They are provided as a rough guide to magnitudes of values . When calculating budgets, values based on careful local measurements are always preferable to tabulated data from compendia. Coastal Ecosystem Metabolism These are laid out in an order that reflects likely knowledge about the system, first for carbon metabolism and then for nitrogen metabolism. It can be somewhat lower or higher, but numbers outside of this range should be looked at with caution. There can be exceptions to this, if the system receives extreme loads of either inorganic sewage nutrients or labile organic matter.
Many marine systems have no observable nitrogen fixation.
Some coral reef, mangrove, and tropical seagrass communities may exhibit rates 20 or more times this upper limit. As a general rule, though, few systems will have nitrogen fixation faster than this rate. The main requirement seems to be relatively rapid respiration, with benthic respiration being more efficient than planktonic respiration at promoting rapid denitrification.