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System-wide Monitoring Program

Synthesis of the Water Quality Data
ABSTRACT

Estuaries are among the most productive aquatic systems. Although human civilizations have historically depended on and benefited from estuarine resources, impacts from anthropogenic disturbances on estuarine habitats have only been recently recognized. Increased awareness of the ramifications of these disturbances led to creation of the Coastal Zone Management Act (CZMA) of 1972, which resulted in establishment of the National Estuarine Research Reserve (NERR) program. The NERR system provided an ideal network for the establishment of a national water quality monitoring program; thus, the System-wide Monitoring Program (SWMP) was initiated in 1995. The System-wide Monitoring Program of the NERR program tracks short-term variability and long-term changes in water quality variables estuarine Reserve sites nationwide. Unlike most of the existing national/regional water quality monitoring programs that collect short-term or periodic data (days to weeks), the SWMP collects long-term water quality and ecological data. Water quality variables (depth, temperature, salinity, dissolved oxygen (mg/L and % saturation), pH, and turbidity) are recorded nearly semi-continuously (every 30 minutes) throughout the entire year via unattended, automated data sondes (YSI 6000â or YSI 6600â). The long-term nature of the SWMP data set makes it possible to examine both intra-annual (seasonal) and inter-annual patterns in estuarine systems, as well as on the effects of large scale (e.g., El Niño and La Niña climatic conditions, hurricanes, Nor’easters) and localized (i.e., floods, drought) episodic events.

Proposed in 1993 and initiated in 1995, the SWMP is currently in operation at 22 Reserves in the NERR system. The Reserves represent nearly 440,000 acres of protected estuarine waters, wetlands, and uplands from the five major coastal/estuarine regions in the United States (West Coast, Northeast and Great Lakes, Mid-Atlantic Coast, Southeast Coast, and the Gulf of Mexico and Caribbean Sea). Furthermore, the NERR SWMP represents almost every recognized climatic zone (Savannah, Steppe, Mediterranean, Humid sub-tropical, Cold temperate and Polar) as well as more than 15 biogeographic zones within these major climatic zones. Within the contiguous United States, the SWMP is represented by almost every degree of geographic latitude between 26°N and 43°N, approximately 1,000 miles north to south.
  • Substantial efforts were made to collect, quality assure, and archive the data collected by the SWMP; however, until recently, relatively little effort had been made to analyze these data. Water quality data for 44 sites from the SWMP between 1996 and 1998 are analyzed in this report. Several important findings from this study are listed below.
  • Generally, depth, salinity, and dissolved oxygen (mg/L or percent saturation) were dominated by 12.42 hour cycles at sites that experienced moderate daily tidal amplitudes (2-4 m). Twenty-four hour cycles (i.e., day-night cycle, wind, man-made perturbations) dominated sites where salinity was characterized as very low (tidal freshwater environment) or very high (marine environment), and where tidal effects were minimal.
  • Twenty-four hour cycles accounted for 30-50% of water temperature variance sites at most sites and 12.42 hour cycles accounted for <20% of water temperature variance at most sites. In the summer, water temperature fluctuated by as much as 10°C over 24 hours at some sites.
  • Hypoxia (DO < 28% saturation) was strongly influenced by latitude and climate. Half of the sites where hypoxia was observed (on average) for more than 20% of the first 48 hours post-deployment were located in the Gulf of Mexico and Caribbean; however, 92% of hypoxia events persisted less than 8 hours. Hypoxia was most frequently observed during summer.
  • Temporal and spatial distribution of supersaturation (DO > 120% saturation) events was not as clear as the temporal and spatial distribution of hypoxic events. Supersaturation events primarily occurred in cooler months, particularly winter; however supersaturation events were observed in all seasons. Although supersaturation events sometimes co-occurred with hypoxic events during the same day, supersaturation was negatively correlated with hypoxia.
  • At 92% of the sampling sites evaluated (25 of 27), aquatic respiration exceeded aquatic production. Water temperature was significantly correlated with aquatic metabolic rates at most sites; however, salinity was only significantly correlated with aquatic metabolic rates at half of the sites evaluated. Metabolic rates were not noticeably different among geographic regions; however, metabolic rates were strongly influenced by habitat type.

The synthesis results provide valuable information about how estuaries function. In addition, the findings of this synthesis revealed the short-term dynamic properties of water quality variables in shallow estuarine systems on a daily basis. Tidal cycles at most of the sites evaluated ranged from 2-4 m, resulting in nearly dry water bodies at low tide and submerged shorelines at high tide. Subsequently, daily fluctuations in temperature, salinity, and dissolved oxygen varied by as much as 10°C, 15 ppt, and > 100% saturation, respectively. The similarity in magnitude of fluctuations in water quality variables among different sites suggested that the sites in the NERR SWMP were representative of shallow water environments, but might not be representative of all water bodies within each Reserve. This synthesis also provided insight into the immediate impact on water quality and duration of the recovery period to return to pre-storm conditions in the wake of Hurricanes Bertha and Fran, two major hurricanes that catastrophically affected the mid-Atlantic coast in 1996. Had data sondes not been deployed before, during, and after these storms, this information would not have been available.

The NERR SWMP represents tremendous progress towards developing a water quality-monitoring program to monitor the health and functionality of this Nation’s estuaries. Establishment of estuarine reserves and the NERR SWMP present opportunities to educate the public about water quality issues, with specific emphasis on the causes and consequences of degraded water quality. Water quality data from the NERR SWMP also provide necessary background data from which specific, experimental hypotheses can be formulated to systematically evaluate the effects of anthropogenic influences on estuarine ecosystems and the requirements to restore the functionality of these estuaries to their undisturbed conditions. Only with exhaustive, objective research can the ramifications of disturbances to natural processes occurring within estuaries be fully understood.

During the course of preparing this Synthesis Report, a list of recommendations was developed for both Reserves and future synthesis efforts. These recommendations are discussed in greater detail in the Discussion section (pp. 262-270), but are briefly presented here.

  • Reserve staff should consult with physical oceanographers familiar with sampling sites to document and understand circulation patterns at the SWMP sites, as this information may directly determine how and why sampling sites are selected.
  • Reserves should submit a justification of how and why sampling sites were selected and what habitat each sampling site represents.
  • Reserves should compile appropriate ancillary data about sampling sites that are needed to interpret water quality data. Examples of such ancillary data include actual precipitation and flow rate data (rather than annual estimates or averages), nutrient data, and calculation of waterbody area and drainage basin area where data sondes are located.
  • Reserves should agree upon and standardize data sonde deployment practices and provide the necessary training to implement these standardized practices.
  • Reserves should carefully examine dissolved oxygen data for “instrument drift” to determine which records should be retained and which records should be eliminated.
  • Reserves should manage their data using a readily available relational database (i.e., MS Access) and provide regular summaries of data similar to those presented in this report.
  • Future analytical efforts should include an expert panel during all aspects of the project.
  • Future analytical efforts should explore use of Principal Component Analysis using actual measurements for ancillary data, or appropriate multivariate analyses that incorporate both quantitative data and ordinal scale data (i.e., CART).