Peat Temperature Regime of a Minnesota Bog and the Effect of Canopy Removal

Abstract

Peat bogs occupy approximately 6 000 000 ha in the cool sub-humid northern Lake States of the U.S.A. These peatlands are intimately associated with the regional water resources, often serving as the source of streamfiow. They also represent unique wetland ecosystems. Temperature is an important characteristic both of the bog environment and the quality of streamflow water. Alteration of peat temperature could result in changes in the surface vegetation and changes in microbial activity, so affecting the amount of organic matter accumulated (Clymo 1965; Lather & Cragg 1967; Moore & Bellamy 1974) and the quality of streamfiow water. Therefore, it is necessary to determine the temperature regimes of peat bogs in both undisturbed and disturbed situations prior to any large-scale alterations of management and energy input. Accordingly, temperature regimes were determined in a strip-cut black spruce bog to evaluate the effect of canopy removal. METHODS The study bog, located in northern Minnesota on the Marcell Experimental Forest (c. 47032'N, 93028'W), is approximately 560 m long and 140 m wide with the long axis oriented north and south. The peat profile of this lake-filled, forested bog has been described by Boelter (1964). The bog is isolated from the regional groundwater system. Precipitation and run-off from the adjacent uplands comprise the water input to the bog. Outflow is primarily as intermittent surface streamflow from the south end of the bog. In the winter of 1968-69, 30-m-wide strips were clear-cut, in an east-west direction, leaving 45-m-wide strips of sixty-two-year-old black spruce (Picea mariana (Mill.) B.S.P.). The crown closure of the forested strips was& approximately 7500. The strips were logged when snow cover was ample, so that disturbance of the surface vegetation was negligible, and a luxuriant sedge cover rapidly established in the following summer (Brown 1972). Eight temperature stations were located at the south end of the bog and eight at the north end. Two stations were located in the centre of clear-cut strips, two were in the centre of the forested strips and four were on the boundaries between strips. Peat depth at the temperature stations ranged from 2 to 2-8 m. Each temperature station consisted of a series of copper-constantan thermocouples, located at depths of 0-025, 0 3, 1 and 2 m below the interface of the living sphagnum moss and the organic soil material. The thermocouples were inserted through a wooden stake 2-5 x 2-5 cm and 2 m long; the stake was pushed into the peat to the desired depth. Air temperatures were measured at two locations in the clear-cut strips and two locations in the non-cut strips by shaded thermocouples 1 m above the bog surface. Temperatures were read with a portable potentiometer. A battery-operated resistance heating unit was