Postdoctoral Fellowship: OCE-PRF: Dynamics of low-inflow estuaries and their response to increasing aridification

Estuaries support unique ecosystems and provide valuable economic benefits, such as aquaculture farms and recreation. They require careful management in the face of a changing climate and increasing coastal development. Estuaries with low river inflow for part of the year, found for example in California, Texas, and Latin America, are particularly vulnerable to depletion of freshwater resources and increasing drought conditions. However, predicting the response of a low-inflow estuary to these new conditions is challenging. This challenge arises in part because low-inflow estuaries behave differently than traditional estuaries which have year-round river flow. Most theory for estuary circulation focuses on traditional estuaries and does not apply well to low-inflow estuaries. Our project aims to fill this knowledge gap by testing how low-inflow estuaries respond to extreme weather and drought. The project results will generate a new understanding of the circulation of low-inflow estuaries. It will also help inform coastal managers on how low-inflow estuaries are likely to respond to future variability. The research will be paired with an educational component including school labs and field trips to promote ocean science among students.

The proposed project aims to enhance knowledge of future changes to low-inflow estuaries using models. For high-inflow systems, idealized modeling studies have investigated the estuarine adjustment to changes in river runoff or tidal forcing. However, analogous studies for low-inflow estuaries are lacking, despite the global prevalence of low-inflow systems. This research will develop numerical simulations of low-inflow estuaries using the hydrodynamical model ROMS (Regional Ocean Modeling System). The primary goal of the simulations will be to evaluate the circulation response to strong surface thermodynamic forcing and periodic but intense freshwater pulses mimicking future climate variability. The experiments will also test the conditions necessary for the formation of mid-estuary density minima (thermal plugs) and maxima (salt plugs) features which can impact residence time and mixing. Both density-driven and tidally driven circulation regimes will be generated by varying factors such as estuary depth, tidal amplitude, and air temperature. Using a range of parameters will enable broad applicability of results. Passive dye experiments will also be run to quantify flushing timescales and their response to extreme weather. Therefore, in addition to providing a physical understanding of low-inflow estuaries, the results will have direct relevance to biological and chemical analysis of low-inflow estuary ecosystems. The proposed research will generate new ideas for understanding the physics of low-inflow estuaries, helping to build a contemporary framework. This framework can then form the basis of future interdisciplinary research.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Award Number: 2545240
Principal Investigator: Robert Sanchez
Funds Obligated: $168,570
State: CA