Water quality monitoring in the Jacques Cousteau National Estuarine Research Reserve System.
KEY WORDS: Mullica River-Great Bay Estuary, physical-chemical variables, water quality, system-wide monitoring
The Jacques Cousteau National Estuarine Research Reserve (JCNERR) is the 25th program site of the National Estuarine Research Reserve System (NERRS) (Figure 1). The principal mission of the JCNERR program is to conduct long-term scientific research and monitoring to characterize the natural and anthropogenic processes governing stability and change in the Mullica River, Great Bay, Lower Barnegat Bay, Little Egg Harbor, Little Bay, Reeds Bay, Absecon Bay, and contiguous nearshore ocean waters, and to provide the data necessary to effectively address coastal resource management problems. The reserve program also focuses on improving the protection of estuarine resources for designated uses such as public health, recreation, and support of the estuarine ecosystem. In addition, it enhances public awareness and understanding of the estuarine and watershed areas in the region through public education, interpretation, and outreach.
The Institute of Marine and Coastal Sciences at Rutgers University is the lead institution overseeing operations of the JCNERR program. Rutgers University has been collecting water quality data and conducting basic and applied research within the Mullica River-Great Bay estuarine system since the 1950s (Durand and Nadeau, 1972; Durand, 1988). With the acquisition of its marine field station on Great Bay in 1972, the University began collecting extensive environmental data on Great Bay and contiguous waters. Other collaborative agencies and partners in the program include the Richard Stockton College of New Jersey, New Jersey Department of Environmental Protection, U.S. Fish and Wildlife Service, U.S. Geological Survey, Pinelands Commission, and Tuckerton Seaport.
The JCNERR is unique for several reasons. The Mullica River-Great Bay Estuary exhibits exceptional environmental quality, and is generally considered one of the most pristine and least (anthropogenically) impacted estuarine systems in the densely populated urban corridor of the northeastern United States (Durand, 1988; Able et al., 1992, 1999). As such, it serves as an ideal reference site for comparison with other estuaries. This is largely attributed to the extensive undeveloped lands of the Pinelands National Reserve (PNR), state wildlife management areas, and federal refuges surrounding these waters (Figure 1). The PNR, totaling nearly 450,000 ha, encompasses much of the forested land in surrounding watershed areas, and it restricts future development in the system (Psuty et al., 1993; Zampella et al., 2001). The terrestrial, wetland, and aquatic habitats of the JCNERR are entirely in public ownership, and the state and federal managed lands provide a significant level of resource protection.
The boundaries for the JCNERR are designed to constitute a natural ecological unit. They enclose a core area of contiguous wetlands, riparian habitats, open waters in Great Bay, and nearshore ocean areas off Little Egg Inlet. The buffer zone includes upland-forested areas adjacent to the core wetland habitats. The Mullica River-Great Bay Estuary forms a highly productive system, which supports a rich diversity and high population abundance of finfish, shellfish, and wildlife.
A major component of the reserve program is the monitoring of estuarine water quality. Water quality data are important because they help to characterize the overall environmental quality of the estuarine system. The purpose of this article is to analyze water quality conditions at three designated system-wide monitoring sites in the reserve (i.e., Lower Bank, Chestnut Neck, and Buoy 126). A primary reason for selecting these station locations is the well-defined salinity gradient occurring along the Mullica River-Great Bay Estuary.
The JCNERR is located in southern New Jersey (~39[degrees]N, 74[degrees]W) approximately 15 km north of Atlantic City. It consists of a wide array of aquatic, terrestrial, and wetland habitats, which cover an area of more than 45,000 ha (Figure 1). The areal extent includes a part of the Mullica River-Great Bay drainage basin as well as Lower Barnegat Bay, Little Egg Harbor, Great Bay, and the back bays (i.e., Little Bay, Reeds Bay, and Absecon Bay) as far south as Absecon. The downstream boundary extends about 9 km onto the adjacent inner continental shelf to the Long-term Ecosystem Observatory (LEO-15), a 2.8 [km.sup.2] offshore research site of Rutgers University. LEO-15 is located at a shallow (~15 m deep) sand ridge (Beach Haven Ridge) that measures about 4.5 km long and 1 km wide on the inner continental shelf off Little Egg Inlet (Figure 2).
Open water is the predominant habitat in the reserve, encompassing 27,599 ha (~60% of the area). Marsh blankets an additional 13,034 ha (>28% of the area) and forest cover, 4,616 ha (~10% of the area). Developed landscape provides the least cover (slightly over 1% of the area), accounting for 553 ha. Domestic development near the reserve is relatively sparse; it is concentrated in two small communities, Mystic Island and Tuckerton, whose boundaries extend to within 3 km of the Great Bay shoreline (Psuty et al., 1993). Thus, natural habitats dominate the reserve, being comprised of lowland and upland forests, wetlands, open estuarine and nearshore ocean waters, and barrier islands.
The Great Bay-Little Egg Harbor estuarine complex, which lies in the central portion of the Mid-Atlantic Bight, comprises shallow, polyhaline embayments bordered by extensive salt marshes and more than 280 km of shoreline. Covering an area of 41.6 [km.sup.2], Great Bay forms a roughly circular embayment with a diameter of about 7 km. Little Egg Harbor is a larger, irregularly-shaped, bar-built estuary, covering approximately 125 [km.sup.2]. Both are shallow water bodies with an average depth of <2 m at mean low water (Chizmadia et al., 1984; Durand, 1984). Because of their shallow depths, these two systems respond relatively rapidly to air temperature changes. They are characterized by a broad annual temperature range (< 0 to 30[degrees]C) and a moderate tidal range (< 0.5-1 m in Little Egg Harbor and > 1.1 m near the mouth of Great Bay) (Szedlmayer and Able, 1996). Salinity in the embayments generally ranges from ~10[right arrow]32%.
Subtidal motion in the coastal bays of the JCNERR is principally driven by coastal pumping remotely forced by coastal sea level (Chant, 2001). In the Intracoastal Waterway channel inside of Little Egg Inlet, strong tidal movement is distorted by overtides and residual motion (Chant et al., 2000). Flood currents moving northward into Little Egg Harbor diverge into northwestward- and northeastward-flowing components, producing complex circulation patterns in the central basin. During ebb tide, the currents are reversed, and they flow southward. Tidal currents typically range from ~0.5-1.0 m/s in the lower estuary, decreasing in magnitude upestuary (Chant, 1997).
Tidal currents enter Great Bay through Little Egg Inlet at a velocity of greater than 2 m/s. They flow eastward along the northern part of the bay and merge with freshwater discharging from the Mullica River that flows along the southern margin of the bay westward toward Little Egg Inlet. This current flow pattern creates a counterclockwise gyre in the central basin (Durand, 1988).
The JCNERR is characterized by temperate climatic conditions typical of the Mid-Atlantic region. The seasons are well defined; however, seasonal air temperatures vary considerably from year to year as in other temperate systems. The coldest temperatures occur during January, and the warmest temperatures, during July. The average winter temperature range is 0-2.2[degrees]C, compared to an average summer temperature range of 22-24[degrees]C. The Atlantic Ocean moderates seasonal temperatures in the lower drainage basin and bays. Farther inland away from the influence of the ocean, air temperature extremes can be great. For example, winter air temperatures less than -20[degrees]C have been recorded in the Pine Barrens region, with summer air temperatures occasionally exceeding 38[degrees]C (Forman, 1998).
Winds predominate from the northwest and southwest. The prevailing winds during the December through March period are from the northwest. Southerly onshore winds predominate in the late spring and summer. Wind velocities are generally less than 15 km/ hr. Warm tropical air masses from the south and southwest deliver hot, humid weather conditions during summer. Afternoon sea breezes reduce summer temperatures within 10-15 km of the coastline (Kennish, 2001).
