Quantification of groundwater recharge in urban environments.

Groundwater management in urban areas requires a detailed knowledge of the hydrogeological system as well as the adequate tools for predicting the amount of groundwater and water quality evolution. In that context, a key difference between urban and natural areas lies in recharge evaluation. A large number of studies have been published since the 1990s that evaluate recharge in urban areas, with no specific methodology. Most of these methods show that there are generally higher rates of recharge in urban settings than in natural settings. Methods such as mixing ratios or groundwater modeling can be used to better estimate the relative importance of different sources of recharge and may prove to be a good tool for total recharge evaluation. However, accurate evaluation of this input is difficult. The objective is to present a methodology to help overcome those difficulties, and which will allow us to quantify the variability in space and time of the recharge into aquifers in urban areas. Recharge calculations have been initially performed by defining and applying some analytical equations, and validation has been assessed based on groundwater flow and solute transport modeling. This methodology is applicable to complex systems by considering temporal variability of all water sources. This allows managers of urban groundwater to evaluate the relative contribution of different recharge sources at a city scale by considering quantity and quality factors. The methodology is applied to the assessment of recharge sources in the Barcelona city aquifers.

Characterizing redox conditions and monitoring attenuation of selected pharmaceuticals during artificial recharge through a reactive layer.

A permeable reactive layer was installed at the floor of an infiltration basin. The reactive layer comprised 1) vegetable compost to provide a sorption surface for neutral organic compounds and to release easily degradable organic matter, thus generating a sequence of redox states, and 2) minor amounts of clay and iron oxide to increase sorption of cationic and anionic species, respectively. Field application of this design was successful in generating denitrification, and manganese-, and iron-reducing conditions beneath the basin. This, together with the increase in types of sorption sites, may explain the improved removal of three of the four selected pharmaceuticals compared with their behavior prior to installation of the layer. After installation of the reactive layer, atenolol concentrations were below the detection limits in the vadose zone. Moreover, concentrations of gemfibrozil and cetirizine were reduced to 20% and 40% of their initial concentrations, respectively, after 200 h of residence time. In contrast, prior to installation of the reactive layer, the concentrations of these three pharmaceuticals in both the vadose zone and the aquifer were more than 60% of the initial concentration. Carbamazepine exhibited recalcitrant behavior both prior to and after the reactive barrier installation.

Quantifying chemical reactions by using mixing analysis.

This work is motivated by a sound understanding of the chemical processes that affect the organic pollutants in an urban aquifer. We propose an approach to quantify such processes using mixing calculations. The methodology consists of the following steps: (1) identification of the recharge sources (end-members) and selection of the species (conservative and non-conservative) to be used, (2) identification of the chemical processes and (3) evaluation of mixing ratios including the chemical processes. This methodology has been applied in the Besòs River Delta (NE Barcelona, Spain), where the River Besòs is the main aquifer recharge source. A total number of 51 groundwater samples were collected from July 2007 to May 2010 during four field campaigns. Three river end-members were necessary to explain the temporal variability of the River Besòs: one river end-member is from the wet periods (W1) and two are from dry periods (D1 and D2). This methodology has proved to be useful not only to compute the mixing ratios but also to quantify processes such as calcite and magnesite dissolution, aerobic respiration and denitrification undergone at each observation point.

Using EMMA and MIX analysis to assess mixing ratios and to identify hydrochemical reactions in groundwater.

This study presents a methodology using an end-member mixing analysis (EMMA) and MIX to compute mixing ratios and to identify hydrochemical reactions in groundwater. The methodology consists of (1) identifying the potential sources of recharge, (2) characterising recharge sources and mixed water samples using hydrogeochemistry, (3) selecting chemical species to be used in the analysis and (4) calculating mixing ratios and identification of hydrochemical reactions in groundwater. This approach has been applied in the Besòs River Delta area, where we have collected 51 groundwater samples and a long data register of the hydrogeochemistry of the Besòs River created by the Catalan Water Agency is also available. The EMMA performed in the Besòs River suggests that 3 end-members are required to explain its temporal variability, accounting for the species chloride, sulphate, sodium, bicarbonate, calcium, magnesium, potassium, ammonium, total nitrogen, and electrical conductivity. One river end-member is from the wet periods (W1), and two are from dry periods (D1 and D2). These end-members have been used to compute mixing ratios in groundwater samples because the Besòs River is considered the main recharge source for the aquifer. Overall, dry season end-members dominated over the wet season end-member, in a proportion of 4:1. Moreover, when departures from the mixing line exist, geochemical processes might be identified. Redox processes, carbonate dissolution/precipitation and ion exchange processes may occur in Besòs Delta aquifer.

