Currently, I work as a Postdoctoral Research Associate at Princeton University/NOAA Geophysical Fluid Dynamics Laboratory. During my graduate programs at the Virginia Institute of Marine Science(VIMS), I used observations and numerical models to study how physical and biogeochemical processes affect hypoxia and acidification in coastal and estuarine systems. I am interested in (1) interactions between physical and biogeochemical processes within marine ecosystems, (2) impacts of local human activities and global climate change on marine ecosystems, and (3) numerical modeling and data analyses. I love DIY LEGO (e.g., LEGO Chesapeake Bay), and people say that I am a good cook.

Education

• Ph.D., Marine Science, VIMS (William & Mary), 2023
• M.S., Marine Science, VIMS (William & Mary), 2018
• B.S., Oceanography, Nanjing University, 2015

CV

Last updated March 2023. Click here

Teaching Experience

Fall 2021 Teaching Fellow at William & Mary: designed and taught the undergraduate-level course Ocean and Coastal Acidification. Syllabus

Research and Publications

1. Response of Chesapeake Bay hypoxia and carbonate system to global and local drivers

(a) Hypoxia and acidification are two phenomena severely threatening the coastal environment and both are critical for stakeholders whose livelihoods depend on the health of these waters. My M.S. research focused on developing and applying coupled physical-biogeochemical models to investigate the impact of two often-neglected sources of nitrogen—direct atmospheric nitrogen deposition and continental shelf nitrogen fluxes—on Chesapeake Bay hypoxia, and comparing these impacts to those of changing nitrogen concentrations in the rivers. This work is published in Journal of Geophysical Research: Oceans and received the VIMS Best Student Paper Award.

Impacts of atmospheric nitrogen deposition and coastal nitrogen fluxes on oxygen concentrations in Chesapeake Bay. Da et al. (2018) Link to paper

(b) For my Ph.D. research, I investigated a less studied water quality issue in the Chesapeake Bay: coastal acidification. One of the knowledge gaps I addressed was that the complex trends of Chesapeake Bay acidification over the past three decades are controlled by multiple global- and local-scale drivers. To better understand how these trends differ seasonally and spatially, I combined long-term water quality data analyses and numerical model simulations. This study, published in Journal of Geophysical Research: Oceans, suggests that the spatiotemporal variability of decadal changes in the Chesapeake Bay carbonate system is much greater than that observed in the open ocean, due to a combination of influences from the watershed, atmosphere and ocean.

Mechanisms driving decadal change in the carbonate system of a coastal plain estuary. Da et al. (2021). Link to paper

2. Carboante system variability in tidal tributaries of the Chesapeake Bay

(a) Dissolved inorganic carbon (DIC) and total alkalinity (TA) dynamics in tidal tributaries are sensitive to multiple ocean and watershed drivers, including tidal cycles and inputs from wetlands and rivers. However, development and application of numerical models that simultaneously address these drivers are limited. I helped develop a 3-D hydrodynamic-biogeochemical model forced with empirical inputs from tidal wetlands to investigate the carbonate system in the York River Estuary, a small tributary of the Chesapeake Bay. Model results highlight that wetland inputs account for ~1/3 of the total DIC and TA inputs to the estuary. Strong quasi-monthly variability in DIC and TA is driven by tidal cycles, which cause fluctuations between net heterotrophy and net autotrophy. Carbonate chemistry in tidal tributaries experiences complex transformations due to rivers, tidal wetlands, and tides; considering all three drivers are essential for investigating coastal carbon and alkalinity cycling.

Controls on the carbonate system of a coastal plain estuary: rivers, tidal wetlands, and tidal cycles. Estuaries and Coasts. In review.

(b) These relatively shallow regions are important sites for the shellfish aquaculture industry as well as oyster restoration, and could be more susceptible to coastal acidification due to terrestrial runoff and climate change. Therefore, I further investigated the impact of extreme river discharge and climate change on calcium carbonate saturation state (Ω) in the York River Estuary. Model results show that year-to-year differences in river discharge produce differences in Ω that are comparable in magnitude to the long-term reductions in Ω projected to occur over the next 50 years. Although a similar high discharge event in the future will have 20–40% less of an impact on Ω, increasing atmospheric CO₂ will decrease baseline Ω. Shallow regions in the lower YRE, where most oyster reefs are located, typically recover faster after a high discharge event compared to regions farther upstream.

This study is in preparation for publication, and a link to my dissertation will be available soon.

3. Collaborative research

I have been actively involved in multiple collaborative projects throughout my graduate studies. Efforts regarding biogeochemical model improvements led to two publications, with one studying the impact of future climate change and nutrient reductions on Chesapeake Bay hypoxia, and the other one focusing on the drivers and extent of Chesapeake Bay warming over the past three decades. Additionally, I participated in multiple observational studies on Chesapeake Bay acidification, resulting in three co-authored publications led by researchers from VIMS, CSIRO Oceans and Atmosphere (Australia), and the Pennsylvania State University. Because of my interest in estuarine hydrodynamics, I attended the Estuarine & Coastal Fluid Dynamics Summer School at the University of Washington, and worked in a group to collect field measurements, to analyze numerical model outputs, and to write a report on tides, mixing, and exchange in the San Juan Channel, WA. Specifically, I used model outputs to compute net tidal energy flux, buoyancy flux and dissipation within the San Juan Channel.

Co-authored publications

Hinson, K., Friedrichs, M.A.M., St-Laurent, P., Da, F., and Najjar, R.G. (2020). Extent and causes of Chesapeake Bay warming. Journal of the American Water Resources Association. Paper

Herrmann, M., Najjar, R.G., Da, F., Goldberger, S., Friedman, J.R., Friedrichs, M.A.M., Menendez, A., Shadwick, E.H., Stets, E.G. and St-Laurent, P. (2020). Challenges in quantifying air‐water carbon dioxide flux using estuarine water quality data: Case study for Chesapeake Bay. Journal of Geophysical Research: Oceans, 125, e2019JC015610. Paper

Friedman, J.R., Shadwick, E.H., Friedrichs, M.A.M., Najjar, R.G., DeMeo, O.A., Da, F. and Smith, J. (2020). Seasonal variability of the CO2 system in a large coastal plain estuary. Journal of Geophysical Research: Oceans, 125 (1) Paper

Shadwick, E.H., Friedrichs, M.A.M., Najjar, R.G., DeMeo, O.A., Friedman, J.R., Da, F. and Reay, W.G. (2019). High-frequency CO2-system variability over the winter-to-spring transition in a coastal plain estuary. Journal of Geophysical Research: Oceans, 124 (11), 7626-7642. Paper

Signorini, S.R., Mannino, A., Friedrichs, M.A.M., St-Laurent, P., Wilkin, J., Tabatabai, A., Najjar, R.G., Hofmann, E.E., Da, F., Tian, H., and Yao, Y. (2019). Estuarine dissolved organic carbon flux from space: with application to Chesapeake and Delaware Bays. Journal of Geophysical Research: Oceans, 124 (6), 3755-3778. Paper

Irby, I.D., Friedrichs, M.A.M., Da, F. and Hinson, K.E. (2018). The competing impacts of climate change and nutrient reductions on dissolved oxygen in Chesapeake Bay. Biogeosciences, 15, 2649-2668. Paper