Steven Yergeau, Director of Research

Save the Sound, Inc., 185 Magee Avenue, Stamford, CT 06902

Near-shore water quality gathered in Save the Sound’s water quality monitoring program are analyzed in relation to seasonal algal blooms and the extent and duration of hypoxic events. Dissolved oxygen, chlorophyll a, and phytoplankton taxa were determined weekly between May and October, 1997 at 5 or 6 stations in each harbor.

Results from the 1997 testing season in four harbors (Echo Bay in New Rochelle, NY; Milton Harbor in Rye, NY; Cos Cob Harbor in Greenwich, CT; Stamford Harbor in Stamford, CT) are compared to see the influences of industrial and residential impacts on the phytoplankton populations. Correlations between chlorophyll a, as a measure of algal biomass, and dissolved oxygen are investigated in relation to different stations and the different harbors. Phytoplankton population structure is also examined for the degree of similarity to naturally balanced assemblages to determine the effects of environmental change on the populations.

There is a complex system of rivers, bays, wetlands, and beaches that bind and nourish Long Island Sound. This system thrives on a delicate balance of vital elements, and this balance is threatened by the pressures of human activities. The vitality of Long Island Sound is an integral part of the economy and ecology of the region (Altobello, 1992). Many people live near the Sound and enjoy fishing, boating, swimming, and birding. In fact, ten percent of the United States’ population lives within 50 miles of Long Island Sound (Long Island Sound Study, 1994). The Sound is one of the most productive estuaries in the nation, supporting a diverse assemblage of marine life. It is estimated that the Sound contributes approximately $5.5 billion annually to the regional economy, with recreational and commercial fishing alone contributing over $1 billion per year (Altobello, 1992).

Long Island Sound undergoes seasonal hypoxic events where levels of dissolved oxygen drop below 3.0 milligrams per liter (mg/l), usually at the height of summer (Yergeau and Ayala, 1998). Oxygen enters the water from the churning action of the tides and wind, and from photosynthesis of marine plants. In the marine environment, nitrogen generally acts as the limiting nutrient for algal growth. As with many estuaries, there is an overabundance of nitrogen in Long Island Sound. Nitrogen enters the Sound through many sources such as sewage treatment plants, leaking septic systems, storm-water runoff, and acid rain all of which lead to algal blooms (American Oceans Campaign, 1996). When the algae die and sink to the bottom, oxygen is consumed during their decomposition by naturally occurring bacteria (Long Island Sound Study, 1994). This increased demand for oxygen is in addition to the normal oxygen use from the metabolic activities of animals and plants. Hypoxia (oxygen levels below 3.0 mg/l) can be most severe during the summer when stratification prevents highly oxygenated surface water from mixing with the poorly oxygenated bottom water. Severe hypoxic events have occurred in the Sound that have resulted in large fin fish and shellfish kills (Long Island Sound Study, 1994; Brosnan and Stubin, 1992; Miller et al., 1992; and Poucher et al., 1992). This period of low dissolved oxygen in the Sound has been identified by the Long Island Sound Study as the highest priority upon which New York, Connecticut, and the U.S. Environmental Protection Agency are focusing their efforts and resources (Long Island Sound Study, 1994).

The states of Connecticut and New York have set criteria or water quality standards for water resources depending on a water body’s class and/or designated use(s). Dissolved oxygen should not be less than 5.0 mg/l at any time for: protecting marine fish, shellfish, and wildlife habitat; harvesting shellfish for transfer to approved areas for purification prior to human consumption; primary contact (swimming) and secondary contact (navigation); and recreation (Class SB Waters) (CT DEP, 1992; NYS DEC, 1991). Dissolved oxygen should not be less than 6.0 mg/l (Connecticut water quality standard) or 5.0 mg/l (New York water quality standard) at any time for shellfish harvesting for direct human consumption (Class SA Waters) (CT DEP, 1992; NYS DEC, 1991).

