Predicting Water Resource Impacts of Unconventional Gas Using Simple Analytical Equations.

The rapid expansion in unconventional gas development over the past two decades has led to concerns over the potential impacts on groundwater resources. Although numerical models are invaluable for assessing likelihood of impacts at particular sites, simpler analytical models are also useful because they help develop hydrological understanding. Analytical approaches are also valuable for preliminary assessments and to determine where more complex models are warranted. In this article, we present simple analytical solutions that can be used to predict: (1) the spatial extent of drawdown from horizontal wells drilled into the gas-bearing formation, and rate of recovery after gas production ceases; (2) the potential for upward transport of contaminants from the gas-bearing formation to shallow aquifers during hydraulic fracturing operations when pressures in the gas-bearing formation are greatly increased; and (3) the potential downward leakage of water from shallow aquifers during depressurization of gas-bearing formations. In particular, we show that the recovery of pressure after production ceases from gas-bearing shale formations may take several hundred years, and we present critical hydraulic conductivity values for intervening aquitards, below which the impact on shallow aquifers will be negligible. The simplifying assumptions inherent in these solutions will limit their predictive accuracy for site-specific assessments, compared to numerical models that incorporate knowledge of spatial variations in formation properties and which may include processes not considered in the simpler solutions.

Convergence of tree water use within an arid-zone woodland.

We examined spatial and temporal patterns of tree water use and aspects of hydraulic architecture in four common tree species of central Australia--Corymbia opaca, Eucalyptus victrix, E. camaldulensis and Acacia aneura--to better understand processes that constrain water use in these environments. These four widely distributed species occupy contrasting niches within arid environments including woodlands, floodplains and riparian environments. Measurements of tree water use and leaf water potential were made at two sites with contrasting water table depths during a period of high soil water availability following summer rainfall and during a period of low soil water availability following 7 months of very little rainfall during 2007. There were significant differences in specific leaf area (SLA), sapwood area to leaf area ratios and sapwood density between species. Sapwood to leaf area ratio increased in all species from April to November indicating a decline in leaf area per unit sapwood area. Despite very little rainfall in the intervening period three species, C. opaca, E. victrix and E. camaldulensis maintained high leaf water potentials and tree water use during both periods. In contrast, leaf water potential and water use in the A. aneura were significantly reduced in November compared to April. Despite contrasting morphology and water use strategies, we observed considerable convergence in water use among the four species. Wood density in particular was strongly related to SLA, sapwood area to leaf area ratios and soil to leaf conductance, with all four species converging on a common relationship. Identifying convergence in hydraulic traits can potentially provide powerful tools for scaling physiological processes in natural ecosystems.

Development of saline ground water through transpiration of sea water.

As vegetation usually excludes salt during water uptake, transpiration will increase the salinity of the residual water. If the source water is sea water, then the residual water may become highly saline. In the unconfined coastal aquifer of the tropical Burdekin River delta, northeastern Australia, areas of highly saline ground water with chloride concentrations up to almost three times that of sea water occur up to 15 km from the present coastline, and are attributed to transpiration by mangrove vegetation during periods of high sea level. Radiogenic ((14)C) carbon isotope analyses indicate that ground water with chloride concentrations between 15,000 and 35,000 mg/L is mostly between 4000 and 6000 years old, at which time sea level was 2 to 3 m higher than present. Stable isotope analyses of oxygen-18 and deuterium show no evidence for evaporative enrichment of this water. Oxygen-18, deuterium, and stable (delta(13)C) carbon isotope analyses of ground water and soil water point to a recharge environment beneath the mangrove forests during this postglacial sea level high stand. During that period, transpiration of the mangrove forests would have led to high chloride concentrations in the residual ground water, without inducing isotopic fractionation. Due to the higher density, this hypersaline water moved downward through the aquifer by gravity and has formed lenses of highly saline ground water at the bottom of the unconfined aquifer.

Determining soil and ground water use of vegetation from heat pulse, water potential and stable isotope data.

A simple model of water uptake by vegetation is used to aid the discrimination of plant water sources determined with isotope data. In the model, water extracted from different soil depths depends on the leaf-soil potential difference, a root distribution function and a lumped hydraulic conductance parameter. Measurements of plant transpiration rate, and soil and leaf water potentials are used to estimate the value of the conductance parameter. Isotopic ratios in soil water and xylem are then used to constrain the root distribution. The model is applied to field measurements of transpiration, leaf water potential and 18O composition of xylem water on Corymbia clarksoniana, Lophostemon suaveolens, Eucalpytus platyphylla and Melaleuca viridiflora, and soil water potential and 18O composition of soil water to 8.5 m depth, in an open woodland community, Pioneer Valley, North Queensland. Estimates of the water uptake from various depths below the surface are determined for each species. At the time of sampling, the proportion of groundwater extracted by the trees ranged from 100% for C. clarksoniana to <15% for L. suaveolens and E. platyphylla. The advantages of the model over the traditional approach to determining sources of water used by plants using isotope methods are that it: (1) permits more quantitative assessments of the proportion of water sourced from different depths, (2) can deal with gradational soil water isotope profiles (rather than requiring distinct values for end-members), and (3) incorporates additional data on plant water potentials and is based on simple plant physiological processes.

