Water Quality in the Yukon River Basin
The Yukon River Basin, which encompasses 330,000 square miles in northwestern Canada and central Alaska (Fig. 1), is one of the largest and most diverse ecosystems in North America. The Yukon River is also fundamental to the ecosystems of the eastern Bering Sea and Chukchi Sea, providing most of the freshwater runoff, sediments, and dissolved solutes. Despite its remoteness and perceived invulnerability, the Yukon River Basin is changing. For example, records of air temperature during 1961- 1990 indicate a warming trend of about 0.75 °C per decade at latitudes where the Yukon River is located. Increases in temperature will have wide-ranging effects on permafrost distribution, glacial runoff and the movement of carbon and nutrients within and from the basin. In addition, Alaska has many natural resources such as timber, minerals, gas, and oil that may be developed in future years. As a consequence of these changes, several issues of scientific and cultural concern have come to the forefront. At present, water quality data for the Yukon River Basin are very limited. This fact sheet describes a program to provide the data that are needed to address these issues.
Ice jam on the lower Yukon River near Pitkas Point
(photo courtesy of the National Weather Service)
Predicted warming of arctic and sub-arctic ecosystems, including the Yukon Basin, has the potential of making vast amounts of organic carbon and nutrients currently stored in permafrost available for decomposition and for release to nearby wetlands, lakes and streams. This will have global effects on the atmospheric concentrations of greenhouse gases such as carbon dioxide and methane. It may also have regional effects on all levels of stream productivity in the Yukon Basin, including salmon populations. Other potential effects of warming include increased fire frequency and consequent increased soil erosion. Potential effects of development may include increased sediment loads to streams and rivers that can result in the alteration of fish spawning areas. Groundwater aquifers that feed the Yukon River and its tributaries may also be contaminated. Because studies in the early 1990's showed elevated levels of toxophene, DDT, and PCBs in fish from Lake Laberge, near the headwaters of the Yukon River in the Yukon Territory, Canada, concerns have been expressed in the region regarding atmospheric transport of persistent, bioaccumulative organic contaminants.
Fall colors along the Yukon River downstream of Stevens Village (photo courtesy of Alaska Geographic).
Rivers integrate the constituents and characteristics of the landscape through which they flow. Water chemistry measured at any one point in a river reflects a complex combination of natural processes and human activities that occur upstream. Since 1995,the National Stream Quality Accounting Network (NASQAN) of the U.S. Geological Survey has focused on monitoring the quality of the water in the Nation's largest river systems. NASQAN provides an authoritative baseline of data compiled from measurements that are repeatable and that are obtained through the use of well-documented methods. These baseline data are needed to:
- characterize large sub-basins of these rivers,
- determine regional source areas of soluble substances and sediment in the water,
- assess the effects of human activities on observed concentrations and amounts of soluble substances and sediment in the water.
The acquisition and interpretation of these data are the focus of the Yukon River Basin study.
Figure 1. Location of the Yukon River Basin in Canada and Alaska.
As a Federal earth science and natural resources agency with core competencies in acquiring and managing long-term national databases and in conducting long-term, broad-scale multidisciplinary studies, the USGS is uniquely suited to perform the present baseline assessment of the Yukon River. The USGS is well-positioned to repeat this work in coming decades if, for example, significant melting of the permafrost or changes in mining activity and pesticide use occur.
Science Goals and Strategic Planning
The program, still in its early stages, has been initiated with funding primarily from the NASQAN program; other USGS contributors include the Earth Surface Dynamics, Mineral Resources, and Biomonitoring of Environmental Status and Trends programs. Collaborators who have been actively involved in the project development to date include other Federal agencies, the State of Alaska, universities, and tribal agencies.
The water quality of the Yukon River will be assessed by collecting water samples at a network of fixed sites, conducting a spatial synoptic sampling to produce a "snapshot" of water quality in the basin, and sampling lake sediment cores.
Fixed site network. Water-quality data collected at the fixed site network over the five-year study period will establish a reference database. This database will allow the determination of the amount of a particular constituent that flows past each station (called the mass flux). The mass flux of a constituent at one site can be compared with the mass flux of the constituent at the other fixed sites to identify source areas of contaminants, monitor transport through the river system, and estimate delivery of contaminants to the ocean.
