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<br />I <br /> <br />I <br /> <br />I <br /> <br />( <br /> <br />Int.-{)ducti{)n <br /> <br />) <br /> <br />I <br /> <br />The guidelines, criteria, and other information <br />in this volume were originally compiled for <br />use by personnel conducting studies for the <br />Department of the Interior's National <br />Irrigation Water Quality Program (NIWQP). <br />The purpose of these studies is to identify and <br />address irrigation-induced water quality and <br />contamination problems associated with any <br />of the Department's water projects in the <br />Western States. When NIWQP scientists <br />submit samples of water, soil, sediment, eggs, <br />or animal tissue for chemical analysis, they <br />face a challenge in determining the sig- <br />nificance of the analytical results. How much <br />of a given chemical constituent is "normal" in <br />the tested medium? How much is unusually <br />high? What adverse effects-if any-may <br />result from the reported concentration? <br />Studies that address these questions are <br />myriad: they are widely scattered in the <br />literature, they use many different approaches <br />and testing protocols, and they yield greatly <br />varying-and sometimes contradictory- <br />results. The chapters in this volume are <br />intended to: (1) identify the most important, <br />most relevant studies for several "constituents <br />of concern" that are commonly encountered in <br />environments affected by irrigation drainage; <br />(2) present a sampling of notable results from <br />these studies in tables organized according to <br />tested medium; (3) explain further, in the <br />accompanying text, the significance of these <br />results; and (4) give full and accurate <br />references to the original studies, for those <br />who desire more detailed information. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />Although this volume is targeted for scientific <br />specialists, it may also be of interest to <br />government officials, farmers, ranchers, <br />conservationists, reporters, and anyone else <br />interested in the environmental health of <br />freshwater ecosystems. These readers may <br />find the glossary in Appendix II especially <br />helpful. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />The limitations of This Volume <br /> <br />It is important to note five limitations on the <br />material presented here: <br /> <br />(1) Out of the hundreds of substances known <br />to affect wetlands and water bodies, this <br />volume focuses on only nine constituents <br />or properties commonly identified during <br />NIWQP studies in the Western United <br />States-salinity, DOT, and the trace <br />elements arsenic, boron, copper, mercury, <br />molybdenum, selenium, and zinc. <br />Financial and time restraints do not allow <br />consideration of other contaminants at <br />this time. <br /> <br />(2) For the most part, these are only guide- <br />lines, merely reports of toxic effects that <br />were noted for certain concentrations in <br />particular circumstances. Individual. <br />constituents may be more or less toxlC at <br />other sites or for other species, depending <br />on many factors. Some of these com- <br />plicating factors are described in the. <br />following section on data interpretatIon, <br />which readers are urged to review before <br />attempting to apply these guidelines. <br /> <br />(3) Caution is particularly appropriate in <br />using the summary tables (the first <br />numbered table in each of the chapters). <br />These are designed to give only a general <br />indication of concentrations that may be <br />troublesome in various types of media. In <br />some cases the "no effect" and "threshold" <br />values for a class of organisms have been <br />distilled from hundreds of individual <br />studies of the diverse species that make <br />up the class. In other cases, we have had <br />to rely on only a handful of studies to set <br />tentative values for the entire class. <br />Readers should make no final, formal <br />decisions regarding the toxicity of <br /> <br />8 <br />