Mechanical abrasion and organic matter processing in an Iowa stream

Rates of organic matter processing are key parameters for studies of stream ecosystem function and stream community ecology. Most studies of organic matter processing in streams use leaves in leafpacks or litterbags, which are immobilized and partly shielded from contact with stones in transport and in the stream bottom. As a result, these studies may underestimate the contribution of mechanical abrasion to overall processing rate (of coarse organic detritus to fine particles). We compared leaf processing rates in litter bags with and without stones (5 cm crushed limestone ballast) in Big Mill Creek, eastern Iowa. In two of three experiments, processing was significantly more advanced in bags with stones than in bags without stones: the fraction of leaf mass reduced to small fragments (1.4–9.5 mm) was 45% and 93% higher in bags with stones. In a fourth experiment, we compared the effects of stones and shredders (Gammarus pseudolimnaeus, at near-natural densities) on fragmentation of leaves in litterbags. This experiment indicated that mechanical and biological agents of processing are roughly equally important in Big Mill Creek. Our results indicate that mechanical abrasion can be an important contributor to organic matter processing in streams. If so, it may be an important source of the finer particles used by collectors. Litterbag and leafpack experiments may underestimate total processing rates and overestimate the relative importance of processing by microbes and invertebrates.

[1]  R. Eckhardt.  Statistics of natural selection , 1987 .

[2]  R. Newman.  Effects of shredding amphipod density on watercress Nasturtium officinale breakdown , 1990 .

[3]  B. Hill,et al.  Microbial colonization, respiration, and breakdown of maple leaves along a stream-marsh continuum , 1995, Hydrobiologia.

[4]  T. Cuffney,et al.  Experimental evidence quantifying the role of benthic invertebrates in organic matter dynamics of headwater streams , 1990 .

[5]  B. R. Taylor,et al.  Variable effects of air-drying on leaching losses from tree leaf litter , 1996, Hydrobiologia.

[6]  G. T. Peters,et al.  Effects of forest disturbance on leaf breakdown in southern Appalachian streams , 1991 .

[7]  E. F. Benfield,et al.  Leaf pack processing in a pastureland stream , 1977 .

[8]  J. Webster,et al.  The role of macroinvertebrates in stream ecosystem function. , 1996, Annual review of entomology.

[9]  G. Ward.  Size distribution and lignin content of fine particulate organic matter (FPOM) from microbially processed leaves in an artificial stream: With 2 figures and 2 tables in the text , 1984 .

[10]  S. Heard.  Short-term dynamics of processing chain systems , 1995 .

[11]  P. Boon,et al.  A review of methodology used to measure leaf litter decomposition in lotic environments: Time to turn over an old leaf? , 1991 .

[12]  Jacob Cohen.  Statistical Power Analysis for the Behavioral Sciences , 1969, The SAGE Encyclopedia of Research Design.

[13]  S. Heard.  Processing Chain Ecology: Resource Condition and Interspecific Interactions , 1994 .

[14]  F. O. Howard,et al.  The Utilization of Leaf Litter by Stream Detritivores , 1973 .

[15]  K. Cummins,et al.  An Introduction to the Aquatic Insects of North America , 1981 .

[16]  Jackson R. Webster,et al.  VASCULAR PLANT BREAKDOWN IN FRESHWATER ECOSYSTEMS , 1986 .

[17]  W. McDiffett,et al.  The Transformation of Energy by a Stream Detritivore, Pteronarcys Scotti (Plecoptera) , 1970 .

[18]  M. Gessner,et al.  Bacteria, fungi and the breakdown of leaf litter in a large river , 1995 .

[19]  G. Ward.  Size distribution and lignin content of fine particulate organic matter (FPOM) from microbially processed leaves in an artificial stream , 1984 .

[20]  M. Gessner,et al.  Breakdown and Invertebrate Colonization of Leaf Litter in Two Contrasting Streams, Significance of Oligochaetes in a Large River , 1993 .

[21]  K. Cummins,et al.  Processing of confined and naturally entrained leaf litter in a woodland stream ecosystem1 , 1980 .

[22]  J. Richardson,et al.  Shredder-collector facilitation in stream detrital food webs: is there enough evidence? , 1995 .

[23]  R. Petersen,et al.  Microbial and Animal Processing of Detritus in a Woodland Stream , 1989 .

[24]  S. R. Reice.  The role of animal associations and current velocity in sediment-specific leaf litter decomposition , 1977 .

[25]  R. Dennis Cook,et al.  The Statistics of Natural Selection. , 1987 .

[26]  D. J. D'Angelo,et al.  Natural and constrainment-induced factors influencing the breakdown of dogwood and oak leaves , 1992, Hydrobiologia.

[27]  J. Webster,et al.  Stream detritus dynamics: Regulation by invertebrate consumers , 2004, Oecologia.

[28]  J. Sedell,et al.  Detritus Processing by Macroinvertebrates in Stream Ecosystems , 1979 .

[29]  Robert C. Petersen,et al.  Developments in Stream Ecosystem Theory , 1985 .

[30]  J. Webster,et al.  Effects of forest clearcutting on leaf breakdown in a southern Appalachian stream , 1982 .

[31]  S. Perry,et al.  Comparison of leaf processing rates under different temperature regimes in three headwater streams , 1996 .

[32]  C. Cushing,et al.  Effect of excluding shredders on leaf litter decomposition in two streams , 1986 .

[33]  J. McArthur,et al.  Community Dynamics of Leaf Litter Breakdown in a Utah Alpine Stream , 1988, Journal of the North American Benthological Society.