Earth & Environmental Sciences
Peat Accumulation of a Sphagnum Poor Fen in Temperate East Pennsylvania during the Holocene
Climate change can greatly affect the carbon balance of peatlands by influencing production and decomposition. Studying boreal peatlands along the edge of their southern range may provide insight into boreal peatland responses to warmer climates. Here we present results of AMS dating (n=9), 268 bulk density measurements and macrofossil analysis of a 10.7-m peat core from Tannersville Bog, one of the southernmost (41N) low altitude (277 m) Sphagnum peatlands along the eastern seaboard of North America. Results indicate a concave peat-age pattern over the last ~11 cal ka, similar to patterns documented in oceanic bogs but different from those of continental fens. The peat-addition rate of ~120 g per square meter per year was higher than most boreal peatlands, but catotelm decomposition rate was similar (0.0002 yr-1) to other peatlands. Apparent accumulation rates ranged from 13 to 109 gC per square meter per year, with a time-averaged mean of 28 gC per square meter per year. This relatively high accumulation rate may have been caused by high primary production (rather than low acrotelm decomposition) associated with a warmer and wetter climate. Plant macrofossil data indicate a major transition from rich fen to poor fen at ~1.2 cal ka, possibly triggered by a dry and/or variable climate as documented at other sites in the region. Our results imply that a warmer and wetter climate may increase carbon storage in some regions for certain types of peatlands.
Diminished Mercury Emission From Water Surfaces by Duckweed (Lemna minor)
Aquatic plants of the family Lemnaceae (generally referred to as duckweeds) are a widely distributed type of floating vegetation in freshwater systems. Under suitable conditions, duckweeds form a dense vegetative mat on the water surface, which reduces light penetration into the water column and decreases the amount of exposed water surface. These two factors would be expected to reduce mercury emission by limiting a) direct photoreduction of Hg(II), b) indirect reduction via coupled DOC photooxidation-Hg(II) reduction, and c) gas diffusion across the water-air interface. Conversely, previous studies have demonstrated transpiration of Hg(0) by plants, so it is therefore possible that the floating vegetative mat would enhance emission via transpiration of mercury vapor. The purpose of this experiment was to determine whether duckweed limits mercury flux to the atmosphere by shading and the formation of a physical barrier to diffusion, or whether it enhances emission from aquatic systems via transpiration of Hg(0).
Deionized water was amended with mercury to achieve a final concentration of approximately 35 ng/L and allowed to equilibrate prior to the experiment. Experiments were conducted in rectangular polystyrene flux chambers with measured UV-B transmittance greater than 60% (spectral cutoff approximately 290 nm). Light was therefore able to penetrate the flux chamber from the sides as well as the top throughout the experiment, limiting the effect of shading by duckweed on the water surface. Flux chambers contained 8L of water with varying percent duckweed cover, and perforated plastic sheeting was used as an abiotic control. Exposures were conducted outside on days with little to no cloud cover. Real time mercury flux was measured using atomic absorption (Mercury Instruments UT-3000). Total solar and ultraviolet radiation, as well as a suite of meteorological parameters, were also measured. Results indicate that duckweed diminishes mercury emission from the water surface as compared to open water controls. Decreases in emission rate varied linearly with percent duckweed cover, with lower fluxes occurring at higher percent cover. Mercury flux in the duckweed treatments as compared to open water treatments decreased from 17% in the lowest percent cover treatment to 67% in the highest percent cover treatment. The observed decrease in mercury emission suggests that duckweed limits emission via the formation of a physical barrier to diffusion.
Towards predicting streamflow based on SWE, melt timing, and topography in subarctic heterogeneous terrain
Snowmelt onset date and snow water equivalent (SWE) are major factors that influence the spring runoff in high latitude, snow dominated basins. We combine AMSR-E L3 daily SWE from March to June 2003-2006, daily hydrological records from 3 sites on the Pelly and Ross Rivers, Yukon Territory [Pelly Crossing N62.82, W136.58, Faro N62.22,W133.37, and Ross River N61.99,W132.37], and a 1:250,000 DEM to develop a technique to predict streamflow in subarctic heterogeneous terrain. The AMSR-E L3 SWE algorithm was developed for global snow cover distributions; it is not optimized for heterogeneous terrain. Field data suggest that it underestimates the SWE in this area. We assume it represents the minimum SWE per pixel. SWE variations of the Pelly River basin (49,000 km2) and its two nested sub-basins (22,100 km2 and 7,250 km2), show that SWE had an apparent drop shortly after the snowmelt onset date determined from Tb and diurnal amplitude variations (DAV), which are also correlated with temperature change. During the early stage of snowmelt, high and low elevations have no significant SWE difference. After mid-April, the most intense melt period at lower elevations, low elevation SWE drops far below high elevation SWE, which is just beginning the melt process. Initial melt and the drop in low elevation SWE likely cause the first small discharge peak in the hydrograph. When the SWE throughout the basin approaches 0 mm for more than 3 days, it is followed by the peak flow. The largest basin has an ~14 day lag between the SWE drop and the flow increase, while the smaller basins have an about 9 day lag. Snow distribution, melt, runoff, and the lag times vary due to diverse terrain and microclimate factors such as: forest cover, permafrost, temperature and precipitation. By combining topography, snow distribution and melt timing, we have developed an understanding of basin-specific stream discharge response to spring thaw. Passive microwave derived daily SWE data combined with terrain and melt timing have significant potential for constraining and predicting stream flow timing and magnitude during the melt season in subarctic regions.
Direct measurement of hematite individual particle anisotropy: implications for inclination shallowing in red bed DRMs.
Methods to correct for the observed inclination shallowing in sedimentary rocks have been proposed that are based on either models of the geomagnetic field and the resulting directional distribution of paleomagnetic vectors or the magnetic anisotropy of the magnetic minerals carrying the remanence. One limitation of the anisotropy method for hematite-bearing red beds has been the isolation and determination of a rocks detrital hematite individual particle anisotropy. Up to now, our red bed inclination shallowing corrections have been dependent on estimates of hematite individual particle anisotropy using data fit to theoretical correction curves. › Continue reading
A fluvial record of active fault-propagation folding, Salsomaggiore anticline, northern Apennines, Italy
The Salsomaggiore anticline in the northern Apennines is an actively growing fault-propagation fold that is flanked by a suite of early Middle Pleistocene (~0.8 Ma) to Recent fluvial terraces, which reveal a foreland-migrating wave of coupled incision and aggradation, interpreted to reflect the response of a fluvial system to progressive vertical and lateral fold-propagation. This ~10km-wavelength fold resides ~25 km hinterward of the modern structural front and exhibits a complex growth history extending back to at least the middle Miocene. Langhian-Messinian, marginal- to deep-marine clastics are folded about a NW-SE trending axis, record the majority of fold growth, and are superimposed by the Ligurian nappe and Pliocene-Recent deep-marine, marginal-marine, and fluvial strata with shallowing upward dips. Active growth is documented by fluvial terraces, recent seismicity, deflected stream channels, first-order stream gradients, and long-profile modeling. › Continue reading