Effect of a Leaf-Shredding Invertebrate on Organic Matter Dynamics and Phosphorus Spiralling in Heterotrophic Laboratory Streams

• Published in: Oecologia 1985-05, Vol.66 (2), p.199-206
• Main Authors: Mulholland, P. J., Elwood, J. W., Newbold, J. D., Ferren, Leigh Ann
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Biomass; Cobbles; Fresh water ecosystems; Freshwater; Fundamental and applied biological sciences. Psychology; Lotic systems; Nutrient utilization; Phosphorus; Respiration; Seston; Snails; Streams; Surface areas; Synecology
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/BF00379855

The effect of invertebrate shredders on organic matter dynamics and phosphorus spiralling was studied over a 30-week period in laboratory streams. The streams were fed by groundwater, layered with cobble and gravel from a natural stream, covered with opaque material to eliminate algal growth, and initially contained 195 g/m2of autumn-shed leaves. Four weeks after leaf addition, leaf-shredding snails (Goniobasis clavaeformis) were added to each of three streams in densities of 75, 220, and 800/m2. A fourth stream contained no snails and served as a control. Presence of snails increased the loss rates of coarse particulate organic matter (CPOM) and total organic matter (TOM), primarily by increasing leaf fragmentation and seston export. Although snail feeding increased specific metabolism of microbes associated with CPOM and cobble surfaces, it was not enough to compensate for reduction in bacterial cell numbers per unit surface area and in stream TOM. Consequently mineralization of detritus and wholestream phosphorus utilization rate were maximum in the stream with no snails and decreased with increasing snail density. From previous simulations of a stream model based on the nutrient spiralling concept, we predicted that there should be an intermediate shredder density which would minimize phosphorus spiralling length (maximize phosphorus utilization) in a natural stream nearby. Our current results conflict with the model-based predictions primarily because the increase in microbial metabolism was less important than reduction in bacterial cell numbers and total benthic organic matter resulting from snail feeding. Although our results indicate macroinvertebrate shredders reduce phosphorus utilization in headwater streams, shredders may increase nutrient utilization downstream where riparian inputs are lower, thus linking low- and high-order streams.