Bridget Tracy
Published: 2011
Total Pages: 114
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The purpose of this study is to track the loading of carbon (C) to Lake Tahoe as well as the losses of C from the lake for the period of a year (September 2009-September 2010) in order to: better characterize the sources, sinks, and losses of C to and from the lake; determine whether Lake Tahoe is at a quasi-steady state with respect to C loading; understand whether Tahoe acts as a net sink or source of C; and to understand how the lake fits into the C plumbing of the entire basin. The results indicate that the largest source of C to Lake Tahoe is derived from stream flow: 4.33 *106 kg C/yr ± 2.02 *106 kg C/yr (90%CI), with 34% in the form of dissolved organic C (DOC), 45% as dissolved inorganic C (DIC), and 21% as particulate C (PC). The largest loss occurs as CO2 efflux to the atmosphere across the lake surface: 6.52 *106 kg C/yr ± 11.02 *106 kg C/yr (90%CI). The annual allochthonous inputs total less than the annual C losses: 5.41 *106 kg C/yr ± 3.73 *106 kg C/yr (90%CI) vs 8.64 *106 kg C/yr ± 11.03 *106 kg C/yr (90%), indicating a negative net ecosystem carbon balance. However, the total losses do not strongly outweigh inputs and large uncertainties temper the conclusion that net ecosystem carbon balance is strongly negative. The CO2 efflux is four times the load of C lost to lake sediments, illustrating that Lake Tahoe could be a net source of C to the atmosphere. Most C fluxes are influenced by hydrologic fluxes in the lake basin. The 2009 through 2010 study period experienced lower than average stream inflow and outflow. However, lower levels of C influx in a dry year are nearly balanced by depressed C loss associated with corresponding lower stream outflow. Total annual inputs and losses measure less than 1% of the total standing stock of in-lake C: 1621*106 kg C/yr ± 322 *106 kg C/yr (90%), which is overwhelmingly comprised of DIC (94% DIC). The pool of in-lake C accounts for approximately 9% of the total basin C. Efflux annually transfers approximately 2% of the net primary productivity of the adjacent terrestrial landscape to the atmosphere. Uncertainty in budget estimates is evaluated and the effect on conclusions is discussed.