Comparative water use by the riparian trees Melaleuca argentea and Corymbia bella in the wet-dry tropics of northern Australia.

We examined sources of water and daily and seasonal water use patterns in two riparian tree species occupying contrasting niches within riparian zones throughout the wet-dry tropics of northern Australia: Corymbia bella Hill and Johnson is found along the top of the levee banks and Melaleuca argentea W. Fitzg. is restricted to riversides. Patterns of tree water use (sap flow) and leaf water potential were examined in four trees of each species at three locations along the Daly River in the Northern Territory. Predawn leaf water potential was higher than -0.5 MPa throughout the dry season in both species, but was lower at the end of the dry season than at the beginning of the dry season. Contrary to expectations, predawn leaf water potential was lower in M. argentea trees along the river than in C. bella trees along the levees. In contrast, midday leaf water potential was lower in the C. bella trees than in M. argentea trees. There were no seasonal differences in tree water use in either species. Daily water use was lower in M. argentea trees than in C. bella trees. Whole-tree hydraulic conductance, estimated from the slope of the relationship between leaf water potential and sap flow, did not differ between species. Xylem deuterium concentrations indicated that M. argentea trees along the riverbank were principally reliant on river water or shallow groundwater, whereas C. bella trees along the levee were reliant solely on soil water reserves. This study demonstrated strong gradients of tree water use within tropical riparian communities, with implications for estimating riparian water use requirements and for the management of groundwater resources.

Pineapple juice as a negative oral contrast agent in magnetic resonance cholangiopancreatography: a preliminary evaluation.

The quality of magnetic resonance cholangiopancreatography (MRCP) images is frequently degraded by high signal from the gastrointestinal tract. The aim of this study is to evaluate pineapple juice (PJ) as an oral negative contrast agent in MRCP. Preliminary in vitro evaluation demonstrated that PJ shortened T(2) relaxation time and hence decreased T(2) signal intensity on a standard MRCP sequence to a similar degree to a commercially available negative contrast agent (ferumoxsil). Electrothermal atomic absorption spectrometry assay demonstrated a high manganese concentration in PJ of 2.76 mg dl(-1), which is likely to be responsible for its T(2) imaging properties. MRCP was subsequently performed in 10 healthy volunteers, before and at 15 min and 30 min following ingestion of 400 ml of PJ. Images were assessed blindly by two Consultant Radiologists using a standard grading technique based on contrast effect (degree of suppression of bowel signal), and image effect (diagnostic quality). There were statistically significant improvements in contrast and image effect between pre and post PJ images. There was particularly significant improvement in visualization of the pancreatic duct, but no significant difference between 15 min and 30 min post PJ images. Visualization of the ampulla, common bile duct, common hepatic and central intrahepatic ducts were also significantly improved at 15 min following PJ. Our results demonstrate that PJ, may be used as an alternative to commercially available negative oral contrast agent in MRCP.

Audit of quality in a radiological department--a pilot study.

As part of the development of an auditing system for this department, a pilot study was designed to audit the quality of the product leaving the department. One hundred and six patient investigations were reviewed. For each investigation 26 items which were considered to reflect the quality of information on the request card, the films, the report and the condition of the film packets were assessed using a simple scoring system. Overall performances for various aspects of the departmental 'product', and for groups of staff within the department, were derived from these scores. Several problem areas were identified. Individual items were then scrutinized for recurring low scores and where scores fell outside a predetermined range steps were taken to improve standards. The scoring system developed is simple, easy and effective in use. It is considered that audit of quality is worthwhile and should be extended to become a routine part of departmental management.

Duplex sonography in splenomegaly.

