Microbial and Animal Processing of Detritus in a Woodland Stream

Abstract

The detritus standing crop, microbial respiration, and macroinvertebrate biomass were examined in monthly samples from the riffle sections of a first-order woodland stream. Total detritus was remarkably constant; the average (with 95% cL) ash-free dry mass standing crop was 426.4 ± 85.9 glm 2 over the 14 mo of the study. Throughout the year benthic detritus was dominated by fine particulate detritus ( < 1 mm), which made up 68.9% of the total ash-free dry mass. Woody debris made up 8%, whole leaves 3.5%, and leaffragments and other coarse particulate detritus accounted for 19.7% ofthe total standing crop. Decreases in standing crop were attributable to microbial respiration, macroinvertebrate assimilation, and downstream export. Microbial respiration annually removed 150% of the average standing crop, with the major effect on the smallest particle size category. Macroinvertebrate assimilation, defined as the sum of respiration and growth, removed 11.6% of the detritus standing crop annually. Shredders accounted for 20% of total animal assimilation, with the remaining 80% attributable to collectors and grazers. Based on monthly changes, it appears that total detritus standing crop is the result of the past discharge regime, which determines the overall amount of detritus present, and the rate of biological (microbial and invertebrate) processes, which determine the size and quality ofthe detritus particles. This suggests that detritus in streams, while strongly affected by both biotic and abiotic factors, may be in equilibrium within physical and biological constraints such that an annual steady-state system exists, similar to that for soil systems.

Microbial respiration and chemical composition of different sediment fractions in waterbodies of the upper Paraná River floodplain, Brazil

“…Some studies have demonstrated a consistent increase in microbial heterotrophic activity as detritus becomes smaller (Hargrave, 1972;Petersen et al, 1989). The nutritive value (e.g., organic matter content) of the sediment and the detritus may be an important predictor of microbial heterotrophic activity, as has been shown for bacteria (Findlay et al, 1986;Cole et al, 1988).…”

“…The following fractions were considered: ultra-fine particles (< 70 µm), fine particles (70-300 µm), medium particles (300-1,000 µm) and coarse particles (> 1,000 µm). This size classification follows that proposed by Petersen et al (1989) for organic matter, with minor modifications. Petersen et al (1989) used the following classification: ultra-fine particles (0.5-75 µm), fine particles (75-250 µm), medium particles (250-1,000 µm) and coarse particles (> 1,000 µm).…”

“…This size classification follows that proposed by Petersen et al (1989) for organic matter, with minor modifications. Petersen et al (1989) used the following classification: ultra-fine particles (0.5-75 µm), fine particles (75-250 µm), medium particles (250-1,000 µm) and coarse particles (> 1,000 µm). Larger organisms (benthic fauna such as the Chironomidae) occasionally present in the coarse fraction were removed before beginning the incubations.…”

Effect of Flow Fluctuations on Patch Dynamics and Chironomid Distribution in a Medium-Sized Lowland River

“…A 1 mm sieve was used to separate BPOM into coarse BPOM (>I mm, BCPOM) and fine BPOM ( 4 mm BFPOM), according to Petersen et al (1989). Samples were then dried at 60°C, weighed, ashed at 60O0C, and reweighed.…”

Comparisons of the Colonisation by Invertebrates of Three Species of Wood, Alder Leaves, and Plastic “Leaves” in a Temperate Stream

“…It is a source of biologically-fixed energy to stream food webs. Wood is more biologically stable (GULIS et al, 2004) and less seasonal (PETERSEN et al, 1989) than other kinds of detritus, and studies have demonstrated that wood can serve as a food source for some species of stream invertebrates ANDERSON, 1982, 1987;BON-DAR et al, 2005). However, few studies have looked at the nutritional significance of small woody debris in stream ecosystems, whereas the predominant focus has been on leaves as a food resource in these systems (e.g., RICHARDSON, 1991RICHARDSON, , 1992WALLACE et al, 1999).…”