April 5, 2004 — Scientist Jane Caffrey, Ph.D., of the University of West Florida, is publishing a study in the next edition of Estuaries on the metabolic rates of estuaries within the NOAA National Estuarine Research Reserve System. Metabolic rates are useful indicators of the health of estuaries (coastal areas where rivers meet the sea). Caffrey’s research is the largest and most geographically diverse analysis of (baseline) metabolic rates using identical measurements to date.

“We can make an analogy between ecosystem metabolism as an indicator of an estuary’s health and using the human pulse rate to measure our own body’s health,” states Caffrey. “Ecosystem metabolism provides an index for the estuary’s health in three ways: 1) the magnitude of production or consumption in the ecosystem, which we can think of as the estuary’s pulse rate; 2) the seasonal changes in production and consumption, which is like the periodic rhythm of the pulse and 3) the difference between production and consumption, which is similar to a human’s overall metabolic balance. This third component is called net ecosystem metabolism.”

Most metabolic research focuses on larger, deeper systems. This study examines specific estuarine sites, and it does this on a national basis. Caffrey studied 42 sites within 22 of NOAA’s 26 National Estuarine Research Reserves using data collected through the NOAA System-wide Monitoring Program. SWMP provides reliable, continuous data at frequent intervals. Each estuarine reserve collects SWMP data using identical protocols, and each reserve represents a different type of estuarine system in the United States.

“SWMP measures many water quality variables. The key variable that I use for determining metabolic rate is dissolved oxygen,” states Caffrey. “If we go back to the human body analogy, measuring dissolved oxygen is like examining how the estuary is breathing.”

Caffrey looked at nutrient and chlorophyll a data collected by estuarine reserves through SWMP and compared it with data from other studies. She also used dissolved oxygen, temperature and salinity collected through SWMP. She categorized each study area by the dominant habitat adjacent to the SWMP collection point.

Estuaries are very complex systems. Metabolic rates may vary among estuaries and even change within the same estuarine system. Some estuaries even switch between producing and consuming based on temperature changes or fluctuation in the water’s depth. As a result, Caffrey looked at trends over a seasonal and an annual basis, and she discovered some very interesting patterns.

The most significant result of this study is that the type of habitat adjacent to the monitoring site explains the general trends in net ecosystem metabolism. Marsh and mangrove creeks are typically heterotrophic — meaning they consume organic material. While submerged aquatic vegetation, such as eelgrass, are usually autotrophic — meaning they produce organic material. Caffrey found that freshwater sites tend to consume more organic material than saltier areas. Larger systems tend to be more balanced; smaller systems tend to be more consuming.

Temperature was the most important environmental factor explaining the variation in metabolic rates at different sites. The highest rates of consumption and production occurred in the Southeastern estuaries during the summer months.

Nutrients were the second most important environmental factor explaining variations in metabolic rates. Sites with high nitrogen loading were less heterotrophic (consuming) and closer to balance than sites with low nutrient loading. This agrees with other studies that have shown that when nitrogen is added to estuaries, primary production increases faster than its consumption (respiration).

“Water quality monitoring programs like SWMP are extremely useful for estimating an estuary’s level of production and consumption — its net metabolic rate,” according to Caffrey. “The reason that I am able to do this research is because SWMP provides quality controlled data using the identical parameters at many sites across the United States. This is interesting because SWMP was not initially designed for this purpose. These sorts of analyses have the potential to provide unique insights into how the nation’s estuaries function, a value not anticipated by the reserve system.”

This research provides a baseline for specific U.S. estuaries that coastal managers can potentially use to evaluate changes in water quality and the reason for those changes. In this way, Caffrey’s work is analogous to a doctor collecting baseline data to use in monitoring the long-term health of their patients. "Caffrey's research has certainly taken water quality monitoring to a new level," said Richard Spinrad, NOAA National Ocean Service assistant administrator. "This research also supports the Agency's Strategic Plan mission goals to bring improved ecosystem-based management to the nation's coastal and ocean resources and further emphasizes the value of the National Estuarine Research Reserve System."

Relevant Web Sites
NOAA National Estuarine Research Reserve System

NOAA's 26 National Estuarine Research Reserves

NOAA System-wide Monitoring Program

NEW RESEARCH OF NOAA DATA USES METABOLIC RATES TO HELP DETERMINE THE HEALTH OF ESTUARIES

Media Contact:
Glenda Powell , NOAA Ocean Service, (301) 713-3066 ext. 191 or Ben Sherman, NOAA Ocean Service, (301) 713-3066 ext. 178