How do Hydrodynamic Conditions Influence Algal Species Competition in the Sacramento-San Joaquin Delta?
Sienna White, University of California, Berkeley
Maximizing time in the photic zone is a critical component dictating the success of an algal species. However, access to the photic zone is complicated by factors like stratification and turbulent mixing. Some algal species (diatoms) have compensated for their limited time in the photic zone by maximizing growth rate, such that when they are in the photic zone they can synthesize carbon as quickly as possible. However, diatoms cannot swim—instead, they sink downward with a slight negative buoyancy. Other species of algae (cyanobacteria) have developed vacuoles that allow for positive buoyancy, but these species tend to have lower growth rates, and their vertical velocities are easily overpowered by vertical mixing.
There is a strong interest from both scientific and management perspectives in understanding what factors dictate the dominance of cyanobacteria, a harmful algal species, over diatoms, which are often beneficial to estuarine ecosystems. This question is especially at play in the Sacramento-San Joaquin Delta, a highly engineered estuary in Northern California. The Delta receives large inputs of anthropogenic nutrients from wastewater treatment plants which result in elevated dissolved inorganic nitrogen levels (Novick et al., 2015), placing the estuary at a high risk for algal blooms (Paerl, 2012; Dahm et al., 2016) including risk for bloom events with toxic algal species (commonly referred to as harmful algal blooms (HABs)).
For our work, we explore the physical mechanisms dictating competition between diatoms and harmful cyanobacteria by simulating the two species in an idealized one-dimensional water column model. Specifically, we investigate the hypothesis set forth by Huisman et al. (2004) that the magnitude of turbulent dissipation determines regimes shifts between sinking and floating species of algae. We base our idealized model on the Stockton Shipping Channel in the Sacramento-San Joaquin Delta, a 10-meter deep regularly dredged channel that has routinely experienced harmful algal blooms throughout the past decade. Using our model, we simulated a three-day period and sample growth, loss, and swimming rates from empirical estimates from literature to parametrize population dynamics. Our results focus on how the final biomass of an algal species varies as a function of turbulent dissipation, stratification, and initial concentration. We also investigate how the phasing of temporal forcings, such as simulated tides, surface water heating, and diurnal wind, affect a species’ dominance by determining access to the photic zone.
Works Cited
Dahm, C. N., A. E. Parker, A. E. Adelson, M. A. Christman, and B. A. Bergamaschi. “Nutrient Dynamics of the Delta: Effects on Primary Producers.” San Francisco Estuary and Watershed Science 14, no. 4, 1-36 (2016). https://doi.org/10.15447/sfews.2016v14iss4art4.
Huisman, J., J. Sharples, J. M. Stroom, P. M. Visser, W. E. A. Kardinaal, J. M. H. Verspagen, and B/ Sommeijer. “Changes in Turbulent Mixing Shift Competition for Light Between Phytoplankton Species.” Ecology 85, no. 11 (2004): 2960–70. https://doi.org/10.1890/03-0763.
Novick, E., Holleman, R., Jabusch, T., Sun, J., Trowbridge, P., Senn, D., Guerin, M., Kendall, C., Young, M. and Peek, S. “Characterizing and quantifying nutrient sources, sinks and transformations in the Delta: synthesis, modeling, and recommendations for monitoring.” San Francisco Estuary Institute, Technical Report. (December 2015).
Paerl, H. W., and V. J. Paul. “Climate Change: Links to Global Expansion of Harmful Cyanobacteria.” Water Research, Cyanobacteria: Impacts of climate change on occurrence, toxicity and water quality management, 46, no. 5 (April 1, 2012): 1349–63. https://doi.org/10.1016/j.watres.2011.08.002.