What Wetlands Do, and How They Do It

Those who question the wisdom of wetland regulations sometimes tell a story about a landowner who proposes to build a fine home on a tract of land that is largely wetland. This landowner lives in a region where wetlands are abundant but is denied permission to build on grounds that construction would involve filling a wetland. Because he owns considerable property, the owner moves to higher ground, clears five acres of mature upland timber, and builds his home quite legally in this way. The irony is that the mature upland timber is much scarcer locally than wetland, and the stupidity of the regulation is to have forced someone to destroy the scarcer of two resources. The names, places, and other particulars of this story vary with the teller, but there is little doubt that wetland regulation has sometimes caused an environmental loss greater than the value of the wetland that is preserved. Perhaps the landowner in the story could have been given an exemption had he only been allowed to argue the great value of mature upland forest in his particular region. As a practical matter, however, special pleading can defeat the intent of almost any regulation. Thus, the rigidity in the regulation may be justified by its need to be faithful to the general intent of the underlying law and not by a need to be rational in every case. At any rate, the story may be specious as a generalization in that the Army Corps in most cases would have granted a permit to an individual for a small wetland conversion, or the conversion would have been covered under a general permit for small conversions (chapter 1). Those who question the wisdom of wetland regulations sometimes tell a story about a landowner who proposes to build a fine home on a tract of land that is largely wetland. This landowner lives in a region where wetlands are abundant but is denied permission to build on grounds that construction would involve filling a wetland. Because he owns considerable property, the owner moves to higher ground, clears five acres of mature upland timber, and builds his home quite legally in this way.

Where We Are, and How We Got Here

English is a subtle language with many words that offer fine shades of meaning, but it also can be blunt and unequivocal. Dictionaries were not made for words such as hairdo, ballpark, or pigpen. The law, however, as practiced by Americans, can mutate the meaning of even the humblest word. If the law concerns itself with pigpens, then we must know whether a pigpen still exists when the pigs are removed and, if so, for how long. We must know if a pen originally built for cattle can become a pigpen if occupied by pigs and if pigpens are the same in all parts of the nation. In short, we must have federal guidance, regional interpretations, legal specialists, and technical authorities on pigpens. So it is with wetlands. The chapters of this book will show how troublesome the definition of wetlands has become since the federal government began regulating them. In the meantime, it will suffice to define wetlands informally as those portions of a landscape that are not permanently inundated under deep water, but are still too wet most years to be used for the cultivation of upland crops such as corn or soybeans. Wetlands, in other words, coincide pretty well with the common conception of swamps, marshes, and bogs. Government has had its hand in wetlands for about 150 years. Between the 1850s and 1970s, the federal government was intent on eliminating wetlands. Since then, it has been equally intent on preserving them. An individual who behaved in this manner would seem at least irresponsible. Many critics of federal wetland policy have in fact given the government a sound thrashing for its inconsistency, but the shift from elimination to protection of wetlands has continued nevertheless. Blaming government is the duty of a free people, and also good sport. Even so, the obvious truth about wetland regulation is that government has merely reflected a change in public attitude toward wetlands. Most Americans now believe that wetlands should be saved throughout the nation, except possibly on their own property. Americans did not always feel this way. Most European colonists of North America came from homelands that were essentially tame.

Mother Earth

The virtue of soil is one of only a few axioms of American culture. Respect for soil, which can be instilled at an early age without rousing political or religious controversy, is the mark of agrarian origins. Nevertheless, or perhaps for this very reason, the average American knows more about asteroids than about soil. Even scientists, who are responsible for knowing pretty much everything, seem generally less aware of soil than of water, air, or even rock. Thus, this chapter requires a primer on the nature of soil. The USDA, which is the center of gravity for soil science in the United States, has defined soil as “earthy materials . . . on the earth’s surface . . . capable of supporting plants out-of-doors.” To the thoughtful novice, this may seem a woefully unsatisfactory definition. In fact, one might feel downright indignant upon consulting a dictionary only to find that “earthy” means “having properties of soil.” Thus, the USDA seems to be saying that soil is something that is like soil. This could be a simple case of cheating or perhaps a devilishly clever means of suppressing debate about the definition of soil. Further reflection, however, suggests that the reference to plants is more significant than it first appears to be. Plants do not grow on bare rock, shifting sand, or the bottoms of oceans, all of which are non-soil substrates. Thus, the USDA definition may say it all, but is masterfully understated in doing so. Soil science textbooks are also a source of definitions, some of which are gratifyingly descriptive. Birkeland’s (1984) textbook, which gives a geological perspective on soil, specifies that soil is a natural entity; is composed of mineral or organic constituents, or both; differs from the material from which it was originally derived; and reflects the operation of pedogenic processes. Pedogenic processes, in turn, include the addition of organic matter from plants and other substances from the atmosphere; removal of substances by water through erosion or leaching; and a variety of internal transformations and transfers involving organic matter and minerals.

