Table S1 Data from ramped pyrolysis 14C analysis individual temperature intervals River-Year Depth Interval Collection Year Measurement Year High Temperature Interval mmol CO2 fM 1s fM d13C 1s d13C d14C 1s d14C D14C 1s D14C MR-2008 Surface 2008 2010 335 17.5 0.8777 0.0043 -26.28 0.1 -122.3 4.3 -122.5 4.3 MR-2008 Surface 2008 2010 395 17.93 0.8212 0.0051 -24.59 0.1 -178.8 5.1 -179.0 5.1 MR-2008 Surface 2008 2010 446 18.12 0.796 0.0057 -24.1 0.1 -204 5.7 -204.2 5.7 MR-2008 Surface 2008 2010 508 19.1 0.7471 0.0055 -25.12 0.1 -252.9 5.5 -253.1 5.5 MR-2008 Surface 2008 2010 1000 24.31 0.683 0.0039 -25.97 0.1 -317 3.9 -317.2 3.9 MR-2008 Inter. 2008 2010 354 18.8 0.8687 0.0044 -26.41 0.1 -131.3 4.4 -131.5 4.4 MR-2008 Inter. 2008 2010 424 18.2 0.8517 0.0041 -24.66 0.1 -148.3 4.1 -148.5 4.1 MR-2008 Inter. 2008 2010 480 18 0.8027 0.0045 -24.67 0.1 -197.3 4.5 -197.5 4.5 MR-2008 Inter. 2008 2010 538 19.7 0.7667 0.0042 -25.51 0.1 -233.3 4.2 -233.5 4.2 MR-2008 Inter. 2008 2010 1000 24.61 0.6858 0.0035 -26.59 0.1 -314.2 3.5 -314.4 3.5 MR-2008 Bottom 2008 2010 341 20 0.8587 0.0049 -26.95 0.1 -141.3 4.9 -141.5 4.9 MR-2008 Bottom 2008 2010 407 18.1 0.8339 0.0061 -24.81 0.1 -166.1 6.1 -166.3 6.1 MR-2008 Bottom 2008 2010 460 18.3 0.7879 0.0058 -24.28 0.1 -212.1 5.8 -212.3 5.8 MR-2008 Bottom 2008 2010 520 19.6 0.76 0.0056 -25.27 0.1 -240 5.6 -240.2 5.6 MR-2008 Bottom 2008 2010 1000 24.24 0.7047 0.0035 -26.06 0.1 -295.3 3.5 -295.5 3.5 MR-2009 Surface 2009 2010 321 14.26 0.9856 0.0026 -24.17 0.1 -14.4 2.6 -14.5 2.6 MR-2009 Surface 2009 2010 375 14.48 0.9746 0.0036 -22.48 0.1 -25.4 3.6 -25.5 3.6 MR-2009 Surface 2009 2010 419 14.55 0.9182 0.0023 -22.44 0.1 -81.8 2.3 -81.9 2.3 MR-2009 Surface 2009 2010 466 15.46 0.8924 0.0023 -22.4 0.1 -107.6 2.3 -107.7 2.3 MR-2009 Surface 2009 2010 1000 28.37 0.856 0.0023 -24.12 0.1 -144 2.3 -144.1 2.3 MR-2009 Inter. 2009 2010 323 19.6 - - - - - - - - MR-2009 Inter. 2009 2010 379 16.4 0.984 0.0042 35 0.1 -16 4.2 -16.1 4.2 MR-2009 Inter. 2009 2010 425 19.6 0.9402 0.0024 20 0.1 -59.8 2.4 -59.9 2.4 MR-2009 Inter. 2009 2010 475 23.5 0.8826 0.0022 20 0.1 -117.4 2.2 -117.5 2.2 MR-2009 Inter. 