Wave interactions with plumes can trap potentially polluted water near shore

Graduate student Angelica Rodriguez just published her research results in Geophysical Research Letters (with co-authors Giddings and Kumar (UW)) and is highlighted in the Scripps news. The paper, “Impacts of Nearshore Wave‐Current Interaction on Transport and Mixing of Small‐Scale Buoyant Plumes” uses idealized modeling of the interaction between small buoyant plumes (e.g., rivers, creeks, storm drains, etc.) and the surfzone to assess their interaction. Under strong waves and/or small outflows, buoyant outflow plumes were effectively trapped close to the coastline, spreading alongshore instead of cross-shore. This has major implications for transport of pollutants that typically accompany freshwater outflows and can hopefully improve beach water quality sampling and management.

The coupling between plumes and waves has been studied before on large scale plumes, but the interaction between smaller plumes and the surfzone – the region where surface gravity waves break near shore – has been investigated here for the first time. Using an idealized model domain representative of the scales of estuaries and plumes common in Southern California, we coupled a hydrodynamic model (ROMS) with a wave model (SWAN) using the COAWST modeling framework. This modeling framework allowed us to look at wave-current interactions and assess the impact of the surfzone on small buoyant outflows. Importantly, we found that vigorous mixing due to waves in the surfzone vertically mixed the buoyant outflow in the surfzone and wave-driven velocities reduced offshore plume propagation, while enhancing alongshore spreading.

Can seagrass help ameliorate ocean acidification?

This important question is addressed in a new paper “Expected limits on the ocean acidification buffering potential of a temperate seagrass meadow,” led by David Koweek at the Department of Global Ecology, Carnegie Institution for Science, Stanford. A press-release from the Carnegie Institution and a blog post by David Koweek do an excellent job summarizing the paper in detail.

This paper is the culmination of an interdisciplinary collaboration amongst seagrass ecologists, chemists, climate scientists, and physicists to address the buffering potential of seagrass meadows against ocean acidification, a critical topic as we face a changing climate. We employed a numerical box model coupled with hydrodynamics and a complex bio-geochemical seagrass/chemistry model to investigate the ability for an estuarine seagrass meadow to buffer the acidity of incoming oceanic water (i.e., to counteract ocean acidification). Overall, buffering capacity was found to be relatively weak, about equivalent to turning back the clock a few decades, which is a small offset to the 150 years of ocean acidification that has already occurred and is worsening. Thus the results suggest that while buffering does occur, it is not enough for long-term ocean acidification mitigation. However, there were brief periods of time when buffering capacity was high; that coupled with new information about how organisms can adapt to changing environments, as well as other potential mitigation approaches, provide potential opportunities to use seagrass as part of a broader strategy to ameliorate local ocean acidification in estuaries. The model for this work was parameterized specifically to Tomales Bay, a northern California large estuary, however the resulting publicly available box-model is designed so that it can be tested under varying conditions.

This work is a contribution of the Seagrass Ocean Acidification Amelioration Workshop of the Bodega Marine Laboratory, financial support for which was provided by California Sea Grant and the Coastal & Marine Sciences Institute of the University of California, Davis. Partial support was provided by the National Science Foundation.

Summer undergraduate projects!

This summer Alex Makic and Adrian Urrea have been working in the lab as undergraduate researchers.

Alex, from Colorado College, majoring in Physics with an Emphasis in Environmental Science, worked for a month in the lab on helping to analyze drone imagery taken above Los Penasquitos Lagoon and adjacent beaches to examine morphological changes over time as part of a California Division of Boating & Waterways funded project. He returns to college in early August, but has already made excellent progress this summer! In addition to working with us, he also worked with Octavio Aburto’s lab assessing Mangrove habitats in Baja California.

Adrian was part of a team of students who worked with Jeff Crooks and I during the 2018 Spring quarter to develop a bio-sensor. Adrian has continued to work in the lab this summer, further developing the sensor which will measure oyster shell gape to study how they respond to surrounding conditions. He is working to improve the sensor, add components (temperature and heart-rate sensors), finalize its calibration, run a field test, and build more of them!

Workshop on the future of coastal and estuarine modeling

18 – 21 June 2018, Giddings attended and presented at the NSF sponsored Workshop on the future of coastal and estuarine modeling. Presentations ranged from numerical discretization schemes, to nonhydrostatic versus hydrostatic code, to the state of the art in wave model-hydrodynamic model coupling. It was a very interesting several days discussing where we are in coastal and estuarine modeling and what are the major hurdles as well as opportunities ahead.

Border 2020 stakeholder kickoff meeting

13 June 2018 – The EPA hosted a kickoff meeting for two new Border 2020 funded projects aiming to reduce coastal water pollution along the US/Mexico Pacific border. Falk Feddersen and Sarah Giddings presented an introduction to their recently funded Border 2020 Border Environment Cooperation Commission (BECC) project entitled: “Evaluating the 2017 Tijuana River Estuary cross-border wastewater spill sources and coastal impacts.” This work builds off of modeling work started during the CSIDE project, but is heavily focused on the applied aspects of this research, specifically understanding the sources and impacts from a particularly large spill that resulted in extended beach closures in early 2017. We got great feedback from stakeholders (government agencies, public, other research groups, nonprofits, etc.) and also heard more about a complimentary observational project SCCWRP is leading under the same grant program.

scripps oceanography uc san diego