Representative results of gel electrophoresis of amplified DNA.

<p>Shows the presence of the yellow perch barcode sequence (CO1) in sediment samples from 55 cm and 125 cm depths in the Lower Saint Regis core. YP = Yellow perch barcode. C = No-template control lane. Arrow indicates 100 base pair position on molecular ruler lane.</p

Sequence alignment.

<p>Cloned insert with yellow perch mitochondrial cytochrome oxidase subunit 1 (GenBank voucher PEFL-ON-BLAC-4–3).</p

Site maps.

<p>A. Approximate range of yellow perch in the United States shown in gray (after reference 8). Note the prominent gap in northern New York, with the Adirondack Park boundary superimposed in bold. Scattered relict populations along the Florida coast (reference 33) not shown. B. The Adirondack State Park, NY. Lower Saint Regis Lake indicated by star. LC = Lake Champlain. LO = Lake Ontario. C. Saint Regis chain of lakes in Paul Smiths, NY. Coring site indicated by star.</p

Comparison of temperature and precipitation in eastern Massachusetts since A.D. 1880 with ice-out and microfossil records from Walden Pond.

<p>(a, b) Precipitation and temperature, respectively, at Bedford, MA. (c) Ice-out dates at Houghton's Pond, MA. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191755#pone.0191755.ref047" target="_blank">47</a>] (d,e) Spring ice-out dates at Walden Pond recorded by Thoreau [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191755#pone.0191755.ref001" target="_blank">1</a>],[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191755#pone.0191755.ref004" target="_blank">4</a>],[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191755#pone.0191755.ref048" target="_blank">48</a>] and Primack [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191755#pone.0191755.ref004" target="_blank">4</a>], respectively. (f, h) Percentages of <i>Asterionella</i> and <i>Synedra</i> (A&S) in cores WAL-3 and WAL-15, respectively. (g,h) Ratios of chrysophyte scales to diatoms (S:D) in cores WAL-3 and WAL-15, respectively. Horizontal dotted line indicates mean ice-out date at Walden Pond since A.D. 1880. Vertical dotted lines (1,2) indicate approximate onset of main increase in A&S percentages in cores WAL-3 and WAL-15, respectively.</p

Percent abundances of the most common diatom taxa and %LOI in core WAL-3.

<p>Horizontal dotted lines: (1) Onset of low <i>Cyclotella</i> percentages. (2) Decrease in %LOI indicating reduced organic matter content in the sediments. (3) Onset of increased <i>Asterionella and Synedra</i> percentages. (4) First peak of chrysophyte scale abundances. Letter "A" indicates last occurrence of <i>Mallomonas allorgei</i>.</p

Percentages of the most common diatom taxa and %LOI in core WAL-4.

<p>Horizontal dotted line indicates transition to high percentages of <i>Asterionella</i> and <i>Synedra</i>.</p

Percentages of the most common diatom taxa and %LOI in core WAL-1.

<p>Horizontal dotted line indicates transition to high percentages of <i>Asterionella</i> and <i>Synedra</i>.</p

Age-depth relationships for Walden Pond cores WAL-3 and WAL-15.

<p>Solid lines represent the upper and lower 95% confidence intervals of the BACON age models. Dotted lines indicate the "best" model based on the weighted mean ages. Horizontal bars represent calibrated radiocarbon ages. Note the slightly different age scales in the two charts.</p

Location maps.

<p>(a) Southern New England, with the location of Walden Pond indicated by a star. (b) Walden Pond bathymetry with coring sites indicated. Numbers correspond to the numbers of the "WAL" cores discussed in the text. Regional map from <a target="_blank">http://d-maps.com/carte.php?num_car=7175&lang=en</a> under a CC BY license, with permission from <a href="http://d-maps.com" target="_blank">d-maps.com</a>, original copyright 2007.</p

Comparison of sediment core records representing hydroclimate at Walden Pond and elsewhere in the northeastern United States.

<p>a, b. Percent planktonic diatoms in Walden Pond cores WAL-3 and WAL-15, respectively. Data after ca. A.D. 1930 primarily represent increased cultural eutrophication rather than climate alone. c. Composite hydroclimate record derived from varved sediments of a lake and estuary in New York and Massachusetts, respectively [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191755#pone.0191755.ref038" target="_blank">38</a>]. Horizontal bars represent drought periods at Little Pond, MA (upper)[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191755#pone.0191755.ref036" target="_blank">36</a>] and the New England region (lower)[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191755#pone.0191755.ref034" target="_blank">34</a>]. Vertical dotted lines #1–2 bracket the A.D. 1150–1300 interval, line #3 indicates approximate onset of cultural eutrophication. Asterisks indicate core-intervals with calibrated radiocarbon ages.</p