The SCWRS offers direct river access, a small fleet of boats, outboard motors and trailers. Boats include an 18-foot jon boat, a 12-foot lightweight rowboat, a Zodiac inflatable two-person boat, and two 17 foot, aluminum canoes. Standard equipment for limnological work is available, including field meters and samplers for water, plankton and benthos, and two GPS units, which are compatible with laptop PCs. More specialized equipment for hydrological monitoring includes data loggers, piezometers, and well-leveling potentiometers. Equipment is available for sediment coring with gravity corers, Livingstone corers, surface piston corers, and more than 70 meters of lightweight magnesium-zirconium drive rod. An automated weather station provides continuous recording of meteorological data that can be downloaded via modem.
The Technical Assistance Program for Watersheds (TAPwaters) is dedicated to the use of geographic information system (GIS) and hydrological modeling technology for the advancement of watershed research and management. The TAPwaters office is located in the Spring Creek annex and houses two high-end workstations, a 4x5-ft. digitizing tablet, and a 54-inch wide-format plotter. A continuing task for the TAPwaters office will be to produce watershed models for tributaries to the St. Croix River, and to eventually build a basin-wide model of the St. Croix to provide regional context for managing nutrient and sediment loads to the riverway. For more information on the TAPwaters program, contact Senior Scientist.
St. Croix Laboratory
Researchers at the SCWRS laboratories perform analyses on various environmental samples, with most analyses focused on sediment and water. Procedures carried out in the laboratory range from sediment loss on ignition, to nutrient analyses of waters and aqueous sediment extracts, Lead-210 dating, and radioisotopic analyses of soils and sediments. The focus of the laboratory is guided by the scope of staff projects.
The main laboratory includes standard equipment such as fume hoods, an oven, furnace, analytical balances, pH meter, centrifuge, platform shaker, shaking water bath, water purification system, and walk-in cold room. This equipment is available to researchers on per day, or per sample, basis.
The SCWRS offers specialized analytical equipment such as a Lachat automated ion analyzer, Dionex DX-100 Ion Chromatograph, Phoenix 8000 UV persulfate carbon analyzer (with solids attachment), UV-Vis spectrophotometer and bulk freeze dryer. The research station operates a lead-210 lab with alpha spectrometers for dating sediments and a gamma spectrometry lab for radioisotope tracer analysis. This equipment is also available to researchers on a limited basis for set-up, per sample, and waste disposal fees; provided SCWRS analysts perform the analyses.
A fee schedule for analyses, laboratory use and other research services is available.
Why Date Sediments?
Lake sediments and peat cores are widely used to study environmental history, and one of the most important ingredients in such studies is an accurate chronology. Cores are usually dated with two goals in mind: (1) to establish the timing of past environmental change, and (2) to determine the accumulation of materials (e.g. sediment, pollutants, micro-fossils) in the lake or wetland.
For studies of human impacts (e.g. pollution, eutrophication, erosion), which typically focus on the last 100-200 years, the dating method of choice is 210Pb. Lead-210 is a naturally occurring radioisotope in the 238U-decay series formed by decay of 226Ra, and the subsequent evasion of the intermediary 222Rn (an inert gas) from the earth's surface. Radon-222 decays through a series of short-lived daughters to 210Pb which is stripped from the atmosphere in precipitation and accumulates in lake sediments and wetlands where it decays away with a half-life of 22 years. Cores are typically dated by analyzing a series of stratigraphic levels from the core surface to a depth where unsupported 210Pb is no longer measurable (roughly 5-8 half-lives). From the resulting 210Pb profile, dates are calculated according one of several mathematical models that make assumptions regarding the accumulation of 210Pb and sediment at the core site.
Additional dating markers should be sought whenever possible to validate the 210Pb chronology. This is especially critical for sites with disturbed watersheds and highly variable sedimentation rates, which are more prone to errors in 210Pb dating. Among the most important of these ancillary dating tools is 137Cs, which provides maker horizons for the 1964 peak from atmospheric nuclear testing and, in Europe, the 1986 peak from the Chernobyl nuclear accident.
The radiometric dating laboratory at the St. Croix Watershed Research Station is equipped with an EG&G Nuclear alpha spectrometry system (24 detectors), polonium distillation equipment, and 209Po and 210Pb standards. This capacity allows one to two lake sediment or peat cores to be dated each week. In addition, the Station has two EG&G Nuclear ultra-low background gamma spectrometers (well-detectors) for measurement of environmental levels of 137Cs, 7Be, 226Ra, and 210Pb by non-destructive direct gamma assay. The SCWRS dating labs are in near-continuous use for both "in-house" and outside research projects. More than 1,000 cores have been dated for research projects involving 100 institutions and university departments since 1996.
Four carrels are available for microscope studies. Research grade stereo and compound microscopes with digital imaging are available. A Leica dissecting scope, Nikon compound scope and three Olympus compound scopes with phase, darkfield, brightfield, or nomarski are current equipment. Cameras and computer interface are also available. Scopes and accessories are subject to availability.
Appleby, P. G. 2001. Chronostratigraphic techniques in recent sediments. Pages 171-203 in W. M. Last and J. P. Smol, editors. Tracking Environmental Change Using Lake Sediments. Volume 1: Basin Analysis, Coring, and Chronological Techniques. Kluwer Academic Publishers, Dordrecht.
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