During the summers of 1987-93, from half to two-thirds of the Sound’s bottom waters experienced dissolved oxygen levels below 5 milligrams of oxygen per liter of water (mg/l) (Figure 2). Levels of dissolved oxygen of 5 mg/l and higher are generally accepted as being protective of the Sound’s estuarine life. In 1989, a particularly bad summer, more than 500 square miles (40 percent) of the Sound’s bottom waters had dissolved oxygen levels less than 3 mg/l. During most of these years, dissolved oxygen in a portion of the Sound (up to 50 square miles) fell below 1 mg/l and in 1987 anoxia, the absence of any oxygen, was recorded in a portion of the Western Narrows.
These low levels of dissolved oxygen cause significant, adverse ecological effects in the bottom water habitats of the Sound. To date, research shows that the most severe effects (such as mortality) occur when dissolved oxygen levels fall below 1.5 mg/l at any time and below 3.5 mg/l in the short-term (i.e., 4 days), but that there are probably mild effects of hypoxia when dissolved oxygen levels fall below 5 mg/l. The levels regularly observed in the Sound during late summer:
Excessive discharges of nitrogen, a nutrient, are the primary cause of hypoxia. Nitrogen fuels the growth of planktonic algae. The algae die, settle to the bottom of the Sound and decay, using up oxygen in the process.
Natural stratification of the Sound’s waters occurs during the summer when warmer, fresher water “floats” on the top of cooler, saltier water that is more dense. This natural stratification forms a density difference between the two layers called a pycnocline. This prevents mixing of surface and bottom waters.
Oxygen from the atmosphere and photosynthesis keep the surface layer well oxygenated, but the oxygen cannot pass through the pycnocline into the bottom layer very easily. Decaying algae and other organic material in the sediment and animal respiration in the bottom layer use up oxygen faster than it is replenished. Hypoxia develops and usually persists as long as the stratification lasts (usually one to two months in late summer).
But hypoxia in Long Island Sound is too complex to fully understand using direct observations alone. Natural variations in weather and other physical factors affect the extent and severity of hypoxia. The Management Conference has constructed mathematical models in order to understand the relationship among natural variations, human-caused pollutant loadings to the Sound, and dissolved oxygen levels in the Sound. Work has been completed on LIS 2.0, a two-dimensional water quality model that provides the technical basis for the hypoxia management actions described in the plan. In June 1994, the Management Conference will complete work on LIS 3.0, a three-dimensional water quality model that will better define the area impacted by hypoxia. LIS 3.0 will be used as a tool to implement the plan and establish a detailed, cost-effective management program to reduce hypoxia.
LIS 2.0 provides a level of detail that allows the Management Conference to draw some clear conclusions about hypoxia in the Sound, its causes, and its solutions. Using LIS 2.0, the Management Conference has simulated water quality conditions as they were in the past, as they are today, and as they would be in the future under alternative nitrogen control scenarios. The model provided a cost-effective way of understanding the Sound and hypoxia.
Understanding the components of the load of nitrogen entering the Sound is fundamental to understanding the plan (Figure 3):
The goal of the hypoxia management plan is to eliminate adverse impacts of hypoxia resulting from human activities.
Achievement of this goal will require very large investments of capital, a long-term commitment, and the assistance of the New York-New Jersey Harbor Estuary Program. Therefore, the Management Conference has established interim targets for dissolved oxygen and has outlined a phased approach to achieving them, using what is known now to support early phases and committing to take additional steps as increased understanding of the environment will dictate in the future.
Using scientific information on the relationship between oxygen levels and ecological effects, the Management Conference has established interim target levels for oxygen that, if achieved, would minimize the adverse impacts of hypoxia. In summary, the interim dissolved oxygen targets for the bottom waters of the Sound are to:
The Management Conference is implementing a phased approach to reducing nitrogen loadings to the Sound from point and nonpoint source discharges within the Sound’s drainage basin.
Phase I was announced in December 1990. It called for a freeze on point and nonpoint nitrogen loadings to the Sound in critical areas at 1990 levels. It committed the states and local governments to specific actions to stop a 300-year trend of ever- increasing amounts of nitrogen entering the Sound.
The states have moved aggressively to implement the freeze, seeking the full cooperation of local governments.
Phase I agreements to control nonpoint sources centered around three categories:
Phase II includes firm commitments to reduce the annual, human-caused nitrogen load of 40,800 tons from in-basin sources by approximately 7,600 tons (or 18.6 percent). This includes complete compensation for the 2,800 tons per year increase associated with the end of ocean dumping and a 4,800 tons per year reduction from the 1990 freeze baseline.
The benefits of Phase II nitrogen reductions, as forecast by the LIS 2.0 model, will be substantial. Summertime minimum dissolved oxygen concentrations in the bottom waters of the western Sound will be raised on average from 1.5 mg/l to about 2.4 mg/l. The amount of estuarine habitat presently degraded will be reduced by about 10 percent. The area most severely affected by hypoxia will shrink by more than 30 percent.