To determine the extent of hypoxic events in the coastal areas of Long Island Sound, water quality monitoring efforts are underway using chemical indicators. The development of a biological indicator for monitoring estuarine water quality to supplement dissolved oxygen concentration measurements can aid in the expansion of monitoring efforts in large coastal bodies of water, such as Long Island Sound. The measure being investigated by Save the Sound, a diversity index based on phytoplankton presence or absence (from now on referred to as the phytoplankton diversity index, or PDI) has been developed and assessed (Yergeau, Lang, and Teeters, 1997). The PDI is incorporated into Save the Sound’s water quality monitoring program to supplement data on dissolved oxygen, pH, Secchi disk depth, temperature, salinity, and chlorophyll a concentration, and to help analyze and report on water quality data collected on a weekly basis from harbors in Long Island Sound. Phytoplankton were chosen as the indicators of water quality since microalgae have short generation times and respond quickly to changing water quality conditions (Yergeau, Lang, and Teeters, 1997). The purpose of Save the Sound’s water quality monitoring program is to collect baseline data to be used in determining status and trends in embayments not included in larger research programs and to provide information on remediation of those areas. The results are used to supplement regional monitoring efforts, to provide data for further scientific research, to educate citizens about Long Island Sound pollution, and to advocate for better land and water use practices and improved pollution control.

Two Connecticut and two New York harbors were tested weekly from May 17 to October 11, 1997. Surface (0.5 meter (m) below water surface) and bottom (total water depth minus 0.5 m) measurements included dissolved oxygen, salinity, temperature, and Secchi disk depth. Photosynthetic pigment chlorophyll a was sampled weekly at the surface (1.0 m below water surface) and analyzed as a measure of algal biomass. Algal diversity was sampled bi-weekly at the surface (1.0 m below water surface). In all harbors, measurements were taken from boats in the morning starting at approximately 7:00 am and running to approximately 9:00 am.

Echo Bay: New Rochelle, NY (Figure 1)

Echo Bay is a wide harbor with industrial development surrounding the waterfront. On the western bank are residential areas and Hudson Park, a multiple use outdoor facility. On the northern shore is the sewage treatment plant that treats waste from different towns within Westchester County with the majority coming from New Rochelle. In the center of Echo Bay is Five Islands Park, a complex with areas for boating, fishing, and swimming.

In the northeast section is the Mill Pond fed by the Premium River. This area is filled with tidal flats and marsh areas beneficial to a variety of wildlife. The Mill Pond is separated from Echo Bay by a dam that creates a waterfall into the harbor. In the northwest reaches, Echo Bay is fed by the Stephenson Brook, a culverted stream that runs underneath the city.

Milton Harbor: Rye, NY (Figure 2)

Milton Harbor is a narrow harbor with primarily residential, marina, and mooring areas. The dredged channel has approximately 2.0 m of water between the head of navigation and Milton Point and averages 2.5 m deep beyond Milton Point. There is a large tidal flat area on the northeastern quadrant. The harbor is fed by Blind Brook, which originates at the Westchester Airport. The Marshlands Conservancy and a golf course are on the western bank of the harbor. Hen Island is a residential island accessible by boat only.

Cos Cob Harbor: Greenwich, CT (Figure 3)

Cos Cob Harbor is an extension of the Mianus River. The harbor is divided into the inner and outer areas by the Metro North Railroad Bridge. The inner harbor has mudflats on the east bank which occupy more than half the width of the harbor. On the west side, there are several marinas running the entire length of the harbor just to the south the Mianus River Dam. In the outer portion, there are large homes and Riverside Yacht Club on the east side of the harbor. The west side consists of mostly undeveloped land and the remains of the Cos Cob Power Plant.

Stamford Harbor: Stamford, CT (Figure 4)

Stamford Harbor is primarily industrial in its surrounding land use, however there are also residential and mooring areas dotting its shores. The harbor is divided into east and west branches, forming a Y’. The Woodland Cemetery and Kosciusko Park peninsula divides the two branches. Both the east and west branches have small tidal flat areas along the shores of the peninsula. On the western bank of the west branch is Southfield Park, a public beach adjacent to the Hoffman fuel dock.

The east branch of the harbor is separated and protected from the mouth of Long Island Sound by a hurricane barrier. Along the entire western bank of the east branch are tidal mudflats. A condominium complex is located just behind a series of boat slips and docks. To the north is the Stamford sewage treatment plant and its freshwater outlet at the dead end of the East Branch.

