Date of Award
Doctor of Philosophy (PhD)
Dr. Henry P. Schwarcz
Dr. Michael J. risk
Stable isotope ratios of carbon, nitrogen, hydrogen and oxygen were used here, to trace the extent of terrestrial input to estuarine bivalves (Mytilus edulis) during the summer of 1984 and 1985. Salinity records indicate a stronger river influence in 1985 compared to 1984.
Fatty acids ratios (C24/C16, C24/C14) are intercalibrated with stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) to characterize the sediments of a Negro Harbour, a small estuary which receives mixed terrestrial input. The relative contribution of terrestrial and organic matter calculated through fatty acid and stable isotope ratios were generally in agreement for sample sites in the upper part of the estuary. However, changes in the relative contribution of peat compared to higher terrestrial plants are more readily noticed using fatty acid ratios than with isotope ratios.
δ¹³C and δ¹⁵N were both compared in the organic matrix (lifetime average diet) and in the flesh (short-time variation) as well as in the stomach content (which were assumed to reflect the diet), the sediments, POC and marine plants. Based on δ¹³13C of the flesh more so than for δ¹⁵N values, it seems that Mytilus edulis take up some of the terrestrial material coming from Clyde river. The uptake was higher in 1985 which agrees with the river influence being stronger during that period of time.
The isotopic fractionation between the organic matrix of M. edulis and the stomach content (assumed to be the immediate diet) average about 4‰ for carbon and 2.0‰ for nitrogen. There seems to be less fractionation between the flesh and the organic matrix using nitrogen isotope compared to carbon isotope ratio. δ¹³C and δ¹⁵N of organic matrices do not change over a period of one year and are therefore useful in evaluating long-term changes in diet of bivalves and regional differences. The organic matrix resemble in certain characteristics, the collagen of bone, which is widely used in paleodiet studies. Thus, the organic matrix could be used in well preserved fossils to learn about the past diet of molluscs.
Stable isotopes of carbon and oxygen of the calcitic shell of M. edulis were also investigated since carbonates are often used to indicates freshwater input in paleoenvironments. In general, shells were close to equilibrium with the surrounding water. But, the results obtained here showed that the use of carbonates to detect past estuarine environment could lead to misinterpretation due to possible biological effects that inhibits calcification (as noted near the head of the estuary).
LeBlanc, Caroline, "Terrestrial input to estuarine bivalves as measured by multiple stable isotopes tracers" (1989). Open Access Dissertations and Theses. Paper 1874.