Taconite Inlet Project


2. Methods

On the lake several techniques were employed to monitor sediment flux from diurnal to seasonal periods. Research at Lake C2 was conducted over three field seasons of varying length:

Prior to early season runoff, baseline measurements were taken and instruments and samplers that overwintered were recovered. Observations and various types of sampling were undertaken from the lake-ice surface at a series of stations located in a grid-like pattern in front of the main inlet stream. Other outlying stations were sited in peripheral locations as needed. (Map of Lake C2 showing stations)


CTD-Profiling

Measurement of temperature, conductivity, dissolved oxygen and light transmission in the water column were taken using a Seabird Instruments Seacat SBE 19 profiler, equipped with a Sea Tech transmissometer with 25-cm path length. Vertical casts were made with the instrument which was lowered at a rate of two seconds per meter from the ice surface. Values were recorded at a frequency of two measurements per second and stored on board. The transmissometer data were used to measure relative changes in light transmission (as a proxy for suspended sediment concentration) at depth and spatially in the lake over the course of each field season. In 1990 the Seacat instrument was utilized to provide background measurements and some water column profiles of selected runoff events. In the 1991 and 1992 field seasons, a more rigorous sampling program included daily or twice-daily sampling of a representative grid of samples across the lake. During peak runoff, measurements were taken at 4-hour intervals (0100, 0500, 0900, 1300, 1700, and 2100 hrs) at two sites near the main inlet.


Secchi disk surveys

Secchi transparency surveys were also undertaken twice daily at the observation holes on the ice surface with a standard 20 cm diameter, black and white quadrant Secchi disk to approximate the relative concentration and spatial distribution of suspended sediment in the surface sediment plume.


Sediment Traps

Sediment trap arrays were deployed at sites on the grid pattern over the three-year period. The trap arrays consisted of 1-liter wide-mouth Nalgene poly bottles suspended vertically on 6 mm diameter polypropylene line just below the water surface, above and below the chemocline of the lake, and just above the sediment/water interface. Most traps were designated as seasonal traps which were deployed before runoff started each year. Another set of sediment traps were depolyed approximately 100meters offshore of the main inlet delta.

Sediment Transport and Deposition index page

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