Diel surface temperature range scales with lake size

Ecological and biogeochemical processes in lakes are strongly dependent upon water temperature. Long-term surface warming of many lakes is unequivocal, but little is known about the comparative magnitude of temperature variation at Diel timescales, due to a lack of appropriately resolved data. Here we quantify the pattern and magnitude of Diel temperature variability of surface waters using high-frequency data from 100 lakes. We show that the near-surface Diel temperature range can be substantial in summer relative to long-term change and, for lakes smaller than 3 km2, increases sharply and predictably with decreasing lake area. Most small lakes included in this study experience average summer Diel ranges in their near-surface temperatures of between 4 and 7°C. Large Diel temperature fluctuations in the majority of lakes undoubtedly influence their structure, function and role in biogeochemical cycles, but the full implications remain largely unexplored

Mean (±95% CI) Carbon emissions.

<p>a) CO₂ fluxes of total sediment respiration (R_S) (solid line with filled squares), heterotrophic respiration (R_H) (dashed line with open circles) in control plots and CO₂ fluxes from treated plots (broken line with open squares) and b) CH₄ emissions in <i>R. mucronata</i> forest at Gazi bay Kenya. Vertical broken lines indicate periods when trees were girdled and cut in the treatment plots. Sampling for baseline, girdled and cut periods were done from June 2009 to August 2009 (84 days), December 2009 to May 2010 (189 days) and May 2010 to April 2011 (343 days), respectively. The controls and the treatment consisted of five replicates each.</p

Trends in δ¹³C of sediment respired CO₂ in control and treated sites in <i>R. mucronata</i> forest at Gazi bay, Kenya.

<p>Values are means ±95% CI. Vertical broken line indicates when the trees were clear-cut in treatment plots. The controls and the treatment consisted of five replicates each.</p

Trends in surface elevation change in control and treated sites in <i>R. mucronata</i> forest at Gazi bay, Kenya.

<p>Error bars are 95% CI. Vertical broken lines indicate periods when trees were girdled and cut in the treatment plots. Baseline, girdled and cut periods ran from March 2009 to October 2009 (205 days), December 2009 to May 2010 (189 days) and May 2010 to April 2011 (343 days), respectively. The controls and the treatment consisted of five replicates each.</p

Nested design ANOVA for carbon fluxes in <i>R. mucronata</i> secondary forest, with mean data for each of six chambers per plot nested within treatment; the data for CO₂ were log-transformed.

<p>Nested design ANOVA for carbon fluxes in <i>R. mucronata</i> secondary forest, with mean data for each of six chambers per plot nested within treatment; the data for CO₂ were log-transformed.</p

Belowground roots and sediment biochemical characteristics in control and cut plots in <i>R</i>.<i>mucronata</i> forest at Gazi bay, Kenya.

<p>Values are means ±95% CI, OC_R =  organic carbon content of mangrove roots, δ¹³C_R and δ¹³C_S =  carbon isotopic value of mangrove roots and sediment organic matter, respectively, and TOC and TN =  total carbon and nitrogen content of the sediment organic matter, respectively.</p><p>*Sediment C stocks to 1 m depth.</p><p>Belowground roots and sediment biochemical characteristics in control and cut plots in <i>R</i>.<i>mucronata</i> forest at Gazi bay, Kenya.</p

Relationship between the diel range in lake surface water temperature and surface area.

<p>Relationship between the observed (light violet circles) and theoretical (red circles) diel surface temperature range with lake area during summer, with the solid line illustrating the fitted generalised additive model with 95% confidence interval shown by the shaded region; lake surface areas where the diel temperature range changes significantly (P < 0.001) are shown with a red line.</p

Temporal variability in near-surface lake water temperature.

<p>(a) Seasonal variability in the diel temperature range for 96 Northern Hemisphere lakes with 95% confidence intervals (note that not all lakes had data for the whole year). (b) Individually normalized (zero-mean) summer average diel cycle for the lakes that had the highest (red) and lowest (blue) 10% of diel temperature ranges measured. The bold lines represent the mean diel cycle for the 10% considered and the horizontal black line indicates zero. For clarity, we excluded Jekl Bog, which had the highest diel cycle, from this figure. (c) Example of hourly-resolution near-surface lake water temperature variation at Jekl Bog (surface area 2.5 x 10³ m², red), and Sparkling Lake (surface area 6.2 x 10⁵ m², blue), both situated in Wisconsin, USA.</p

Summary output from the fitted statistical model.

<p>Summary of the model used to describe the influence of surface area (A₀), the percent transmission per metre (I_z), altitude above sea level (h), and latitude (φ), as shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0152466#pone.0152466.e003" target="_blank">Eq 3</a>, on the diel surface temperature range. EDF is the effective degrees of freedom for the spline representing each covariate. Ref. DF is the reference degrees of freedom used in the statistical test of “no effect” for each smooth. F is the test statistic and <i>p</i> the approximate <i>p</i>-value of the test. <i>I</i>_<i>z</i> is the percent transmission per meter.</p

Estimated ecological and biogeochemical consequences of the diel surface temperature range.

<p>Potential bias in estimates of CO₂ and O₂ solubility and rates of processes with Q₁₀ values of 2 or 4 for a diel temperature range of 1 (blue) or 7°C (red).</p