INVERTEBRATE COMMUNITY RESPONSE TO EXPERIMENTAL LIME (CA(OH)(2)) TREATMENT OF AN EUTROPHIC POND

Calcium hydroxide (Ca(OH)2), or hydrated lime, has recently been reint roduced in western Canada as a treatment to reduce macrophytes and alg ae in eutrophic waters. We examined the effects and recovery of aquati c invertebrates of the Ca(OH)2 treatment (250 mg L-1) of one half of a divided eutrophic pond compared to the untreated half. Nine weeks fol lowing treatment, total invertebrates on the untreated side were prese nt at 1917 +/- 555 individuals m-2, and on the treated side at 822 +/- 186 individuals m-2. Notably, Chironomidae represented 13% of inverte brates on the untreated half, but dominated numerically with 72% on th e treated half of the pond. The remaining five most abundant taxa in t he untreated side were 88%-99% less abundant in the treated half of th e pond. Diversity and evenness were twice as high for the untreated ha lf as for the treated half of the pond. Because macrophytes were also extirpated with the Ca(OH)2 treatment, macrophyte-associated taxa were absent or at low numbers in the treated half. The death of organisms on the treated side of the pond may have been caused (directly or indi rectly) by the pH shock associated with Ca(OH)2 treatments. Slow recol onization by most invertebrates during the year of treatment was proba bly due to the lack of heterogeneous macrophyte habitat. Follow-up sam pling 3 years later indicated that the pond completely regained the ab undance and biological diversity of flora and fauna.