In Echo Bay and Milton Harbor, dissolved oxygen (measured in mg/l) and temperature (recorded as degrees Celsius (°C)) were measured using a Yellow Springs Instrument (YSI) model 58 Dissolved Oxygen meter with digital display, stirring unit, and 5700 field probe. Dissolved oxygen readings were not adjusted for salinity in the field, but were corrected using calculations in a computer database (Yergeau, 1997). Salinity (reported as parts per thousand (ppt)) was measured using a YSI model 33 Salinity-Conductivity-Temperature (SCT) meter with analog display. Salinity measurements were compensated for changes in temperature manually by direct dial (Yergeau, 1997).

The volunteers air calibrated the dissolved oxygen meter and red-lined the SCT meter before they began each testing session. Each day the dissolved oxygen probe was also checked for air bubbles and the membrane was changed, if necessary. The salinity and dissolved oxygen probes were attached to a platform and readings were taken at the surface (probes at 0.5 m below the water’s surface), at one meter intervals, and at the bottom (probes 0.5 m above the bottom).

In Cos Cob Harbor and Stamford Harbor, a Hydrolab H20 Multiprobe was used to measure dissolved oxygen, salinity, temperature, and pH. The volunteers air calibrated the probes before they began each testing session. Each day the dissolved oxygen probe was also checked for air bubbles and other membrane problems. The instrument automatically adjusts dissolved oxygen readings for salinity and temperature, and automatically adjusts salinity readings for temperature. No additional calculations were used to correct these values (Yergeau, 1997).

Water clarity was measured by using a Secchi disk. Secchi disk depth was determined by taking the average of the water depth that the disk disappears from sight and the depth at which it reappears into view (Yergeau, 1997). Two volunteers perform this measurement and these two averages are then averaged for the final reading at that sampling site.

Water samples for chlorophyll a analysis were collected using a Van Dorn sampler. Water samples were taken at 1.0 m below the water surface. The mixed water sample was filtered on the boat using a manifold and hand pump. The volume of water filtered was determined by comparing the color on the filter to a color chart after a dark green or dark brown color was reached on the filter paper. The filter apparatus was rinsed three times with distilled water after each use. The filter was placed in a foil packet, labeled, and stored on ice until it was transferred to the laboratory freezer. Any samples held longer than three weeks in the laboratory were noted in the sample log book as such, since there may be possible degradation of the chlorophyll in those samples (Greenberg et al., 1992).

Chlorophyll a extraction and analysis was performed at Save the Sound’s water quality laboratory by a member of the research staff or by trained technicians following Standard Methods’ protocols (Greenberg et al., 1992). Pigments were extracted after grinding the filter with a Teflon pestle in a 55.0 milliliter (ml) grinding tube with a 90% aqueous acetone solution. The samples were clarified in a centrifuge for 20 minutes, then analyzed using a UV/VIS spectrometer with a 2.0 nanometer (nm) band width. A band width of 2.0 nm is necessary since chlorophyll has a narrow absorption peak and a larger-sized band width would underestimate the chlorophyll a concentration (Greenberg et al., 1992). The following exception to Standard Methods was performed: after being clarified, the samples were resuspended and centrifuged two more times to insure 99.1% retrieval of chlorophyll a (Yergeau, 1997).

Chlorophyll concentrations were corrected for pheophytin a, so that chlorophyll a values were not overestimated (Greenberg et al, 1992). The correlation between dissolved oxygen and chlorophyll a was calculated using Lotus 1-2-3 version 5 and the correlation coefficient (r) was compared to critical values to determine statistical significance at the 1% level (Rohlf and Sokal, 1981).

Water samples for phytoplankton identification were collected using a Van Dorn sampler. Water samples were taken at the surface (1.0 m below the surface of the water). The mixed water sample was poured into a 500 ml opaque brown bottle containing 15.0 ml of Lugol’s solution to preserve the sample. The 500 ml samples are measured in a graduated cylinder and filtered to concentrate the phytoplankton and to facilitate identification. An amount of filtered water equal to 1/100th of the original sample size was used to wash the sample off the filter (for a 100x concentrated sample). Three (3) slide views from this 100x concentrated sample are then observed, with phytoplankton identified, and indication of presence or absence noted. Samples were analyzed within three weeks time to ensure there was no degradation of the sample and to coincide with the chlorophyll a analysis (Yergeau, 1997).

The PDI was determined using the calculations given in Yergeau, Lang, and Teeters, 1997. The resulting number, based simply on the presence or absence of the taxa within three (3) slides, falls between 0 and 20, with an increase in diversity as PDI increases.

