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Climate change drives coherent trends in physics and oxygen content in North American lakes
Michelle E. Palmer1**, Norman D. Yan1,2, and Keith M. Somers2
1Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, M3J 1P3; 2Dorset Environmental Science Centre, 1026 Bellwood Acres Road, P.O. Box 39, Dorset, Ontario, P0A 1E0
email:
Electronic Supplementary Material
Online Resource 1
Below is a description of the lake parameters used to characterize the thermal status and oxygen content for the study lakes in Ontario and Wisconsin.
Lake thermal status was characterized using measures of stratification, mean temperature, heat content, and stability. The planar thermocline depth (Zthermo, in m) was the depth of greatest change in temperature ≥1ºC m-1 (Hutchinson 1957). During thermal stratification, the depth of the metalimnion (Zmeta) and hypolimnion (Zhypo) were determined as in Ingram (2004). During thermal homogeneity, Zthermo, Zmeta, and Zhypo were recorded as maximum lake depth (Robertson and Ragotzkie 1990). Maximum solar heat input was measured as the surface temperature (Tsurf). Mean lake temperature (Tlake) represented the sum, for each 1 or 2m stratum, of relative stratum volume multiplied by the mean temperature of the stratum (Birge 1915). Mean epilimnetic (Tepi), metalimnetic (Tmeta), and hypolimnetic (Thypo) temperature were similarly calculated. Heat content (H, in calories cm-2), the amount of heat beneath the average square centimeter of a lake’s surface area, was the sum, for each stratum, of the product of stratum volume, mean temperature, thermal capacity, and density (Cole 1994). Lake thermal stability (S), the amount of work per unit area required to mix a thermally-stratified lake to homothermy without the addition or subtraction of heat (Schmidt 1928), was calculated following Idso (1973) and expressed in g-cm cm-2 (Kjensmo 1994). The 10ºC depth (Z10º), a proxy of available cold-water fish habitat (Magnuson et al. 1990; Keller et al. 2005), was also determined.
Lake oxygen status was characterized using ecologically important measures of DO content. Volume-weighted metalimnetic (VWMO) and hypolimnetic (VWHO) oxygen content (in mg L-1) were the sum, for each stratum, of volume multiplied by DO and divided by the total volume for the metalimnion or hypolimnion, respectively (Quinlan et al. 2005). Total water volume with DO content ≤4mg L-1, a lower limit oxygen threshold for common cold water fish species (Brooke and Colby 1980; Evans et al. 1991), was also calculated (VDO4, in m3´105).
References
Birge EA (1915) The heat budgets of American and European lakes. Trans Wisconsin Acad Sci 18:1-47.
Brooke LT, Colby PJ (1980) Development and survival of embryos of lake herring at different constant oxygen concentrations and temperatures. Prog Fish-Cult 42:3-9.
Cole GA (1994) Textbook of limnology, 4th edn. Waveland Press, Prospect Heights
Evans DO, Casselman JM, Willox CC (1991) Effects of exploitation, loss of nursery habitat, and stocking on the dynamics and productivity of lake trout populations in Ontario lakes. Lake Trout Synthesis, Ontario Ministry of Natural Resources, Toronto
Hutchinson GE (1957) A treatise on limnology volume 1 geography, physics, and chemistry. Wiley, New York
Idso SB (1973) On the concept of lake stability. Limnol Oceanogr 18:681-683.
Ingram R (2004) Dorset Environmental Science Centre: lake sampling methods. Ontario Ministry of the Environment Technical Report, Dorset.
Keller W, Heneberry J, Leduc J (2005) Linkages between weather, dissolved organic carbon, and cold-water habitat in a Boreal Shield lake recovering from acidification. Can J Fish Aquat Sci 62:341-347.
Kjensmo J (1994) Internal energy, the work of the wind, and the thermal stability in Lake Tyrifjord, southeastern Norway. Hydrobiologia 286:52-59.
Magnuson JJ, Benson BJ, Kratz TK (1990) Temporal coherence in the limnology of a suite of lakes in Wisconsin, USA. Freshwater Biol 23:145-159.
Quinlan R, Paterson AM, Smol JP, Douglas MSV, Clark BJ (2005) Comparing different methods of calculating volume-weighted hypolimnetic oxygen (VWHO) in lakes. Aquatic Sci 67:97-103.
Robertson DM, Ragotzkie RA (1990) Changes in the thermal structure of moderate to large sized lakes in response to changes in air temperature. Aquatic Sci 52:360-380.
Schmidt W (1928) Über Temperatur und Stabilitätsvhältnisse von Seen. Georg Ann 10:145-177.
Online Resource 2
Below is a table summarizing the correlation of lake properties to the first two axes of the principal components analyses used to summarize temporal trends in the Ontario (DESC) and Wisconsin (NTL-TLA) lake districts. Correlations greater than 0.7 are indicated by bold-face type. Lake property abbreviations are defined in Table 2 in the associated article.
DESC / NTL-TLAAxis 1 / Axis 2 / Axis 1 / Axis 2
Variance explained (%) / 69.7 / 20.1 / 64.1 / 29.3
Lake property
Tsurf / 0.92 / - 0.35 / 0.97 / - 0.21
Tepi / 0.94 / - 0.31 / 0.97 / - 0.23
Tmeta / 0.81 / 0.07 / 0.86 / - 0.13
Tlake / 0.98 / 0.08 / 1.00 / - 0.02
H / 0.98 / 0.11 / 1.00 / - 0.01
S / 0.94 / - 0.26 / 0.81 / - 0.46
Zthermo / - 0.37 / 0.87 / - 0.47 / 0.85
Zmeta / - 0.49 / 0.73 / - 0.41 / 0.89
VWMO / ─ / ─ / 0.26 / - 0.91
Online Resource 3
Below is a figure of the redundancy analysis ordination triplots of the forward selected chemistry and morphometry variables (lines) in relation to the change in lake physical properties and oxygen content (open symbols) for the (a) Ontario, DESC and (b) Wisconsin, NTL-TLA lakes (closed symbols). Lake property abbreviations are defined in Table 2 in the associated article.