Temporal and spatial variability of carbonate chemistry in a Tillamook Bay tributary: tracing acidification from the river to the bay

Coastal acidification from rising atmospheric carbon dioxide can be exacerbated by local factors such as land inputs of inorganic carbon and nutrients. In Tillamook Bay, OR, the possibility of local factors enhancing acidification and impacting oyster aquaculture in the bay is a concern due to extensive agriculture in the watershed. The US EPA has been monitoring water conditions in Tillamook Bay tributaries since the summer of 2016, and preliminary findings showed increased dissolved inorganic carbon (DIC) downstream of agricultural areas. To determine the causes of elevated DIC, changes attributed to land-based inputs must be distinguished from natural temporal variability and in-stream processing. We initiated a study to assess temporal variability by conducting a day-long time series of DIC and partial pressure of CO2 (pCO2) at locations upstream and downstream of agricultural areas along the Trask River. To quantify in-stream processing (periphyton photosynthesis and respiration), stream rocks were placed in sealed microcosm chambers for 7 hours, and changes in dissolved oxygen and carbonate chemistry were measured. Initial and final concentrations of dissolved oxygen (DO), DIC, and pCO2 in each container were compared to the conditions in the stream itself. Time series data show that DIC was lower upstream and decreased more throughout the day. In chambers, the ΔDIC: ΔDO ratio is consistent with stream photosynthesis-respiration stoichiometry at both sites, while in streamwater, the ΔDIC: ΔDO ratio is much lower downstream. In-stream processing can account for most of the changes in DIC in the chambers, but not in the streamwater, suggesting that elevated DIC levels can be attributed to inputs of inorganic carbon from land-based sources.

Ernest-Beck A., 2019. Temporal and spatial variability of carbonate chemistry in a Tillamook Bay tributary: tracing acidification from the river to the bay. BSc thesis, Western Washington University, 19 p. Thesis.

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