Gobler, C. J. Marine Sciences Research Center, gobler@msrc.sunysb.edu
Sanudo-Wilhelmy, S. J. Marine Sciences Research Center, ssanudo@ccmail.sunysb.edu

 
THE INFLUENCE OF GROUND WATER INPUTS ON BROWN TIDES
 
Brown Tide blooms of Auerococcus anophagefferens have been previously hypothesized to occur during years of below average groundwater discharge to Long Island bays. West Neck Bay (WNB) represents a paradox to this hypothesis since it receives abnormally high groundwater seepage and is host to Brown Tide blooms more frequently than any other place on Long Island. To better understand the influence of groundwater inputs on Brown Tides, a weekly field campaign was established during which changes in water column chemistry and phytoplankton dynamics were related to groundwater composition and flow rates in WNB during 1998. During the month of June, a mixed assemblage phytoplankton bloom (30 g / L chlorophyll a) developed in WNB of which Aureococcus (0.5 - 1.0 x 10^8 cells / L) represented only 10 to 25% of the algal population. This period was characterized by elevated ground water flow and significant levels of nitrate (2- 30 M) within WNB. Analysis of ground water in shallow wells (2 - 10 m) and benthic seepage chambers surrounding the coastline of WNB revealed nitrate levels ranging from 50 - 450 M, implicating ground water as the primary source of N to WNB. As groundwater seepage, nitrate levels, and total phytoplankton biomass in WNB diminished during early July, Aureoccocus became the dominant phytoplankter, representing nearly 100% of the algal community. Observed reductions in water column nitrate (2.7 M decrease) and low molecular weight (LMW; < 1 kDa) organic nitrogen (2.4 M decrease) during the peak of the Brown Tide (6 x 10^8 cells / L) accounted for 50% of the particulate organic N formed (0.16 mg / L), suggesting Aureococcus utilization of these nitrogen sources. It is concluded that rather than repressing Brown Tide blooms, ground water inputs to WNB can stimulate Aureococcus growth by directly supplying nitrate and by initiating phytoplankton blooms prior to the Brown Tide which supply remineralized LMW organic nitrogen. Data on behavior of bioactive trace metals during the bloom and field bioassay experiments involving organic and inorganic N will also be presented.
 
Day: Friday, Feb. 5
Time: 09:30 - 09:45am
Location: Eldorado Hotel
 
Code: SS42FR0930E