| The hyporheic distributions of abundance and biomass of macroinvertebrates were determined in two headwater streams differing primarily in their parent geology and substratum type. Monthly (total macroinvertebrates) and biweekly (Chironomidae) samples were taken from March 1999 to February 2000 at 10 cm depth intervals to 50 cm in Hendrick Mill Branch (Blount County, Alabama, Valley and Ridge physiographic province, cobble/gravel substrate) and Payne Creek (Hale County, Alabama, Coastal Plain physiographic province, sand substrate). Data were compared by site and depth using 2-way ANOVA and Tukey's HSD post hoc multiple comparison test. The total abundance and biomass in Hendrick Mill Branch were 143,977/m2 and 10.2 g/m2, respectively. Total abundance and biomass were 35,542/m2 and 1.5 g/m 2 in Payne Creek stream sites and 40,562/m2 and 3.2 g/m2 in wetland sites. The majority of total abundance in both streams were chironomids, worms, and microcrustaceans. For biomass, larger insect larvae (i.e., Megaloptera, Ephemeroptera) were dominant. Greater than 50% of the total annual invertebrate abundance and >75% of total annual invertebrate biomass was found at the benthic surface in both streams. Many taxa had significantly more biomass in the benthic sediments than any other depth interval. The majority of taxa sampled at the surface were also found in the hyporheic zone during the year (50–75% of taxa, depending on the stream) and some (i.e., chironomids, worms, mircocrustaceans) had apparent substantial hyporheic distributions with >50% of their annual mean biomass resident in the hyporheic zone. In Payne Creek wetland sites, almost no taxa penetrated below the benthic substrate. Annual secondary production within the family Chironomidae followed similar depth distributions to overall biomass and suggested that Hendrick Mill Branch (63 g m−2 y−1) and Payne Creek (8 g m−2 y−1) were highly productive, equal to or exceeding all previous production estimates in similar streams based on stream size and substrate type. Physical and chemical characteristics (i.e., dissolved oxygen, sediment grain size, water temperature variation) directly related to the parent geologies of these streams are proposed as the likely cause of the patterns in hyporheic distribution between Hendrick Mill Branch and Payne Creek. |