2009 2010 1000 52.3 0.8133 0.0019 20 0.1 -186.7 1.9 -186.8 1.9 MR-2009 Bottom 2009 2010 316 20.9 0.9367 0.0023 20 0.1 -63.3 2.3 -63.4 2.3 MR-2009 Bottom 2009 2010 375 24 0.9259 0.002 15 0.1 -74.1 2 -74.2 2 MR-2009 Bottom 2009 2010 420 23.7 0.8632 0.002 20 0.1 -136.8 2 -136.9 2 MR-2009 Bottom 2009 2010 459 20.2 0.8211 0.002 20 0.1 -178.9 2 -179.0 2 MR-2009 Bottom 2009 2010 1000 41.3 0.7688 0.0019 20 0.1 -231.2 1.9 -231.3 1.9 MRO-2009 Surface 2009 2010 349 16.6 0.9108 0.0022 -26.78 0.1 -89.2 2.2 -89.3 2.2 MRO-2009 Surface 2009 2010 411 15.9 0.8927 0.0021 -24.39 0.1 -107.3 2.1 -107.4 2.1 MRO-2009 Surface 2009 2010 461 16.6 0.85 0.0021 -23.69 0.1 -150 2.1 -150.1 2.1 MRO-2009 Surface 2009 2010 533 21.6 0.8009 0.0019 -24.61 0.1 -199.1 1.9 -199.2 1.9 MRO-2009 Surface 2009 2010 1000 27.7 0.7034 0.0025 -25.96 0.1 -296.6 2.5 -296.7 2.5 MRO-2009 Inter. 2009 2010 362 15 0.8551 0.0024 - - -144.9 2.4 -145.0 2.4 MRO-2009 Inter. 2009 2010 432 13.5 0.8625 0.0021 -24.14 0.1 -137.5 2.1 -137.6 2.1 MRO-2009 Inter. 2009 2010 492 13.1 0.8118 0.0018 -23.7 0.1 -188.2 1.8 -188.3 1.8 MRO-2009 Inter. 2009 2010 572 15 0.7398 0.0017 -24.57 0.1 -260.2 1.7 -260.3 1.7 MRO-2009 Inter. 2009 2010 1000 12.2 0.6084 0.0023 -24.52 0.1 -391.6 2.3 -391.7 2.3 AR-2009 Surface 2009 2010 318 14.7 - - - - - - - - AR-2009 Surface 2009 2010 378 16.4 0.9167 0.0027 25 0.1 -83.3 2.7 -83.4 2.7 AR-2009 Surface 2009 2010 420 15 0.8842 0.0021 20 0.1 -115.8 2.1 -115.9 2.1 AR-2009 Surface 2009 2010 496 28.8 0.8536 0.0018 15 0.1 -146.4 1.8 -146.5 1.8 AR-2009 Surface 2009 2010 1000 44.2 0.8139 0.0017 15 0.1 -186.1 1.7 -186.2 1.7 AR-2009 Inter. 2009 2010 312 15.9 0.949 0.0024 20 0.1 -51 2.4 -51.1 2.4 AR-2009 Inter. 2009 2010 371 18.8 0.9464 0.0019 15 0.1 -53.6 1.9 -53.7 1.9 AR-2009 Inter. 2009 2010 420 21.8 0.885 0.0018 15 0.1 -115 1.8 -115.1 1.8 AR-2009 Inter. 2009 2010 464 19.3 0.8628 0.0019 20 0.1 -137.2 1.9 -137.3 1.9 AR-2009 Inter. 2009 2010 1000 45.2 0.8449 0.0028 25 0.1 -155.1 2.8 -155.2 2.8 ARO-2009 Surface 2009 2010 325 17 0.909 0.0021 -26.02 0.1 -91 2.1 -91.1 2.1 ARO-2009 Surface 2009 2010 385 18.7 0.8679 0.0019 -24.43 0.1 -132.1 1.9 -132.2 1.9 ARO-2009 Surface 2009 2010 437 19.2 0.8109 0.0022 -23.8 0.1 -189.1 2.2 -189.2 2.2 ARO-2009 Surface 2009 2010 502 18.7 0.781 0.0018 -25.26 0.1 -219 1.8 -219.1 1.8 ARO-2009 Surface 2009 2010 1000 22.1 0.7004 0.0019 -24.81 0.1 -299.6 1.9 -299.7 1.9