Goldie is back in the lab after spending the summer of 2014 on Great Pond.
The following slides show typical views of Great Pond’s current temperature, oxygen, and plankton abundance while the buoy was deployed. We welcome your comments on new or improved ways to display the data.
1) A cartoon of the lake conditions. Most items like wind, oxygen and temperature are physical measurements. Surface flow, upwelling/downwelling, and Secchi depth are computed parameters. We are still working on the upwelling/downwelling arrow. Secchi depth is only displayed during the day since we use light attenuation to compute this value.
4) Temperature at all depth in Great Pond (top panel) and biomass (bottom panel). Notice how the surface of the lake warms in the summer and cools in the fall. Mixing events are marked by sudden changes in temperature. These are often followed a week later by blooms.
5) Heat maps of Great Pond on 2014 and 2013. This is the same data shown in Figure 4, but plotted as a contour map (also known as a heat map).
The graphs below show some of the 2013 data for Great Pond, Belgrade Lakes, Maine. Watch the real-time 2014 data and compare to the lake in 2013.
Graph of average water temperatures at different depths over 2013, as graphed by Lake Analyzer. This heat plot shows the temperature using the color scale on the right. Notice the warm surface water (25 0C) during the months of July and August. Rapid changes in temperature result in a thermocline (temperature gradient) which becomes a barrier to water mixing. Notice that the thermocline is weak or absent in the spring and fall when the lake mixes top to bottom.
Calculated thermocline depths as function of time. We used Lake Analyzer to perform these calculations.
Water temperature determines water density and less dense water floats. During the summer the less dense warm water floats on top of the cold deep water. It takes energy to mix the layers of water. The Schmidt Stability (St) is a calculation of the lakes resistance to mixing. It is defined as the amount of work (wind energy) needed to de-stratify the lake (Schmidt, 1928). It is used to estimate changes in dissolved oxygen. St is largest when the thermocline is the most developed.
The Lake Number (Ln) is a calculated a ratio of the stabilizing force of gravity associated with density stratification to the destabilizing forces of wind, inflow, outflow, and cooling. It is an indication of deep mixing in lakes and can also be used to estimate changes in deep water dissolved oxygen concentrations. The assumption is made that wind is the dominating destabilizing force, and the other destabilizing forces are negligible. When Ln = 1, wind is just sufficient to force the seasonal thermocline to be deflected to the surface at the upwind end of the lake. When Ln > 1, stratification is dominant. When Ln < 1, stratification is weak with respect to wind stress (Robertson and Imberger, 1994). St differs from Ln in that it is a measure of the stratification within the lake while Ln is a measure of mixing occurring (Robertson and Imberger, 1994). Notice that the lake is most stable with respect to mixing during the warm, summer months, but mixing events do occur – particularly in June and September.
Imberger, J., Patterson, J.C. Physical limnology. Advances in Applied Mechanics, 27 (1990), pp. 303–475
Read, Jordan S., Hamilton, David P., Jones, Ian D., Muraoka, Kohji, Winslow, Luke A., Kroiss, Ryan, Wu, Chin H., Gaiser, Evelyn. Derivation of lake mixing and stratification indices from high-resolution lake buoy data, Environmental Modelling & Software, Volume 26, Issue 11, November 2011, Pages 1325-1336, ISSN 1364-8152, http://dx.doi.org/10.1016/j.envsoft.2011.05.006.
Robertson, D.M., Imberger, J. 1994. Lake Number, a quantitative indicator of mixing used to estimate changes in dissolved-oxygen. Internationale Revue der gesamten Hydrobiologie, 79, pp. 159–176.
Schmidt, W. Über Temperatur and Stabilitätsverhaltnisse von Seen. Geographiska Annaler, 10 (1928), pp. 145–177
Thompson, R.O.R.Y., Imberger, J., 1980. Response of a numerical model of a stratified lake to wind stress. In: Proc. 2nd Int. Symp. Stratified Flows, Trondheim, June 1980. vol. 1, pp. 562–570.