LIMESTONE TREATMENT OF WHETSTONE BROOK, MASSACHUSETTS .3. CHANGES IN THE INVERTEBRATE FAUNA

We monitored the invertebrate fauna in Whetstone Brook for 3 years bef ore and after limestone treatment to mitigate low pH conditions caused by acid precipitation. Sampling was conducted during the spring, summ er, and fall by both qualitative and quantitative methods, The fauna i n Whetstone Brook in tile control and treatment sections was dominated by chironomids (Diptera), simuliids (Diptera), Leuctra (Plecoptera) a nd Hydropsyche (Trichoptera) in both pretreatment and treatment period s. The acid-sensitive mayfly genera Epeorus increased during liming in the treated section of the stream but also declined during the same p eriod in the control section. Annelida increased during the treatment period in both sections of the stream. The chironomid and black fly po pulations were not affected by liming. The lack of impact to the black fly population was surprising because larvae are obligate filter-feed ers and feed on suspended seston in the same size range as the limesto ne slurry that was used to treat Whetstone Brook. Treatment did not ch ange species diversity and taxa richness in the treated section of Whe tsone Brook, but both indices declined during the treatment period in the control section of Whetstone Brook. This decline was attributed to the poorer water quality of the untreated section of Whetstone Brook during the treatment period, which was due to higher-than-average prec ipitation. Percent community similarity analysis indicated that the co mmunity composition changed more in the treated section of Whetstone B rook than in the control section as a result of treatment, We conclude that the invertebrate fauna in the treated section of Whetstone Brook was not negatively affected by liming, but that population density an d diversity did not increase.