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USGS2000

Environmental Contaminants and Terrestrial Vertebrates: Effects on Populations, Communities, and Ecosystems

The desire of resource managers, risk assessors, and the general public to better understand the consequences of environmental contamination has produced a strong and growing need for information on the effects of contaminants on populations and groups of species, and over moderate to large areas of land or water. However, the problems associated with research involving populations and groups of species or large and complex geographic areas, especially in terrestrial environments, are well known within the scientific community. With the previous thoughts in mind, an interactive symposium was held at the University of Maryland in October 1998. The purpose of the symposium was to review and critically evaluate our understanding of the effects of contaminants on terrestrial vertebrates at levels of organization above that of the individual. Invited background and technical presentations provided a common baseline of information for symposium participants. Discussion groups were then asked to critically evaluate the topics of two technical sessions. Several presentations of recent or ongoing research provided participants with examples of current approaches to assessments of the effects of contaminants on terrestrial vertebrates at the population or higher level of organization. The book consists of 10 chapters written by presenters at the symposium and three chapters conveying the reports of discussion group.

SETAC Special Publications Series.↗
USGS2002

Final report: Initial ecosystem response of salt marshes to ditch plugging and pool creation: Experiments at Rachel Carson National Wildlife Refuge (Maine)

This study evaluates the response of three salt marshes, associated with the Rachel Carson National Wildlife Refuge (Maine), to the practice of ditch plugging. Drainage ditches, originally dug to drain the marsh for mosquito control or to facilitate salt hay farming, are plugged with marsh peat in an effort to impound water upstream of the plug, raise water table levels in the marsh, and increase surface water habitat. At two study sites, Moody Marsh and Granite Point Road Marsh, ditch plugs were installed in spring 2000. Monitoring of hydrology, vegetation, nekton and bird utilization, and marsh development processes was conducted in 1999, before ditch plugging, and then in 2000 and 2001 (all parameters except nekton), after ditch plugging. Each study site had a control marsh that was monitored simultaneously with the plugged marsh, and thus, we employed a BACI study design (before, after, control, impact). A third site, Marshall Point Road Marsh, was plugged in 1998. Monitoring of the plugged and control sites was conducted in 1999 and 2000, with limited monitoring in 2001, thus there was no ?before? plug monitoring. With ditch plugging, water table levels increased toward the marsh surface and the areal extent of standing water increased. Responding to a wetter substrate, a vegetation change from high marsh species (e.g., Spartina patens) to those more tolerant of flooded conditions (e.g., Spartina alterniflora) was noted at two of the three ditch plugged sites. Initial response of the nekton community (fishes and decapod crustaceans) was evaluated by monitoring utilization of salt marsh pools using a 1m2 enclosure trap. In general, nekton species richness, density, and community structure remained unchanged following ditch plugging at the Moody and Granite Point sites. At Marshall Point, species richness and density (number of individuals per m2) were significantly greater in the experimental plugged marsh than the control marsh (<2% of the control marsh was open water habitat vs. 11% of the plugged marsh). The response of birds, categorized as waterfowl & waterbirds, shorebirds & wading birds, gulls & terns, and miscellaneous (raptors, passerines, other), was variable. Following ditch plugging, bird species richness increased at the Granite Point site (1999 pre-plug = 15.4, 2000 post-plug = 26.2, 2001 post-plug = 38.7). Because of a low sample size at Moody Marsh, reliable statements on species richness cannot be made. Density of birds (no. of birds per ha) remained unchanged with ditch plugging at Granite Point Marsh, although there was a strong, but not statistically significant, trend toward increased density. This study only reports on initial responses of marsh functions to ditch plugging. Monitoring should continue at these sites, and perhaps at additional sites, for the next decade or so. A monitoring plan is recommended. Long-term monitoring will include evaluation of salt marsh development processes using SET (surface elevation table) methodology. There is concern, although not confirmed, that as ditch-plugged marshes become wetter and marsh grass production declines their ability to keep pace with sea level rise could be jeopardized. It is suggested that ditch plugging should be considered an experimental marsh management technique. Additional monitoring on the physical and habitat responses of ditch-plugged marshes is required, along with assessments of other techniques aimed at restoring open water habitat to the marsh surface.

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USGS1975

Some effects of pollutants in terrestrial ecosystems

Summary: Pollutants tend to simplify plant and animal communities by causing a progressive loss of species. At the extreme, this leads to erosion and loss of soil fertility. Weedy, broadly adapted species increase. Among animals, carnivorous species and groups are often the first to suffer. This is partly because of their exposure at the top of the food chain, and partly, it appears, because of physiological differences. Species differences in susceptibility are abundant and are often critical. One result is that when one pest is controlled another is likely to flare up. Resistance appears commonly in insects and is known in other fast-breeding forms, including fishes, frogs, and rodents. Resistant individuals can carry toxicant loads that make them dangerous food for other animals. Some groups, including mollusks and annelids, are naturally resistant to many organohalogens and tend to accumulate them. Animals such as birds may carry lipophilic pollutants in large amounts with apparent safety until forced to draw upon their fat. They may then suffer delayed mortality, and no doubt suffer reproductive or behavioral effects at sublethal levels. Lipophilic pollutants in the brain rise when body lipids decrease and fall when body lipids increase. Mutagenesis can be caused by some common pollutants and the mutagenic properties of most chemicals are far too little known. Fortunately, common pesticides are not likely to be strong mutagens. Mutagenicity may be affecting certain long-lived and slow-breeding species in the wild, but most species have enough population turnover to swamp an occasional mutagenic event. Behavioral changes can be caused by relatively low levels of contaminants, but it is often hard to demonstrate them without using high dosages. Reproduction may or may not be affected adversely by low exposures. At certain exposures that are below the toxic levels of a chemical, a biostimulatory effect is to be expected. Food chain accumulations definitely do occur when persistent chemicals enter organisms that eliminate them poorly. However, loss of chemicals in the food chain must be more common than accumulation. The great concentration from water to aquatic organism is chiefly a physical phenomenon, not a food chain effect, but it affords high starting levels for these chains. Terrestrial food chains often start at a high level with heavily contaminated, struggling prey. Litter feeders are another important base. Vegetation may be contaminated enough to be dangerous to animals that eat it. Dermal and respiratory routes of intoxication occur in the wild, but the oral route is far more important at most times and places. The organisms that govern soil fertility and texture are affected more by cultivation than by pesticides. Above ground, growing knowledge of resistance, species differences, and biological controls is leading to integrated control, in which use of chemicals is limited and specific. We do not know what is happening to most nontarget invertebrates. Amphibians and reptiles may be killed by applications of insecticides, but are not highly sensitive and can carry large residues. Effects of these residues on reproduction are little known. Heavy kills of birds by pesticides still occur in the field. Fish-eating and bird-eating birds also undergo shell thinning and related reproductive troubles in many areas, sometimes to the point of population decline and local or regional extermination. DDE most often correlates with shell thinning in the wild and in experiments. No other known chemical approaches DDE in causing severe and lasting shell thinning. Herbivorous birds seem to be largely immune to this effect. It is uncertain how much dieldrin and PCBs contribute to embryotoxicity in carnivorous birds. Mammals may be killed by the more toxic pesticides, but some of the commonest small rodents are so resistant, and lose their residues so rapidly, that they are of little

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