The aetiology of splenomegaly is seldom clear from either clinical or imaging assessment of the spleen. In the majority of cases sonographic assessment of the spleen produces a homogeneous enlargement of variable echodensity, but with very poor correlation with pathology. A study has been undertaken to assess the Doppler characteristics of the splenic artery in splenomegaly, excluding cases of portal hypertension in an attempt to provide further diagnostic information. Duplex assessment of 18 normal subjects and 10 patients with splenomegaly due to five different causes was undertaken. Analysis of waveform, peak frequency and pulsatility index were compared and failed to demonstrate any significant change. In the normal subject there is a broad systolic spectrum related to the tortuosity of the splenic artery, with persistence of forward flow throughout diastole, a reflection of the low peripheral resistance of the spleen. In splenomegaly the broad systolic spectrum is unchanged, since vessel tortuosity persists. Pathological and physiological assessment of the spleen in splenomegaly shows that a low resistance circulation persists, explaining maintenance of the diastolic flow pattern in splenomegaly. Increased blood flow to the spleen in splenomegaly occurs either as a result of an increase in vessel diameter or an increase in flow velocity, or a variable combination of the two which does not seem to be governed by specific pathology. An increase in peak frequency in some cases reflected some increase in flow velocity but provided no useful correlation. Analysis of the pulsatility index supported the above findings without adding further information.

Chest radiographs after permanent pacing. Are they really necessary?

The chest radiographs of 600 consecutive patients undergoing insertion of a permanent cardiac pacemaker were reviewed to determine the incidence and nature of abnormalities present. Abnormalities were detected on the chest radiographs of 131 patients (21.8%). Unsatisfactory electrode tip position and other features related to the electrode wire were commonest (14.4%). Complications related to the lungs and pleura were present in 5.5%, and those related to the generator and pouch least frequent (1.9%). Complications occurred more frequently following installation of a replacement system (48.3%) compared to new systems (17.2%). Important complications not initially detected included pneumothorax (8/15) and poor electrode loop (26/27). Chest radiographs following permanent cardiac pacing frequently demonstrate significant abnormalities whose detection is improved by awareness of their incidence and nature.

A model of gastric emptying in cats shows solid emptying is promoted by MK-329: a CCK antagonist.

The effect of MK-329, a potent, orally active, nonpeptidal cholecystokinin (CCK) antagonist, was measured on the gastric emptying rate of a solid meal in cats. External scintigraphy of cats that had been fed a meal of technetium-99m-(99mTc) labeled rabbit liver and light cream allowed the measurement of the emptying rates of either the liquid or solid portion of a meal under physiologic conditions. In cats, liquids emptied 2.6 times faster than solids [163 +/- 11 min vs. 62 +/- 3 min (mean +/- s.e.)]. At 3 or 10 mg/kg p.o., MK-329 gastric emptying was significantly accelerated, with the mean half-time of emptying being decreased by 34 +/- 11% (mean +/- s.e.) of the control half-times (p less than 0.02). Using only responders (five of six animals), mean half-time was decreased by 55 +/- 4% of the control half-times. CCK is important in regulating the emptying of solid food from the stomach because the CCK antagonist MK-329 accelerates that emptying.

Intradiploic leptomeningeal cyst of the frontal bone occurring as a complication of head injury in an adult.

Intradiploic cysts are rare complications of skull fractures. Only five cases of cranial intradiploic cyst can be found in the literature, all affecting the occipital bone. In all, the primary injury occurred in childhood and the cyst presented many years later. The case described here is of a frontal intradiploic leptomeningeal cyst developing in an adult as a sequel to a skull injury 12 months earlier. Intradiploic cysts occurring after fractures in adulthood do not appear to have been described previously.

The distribution of pulmonary shadowing in farmer's lung.

Reports of the radiological features in farmer's lung are inconsistent. We have reviewed clinical and radiological findings in eight patients with farmer's lung in the acute and sub-acute phases. In the acute phase the main feature is transient widespread diffuse shadowing of air space consolidation. In the sub-acute phase, the predominant feature is fine nodular shadowing tending to involve either the upper half or upper two-thirds of the lungs with relative sparing of the basal segments. This is in accordance with both the pathophysiological behaviour of the inhaled particulate antigen and the subsequent distribution of pulmonary changes in chronic farmer's lung.

Effects of atropine upon various components mediating postprandial gastric acid secretion in dogs.

Dose-response curves in chronic gastric fistula dogs were first obtained to chemical stimulants of the three accepted physiological excitatory components regulating postprandial gastric acid secretion. These were: 2-deoxy-D-glucose, a central vagal stimulant; gastrin, a hormone; and histamine, a paracrine factor. Using equiactive doses of each, a dose of atropine just maximal for suppressing all of the anatomical phases of food-induced acid secretion in vagally innervated pouch dogs was found to inhibit substantially the responses to all three of the above stimulants. The above results argue in favor of an interdependent model among the above factors for regulating postprandial gastric acid secretion in the dog.

Case report: renovascular hypertension in Takayasu's disease treated by percutaneous transluminal angioplasty.

Systemic hypertension secondary to renal artery stenosis is a common complication of Takayasu's disease. A case of Takayasu's disease is presented, in which hypertension was relieved by percutaneous transluminal angioplasty of a unilateral renal artery stenosis.

