Thesis Defense: Tim Wahl

A Thesis Defense from UNC Marine Sciences graduate student, Tim Wahl. Presented by the UNC at Chapel Hill Department of Marine Sciences. The location of this event will be in seminar room G201 on the ground floor of Murray Hall on UNC-CH campus in Chapel Hill, NC. This event will be held on Monday, April 22nd at 12:20pm. This seminar will also be broadcast live to both UNC’s Institute of Marine Sciences room 222 and online via Zoom.

Seminar Title: Temporal Variability of DIN, Chlorophyll, and DOC in Florida Bay following Hurricane Irma

Abstract: On September 10, 2017 Hurricane Irma passed over the Florida Keys with 130 mph winds causing extreme damage to both aquatic environments and populated land areas. The hurricane winds caused water to recede over 100 meters from the Florida bayside shoreline along the Middle Keys, resulting in catastrophic damage to nearshore benthic communities including sponges, whose total biomass decreased by approximately 95 ± 5 % in one shallow embayment field site. A post-Irma time-series study was conducted featuring monthly water column sampling at 12 stations, including Middle Keys embayments, nearshore waters, and a western Bay basin. The study sought to understand how episodic storm and bloom events could influence temporal variability of dissolved inorganic nitrogen (DIN) concentrations and related parameters. The monthly whole water samples were filtered for chlorophyll-a (Chl-a) measurements and then analyzed for nitrate/nitrite (NOx-), ammonium (NH4+), and dissolved organic carbon (DOC). The results revealed drastic changes in water quality following Hurricane Irma; however, after four months, concentrations returned to near pre-Irma levels. Year-long temporal measurements of DIN revealed no change from pre-hurricane concentrations for DIN, compared to 25-year average from a longer multi-year survey. DIN levels spiked following sediment resuspension of NH4+-enriched pore-waters into the overlying water column caused by a storm in December 2017. The decimation of sponge biomass plus potentially greater relative contributions of DIN from storm-perturbed sediments will require new models for nitrogen budgets in Florida Bay.