NOTE: All volunteers and laboratory technicians are trained thoroughly by Save the Sound’s research staff, with particular attention given to consistency of data collection. Volunteers must complete a six hour training course (classroom and field work) before they can participate in the program (Yergeau, 1997).

Echo Bay: New Rochelle, NY (Table 1 & Figure 5)

The water quality in Echo Bay was fair during the testing season. Four out of the five stations experienced violations of the water quality standard (5.0 mg/l dissolved oxygen) at least once. Station 5 stayed above the water quality standard for that same period.

Dissolved oxygen levels were the lowest at the stations closest to Stephenson Brook. Station 1, at the Stephenson Brook outfall, had the worst water quality compared to the other stations in the harbor. The dissolved oxygen dropped in mid-July (7/12) and rebounded in July and August, but dropped below the standard in the middle of August (8/17) and did not recover until mid-September (9/14).

Station 2, located at the northern end of Hudson Park, had poor water quality compared to other stations in the harbor with dissolved oxygen levels violating the water quality standard at the beginning of August (8/2) and remaining below the standard for the rest of the month.

Station 5 had the best water quality in the harbor. The water quality remained above the standard for the entire testing season at this site.

Surface levels of chlorophyll a were similar at stations 2, 3, 4, and 5. Levels of chlorophyll at these stations were relatively low, with most of the values between 10.0 and 15.0 µg/l, indicating some development of small algal blooms. Chlorophyll a concentrations ranged from 1.1 µg/l to 26.4 µg/l. A large algal bloom was detected at station 4 when chlorophyll concentration was 26.4 µg/l. The average chlorophyll value was 11.4 µg/l. Chlorophyll a and dissolved oxygen were positively correlated with statistical significance at the 1% level (r= 0.24). The PDI averaged 12.15 for the season.

Milton Harbor: Rye, NY (Table 1 & Figure 5)

The water quality in Milton Harbor was poor during the testing season. Dissolved oxygen was below the water quality standard (5.0 mg/l dissolved oxygen) at every station at least once during the season.

Dissolved oxygen levels were the lowest at the stations closest to Blind Brook. Stations 1 and 2 had the poorest water quality; violations of the water quality standard occurred most often at these sites. The lowest level observed in this harbor (2.9 mg/l) occurred at station 1, the most inward site, on July 12.

Stations 5 and 6, located towards the deeper portions of the harbor, had the highest dissolved oxygen levels. Oxygen levels were above or equal to the water quality standard throughout most of the testing season.

Surface levels of chlorophyll were similar in stations 1, 2, 3, and 4. Chlorophyll a values at these stations were moderate with most of the values between 10.0 and 20.0 µg/l, indicating some development of algal blooms. Chlorophyll a concentrations ranged from a high of 23.8 µg/l to a low of 0.2 µg/l. The average chlorophyll value was 10.4 µg/l for 1997. Chlorophyll a and dissolved oxygen were negatively correlated with statistical significance at the 1% level (r= -0.59). PDI averaged 11.87 for the season.

Cos Cob Harbor: Greenwich, CT (Table 1 & Figure 5)

Overall, the water quality in Cos Cob Harbor was poor during the testing season. Dissolved oxygen levels were below the water quality standard (5.0 mg/l dissolved oxygen) at every station at least once during the season.

The stations closest to the Mianus River had the worst water quality. The duration that oxygen levels were below the water quality standard was longer and hypoxia (<3.0 mg/l dissolved oxygen) occurred more frequently at these sites. Station 1, located just south of the Mianus River Dam and Route 1, had the worst water quality compared to other stations in the harbor. At station 1, dissolved oxygen levels were below the water quality standard in the bottom water for most of the last half of the testing season (8/2-10/11) and went hypoxic twice: in mid-July (7/19) and early August (8/2).

At station 6, located at the mouth of the harbor, bottom water oxygen levels were below the water quality standard only four times: twice in late July (7/12); once at the end of August (8/24); and again in September (9/20).

