Estuaries are eternally enriched. Their positions at the foot of watersheds and their convenience as receiving bodies for the wastes of cites, towns and farms results in continuous addition of nutrients - those elements and compounds which are essential for organic production. Such materials must be added to these complex bodies of water to sustain production, since there is a net loss of water and its contents to the oceans. Enrichment from land and the ocean and the subsequent cycling of the original chemicals or their derivatives contribute to the extraordinarily high values of estuaries...