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Given the difficulty of separating the three Picea species—P. glauca, P. mariana, and P. rubens (white, black, and red spruce)—in the pollen record, little is known about their unique histories in eastern North America following deglaciation. Here we report the first use of a classification tree analysis (CART) to distinguish pollen grains of these species. It was successfully applied to fossil pollen from eight sites in Maine and one in Massachusetts. We focused on the late glacial/early Holocene (14,000 to 8000 cal yr B.P.) and the late Holocene (1400 cal yr B.P. to present)—the two key periods since deglaciation when Picea has been abundant in the region. The result shows a shift from a Picea forest of P. glauca and P. mariana in the late glacial to a forest of P. rubens and P. mariana in the late Holocene. The small number of P. rubens grains identified from the late glacial/early Holocene samples (<5%) suggests that that species was either absent or rare at most of the sites. The occurrence and distribution of the three species do not reveal any geographic or temporal trend during late glacial time, but the data suggest that they were distributed in local patches on the landscape. The results of this study indicate that the recent population expansion of Picea (1000 to 500 cal yr B.P.) was likely the first time since deglaciation that P. rubens was abundant in the region. 相似文献
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Ronald B. Davis Dennis S. Anderson Sushil S. Dixit Peter G. Appleby Molly Schauffler 《Journal of Paleolimnology》2006,35(4):669-697
This study contrasts the effects of human disturbances on two very different lake/catchment systems: Hatch Pond and Beaver
Lake, New Hampshire. Hatch is in a steep mountain catchment remote from urban/industrial centers, and is a small, relatively
deep, primarily seepage lake with moderate flushing rate. The catchment has been continuously forested, but disturbed by partial
loggings and a forest fire. Beaver’s more extensive and gently sloping catchment is much closer to urban/industrial centers,
and has been agricultural and recently suburban. Beaver is a larger but shallower drainage lake with much more rapid flushing
than Hatch. We compared the sedimentary records and inferred limnological responses to catchment land uses and air pollution
inputs of these mesotrophic lakes, and interpreted differing responses as a function of basic differences between the lakes
and their catchments. Some chemical and biological variables in the sediment of both lakes respond sensitively to the first
disturbances of the catchments by Euro-American settlers. Diatom-inferred Cl at both lakes indicates a modest increase of
salinity at this time. Hatch sediment contains a record of soil erosion starting
1810 with first logging and fire. For ~125 years, erosion was largely of upper eluviated soil, but by
1935 it reached deeper into the illuviated (enriched) horizon. Maximal lake trophic state based on diatom-inferred limnological
variables occurred in the mid-1900’s period of maximum sedimentation of illuviated soil. The sediment record since
1964 reflects forest maturation, and soil stabilization and acidification, but not lake acidification. At Beaver, the limnological
effects of forest clearance and agriculture starting ~1700 were relatively mild due to gentleness of slopes and soil characteristics
favoring stability. A near doubling of earth elements, and major increases in trace metal pollutants and coal combustion particles
(CCP) occurred in sediment dating around 1900. Landscape analysis as well as historical and sedimentary records preclude the
catchment as the major source of these increases. The most likely source is atmospheric fallout of CCP with its metal load.
Despite controls on CCP and other emissions starting 1960, concentrations of earth elements and trace metals in Beaver sediment
remain high due to soil mobilization by residential development of the catchment. The trophic state of Beaver Lake has increased,
but the relative increase has been smaller than at Hatch, despite more intensive land uses and greater aerial inputs at Beaver.
We propose that this lesser eutrophication is due to rapid flushing of Beaver Lake with stream water from relatively undeveloped
parts of the extensive catchment, and lower sensitivity to nutrient inputs of this naturally more eutrophic lake. A major
shift from unicellular to colonial chrysophytes at Hatch starts in the late-1800’s, and at Beaver in the early 1900’s. Colonial
taxa in lesser quantities appear at the time of first settlement of the Beaver catchment. At both lakes the shifts are correlated
with increasing metal fluxes from the opening of catchment biogeochemical cycles, as with the aforementioned erosional sequence
at Hatch. But at Hatch aerial inputs of trace metals, and at Beaver aerial inputs major and trace metals associated with CCP
are also correlated with the major chrysophyte shift. It appears that the chrysophytes have responded to stressors associated
with both catchment disturbance and regional atmospheric inputs. 相似文献
3.
Treadaway Victoria Atlas Elliot Schauffler Sue Navarro Maria Ueyama Rei Pfister Leonhard Thornberry Troy Rollins Andrew Elkins James Moore Fred Rosenlof Karen 《Journal of Atmospheric Chemistry》2022,79(2):81-100
Journal of Atmospheric Chemistry - Rapid transport by deep convection is an important mechanism for delivering surface emissions of reactive halocarbons and other trace species to the tropical... 相似文献
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