Precipitation, mainly in the form of rain, averages between 100 and 122 cm/yr (Able et al., 1999). It is relatively evenly distributed year-round. Heavy precipitation accompanies northeasters in the winter; thunderstorms caused by localized convection frequently develop during the summer and early fall. The northeasters typically form in waters off the southeast coast of the United States and move north and northeast producing strong winds, heavy surf, and occasional tidal flooding. The thunderstorms are usually of high intensity and short duration. Extratropical storms and hurricanes arise during late summer and early fall, although they often pass east of the reserve. These storms can also generate destructive winds and considerable precipitation (e.g., 10 cm or more) that have the potential to cause serious flooding problems, soil erosion, and structural damage (Kennish, 2001).
The Gulf Stream plays a vital role in the development of northeasters. This northward flowing, warm-water current parallels the eastern seaboard, heating the overlying air and creating a front along the coast. Subsequently, surface low pressure systems can form as jet stream disturbances move over this newly formed temperature gradient. Heavy rains and strong winds often ensue because of the large amount of moisture from the ocean and the aforementioned temperature gradient of the coastal front. Strong winds from the east and northeast associated with these storms cause barrier beach erosion, overwashes, and backbay flooding. In severe storms, wind gusts have exceeded 90 km/hr, and sustained winds, 80km/hr. During any given calendar year, three to five coastal storms generally occur in the region, with the most severe observed in the fall (Kennish, 2001).
MATERIALS AND METHODS
As part of the System-wide Monitoring Program (SWMP), the JCNERR records water quality data semi-continuously (i.e., every 30 minutes) at three monitoring sites (Lower Bank, Chestnut Neck, and Buoy 126; Figure 3) in the Mullica River-Great Bay Estuary using Yellow Springs Instrument Company (YSI[TM]) Model 6000 UPG data loggers with sensors. These instruments run unattended in the field but must be periodically re-programmed. They relay water quality measurements (i.e., temperature, salinity, dissolved oxygen (mg/l and % saturation). pH, turbidity, and depth) to internal memory. The data are subsequently uploaded to a personal computer, where they are processed to generate basic statistics and plots. These data have useful applications in addressing short-term and long-term episodic events in estuarine waters of the reserve, including patterns of circulation and the effects of upwelling detected on the inner continental shelf at LEO-15 (Figure 3). It is important to note that, while relatively continuous data have been recorded by the data loggers at the various monitoring sites, data gaps do exist because of equipment failure, unusual environmental events, and adverse weather conditions.
Meteorological data are also collected on a near continuous basis in the JCNERR, specifically on a meteorological tower at the Rutgers University Marine Field Station on Great Bay. Data collected include wind speed and direction, air temperature, short wave radiation, barometric pressure, and relative humidity. These data provide valuable information on the atmospheric influences of water quality in the system.
Water quality and meteorological data are stored on computer systems at the Rutgers University Marine Field Station as well as at Rutgers' Institute of Marine and Coastal Sciences in New Brunswick, New Jersey. The reserve also submits these data to the Centralized Data Management Office (CDMO) located at the Belle W. Baruch Institute for Marine Biology and Coastal Research at the University of South Carolina, Charleston, South Carolina. The CDMO serves as the principal technical support for NERRS SWMP. More specifically, it manages the basic infrastructure and data protocol to support the accumulation and exchange of data, metadata, and information within the framework of NERRS sites, coastal zone management (CZM) programs, and other state and federally-funded education, monitoring and research programs. The CDMO plays a vital role in quality control of data and metadata for the NERRS program. Additional details on the CDMO can be obtained on the Internet at http://inlet-geol.sc.edu/nerrinfo.html.
Operational quality assurance and quality control (QA/QC) checks of water quality data collected in the reserve are conducted biweekly. In addition, a research technician at the site reviews the data seasonally for QA/QC purposes. Finally, the CDMO conducts a QA/QC check of the data each year. A potentially significant problem is the apparent systematic downward "drift" in dissolved oxygen measurements recorded by the data loggers 3-5 days after their deployment. The data are examined for spurious readings, notably those associated with instrument drift (e.g., due to probe fouling), and those determined to be suspect by either the reserve site or the CDMO are deleted from the database.
Temperature, salinity, dissolved oxygen, pH, turbidity, and water depth are summarized for each SWMP site in tabular and graphical form. Aside from comprehensive simple statistics generated for these parameters, such as mean, range, and standard deviation values, ANOVAs and t-tests are used to compare water quality data between sites and years for the 1999 and 2000 monitoring period. Mean seasonal values of the data at each site are also plotted to examine seasonal and inter-annual variability. Seasons are defined as winter (December-February), spring (March-May), summer (June-August), and fall (September-November). The data year 1999 encompasses the monitoring period from December 1, 1998 through November 30, 1999. The data year 2000, in turn, covers the monitoring period from December 1, 1999 through November 30, 2000. A complete array of simple statistics recorded for water quality variables by site and season at the three SWMP sites (i.e., Buoy 126, Chestnut Neck, and Lower Bank) during the 1999 and 2000 monitoring period are available over the Internet at http://marine.rutgers.edu/rumfs/Pg_1.htm.
Between 1976 and 1996, Rutgers University monitored three physical-chemical variables (temperature, salinity, and turbidity) at a single site on Great Bay (i.e., Rutgers University Marine Field Station) in the reserve (Figure 3). Commencing in 1996, the University expanded its water quality monitoring effort by using data loggers to measure six physical-chemical variables at additional sites. In August 1996, data loggers were deployed at two sites in the bay (Buoy 126 and Buoy 139). Subsequently, they were also deployed in the Mullica River at Chestnut Neck (September 1996) and Lower Bank (October 1996), as well as at Little Sheepshead Creek (April 1997), Nacote Creek (May 1997), and Tuckerton Creek (November 1998). The Nacote Creek monitoring site was discontinued in April 1998. A limited data logger deployment (March-June 2000) was conducted in Lake Pohatcong and at Mill Run. Data logger deployment was temporarily discontinued at Buoy 139 in Great Bay in July 1999. In total, data loggers were deployed at 21 sites in the reserve during the 1990s (Figure 3). Most of these sites (n = 15) were temporary deployments associated with specific research projects (Table 1).
The JCNERR currently monitors physical-chemical variables at five sites using YSI 6-series data loggers (Figure 3). Two additional monitoring sites (Buoy 139 in Great Bay and Buoy 115 in Little Egg Harbor) were activated in June 2002. The data loggers are programmed to simultaneously record six physical-chemical variables every 30 minutes. These variables include temperature, salinity, dissolved oxygen (mg/l and % saturation), pH, turbidity, and water depth. The instruments are then switched out with newly programmed data loggers at the end of the deployment period (~14 days). The SWMP monitoring network in the Mullica River-Great Bay Estuary covers a distance of 33 km, extending from the freshwater/saltwater interface at Lower Bank in the Mullica River to the polyhaline waters of Great Bay at Buoy 126. As noted previously, physical-chemical data are also measured in nearshore ocean waters at LEO-15. Physical-chemical data recorded at the five SWMP sites can be accessed over the Internet at http://marine.rutg ers.edu/rumfs/Pg_1.htm.
Each data logger is deployed by inserting it inside a 3-6 m length of Schedule 40 PVC pipe. The pipe is deployed in a vertical position, being attached to a buoy, bridge piling, or other stabilized structure. Prior to deploying the PVC pipe, slots 2.5 cm wide and 20 cm long are cut 15 cm above the bottom of the pipe such that they encircle it. A 1.2 cm bolt is placed below the slots to prevent the data logger from falling through the pipe when deployed. A PVC cap with a locking mechanism is then placed over the pipe. A rope is attached to the cap, and the opposite end is fastened to the bail of the data logger for retrieval of the instrument.
