College - Author 1
College of Science and Mathematics
Department - Author 1
Biological Sciences Department
Degree Name - Author 1
BS in Marine Sciences
Emily Bockmon, College of Science and Mathematics, Chemistry and Biochemistry Department
Ryan Walter, College of Science and Mathematics, Physics Department
Anthropogenic stressors such as increased atmospheric carbon dioxide (CO2) are impacting carbonate chemistry in the global ocean by decreasing the pH, a process known as ocean acidification. (Doney et al., 2009; Feely et al., 2009; Orr et al., 2005). The direct impact of anthropogenic CO2 emissions on the nearshore coastal ocean and estuarine environments is largely uncertain (Duarte et al., 2013). In particular, estuaries are highly dynamic and productive biogeochemical systems (Bauer et al. 2013; Wang et al. 2016); however, information regarding the spatial and temporal variations of carbonate chemistry within these environments is limited (Cai et al. 2011; Hofmann et al. 2011; Waldbusser et al. 2011).
The variability of the carbonate chemistry in estuaries is driven by both physical and biological processes (Flecha et al., 2015; Joesoef et al., 2017). Physical processes are largely governed by the interplay between freshwater discharge and tidal forcing (and mixing). Spatially, the back of an estuary (i.e, the head) is typically more strongly influenced by riverine input while the front of an estuary (i.e., the mouth) is regulated by tidal forcing and oceanic inputs. Biological processes influence the carbonate chemistry predominantly via primary production, microbial respiration (Waldbusser & Salisbury 2014), precipitation (calcification) and dissolution of calcium carbonate (Wolf-Gladrow et al., 2007). Primary production, from autotrophic organisms such as phytoplankton, macroalgae, and eelgrass, can increase seawater pH and dissolved oxygen (DO) of the surrounding water through the consumption of CO2 and the release of oxygen (O2) (Middelboe and Hansen 2007). Marine respiration decreases pH and DO through the consumption of O2 and the release of CO2.
Seasonally, low-inflow estuaries (LIEs) are a class of estuaries typically found in Mediterranean climates whereby freshwater input is minimal during the summer “dry” season and increases during the winter “wet” season (Largier, 2010; Walter et al., 2018). These seasonally LIEs are relatively understudied compared to classically defined estuaries with freshwater input throughout the year (Largier, 2010; Walter et al., 2018). The summertime is characterized by minimal freshwater input and high evaporation which can create a hypersaline environment if residence times are long (Largier, 2010). During periods of low river discharge, the water movement in the estuary is largely driven by the tides. Additionally, increased solar intensity during the summer can promote net autotrophy, leading to increased pH in the estuary (Brodeur et al., 2019; Middelboe et al., 2006). Conversely, the winter “wet” season involves periods of increased precipitation, followed by freshwater discharge. During these intermittent events, variable changes to the estuary (i.e. nutrient/sediment input, mixing, biological response), resulting from riverine input, may alter the carbonate chemistry.
Estuaries are highly dynamic and provide important functions to the environment (i.e. sequesters carbon, supports biodiversity) and changes to carbonate chemistry can impact these biological processes (Doney et al., 2009). Thus, it is essential to understand the factors influencing carbonate chemistry variability in estuaries. Recent work has illustrated the range of time scales at which carbonate chemistry varies in coastal systems, and therefore, continuous, high-frequency sampling is necessary to observe the variations in a dynamic estuarine environment (Waldbusser & Salisbury, 2014; Hoffmann et al., 2011). In addition, Hoffmann et al., (2011) have shown efficacy using autonomous pH sensors to sample in coastal regions. Here, I present the first continuous, high-frequency pH data during a winter ‘wet’ period in a LIE located on the Central California Coast (Morro Bay Estuary). The overall objective of this study is to understand the primary drivers of pH variability (both spatially and temporally).