8 research outputs found
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
Relationship between the Concentrations of Dissolved Organic Matter and Polycyclic Aromatic Hydrocarbons in a Typical U.K. Upland Stream
Concentrations of total and freely
dissolved polycyclic aromatic
hydrocarbons (PAHs) and dissolved organic carbon (DOC) were measured
in water collected during four sampling events at five sites from
the River Wyre. The sites are typical of streams draining upland organically
rich soils in northwest U.K. Freely dissolved PAHs were separated
from those associated with DOC using a flocculation method. The sum
of concentrations of the total and freely dissolved PAHs analyzed
ranged from 2.71 to 18.9 ng/L and 2.61 to 16.8 ng/L, respectively.
PAH concentrations and PAH fluxes derived from concentrations and
water flow rates generally increased downstream, the trend in the
latter being more pronounced. The concentration of individual PAHs
containing five or more aromatic rings was found to be strongly correlated
to the DOC concentration (<i>p</i> < 0.0001), suggesting
common terrestrial sources and hydrological pathways. In contrast,
no significant relationships were observed between concentrations
of PAHs with four or fewer rings and DOC. Concentrations of PAHs with
more than four rings showed similar seasonal variation as DOC concentration
(peaking in the late summer), while variation in two or three ring
PAHs was out of phase with DOC (peaking in the winter). As the PAH–DOC
relationship appeared partly dependent on the molecular weight of
the PAHs, a linear regression function that included an interaction
between this variable and DOC concentration was used to model PAH
concentrations over a 2 year period to estimate annual fluxes. The
relationship identified between PAH concentrations and DOC should
help to enhance interpretation of PAH monitoring data that are currently
sparse both spatially and temporally and, thus, enable more robust
assessments of the potential risks of these environmental pollutants
to sensitive aquatic organisms and human water supplies
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 10<sup>3</sup> m<sup>2</sup>, red), and Sparkling Lake (surface area 6.2 x 10<sup>5</sup> m<sup>2</sup>, blue), both situated in Wisconsin, USA.</p
First derivatives of the fitted generalised additive model.
<p>The red line indicates those parts of the model fit that are statistically significantly changing and the shaded region shows the 95% confidence intervals.</p
Fitted splines for the Generalised Additive Model.
<p>The y-axis is the additive contribution of the spline to the fitted model over the range of the covariate. The smooth functions are subject to centring constraints and are plotted here on different scales for clarity. The shaded region is an approximate 95% confidence interval on the function; however, it excludes uncertainty in the model's constant term, β<sub>0</sub>, hence the narrowness of the interval at the “middle” of the distribution for the smooths of altitude and latitude.</p
Summary output from the fitted statistical model.
<p>Summary of the model used to describe the influence of surface area (A<sub>0</sub>), the percent transmission per metre (I<sub>z</sub>), 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><sub><i>z</i></sub> is the percent transmission per meter.</p
Estimated ecological and biogeochemical consequences of the diel surface temperature range.
<p>Potential bias in estimates of CO<sub>2</sub> and O<sub>2</sub> solubility and rates of processes with Q<sub>10</sub> values of 2 or 4 for a diel temperature range of 1 (blue) or 7°C (red).</p