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Evaluating Freshwater Mussel Shell δ 13 C Values as a Proxy for Dissolved Inorganic Carbon δ 13 C Values in a Temperate River
Author(s) -
Graniero L. E.,
Gillikin D. P.,
Surge D.
Publication year - 2021
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2020jg006003
Subject(s) - dissolved organic carbon , isotopes of carbon , environmental science , environmental chemistry , temperate climate , atmospheric sciences , hydrology (agriculture) , chemistry , total organic carbon , ecology , geology , biology , geotechnical engineering
The stable isotope ratio of dissolved inorganic carbon (δ 13 C DIC ) in rivers reflects the dominant vegetation type in the surrounding watershed, rates of chemical weathering, atmospheric CO 2 fluxes, and the relative rates of photosynthesis and respiration. Reconstructing past δ 13 C DIC values may reveal changes in these characteristics before watersheds experience land‐use change and/or climate change. This study uses freshwater mussels, Elliptio complanata , and coeval environmental data to assess how high‐resolution changes in the oxygen and carbon isotope ratios of shell carbonate (δ 18 O shell and δ 13 C shell , respectively) can be used as proxies of paleotemperature and paleo‐DIC in rivers. To test our hypotheses, we analyzed time‐series δ 18 O shell and δ 13 C shell values, δ 13 C values in bivalve tissues, and environmental data collected fortnightly from the Neuse River, North Carolina. Shell microsamples milled every 150 μm along the maximum growth axis represent an average of 12 ± 5 days ( n = 524; excluding periods of growth cessation of >30 days), which is similar to the environmental data resolution (∼14 days). Serially sampled δ 18 O shell and δ 13 C shell values did not capture the full range of environmental conditions due to growth cessation during winter shutdown and extreme weather events. Low water temperature and elevated turbidity appear to be significant drivers of growth cessation. Spatial and temporal differences in the amount of metabolic carbon incorporated in the shell (∼0%–44%) likely occur due to variable mussel metabolic rates within and among study sites. Though high‐resolution δ 13 C shell values did not reflect variations in δ 13 C DIC values, average δ 13 C shell values were indicative of average δ 13 C DIC values in the Neuse River.