater, intense laundering in the river, agriculture and animal grazing are the main contributors to low water quality, associated with seasonality and low contents of dissolved oxygen due to its consumption by organic matter. The multivariate analysis allows the evaluation of the changes in water quality, in fast-growing cities where the climate has a clear seasonality. Keywords Angola · Groundwater · Quality · Surface water · Seasonality Introduction Groundwater is a major source of potable water. However, with the rapid growth of population and expansion of the urban areas, groundwater quality becomes vulnerable to human activity. The urbanization leads to important changes in the groundwater balance, due to soil impermeabilization, new discharge patterns and water abstraction from wells. The surface and groundwater quality is severely afected by urbanization, especially in the expanding cities of develop- ing countries, lacking urban planning and where the city has poor urban wastes, wastewaters and sewage collecting sys- tems (Ako et al. 2014; Odoh et al. 2012; Singh et al. 2013; Islam et al. 2015; Lapworth et al. 2017). The inputs from industry, urbanized areas and agricul- tural practices are major causes of surface and groundwater Deceased: Benedito Zeferino. * M. Manuela Vinha G. Silva mmvsilva@ci.uc.pt 1 CEMMPRE, University of Coimbra, Coimbra, Portugal 2 Earth Sciences Department, University of Coimbra, Coimbra, Portugal 3 ISCED-Huíla, Luanda, Angola 4 CITEUC, University of Coimbra, Coimbra, Portugal 5 Lubango, Angola