The problem is one of fertility, of course, and stems from the huge quantities of nitrogen and phosphorus perennially present in the water. Some of this comes down from the upper river—where, as we noted, much of it derives from land runoff—but by far the greatest part of it originates at the metropolis and enters the river through the effluent of waste treatment plants. Efficiency of operation has hardly anything to do with it, for even the best standard treatment has little effect on nutrients.
Eutrophication is the scientific name of this kind of overenrichment. It is occurring in many places, Lake Erie being the best-known single example in this country. Though its causes are mainly known, the process itself is still not fully understood, particularly in regard to the function of nitrogen and the way it works. But the other key element, phosphorus, has been more amenable to study and to possible action. It occurs in body wastes, in artificial fertilizers, as a by-product of natural decay, and very notably in detergents. Some eight tons of it are released into the estuary each day from the treatment plants in addition to the undetermined but much smaller amounts arriving from upriver, and the usual overall accumulation is enough to make the river's phosphorus content exceed that considered desirable all the way from Theodore Roosevelt Island to Quantico, Virginia, and below, which represents the general extent of the summertime "blooms."
Dilapidation begets disrespect, and the abused and often repellent waters of the upper estuary are undoubtedly subjected to much additional miscellaneous pollution by people who believe perhaps that a little more cannot possibly matter. Again, Federal or Federally connected institutions have not been setting the best possible example, and there are many of them around the capital city. Unwarranted waste discharges of one kind or another have been traced to most of the military installations fronting the river, to military hospitals, to government heating plants, to the National Zoo, to National Parks, and to similar Federal sources including the marinas already mentioned. In most cases, measures are now being taken to eliminate these discharges, but it is a commentary on the complexity and difficulty of the whole task of dealing with pollution that at the level of government where real concern with the problem has been acute for a decade or more, and furthermore at and around the very seat of that government, such practices should have persisted this long.
Junk and debris of all descriptions infest the metropolitan river, floating about, washing onto the shores, poking up stolidly here and there out of mudflats. Most items in a dreary inventory that might be compiled would turn out to be something that was discarded somewhere it didn't belong by someone who did not want to go to the trouble to put it where it did belong. Therefore, the main source is undoubtedly simple disregard for the sensibilities and rights of others, multiplied and complicated by the immense number of people in the metropolis and the wide territory they occupy. In our study of Rock Creek last year, some powerful subsidiary reasons for the prevalence of debris turned up also, ranging to streetcleaning methods and the inconvenient hours kept by some public dumps where citizens have to carry their larger trash. Metropolitan problems are seldom simple, and many of them in one way or another manage to inflict a part of their complexity on the river at the national capital, which is sad but possibly appropriate in a time like the present.
The lower estuary
Downriver from the main effects of the metropolitan complexities, the widening brackish and salt portions of the Potomac estuary form a generally healthy body of water, though changes loom as the metropolis moves inexorably outward from its center and as hitherto remote Tidewater areas are brought more and more under the influence of modern ways of being. Localized problems of pollution point to general dangers that will certainly materialize unless safeguards are set up in time, for estuaries are delicate, immensely productive, and still somewhat mysterious aquatic environments that have been and still are too much taken for granted.
Rapid human intrusion on estuaries during the past twenty years has been making apparent their phenomenal value in a natural condition. Vulnerable, attractive to diverse interests that work their beds for sand and gravel and fill in their marshes for development and casually pollute them, they have recently been called America's most endangered natural habitat. They are almost unbelievably fertile places, with involved biological cycles that can convert the fertility into usable food at rates per acre far exceeding those of the finest farm land; in terms of money, one recent set of experiments indicates the possibility of attaining an annual shellfish production on tended beds worth over $26,000 an acre.