Effect of salt harvesting on ground water quality in Gongoni, Kilifi county

Abstract

Fresh water is essential for the existence and development of any community. In Gongoni, Kilifi County, groundwater forms the primary source of fresh water. The presence of salt harvesting activities in the area and the concentration of pit latrines within their vicinity pose major pollution risks to these water sources. Salt harvesting ponds, which play a key role in concentrating sea water during the salt harvesting process, have a potential of affecting the quality of ground water. It is with this background that this study investigated the activities affecting the quality of ground water sources in Gongoni. The study examined the effect of the high concentration of the seawater in the salt harvesting ponds and the subsequent discharge of the mother liquor after the crystallization process. This was done by analyzing the chemical content of water collected from different ground water sources from the area. The study also involved a survey through snowball sampling that relied on referral networks, mostly the public health officers in the locality. Through this sampling technique, 16 ground water sources were identified and samples collected for chemical and microbiological analysis. Ground water sources in neighboring areas with no salt harvesting activities were sampled for comparative laboratory analysis. Microbiological analysis was also carried out to lessen the possibility of bias from considering salinity levels only. The data from the analysis was collated and analyzed using the Statistical Package for Social Science (SPSS) independent samples to test and Spearman’s correlation coefficients. The sampled Gongoni water sources recorded higher levels of the measured parameters (TDS, Salinity, Chloride, and Sodium) than those from Mambrui, Ngomeni and selected secondary data from Mombasa County wells without salt harvesting activities. They had a mean of one thousand nine hundred and sixty nine mg/l compared to that of Mambrui and Ngomeni with a mean of one thousand and fifty mg/l. The secondary data from Mombasa County had a mean of one thousand five hundred mg/l. Similarly, E. coli and total coliform levels were also above the permissible Kenyan and WHO standard limit of 0 MPN/100ml for treated water and 10 MPN/100mls for untreated water. E colli had the highest levels recorded at two thousand four hundred MPN/100mls and lowest value was five hundred and thirty eight MPN/100mls. The highest coliform values were recorded at two thousand and thirty nine MPN/100mls and the lowest was two thousand four hundred MPN/100mls. In spite of this, the differences were not statistically significance when compared to the samples from Mambrui and Ngomeni where salt harvesting activities take place. The existence of higher levels of tested parameters in Gongoni water sources compared to those in neighboring communities could be attributed to both salt harvesting activities and salt water intrusion. The study recommends that water from these sources should be pretreated to make it suitable for human use. This can be done through filtration or chemical treatment such as chlorination.