Waste Water Pollution in Long Island Sound
We saw in the previous web page Deformed Forams in Biscayne Bay that foram test deformities and the presence of "opportunistic" taxa were indicators of environmental stress. Biscayne Bay is a normal marine habitat and stress there was likely related to pollution, since the most badly stressed sites were near probable pollution entry points.
This next setting is quite different. Long Island Sound is an estuary located close to New York City, where river-borne water mixes with salty marine water before it flows into the open sea - in this case, eastward into the Atlantic Ocean. As a result, Long Island Sound suffers from a variety of stresses, some natural such as mixed salinities and a range of annual water temperatures, and some man-made such as metal and waste water contamination. In addition, parts of western Long Island Sound periodically become severely depleted in oxygen. Unraveling the interactions of various stress factors is a challenge; but this study shows us how that challenge is being addressed with the help of benthic foram data.
(Credit: Harley Knebel, US Geologic Survey, US Department of the Interior)
Long Island Sound is located on the east coast of the United States, south of the state of Connecticut and north of Long Island, New York (see map above). It is surrounded by one of the biggest population centers in the US, where populations have increased substantially during the last 100 years, and particularly during the last 50.
What was their research plan? Sea floor grab samples were collected throughout Long Island Sound during 1996 and 1997. Scientists analyzed samples for benthic foram species abundance, and then mapped the data. Next they compared their results with results reported from the 1961-1962 and 1948 studies in order to understand how conditions might have changed. Understanding when possible changes occurred may help them understand the causes. In addition to abundance studies, the scientists ran oxygen and carbon isotope analyses on tests of Elphidium excavatum collected during the 1996-97 and 1961-62 field seasons.
The following maps show benthic foram sampling sites for the three studies.
(Credit: Thomas et al., 2000; US Geologic Survey, US Department of the Interior)
What did they find? Table 1 shows the relative abundances of four species of benthic forams reported for each of the three study periods. Studies in 1948 and 1961-62 were consistent, indicating that conditions in Long Island Sound remained stable during that period. However, a significant change in the benthic foram community took place between the early 1960's and 1996-97. Changes are highlighted in yellow in Table 1. Immediately below Table 1 is a series of images showing what the four key foram species looked like.
|Elphidium excavatum||Buccella frigida|
|Eggerella advena||Ammonia beccarii|
Where are these changes occurring? The two following maps show the distribution of Eggerella advena and Ammonia beccarii in all three studies. Eggerella advena decreased significantly in relative abundance, with most of that change apparent in central Long Island Sound. In contrast, Ammonia beccarii increased in relative abundance in western Long Island Sound. (Hint: look carefully for red and yellow data points to see the areas of change.)
Comparison of oxygen isotope data in tests from 1996-97 and 1961-62 studies suggested that salinity within Long Island Sound had remained stable. This natural variable apparently was not responsible for the relative abundance changes. In addition, carbon isotope data from the same samples varied strongly from west to east with lighter delta13C values in the western portions (Thomas et al., 2000b). The 1961-62 samples were generally heavier in delta13C suggesting that organic carbon was being oxidized at a greater rate in the 1990's than in the 1960's and in the west more than in the east.
What do these results tell us? The species changes demonstrated in the 1990's study suggested that Long Island Sound was experiencing higher levels of stress than in the 1940's and 1960's. In addition, the presence of Ammonia beccarii in the western part of the sound suggested that the stress was most intense there. The stress did not appear to be related to salinity changes.
What could be causing the stress? Scientists did not know for sure, but their hypothesis was that it is due to increased levels waste water effluent (treated sewage). Why did they think so? Well, scientists performed a parallel study in which they measured the amount of a bacteria spore called Clostridium perfringens in sea floor samples throughout Long Island Sound. This spore is found in human excrement and is an indicator of sewage pollution. Clostridium perfringens bacteria spores were more abundant in the western and central portions of the sound. Red areas highlight the largest concentrations.
In addition, samples with the highest numbers of Clostridium perfringens bacteria spores generally also had the highest Ammonia percentages (see graph below).
(Reprinted from Journal of Coastal Research Special Issue CERF, 16(3), 641-655, Thomas, E., Gapotchenko, T., Varekamp, J.C., Mecray, E.L., & Buchholtz ten Brink, M.R., Benthic Foraminifera and environmental changes in Long Island Sound, Copyright 2000, with permission from Journal of Coastal Research)
Scientists speculated that excessive nitrogen in waste water effluent had caused the food sources for these forams (single-celled floating algae at the base of the food web) to change from predominately diatoms to predominately cyanobacteria and dinoflagellates. Ammonia thrived on these new sources of food, and increased in percentage relative to Elphidium which preferred diatoms. Other contributing factors may have been decreasing oxygen levels and increasing temperatures.
As you can see, interpretation of benthic foram data in pollution studies is not a simple matter. Many factors, both natural and man-made, may play a role in the health and distribution of foram species.
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Revised on: January 19, 2005