Jennifer Harden, PhD (Former Employee)

Soils in Alaska, and in high latitude terrestrial ecosystems in general, contain significant amounts of organic carbon, most of which is believed to have accumulated since the start of the Holocene about 10 ky before present. High latitude soils are estimated to contain 30-40% of terrestrial soil carbon (Melillo et al., 1995; McGuire and Hobbie, 1997), or ~ 300-400 Gt C (Gt = 1015 g)...

Isotopes of Be and C were used to reconstruct loess accumulation, hillslope evolution, and agricultural modification in soils of western Iowa. While both elements are derived from additions by the atmosphere (via plants in the case of carbon), the differences in element cycling allow erosional and depositional processes to be separated from biochemical processing. Based on 10Be, loess...

We examine soil organic matter (SOM) turnover and transport using C and N isotopes in soil profiles sampled circa 1949, 1978, and 1998 (a period spanning pulse thermonuclear 14C enrichment of the atmosphere) along a 3‐million‐year annual grassland soil chronosequence. Temporal differences in soil Δ14C profiles indicate that inputs of recently living organic matter (OM) occur primarily in...

The conceptual framework used by ecologists and biogeochemists must allow for accurate and clearly defined comparisons of carbon fluxes made with disparate techniques across a spectrum of temporal and spatial scales. Consistent with usage over the past four decades, we define "net ecosystem production" (NEP) as the net carbon accumulation by ecosystems. Past use of this term has been...

In order to quantify the historical changes in carbon storage that result from agricultural conversion, this study compared the carbon dynamics of two sites in the loess region of Iowa: a native prairie and a cropland. Field data were obtained to determine present-day carbon storage and its variability within a landscape (a stable ridgetop vs. eroding upper-midslope vs. depositional...

The conversion of land from its native state to an agricultural use commonly results in a significant loss of soil carbon (Mann, 1985; Davidson and Ackerman, 1993). Globally, this loss is estimated to account for as much as 1/3 of the net CO2 emissions for the period of 1850 to 1980 (Houghton and others, 1983). Roughly 20 to 40 percent of original soil carbon is estimated to be lost as...