CHARACTERIZATION OF ENERGY AND POTENTIAL CONTAMINANT PATHWAYS IN SUBARCTIC ESTUARINE HABITATS: ECOLOGY OF TIDAL FLAT COMMUNITIES OF THE COPPER RIVER DELTA, ALASKA Final Report to the Prince William Sound Regional Citizens Advisory Council

2 Summary Vast expanses of intertidal sand/mudflats serve as a critical link in the food web of nearshore biological communities in many coastal areas of Alaska. The rich abundance of benthic invertebrates residing within the sediments of intertidal flats and the large network of subtidal channels that bisect these flats provide a significant prey resource for numerous species of fish, crabs, birds, and marine mammals. One of the largest expanses of intertidal mud/sand flats occurs in the Copper River Delta and southeastern Prince William Sound (Orca Inlet). The estuarine nature of this system results in mixing of nutritional sources from riverine, estuarine and marine ecosystems, which fuel secondary productivity. Here, we investigated linkages between riverine and oceanic influences and the nutritional baseline for mudflat food webs in the Copper River Delta and Hartney Bay in Southeastern Prince William Sound, using stable isotopes of naturally occurring carbon (C) and nitrogen (N), which are both essential elements for growth. Isotopes of C and N have been used in numerous studies of marine and freshwater food webs. The proportion of N that occurs as 15 N versus 14 N, the latter being the more common form, gives information on source of N (marine derived N is enriched in 15 N compared to terrestrial derived N) and trophic position (higher 15 N are associated with organisms feeding higher in the food web). The ratio of C isotopes is useful in determining the source of energy because the ratio is conserved to a higher degree than N as energy is assimilated up the food web. In general, terrestrial primary producers have lower δ 13 C values than primary producers in the marine environment. Differences among δ 13 C (a calculation that relates the relative concentration of 13 C to the more common 12 C) and δ 15 N (a calculation that relates the relative concentration of 15 N to the more common 14 N) were determined for several portions of the food web: particulate organic matter (organic material in the water column), sediment organic material (includes detritus and microalgae that feed benthic invertebrates), macroalagae, benthic invertebrates, and demersal (bottom-feeding) fishes. Variations in δ 13 C and δ 15 N were detected at each trophic level of the food web and tended to indicate differences in nutrient sources between the more oceanic influenced Hartney Bay mud flat community and the mudflat community of the riverine influenced …