Soil Freeze-thaw Cycles Research Articles

Use of a sentinel system for field measurements of Cryptosporidium parvum oocyst inactivation in soil and animal waste.

A small-volume sentinel chamber was developed to assess the effects of environmental stresses on survival of sucrose-Percoll-purified Cryptosporidium parvum oocysts in soil and animal wastes. Chambers were tested for their ability to equilibrate with external chemical and moisture conditions. Sentinel oocysts were then exposed to stresses of the external environment that affected their viability (potential infectivity), as indicated by results of a dye permeability assay. Preliminary laboratory experiments indicated that temperatures between 35 and 50 degrees C and decreases in soil water potential (-0.003 to -3.20 MPa) increased oocyst inactivation rates. The effects of two common animal waste management practices on oocyst survival were investigated on three dairy farms in Delaware County, N.Y., within the New York City watershed: (i) piling wastes from dairy youngstock (including neonatal calves) and (ii) spreading wastes as a soil amendment on an agricultural field. Sentinel containers filled with air-dried and sieved (2-mm mesh) youngstock waste or field soil were wetted and inoculated with 2 million oocysts in an aqueous suspension and then placed in waste piles on two different farms and in soil within a cropped field on one farm. Controls consisted of purified oocysts in either phosphate-buffered saline or distilled water contained in sealed microcentrifuge tubes. Two microdata loggers recorded the ambient temperature at each field site. Sentinel experiments were conducted during the fall and winter (1996 to 1997) and winter (1998). Sentinel containers and controls were removed at 2- to 4-week intervals, and oocysts were extracted and tested by the dye permeability assay. The proportions of potentially infective oocysts exposed to the soil and waste pile material decreased more rapidly than their counterpart controls exposed to buffer or water, indicating that factors other than temperature affected oocyst inactivation in the waste piles and soil. The effect of soil freeze-thaw cycles was evident in the large proportion of empty sentinel oocysts. The potentially infective sentinel oocysts were reduced to <1% while the proportions in controls did not decrease below 50% potentially infective during the first field experiment. Microscopic observations of empty oocyst fragments indicated that abrasive effects of soil particles were a factor in oocyst inactivation. A similar pattern was observed in a second field experiment at the same site.

Fluxes of CO2 and CH4 in high latitude wetlands: measuring, modelling and predicting response to climate change

This review covers selected aspects of recent international efforts to measure and model greenhouse gas emission from northern wetlands, to identify the environmental factors that control gas emission, and to investigate wetlands’responses (particularly with respect to gas emission) to global change. Both bottom-up and top-to-bottom approaches, based respectively on local observations plus inventory of gas fluxes and inverse modelling of global circulation, agree on the size of the high latitude (>60°N) contribution to global methane, which should be about 13% or 70 Tg/year. It has been shown that winter and spring fluxes are an essential part in the annual budget of CH4 and especially CO2 exchange (varying from 5 to 50%). Soil micro-organisms were shown to be able to respire during winter even at-16°C. In comparison to aerobically respiring organisms, anaerobic methanogenic bacteria were less active in frozen soil, although they are subjected to significant stimulation by soil freeze-thaw cycles. The absence of immediate coupling of methanogenesis with plant photosynthesis implies that substrates for methane formation are derived from peat decomposition rather than from root exudation.

Nitrous oxide emission from an agricultural soil subjected to different freeze-thaw cycles

Nitrous oxide (N 2O) emissions from soils have been implicated as the causes of potential greenhouse warming and important nitrogen (N) loss. Soil freeze-thaw cycles have a significant effect on N 2O emission. In this study, potential rates of N 2O emission from an agricultural soil were examined in the laboratory by a soil core method. Spring soil cores from a sandy loam under conventional tillage and inorganic fertilizer management practices were distributed to four different freeze-thaw treatment groups. One group of the soil cores was not refrozen during the experiment, with the others subjected to one, two and three freeze-thaw cycles, respectively. The N 2O flux from the soil core increased with increasing numbers of freeze-thaw cycles. The means of the fluxes ranged from 0.24 to 0.65 kg ha −1 day −1 for non-frozen soil cores and about 60% higher value were found for one freeze-thaw cycle treatment. The results also showed that the first freeze-thaw cycle promoted N 2O flux as a pulse and the same patterns were found for additional freeze-thaw cycles. The information in this study should allow estimation of the potential rates of N 2O emission contributed by freeze-thaw events for specific locations based on the soil climate data for the location.

Preliminary analysis of meteorological and seasonal influences on crustal gas emission relevant to earthquake prediction

abstract The emission of gas from the Earth's crust is a complex process influenced by meteorological and seasonal parameters. The use of gas emission as a tool in earthquake prediction will require an understanding of these influences. Radon emanation has been integrated over weekly intervals and free mercury vapor emission over 212 hour intervals at a low seismic risk site in Colorado. Radon measured by the Track Etch® technique ranged from 136 to 1750 tracks/mm2 (81 to 1040 pC/liter) over the 1-yr period of the experiment. There was a strong correlation of radon emanation with: instrument vault temperature, barometric pressure, outside temperature, soil temperature, and whether or not the surface soil was frozen. Seasonal influences on radon emanation are important with 94 per cent of the variance being accounted for by the measured meteorological and seasonal parameters. Mercury concentrations in the instrument vault ranged from &amp;lt;1 to 53 ng/m3 over the 1 yr. Mercury emission correlates with vault temperature, vault relative humidity, outside temperature, barometric pressure, soil temperature and moisture, and the soil freeze-thaw cycle. Diurnal cycles are common but do not occur on all days. Other short-term noise in mercury emission is also important and phase shift or phase lag effects are important. Only 32 per cent of the variance in mercury emission can be accounted for by the measured meteorological and seasonal parameters. The short-term noise coupled with phase lags are important factors in mercury emission rates.