At the end of the deployment period, the data logger is removed from the PVC pipe, and then a YSI 600 data logger attached to a YSI 610-DM handheld unit is lowered into the pipe to record in-situ post-retrieval conditions at the same depth. These post-retrieval readings are compared to the last deployment values to provide "ground-truthing." Irregular and spurious data observed during this process are documented on deployment records. A newly calibrated and programmed YSI data logger is subsequently switched with the previously deployed instrument. The replaced data logger is returned to the laboratory for downloading of data, re-calibration, and re-programming prior to being exchanged at a different monitoring site.
The beginning and end of each data file are compared to the YSI 600 readings, and the data are checked for probe failure and fouling. The data loggers are programmed to start recording data a few hours before being deployed in the field. Records are maintained indicating which data loggers are used at each location and if any specific problems exist with individual data loggers or probes.
Uploading, cleaning, maintenance, and calibration are conducted as described in the YSI Operating Manual (Sections 3, 4, and 7; YSI, Inc.). A two-point calibration is used for pH, the first being pH 7 followed by pH 4. The lower pH standard is used because of the more acidic properties of the Mullica River. A standard of 20,000 us/cm is employed to calibrate for conductivity.
The membrane on the oxygen probe is changed with every deployment in the summer months when fouling is frequent. It is stretched over the face of the probe and is burned in by allowing the data logger to run in an unattended sampling mode, recording every 30 minutes for at least 6 hours. Dissolved oxygen is calibrated using a calibration cup filled with approximately 0.8 cm of tap water, which creates a 100% water-saturated air environment for the sensor when the data logger is placed in the cup. The sensors are allowed to equilibrate in the cup before dissolved oxygen (% saturation) is calibrated. Dissolved oxygen calibrations are performed immediately before deployment. Data loggers are allowed to sample inside the calibration cup at least one hour following retrieval to assure the membrane functioned properly during deployment.
The 100 NTU (National Turbidity Units) standard for calibrating turbidity is purchased from a supply house. Turbidity wipers are replaced after every deployment. Used conductivity, pH, and turbidity standards are stored for rinsing probes and post-deployment calibrations, which are performed immediately after the data loggers return from the field and before they are cleaned. These standards are then discarded after their second use. Servicing an instrument generally takes about two hours for each data logger in addition to the time required for retrieval and deployment.
The longest monitored SWMP site in the reserve is Buoy 126, located at 39[degrees]30.478'N, 74[degrees]20.308'W on the eastern side of Great Bay approximately 100 m from the nearest land mass (i.e., natural marsh island) (Figure 3). Semidiurnal tides (range = 0.68-1.55 m) characterize the site, and tidal currents range from 1-2 m/s. Bottom sediments consist of fine- to coarse-grained sands.
The Chestnut Neck SWMP site is located in the Mullica River at 39[degrees]32.872'N, 74[degrees]27.676'W (Figure 3). The width of the river at this location is about 250 m. Tides are semidiurnal here with tidal currents being less than 0.5 m/s during both ebb and flood tide. The data logger is attached to the dock of a small marina along the south shore of the river adjacent to the main channel. The bottom sediments here consist of sand.
The second SWMP data logger site in the Mullica River is farther upstream at Lower Bank (39[degrees]35.618'N, 74[degrees]33.091'W; Figure 3). At this location, the Mullica River is approximately 200 m wide, and a data logger is attached to the center of a bridge spanning the river. Semidiurnal tides characterize the Lower Bank site, ranging from 0.46 m to 1.55 m. Tidal currents at this site are relatively rapid (> 0.5 m/s). As a result, bottom sediments consist of cohesive fine sand.
In addition to these three SWMP sites, physical-chemical data (temperature and salinity as well as dissolved oxygen in summer) are measured in nearshore ocean waters at LEO-15, about 9 km east of Little Egg Inlet (Figure 3). At LEO-15, continual observations of coastal ocean processes are made at two instrumented platforms (known as Node A, 74[degrees]15.73'W, 39[degrees]27.70'N and Node B, 74[degrees]14.75'W, 39[degrees]27.41'N) anchored to the seafloor and spaced 1.5 km apart. Optical fibers transfer site data in 1-second intervals to computers at the Rutgers University Marine Field Station. These data are fed to the Internet and are made immediately available at the Institute of Marine and Coastal Sciences at Rutgers University in New Brunswick, New Jersey.
Water quality has been monitored in Tuckerton Creek since November 1998, and a data logger is now providing real time data to the Institute of Marine and Coastal Sciences, as well as to the visitors of the historic Tuckerton Seaport. Tuckerton Creek is a tidally influenced water body with freshwater inflow from nearby Lake Pohatcong. Similar to the Mullica River, Tuckerton Creek receives significant amounts of tannic acids leached from soils of the Pine Barrens. Lake Pohatcong and Mill Run were sampled with YSI data loggers in the spring of 2000 to obtain additional data for a potential fish stocking program and the installation of a fish ladder on Lake Pohatcong. Both are freshwater sites with low pH. Water quality has been monitored continuously in Little Sheepshead Creek since April 1997 in support of long-term ichthyoplankton sampling, which has been conducted at this site for the past decade by Rutgers University Marine Field Station personnel.
The final component of the SWMP program at the reserve site is the meteorological platform at the Rutgers University Marine Field Station, which collects wind speed and direction, air temperature, short wave radiation, barometric pressure, and relative humidity at 1-second intervals. The meteorological station is unique in that it has two data collection platforms (at 10 m and 19 m elevation), and all data are available in near real time on the Institute of Marine and Coastal Sciences website (http://marine.rutgers.edu).
Individual instruments on a Woods Hole Oceanographic Institution (WHOI) IMET Meteorological Sensor System measure the aforementioned environmental variables and relay the data by RS485 to the Rutgers University Marine Field Station in 1-minute average intervals, where they are stored on computer. A network connection between the field station and the main campus of Rutgers University in New Brunswick enables all data collected by sensors on the meteorological tower to be archived at the Institute of Marine and Coastal Sciences at Cook College. This archiving system is known as RODAN (Rutgers Ocean Data Access Network).
The current sensors on the meteorological tower all meet World Ocean Circulation Experiment (WOCE) standards. The WHOI IMET system consists of autonomous intelligent sensor modules interconnected using the E1A-485 standard. Each module contains a microcontroller programmed to handle the unique needs of the individual sensor. A module typically samples its sensor once per second, producing 1-minute averages. When prompted, a module provides data calibrated in scientific units. The modules in the installation include: (1) wind speed and direction; (2) barometric pressure; (3) relative humidity; (4) air temperature; and (5) short wave radiation.
The WHOI IMET weather station was initially installed to support the broad array of research conducted at LEO-15 and the Rutgers University Marine Field Station with atmospheric weather data. Meteorological conditions above the sea surface have a direct link to subsurface conditions, and therefore are critical to interpreting physical-chemical data in the ocean waters. The live streaming data on the Internet also provide the public with local weather conditions; the archived data, also available on-line, serve as a long-term reference for evaluating changes and trends within the estuary. Because of the close proximity of the meteorological tower to the Buoy 126 (SWMP) site, meteorological data collected at the Rutgers University Marine Field Station site are also valuable for the SWMP program.
Water quality varies considerably from the Lower Bank to LEO-15 monitoring sites. Although waters of both the Mullica River and Great Bay are relatively pristine, some fundamental differences in water chemistry are apparent. For example, the river contains high concentrations of tannins and humic compounds which discolor the water dark brown. These substances originate in the Pine Barrens. They tend to sorb to particulate matter and settle to the bay bottom. Thus, water clarity in the bay is greater than in the river.
