Deep groundwater cycle in Xiongxian geothermal field

ABSTRACT The deep karstic aquifer containing hot water is ideal for space heating and maybe also for geothermal power generation. The hot water is characterized by high single-well yield, low salinity, gravity injection and less impact on environment when it is exploited. In order to run a karstic geothermal field sustainably, it is of high importance to identify the local groundwater circulation pattern in the field. Here we take Xiongxian geothermal field as an example to get insights into the characteristics of local groundwater circulation in karstic aquifers. Groundwater samples and surface water samples were collected, and analyzed for their hydrochemical and isotopic contents. Results show that the TDS of groundwater in karstic aquifers is between 1.9 and 2.6 g/L. According to the data of water table, the local groundwater flow direction is from Southwest to Northeast. This is confirmed by the TDS data, which increases gradually in this direction. However, this is orthogonal to the regional groundwater flow direction that is from Northwest to Southeast. This phenomenon highlights the control of aquifer lithology and geological structures on the groundwater flow field. Isotopic data illustrates some oxygen isotope shifts, although the reservoir temperature is less than 90 ℃. Finally, a conceptual model is proposed to depict the deep groundwater cycle in Xiongxian geothermal field, which will serve as a basis for the further simulated model for exploitation strategy and could be used as a reference in similar karstic aquifers

New Debris Disks Around Nearby Main Sequence Stars: Impact on The Direct Detection of Planets

Using the MIPS instrument on the Spitzer telescope, we have searched for infrared excesses around a sample of 82 stars, mostly F, G, and K main-sequence field stars, along with a small number of nearby M stars. These stars were selected for their suitability for future observations by a variety of planet-finding techniques. These observations provide information on the asteroidal and cometary material orbiting these stars - data that can be correlated with any planets that may eventually be found. We have found significant excess 70um emission toward 12 stars. Combined with an earlier study, we find an overall 70um excess detection rate of $13 \pm 3$% for mature cool stars. Unlike the trend for planets to be found preferentially toward stars with high metallicity, the incidence of debris disks is uncorrelated with metallicity. By newly identifying 4 of these stars as having weak 24um excesses (fluxes $\sim$10% above the stellar photosphere), we confirm a trend found in earlier studies wherein a weak 24um excess is associated with a strong 70um excess. Interestingly, we find no evidence for debris disks around 23 stars cooler than K1, a result that is bolstered by a lack of excess around any of the 38 K1-M6 stars in 2 companion surveys. One motivation for this study is the fact that strong zodiacal emission can make it hard or impossible to detect planets directly with future observatories like the {\it Terrestrial Planet Finder (TPF)}. The observations reported here exclude a few stars with very high levels of emission, $>$1,000 times the emission of our zodiacal cloud, from direct planet searches. For the remainder of the sample, we set relatively high limits on dust emission from asteroid belt counterparts