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111.
Throughout the Holocene, northern peatlands have both accumulated carbon and emitted methane. Their impact on climate radiative forcing has been the net of cooling (persistent CO2 uptake) and warming (persistent CH4 emission). We evaluated this by developing very simple Holocene peatland carbon flux trajectories, and using these as inputs to a simple atmospheric perturbation model. Flux trajectories are based on estimates of contemporary CH4 flux (15–50 Tg CH4 yr−1), total accumulated peat C (250–450 Pg C), and peatland initiation dates. The contemporary perturbations to the atmosphere due to northern peatlands are an increase of ∼100 ppbv CH4 and a decrease of ∼35 ppmv CO2. The net radiative forcing impact northern peatlands is currently about −0.2 to −0.5 W m−2 (a cooling). It is likely that peatlands initially caused a net warming of up to +0.1 W m−2, but have been causing an increasing net cooling for the past 8000–11 000 years. A series of sensitivity simulations indicate that the current radiative forcing impact is determined primarily by the magnitude of the contemporary methane flux and the magnitude of the total C accumulated as peat, and that radiative forcing dynamics during the Holocene depended on flux trajectory, but the overall pattern was similar in all cases. 相似文献
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Host finding by aphids in the field 总被引:2,自引:0,他引:2
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STEVE MIHOK JONATHAN K. STILES ENOCH MPANGA REARDON O. OLUBAYO 《Medical and veterinary entomology》1994,8(1):47-50
Abstract. Midgut protease activity in Glossina morsitans centralis and G. m. morsitans , at 48h post bloodmeal averaged 1.8IU of trypsin-like activity. These two tsetse subspecies differ in their susceptibility to trypanosome infection. Except for low levels in flies fed on waterbuck blood (0.7IU), activity did not differ in flies fed a variety of host bloods (goat, pig, cow, buffalo, eland) and trypanosome species ( Trypanosoma congolense, T.brucei, T.simiae ). Protease activity was also not correlated with infection rates, despite large differences in infection rates among experiments. Nevertheless, addition of 0.06M D(+)-glucosamine to parasitaemic blood resulted in a three-fold reduction in protease activity, coincident with a large increase in infection rate. This effect did not occur when parasites or D(+)-glucosamine were added alone to the bloodmeal, suggesting that the effect was due to metabolism of D(+)-glucosamine by parasites. 相似文献
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LINDA D. JONES ELIZABETH HODGSON TREVOR WILLIAMS STEVE HIGGS PATRICIA A. NUTTALL 《Medical and veterinary entomology》1992,6(3):261-265
Tick saliva (or salivary gland extract) potentiates the transmission of Thogoto (THO) virus to uninfected ticks feeding on a non-viraemic guinea-pig. This phenomenon has been named saliva activated transmission (SAT). To investigate the potential of different haematophagous arthropods to mediate SAT, guinea-pigs were infested with uninfected R.appendiculatus Neumann nymphs and inoculated with THO virus and salivary gland extract (SGE) derived from a range of ixodid (metastriate and prostriate) or argasid ticks, or mosquitoes; control guinea-pigs were inoculated with virus alone. Enhancement of THO virus transmission was observed only when SGE was derived from metastriate ticks. Comparison with the vector potential of these various arthropod species revealed that enhancement of THO virus transmission was specific for ticks which were competent vectors of the virus. The data indicate a correlation between vector competence and the ability of haematophagous arthropods to mediate SAT of THO virus. 相似文献
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A. P. KERSHAW 《Austral ecology》1979,4(3):253-263
Modern pollen representation of aquatic vegetation communities at three sites on the Atherton Tableland is examined. Indicator pollen taxa are identified and are used to interpret the aquatic pollen components of two pollen diagrams from one of the sites. It is believed that detailed estimates of changes in lake water level have been derived from the identified fossil plant communities. 相似文献
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A. P. KERSHAW 《The New phytologist》1971,70(4):669-681
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