FIGURE A.4a Annual average concentration of chlorophyll compared to inorganic nitrogen inputs in a variety of natural estuaries and in experimental mesocosms at the Marine Ecosystem Research Laboratory, University of Rhode Island. The mesocosms were fertilized with nutrients. Data are from Nixon and Pilson (1983). Chlorophyll is a measure of phytoplankton abundance. Bars to the right indicate ranges of chlorophyll believed to characterize lakes as being oligotrophic, mesotrophic, or eutrophic. Dashed horizontal lines represent the mean chlorophyll values for each classification (Wetzel 1983). See text for a discussion of the applicability of this classification to estuaries.

tion of this lake-based approach to the trophic status of estuaries may not provide sufficient protection. This is the case, in part, because such trophic guidelines are based on phytoplankton response to nutrients yet problems such as those experienced in Kaneohe Bay are the result of benthic algae overgrowing the coral.

Jaworski (1981) proposed ''permissible" nutrient inputs to protect shallow (4-meters to 9-meters deep) temperate-zone estuaries from eutrophica-



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