Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Indicator

Coastal Ocean: For each year, the average chlorophyll-a (referred to here as chlorophyll) concentration (parts per billion, or ppb) for the season with the highest average is reported; this is referred to as the “seasonal mean maximum.” Data are reported for each region in a band of coastal water extending 25 miles from the shoreline. This boundary was chosen so the index would be more sensitive to changes in nutrients input from terrestrial sources than influences from the deep sea. Estuaries: It is proposed to report the percentage of U.S. estuary area that has seasonal mean maximum chlorophyll values below 5 ppb, from 5 to 20 ppb, and above 20 ppb.

The Data

Coastal Ocean: Data from the National Aeronautical and Space Administration’s (NASA) Sea viewing Wide Field-of-view Sensor (SeaWiFS; see http://seawifs.gsfc.nasa.gov) were analyzed for the nine ocean regions by the National Ocean Service, National Oceanographic and Atmospheric Administration (NOAA). “Water leaving radiance” (reflectance, or light reflected from the sea surface) is used to estimate chlorophyll concentrations at the surface using a series of assumptions accepted by the scientific community. The data utilized for this analysis are termed “level 3.” In all cases, seasonal maxima were determined for strips of water 25 miles wide along the coast. These strips were analyzed using square pixels 6 miles on a side. Note that earlier data from the Coastal Zone Color Scanner are available; however, they are not directly comparable to the SeaWiFS data.

The Data Gap

Coastal Ocean: Algorithms used to translate water leaving radiance into chlorophyll concentration currently provide only rough estimates of concentration in those waters where concentrations of suspended sediments and colored dissolved organic matter are high; for example, near-shore waters influenced by surface and groundwater discharges, coastal erosion, and sediment resuspension. A major research effort is currently under way to improve coastal algorithms. Spatial resolution is also a problem. The data presented here are based on a fairly coarse scale (6-mile resolution), but data with 10 times more resolution will soon be available. In order to provide more reliable estimates, satellite data need to be analyzed together with field (in situ measurements) data that typically are not available electronically and, therefore, not easily accessible. In addition, techniques for integrating the two types of data are needed. Currently, data showing relative changes in chlorophyll within a region can be trusted; however, data showing actual concentrations for any given region may be off by a factor of two. Thus, unless differences are large, meaningful comparisons between regions are not yet possible.

Estuaries: As discussed in the text, no regularly reported data are available for this portion of the indicator. Data from NOAA’s National Estuarine Eutrophication Assessment (see http://spo.nos.noaa.gov/projects/cads/nees/Eutro_Report.pdf) suggest that 40 percent of the area of major estuaries has “high” chlorophyll levels (>20 ppb), with another 46 percent having “moderate levels” (5–20 ppb). At the extremes, the north and south Atlantic regions had mostly low-to-moderate levels, while three-quarters of the estuary area in the mid-Atlantic had high chlorophyll levels. These results are not based on quantitative data analysis but on the knowledge of scientists familiar with the estuaries in each region. Monitoring data do exist for some estuaries, but need to be assembled into a uniform, national database, and new programs would be required for the remaining estuaries. A combination of aircraft and satellite remote-sensing and in situ measurements will be required to determine the estuarine component of this indicator.