Testing the applicability of the SASS5 scoring procedure for assessing wetland health: a case study in the KwaZulu-Natal midlands, South Africa

Abstract

A study was undertaken between 29th January and 17th February 2004 to test the applicability of the South African Scoring System Version 5 (SASS5) scoring and calculation procedure in nutrient-enriched palustrine wetlands in the midlands of KwaZulu-Natal, South Africa. Four reference wetlands and three dairy-effluent impacted wetlands were sampled. Six macroinvertebrate samples were collected with a SASS net from each wetland. For each sample, the macroinvertebrates were identified and assigned a predetermined SASS5 tolerance score. Data for selected physico-chemical variables, macrohabitat condition, biotope suitability and organism detectability were collected to assist in interpretation of results. Thirty-eight taxa, identified to family level, were collected during sampling. Total SASS5 scores ranged from 15 to 82. Five of the wetlands had mean SASS5 scores of between 46 and 59. Five of the wetlands had an intra-wetland SASS5 score range of greater than 30. Average score per taxa (ASPT) values ranged from 3.3 to 5.5, and few high scoring (≥ 8) taxa were collected. There was no significant difference in SASS5 scores between samples collected above, at, and downstream of, an effluent discharge point within the same impacted wetland. SASS5 scores for reference wetlands were also not significantly higher than those recorded for impacted wetlands. Comparison of ranked SASS5 scores and environmental data did suggest a relationship between the variables, but this was not significant. Based on the SASS5 score water quality guidelines, all sampled wetlands were considered to have impacted water quality. However, this was not supported by the macrohabitat and physico-chemical results. There are a number of possible reasons for the low SASS5 scores: the lack of biotopes present in wetlands compared to rivers (most notably the absence of the stones-in-current biotope), lower levels of dissolved oxygen present compared to rivers, limited habitat availability due to low rainfall during the sampling season, and the limited detectability of organisms due to large amounts of substrate in the samples. Without modification, SASS5 appears unsuitable for assessing wetlands. However, variation in taxon composition — within impacted wetlands and between reference and impacted wetlands, revealed through multivariate analysis — suggests that macroinvertebrates are responsive to changes in wetland condition, and thus show potential as indicators of wetland water quality. It is recommended that a habitat or biotope index be further developed and used in conjunction with any future wetland macroinvertebrate bioassessment protocols.

Keywords: bioassessment; environmental impacts; macroinvertebrates; microhabitats; palustrine wetlands; sampling methods; SASS5; water quality

African Journal of Aquatic Science 2006, 31(2): 229–246