The fixed station network will consist of five sites (Fig. 2): Yukon River at Eagle (site 1), Porcupine River near Fort Yukon (site 2), Yukon River near Stevens Village (site 3), Tanana River at Nenana (site 4), and the Yukon River at Pilot Station (site 5). Stations have been selected to divide the basin into homogenous units and to isolate areas that are of particular interest. The Porcupine River, for example, is a watershed underlain by continuous permafrost, and the Tanana River is a glacial watershed. Water at these stations will be sampled approximately eight times per year (once under ice and seven times during open water) and analyzed for the constituents and characteristics listed in Table 1. Sampling at the fixed sites was begun in October 2000.
Table 1. Water quality constituents Nutrients Nitrogen, phosphorus (total and dissolved) Organic Carbon Total and dissolved, particulate Trace Elements Arsenic, aluminum, antimony, barium, beryllium, boron, cadmium, chromium, cobalt, copper, lead, lithium, manganese, mercury, molybdenum, nickel, selenium, silver, strontium, thallium, uranium, vanadium, zinc (particulate and dissolved) Major Ions Calcium, chloride, dissolved solids, fluoride, iron, magnesium, potassium, silica, sodium, sulfate
Synoptic sampling: The term "synoptic" refers to displaying conditions as they exist simultaneously over a broad area. Three spatial synoptic samplings will be performed during 2002 or 2003. The first will be conducted during the low-flow period in spring, while ice is still present. The purpose of this sampling is to characterize the effects of groundwater inputs of carbon from wetlands to the river. Access to the sites will be by airplane. The second synoptic sampling will be conducted during the peak snowmelt period in June, and will focus on contaminants in the river. Water at sites along the mainstem of the Yukon River and its tributaries from Whitehorse, Yukon Territory, Canada to Pilot Station, Alaska will be sampled; samples will be collected from a boat. The third synoptic sampling will be conducted in late August, during glacier runoff and the late-summer chum salmon run. Samples will again be collected by boat from sites along the mainstem of the Yukon and its tributaries from Whitehorse to Pilot Station. Fish sampling and transport of sediment (and contaminants associated with sediment) will be the focus of this sampling. During the year(s) when the synoptic samples are collected, water-quality sampling at the fixed stations will be reduced.
Lake-sediment sampling. In addition to these river studies, the historical trends and seasonal input of atmospherically transported contaminants will be investigated by examining sediment cores collected from eight lakes in the Yukon River Basin. Each core will be sectioned and analyzed for trace elements and organic compounds. The historical deposition record can then be reconstructed by determining the concentrations of hydrophobic organic chemicals and trace elements in each age-dated segment. This work will be supplemented by studies of snow and vegetation to assess current seasonal inputs of trace elements to selected watersheds.
The data obtained from the fixed site and synoptic samplings will be used to address the following scientific issues in the Yukon River Basin:
Carbon cycling. Climatic warming of the Yukon River Basin in the late 20 th century has resulted in lengthening of the growing season, partial melting of permafrost, drying of upland soils, shrinking of wetlands, and increased fire frequency. If this warming trend continues, the timing and magnitude of carbon and nutrient delivery to the Yukon River and its tributaries, as well as the fate of these constituents, are likely to change. A combination of methods will be used to determine the origin, quantity, chemical characteristics, fate and transport of carbon at specific locations along the river and at high and low flow, from headwater streams to the Yukon Delta.
Mercury. Mercury is one of the most serious contaminant threats to human health and aquatic resources. Nearly all of the mercury in fish is methylmercury, a highly neurotoxic form that biomagnifies to high concentrations toward the top of aquatic food webs. The goal of this study is to provide information on concentrations and chemical forms of mercury in water, sediment, and biota from the Yukon River Basin. Samples will be acquired during each sampling at the fixed sites. In addition, during synoptic sampling, samples of peat will be collected from the permafrost areas, where enhanced thawing due to global warming may result in the release of currently bound mercury. River sampling will include identification of transport phases of inorganic and methylmercury (dissolved, colloidal, and particulate), assessment of mercury methylation rates in wetland and river sediments, and measurement of release rates of gaseous mercury from water, soil, and wetland surfaces.
