Acid-iron waste disposal and the summer distribution of standing crops in the New York bight

Abstract Ecological consequences arising from the disposal of 50 million tons of acid-iron industrial waste in the coastal waters off New York over the past 22 yr were assessed. Most of the data were obtained at two identical grids of stations which enabled comparisons of hydrographic, chemical and biological conditions within the acid-iron disposal area with similar parameters in a nearby control area. Supplementary information on benthos and sediment was obtained at other locations peripheral to the two station grids and in Hudson Gorge, and these were used to construct a synoptic picture of the physio—chemical conditions and standing crops in the New York Bight. At each grid station the hydrographic measurements made were temperature, salinity and light penetration; chemical observations consisted of dissolved oxygen, dissolved and suspended iron, total inorganic nitrogen and phosphate; while chlorophyll α, zooplankton and benthos biomass provided a measure of the abundance of standing crops. Trace metal spectra (Fe, Zn, Co, Cu, Pb, Cr, Ni and Cd) were determined on selected zooplankton, benthos and sediment samples. Laboratory toxicity studies were conducted on phytoplankton and zooplankton species at several concentrations of acid-iron waste in seawater. The maximum concentration of iron in the water column (832 μg 1−1) occurred as suspended material within a restricted area of the acid grid. In terms of raw acid-iron effluent this suggests a maximum in situ concentration of 1 part waste in 39,000 parts of seawater thereby providing a useful guide for the design of laboratory toxicity studies. Despite the abundance of suspended iron in the overlying water of the acid-grid the average concentrations of iron in the sediments of both the acid and control grids were remarkably similar, while sediments from the nearby Hudson Gorge were notably richer in iron. However, a comparison of previous measurements in the study area dating back to 1948 indicates that there has been no accumulation of iron within the sediments below the disposal area or Hudson Gorge over the past 22 yr. The phytoplankton toxicity experiment conducted with an acid-iron waste concentration four times greater than that observed in the field showed no adverse effect on phytoplankton growth or diversity. Similar experiments with copepods caused either failure of these organisms to reproduce or a delay in the time required to transform eggs into adults. Although the average zooplankton abundance within the control grid exceeded that of the acid grid by about 30 per cent, the range of values describing zooplankton abundance in the two areas was similar. This difference was attributed to a transitory large scale patchiness in the area and not to toxicity of acid-iron waste. A positive correlation was found between Fe:C in zooplankton and the amount of particulate iron present in the seawater. The average number of benthic animals on the bottom of the acid grid area was significantly less than in the sediment of the control grid but there was no difference in biomass or species diversity between the two areas. As was the case with zooplankton the higher Fe:C in the benthos corresponded to the higher iron in the sediment of Hudson Gorge and acid-grid. The heavy metal content of zooplankton, benthos and sediment showed that samples from the acid grid were significantly richer in these elements than the comparable control area samples. However, a broader comparison showed that samples from Hudson Gorge contained the maximum amounts of lead and chromium in benthos as well as the maximum concentrations of all eight metals in the sediment. These data are consistent with the possibility that entrapment in the gorge sediments may be the ultimate fate of the heavy metal enrichment in the New York Bight area and that sources of heavy metals other than acid-iron waste may be substantial. The remaining data reviewed in this study did not demonstrate any adverse in situ effects of acid-iron waste on the distribution of such parameters as dissolved oxygen, chlorophyll α and plant nutrients. Present indications are that the disposal of acid-iron waste in the New York Bight appears to influence standing crops in minor ways considering the magnitude and nature of the waste material involved.