A particularly strong approach for the future is a balanced combination of natural abundance analyses and isotope addition experiments. Natural abundance analyses can provide an assessment of the background conditions while creatively targeted isotope additions would afford opportunities to resolve trophic ambiguities, monitor changes in trophic dynamics in response to environmental factors (e.g. nutrient enrichment, fragmentation, and disturbance), or examine export of organic matter to other habitats. Despite the numerous difficulties of applying isotope additions in such open systems, advances continue to be made to permit isotope additions in the field. Along with direct isotope additions via spraying (Ottosen et al., 2001; Carman and Fry, 2002; Fry et al., 2003) or incorporation into fertilizer (Mutchler et al., 2004), organisms themselves could be labeled in the laboratory and 'released' into the field. Isotope signatures of specific beds (Stapel et al., 2001) or unvegetated sediments could be manipulated and the fate of the tracer monitored. Indeed, multiple isotope additions (e.g. 13C, 15N, and34S) may be applied (Carman and Fry, 2002).
Was this article helpful?