Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska
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uses science for a changing world Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska Professional Paper 1685 U.S. Department of the Interior U.S. Geological Survey Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska Larry P. Gough, Editor Professional Paper 1685 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey Charles G. Groat Director U.S. Geological Survey, Reston, Virginia: 2004 For sale by U.S. Geological Survey Information Services Box 25286, Denver Federal Center Denver, CO 80225 This report and any updates to it are available online at: http://pubs.usgs.gov/pp/p1685/ Additional USGS publications can be found at: http://geology.usgs.gov/products.html For more information about the USGS and its products: Telephone: 1-888-ASK-USGS (1-888-275-8747) World Wide Web: http://www.usgs.gov/ Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement of the U.S. Government. Although this report is in the public domain, it contains copyrighted materials that are noted in the text. Permission to reproduce those items must be secured from the individual copyright owners. Cataloging-in-publication data are on file with the Library of Congress (URL http://www.loc.gov/). COVER Fortymile River near the mouth of Moose Creek. This section of the river, just a few miles west of the United States-Canadian border, cuts through supracrustal metasedimentary rocks of the Taylor Mountain assem blage. The geochemical influence of this and other lithologic units on surface-water chemistry and fish-tissue bio- geochemistry is the subject of the first two chapters in this report. The brown color of the river water is due to the abundance of natural organic matter, which plays a role in the transport and complexation of dissolved metals—the subject of the third chapter in this report. Manuscript approved for publication, October 30,2003 Produced in the Western Region, Menlo Park, California Text edited by George A. Havach Layout and design by Sara Boore Ill Contents [Numbers designate chapters] Introduction ........................................................................................... ...^^ 1 By Larry P. Gough 1. Geochemical Processes and Geologic Framework Influencing Surface-Water and Sediment Chemistry in the Fortymile River Watershed, East-Central Alaska..................... 3 By Bronwen Wang, Richard B. Wanty, and Jim Vohden 2. Biogeochemistry, Stable-lsotopic Composition, and Feeding Habits of Arctic Grayling (Thymallus arcticus) in the Lower Fortymile River, Eastern Alaska...................................... 21 By Larry P. Gough, James G. Crock, Robert R. Seal, Bronwen Wang, and PhyllisWeber-Scannell 3. Comparative Characteristics of Natural Organic Matter in the Fortymile River, Alaska ............ 45 By Donald L. Macalady, Kaylene Ritter, Aaron D. Redman, and Magnus Skold 4. U.S. Geological Survey Reports on the Fortymile River Watershed — Products of Recent Mineral Resources Program Studies.................................................................................... 53 Introduction By Larry P. Gough The collection of three papers that follow results from cally active, possibly even toxic, in plants and animals). By hydrologic, geologic, geochemical, and biogeochemical understanding the predevelopment baselines, changes sus studies begun in 1997 in the Forty mile River watershed, pected to have been caused by human activity can be defined east-central Alaska. These studies are the latest in a series of and quantified. publications (see bibliography at end of this report), resulting The chapters in this report provide a framework for the from work focused on the mineral-rich Yukon-Tanana Upland analysis of future, potential changes in geochemical and bio (YTU) physiographic region (Interior Highlands Ecoregion), geochemical signatures, because they report the quantitative conducted by the U.S. Geological Survey (USGS)'s Mineral analysis of water, sediment, rocks, and fish tissue. They also Resources Program. report on the processes that affect the mobility and bioavail- The YTU has a long history related to the mining and ability of certain trace elements. The chapter by Wang and oth mineral industry. Placer gold was first discovered in the For- ers discusses major- and trace-element chemistry in relation to tymile River in 1886, and both alluvial and lode deposits have regional lithologic units within the Fortymile River watershed. been exploited within the region. The development of low- to The major-ion chemistry of the waters reflects a rock-domi high-grade, high-tonnage, intrusion-related Au deposits (such nated aqueous system with but limited interaction with the as Fort Knox, True North, and Pogo) since the early 1990s is geologic materials of the region. The authors discuss in detail a new resource that has spurred a resurgence of exploration the multiple and varied reasons for this apparent paradox. The activity. Numerous State and Federal regulations require that chapter by Gough and others examines the chemistry of fish the degree of potentially adverse environmental impact from tissue (Arctic grayling) and reports functional biogeochemical these exploration and mining activities be quantified, espe baseline values and (or) ranges for numerous elements, includ cially for surface-water quality and its influence on the health ing mercury. This chapter also examines the nitrogen-, carbon-, of aquatic biota. By helping to establish regional premining and sulfur-isotopic composition of fish tissue in relation to baselines, these and other studies will aid regulatory decisions grayling food sources and trophic position in the food web. at the local, State, and Federal levels, as well as help the min Finally, the chapter by Macalady and others discusses the role ing companies formulate efficient mitigation plans. of dissolved natural organic matter on the mobility of trace The USGS, the Bureau of Land Management, and the elements in waters. Measurements of the copper-complexation Alaska Department of Natural Resources are cooperating in capacities of these samples confirm that the dissolved organic project work to provide the scientific data for upcoming deci matter has very low metal-binding capacities. The authors sions that involve State and Federal land-use options and their discuss the importance of this discovery in relation to future regulations. One important question that relates to resource potential mining activities. development is "what are the regional predevelopment The bibliography at the end of this report lists all the pub geochemical 'signatures' (or baselines) for water and biota, lications that were generated by this project from 1997 to the and what impact do natural processes have on the variation present, some of which are available in their entirety online, in those 'signatures'"? This question is especially important whereas others may be obtained from the USGS library (URL because it applies to trace elements, particularly if those trace http://library.usgs.gov/) or from USGS Information Services elements have environmental importance (that is, are metaboli- (URLhttp://mapping.usgs.gov/esic/to_order.html). Chapter 1 Geochemical Processes and Geologic Framework Influencing Surface-Water and Sediment Chemistry in the Fortymile River Watershed, East-Central Alaska By Bronwen Wang, Richard B. Wanty, and Jim Vohden1 Contents stream-sediment samples, respectively. Total aqueous REE concentrations were positively correlated with the amount of sus Abstract.......................................................................................................... 3 pended colloidal matter but not correlated with the pH of the water. Introduction................................................................................................... 3 Geologic Setting............................................................................................ 4 Methods......................................................................................................... 6 Results .......................................................................................................... 7 Introduction Aqueous Chemistry............................................................................ 7 Stream Sediment................................................................................ 8 The Fortymile River lies within the "Tintina Gold Belt" Rare-Earth Elements.......................................................................... 9 and is within the Yukon-Tanana Upland physiographic prov Summary........................................................................................................17 ince (fig. 1). Placer gold has been mined in the Fortymile River References Cited ..........................................................................................17 region since 1886 (Mertie, 1938; Yeend, 1996), and gold explo ration and development in the Tintina Gold Belt has recently Abstract expanded because of the discoveries of the Fort Knox, True North, and Pogo deposits (Goldfarb and others, 2000). Between We have analyzed major, trace, and rare-earth elements 1997 and 1998, the U.S. Geological Survey and the Alaska in water and stream-sediment samples from 33 sites within the Department of Natural Resources conducted a cooperative study Fortymile