Study Design

Photo by USGS.

Objective

To develop a 'baseline' characterization of water quality in the Yukon Basin against which future changes in water quality can be measured.

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

Approach

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.

This will require the collection of a depth- and width-integrated sample (also known as EDI, Equal Discharge Increments) along with a discharge measurement at each measurement point.

Baseline Data

The five fixed stations represent areas of extensive permafrost and wetlands (Porcupine River), sediment laden glacial melt water (Tanana River), the Yukon River headwaters upstream of Alaska (Yukon River at Eagle), the Yukon River below Yukon Flats (Yukon River at Stevens Village) and the Yukon River near its mouth (Yukon River at Pilot Station).Water at these stations will be sampled approximately eight times per year (once under ice and seven times during open water) and analyzed for sediment load and concentrations, and a broad range of constituents, including major ions, nutrients, dissolved and sediment-associated trace elements, biological indicators (such as dissolved oxygen, chlorophyll-a and the stable isotopic composition of nitrogen, carbon, and sulfur of particulate organic matter), and various forms of organic carbon.

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.

Intensive (synoptic) Data

The term "synoptic" refers to displaying conditions as they exist simultaneously over a broad area.The primary objective of the intensive or synoptic sampling is to measure the instantaneous flux of as many constituents as possible at as many sites as possible along the entire reach of the Yukon River.

The first synoptic sampling will be conducted during the peak snowmelt period in June, and will focus on contaminants in the river. The second synoptic sampling will be conducted in late August, during glacier runoff and the late-summer chum salmon run. 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. During the year(s) when the synoptic samples are collected, water-quality sampling at the fixed stations will be reduced. Data from these intensive samplings increase understanding of carbon source areas, within-stream dissolution of suspended carbonates, metabolism of organic carbon, and the flux carbon gases to the atmosphere. Also included during intensive sampling will be measurements of "non-standard" constituents such as gas fluxes, methyl-Hg, and isotopes.

Lake-Sediment Cores

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 specific 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.

Sampling Sites

Sample sites will be selected based on a combination of safety, logistics, and research interests. For example, the braided nature of some tributaries prohibits a discharge.

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U.S. Department of the Interior \| U.S. Geological Survey URL: http://ak.water.usgs.gov/yukon/program/design/2001Objectives.php Page Contact Information: E-mail comments or questions to Bob Ourso Last modified: April 28 2006 11:52:25.