Gastric antisecretory and pharmacologic properties of N,N-dimethyl-N'-(2-diisopropylaminoethyl)-N-(4,6-dimethyl-2-pyridyl)ur ea (L-634,366).

N,N-Dimethyl-N'-(2-diisopropylaminoethyl)-N-(4,6-dimethyl-2-pyridyl)urea (L-634,366) was selected from a series of pyridylurea compounds with antisecretory activity as a potential therapeutic agent for the treatment of ulcer disease. L-634,366 was an effective inhibitor of gastric secretion evoked by gastrin, histamine and 2-desoxy-D-glucose (2-DG) in conscious dogs. Orally, L-634,366 was slightly less potent than the reference H2 receptor blocker, cimetidine as an inhibitor of secretion evoked by histamine, but was equipotent as an inhibitor of secretion evoked by gastrin and 2-DG. In vitro L-634,366 was a weak antagonist of histamine (H2) receptor responses in the guinea-pig atria and rat uterus; in the atria the antagonism appeared to be noncompetitive. In the anesthetized dog, L-634,366 possessed weak anticholinergic activity as compared to atropine in reducing vagally mediated cardiovascular, antral motor responses and with regard to antagonizing the pressor response to the muscarinic stimulant, McN 343-A. The anticholinergic activity of L-634,366 was lower and more selective than that of pirenzepine or atropine in producing mydriasis in mice, in antagonizing acetylcholine induced bradycardia in guinea-pig atria, methacholine and acetylcholine elicited contractions in the guinea-pig ileum and QNB binding to muscarinic receptors. L-634,366, like carbenoxolone, increased incorporation of 3H-glucosamine in gastric mucous indicating an increase in synthesis or turnover of mucous. L-634,366 is a novel compound possessing a broad spectrum of antisecretory activity; in vitro studies suggested a weak noncompetitive inhibition of the histamine-H2 receptor in atria.

Effects of H2-receptor antagonists upon physiological acid secretory states in animals.

The results reported in this paper indicate that representative H2-receptor antagonists are capable of maximally inhibiting gastric acid secretion in animals under the two general circumstances in which it occurs physiologically. Interdigestive or basal secretion was examined in chronic gastric fistula rats and food-stimulated secretion in vagally innervated, lesser curvature pouch dogs. The H2 antagonists studied and omeprazole, an inhibitor of the proton pump H+, K+-adenosine triphosphatase, also decreased pepsin secretion in rats, although not to the same maximal degree as acid secretion. Gastric emptying was increased by each H2 antagonist but only at high acid inhibitory doses. Omeprazole, in contrast, did not alter gastric emptying at a similar antisecretory dosage level. In dogs, a representative H2-receptor antagonist markedly inhibited food-stimulated acid secretion. These data suggest that the predominant effect of omeprazole and H2-receptor antagonists upon gastric function is to inhibit acid secretion and that H2-receptor antagonists may be capable of maximally inhibiting endogenous acid secretion in humans, as does omeprazole, if given under proper conditions.

Apparent irreversible H2-receptor blocking and prolonged gastric antisecretory activities of 3-N-(3-[3-(1-piperidinomethyl)phenoxy]propyl) amino-4-amino-1,2,5-thiadiazole-1-oxide (L-643, 441).

L-643,441 is a highly potent histamine H2-receptor antagonist in guinea-pig atria, acting via a unique mechanism. Unlike ranitidine, the onset of action of this compound was slow and its inhibitory action persisted after repeated washing of the tissues. Preincubation of atria with ranitidine, however, protected the H2-receptor from the apparently irreversible antagonism of L-643,441. H2-receptor antagonism produced by L-643,441 was not surmountable by increasing the concentration of dimaprit. The compound did not alter the response of this tissue to isoproterenol or affect basal atrial rate under conditions in which maximal H2-receptor blockade was achieved. In dogs, L-643,441 was effective both orally and i.v. in inhibiting gastric acid secretion evoked by histamine, gastrin, 2-deoxy-D-glucose and food. Orally, it was equipotent with ranitidine against histamine-induced secretion, but the duration of action of L-643,441 was substantially longer.

Subcutaneous administration of somatostatin analogs as a major factor in the enhancement of the duration of action.

Somatostatin and Des(Ala1Gly2)desaminol[Cys3]descarboxy-]Cys14[-]D-Trp8[dicarba3,14-somatostatin (Ia) are more potent inhibitors of glucagon, insulin and growth hormone release than the L-Trp8 analog (Ib). However when infused intravenously, these three compounds are equipotent but short-acting inhibitors of pentagastrin evoked gastric secretion in the dog. The duration of inhibition of equieffective antisecretory doses is significantly increased following subcutaneous administration 30 min prior to a food stimulus. The longest duration of antisecretory action is seen with the D-Trp8 analog (Ia) after subcutaneous administration.