Responses of Aquatic Insects to Cu and Zn in Stream Microcosms: Understanding Differences Between Single Species Tests and Field Responses

Abstract

Field surveys of metal-contaminated streams suggest that some aquatic insects, particularly mayflies (Ephemeroptera) and stoneflies (Plecoptera), are highly sensitive to metals. However, results of single species toxicity tests indicate these organisms are quite tolerant, with LC50 values often several orders of magnitude greater than those obtained using standard test organisms (e.g., cladocerans and fathead minnows). Reconciling these differences is a critical research need, particularly since water quality criteria for metals are based primarily on results of single species toxicity tests. In this research we provide evidence based on community-level microcosm experiments to support the hypothesis that some aquatic insects are highly sensitive to metals. We present results of three experiments that quantified effects of Cu and Zn, alone and in combination, on stream insect communities. EC50 values, defined as the metal concentration that reduced abundance of aquatic insects by 50%, were several orders of magnitude lower than previously published values obtained from single species tests. We hypothesize that the short duration of laboratory toxicity tests and the failure to evaluate effects of metals on sensitive early life stages are the primary factors responsible for unrealistically high LC50 values in the literature. We also observed that Cu alone was significantly more toxic to aquatic insects than the combination of Cu and Zn, despite the fact that exposure concentrations represented theoretically similar toxicity levels. Our results suggest that water quality criteria for Zn were protective of most aquatic insects, whereas Cu was highly toxic to some species at concentrations near water quality criteria. Because of the functional significance of aquatic insects in stream ecosystems and their well-established importance as indicators of water quality, reconciling differences between field and laboratory responses and understanding the mechanisms responsible for variation in sensitivity among metals and metal mixtures is of critical importance.

Recovery of a mining-damaged stream ecosystem

“…Whereas both fish and invertebrates may be sensitive to low Cu concentrations that were elevated only 3 to 5X above background concentrations (e.g., Besser et al, 2007;Mebane and Arthaud, 2010;Clements et al, 2013), we found no reports of Co having any direct adverse effects to fish at environmentally relevant concentrations. In a 60-day growth and survival test of Rainbow Trout fry using dilution water from upper Panther Creek, the lowest observed effect was a 5% reduction in growth at 242 µg/L (Pacific EcoRisk, 2005).…”

“…As of 2013, abundances of the common mayflies Caudatella hystrix, Ephemerella, Cinygmula, and Rhithrogena were 50 to 60% that of reference, at which time smoothed Cu concentrations were about 0.6X the chronic criterion. Reductions in total mayfly abundance on the order of 50% have been observed with 10-day aquatic insect microcosm exposures to Cu at only 0.8X the mean BLM-based chronic criterion (Clements et al, 2013), which suggests that Cu concentrations at BD-km5.3 averaging about 0.6X the Cu criterion could plausibly have caused reduced abundances of particularly Cu sensitive mayflies.…”

“…Conventional short-term toxicity tests with field-collected stream insects have produced exorbitantly-high effect values relative to apparent effects from field studies, longer-term community microcosm tests, or to short-term tests with fish or cultured, small crustaceans such as amphipods or daphnids (Brinkman and Johnston, 2008;Brix et al, 2011;Mebane et al, 2012;Clements et al, 2013;Poteat and Buchwalter, 2014). For example, 137 µg/L Cu was required to reduce the survival of the mayfly Rhithrogena hageni by 50% in a 96-hour laboratory toxicity test (Brinkman and Johnston, 2008), yet recovery of Rhithrogena sp.…”

The effects of the pharmaceutical carbamazepine on life history characteristics of flat-headed mayflies (Heptageniidae) and aquatic resource interactions

“…This in vitro experiment demonstrated that environmentally relevant concentrations of carbamazepine could have chronic effects on Stenonema and Chaetophora. While data obtained from these types of in vitro experiments are useful in understanding the effects of anthropogenic stressors, the results commonly underestimate the sensitivity of freshwater organisms in situ (Buchwalter et al 2007;Clements et al 2013). In order to fully understand the effects carbamazepine has on freshwater ecosystems, more research focusing on chronic exposures of this pharmaceutical pollutant at environmentally relevant concentrations is needed (Murray et al 2010;Rosi-Marshall and Royer 2012;Hughes et al 2013).…”

Relationships between the psychiatric drug carbamazepine and freshwater macroinvertebrate community structure

“…Anthropogenic stressors associated with an increasing human population threaten biodiversity and reduce services provided by freshwater ecosystems (Vörösmarty et al, 2010;Dodds et al, 2013). Freshwater pollutants degrade habitat quality (Schulz et al, 2002;Clements et al, 2013), alter species composition (Muñoz et al, 2009;Beketov et al, 2013), and reduce macroinvertebrate richness, which is related to the pollution tolerance of taxa ( Fig. 1; Wogram and Liess, 2001).…”