Depicting the Need for High Temporal Resolution pH and Oxygen Variability in a Dynamic Alaskan Estuary

Acidification in nearshore waters are influenced by a multitude of drivers that shape the dynamics of pH and carbonate chemistry variability on diurnal, seasonal, and yearly time scales. Monitoring efforts aimed at characterizing high temporal resolution are lacking in many nearshore systems, particularly in high latitude regions such as Alaska. Kachemak Bay, located in the northern Gulf of Alaska, is bisected by Homer spit into upper and lower basins with disparate chemical drivers. This study measured the along bay heterogeneity of pH and oxygen variability to better understand the chemical environment of these biologically productive waters that serve as regions for shellfish restoration. SeaFET^TM pH and oxygen sensors were deployed in Jakolof Bay located in the outer basin, and Bear Cove—less biologically diverse relative to Jakolof Bay—in the inner basin for 12 months. Quality control included propagated measurement uncertainty, which is presented as a standard method when analyzing data from SeaFET^TM sensors. Time series analyses indicate that both locations within Kachemak Bay are net autotrophic systems for short durations in the summer and experience large diurnal fluctuations in pH >0.3 units on tidal scales (3–6 h). Finally, we utilize spectral analysis of pH as a tool to identify correlations between oxygen and tidal amplitude as a means to identify potential drivers of pH variability. These findings of high temporal resolution pH variability are presented in the context of a biological viewpoint were the frequency and duration of exposure to acidification is more relevant than static means.