CHAPTER 10 



samples filtered with Whatman GF/F filters were analyzed 

 for nitrate, nitrite, phosphate, and silicate by NOAA 

 Atlantic Oceanographic and Meteorological Laboratories 

 (AOML), Ocean Chemistry Laboratory, on a four-chan- 

 nel Technicon Auto Analyzer using procedures outlined 

 in Hazelworth et al. (1974). Samples for dissolved organic 

 carbon (DOC) were filtered using precombusted, rinsed 

 glass fiber filters (Whatman GF/F) and analyzed by the 

 University of Delaware Marine Chemistry Laboratory 

 using the method of Menzel and Vacarro (1964) as 

 adapted by Sharp (1973). 



Chlorophyll a was determined spectrophotometrically 

 and corrected for phaeopigments (Strickland and Parsons 

 1972). Chlorophyll-^ netplankton (>20(xm) and nanno- 

 plankton (<20|xm) size fractions were determined by se- 

 rial filtration of seawater samples through 20 |xm Nitex 

 and 0.45 ixm Millipore filters and reading acetone extracts 

 on a fluorometer (Strickland and Parsons 1972). Phyto- 

 plankton in whole water samples, preserved with KI-L, 

 were speciated and enumerated using an inverted micro- 

 scope . 



Phytoplankton primary productivity was measured us- 

 ing the '■'C method as described by O'Reilly et al. (1976) 

 and O'Reilly and Thomas (in press). Zooplankton larger 

 than 300 \xm were removed with a Nitex screen before 

 incubation, during subsampling of Niskin bottles. Dupli- 

 cate light and dark bottles were incubated under sunlight 

 (simulated in situ 100%, 68%, 47%, 30%, 11%, 4%, and 

 1%) and artificial light (photosynthetic capacity at satu- 

 rating — 0.089 ly/min — light intensities). Following incu- 

 bation, the organic '^C activity in netplankton (>20 |xm), 

 nannoplankton (<20 ixm but >0.45 |xm), and dissolved 

 organic matter (<0.45 jim) size fractions was determined 

 by serial filtration through 20-fjLm and 0.45-fjLm filters and 

 subsequent acidification and counting in a liquid scintil- 

 lation counter. 



The rate of oxygen consumption (total plankton respi- 

 ration) for each depth in the water column was estimated 

 from changes in D.O. occurring between five initial and 

 five final whole water samples incubated in acid-cleaned, 

 baked (232° C for Ih) 300-ml BOD bottles. Of these 10 

 samples, 5 initial samples from each depth were fixed 

 immediately according to the azide modification of the 

 Winkler method (American Public Health Association 

 1975) and 5 final samples were incubated in the dark at 

 ±r C of in-situ temperature for 12 to 24 hours, fixed as 

 before, and fitrated using phenylarsine oxide in place of 

 sodium thiosulphate and thyodene in place of starch 

 (Kroner et al. 1964; U.S. EPA 1974). The average coef- 

 ficient of variability for the five initial determinations was 

 2.20 percent (N = 134). 



Seabed (sediment plus bottom 12 cm of water) oxygen 

 consumption rates were measured as described by Thomas 

 et al. (1976b) after Pamatmat 1971. Rates of oxygen con- 



sumption by the seabed and water column are expressed 

 both as oxygen consumed and as equivalent carbon oxi- 

 dized, assuming a respiratory quotient (RQ) of 1 so that 

 comparisons between production and decomposition of 

 organic matter can be made. 



Total direct bacterial counts were made on surface and 

 bottom water samples using a fluorescence technique 

 (Hobbie et al. 1977). Bacterial biomass was calculated 

 from cell measurements obtained from photographs and 

 transparencies made of the bacteria during the counting 

 procedure. 



HYDROGRAPHIC AND 

 NUTRIENT CONDITIONS 



Figures 10-2 and 10-3A and 3B show the location, size, 

 and shape of the low D.O. area and hydrographic con- 

 ditions at the time of the cruise (about 2 months after the 

 onset of severe oxygen depletion). Bottom water tem- 

 perature was highest and salinity lowest along the New 

 Jersey coast and toward the Hudson-Raritan estuary (fig. 

 10-2). The exception was station 41 (off Monmouth 

 Beach, N.J.), which appeared affected by cooler and more 

 saline water from the Hudson Shelf Valley. A strong ther- 

 mocline and halocline combined to produce a sharp pyc- 

 nocline (fig. 10-3A). At station 217 in the middle of the 

 low D.O. area (fig. 10-33), the water was saturated with 

 oxygen immediately above the pycnocline, while imme- 

 diately below it was anoxic. Below the pycnocline in the 

 anoxic area sulfide concentrations were especially high 

 (fig. 10-3B)— 18.0 |jlM/1 at stations 213 (fig. 10-5) and 

 pH was particularly low (7.3 to 7.4) compared to sur- 

 rounding areas (7.5 to 7.9). 



The highest concentrations of nitrate and nitrite (fig. 

 10-4A) were found in the estuarine surface outflow, in 

 the near-bottom water of the Hudson Shelf Valley (station 

 76) and in the colder, more saline bottom water away 

 from the anoxic area (station 227). Beyond the Apex both 

 nitrate and nitrite were depleted or nearly depleted in the 

 waters above the pycnocline. In bottom water on the pe- 

 rimeter of the anoxic area, small quantities of nitrite were 

 present, whereas nitrate was absent. In the anoxic area 

 concentrations of both nitrate and nitrite were highest just 

 below the pycnocline where D.O. concentrations were 

 zero. Otherwise, their concentrations were zero except for 

 a trace of nitrite at the bottom depth at station 217. 



Ammonium concentration decreased from the estuary 

 seaward, approaching zero to 0.5 fiM/l in surface water 

 at the outer Apex (station 76) and beyond (fig. 10-4A). 

 The highest concentrations of ammonium (30 |jlM/1) were 

 found in the estuary. Away from the estuary, ammonium 

 concentrations were highest in the bottom water of the 

 oxygen-depleted area (station 213, 19 fjLM/1. fig. 10-5). 



233 