Eye of Newt

Whoever would identify a wetland objectively must cook up some combination of evidence from hydrology, soil, and vegetation. Many recipes have been proposed, but all have proven unappealing to many and downright nauseating to some. Some favor one ingredient over the other two, while others insist on all three. These differences go beyond mere matters of taste; they relate directly to probability of error and feasibility of practice. Use of observations or measurements to make conclusions always involves some probability of error. Statistics is the discipline to which we turn in our attempt to attach probabilities of error to a particular judgment. That judgments about wetlands lie within the reach of statistics seems to be forgotten most of the time. Statistics, while regarded by many as an ugly discipline, has been reborn in several more comely forms. One of these is risk analysis, which involves the assignment of probability to outcomes that society views as undesirable. Given that risk analysis has been recently as much a rage as statistics itself was a generation ago, wetland identification should be steeped in it, but this is not the case. In arguing over the identification of wetlands, critics of a particular type of evidence are likely to say that it is unreliable. No such generalization is reasonable; the reliability of a particular type of evidence depends on the situation. For example, a plant community strongly dominated by obligate wetland plant species (or equivalently, showing a prevalence index below 2) will support the identification of a wetland with very little risk of error if there has been no recent change in hydrology. The risk thus could be framed as a statement of conditional probability: given that hydrologic conditions have not changed recently, strong dominance of the plant community by obligate wetland species indicates the presence of wetland with a probability exceeding 90%.2 On the other hand, dominance of facultative species (e.g., prevalence index of 2.5) would be a very different matter.

What a Wetland Is, and Isn’t

Uneven distribution of water causes the landscape to be divided into four parts: lakes, streams, uplands, and wetlands. Lakes are distinguished from the rest by the presence of water standing at considerable depth over long intervals. As a rule of thumb, the water of a lake is deep enough to prevent the growth of rooted vegetation over most of its area. Streams (and rivers, which are simply large streams) are moving waters confined by a channel. Uplands are seldom or never covered with water and are fully saturated to points near the surface only during cold weather or for short intervals during the growing season. Parts of the landscape that remain after the exclusion of lakes, streams, and uplands are wetlands. Wetlands may be inundated constantly, seasonally, or never. If never inundated or inundated seasonally—as are the lands on river floodplains—wetlands can be dry at the surface. Even so, they will be very wet just underneath for all or much of the growing season. Wetlands thus are places where heavy equipment is likely to churn up mud even after the weather has been dry for some time. Water provokes important responses from plants, animals, and microbes that in turn cause uplands, wetlands, lakes, and streams to be fundamentally different from each other. Where water stands for long periods at a depth of several feet, we find organisms with life cycles that presume the constant presence of water, and the sediment lacks the properties of a true soil. Where the land is characteristically dry at and near the surface during the growing season, the assortment of species is different, and typically there is a soil with well-defined structure in the form of layers (horizons). Wetlands are different from either of these in that their resident communities can tolerate water saturation or inundation for long intervals but usually can withstand desiccation of the surface as well. They form soils, but of a class distinct from the soils of uplands. Thus, the uneven distribution of water causes some predictable kinds of variation in living communities and soils, both of which can be used in defining and mapping wetlands.

