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14. Methane emissions from tundra environments in the Yukon-Kuskokwin Delta, Alaska

Author

Bartlett, Karen B, Crill, Patrick M, Sass, Ronald L, Harriss, Robert C, and Dise, Nancy B

Subjects
Geophysics
Abstract

This paper reports CH4 flux to the atmosphere from a variety of tundra environments near Bethel, Alaska during the summer months of 1988. Emissions from wet meadow tundra averaged 144 +/- 31 mg/sq m/d and ranged from 15.6 to 426 mg/sq m/d varying with soil moisture and temperature. Flux from the drier upland tundra was about two orders of magnitude lower and averaged 2.3 +/- 1.1 mg/sq m/d. Tundra lakes emit CH4 from the open water surface as well as from fringing aquatic vegetation; the presence of vegetation significantly enhanced flux over open water rates. Calculated diffusive fluxes from open water varied with lake size, the large lakes emitting 3.8 mg/sq m/d and small lakes emitting an average of 77 mg/sq m/d. An updated estimate of global emissions from tundra indicates an annual fluxes of approximately 11 +/- 3 Tg CH4.

Published
1992

32. A 3-year field measurement of methane and nitrous oxide emissions from rice paddies in China: Effects of water regime, crop residue, and fertilizer application.

Author

Jianwen Zou, Yao Huang, Jingyan Jiang, Xunhua Zheng, and Sass, Ronald L.

Subjects
AIR pollution, DRAINAGE, RECLAMATION of land, NITROGEN oxides, NITROUS oxide, GLOBAL warming
Abstract

A 3-year field experiment was conducted to simultaneously measure methane (CH4) and nitrous oxide (N2O) emissions from rice paddies under various agricultural managements including water regime, crop residue incorporation, and synthetic fertilizer application. In contrast with continuous flooding, midseason drainage incurred a drop in CH4 fluxes while triggering substantial N2O emission. Moreover, N2O emissions after midseason drainage depended strongly on whether or not fields were waterlogged due to intermittent irrigation. Urea application tended to reduce CH4 emissions but significantly increased N2O emissions. Under a water regime of flooding-midseason drainage-reflooding-moist intermittent irrigation but without water logging (F-D-F-M), both wheat straw and rapeseed cake incorporation increased CH4 emissions by 25 2%, and rapeseed cake increased N2O by 17% while wheat straw reduced N2O by 19% compared to controls. Seasonal average fluxes of CH4 ranged from 25.4 mg m-2 d-1 when no additional residue was applied under the water regime of flooding-midseason drainage- reflooding to 116.9 mg m-2 d-1 when wheat straw was applied at 2.25 t ha-1 under continuous irrigation flooding. Seasonal average fluxes of N2O varied between 0.03 mg N2O-N m-2 d-1 under continuous flooding and 5.23 mg N2O-N m-2 d-1 under the water regime of F-D-F-M. Both crop residue-induced CH4, ranging from 9 to 15% of the incorporated residue C, and N2O, ranging from 0.01 to 1.78% of the applied N, were dependent on water regime in rice paddies. Estimations of net global warming potentials (GWPs) indicate that water management by flooding with midseason drainage and frequent water logging without the use of organic amendments is an effective option for mitigating the combined climatic impacts from CH4 and N2O in paddy rice production. [ABSTRACT FROM AUTHOR]

Published
2005
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34. Z band dynamics as a function of sarcomere length and the contractile state of muscle

Author

Goldstein, Margaret A., Michael, Lloyd H., Schroeter, John P., and Sass, Ronald L.

Abstract

The Z band in skeletal muscle has two distinct structural states —a relaxed (small square or ss) form and a maximally activated (basket weave or bw) form. We have examined by electron microscopy and optical diffraction Z lattice forms and dimensions and A band spacings in relaxed, tetanized, stretched, and stretched‐and‐tetanized rat soleus muscle. We have tested the independent contributions of passive load, active tension, and sarcomere length to Z band state. As the A band spacing decreased with increasing load and increasing sarcomere length in the untetanized muscles, the Z lattice remained in the ss form and the Z spacing changed only slightly. Computer‐enhanced images from digitized electron micrographs showed that the ss Z lattice resisted deformation regardless of load or method of stretching. In contrast, when the muscle was tetanized at sarcomere lengths of up to 2.7 μm, the Z lattice assumed the bw form and the Z spacing was increased by 20%. Regardless of lattice form, Z spacing did not vary significantly with sarcomere length. Images from freeze‐substituted preparations showed both lattice forms comparable to those in images from glutaraldehyde‐fixed muscles. Thus, Z band state appears to be a function of the presence (or absence) of active tension. Our previous three‐dimensional model is compatible with these observations and with the substructures revealed by computer‐enhanced images of both lattice forms.—Goldstein, M. A.; Michael, L. H.; Schroeter, J. P.; Sass, R. L. Z band dynamics as a function of sarcomere length and the contractile state of muscle. FASEB J.1: 133‐142; 1987.

Published
1987
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