Plans for future studies
Plans for future studies are described below. Implementation of these plans is dependent on the availability of funds.
Fixed site network. Increasing the number of fixed sites in the network would enable us to increase our knowledge of the Yukon River Basin, and enlarge our database. The Koyukuk River is another basin underlain by continuous permafrost, and the White River is another glacial basin that could be added to the network. The Water Survey of Canada currently collects streamflow data on the Pelly and Stewart Rivers, and on the Yukon River above the White River. Adding one or more of these sites to the fixed station network and conducting full sampling at the fixed sites during the years when synoptic sampling is underway would be a significant enhancement to the program.
Microbial contaminants. Poor containment of sanitary wastes in villages along the Yukon River creates the potential for microbial contamination of surface waters used for human consumption. Water would be sampled and assayed for fecal-contamination indicator bacteria and Helicobacter pylori, a newly emerging pathogen of concern as a cause of stomach ulcers and other diseases in humans.
Heavy metals and organochlorine compounds. In the Yukon River Basin, persistent contaminants such as organochlorine pesticides, PCBs, and mercury are of concern. Yukon River chinook salmon and chum salmon are an important natural, commercial, and cultural resource. Little is known, however, about the dynamics of contaminants in the river's salmon populations. Fish runs from the ocean have been shown to contribute contaminants to the watersheds in which spawning occurs. The objectives of this study are to (1) develop baseline data on metals and organochlorine contaminants in chinook salmon and chum salmon from the Yukon River, and (2) determine whether salmon serve as a contaminant transport pathway to the Yukon River ecosystem and, if so, estimate their contribution to the contaminant load.
Persistent organic pollutants. Persistent organic pollutants (POPs) and currently used pesticides are transported to the Yukon River Basin by the atmosphere and deposited on terrestrial and aquatic ecosystems through wet (rain, snow) and dry (dustfall, air-water exchange) processes. Information on concentrations of POPs in the atmosphere of the Yukon River Basin is minimal, and no information is available on atmospheric concentrations of the current high-use pesticides. The objectives of this study are to (1) quantify atmospheric vapor and particle phase concentrations of selected POPs and current high use pesticides throughout the year in the Yukon River Basin, (2) quantify water column concentrations of POPs in the Yukon River, and (3) based on the measured air and water concentrations, estimate the magnitude of dry depositional processes of these chemicals to surface waters.
Estimating land cover change. Vegetative cover has a major effect on terrestrial carbon dioxide fluxes. The development of a baseline Geographic Information System (GIS) data set characterizing land cover in the Yukon River Basin will enable comparative studies in future years to assess changes associated with fire and climate change.
Set net on the Yukon River near Tanana (photo courtesy of Alaska Geographic.)
Rivers are great integrators of what is happening in their watersheds. The water, sediment, natural and man-made chemicals that move downstream are indicators of the status of the landscape. As the Yukon basin changes over the coming decades, it will be valuable to have a detailed and reliable baseline of information from the Yukon River so that future generations of scientists and resource managers can understand the changes that are occurring, predict future changes, and make decisions about our global and regional resources. The Yukon is important not only for the vast area that it drains, but the much larger Arctic environment worldwide that it typifies. The USGS plans to work with others to lay down the first comprehensive baseline of data to describe this vast watershed that is so sparsely populated and studied, and yet subject to large potential changes in the decades to come.
NASQAN and many other USGS programs are combining resources to develop a water-quality database for the Yukon River Basin. We would like to expand the program and we are seeking partners who are able to take advantage of the sampling platform provided by NASQAN to extend this characterization. We have identified key areas that we believe are important for future studies, and we are open to other suggestions for collaboration. Please feel free to contact the responsible individuals for more information.
Gordon Nelson, District Chief
4230 University Drive, Suite 201
Tim Brabets, Basin Coordinator
4230 University Drive,Suite 201
NASQAN (National Stream Quality Accounting Network)
Tim Miller, NASQAN Coordinator
Office of Water Quality
NRP (National Research Program)
12201 Sunrise Valley Drive
Mail Stop 430
U.S. Department of the Interior, U.S. Geological Survey, Factsheet FS-050-01, June 2001