Effects of sewage waste stabilization lagoon effluent on stream invertebrates

Abstract

The ecological impact of discharge to streams of domestic sewage waste stabilization lagoon effluent was investigated. Benthic invertebrates were compared upstream and downstream of discharges to eight New Zealand streams where effluent dilution ranged from 6-to 484-fold. The percentage of common invertebrate taxa whose density changed significantly (ANOVA, P < 0.05) downstream declined in proportion with the log of the effluent dilution (r = -0.87) and increased with downstream increase in benthic respiration (r ; 0.91) and several intercorrelated indicators of organic enrichment (log biochemical oxygen demand, r = 0.91; log suspended solids (SS), r --0.84). However, these changes in invertebrate densities did not always reflect degraded community structure. The nature and direction of changes suggests a subsidy-stress gradient of responses. Increases in SS of > 4 g m -3 were associated with significant changes in density of > 50 percent of the common taxa and > 50 percent reduction of the densities of the sensitive Ephemeroptera, Plecoptera, and Trichoptera (EPT). However, EPT densities increased by up to 50 percent at lower organic solids loadings. No general relationships were found between relative densities of functional feeding groups and metabolic or water quality variables. These findings confirm that early warning of enrichment stress is more easily seen at the species level than at the functional level. I n t r o d u c t i o nWaste stabilization (oxidation) ponds are widely used for sewage treatment throughout the world, and are the most common method of domestic sewage treatment prior to discharge to running waters in New Zealand (Hickey et al., 1989).Sewage waste stabilization lagoon effluents contain high levels of organic matter, plant nutrients, and potentially-toxic ammonia (Hickey et al., 1989). These constituents have the potential to cause substantial direct and indirect stress on stream invertebrate communities by altering food supply, habitat, and water quality.We hypothesized that discharge of waste stabilization lagoon effluents to streams would cause a 'subsidy-stress' gradient of invertebrate community responses (sensu Odum et al., 1979), involving positive and negative effects depending upon the contaminant concentrations in the receiving water (largely a function of effluent dilution, given a standard lagoon design (Hickey et al., 1989)). At moderate dilutions 'subsidy' effects were predicted, where productivity is enhanced without substantially altering community structure. In contrast, at low dilutions the over-supply of organic material and toxicity of ammonia were expected to stress the community, eliminating or restricting many species and allowing dominance by opportunistic, tolerant species.This study aimed to quantify the effects on benthic invertebrate abundance and c o m m u n i t y composition of sewage waste stabilization lagoon effluent at receiving water dilutions at which earlier work (Hickey et al., 1989) indicated a wide range of potential community responses from stre...

Organic matter, nutrients, and optical characteristics of sewage lagoon effluents

“…In particular, bacterial indicators were not measured, being related to public health rather than ecological impact. This paper reports a characterisation of lagoon effluents using the dataset on lagoon effluent quality compiled as part of the ecological studies of Welch et al (1992) and Quinn & Hickey (1993). We extend and complement the information on effluent character of sewage lagoons in our 1989 study by presenting data for a wider range of variables.…”

“…Based on the study of streams receiving some of the lagoon effluents characterised here, Quinn & Hickey (1993) concluded that organic paniculate matter is the constituent in lagoon effluent most strongly influencing benthic invertebrate communities. They found that increases in SS above about 4 g m~3 resulted in marked reductions (> 50%) in the density of sensitive invertebrate groups.…”

“…Five of the lagoon systems were sampled up to three times each in both summer and winter, one (Waipawa) was sampled three times in winter only, and the other five lagoon systems were each sampled once only. This sampling design is clearly not ideal for the purpose of assessing lagoon effluent quality, and reflects the fact that the lagoon effluent sampling was carried out to support a study of ecological effects of lagoon discharges at different dilution ratios in receiving streams (Welch et al 1992;Quinn & Hickey 1993). However, as we show below, the effluent characteristics are broadly similar to those reported in our 1989 study, and seasonal patterns are weak, so we do not think that the overall picture of lagoon effluent quality presented here is compromised.…”

“…consider management issues with sewage lagoon effluents, including monitoring requirements and possibilities for upgrading lagoon effluent quality. Particular attention is given to potential effects on receiving streams, guided by recent work on ecological responses of such streams (Welch et al 1992;Quinn & Hickey 1993) and recently published guidelines (Ministry for Environment 1992. (1974) specifications.…”

“…As part of a suite of studies (Welch et al 1992;Quinn & Hickey 1993) of the effects of sewage lagoon effluents on the ecology of receiving streams at different dilution levels, 11 lagoon systems were sampled and a wide variety of characterising variables (26) measured. Lagoon solids were characterised by measurements of chlorophyll a (Chi.a, an index of phytoplankton biomass) and volatile solids, as well as total solids.…”