Geology topics
Y. Lin
Publications and source records attributed to Y. Lin.
Mars science helicopter: Compelling science enabled by an aerial platform
This whitepaper describes two conceptual vehicle designs, including possible tradeoffs within those designs, which would enable a wide array of innovative science investigations. In addition to describing vehicle capabilities, flight characteristics, and the breadth of enabled science for the two helicopter designs, we also introduce three mission concepts that showcase investigations made possible by MSH. We conclude with recommendations concerning the future of rotorcraft exploration at Mars.
Rate of tree carbon accumulation increases continuously with tree size
Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations. Our ability to understand and predict changes in the forest carbon cycle—particularly net primary productivity and carbon storage - increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands. Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree, in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation) decrease, remain constant, or increase as trees increase in size and age. Here we present a global analysis of 403 tropical and temperate tree species, showing that for most species mass growth rate increases continuously with tree size. Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree. The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-level productivity can be explained, respectively, by increases in a tree’s total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density. Our results resolve conflicting assumptions about the nature of tree growth, inform efforts to understand and model forest carbon dynamics, and have additional implications for theories of resource allocation and plant senescence.
Simulation of the shallow hydrologic system in the vicinity of Middle Genesee Lake, Wisconsin, using analytic elements and parameter estimation
Middle Genesee Lake is a ground-water flow-through lake located in a developing area in southeastern Wisconsin. Because the lake is in good connection with the shallow ground-water system, hydrologic stresses to the shallow ground-water system could adversely affect the lake system. In order to assess the effects of potential stresses on the lake, a study was completed by the U.S. Geological Survey, in cooperation with the Middle Genesee Lake Management District. The objective of the study was to identify areas that contribute ground water to the lake and estimate the hydrologic budget of the lake and hydraulic parameters affecting ground-water flow. A two-dimensional, steady-state analytic element model of the lake and surrounding area was developed using the computer code GFLOW. A parameter estimation model, UCODE, was used to optimize the calibration to measured water levels and streamflow. The calibrated model was used to evaluate the effect of three hypothetical stress scenarios on the stage of Middle Genesee Lake; the simulations were linked to UCODE, which formally incorporated parameter uncertainty into 95-percent confidence intervals around the simulated value. The scenarios included: (1) pumping from upgradient irrigation wells, (2) pumping from Lower Genesee Lake to lower lake levels, and (3) reduction in recharge resulting from development. The results of the simulations demonstrated that lake levels could be affected by hydrologic stresses in the shallow hydrologic system, with effects ranging from a 2.7 feet decline in lake stage resulting from pumping in Lower Genesee Lake to a 0.1 feet decline in lake stage from development in part of the upgradient recharge area. The range of lake stage decline increased when parameter uncertainty was included, from a decline of 3.1 feet for pumping from Lower Genesee Lake to no reduction in lake stage for the development in the recharge area. Whereas these simulated effects are within the natural variation in lake stage, they represent a systematic reduction of ground-water flow to the lake. Therefore, these hypothetical stresses are expected to establish a new, lower, baseline lake stage over which the natural variation due to climatic effects are added and subtracted.