Provincetown Center for Coastal Studies | Coastal Ecology

Working in collaboration with researchers and laboratories from Boston University and the Georgia Institute of Technology (Georgia Tech), CCS will apply cutting-edge technology to identify and track inorganic nitrogen released by the 9.5 mile-long outfall pipe tunneled beneath Massachusetts Bay. Once on line, the outfall will discharge an average of 370 million gallons of effluent a day.

While the Massachusetts Water Resource Authority’s Bays Eutrophication Model predicts that there will be no adverse effects on the water quality or marine life in Cape Cod Bay, the Cape Cod Commission’s Science Advisory Panel remains concerned. “The use of an offshore pipe to release effluent has raised concerns that the cleanup of Boston Harbor may be at the expense of Cape Cod Bay,” said panel member and CCS Senior Scientist Dr. Charles Mayo, who will supervise data collection for the project. “Because primary and secondary sewage treatment does little to remove nutrients from the effluent, the addition of nutrients offshore could promote blooms of plant plankton that can deplete oxygen and cause sensitive animals to suffocate. These blooms can also alter the food web upon which animals such as the endangered right whale rely.”
“The study,” said Borrelli, “represents an unprecedented field program designed to quantify the contribution of different sources of nitrogen to plankton nutrition in different portions of the bay. Previous studies have shown that the nitrogen in sewage has a distinctive isotopic? signature, making it possible to follow its movement within an ecosystem.” The technique has been refined by Dr. Joseph Montoya at Georgia Tech, one of the principle investigators of the project, to trace pollution to point sources in estuarine environments.

Dr. Montoya noted that while the project is designed to complement the MWRA monitoring effort, “Our sampling program, because of the large number of stations, is better matched to the inherent spatial and temporal scales of variability within Cape Cod Bay than the ongoing surveys carried out by MWRA, and, therefore, much more likely to capture the dynamics of nutrient transfer with the bay.” Water and plankton samples are being collected at twenty different stations in Cape Cod Bay, year-round, during bi-monthly cruises aboard the R/V Shearwater.

CCS monitoring will provide at least one early-warning indicator to help the MWRA assess the impact of sewage on Cape Cod Bay and, if necessary, take corrective action. Tracking nitrogen from the effluent will also inform future sewage treatment plans and their effects upon the Cape Cod Bay food web, one of the critical feeding grounds of the right whale. CCS research has shown that, in the winter up to one third of the 300 remaining right whales in the North Atlantic grazes the plankton-rich waters of the bay.

First-year funding currently includes approximately $20,000 from the Cape Cod Commission, $50,000 from the Massachusetts Environmental Trust through proceeds generated by the sale of the Massachusetts right whale license plates, and another $50,000 from private contributions. The anticipated cost of the three-year project is about $500,000. Borrelli said that CCS has established a fund to receive additional private contributions in support of the research. “I urge those who care about the future of Cape Cod Bay to contribute to the fund,” said Borrelli. “Whatever the amount, whether a dollar or ten thousand dollars, I believe it is important for private citizens register their support for a clean, beautiful, and productive bay.”

*Isotope. Any of two or more species of atoms of a chemical element with the same atomic number and nearly identical chemical behavior but with differing atomic mass or mass number and different physical properties.

Isotopes Demystified: Monitoring Chemistry for Laymen

The Bays Monitoring Initiative is aimed at developing a long-term understanding of the natural character of Cape Cod Bay and the human influences upon it. The incentive for such studies comes from a long-term view of the management and mismanagement of other coastal embayments, such as Chesapeake Bay, Delaware Bay and Long Island Sound.

Intended to be pro-active, to develop the foundation of understanding of the bay’s ecosystem before natural and man-made changes degrade its precious resources, the research plan consists of two components. The first component consists of nitrogen studies to be conducted by Dr. Montoya and Dr. Mayo, which will track the progress of the sewage effluent through the water and food web of the bay. The second is right whale investigations, which include the ongoing habitat work conducted by Dr. Mayo and Associate Scientist Ed Lyman, as well as right whale surveillance, conducted by Dr. Moira Brown.