Drugs of abuse in urban groundwater. A case study: Barcelona.

This study is concerned with drugs of abuse (DAs) and their metabolites in urban groundwater at field scale in relation to (1) the spatial distribution of DAs in Barcelona's groundwater, (2) the depth of the groundwater samples, (3) the presence of DAs in recharge sources, and (4) the assessment of the fate of DAs in Barcelona aquifers. To this end, 37 urban groundwater samples were collected in the city of Barcelona and a total of 21 drugs were analyzed including cocainics, amphetamine-like compounds, opioids, lysergics and cannabinoids and the prescribed drugs benzodiazepines. Overall, the highest groundwater concentrations (around 200 ng/L in SAP-4) and the largest number of detected DAs were found in zones basically recharged by a river that receives large amounts of effluents from waste water treatment plants (WWTPs). In contrast, the urbanized areas yielded not only lower concentrations but also a much smaller number of drugs, which suggests a local origin. In fact, cocaine and its metabolite were dominant in more prosperous neighborhoods, whereas the cheaper MDMA was the dominant DA in poorer districts. Measured concentrations were consistently smaller than those estimated from the waste water fraction in groundwater samples, suggesting that DAs undergo removal processes in both reducing and oxidizing conditions.

Low reticulocyte hemoglobin content is associated with a higher blood transfusion rate in critically ill patients: a cohort study.

BACKGROUND: Intensive care unit (ICU) patients often need blood transfusion, but no reliable predictors of transfusion requirements are available at ICU admission. The authors hypothesized that ICU patients with functional iron deficiency may be at higher risk for developing anemia, requiring blood transfusion. Their objective was to determine whether low reticulocyte hemoglobin content (CHr) was associated with transfusion requirements in ICU patients. METHODS: This is a prospective cohort study in a general ICU. The authors studied 62 patients, after excluding those transfused on or before ICU admission. The authors recorded age, diagnosis, severity score, presence of sepsis, ICU complications, ICU treatments, and transfusion-free interval. Threshold for low CHr was 29 pg. The authors also recorded ICU and hospital outcome. The statistical analysis included Cox proportional hazard function for transfusion. RESULTS: Twenty-three patients (37%) presented with low CHr on ICU admission and tended to be sicker and more likely to have sepsis than those with normal CHr. They were also more prone to complications, particularly acute renal failure (39 vs. 13% P = 0.02) and ICU-acquired infection (30 vs. 10% P = 0.04). The overall transfusion rate was 22.6%, being higher in low-CHr patients than in normal-CHr patients (39.1 vs. 12.8%, P = 0.02). After adjusting for severity of illness, age, trauma, and hemoglobin level, low CHr remained significantly associated with transfusion, with a hazard ratio of 3.6 (95% CI, 1.2-10.7; P = 0.02). Median ICU stay was also longer in patients with low CHr (8 vs. 5 days, P = 0.01). Differences in mortality did not reach statistical significance. CONCLUSION: Low CHr is common at ICU admission and is associated with higher transfusion requirements.

Ward mortality in patients discharged from the ICU with tracheostomy may depend on patient's vulnerability.

OBJECTIVE: To determine the effect of discharge from the ICU with a tracheostomy tube on ward mortality and its relation to patient vulnerability. DESIGN AND SETTING: Retrospective single-center cohort study. METHODS: Database (2003-2006) review of patients undergoing mechanical ventilation (MV) > 24 h and discharged from the ICU with or without tracheostomy tube in place and followed up to hospital discharge or death. We recorded clinical characteristics, complications, major ICU procedures, subjective prognosis at ICU discharge (Sabadell score), and hospital outcome. Factors associated with ward mortality were analyzed by multiple logistic regression. RESULTS: From 3,065 patients admitted to the ICU, 1,502 needed MV > 24 h. Only 936 patients (62%) survived the ICU and were transferred to the ward; of these, 130 (13.9%) had a tracheostomy tube in place. Ward mortality was higher in patients with a tracheostomy tube in place than in those without (26 vs. 7%, P < 0.001). Increased ward mortality among cannulated patients was seen only in those with intermediate Sabadell score (24 vs. 9% in score 1, P = 0.02, and 38 vs. 24% in score 2, P = 0.06), but not in the "good prognosis" (2 vs. 2%, score 0) and "expected to die in hospital" (80 vs. 75%, score 3) groups. Multivariate analysis found three factors associated with ward mortality: age, tracheostomy tube in place, and Sabadell score. CONCLUSION: Lack of tracheostomy decannulation in the ICU appears to be associated with ward mortality, but only in the group with a Sabadell score of 1.