Data collected at the monitoring sites are also useful for investigating problems related to estuarine circulation. For instance, because Buoy 126 lies in close proximity to Little Egg Inlet, investigators have been able to examine the effects of ocean water transported into Great Bay by tidal currents. The effects may be apparent on both the water quality and biological characteristics of the lower bay. The upwelling of water from the coastal ocean into the bay may significantly influence the transport of larval fish and other organisms upestuary. This colder ocean water which enters the bay can also have dramatic effects on the growth rates of organisms inhabiting the estuary. The data collection network provides the means to effectively track the effects of certain events within the estuary such as occurrences of upwelling, storms, and storm surges. In addition, it yields information of value in interpreting the biological effects of these events. Meteorological conditions, including wind speed and directi on, air temperature, short wave radiation, barometric pressure, and relative humidity recorded at the Rutgers University Marine Field Station are likewise important in assessing the aforementioned meteorological and oceanographic events (Able et al., 1992, 1999).
Data Years 1996-1998
Wenner et al. (2001) analyzed water quality data collected at 44 NERRS sampling sites nationwide, including those of the JCNERR. This analysis covered the data years between 1996 and 1998. The following discussion of water quality data for the JCNERR largely derives from the work of Wenner et al. (2001) based on water sampling conducted by JCNERR personnel.
Focusing on two sampling sites in the JCNERR system (i.e., Lower Bank and Buoy 126), Wenner et al. (2001) presented a suite of graphical data analysis techniques and statistical testing procedures to assess water quality conditions. At the Lower Bank site, data recorded during 41 data logger deployments between August 1996 and November 1998 and analyzed statistically included temperature, salinity, and dissolved oxygen. The data loggers were deployed at a mean depth of 1.7 m below sea level and 0.3 m above the river bottom. Mean seasonal water temperatures at the site typically varied from 2-5[degrees]C in winter and 24-26[degrees]C in summer, with the minimum and maximum temperatures being -0.2[degrees]C (January 1997) and 30.1[degrees]C (July 1997), respectively. Tidal cycles were responsible for 60% of the temperature variance based on harmonic regression analysis.
Salinity at the Lower Bank site averaged 0-2[percent thousand] in winter and spring and 2-8[percent thousand] in summer and fall 1997-1998. The salinity ranged from a minimum of 0[percent thousand] to a maximum of 15.6[percent thousand]. Nearly every month of data contained 0[percent thousand] salinity readings at this site.
During the 1996-1998 period, hypoxia (DO [less than or equal to] 2 mg/l) was observed at all estuarine reserves in the Mid-Atlantic region except the JCNERR. Dissolved oxygen at Lower Bank typically ranged from 85-105% saturation year-round. Mean dissolved oxygen values were lowest in summer (80-100% saturation) and highest in winter (105-125%). In addition to the absence of hypoxia at the study site, super-saturation was documented periodically during the sampling period. The percent saturation fluctuated 20-40% over daily and biweekly cycles during the year. Wenner et al. (2001) ascribed 38%, 34%, and 28% of the dissolved oxygen variance to diel cycles, tidal cycles, and tidal-diel cycle interaction, respectively.
Water temperature at Buoy 126 followed a similar seasonal cycle as at Lower Bank. Between 1996 and 1998, water temperature at Buoy 126 ranged from -1.4[degrees]C (January 1997) to 28[degrees]C (August 1998). Mean winter temperatures were typically 4-6[degrees]C, and mean summer temperatures, 22-24[degrees]C. Daily (1-2[degrees]C) and biweekly (3-10[degrees]C) temperature fluctuations were observed year-round. Tidal cycles accounted for 60% of the temperature variance as demonstrated by harmonic regression analysis.
Salinity at Buoy 126 ranged from 13[percent thousand] (May 1998) to 35.4[percent thousand] (April 1997). The mean salinity for the data set was 25-31[percent thousand], although strong daily and biweekly variations were documented. Tidal cycles were responsible for 82% of the salinity variance as shown by harmonic regression analysis.
Mean dissolved oxygen at Buoy 126 regularly exceeded 100% saturation, with the range generally between 85-120% saturation. As at Lower Bank, hypoxia was never evident at Buoy 126. While moderate fluctuations (20-40%) in % saturation were discerned for daily and bi-weekly cycles, supersaturation was documented during eight months in the summer and fall seasons of 1996-1998. Wenner et al. (2001) ascribed 41% of dissolved oxygen variance at this site to interaction between tidal and diel cycles, 34% of dissolved oxygen variance to tidal cycles, and 25% of dissolved oxygen variance to diel cycles. Based on observations at Buoy 126 and Lower Bank, the Mullica River-Great Bay estuary appears to be a well-oxygenated system.
Able et al. (1992) summarized a long-term database on temperature, salinity, tides, and other hydrographic conditions at the Rutgers University Marine Field Station. This database was generated over the 15-year period from 1976 through 1990. It showed that water temperature at the station ranged from 0.1-25.2[degrees]C and salinity from 23.6-34.5[percent thousand]. Highest salinities were registered during the summer and fall seasons. Mean turbidity at the field station ranged from 4.9-17.9 NTU, although no seasonal trends were apparent.
Data Years 1999-2000
JCNERR has compiled summary statistics for environmental variables monitored at the three SWMP sites (i.e., Buoy 126, Chestnut Neck, and Lower Bank) for data years 1999 and 2000 (covering the period from December 1998 to November 2000). The variables of concern include temperature ([degrees]C), salinity ([percent thousand]), dissolved oxygen (mg/l and % saturation), pH, turbidity (NTU), and water depth (m). Tables 2 and 3 show statistical results of ANOVA applications on these data. Environmental variables across sites are compared for 1999 (Table 2) and 2000 (Table 3). Table 4 lists results of t-tests comparing environmental variables between years (1999 and 2000).
Water temperature followed a well-defined seasonal cycle at all three SWMP sites (Figure 4). Minimum (winter) and maximum (summer) temperatures during the 1999-2000 study period were -1.7[degrees]C and 27.9[degrees]C at Buoy 126, -1.3[degrees]C and 29.39[degrees]C at Chestnut Neck, and -0.7[degrees]C and 31.5[degrees]C at Lower Bank. The mean temperature was highest at Lower Bank for both 1999 (15.06[degrees]C) and 2000 (15.26[degrees]C). Analysis of variance (ANOVA) models were run using the SAS statistical software package. The ANOVA determinations indicated no significant difference (P > 0.05) in mean temperatures among monitoring sites during 1999. However, a significant difference (P < 0.05) in mean temperatures among monitoring sites occurred in 2000. The application of standard statistical tests revealed a significantly higher (P < 0.05) mean temperature at Chestnut Neck and Lower Bank than at Buoy 126 in 2000.
The mean temperature at Chestnut Neck and Lower Bank was not significantly different (P > 0.05) between years (1999 and 2000). However, it was significantly different (P < 0.05) between years at Buoy 126 (Table 4). This difference may reflect the effect of coastal upwelling and other aperiodic factors at this site.
A pronounced salinity gradient exists along the mainstream linear dimension of the Mullica River and extending into Great Bay, and this gradient is reflected in salinity measurements obtained at the SWMP sites (Figure 5). Salinity levels are lowest at Lower Bank (generally < 5[percent thousand]), which marks the freshwater/saltwater interface ~25 km upstream of the Mullica River mouth. Intermediate salinity levels (~15[percent thousand]) are found at Chestnut Neck located ~13 km upstream of the Mullica River mouth. Highest salinity levels (>25[percent thousand]) are recorded at Buoy 126.
