|
<br />The Quality of Streams and
<br />Rivers is Affected by
<br />Historical Mining Activities
<br />
<br />Streams affected by mine drain-
<br />age, from abandoned/inactive
<br />mines, are present throughout
<br />much of the Rocky Mountains of
<br />Colorado. Metal mining in the
<br />UCOL has been an important part
<br />of the economy of Colorado since
<br />the late 1800s. As a result, many
<br />streams in the upper part of the
<br />basin contain heavy metals and
<br />other toxic elements that affect
<br />stream-water quality. Knowledge
<br />of mine-drainage effects on a body
<br />of water is essential for assessing
<br />water quality with regard to human
<br />consumption, recreation, and
<br />aquatic life.
<br />
<br />Because of the potential expo-
<br />sure of aquatic organisms to trace
<br />elements in streambed sediment,
<br />trace-element concentrations in
<br />streambed sediment serve as an
<br />indicator of potential toxicity to
<br />aquatic life. Sampling trace ele-
<br />
<br />ments in streambed sediment can
<br />be used to identify stream reaches
<br />affected by mining and can be
<br />used to determine sources of trace
<br />elements. The occurrence and
<br />distribution of trace elements were
<br />characterized by collecting
<br />streambed-sediment samples at
<br />29 sites in mining districts (fig. 6
<br />and table I) and at 8 background
<br />(non-mining) sites in the Southern
<br />Rocky Mountains.
<br />
<br />Concentrations of cadmium,
<br />copper, lead, and zinc in
<br />streambed sediment were high at
<br />some sites downstream from
<br />mining areas (Deacon and Driver,
<br />1999). Median concentrations of
<br />cadmium (Cd) and zinc (Zn) in
<br />samples from most mining districts
<br />exceeded the Canadian Sediment
<br />Quality Guidelines Probable Effect
<br />Level (PEL), which is a sediment
<br />guideline (fig. II). The PEL
<br />defines the concentration level
<br />above which adverse effects to
<br />aquatic biota are predicted to occur
<br />
<br />Table 1. Mining districts and sampling sites in the Southern Rocky Mountains
<br />
<br />Mining district1
<br />
<br />River/Stream [site number(s) in
<br />figure 6f
<br />
<br />Hunter Creek (24)
<br />
<br />Blue River. French Gulch, Swan River
<br />(7,10, II, 12. 13, 14, 15, 16, 17)
<br />
<br />Tenmile Creek (18)
<br />
<br />Oh-Be-Joyful Creek, Coal Creek,
<br />Slate, East Rivers (25, 26, 27, 28)
<br />
<br />Cross Creek, Eagle River (22,23)
<br />
<br />Lake Fork of the Gunnison River,
<br />Hensen Creek (3 I, 32)
<br />
<br />Peru Creek, Snake River (4, 5, 6)
<br />
<br />Canyon Creek, Red Mountain Creek,
<br />Uncompahgre River (33,34,35,36,
<br />37)
<br />
<br />South Fork of Williams Fork,
<br />Williams Fork (2, 3)
<br />
<br />IInformation from Davis and Streufert (1990).
<br />2Background (non-mining) sites 1,8,9,19,20.21.29.30.
<br />
<br />Aspen
<br />Breckenridge
<br />
<br />Climax
<br />
<br />Crested Butte
<br />
<br />Gilman
<br />
<br />Lake City (Carson, Burrows, Sherman
<br />Districts)
<br />
<br />Montezuma
<br />
<br />Ouray (Red Mountain, Sneffels,
<br />Uncompahgre Districts)
<br />
<br />Urad-Henderson
<br />
<br />
<br />Mining land use in the Southern Rocky
<br />Mountains. (Photograph by Jeffrey Deacon,
<br />U,S. Geological Survey,)
<br />
<br />frequently (Canadian Council of
<br />Ministers of the Environment,
<br />1999). National sediment concen-
<br />tration guidelines have not been
<br />established for the United States.
<br />Concentrations of copper and lead
<br />were also elevated and exceeded
<br />the PEL in several mining districts.
<br />The mining and mineralized areas
<br />of the UCOL generally result in
<br />higher trace-element concentra-
<br />tions in streambed sediment than
<br />are detected in other areas studied
<br />within the NAWQA Program
<br />(p. 12).
<br />Collecting samples from sev-
<br />eral types of media provides a
<br />better understanding of trace ele-
<br />ments in the environment. In
<br />addition to streambed sediment,
<br />which can store trace elements, the
<br />overlying stream water can also
<br />be a source of trace-element expo-
<br />sure to aquatic organisms. Because
<br />invertebrates are continuously
<br />exposed to water-quality condi-
<br />tions, these organisms integrate
<br />effects of contaminants over time
<br />and provide a measurement of
<br />water quality. Invertebrate indica-
<br />tors of streams contaminated by
<br />trace elements include reduced
<br />abundance and a shift in commu-
<br />
<br />Major Findings 11
<br />
|