Abstract:

A picophytoplankton bloom dominated by Synechococcus formed in September 2005 in a series of shallow lagoons between Florida Bay and Biscayne Bay and lasted until May 2008. Chlorophyll-a concentrations peaked at >20 µg L⁻¹. The bloom coincided with a massive mortality of sponges and caused massive mortality of the seagrass. However, follow-up analysis to determine if there were any long-term impacts from the bloom on the system is lacking. We used long-term water quality data (chlorophyll-a and nutrient concentrations) collected at 13 stations in the affected region over a 20-yr period to compare environmental conditions before (1995–2004) and after (2009–2014) the bloom. We found that after the bloom, baseline chlorophyll-a concentration significantly increased 45%, from 0.42 (SE 0.02) to 0.77 (SE 0.04) µg chl a L⁻¹, at the stations most impacted by the bloom. Before-After Control-Impact paired analysis suggested these changes were related to the 3-yr bloom and not a larger, regional scale shift. The increase in chlorophyll-a does not appear to be associated with additional changes in water quality, but is potentially due to a reduction in the epibenthic community (e.g., SAV and sponges). Now that the bloom has terminated and the causes of the bloom abated, the system has not returned to its original status, suggesting a lasting impact from the bloom on the ecosystem.

Abstract:

Researchers with the Ocean Chemistry and Ecosystems Division of NOAA’s Atlantic Oceanographic and Meteorological Laboratory conducted 12 monthly cruises in two separate track lines off of Broward County, Florida, from November 2010 through January 2012. The cruise tracks were designed to provide information on three categories of the coastal ocean: (1) the vicinity of the Broward and Hollywood treated-wastewater outfalls; (2) the vicinity of the Hillsboro and Port Everglades inlets; and (3) the interstitial areas in between. Sampling took place from aboard the NOAA R/V Hildebrand using a conductivity-temperature-depth (CTD)/rosette for water samples and water column profiles and appropriately located acoustic Doppler current profiler (ADCP) instruments for ocean current information. Measured discrete parameters included location, depth, salinity, temperature, pH, oxygen saturation (dissolved oxygen, DO), oxidation-reduction (redox) potential (ORP), chlorophyll-a, phaeopigments, total suspended solids (TSS), nitrate (NO₃), nitrite (NO₂), ammonium (NH₄), silicate (Si), orthophosphate (PO₄), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), particulate carbon (PC), particulate phosphorus (PP), particulate nitrogen (PN), and dissolved organic carbon (DOC). CTD profile data included depth, turbidity, ORP, DO, pH, chlorophyll-a, salinity, temperature, and density. A variety of microbiological entities were measured, including fecal indicator bacteria (FIB), selected waterborne pathogens, and molecular microbial source tracking (MST) markers. Community bacterial metagenomic profiles were also generated for selected sample sites. Quality controls of nutrient sample analyses were obtained following National Environmental Laboratory Accreditation Conference (NELAC)-certified procedures. The data obtained present a view of the coastal ocean as having a low “background” concentration of most analytes, interrupted by elevated concentrations near the outfalls and inlets whose excess concentrations decreased rapidly away from the point sources. The waters were found to be oligotrophic, with no evidence of bloom events. A major upwelling event was observed on August 11, 2011, where a ~10°C temperature drop was observed near the southernmost portion of the sampled area.