However, these reductions alone will clearly not meet the interim dissolved oxygen targets nor achieve the goal for dissolved oxygen. Therefore, an additional level of nitrogen reduction will be necessary.
LIS 2.0 was used to begin to estimate nitrogen reductions required to meet the interim dissolved oxygen targets. Of the 40,800 tons per year total, in-basin, human-caused nitrogen load, required reductions are expected to range from 17,000 to 24,000 tons per year (or 42 percent to 59 percent). Achievement of these reductions would require the implementation of the mid- to high-level management scenarios as described in the Management Conference’s 1990 Status Report and Interim Actions for Hypoxia Management. Preliminary cost estimates of these two levels of control for point sources are from $5.1 to $6.4 billion for New York state and from $900 million to $1.7 billion for Connecticut.
Cost estimates for the necessary level of control of nonpoint sources have not been developed but are expected to be substantial.
The benefit of achieving the interim targets would be the elimination of severe hypoxia. Most lethal and sublethal effects of hypoxia would be prevented and most of the severely impacted habitat area would be restored.
However, in order to proceed with such a costly enterprise in a way that obtains the greatest environmental benefits for each dollar spent, approximate Soundwide reductions must be translated into discharge- or zone-specific load reduction targets.
The third phase of the plan, therefore, is to:
The Management Conference has already allocated funds to complete work on LIS 3.0. Resources and staff from existing programs will be used to establish LIS 3.0-based dissolved oxygen targets and nitrogen load reduction targets. The development of zone-by-zone plans to achieve the nitrogen reduction targets has already been initiated, with over $1 million committed. To complete all the zone-by-zone plans by 1997, the Management Conference estimates that $700,000 per year for three years will be needed.
The phased plan to reduce the annual load from point and nonpoint source discharges of nitrogen is depicted in Figure 6.
Full attainment of the goal of eliminating the adverse impacts of hypoxia from human activities (not just eliminating severe hypoxia) will require additional actions beyond the scope of the Long Island Sound Study. The New York-New Jersey Harbor Estuary Program is currently considering the need for nitrogen control on a systemwide basis; nitrogen control in the Harbor could reduce the export of nitrogen and increase the export of oxygen from the Harbor to the Sound. Additionally, New York City has initiated studies to evaluate the efficacy of relocating discharges from the upper and lower East River, thereby reducing these inputs of nitrogen to Long Island Sound.
The Management Conference recommends a long-term program of monitoring and modeling to assess progress in meeting the nitrogen reduction and dissolved oxygen targets, and to assess the ecosystem’s response. This program is essential to ensuring that the management actions that are implemented are benefiting the Sound as expected.
A key element of the program is the use of the LIS 3.0 model. The Management Conference recommends that LIS 3.0 be periodically recalibrated to reflect the changing conditions of the Sound, and be used to explain these changing conditions. Furthermore, the Management Conference recommends that LIS 3.0 be used to evaluate proposals to modify the management plan, as necessary.
A comprehensive hypoxia monitoring and modeling program has been proposed, building upon elements of existing programs, primarily those of the Connecticut Department of Energy and Environmental Protection (CTDEP), the NYCDEP, and the Interstate Sanitation Commission. Full implementation of the monitoring program would require additional funding of $300,000 per year. Recalibration of LIS 3.0 would cost approximately $300,000.
The Management Conference recommends increased funding of the Connecticut and New York State Revolving Fund programs. Based on the preliminary estimates, if the high-level of nitrogen control were selected, the Connecticut State Revolving Fund would need an infusion of $70 million per year in federal Clean Water Act funds and $47 million per year in state funds over 20 years to meet all statewide wastewater control needs, including Long Island Sound nitrogen control needs. The New York State Revolving Fund would need an infusion of $623 million per year in federal Clean Water Act funds and $128 million per year in state funds over 20 years to meet statewide needs, including Long Island Sound nitrogen control needs.
The Management Conference also recommends that the Congress authorize a total of $50 million under Section 119(d) of the Clean Water Act. This section of the Clean Water Act, created by the Long Island Sound Improvement Act of 1990, authorizes grants for projects that will help implement the plan. Appropriations could be spread over a period of five years. The Management Conference would use the $50 million to fund a Long Island Sound Challenge Grant program. A significant portion of appropriated funds would be used to ensure that the Phase III nitrogen control efforts get off to a fast start with full local government cooperation. The portion of these funds allocated for nitrogen control would be used to fund cost-effective point and nonpoint source control actions not involving major capital improvements. Innovative projects would be encouraged.
And finally, the Management Conference recommends that Congress fully fund the nonpoint source control programs under Section 319 of the Clean Water Act and Section 6217 of the Coastal Zone Act Reauthorization Amendments to support additional nonpoint source management activities.