Dr. Yin San Stacy Zhang
Institute of Marine Sciences, University of North Carolina Chapel Hill
Join us October 26th, 2021 for our first monthly webinar @ 1:00 - 2:00 pm U.S. eastern time
(free registration HERE)
Coastal habitat and community responses to tropical cyclones in a temperate, sub-tropical estuary
Major storms can alter coastal ecosystem structure and functioning in a multitude of direct and indirect ways including habitat destruction, stormwater-related water-quality degradation, and mortality of marine organisms, among others. From 2010-2020, multiple hurricanes of varying intensities impacted the southern Outer Banks of North Carolina. Using a combination of monthly trawls and contemporaneous seagrass and oyster reef surveys, we examined habitat continuity and changes in seagrass-associated fish communities to evaluate whether these disturbances changed the nursery role of shallow-water biogenic habitats. Our analysis revealed that fish catch may be depressed for roughly two weeks after storm passage but over longer time frames, appeared largely similar to corresponding no-storm years. The overall resilience exhibited by fishes was likely underpinned by the relative stability of the seagrass habitat itself, which appeared principally undamaged by storms. However, storm intensity plays a large role in overall storm effect, as the greatest magnitude cyclone in our observation period, Hurricane Florence, not only damaged oyster reefs that had previously been unaffected by earlier cyclones but also caused the greatest decline in fish catches. These findings suggest that fish communities and coastal habitats may be insensitive to mild tropical cyclones, but a pressing question appears to be whether they will remain resilient to storm impacts if the frequency and intensity of these disturbances increase as one syndrome of global climate change.
Dr. Cal Buelo
University of Wisconsin Center for Limnology
Join us November 16th, 2021 @ 1:00 - 2:00 pm U.S. eastern time
(free registration HERE)
Quantifying disturbance and recovery in estuaries: tropical cyclones and high frequency measures of oxygen and salinity
Tropical cyclones are important drivers of disturbance in estuaries. Several mechanisms can lead to storm impacts and estuaries are dynamic and diverse systems, making identifying disturbance and recovery difficult and often limiting studies to one or a few sites or tropical cyclones. We applied a new method for detecting disturbance and recovery to long-term and high-frequency measurements of salinity and dissolved oxygen from NOAA’s National Estuarine Research Reserve System, analyzing the impacts of 59 tropical cyclones at 19 estuaries across the eastern United States. We were able quantify disturbance occurrence, timing, recovery time, and severity and ask what storm and location properties are associated with changes in these disturbance characteristics. Salinity disturbances generally started earlier than dissolved oxygen disturbances and lasted longer. Most recoveries occurred within days, though some disturbances lasted weeks or months. Recovery time was positively correlated with disturbance severity for both variables. Both storm (especially precipitation) and location properties were related to disturbance characteristics. Our findings demonstrate the power of high-frequency, long-term, and cross-system data, when combined with appropriate statistical methods, to provide insights that improve understanding and potentially management of estuarine resilience to disturbances.
Dr. Hans W. Paerl
Professor of Marine & Environmental Sciences & Engineering
Institute of Marine Sciences, University of North Carolina
Join us December 7th, 2021 @ 10:00 - 11:00 am U.S. eastern time
(free registration HERE)
The “new normal” high rainfall tropical cyclones: Linkage to harmful cyanobacterial bloom expansion into estuarine and coastal waters
Global warming is generating more intense, elevated rainfall from tropical and extra-tropical storms, which have led to record flooding along the storm tracks, extending from the coast to inland watersheds. In addition to delivering elevated nutrient (N and P) and other contaminant loads to receiving riverine, estuarine, and coastal waters, floodwater also tend to reduce salinity in these waters. The combined effect of elevated nutrient loads and “freshening” of downstream waters is promoting eutrophication (“new production” from a carbon perspective) and expanding the window of opportunity for harmful cyanobacterial blooms, or CyanoHABs, to proliferate. Elevated stormwater runoff events followed by periods of protracted droughts are the perfect “storm scenario” for downstream proliferation of CyanoHABs, which will benefit from elevated nutrient supplies, depressed salinity levels and increases in water residence times. This, combined with warming is a potent combination of changing environmental conditions favoring expansion of CyanoHABs along the entire freshwater to marine continuum. Examples of this scenario are now evident in numerous estuarine and coastal ecosystems, including the Mississippi-Atchafalaya drainage into the northern Gulf of Mexico, Florida’s coastal lagoons and estuaries draining Lake Okeechobee, the Albemarle-Pamlico estuarine complex in North Carolina, the San Francisco Bay Delta, as well as the Yangtze River Delta in China. This scenario presents multiple CyanoHAB mitigation challenges, in that both watershed nutrient loading will need to be reduced to new threshold levels and water retention strategies need to be optimized to retain and process nutrients in the watershed upstream from CyanoHAB sensitive receiving waters.