Lowest salinities at the SWMP sites during the two-year study period were recorded in spring 1999, with mean seasonal values amounting to 0.98[percent thousand] at Lower Bank, 12.73[percent thousand] at Chestnut Neck, and 28.27[percent thousand] at Buoy 126. Highest salinities, in turn, were observed during summer 1999 when drought conditions persisted throughout New Jersey. Mean salinities at this time were 6.49[percent thousand] at Lower Bank, 18.77[percent thousand] at Chestnut Neck, and 30.63[percent thousand] at Buoy 126 (Figure 5). Mean salinities at the three monitoring sites were significantly different (P < 0.05) for both 1999 and 2000. Using standard statistical tests, the mean salinity at Buoy 126 was shown to be significantly greater (P < 0.05) than that at Chestnut Neck and Lower Bank, and the mean salinity at Chestnut Neck was shown to be significantly greater (P < 0.05) than that at Lower Bank. Substantial differences in the salinity levels exert a major controlling influence on the species com position, abundance, and distribution of aquatic organisms at these three SWMP sites.
The mean salinity at Buoy 126 was not significantly different (P > 0.05) between years (1999 and 2000). However, it was significantly different (P < 0.05) between years (1999 and 2000) at Chestnut Neck and Lower Bank. Variable runoff and freshwater input in the Mullica River Basin between years may be responsible for the observed differences at the Mullica River sites.
Consistently high dissolved oxygen levels were documented at the SWMP sites in 1999 and 2000, and hypoxia was not observed. Seasonal variation of dissolved oxygen was conspicuous, with highest values observed during the winter and lowest values during the summer (Figure 6). The highest dissolved oxygen concentrations for both years were registered at Buoy 126, with mean values being 9.54 mg/I and 9.51 mg/l for 1999 and 2000, respectively. The lowest dissolved oxygen levels were measured at Lower Bank in 1999 (mean = 8.98 mg/l) and at Chestnut Neck in 2000 (mean = 8.64 mg/l). Mean dissolved oxygen concentrations (mg/l) were significantly different (P < 0.05) among the three SWMP sites for both 1999 and 2000 (Tables 2 and 3). Standard statistical tests applied to these data revealed that the mean dissolved oxygen concentration at Chestnut Neck was significantly less (P < 0.05) than that at Lower Bank and Buoy 126 in 1999. The mean dissolved oxygen levels at the latter two sites were also significantly different (P < 0.05). During 2000, the mean dissolved oxygen concentration was significantly higher (P < 0.05) at Buoy 126 than at Lower Bank and Chestnut Neck. The mean dissolved oxygen level at Lower Bank was significantly higher (P < 0.05) than at Chestnut Neck.
There was no significant difference (P > 0.05) in the mean dissolved oxygen (mg/L) concentration between the years 1999 and 2000 at Buoy 126 and Chestnut Neck. However, a significant difference (P < 0.05) in mean dissolved oxygen concentration between years was evident at Lower Bank (Table 4). The mean dissolved oxygen concentration exceeded 8 mg/l at all three monitoring sites in 1999 and 2000.
Seasonal averages of dissolved oxygen (% saturation) for the three SWMP sites typically ranged from ~80-120% (Figure 7). Highest dissolved oxygen % saturation values were recorded at Buoy 126. Here, mean dissolved oxygen exceeded 100% saturation for both years of sampling. Supersaturation was periodically observed at all the SWMP sites during the summer and fall seasons.
Salinity and dissolved oxygen concentrations influence pH levels. High concentrations of tannins and humic acids in the Mullica River also affect pH. As a result, pH values at Lower Bank and Chestnut Neck are substantially lower than those at Buoy 126 (Figure 8). The pH progressively increases from upriver areas to the open waters of Great Bay.
In 1999, the mean values of pH recorded at the three SWMP sites were as follows: Lower Bank, 6.14; Chestnut Neck, 7.20; and Buoy 126,8.10. In 2000, the mean values of pH recorded at the three SWMP sites were as follows: Lower Bank, 6.24; Chestnut Neck, 7.37; and Buoy 126,7.95. The mean pH values were significantly different (P < 0.05) among the three SWMP sites for both years of the study. Using standard statistical tests, the mean pH levels at Buoy 126 were found to be significantly greater (P < 0.05) than those at Lower Bank and Chestnut Neck for 1999 and 2000. At Chestnut Neck, the mean pH levels were also significantly greater (P < 0.05) than those at Lower Bank for both years.
The mean pH measurements at Lower Bank were not significantly different (P > 0.05) between years (1999 and 2000). However, the mean pH measurements were significantly different (P < 0.05) between years at both Buoy 126 and Chestnut Neck (Table 4).
Mean seasonal turbidity levels at the SWMP sites were less than 35 NTU during the 1999 and 2000 study period. The highest annual mean turbidity values of 25.04 NTU and 24.23 NTU were registered at Lower Bank in 1999 and 2000, respectively. The mean seasonal turbidity measurements at the three sites typically ranged from 6-32 NTU (Figure 9). The mean turbidity levels were significantly different (P < 0.05) among the three SWMP sites for both 1999 and 2000. Standard statistical tests applied to these data indicate that the mean turbidity values at Lower Bank were significantly greater (P < 0.05) than those at Buoy 126 and Chestnut Neck for both 1999 and 2000. Similarly, the mean turbidity values at Buoy 126 were significantly greater (P < 0.05) than those at Chestnut Neck for both years. In addition, the mean turbidity levels were significantly different (P < 0.05) between years (1999 and 2000) at each of the SWMP sites.
Figure 10 shows water depths recorded at the three SWMP sites during 1999 and 2000. Water depths were greatest at Buoy 126, with mean values of 2.83 m and 3.05 m in 1999 and 2000, respectively. Water depths were more than 1 m shallower at Chestnut Neck and Lower Bank. At Buoy 126, mean depths were significantly greater (P < 0.05) than those at Chestnut Neck and Lower Bank for both years. At Lower Bank, the mean water depth was significantly greater (P < 0.05) than that at Chestnut Neck in 1999, but there was no significant difference (P > 0.05) in the mean water depths at both sites in 2000.
The mean depth at Chestnut Neck and Lower Bank was not significantly different (P > 0.05) between years (1999 and 2000). However, it was significantly different (P < 0.05) between years at Buoy 126.
Tables 2 and 3 summarize results of ANOVAs for environmental variables monitored at the three JCNERR SWMP sites. ANOVAs were run by year, 1999 (Table 2) and 2000 (Table 3), using data derived from semi-continuous recordings of 6-series data loggers. JCNERR currently utilizes nine data loggers in its monitoring program. Data gaps in the database are mainly due to malfunctioning instruments (e.g., probe failure) and adverse weather conditions (e.g., icing problems). The most statistically significant differences are those related to salinity and pH.
Because of the shallow depths in Great Bay, water temperatures closely follow air temperatures. Lowest water temperatures (< 0[degrees]C) typically occur in late January and February, and highest temperatures > 25[degrees]C), in July and August. Seasonal temperatures are similar in the bay and river as is evident from data logger recordings at Buoy 126, Chestnut Neck, and Lower Bank. Freezing of the river and bay has been occasionally reported in late December, January, and February. During cold winters, the entire bay has been frozen.
From February to mid-June, water temperature generally increases linearly from near 0[degreesc]C to -20[degrees]C. Similarly, water temperature typically decreases linearly from ~25[degrees]C in August to -1[degrees]C in January. According to Durand and Nadeau (1972), little thermal stratification exists in most areas of the system.
Wenner (2001), employing scatter plots, documented strong fluctuations (1-2[degrees]C) in daily water temperature at Buoy 126 and Lower Bank. Even stronger temperature fluctuations (3-10[degrees]C) were delineated over bi-weekly intervals at these sites. Harmonic regression analysis ascribed 60% of the temperature variance at both sites to 12.42 hour cycles and attributed an additional 23% of the temperature variance to 24 hour cycles.
