SECONDARY PRODUCTION OF MACROINVERTEBRATE SHREDDERS IN HEADWATER STREAMS WITH DIFFERENT BASEFLOW ALKALINITY

We used the size-frequency method to calculate annual production of th e shredder functional group in four streams on the Allegheny Plateau o f West Virginia. These streams were characterized by different bedrock geology, streamwater pH, and alkalinity. Mean alkalinity was 40.8, 0. 9, 0.7, and 0.0, and mean pH was 7.5, 6.1, 6.0, and 4.3 in the four st reams. The crayfish Cambarus bartoni contributed >55% of shredder biom ass in all streams, but contributed <20% of shredder production. Annua l production of the other common shredder species differed among strea ms. Gammarus minus and Tipula abdominalis contributed 77% of shredder production in the stream with the highest pH. Tipula abdominalis, Pycn opsyche sp., and Peltoperla arcuata together contributed 68% and 54% o f shredder production in the two streams with intermediate pH. Leuctra spp., Amphinemura sp., and Paracapnia angulata contributed 71% of shr edder production in the stream with the lowest pH. Annual production o f the shredder functional group was 3.77 g dry mass/m2 in the highest- pH stream, 2.06 g dry mass/m2 and 1.56 g dry mass/m2 in the intermedia te-pH streams, and 1.19 g dry mass/m2 in the lowest-pH stream. The dif ferences in annual production of different shredder species among stre ams paralleled the results of other studies that have found difference s in macroinvertebrate community structure in relation to differences in pH and alkalinity. However, the annual production of the shredder f unctional group in these streams may also have been affected by differ ences in the riparian vegetation and temperature among streams in addi tion to pH and alkalinity.