Abstract When Pacific salmon (Oncorhynchus spp.) spawn and die, they deliver marine‐derived nutrient subsidies to freshwater and riparian ecosystems. These subsidies can alter the behavior, productivity, and abundance of recipient species and their habitats. Isotopes, such as nitrogen‐15 (15N), are often used to trace the destination of marine‐derived nutrients in riparian habitats. However, few studies have tested for correlations between stable isotopes and physiological responses of riparian organisms. We examined whether increases in δ 15N in terrestrial insect bodies adjacent to salmon spawning habitat translate to changes in percent nitrogen content and body size. This involved comparisons between distance from a salmon‐bearing river, marine‐derived nutrients in soils and insects, soil moisture content, and body size and nitrogen content in two common beetle families (Coleoptera: Curculionidae, Carabidae). As predicted, δ15N in riparian soils attenuated with distance from the river but was unaffected by soil moisture. This gradient was mirrored by δ15N in the herbivorous curculionid beetles, whereas carabid beetles, which feed at a higher trophic level and are more mobile, did not show discernable patterns in their δ15N content. Additionally, neither distance from the river nor body δ15N content was related to beetle body size. We also found that nitrogen‐15 was not correlated with total percent nitrogen in insect bodies, meaning that the presence of spawning salmon did not increase the percent nitrogen content of these insects. We conclude that while salmon‐derived nutrients had entered terrestrial food webs, the presence of δ15N alone did not indicate meaningful physiological changes in these insects in terms of percent nitrogen nor body size. While stable isotopes may be useful tracers of marine‐derived nutrients, they cannot necessarily be used as a proxy for physiologically important response variables.

Seabirds nest almost exclusively on offshore islands where they act as ecosystem engineers. They provide nutrients through guano deposition, and physically alter the environment through burrowing, nesting, and trampling. Seabird populations are adversely affected by invasive mammals and because of their ecosystem engineering role, this has implications across island ecosystems. Consequentially, invasive mammal eradications on islands are a critical conservation tool for both seabird populations and island ecosystems more broadly. However, due to the complex and interacting effects of invasive species and their removal, whole ecosystem recovery is not always assured, or even definable, following eradications. Despite this, monitoring beyond the confirmation of invasive species removal is rare and there is little understanding of what monitoring tools are suitable for assessing ecosystem-level recovery. In this thesis, I investigate the utility of nitrogen stable isotope analysis (SIA N ) as a means for assessing ecosystem function recovery on islands following invasive mammalian predator eradication. Foraging near the top of the marine food web, seabirds fertilise islands with nutrients containing nitrogen that is enriched in the heavy isotope (δ 15 N), and elevated δ 15 N values are traceable across ecosystem components on islands with seabird colonies. On islands with invasive mammalian predators, this marine-terrestrial linkage may be degraded, reflected by reduced δ 1 5 N

# Why is Nitrogen 15 found almost exclusively in marine environments? Tags: isotope - Score: 7 - Views: 1596 - Answers: 1 - Answered: yes - Asked by: John Snow (4603 rep) - Asked: 2016-10-04 - Site: chemistry ## Question Prelude The following story was told to me earlier this summer Every year during October, the Pacific rain creates an ideal spawning condition for the wild Pacific salmon in the coastal forests of British Columbia. Of course, when we think of salmon swimming upstream in the Pacific Northwest, some images might come to mind. Black bears and grizzly bears carry hundreds of kilos of fish out of the water and into the forest to consume. Naturally in the areas proximal to the rivers, fish carcasses are littered throughout, with the bears having ate what they wanted, leaving behind the rest to decompose. Scientists several years ago took to examining the nitrogen uptake and found that trees in nearby the river received a significant amount of their nutrients from the fish. Through their findings they showed a case that reverses the land to sea flow of nutrients. The study has been used to argue for the dedication of resources to rebuild and maintain wild pacific