The relationship between concurrently measured SASS (South African Scoring System) and turbidity data archived in the South African River Health Programme’s Rivers Database

Ak Gordon,Cg Palmer,Nj Griffin

doi:10.4314/wsa.v41i1.4

Abstract

The need for monitoring the biological impacts of instream sediments has long been recognised, yet robust and scientifically defensible tools for doing so are still in the early stages of development because of the difficulties experienced by researchers in characterising the complicated mechanisms of biological effect elicited by sediment particles. Biological monitoring is one such tool, and this paper reports on the initial stages of a study to determine the most applicable approach for measuring the effects of instream sediments on aquatic macroinvertebrates in the South African context. In this first instance, the suitability of the rapid macroinvertebrate biomonitoring tool (the South African Scoring System) was investigated by determining the extent of the correlation between concurrently measured SASS metrics and turbidity data collected for the South African River Health Programme. All three SASS metrics – SASS score, number of taxa (NOT), and average score per taxon (ASPT) – were found to be significantly negatively correlated with turbidity, although variation in the data was high. Turbidity was found to be the major driver of change in ASPT. In contrast, electrical conductivity was the major driver of SASS scores and NOT, with turbidity a close second. When combined, electrical conductivity and turbidity accounted for 80% (SASS score) and 75% (NOT) of the variation in the regression model. Consequently, SASS metrics are a crude, but reliable, indicator of the negative biological implications of excessive instream sedimentation as measured by turbidity. A number of other potential biomonitoring approaches for detecting the impacts of fine sediment exposure are identified for further investigation: spatial analyses of macroinvertebrate assemblages; and the use of structural and functional metrics.Keywords: aquatic macroinvertebrates, suspended sediment, biomonitoring

Highlights

While sediment is a fundamental and necessary part of aquatic ecosystems and their functioning, elevated sediment concentrations influence aquatic biota through both direct and indirect means, producing complex interactions affecting individuals, populations and whole communities (Dunlop et al, 2008)
All three metrics were found to be significantly correlated with turbidity
There were significant negative correlations between concurrently measured turbidity and South African Scoring System (SASS) metrics archived in the Rivers Database, variance in the fitted models remained high

Summary

Introduction

While sediment is a fundamental and necessary part of aquatic ecosystems and their functioning, elevated sediment concentrations influence aquatic biota through both direct and indirect means, producing complex interactions affecting individuals, populations and whole communities (Dunlop et al, 2008). Direct effects on macroinvertebrates from suspended sediment include clogging and/or abrasion of gills (leading to reduced organism condition) and filter-feeding organs (leading to reduced feeding efficiency) (Bilotta and Brazier, 2008; Jones et al, 2011), while settled sediment particles can bury benthic macroinvertebrates and smother eggs causing mortality (Jones et al, 2012). The need to manage instream sediment concentrations is evident. There is no biomonitoring method capable of assessing the direct or indirect effects of elevated instream sediment levels. Gaining an understanding of the most appropriate (in terms of sensitivity and practicality) biomonitoring approach for measuring biological effects of instream sediment is warranted, and is the subject of this paper

Objectives

Methods

Results

Discussion

Conclusion