The nitrogen studies are organized around a set of hypotheses related to the biogeochemistry of nitrogen in the bay. The first hypothesis is that the average isotopic composition of nitrogen in sewage effluent is significantly different from the average isotopic composition of marine nitrogen sources.

What do we mean by “isotopic composition”? Every atom is made up of two kinds of nuclear particles, protons and neutrons, around which electrons revolve. Protons have a positive charge and are balanced by the negative charge carried by the surrounding electrons. Each element is identified by the specific number of protons and electrons making up each atom, but the number neutrons may vary without changing the identity of the element. In the case of nitrogen, about 99.6% of the nitrogen on earth has fourteen nuclear particles (seven protons and seven neutrons), but some have an extra neutron and are thus heavier by one atomic mass unit. This is why the average atomic mass of nitrogen is 14.0067 as opposed to 14.0000 (electrons have no mass).

Any two atoms which have the same number of protons, but which differ in number of neutrons, are “isotopes” of the same element. The difference in atomic mass between 14N and 15N allows scientists to measure the ratio of the two isotopes occurring in samples collected from various different sources. By measuring the ratio of 15N to 14N in samples of effluent obtained from the Massachusetts Water Resources Authority (MWRA) to the ratio of 15N to 14N in samples collected in the Cape Cod Bay before the Outfall goes on line, the study is designed to confirm previous work done by Dr. Montoya showing that the occurrence of 15N is significantly different in the effluent than in the natural marine environment.

The ratio will be measured either at Dr. Montoya’s lab at Georgia Tech or at the Boston University Stable Isotope Lab by a method known as “continuous-flow isotope ratio mass spectrometry”. In the mass spectrometer, atoms are accelerated by high voltages toward a magnetic field. The field deflects the atoms toward a collector plate. The lighter isotopes (14N) are deflected more than the heavier isotopes (15N) and the relative abundance is recorded as the isotopes reach the collector plate at different points.

The fact that the 15N:14N ratio in sewage effluent differs from that in natural seawater is due to small differences in reaction rates that characterize the two isotopes in biological processes. In such processes, any chemical reaction involving nitrogen atoms will tend to discriminate slightly against the heavier isotope. As a result, the product of such a reaction will be depleted in 15N relative to the substrate (original substance). The ratio between the rate of reaction for 14N and the rate of reaction for 15N is called the “isotopic fractionation factor”. This factor has been defined in both laboratory and field studies for a number of planktonic processes. As a result of various biological processes, particulate sewage such as sludge will be depleted in 15N as compared to the sewage effluent, which will be enriched in 15N.

Once the components of the sewage are characterized, and taking the isotopic fractionation factor into account, the researchers expect to be able to map the extent of the influence of the effluent both in the water column and in the food web. They will do this by examining the isotope ratios in both water samples and phytoplankton samples collected at twenty designated stations throughout the Bay.

In order to reveal the movement of nitrogen from the effluent up through the food web, zooplankton collected during the project will be compared with previously collected samples preserved in the CCS lab. The hundreds of samples collected during CCS’s seventeen years of right whale habitat studies are expected to provide a rich history of the changes in anthropogenic (coming from human activities) nitrogen levels within Cape Cod Bay. Results are expected to confirm that anthropogenic nitrogen has increased in recent years.

As the concentration and distribution of sewage nitrogen are characterized, another hypothesis will be examined, namely, that the presence of sewage effluent influences right whale distribution and foraging behavior by affecting the abundance, species and/or distribution of zooplankton which feed on the affected phytoplankton. Data from both previous and upcoming CCS research cruises and aerial surveys will be used to compare the feeding patterns of right whales before and after the Outfall goes on line and to correlate the feeding behavior with the location of affected plankton. Finally, tissue samples from CCS archives and ongoing genetic studies will be examined to explore changes in isotopic composition.

Because so little is currently known about the potential effect of anthropogenic nitrogen on the various species of marine mammals that feed in and pass through the Bay, studies such as this are critical to the success of future management plans.

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