Periphyton Production in an Appalachian Mountain Trout Stream

Periphyton primary production was investigated in a second-order Appalachian Mountain stream and two of its tributaries. Using 14C fixation in recirculating chambers, estimates averaged 2.27 mg C m-2 h-1 in the mainstream and 1.65 and 1.37 mg C m~2 h-1 in the two tributaries. Abiotic factors most influential on primary production rates were light, streamflow and inorganic carbon. Based on annual budgets, the estimated stream energy input attributable to autochthonous primary production was about 3% of allochthonous inputs. However, because of high nutritive value and timing, autochthony may be more important than indicated by annual budgets. Introduction Many studies have indicated that allochthonous organic material is the major energy base for low-order streams {e.g., Nelson and Scott, 1962; Minckley, 1963; Hynes, 1963; Maciolek, 1966; Minshall, 1967; Fisher and Likens, 1972, 1973; Cummins, 1974). However, Minshall (1978) argued that belief in a general dependency of streams on allochthonous organic materials has resulted from a concentration of research effort in small streams in deciduous forests. In studies of such streams, the role of autotrophy has often been disregarded as negligible and not measured. In a recent review on lotie primary production, Wetzel (1975a) emphasized that in any attempt to effectively evaluate the efficiency and dynamics of a detritus-based system, it is essential to measure the magnitude and fluctuations of autotrophy. In general, quantitative measurements of annual primary production in lotie ecosystems are scarce (Likens, 1975). Of the few measurements made of annual primary production in low-order woodland streams, nearly all have been of tangential interest within more general studies and were usually accomplished by biomass accumulation techniques. Biomass accumulation techniques as measures of photosynthetic rate are considered error-prone for various reasons (Wetzel, 1975a). Hoskin (1959, as cited by Wetzel, 1975a) and Hall (1972) used the diurnal oxygen curve method in relatively small streams, but in most low-order streams, relatively high gradients and turbulence preclude using open system oxygen methods. Hansmann (1969) studied three streams, using the oxygen method but employing recirculating chambers to avoid problems produced by turbulence. Chambers improve measurements but in many cases, where primary production is relatively low, accurate measurement requires more sensitive methods than gas exchange techniques. Carbon-14 methodology is about 50 times more sensitive than gas exchange methods (Wetzel, 1975b) and therefore is particularly useful in low-order woodland streams. In this study we have coupled the advantages of using recirculating chambers and carbon-14 methodology to investigate carbon fixation rates in a second-order Appalachian Mountain trout stream and two of its tributaries. Description of Study Area Primary productivity measurements were made in Guys Run, a second-order tributary of the Calfpasture River (James River Basin, Rockbridge Co., Virginia; 79? 39' W long, 38? 58' ? lat) and in two tributaries, Glade Brook and Piney Branch. Most of the 19 km2 watershed of Guys Run is located within the Goshen Wildlife address correspondence to J. R. Webster.