Lake Thermal Regimes Research Articles

Effect of chromophoric dissolved organic matter on epilimnetic stratification in lakes

Empirical studies on lake thermal regimes have shown that stratification is correlated with the concentration of dissolved organic matter (DOM). Thermal stratification has implications for photosynthesis, photoinhibition, photobleaching and carbon cycling. The objectives of this study were to quantify the role of chromophoric DOM (CDOM) on epilimnetic thermal structure and to estimate the contribution of ultraviolet (UV), visible and infrared radiation (IR) to the near-surface warming of lakes as a function of their DOM content. A simplified thermal model was applied, assuming all energy absorbed by the system is converted to heat and excluding mixing and heat losses. For the upper 0.5 m of the water column, the model generated a temperature increase of 1.5 °C after one hour of noon irradiance in a strongly humic lake, as compared to 1 °C in pure water. UV, visible light and IR contributed 6, 32 and 62% of warming in the humic lake, compared to 0, 5 and 95% in pure water. As CDOM absorption coefficient increases, UVA and especially visible light play an increasing role in stratification. Field data also support the significant role of CDOM absorption on near-surface thermocline occurrence. Near-surface stratification was a common feature during summer in a lake with a moderate DOC content (4.8 mg L−1) and color (a320 = 16.4 m−1). Based on a temperature-stability criterion of 0.2 °C m−1, this lake had a stable epilimnion 64% of the time, compared to 53% for a lake that had much lower DOC concentration (1.8 mg L−1) and color (3 m−1).

Cooling lakes while the world warms: Effects of forest regrowth and increased dissolved organic matter on the thermal regime of a temperate, urban lake

Depending on the magnitudes and directions of changes in air temperatures, winds, and underwater light attenuation, lakes may either warm or cool. Here we report a 28‐yr decrease in the whole‐lake average temperature of Clearwater Lake, Canada, despite regional signatures of climate warming. Using a one‐dimensional lake mixing model, we demonstrate that this pattern was attributable to a 35% reduction in surface wind speeds, itself explained by forest regrowth following local SO2 emission reductions and tree planting, and a 10‐fold increase in dissolved organic carbon concentrations causing a substantial increase in vertical light attenuation following deacidification of the lake. Long‐term trends in lake temperatures do not necessarily follow those of air temperatures. The Clearwater Lake data demonstrate that any factors that influence local wind speeds and underwater light attenuation should be considered as modifiers of the effects of climate warming on lake thermal regimes.

Interannual and Seasonal Variability of the Surface Energy Balance and Temperature of Central Great Slave Lake

This paper addresses interannual and seasonal variability in the thermal regime and surface energy fluxes in central Great Slave Lake during three contiguous open-water periods, two of which overlap the Canadian Global Energy and Water Cycle Experiment (GEWEX) Enhanced Study (CAGES) water year. The specific objectives are to compare the air temperature regime in the midlake to coastal zones, detail patterns of air and water temperatures and atmospheric stability in the central lake, assess the role of the radiation balance in driving the sensible and latent heat fluxes on a daily and seasonal basis, quantify magnitudes and rates of the sensible and latent heat fluxes and evaporation, and present a comprehensive picture of the seasonal and interannual thermal and energy regimes, their variability, and their most important controls. Atmospheric and lake thermal regimes are closely linked. Temperature differences between midlake and the northern shore follow a seasonal linear change from 68C colder midlake in June, to 68C warmer in November‐December. These differences are a response to the surface energy budget of the lake. The surface radiation balance, and sensible and latent heat fluxes are not related on a day-to-day basis. Rather, from final lake ice melt in mid-June through to mid- to late August, the surface waters strongly absorb solar radiation. A stable atmosphere dominates this period, the latent heat flux is small and directed upward, and the sensible heat flux is small and directed downward into the lake. During this period, the net solar radiation is largely used in heating the lake. From mid- to late August to freeze up in December to early January, the absorbed solar radiation is small, the atmosphere over the lake becomes increasingly unstable, and the sensible and latent heat fluxes are directed into the atmosphere and grow in magnitude into the winter season. Comparing the period of stable atmospheric conditions with the period of unstable conditions, net radiation is 6 times larger during the period of stable atmosphere and the combined latent and sensible heat fluxes are 9 times larger during the unstable period. From 85% to 90% of total evaporation occurs after mid-August, and evaporation rates increase continuously as the season progresses. This rate of increase varies from year to year. The time of final ice melt exerts the largest single control on the seasonal thermal and energy regimes of this large northern lake.

Seasonality of planktonic ciliated protozoa in 20 subtropical Florida lakes of varying trophic state

The planktonic ciliate populations of 20 Florida lakes ranging from oligotrophic to hypereutrophic were examined monthly for one year. Oligotrophic lakes displayed abundance peaks during fall mixis and biomass peaks in late winter and fall. Mesotrophic systems exhibited a spring-fall bimodality in ciliate abundance with a biomass maxima occurring during fall. Eutrophic/hypereutrophic lakes had pronounced abundance and biomass maxima during summer, with the large ciliates Plagiopyla nasuta and Paramecium trichium often contributing heavily to the midsummer biomass peak. Members of the Oligotrichida numerically dominated abundance and biomass peaks in oligotrophic lakes while the Scuticociliatida dominated the communities of higher trophic states. Total ciliate abundance and biomass were strongly correlated with chlorophyll a concentrations as were various ciliate taxonomic groups. The relationship between ciliate seasonal distribution in these subtropical lakes with lake thermal regimes and trophic state is discussed.

Biogeographic Associations in Fish Assemblages: Local vs. Regional Processes

Six geographic regions along the Laurentian Great Lakes in Ontario, represented by 286 lakes, were examined to identify the existence of regional similarities of fish species composition and their association to geographic location and regional patterns of lake morphology and pH. Lakes differed significantly among regions with respect to surface area, maximum depth, and pH. Species presence/absence data were summarized using correspondence analysis, and the resultant scores were used in multivariate analysis of variance and canonical variates analysis. These results indicated that the fish faunas of the six geographical areas were distinct. Interregional distances based on fish community scores, lake morphology–chemistry data, and geographical distances were contrasted using Mantel's test. Regional faunal similarities were correlated significantly with geographical proximity, but not with lake morphology. We propose that post—glacial dispersal and lake thermal regimes are important determinants in structuring regional patterns of fish assemblages, whereas environmental conditions such as lake depth and pH assume greater importance in determining species compositions of individual lakes.

Modeling the annual thermal regime of lake Ohrid, Yugoslavia, using daily weather data

The time-dependent characteristics of the five weather variables which control the annual thermal response of Lake Ohrid are analyzed in detail. These are daily values for solar radiation, air temperature, humidity, wind speed and cloud cover. A simple numerical model of the lake's thermal response, forced by thermally driven density mixing, is developed and tested using observed thermal profiles for verification. The numerical model successfully reproduces the major features of the lake's thermal regime over a 6 y period from 1972 to 1977, the average root mean square value for the simulated profiles being 1.2°C with extremes of 2.2 and 0.3°C and a standard deviation of 0.4°C.