- University of Guelph
Summary
Measurements made in shallow lakes and tanks have shown that temperatures near and at the surface of substrates respond significantly to changes in solar radiation, water circulation and substrate color. Temperature differences between light and dark colored natural and artificial substrates ranged between 0.8 and 4.0 C°. Diurnal surface temperature ranges on a submerged black wooden disk varied 9C° when incoming solar radiation varied 14% or average daily windspeed changed from 0.9 to 3.6 ms−1. Fluctuations in substrate temperatures were poorly correlated with changes in nearby air or water temperatures.
Methodology
Lake study method.
Preliminary observations were made using a thermistor attached to the tip of a fishing pole. This could be conveniently placed on different substrates in shallow water and the temperature recorded. Lake observations made to define the specific aspects of this study were similar in method to those previously reported (loc. cit.) using a series of thermister probes and a switching box. The thermistor probes and recorder were arranged on August 6, 1973, in the shallow water of a semicircular bay, 10 m in diameter, facing SE, on the shore of Sheep Island, Lake Opinicon (44 ° 37'N; 760° 8'W). Open water temperatures at 1.0 m were taken in the centre of the small bay where there were no macrophytes and the water depth was 3 m. Air temperatures were taken at 2 m with the sensor in the shade and suspended from a lower branch of a hemlock tree (Tsuga). A third probe was placed within 2 m of the shore in the light-colored, sloping sand, I cm below the surface, at water depth of 0.5 m.
Tank studies methods.
The following investigations took place at Guelph University 43°35'N, 80° 4 'W in an open, treeless, level field where an area, 16 m x 19 m, was enclosed by a chain fence 1.9 m high. To reduce windspeeds within the enclosure, a 1.3 m snow fence of wooden slats spaced 5.5 cm apart, having width and thickness of 3.5 and 0.7 cm, was wired onto the lower two-thirds of the chain fence. Wind speed and direction were monitored (Weather Measure Recording Wind System Model W 123-25-12) at the level of the water surface in the test tanks located nearby. Four white cylindrical plastic containers, 77 cm x 47 cm, their outer sides covered with aluminum foil to restrict energy flow through the tank walls, were placed 5 cm apart on a raised plywood platform. In each waterfilled container a wooden disk, 46.8 cm (diameter) x 1.4 cm, was held in position at either 1.5 or 21.5 cm below the water surface. These disks had been painted with boat enamel, one white, one black, one yellow (7.5YR 7/11) and one green (o G 5/8). The color designation was coded using a Munsell color fan. In each tank three stainless steel thermistor probes (2.15 x 0.32 cm) were secured horizontally; one in a groove at the centre of the upper surface of the disk, one 5 cm above the disk and one 20 cm below. Connecting wires were run through holes to the bottom of the disk and thence to the side of the container. The surface probe was held tightly in the colored groove with a thin band of silicone sealant. Two air temperature sensors were suspended on a wooden pole 2 m from the containers, one at the water surface level (103 cm) and the other at 80 cm above the ground. The temperatures were read on an Atkins Model 64 meter switchbox and recorded as a continuous line on a Temperature Recorder model 400, Instrument Corp. of America. In addition to the twelve submerged probes and two for air temperatures, three standards of fixed resistance gave readings 0° , 14.7° and 300 C. These were useful in calibrating the chart record of the readings. Readings for each probe were recorded three times per hour.