Localization of saturated karst aquifer with magnetic resonance sounding and resistivity imagery

To answer one of the main questions of hydrogeologists implementing boreholes or working on pollution questions in a karst environment--i.e., where is the ground water?--numerous tools including geophysics are used. However, the contribution of geophysics differs from one method to the other. The magnetic resonance sounding (MRS) method has the advantage of direct detection of ground water over other geophysical methods. Eight MRSs were implemented over a known karst conduit explored and mapped by speleologists to estimate the MRS ability to localize ground water. Two direct current resistivity imageries (DC-2D imagery) were also implemented to check their capability to map a known cave. We found that the MRS is a useful tool to locate ground water in karst as soon as the quantity of water is enough to be detected. The threshold quantity is a function of depth and it was estimated by forward modeling to propose a support graph to hydrogeologists. The measured MRS's signals could be used to calculate transmissivity and permeability estimators. These estimators were used to map and to draw a cross section of the case study site, which underline accurately the known karst conduit location and depth. We also found that the DC-2D imagery could underline the karst structures: It was able to detect the known cave through its associated faults. We prepared a computer simulation to check the depth of such a cave to induce resistivity anomaly which could be measured in similar conditions.     

Environmental management of marine fish culture in Hong Kong

Marine fish farming is an important commercial practice in Hong Kong. Marine fish farms located in eutrophic coastal waters often face the threat of severe dissolved oxygen depletion associated with algal blooms and red tides. On the other hand, mariculture activities also contribute to pollution. The sustainable management of mariculture requires proper siting of the fish farms and stocking density control. Both of these are related to the carrying capacity of the water body concerned, which is mainly governed by its flushing characteristics. A simple method to determine the carrying capacity of a fish farm has been developed by using three-dimensional (3D) hydrodynamic modelling and its effective coupling with a diagenetic water quality model. A systematic methodology using numerical tracer experiments has been developed to compute the tidal flushing in a fish farm. The flushing time is determined from the results of a numerical tracer experiment using robust 3D hydrodynamic and mass transport models. A unit tracer concentration is initially prescribed inside the region of interest and zero elsewhere; the subsequent mass transport and the mass removal process are then tracked. The fish farms are usually situated in well-sheltered shallow embayments and may not connect directly to the open water. It is found that it is necessary to define both "local" and "system-wide" flushing times to represent the effectiveness of the mass exchange with the surrounding water body and the open sea respectively. A diagenetic water quality model simulating the sediment-water-pollutant interaction is employed to address the response of the water column and the benthic layer to pollution discharges. With the flushing rate reliably computed, the carrying capacity of the fish farm can be determined in terms of key water quality parameters: chlorophyll-a, dissolved oxygen, organic nitrogen and potential lowest dissolved oxygen level on a day of negligible photosynthetic production. The predictions are well-supported by field data.     

Apatite-fission-track geochronology and its tectonic correlation in the Dabieshan orogen,central China

The thermochronology based on a combination ofradiometric age and closure temperature (Tc) is widelyaccepted as a sensitive method to provide constraintson tectonic evolution of the orogen, and numerousadvances as a result of thermochronological applica-tions have been made recently in the Dabieshan oro-gen[1—5]. Zircon U/Pb, hornblende Ar/Ar and biotiteAr/Ar ages with Tc= 800—300℃[6] will yield a wealthof information on the cooling and exhumation of rockscrossing crustal levels of 30—1…     

The first discovery of the middle Lochkovian (Devonian) conodonts in South Gobi,Mongolia

The Tsagaanbulag Formation of the Ulaan-Shand section in the Shine Jinst area was assigned to Silurian (Wenlock-Pridoli) previously. But the present authors have found some very important conodonts, including Lanea omoalpha, Amydrotaxis johnsoni, "Ozarkodina" planililingua, Pedavis sp., from the Tsagaanbulag and Amansair formations, clearly indicating that these two formations should be assigned to middle Lochkovian which are widely distributed in China and Mongolia. The existence of the marine Wenlockain and early Ludlovian deposits in Mongolia is a noteworthy problem.     

MESOSCALE SPECTRA OF THE FREE ATMOSPHERIC MOTION IN MID-LATITUDE SUMMER－UNIVERSALITY AND CONTRIBUTION OF THUNDERSTORM ACTIVITIES

Meridional and vertical wind velocities of the free atmosphere were observed continuously in mid-latitude summer of 1981 by using Platteville ST radar in the eastern Colorado plains in order to obtain the mesoscale spectra. Power spectra were obtained for both meridional and vertical components at heights of 3.3－7.9 km for meridional and 3.3－17.7 km for vertical. Results show that the “-5/3 law” is a good fit to “meridional” spectra for wave periods ranging from ~3 hr to 2 days which are consistent with other published observations and give further evidence to the existence of a universal -5/3 law in mesoscale atmospheric motions. Results also show that for wave periods shorter than 3 hr (to about 10 min), the spectra obviously depart from the –5/3 law and reflect the significant contribution of thunderstorm activities which frequently happen in the mid-latitude summer. Mesoscale spectra of vertical velocity show some characteristics of gravity waves. The mechanism of the observed spectra is discussed.     

应用格林——安布普特模型解决地表水深随时间变化的入渗问题

与简单的入渗模型的消退曲线相比较,格林一安布普特最早提出的模型非常清楚地考虑了表面水深的影响及其对短小河渠的应用。对于纵剖面不连续线以上的饱和带以及其下处于初始含水量状况下的半无限区域里,格一安方程假定土壤含水量纵剖面线是阶跃函数(图1)。