The SWMP sites at Lower Bank, Chestnut Neck, and Buoy 126 lie along a well-defined salinity gradient of the Mullica River-Great Bay system. Lower Bank, which marks the upper end of the estuary ~25 km upstream from the head of Great Bay, is characterized by oligohaline conditions. Limnetic waters occur immediately upstream of Lower Bank. Mesohaline salinities predominate at Chestnut Neck. Polyhaline conditions are found at Buoy 126. Salinity differences among these three sites are statistically significant (P < 0.05).
Salinity from Lower Bank to Deep Point at the mouth of the Mullica River varies in response to tidal action, frequency and intensity of precipitation, evaporation, and freshwater inflow. At Buoy 126, the principal factors affecting salinity levels are proximity to Little Egg Inlet, tidal currents, and winds. SWMP sites in the JCNERR system experience semidiurnal tides, and hence salinities vary appreciably in response to tidal cycles during a 24 hour period. Other factors (e.g., spring-neap tidal cycles and freshwater pulses) account for much of the salinity variation at the time scale of days to weeks. Episodic events, which can cause marked changes in salinity within a short time span, include major storms, floods, and periodic upwelling events. Seasonal variations in salinity are primarily ascribed to seasonal changes in precipitation and freshwater discharge as well as seasonal shifts in wind direction and velocity. During the period from December 1998 to November 1999, salinity at Buoy 126, Chestnut Neck , and Lower Bank ranged from 22.20-32.35[percent thousand], 2.89-26.80[percent thousand], and 0.0-18.5[percent thousand], respectively. During the period from December 1999 to November 2000, salinity at Buoy 126, Chestnut Neck, and Lower Bank ranged from 22.50-.33.30[percent thousand], 4.10-26.90[percent thousand], and 0.0-ll.20[percent thousand], respectively.
Salinity fluxes associated with episodic events can be substantial, approaching the annual variation in mean salinity at a site. Durand (1988) recorded salinities as low as 1[percent thousand] at the Deep Point area near the mouth of the Mullica River after protracted periods of heavy rainfall activity. However, salinities as high as 25-27[percent thousand] were also observed at this site during dry periods in the summer months. Wenner et al. (2001) showed that salinity fluctuations exceeded 10[percent thousand] at the SWMP sites during episodic events in August and December 1996, March and May 1997, and from March to December 1998. Using harmonic regression analysis, they ascribed 82% of salinity variance at the sites to 12.42 hour cycles, 10% of salinity variance to 24 hour cycles, and 8% of salinity variance to interaction between 12.42 hour and 24 hour cycles.
Freshwater enters the Mullica River via surface runoff and groundwater influx in the Mullica River Basin, as well as from direct precipitation on the water surface. A positive correlation exists between periods of high river flow and reduced salinity levels at Lower Bank and Chestnut Neck sites. High river discharges also reduce salinities in upper Great Bay and along the southern perimeter. Salinity at Buoy 126 usually exceeds 25[percent thousand] because ocean water enters at Little Egg Inlet and flows along the northern part of the bay, directly affecting conditions at the monitoring site. While the predominant flow during flood tide is in the northern part of the bay, accounting for higher salinities in this area, the predominant flow during ebb tide is in the southern part of the bay. This flow pattern creates a counterclockwise gyre in the central portion of the bay (Durand, 1988). Strong tidal currents and the shallowness of the bay produce well-mixed conditions, resulting in relatively uniform salinit ies in the water column.
Salinity differences between the three SWMP sites are not only statistically significant but also biologically significant. Planktonic, benthic, and nektonic communities differ considerably along the salinity gradient of the Mullica River, as well as in areas of Great Bay where salinity differences can be substantial (Durand and Nadeau, 1972; Durand, 1988). Salinity is a major factor affecting the species composition, abundance, and distribution of organisms from upestuary to downestuary areas.
The health of estuarine systems is closely coupled to dissolved oxygen concentrations. Oxygen depletion caused by excessive biochemical oxygen demand can lead to hypoxia or anoxia and reduced habitat availability, greater susceptibility of organisms to disease and predation, and increased mortality (Pihl et al., 1992; Winn and Knott, 1992; Borsuk et al., 2001). The impacts of oxygen deficiency are often most conspicuous on benthic communities and habitats (Dauer et al., 1992; Diaz and Rosenberg, 1995). Aside from major shifts in the distribution and abundance of organisms due to severe oxygen depletion, more subtle effects may be manifested by altered behavioral, physiological, and reproductive activity of the biota (Summers et al., 1997; Wenner et al., 2001). In addition to the biochemical oxygen demand, several other factors influence the severity of oxygen depletion in the bottom waters of estuaries, notably exchange of oxygen with the surface layer, vertical density stratification, and the intensity and f requency of mixing (Borsuk et al., 2001).
Oxygen deficiency is becoming a more serious problem in many estuaries as a result of greater loading of organic matter from nearby watersheds, as well as accelerated nutrient-driven phytoplankton and benthic algal production in embayments (Paerl et al., 1998). Consequently, coastal resource programs in many states are emphasizing more intense monitoring of dissolved oxygen in estuarine and coastal marine waters. At NERRS sites nationwide, dissolved oxygen is the target of year-round monitoring efforts.
Oxygen deficiency was never observed at the JCNERR during the monitoring period from August 1996 to December 2000. This is attributed primarily to the relatively strong currents, well-mixed condition, and general lack of thermal stratification of river and bay waters in the system. The mean dissolved oxygen values typically ranged from 85-105% saturation during the study period. A distinct seasonal cycle was apparent, with the highest mean % saturation (100-125%) occurring in winter and the lowest mean % saturation (75-100%) taking place in summer. Supersaturation was observed periodically during all seasons of the year.
Absolute values of dissolved oxygen (mg/l) were relatively high in the JCNERR, with mean annual dissolved oxygen levels exceeding 8.5 mg/l at the three SWMP sites. Highest dissolved oxygen values (mean > 11.0 mg/l) were registered during the winter, and lowest dissolved oxygen values (mean = 6.0-7.0 mg/l), during the summer.
Various factors affect the dissolved oxygen content of riverine and estuarine waters. Included here are temperature, organic carbon loading, salinity, turbulence, and atmospheric pressure. In the JCNERR, higher temperatures and greater loading of organic matter during summer depress dissolved oxygen levels due to accelerated microbial respiration associated with organic degradation processes. Lower temperatures and diminished loading of organic matter result in significantly higher dissolved oxygen levels in winter because chemical and biological oxygen consumption coupled to the decomposition of organic matter declines appreciably.
Although hypoxia has not been observed in the JCNERR, episodes of supersaturation may be a cause of concern. The formation of reactive oxygen species during supersaturation events may have a toxic effect on biota of the system (Dalton, 1995). However, supersaturation events in JCNERR are characteristically ephemeral, and therefore their biotic effects are likely to be small.
Analysis of data from the JCNERR SWMP indicates that this reserve has not experienced the dissolved oxygen problems of many other estuarine systems in the U.S. Dissolved oxygen concentrations in the JCNERR, which are consistently above 6.0 mg/l, reflect the generally high water quality conditions of the JCNERR system. However, monitoring must continue in order to further assess factors controlling seasonal variations of dissolved oxygen, which are considerable.
When proceeding along a salinity gradient from upriver areas to the open waters of Great Bay, pH progressively increases. The pH not only varies with salinity but also with dissolved oxygen concentrations. In addition, large amounts of tannins and humic acids in the Mullica River depress pH levels. Hence, the mean pH levels at Lower Bank and Chestnut Neck for the 1999-2000 period were significantly less (p < 0.05) than the mean pH values at Buoy 126 for the same time period. No significant seasonal trends in pH values were evident at the SWMP sites.