Once and Future Wetlands

A societal conflict as prolonged and complex as the reversal of national policy on wetlands in the United States must contain some lessons for the future. Perhaps we are still too close to the issues to have everything in perspective historically, but two lessons seem obvious. One of these has to do with the channelizing effect of change in public attitudes toward wetlands and the other with the stabilizing effect of science on regulations and policies intended for the protection of wetlands. A look back at the previous chapters suggests that the history of wetland policy in the United States can be divided into three eras: a classical era during which removal was the policy; a modern era during which protection was the policy; and a new era, which appears to be postmodern in the sense that we adjust protection qualitatively in an attempt to make our coexistence with wetlands more comfortable. Politics of the removal era appear to have been relatively tranquil, as congressional action surrounding wetlands developed almost entirely through consultation with a single interest group (i.e., those who saw some economically beneficial potential in federal progams subsidizing or encouraging the removal of wetlands; Tzoumis 1998). The desire for protection, although present in some circles much earlier, became politically potent in parallel with the growth of general public support for environmental legislation. From that time forward, legislation and national policy have consistently been formed in an atmosphere of strongly opposing viewpoints, but the protectionist impulse has prevailed. It seems doubtful now that an open legislative assault on wetland protection would be successful, simply because the public has fully absorbed the idea of protection for about a generation. The fundamental intent of protectionism, however, still could be subverted judicially or administratively; this is the main issue for the future. From 1970 to the present, the politics of wetlands has seemed unstable and even chaotic. Participants in the contest over wetlands typically have viewed the future with a high degree of pessimism. This is especially true for the defenders of wetlands, who fear, and in some cases almost anticipate, reactionary backsliding.

The Cast of Characters

Through the inexorable workings of natural selection, wetlands have come to support a group of species that are especially well adapted to the physical and chemical peculiarities of saturated substrates and shallow water. These species give wetlands their distinctive biological signature and sustain the biotic functions of wetlands (Tiner 1998). The species that occupy wetlands show varying degrees of specialization. Some are so highly specialized that they can live or reproduce only in wetlands; these are called obligate wetland species. A second group contains organisms that are adapted for life in wetlands but are not restricted to wetlands; these are called facultative wetland species. Facultative wetland species show every conceivable shade of association with wetlands: they range from almost obligate to barely facultative. The distribution of obligate wetland species coincides closely with the distribution of wetlands. Thus, one could be tempted to rely heavily on obligate wetland species to find and map wetlands. Inference from obligate wetland species, however, must be tempered with caution. First, the absence of obligate wetland species does not necessarily mean absence of wetland, given that a wetland can be mostly or even entirely occupied by facultative wetland species. In addition, the degree to which a given species is a wetland obligate may not be known with absolute certainty. Where a genetic variant or an unusual set of physical conditions prevails, a species that seemed to be obligate in other situations may prove to be merely facultative and thus not diagnostic proof of the presence of wetland. The perils of absolute reliance on obligate wetland species have turned the attention of wetland mappers to the analysis of entire communities. Although community analysis can be done in a number of ways, the central idea is to score a community according to the proportionate representation of species that show a known facultative or obligate affinity with wetland conditions. The analysis of communities for the purpose of mapping and identifying wetlands has been focused almost entirely on vascular plants (grasses, forbs, shrubs, and trees). Two good reasons for this are the relative ease with which plant communities can be analyzed and the immobility of plants.

Water Is as Water Does

The greatest subtlety of wetlands lies in their hydrology. This is unfortunate, given that the very name wetland invokes images of water on the land. In fact, those who have been impatient with the thicket of indicators by which federal agencies identify wetlands have at times demanded a return to basics in the form of simple inspection for water. One Washington insider even suggested that we might send out her Uncle Dennis to delineate wetlands. If Uncle Dennis, who has a propensity to sit down, returns with a wet bottom, he has been in a wetland; otherwise he has not. The truth is that Uncle Dennis could sometimes wet his shorts in an upland forest or grassland, yet at other times sit comfortably dry on a certified wetland. The hydrologic conditions that separate wetlands from uplands in fact involve four phenomena related to saturation: proximity to the surface, time of year, duration, and frequency. Proximity of saturation to the soil surface is one of the most widely misunderstood aspects of wetlands. In many wetlands, water stands on the surface for extended intervals or, in a few cases, continuously. The significance of standing water (inundation), however, is easily overrated. Inundation is neither necessary nor sufficient for a wetland. Recurrent and prolonged saturation of soil near the surface is sufficient to create and maintain a wetland, even if water never actually stands on the surface. The exact distance within which saturation must approach the surface varies from one region or one wetland type to another but by rule of thumb is about one foot or, scientifically speaking, 30 cm. While plant roots often extend beyond one foot, prolonged saturation of the upper foot blocks penetration of oxygen into the soil, and thus to roots, so completely that most plants cannot survive. Plants that tolerate or thrive in saturated soils are called hydrophytes; they are characteristic of wetlands. Thus, the critical depth for saturation is determined by the differential responses of hydrophytes and non-hydrophytes to prolonged immersion of roots in water. The upper one foot of soil is also the zone of most intense microbial metabolism in soil.