Furthermore, aside from the direct harvest of this wealth from estuaries each year by commercial and sport fishermen, these in-between waters make an indispensable contribution to the entire Atlantic coastal fishery, an industry worth a billion dollars a year. The reason for this is that at least 70 percent of coastal fishes spend some essential part of their life cycle within an estuary—spawning there, or passing through on their way to spawn in running fresh streams, or moving in as fry from the rivers or the open sea to find a "nursery" in one of the varied estuarine habitats—bays, marshes, sandy shorelines, mudflats, tidal creeks, or weed beds.
The oysters from the famous beds in the Saint Mary's River off of the lower Potomac are mainly condemned as unfit for consumption because of local sewage pollution, and these beds are not the only unfit ones, for towns and resorts in the region have been growing and sanitary facilities have not been keeping pace. Already some arms of the superb natural harbors formed by the tributary creeks are noxious with discharges from boats at big marinas, and gravel dredging is stirring up silt to smother bottom life, including shellfish. As Tidewater agriculture revives and modernizes, pesticides and artificial fertilizers are coming to be as much a part of the scene there as in other farming regions, and may be expected to influence the estuary—in fact, they undoubtedly already are doing so in subtle ways with effects not yet apparent.
Yet most of this part of the river is still beautiful and continues to yield good harvests of seafood. The Potomac River Fisheries Commission has been alert to obvious dangers and has moved against them where its powers have permitted, and natives of the area are increasingly alert in protecting the estuary. Many of them depend on it for a living, most are oriented toward it for their pleasures, and until lately a good many of them counted on it for transportation. In a number of different ways, it matters in their lives. And that fact offers some hope for the future, especially if it is fostered and strengthened by overall protective measures.
Techniques for cleaning up
Two main general approaches to water quality improvement exist: treatment of pollution at its source or occasionally after it has entered a stream, and augmentation of the stream's flow to help it assimilate loads of waste beyond its natural capacity. A third possibility in certain situations is the diversion of wastes out of a stream's drainage entirely. In practice, these methods can be varied and combined in any number of ways to fit a need.
To take the last one first, diversion of whole wastes as received from their sources is a total and dramatic means of coping with a pollution problem stemming from collectable wastes, but it often has disadvantages. One of these, of course, is the possibility that the pollution problem may be simply transplanted elsewhere—that the water in which the wastes eventually end up will suffer. Another is loss of water from the stream system. If, as is usual, a town gets its water out of the local river or a tributary and does not give it back after use—preferably well cleaned up—other users downstream are not going to have as much water available to them, and the essential processes and ecology of the river itself may suffer.
The only place such wholesale diversion of wastes has been seriously considered in the Potomac Basin is at metropolitan Washington, whose sewage could feasibly be piped across Chesapeake Bay and the Delmarva peninsula and well out into the Atlantic—possibly, as has been suggested, in combination with sewage from Baltimore. It would be a permanent means of disposal, but very expensive in terms of both investment and operating costs. Furthermore, though in the estuary no downstream users would suffer a loss of water supply, the water content in metropolitan sewage has at times risen as high as 80 percent of the flow of the river above the upstream intakes. The effects of such a subtraction of fresh water on the estuary itself—changes in flow, and in the penetration of salt water upriver, with an inevitable alteration in valuable fisheries and the whole balance of aquatic life established through millennia—could easily turn out to be disastrous.
Standard treatment of pollution at its source consists of the primary and secondary processes we have glanced at, sometimes adjusted to specific industrial wastes. It has to be brought up to peak efficiency along the Potomac, for this is a "known factor" of great significance. Plants can and must be improved physically where necessary, and qualified operators provided for them. Collection systems have to be improved or enlarged in many places. Diminutive plants, doomed to inefficiency by their size and the financial impossibility of hiring expert workers for them, need to be eliminated in favor of regional waste collection and treatment facilities, which are quite feasible, particularly in the watershed units of the upper Basin.
Even so, it has emerged clearly to view in this Potomac study that standard treatment alone is no longer an answer in areas of concentrated or continuous population and industry, where the leftover wastes and the nutrients in the effluent from even well-run standard plants can often add up to a killing load for water.