Surface chlorophyll was similar at stations 2, 3, 4, 5, and 6 in Cos Cob Harbor between. Station 1, however, had the lowest chlorophyll levels for most of the season but experienced the largest bloom in the harbor. Chlorophyll a concentration on June 7 was measured at 41.9 µg/l, indicating a very large bloom. The levels ranged from 0.9 µg/l to 41.9 µg/l. At the other stations in Cos Cob Harbor, chlorophyll a values were low with most of the values between 5.0 and 10.0 µg/l for most of the season. The overall average chlorophyll value was 7.0 µg/l. Chlorophyll a and dissolved oxygen were negatively correlated with statistical significance at the 1% level (r= -0.06). PDI averaged 11.86 for the season.

Stamford Harbor: Stamford, CT (Table 1 & Figure 5)

The water quality of Stamford Harbor was rated as poor during the season. Dissolved oxygen was below the water quality standard (5.0 mg/l dissolved oxygen) at every station at least once in the testing season.

The stations furthest from the mouth of the harbor had the poorest water quality. At stations 1 and 5, in the east and west branches, respectively, the oxygen levels were below or very close to the water quality standard for most of the season (7/2-9/27) and were hypoxic (<3.0 mg/l dissolved oxygen) one time at station 1 and five times at station 5 from August to September. Station 5, located in the West Branch, had the worst water quality with oxygen levels that were above the water standard only three times during the last half of the testing season (7/26-10/11).

At most of the stations (stations 1, 2, 3, and 4), chlorophyll a levels were similar throughout the monitoring season. Chlorophyll a values at these stations were low, with most of the values between 5.0 and 13.0 µg/l. Station 3, however, experienced the largest level of chlorophyll detected during the season. On August 23, the level of chlorophyll a was measured at 43.7 µg/l in the surface water, indicating a very large algal bloom. The overall average chlorophyll value was 7.8 µg/l. Chlorophyll a and dissolved oxygen were negatively correlated with statistical significance at the 1% level (r= -0.23). PDI averaged 12.05 for the season.

These preliminary results show that there is impairment of the harbors studied. They also show that other factors not currently analyzed are influencing dissolved oxygen concentrations and algal bloom formation in areas of Long Island Sound.

In theory, the water quality in the more developed harbors should be worse than the water quality in the less developed harbors. Stamford Harbor and Milton Harbor both followed this logic with their water quality results. Echo Bay and Cos Cob Harbor, however, did not fit with this logic. Echo Bay had the highest rated water quality during this study and Cos Cob Harbor had water quality rated as poor.

The shape of Echo Bay is having an influence on the flushing in and out of nutrients as well as the blooms formed by those nutrients. The widened mouth of Echo Bay allows for a large amount of tidal exchange. Cos Cob Harbor however has a narrow harbor mouth which experiences less tidal exchange.

Cos Cob Harbor also has mostly residential development surrounding its shores. These areas are currently not sewered. Old, failing septic systems may be responsible for the low average dissolved oxygen readings during the course of this study.

It is seen that the rivers and creeks that drain into the harbors had a large influence on their water quality. Those stations closest to these tributaries generally had the lowest dissolved oxygen levels. This is indicative of nonpoint pollution influencing the harbors in this study. Further study of the nutrient inputs, particularly nitrogen, into these harbors would clarify this situation. Human activities, such as discharges from sewage treatment plants and nonpoint source runoff, are responsible for 56% of the total annual nitrogen load in the Sound (Long Island Sound Study, 1994).

A major source of nonpoint pollution is stormwater runoff which carries contaminants, including nutrients, metals, oils, and pesticides. In more developed areas, impervious paving materials prevent rainwater absorption by the soil, thereby increasing the amount of contaminants carried in the runoff. An analysis of rainfall data from 1997 is currently being undertaken to determine the atmospheric contribution to the hypoxia/algae dynamics in these harbors.

The effects of hypoxia on the living marine resources in the Sound depend upon the extent, duration, and intensity of the hypoxic period. It is likely that an increase in the sources and occurrences of coastal pollution, due to human activity, will result in more intense hypoxic events which severely stress and kill commercially and recreationally important fish and shellfish. The areas of concern identified in this study will be watched closely as they will be more severely impacted by poor water quality conditions in the future. Land use practices must be improved around these areas of concern to minimize nonpoint and point source pollution and their potential impact on marine life.

I would like to thank Iliana Ayala, Research Assistant at Save the Sound, and Ann Lang and Robert Teeters, for their hard work during all phases of this study.