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 for human purposes. Many estuaries are able to assimilate large quantities of nutrients despite the great fluctuations which occur with variations in the flow from tributaries. The nutrients can be stored, incorporated in standing crops of plants, released, cycled and exported - and the system frequently achieves high production of plants and and animals without creation of any undesirable results of enrichment. Excessive enrichment with the same elements and compounds can, however, be highly detrimental to estuaries and their uses. Coastal cities are usually located on the estuaries which provided a harbor for the- and which now receive partially treated sewage and other wastes from the expanding population and industrial activity. Conversion of woodlands to agricultural use and the extensive application of fertilizers have resulted in the flow of large quantities of nutrients down the hill or slopes and eventually into the estuary.

Estuaries exist along the edge of the oceans and seas, and are char acterized by the dilution of sea water by inflowing fresher waters. The motion and interaction of these two types of water (fresh and salt water) determine the salinity distribution within the estuary and that, in turn, affects the organisms residing there. The purpose of this vol ume is to review the status of our understanding of estuarine circu lation and how the circulation patterns affect living and nonliving resources in estuaries. For many years, the primary paradigm for estuarine circulation was the two-layered net or nontidal gravitational circulation pattern first proposed by Dr. Donald Pritchard in his studies of the James River estuary. During the last decade or so, research has focused on the many variations about this theme and the factors that control the transport processes. Many of these aspects are covered in the initial papers in this volume. Water movement, of course, is of interest be cause it transports marine organisms, sediments, and pollutants. Es tuarine circulation has a significant effect on estuarine food chains, and on the distribution and abundance of organisms, such as the American oyster, that are freely transported by the currents during larval stages. The intent is to bring together many of these topics in a single volume. This volume is dedicated to Dr. Donald W."

Estuaries exist along the edge of the oceans and seas, and are char acterized by the dilution of sea water by inflowing fresher waters. The motion and interaction of these two types of water (fresh and salt water) determine the salinity distribution within the estuary and that, in turn, affects the organisms residing there. The purpose of this vol ume is to review the status of our understanding of estuarine circu lation and how the circulation patterns affect living and nonliving resources in estuaries. For many years, the primary paradigm for estuarine circulation was the two-layered net or nontidal gravitational circulation pattern first proposed by Dr. Donald Pritchard in his studies of the James River estuary. During the last decade or so, research has focused on the many variations about this theme and the factors that control the transport processes. Many of these aspects are covered in the initial papers in this volume. Water movement, of course, is of interest be cause it transports marine organisms, sediments, and pollutants. Es tuarine circulation has a significant effect on estuarine food chains, and on the distribution and abundance of organisms, such as the American oyster, that are freely transported by the currents during larval stages. The intent is to bring together many of these topics in a single volume. This volume is dedicated to Dr. Donald W."

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 for human purposes. Many estuaries are able to assimilate large quantities of nutrients despite the great fluctuations which occur with variations in the flow from tributaries. The nutrients can be stored, incorporated in standing crops of plants, released, cycled and exported - and the system frequently achieves high production of plants and and animals without creation of any undesirable results of enrichment. Excessive enrichment with the same elements and compounds can, however, be highly detrimental to estuaries and their uses. Coastal cities are usually located on the estuaries which provided a harbor for the- and which now receive partially treated sewage and other wastes from the expanding population and industrial activity. Conversion of woodlands to agricultural use and the extensive application of fertilizers have resulted in the flow of large quantities of nutrients down the hill or slopes and eventually into the estuary.