1) Coastal rivers are viewed as avenues for the downstream transport of freshwater nutrients to coastal areas. However, these same rivers support a seasonal influx of marine nutrients via spawning marine fish returning to the streams where they hatched. Many of these fish die after spawning and deposit marine nutrients within the nutrient-poor freshwater. Although this phenomenon has been documented on the west coast of North America, east coast streams, with their seasonally abundant river herring, have received little attention.

Marine organics are enriched in the heavy isotopes of carbon, nitrogen and sulfur relative to freshwater organics. The heavy isotopes brought to freshwater by the herring will act as tracers of the marine material as it is used by ecosystem components. The project will involve seasonal examinations of the stable isotope geochemistry of two freshwater areas to determine whether marine nutrients are fueling these systems. The project will also explore how diagenesis transformations of fatty acids derived from spawning marine fish once they are incorporated into sediment. This will offer clues to the utility of tracing marine nutrient contributions to sediments using fatty acid biomarkers.

 

2) Stable isotope turnover due to growth and metabolism in a warm water fish species.

The stable isotopes of carbon (12C/13C), nitrogen (14N/15N) and (more recently) sulfur (34S/32S) have become an excellent tool for ecologists and biogeochemists to use for tracing the origins and fates nutrients in ecosystems. The different methods (or enzymes) used for fixation by autotrophs often result in differential uptake of the light isotope for the above elements. The isotope ratio, therefore, becomes a good tracer of nutrients from different part of an ecosystem. Most of the studies published assume that there is an isotopic equilibrium between predator and prey (as well as autotroph and herbivore/omnivore). This assumption is never tested within the studies. There have been a few papers reporting the rate of isotopic turnover associated with diet shift but these are few and mostly focus on small animals with high metabolisms and growth rates. There is a huge demand for laboratory studies addressing the isotopic turnover rates of animals. Juvenile and minnow type fish are an important link between autotrophic production and larger predators. Because of this, we must understand how quickly small (or growing) fish take on the isotope signature of their food source.

Return to Main Programs Page