Zampella and Laidig (1997), Dow and Zampella (2000), and Zampella et al. (2001) showed that there is an association between increases in pH and nutrient enrichment and watershed disturbance in the Pinelands due to agricultural land use, residential development, and wastewater flow. More specifically, higher pH levels in the Pinelands streams are positively correlated with greater concentrations of [NO.sup.-.sub.3], [NH.sup.+.sub.4], total P. [Ca.sup.2+], and [Mg.sup.2+], and all of these variables parallel a Pinelands watershed disturbance gradient. Dow and Zampella (2000) proposed that pH is a potential indicator of Pinelands watershed disturbance and subsequent ecological effects that follow disturbance. Such effects may be manifested as major changes in the species composition, abundance, and distribution of organisms in the Mullica River.
Durand and Nadeau (1972) reported considerably greater water transparency in Great Bay than in the Mullica River. They also observed the highest degree of transparency in the bay during the summer and early fall. Areas upriver exhibited maximum transparency in the winter and minimum transparency in the summer. Reduced input of tannins, humic compounds, and particulate matter from the Pinelands in the winter causes greater transparency in the Mullica River during the colder months of the year. According to Durand and Nadeau (1972), however, more turbid conditions exist in the bay during the winter months apparently because of increased sediment loading.
Results of seasonal turbidity measurements by the JCNERR SWMP initiative corroborate, in part, the findings of Durand and Nadeau (1972). For example, the highest annual mean turbidity among SWMP sites in 1999 (25.04 NTU) and 2000 (24.23 NTU) occurred at Lower Bank. Chestnut Neck had the lowest annual mean turbidity in 1999 (9.69 NTU) and 2000 (7.85 NTU). The highest seasonal mean turbidity levels at Buoy 126 took place during the winter of 1999 (20.09 NTU) and 2000 (20.64 NTU). The lowest seasonal mean turbidity (6.69 NTU) at Buoy 126 was reported in the summer of 2000. At Lower Bank, in turn, the lowest seasonal mean turbidity measurements were registered during the winter in 1999 (18.85 NTU) and fall of 2000 (16.13 NTU). The highest seasonal mean turbidity values at Lower Bank in both 1999 (31.30 NTU) and 2000 (32.39 NTU) were found in the spring. At Chestnut Neck, the seasonal mean turbidity was also highest for both the spring of 1999 (13.25 NTU) and 2000 (11.77 NTU). The lowest seasonal mean turbidity at this site was recorded in the fall of 1999 (5.54 NTU) and the summer of 2000 (4.28 NTU).
As is evident from the JCNERR water quality database, turbidity values vary seasonally and from year to year. Highest turbidity occurs in the Mullica River at Lower Bank based on the 1999 and 2000 database. Although the turbidity is seasonally variable, some trends are evident. Higher turbidity levels generally occur in the bay during winter. However, episodic events such as hurricanes, other major storms, and upwelling events can produce unusually high turbidity levels of relatively short duration which can leave significant spikes in the database during any season.
Spatial variation in turbidity levels can also be substantial in the bay. Turbid waters discharging from the mouth of the Mullica River, for example, concentrate along the southern part of the bay. Clearer ocean water, in turn, can often be traced along the northeast perimeter. This spatial distribution of turbidity is a consequence of the cyclonic circulation pattern in the bay.
Tidal action accounted for much of the variation in depth at the SWMP sites. For example, Wenner et al. (2001) attributed 86% of the depth variance at Buoy 126 between August 1996 and November 1998 to 12.42 hour cycles. Only 7% of the depth variance at this location during the same period was ascribed to both 24 hour cycles and interaction between 12.42 hour and 24 hour cycles. Similar numbers were obtained at Lower Bank. Here, 85% of depth variance between August 1996 and November 1998 was ascribed to 12.42 hour cycles. Only 6% of depth variance at this location was attributed to 24 hour cycles, and 9% of depth variance was ascribed to interaction between 12.42 hour and 24 hour cycles. According to Wenner et al. (2001), therefore, depth is an important factor for evaluating and interpreting temporal variability in parameters associated with tides.
The JCNERR is currently monitoring an array of physical-chemical variables year-round at three SWMP sites in the Mullica River-Great Bay estuarine system using YSI 6-series data loggers. Included among these variables are temperature, salinity, dissolved oxygen (mg/l and % saturation), pH, turbidity, and depth. The three monitoring sites are located at Lower Bank on the Mullica River (~25 km upriver), Chestnut Neck on the Mullica River (~13 km upriver), and Buoy 126 on Great Bay (~3 km west of Little Egg Inlet). Water quality in the Mullica River-Great Bay estuary has historically been excellent because the estuary and neighboring watershed rank among the most pristine and least anthropogenically-impacted systems in New Jersey. Hence, the estuary serves as an excellent reference location to assess human impacts on other shallow coastal bays.
Water temperature variations in the JCNERR are similar to those of other temperate estuaries. At the three SWMP sites, for example, water temperatures range from less than 1.0[degrees]C to more than 30.0[degrees]C over an annual cycle. Temperature minima (< 0[degrees]C) occur in late January and February, and temperature maxima (> 25[degrees]C) take place in July and August. Seasonal temperatures are similar among the SWMP sites.
The Mullica River-Great Bay estuary exhibits a strong salinity gradient. Proceeding from the freshwater/saltwater interface at Lower Bank to the polyhaline waters of Great Bay at Buoy 126, a distance of about 33 km, mean salinity increases from < 5[percent thousand] to nearly 30[percent thousand]. Differences in salinity levels at Lower Bank, Chestnut Neck, and Buoy 126 sites are statistically significant (P < 0.05) for both data years 1999 and 2000. Salinity differences along this gradient have a profound effect on the species composition, abundance, and distribution of organisms in biotic communities.
The Mullica River-Great Bay estuary is a well-oxygenated system. Neither anoxia nor hypoxia has been observed in the estuary. Dissolved oxygen levels regularly exceed 100% saturation, particularly during the colder months of the year. For example, the mean dissolved oxygen levels generally ranged from 85-105% saturation during the monitoring period, with the highest mean % saturation values (100-125%) recorded in winter, and the lowest mean % saturation (75-100%) registered in summer. The absolute values of dissolved oxygen (mg/l), in turn, remained high, with the mean annual dissolved oxygen levels exceeding 8.5 mg/l at the three SWMP sites. The lowest mean seasonal dissolved oxygen concentrations (6.0-7.0 mg/l) occurred in summer. Substantially higher mean dissolved oxygen concentrations (> 11.0 mg/l) were documented in winter.
As in the case of salinity, pH increases significantly from upriver areas to the open waters of Great Bay. The pH at a specific site varies with salinity, dissolved oxygen, and other factors. The large concentrations of tannins and humic acids in the Mullica River depress pH levels at the Lower Bank and Chestnut Neck sites. In contrast, Buoy 126, which is strongly affected by the inflow of nearshore ocean waters, has much higher pH values. Thus, mean pH measurements during the 2000 monitoring period at Lower Bank, Chestnut Neck, and Buoy 126 were 6.24, 7.37, and 7.95, respectively.
Mean annual turbidity levels at the three SWMP sites ranged from 9.69-25.04 NTU in 1999 and 7.85-24.27 in 2000. The Lower Bank site exhibited the highest mean turbidity measurements in 1999 (25.04 NTU) and in 2000 (24.23 NTU). Seasonal turbidity levels varied among sites, with the highest levels at Lower Bank and Chestnut Neck being recorded in the spring, and the highest levels at Buoy 126 being reported in the winter of both 1999 and 2000. Episodic events, such as major storms, often generate the highest turbidity levels, but their effects are of relatively short duration.
