Drinking water quality and farming practices on dairy farms in the greater Mangaung Metro, South Africa

Abstract

Dairy farms produce large volumes of animal waste comprising of manure, urine and dairy wash water. In South Africa, dairy waste is usually discharged onto pastures and land by irrigation or flooding which has been known to pollute groundwater with faecally derived microorganisms and nitrates. This study was undertaken to assess groundwater quality on dairy farms in the greater Mangaung area of the Free State. Secondly, the minor aim was to investigate factors that may influence groundwater quality on the farms. These included farming management practices, dairy farm infrastructure and dairy farm waste disposal. Groundwater quality data was collected on 75 dairy farms in 2009. A follow-up study was undertaken in 2013, however, because many farms had ceased production, only 34 farms were included in this round. The groundwater quality data of the 75 farms assessed in 2009 revealed that many farms were compliant with the South African National Standard for Drinking Water. However, 49% of the farms exceeded the limit for nitrates, 60% for total coliforms and 29% for Escherichia coli. When the data gathered on the 34 farms in 2013 were compared to the same farms’ data of 2009, it was found that 45% of the farms in 2009 and 57% in 2013 demonstrated hardness levels that could pose a risk to sensitive consumer groups, such as infants, the aged and the immune compromised. The groundwater on many farms tested as hard or very hard, while the water on a few farms tested extremely hard. Since water is used in all dairy cleaning operations, these levels of hard water could add an additional cost to the running of a dairy by reducing the life span of equipment and increasing the amount of soap used. On 18.9% of the farms in 2009 and 5.6% in 2013, the counts of coliforms exceeded 1 000 per 100 m l groundwater, posing a serious health risk for all consumers. Groundwater with counts of 10 – 100 coliforms per 100 m l could result in clinical infections in consumers, but counts of 100 – 1 000 coliforms could cause infections, even with once-off consumption. In this study, three of the 2013 farms (8.8%) demonstrated counts of E. coli greater than 100 per 100 m l, posing a serious health risk to the consumers. Counts in the region of 10 – 100 per 100 m l were observed in groundwater of 17.6% of the 2009 farms and 29.4% on the 2013 farms. Therefore, consumers on these farms are at risk of clinical infections. Furthermore, when such poor quality water is used in a dairy, the quality of raw milk and products may be affected. Moreover, the number of farms that presented a health risk increased from 41.2% in 2009 to 50.0% in 2013. One of the most effective ways to communicate water quality information is through the use of an index which aggregates all water quality data into a single value. Through a review of literature, three prominent water quality indexes were selected, evaluated and modified; the Canadian Council of Ministers of the Environment (CCME-WQI), the Weighted (W-WQI) and the Weighted Arithmetic (WA-WQI). Environmental health limits were assigned to eight selected water quality parameters and Water Quality Index (WQI) values calculated using 2013 data. WQI values were categorised into five classes ranging from excellent to unacceptable. When these results were compared with a manual rating of the data, the versatile W-WQI provided the most accurate description of data. The index was then applied to the 2009 and 2013 groundwater quality data of 34 farms. Results revealed an improvement from 2009 to 2013, however, the change was not significant (p = 0.110). Overall, the quality of groundwater on these dairy farms is poor and could pose a health risk to consumers, farm animals and the quality of raw milk and products. During 2013, management practices and infrastructural data were recorded on 34 dairy farms. All farms in this study depend on untreated groundwater for domestic and dairy activities. More than two thirds of the farms (85.3%) disposed of the dairy effluent by means of flooding or collection in shallow soil dams, while only five farmers re-used dairy effluent as fertiliser. The results also indicate that, although dairy farms vary in milk yield and size, they are designed and managed to prevent obvious groundwater contamination by dairy effluent. Possible correlations between farm management practices, infrastructure and the poor water quality revealed a weak negative correlation between the number of cows on a farm and the coliform values in the groundwater ( R 2 = 0.0023). Also, no correlation existed between the number of cows on a farm and the E. coli values or the number of cows and the nitrate values in the groundwater. These results suggested that the link between groundwater pollution and farm management practices and infrastructure are not clear and in need of further investigation. This study supports the findings that groundwater is vulnerable to pollution. In particular, the microbiological quality of the groundwater on the dairy farms was poor. The high levels of coliforms and E. coli in the groundwater confirm faecal pollution that could be indicative of poor sanitary conditions. This water contains high concentrations of microbial organisms and nitrates. Vulnerable groups on the farms are therefore at risk of becoming ill. Furthermore, the use of poor quality groundwater in dairy activities and other agricultural activities, such as the irrigation of crops, may further impact produce quality and could ultimately impact the health of consumers.