The impact of a sugar by-products effluent on the beach Meiofauna at Sezela Beach, KwaZulu-Natal, South Africa
Blair, Alan George.
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Beach meiofauna were chosen as environmental indicators to investigate the impact of Illovo sugar by-products effluent. The effluent is pumped through a 20 cm diameter pipeline into surf zone at Sezela beach on the coast of KwaZulu-Natal, South Africa. Meiofaunal communities were considered appropriate indicators as they are relatively stable both qualitatively and quantitatively on a seasonal and year to year basis. Most meiofauna also do not have planktonic stages in their life cycles, respond rapidly to pollution due to their fast generation times, and they are often abundant with high species diversity in habitats which are subject to considerable natural physical and chemical fluctuations. In this particular study there was a specific concern about trace amounts of furfural in the effluent. Furfural has been used as the active ingredient in a product designed to kill parasitic nematodes in crop fields. A large proportion of the beach meiofauna consists of nematodes. Eight stations were sampled for meiofauna along the beaches at Sezela on 7 different occasions. Seasonal effects on meiofauna and meiofaunal recovery during the period when the factory was not pumping effluent to sea was assessed. Samples were taken on the following dates: 4 July 2000 (winter); 30 August 2000 (winter); 13 December 2000 (spring); 26 January 2001 (summer); 8 March 2001 (summer); 9 April 2001 (autumn); and 2 January 2002 (summer). PRIMER (Plymouth Routines in Multivariate Ecological Research) was used for statistical analysis and included various univariate indices such as species richness, species diversity and evenness. These indices were then analysed using one-way ANOVA to determine any significant difference between sites over the 7 sampling periods and between the different seasons. Clustering and Ordination multivariate analyses were carried out on the community data and physico/chemical data to determine community patterns and relate them to the effluent and environmental data. The Nematode/Copepod ratio was also calculated. Meiofauna were analysed at major taxa level, as well as to nematode feeding groups and harpacticoid copepod and annelid family level, to determine if analysis to major taxa level is adequate as an indicator of pollution impact. The analyses indicated a possible degree of impact at stations close to the effluent discharge when effluent was being pumped to sea and a recovery was noted at the station closest to the discharge when effluent was not being discharged and analysis was conducted to the major taxonomic rank only. No improved resolution was achieved by analysing some of the meiofaunal major taxa to family level or different feeding groups. The analysis of the Nematode/Copepod ratio was shown to correspond with the multivariate analyses, however, this ratio could not reveal the severity of the impact where both nematodes and harpacticoids i.e. total meiofauna had been reduced by adverse conditions. The physical and chemical variables that showed the greatest correlation with the meiofaunal community patterns were sediment grain size, dissolved oxygen and salinity. There was a very strong positive correlation between Kjeldahl nitrogen in the interstitial waters and total numbers of meiofauna. This and the relationship with salinity may have suggested other possible sources of influence such as enrichment from the three estuaries in the area as well as a storm water drain located 150m north of the effluent discharge. A seasonal effect was observed with increased meiofauna numbers in autumn, but this was possibly influenced by the periods when effluent was not being pumped to sea.