The water depth at Buoy 126 was significantly greater (P < 0.05) than that at Chestnut Neck and Lower Bank. The mean water depth at Buoy 126 in 1999 and 2000 amounted to 2.83 m and 3.05 m, respectively. At Chestnut Neck and Lower Bank, the mean water depths were more than 1 m shallower than at Buoy 126 for both years. Most of the depth variance (85-86%) observed at the SWMP sites was attributed to tidal action (i.e., 12.42 hour cycles).
In summary, the Mullica River-Great Bay estuary is a remarkably pristine system characterized by minimal anthropogenic impacts. This is reflected by the excellent water quality in the system. However, with gradually increasing development of watershed areas, it will be necessary to continue monitoring and assessing physicalchemical conditions in this critically important estuary.
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Table 1 Description of permanent and temporary data logger deployments and their research and monitoring objectives. LOCATION SYMBOL DURATION OF STUDY Lower Bank Star 10/96-present Chestnut Neck Star 9/96-present (B126) Intracoastal Waterway Star 8/96-present LEO-15 O 6/97-present Ship Bottom A 2/97-5/97 Ham Island B Summer 94 & 95 Marshelder Island C Summer 94 & 96 Tuckerton Seaport D 11/98-present Rutgers Dorm Pocket Marsh E 1/96-7/96 Little Sheepshead Creek Bridge F 2/96-5/96, 4/97-present New Cove - Holgate G Summer 1997 Rutgers Field Station Creek H 11/95-5/01 Station Creek Upper End H 7/00-11/00 & 2/01-5/01 Marsh Pool Surface and Bottom H 9/96-11/96 Rutgers Field Station - Boat Dock H 1/96-5/97 Little Beach J Summer 94 & 95 Buoy 139 J 8/96-7/99 Little Bay K Summer 94 & 95 Nacote Creek L 5/97-4/98 Hog Island M 5/97-10/97 Lower Mullica River N 6/99-1/00 LOCATION STATUS Lower Bank Ongoing Chestnut Neck Ongoing (B126) Intracoastal Waterway Ongoing LEO-15 Ongoing Ship Bottom Terminated Ham Island Terminated Marshelder Island Terminated Tuckerton Seaport Ongoing Rutgers Dorm Pocket Marsh Terminated Little Sheepshead Creek Bridge Ongoing New Cove - Holgate Terminated Rutgers Field Station Creek Terminated Station Creek Upper End Terminated Marsh Pool Surface and Bottom Terminated Rutgers Field Station - Boat Dock Terminated Little Beach Terminated Buoy 139 Terminated Little Bay Terminated Nacote Creek Terminated Hog Island Seasonal Lower Mullica River Terminated LOCATION OBJECTIVE Lower Bank Permanent NERR Monitoring Site Chestnut Neck Permanent NERR Monitoring Site (B126) Intracoastal Waterway Permanent NERR Monitoring Site LEO-15 Permanent Monitoring Site Ship Bottom Larval Winter Flounder Transport Ham Island Fish Habitat Quality Marshelder Island Fish Habitat Quality Tuckerton Seaport Restoration of Anadromous Fish Rutgers Dorm Pocket Marsh Marsh Characterization Little Sheepshead Creek Bridge Ingress of Larval Fish New Cove - Holgate Winter Flounder Settlement Rutgers Field Station Creek Monitoring RUMFS Seawater Intake Station Creek Upper End Fish Habitat Quality Marsh Pool Surface and Bottom Marsh Pool Fish Microhabitat Rutgers Field Station - Boat Dock Long-Term Variation In Juvenile Fish Abundance Little Beach Fish Habitat Quality Buoy 139 Temporary NERR Monitoring Site Little Bay Fish Habitat Quality Nacote Creek Temporary NERR Monitoring Site Hog Island Impact of Phragmites on Marsh Fishes Lower Mullica River Temporary NERR Monitoring Site Table 2 Results of ANOVAs comparing physical-chemical data across three JCNERR SWMP sites (Buoy 126, Chestnut Neck, and Lower Bank) in 1999. FACTOR SOURCE DF MS F P > F Temperature Site 2 66.65 1.08 0.3404 Error 762 61.77 Salinity Site 2 44200.37 6620.21 <.0001 Error 720 6.68 Dissolved Site 2 13.33 3.45 0.0327 Oxygen (mg/l) Error 333 3.86 pH Site 2 177.46 957.16 <.0001 Error 441 0.19 Turbidity Site 2 16271.96 114.22 <.0001 Error 531 142.46 Depth Site 2 104.74 1726.05 <.0001 Error 720 0.06 Table 3 Results of ANOVAs comparing physical-chemical data across three JCNERR SWMP sites (Buoy 126, Chestnut Neck, and Lower Bank) in 2000. FACTOR SOURCE DF MS F P > F Temperature Site 2 269.39 4.77 0.0087 Error 915 56.53 Salinity Site 2 57893.02 16571.69 <.0001 Error 915 3.49 Dissolved Site 2 59.23 13.47 <.0001 Oxygen (mg/l) Error 624 4.40 pH Site 2 215.18 1776.35 <.0001 Error 873 0.12 Turbidity Site 2 21042.27 211.54 <.0001 Error 825 99.47 Depth Site 2 177.90 4141.36 <.0001 Error 915 0.04 Table 4 Statistical tests comparing physical-chemical measurements between years (1999 and 2000) at each JCNERR SWMP site. T-TESTS FOR BUOY 126 VARIABLE DF T VALUE P > T Temperature 290 -2.03 0.0432 Salinity 262 0.29 0.7755 Dissolved Oxygen (mg/l) 199 1.89 0.0608 pH 191 -5.73 <0.0001 Turbidity 213 3.07 0.0024 Depth 276 -15.77 <0.0001 T-TESTS FOR CHESTNUT NECK VARIABLE DF T VALUE P > T Temperature 255 -0.12 0.9043 Salinity 255 -2.52 0.0122 Dissolved Oxygen (mg/l) 189 1.09 0.2773 pH 242 12.26 <0.0001 Turbidity 235 3.12 0.0020 Depth 255 -1.54 <0.1246 T-TESTS FOR LOWER BANK VARIABLE DF T VALUE P > T Temperature 334 -0.85 0.3947 Salinity 334 -6.60 <0.0001 Dissolved Oxygen (mg/l) 222 2.56 0.0111 pH 295 -1.83 0.0686 Turbidity 270 1.99 0.0471 Depth 334 0.42 0.6745
We would like to acknowledge Roger Hoden of the Rutgers University Marine Field Station and Steve Evert of the Richard Stockton College of New Jersey, who assisted with various aspects of water quality sampling during the study period. Ken Able, Director of the Rutgers University Marine Field Station, is also acknowledged for his involvement in the JCNERRS System-wide Monitoring Program. In addition, we thank Judith McLellan of the Institute of Marine and Coastal Sciences for providing technical support on statistical analysis of the water quality data. This is JCNERR Contribution No. 10011 of the Institute of Marine and Coastal Sciences of Rutgers University.
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MICHAEL J. KENNISH (1) AND SHARON O'DONNELL (2)
(1.) INSTITUTE OF MARINE AND COASTAL SCIENCES RUTGERS UNIVERSITY NEW BRUNSWICK, NEW JERSEY 08901
(2.) RUTGERS UNIVERSITY MARINE FIELD STATION TUCKERTON, NEW JERSEY 08087
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|Author:||Kennish, Michael J.; O'Donnell, Sharon|
|Publication:||Bulletin of the New Jersey Academy of Science|
|Date:||Sep 22, 2002|
|Previous Article:||New Jersey junior academy of science annual meeting.|
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