Design of a water quality monitoring network for the Limpopo River basin in Mozambique

An important means of characterising the health of streams is through measurement andassessment of its chemical, physical and biological parameters. Thus, cost effective andtargeted water quality monitoring programmes are required for proper assessment,restoration and protection of such streams.This research reports on the development of a water quality monitoring network for theLimpopo River Basin in Mozambique located in the Southern part of Africa. In thiscatchment, anthropogenic influences as well as natural processes are responsible for thedegradation of surface waters, impairing their use for various purposes (e.g. drinking,industrial, recreation). The localization of the basin in a drought-prone zone, associatedwith the constant increase on water demand by the four riparian countries (Botswana,South Africa, Zimbabwe and Mozambique) exacerbated the situation when it comes topreservation of the aquatic environment further downstream.For that purpose various physico-chemical, biological and microbiologicalcharacteristics of 23 sites within the Limpopo River Basin in Mozambique were studiedin November (2006) and January (2007). Ecological parameters like dissolved oxygen(DO), pH, nitrate (NO3- - N), total phosphorus, ammonium (NH4+-N), heavy metals,chloride (Cl-), total dissolved solids (TDS), sodium adsorption ratio (SAR), benthicmacroinvertebrates and faecal coliforms were analyzed in-situ or in laboratory andcompared with standards limits to investigate the influence of different sources ofpollution for the final condition of the water. For that, the Mozambican guidelines forreceiving waters and the environmental water quality standards for effluent dischargestogether with the WHO guidelines for drinking water quality were used.The obtained data indicated that sites located at proximities to the border with upstreamcountries were highly contaminated with heavy metals. In contrast, further downstream,the ions concentration, faecal coliforms and elevated organic loads derived fromdischarge of untreated wastewater were responsible for the deterioration of waterquality at sampled sites. The Elephants subcatchment a tributary of Limpopo was foundwith a better water quality whereas the Changane subcatchment together with theeffluent point discharges were polluted as indicated by low DO and high TDS, electricconductivity (EC), total hardness, SAR and low benthic macroinvertebrates taxa. Thedifferences of some parameters were statistically significant (p<0.05) when theconcentrations found in November and in January were tested, suggesting a possibleinfluence of flow increase for the change of concentrations.It was also found that it is possible to apply biological investigations using benthicmacroinvertebrates for assessment of water condition, but additional investigation isrequired to adapt the index scoring to tropical ecosystems since it was developed fortemperate environments.Aiming at a better understanding of water quality trends; detection of receiving watersstandards violations; information gathering for future environmental flow assessment;all to ensure a better water management, a systematic water quality monitoring networkcomposed of 16 stations was proposed. Ambient, operational, effluent and earlywarnings are the main monitoring types recommended. Furthermore, the studyrecommends additional research at a Basin scale to identify the sources and fates ofpollutants, its transport along the main subcatchments and impacts for the downstreamecosystem