US EPA

2500227 

Journal Article 

Pathways of N and C uptake and transfer in stream food webs: an isotope enrichment experiment 

Parkyn, SM; Quinn, JM; Cox, TJ; Broekhuizen, N 

2005 

Yes 

Journal of the North American Benthological Society
ISSN: 0887-3593
EISSN: 1937-237X 

24 

4 

955-975 

10.1899/04-082.1 

WOS:000233839300018 

Landuse change alters the quantity and supply of stream energy resources from allochthonous (catchment-derived) to autochthonous (stream-derived) sources. This alteration has prompted the need for better understanding of C and N pathways through stream food webs. We added stable N-15-NH4, and C-13-acetate isotopes as tracers to experimental stream channels containing I of 4 key basal food resources: autotrophic epilithon, heterotrophic epilithon, fine particulate organic matter (FPOM), and coarse particulate organic matter (CPOM). Our goal was to evaluate the importance of these foods to 2 scrapers (Deleatidium sp. [mayfly] and Potamopyrgus antipodaruni [snail]) and a facultative shredder (Olinga feredayi [caddisfly]). A 511, potential food source, new heterotrophic biofilm, grew on all surfaces during the course of the experiment. Isotope levels in the food resources and the invertebrates were measured weekly during the 3-wk isotope addition and for 2 wk after the addition. Changes in nutrient concentrations between the channel inflows and outflows provided measures of instream net uptake. Net uptake of P by autotrophic epilithon (mean = 0.09-0.24 mg dissolved reactive P [DRP] m(-2) h(-1)) was 3X higher than uptake by other basal resources. Autotrophic epilithon removed substantial quantities of dissolved N, predominantly as NO3-N (2.1-9.3 mg NO3-N m(-2) h(-1)), whereas the other basal resource types removed only NH4-N at a rate that was 2 orders of magnitude slower (mean = 0.04-0.08 mg NH4-N m(-2) h(-1)) than uptake by autotrophic epilithon. NH4-N and dissolved organic C isotope tracers were taken up predominantly by heterotrophic epilithon and new biofilms. We developed a dynamic mixing model to separate the contribution to the invertebrates of each treatment food source relative to the new heterotrophic biolfilm. Mayflies obtained almost 100% of their body C and N from new biofilm except when offered autotrophic epilithon, which contributed > 50% to their diets. Olinga and Potamopyrgus obtained most of their C and N from the treatment food sources, but in the particulate organic matter treatments (FPOM and CPCM) the contribution of new biofilm was much larger (similar to 10-60%). Our results suggest that heterotrophic biofilms are a significant component of stream food webs. 

stream; stable isotopes; nitrogen; carbon; phosphorus; nitrate; autochthonous; allochthonous; biofilms; epilithon; invertebrates; autotrophic; heterotrophic