carbon dioxide
Twelve testable hypotheses on the Geobiology of weathering
Wed, 08/03/2011 - 10:13 — leonmiBrantley S.L., Megonigal J.P., Scatena F.N. et al 2010. Twelve testable hypotheses on the Geobiology of weathering. Geobiology. DOI: 10.1111/j.1472-4669.2010.00264.x
Abstract:
Critical Zone (CZ) research investigates the chemical, physical, and biological processes that modulate the Earth’s surface. Here, we advance 12 hypotheses that must be tested to improve our understanding of the CZ: (1) Solar-to-chemical conversion of energy by plants regulates flows of carbon, water, and nutrients through plant-microbe soil networks, thereby controlling the location and extent of biological weathering. (2) Biological stoichiometry drives changes in mineral stoichiometry and distribution through weathering. (3) On landscapes experiencing little erosion, biology drives weathering during initial succession, whereas weathering drives biology over the long term.(4) In eroding landscapes, weathering-front advance at depth is coupled to surface denudation via biotic processes.(5) Biology shapes the topography of the Critical Zone.(6) The impact of climate forcing on denudation rates in natural systems can be predicted from models incorporating biogeochemical reaction rates and geomorphological transport laws.(7) Rising global temperatures will increase carbon losses from the Critical Zone.(8) Rising atmospheric PCO2 will increase rates and extents of mineral weathering in soils.(9) Riverine solute fluxes will respond to changes in climate primarily due to changes in water fluxes and secondarily through changes in biologically mediated weathering.(10) Land use change will impact Critical Zone processes and exports more than climate change. (11) In many severely altered settings, restoration of hydrological processes is possible in decades or less, whereas restoration of biodiversity and biogeochemical processes requires longer timescales.(12) Biogeochemical properties impart thresholds or tipping points beyond which rapid and irreversible losses of ecosystem health, function, and services can occur.
Climate and Atmosphere-- Puerto Rico
Fri, 07/29/2011 - 14:02 — ckasshttp://earthtrends.wri.org/text/climate-atmosphere/country-profile-148.html
Abstract:
From EarthTrends: The Environmental Information Portal the Web site is a companion to the EarthTrends site, launched in 2001 by the World Resources Institute. Inside these pages you will find time-series information for over 500 variables, more than 2000 country profiles, as well as data tables, maps, and feature stories on a variety of environmental, social, and economic topics. Click here to learn more about EarthTrends.
Impact of experimental drought on greenhouse gas emissions and nutrient availability in a humid tropical forest
Thu, 07/28/2011 - 16:53 — ckassAbstract:
We excluded throughfall from humid tropical forests in Puerto Rico
for a period of three months to determine how drought affects
greenhouse gas emissions from tropical forest soils. We
established five 1.24 m2 throughfall exclusion and five control plots
of equal size in three sites located on ridges, slopes, and an upland
valley dominated by palms (total of 30 plots). We measured weekly
changes in carbon dioxide (CO2) and bi-weekly changes in nitrous
oxide (N2O) and methane (CH4) in response to manipulation. We
additionally measured the effects of throughfall exclusion on soil
temperature and moisture, nutrient availability, and pH. Rainout
shelters significantly reduced throughfall by 22 to 32 % and
decreased soil moisture by 16 to 36% (top 10 cm). Rates of CO2
emissions decreased significantly in the ridge and slope sites (30%,
28%, respectively), but not the palm during the experimental
drought. In contrast, the palm site became a significantly stronger
sink for CH4 in response to drying (480% decline relative to
controls), while CH4 fluxes in the ridge and slope sites did not
respond to drought. Both the palm and ridge site became a sink for
N2O in response to drought and the slope site followed a similar
trend. Soil pH and available P decreased significantly in response
to soil drying; however, available N was not affected. Variability in
the response of greenhouse gas emissions to drought among the
three sites highlights the complexity of biogeochemical cycling in
tropical forested ecosystems, as well as the need for research that
incorporates the high degree of spatial heterogeneity in
experimental designs. Our results show that humid tropical forests
are sensitive to climate change and that short-term declines in rainfall could result in a negative feedback to climate change via
lowered greenhouse gas emissions and increased greenhouse gas
consumption by soils.
carbon isotope characterization of vegetation and soil organic matter in subtropical forests in luquillo, puerto rico
Thu, 07/28/2011 - 16:39 — ckassCarbon Isotope Characterization of Vegetation and Soil Organic Matter in Subtropical Forests in Luquillo, Puerto Rico
Joseph C. von Fischer and Larry L. Tieszen
Biotropica
Vol. 27, No. 2 (Jun., 1995), pp. 138-148
Abstract:
We examined natural abundances of 13C in vegetation and soil organic matter (SOM) of subtropical wet and rain forests to characterize the isotopic enrichment through decomposition that has been reported for temperate forests. Soil cores and vegetative samples from the decomposition continuum (leaves, new litter, old litter, wood, and roots) were taken from each of four forest types in the Luquillo Experimental Forest, Puerto Rico. SOM δ13C was enriched 1.6% relative to aboveground litter. We found no further enrichment within the soil profile. The carbon isotope ratios of vegetation varied among forests, ranging from -28.2% in the Colorado forest to -26.9% in the Palm forest. Isotope ratios of SOM differed between forests primarily in the top 20 cm where the Colorado forest was again most negative at -28.0%, and the Palm forest was most positive at -26.5%. The isotopic differences between forests are likely attributable to differences in light regimes due to canopy density variation, soil moisture regimes, and/or recycling of CO2. Our data suggest that recalcitrant SOM is not derived directly from plant lignin since plant lignin is even more 13C depleted than the bulk vegetation. We hypothesize that the anthropogenic isotopic depletion of atmospheric CO2 (ca 1.5% in the last 150 years) accounts for some of the enrichment observed in the SOM relative to the more modern vegetation in this study and others. This study also supports other observations that under wet or anaerobic soil environments there is no isotopic enrichment during decomposition or with depth in the active profile.
Extreme storm events, landscape denudation, and carbon sequestration: Typhoon Mindulle, Choshui River, Taiwan
Sat, 07/23/2011 - 21:45 — ckassGoldsmith, S. T.; Carey, A. E.; Lyons, W. B.; Kao, S. J.; Lee, T. Y.;
Chen, J. Extreme storm events, landscape denudation, and
carbon sequestration: Typhoon Mindulle, Choshui River, Taiwan.
Geology 2008, 36 (6), 483–486.
Abstract:
We have performed the fi rst known semicontinuous monitoring of particulate organic carbon
(POC) fl uxes and dissolved Si concentrations delivered to the ocean during a typhoon.
Sampling of the Choshui River in Taiwan during Typhoon Mindulle in 2004 revealed a POC
fl ux of 5.00 × 105 t associated with a sediment fl ux of 61 Mt during a 96 h period. The linkage
of high amounts of POC with sediment concentrations capable of generating a hyperpycnal
plume upon reaching the ocean provides the fi rst known evidence for the rapid delivery and
burial of POC from the terrestrial system. These fl uxes, when combined with storm-derived
CO2 consumption of 1.65 × 108 mol from silicate weathering, elucidate the important role of
these tropical cyclone events on small mountainous rivers as a global sink of CO2.
