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

We used the size-frequency method to calculate annual production of the shredder functional group in four streams on the Allegheny Plateau of 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 streams. The crayfish Cambarus bartoni contributed >55% of shredder biomass in all streams, but contributed <20% of shredder production. Annual production of the other common shredder species differed among streams. Gammarus minus and Tipula abdominalis contributed 77% of shredder production in the stream with the highest pH. Tipula abdominalis, Pycnopsyche sp., and Peltoperla arcuata together contributed 68% and 54% of shredder production in the two streams with intermediate pH. Leuctra spp., Amphinemura sp., and Paracapnia angulata contributed 71% of shredder production in the stream with the lowest pH. Annual production of 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 intermediate-pH streams, and 1.19 g dry mass/m2 in the lowest-pH stream. The differences in annual production of different shredder species among streams paralleled the results of other studies that have found differences in macroinvertebrate community structure in relation to differences in pH and alkalinity. However, the annual production of the shredder functional group in these streams may also have been affected by differences in the riparian vegetation and temperature among streams in addition to pH and alkalinity.