1,795 research outputs found
Uncertainty assessment in river flow projections for Ethiopiaâs Upper Awash Basin using multiple GCMs and hydrological models
Uncertainty in climate change impacts on river discharge in the Upper Awash Basin, Ethiopia, is assessed using five MIKE SHE hydrological models, six CMIP5 general circulation models (GCMs) and two representative concentration pathways (RCP) scenarios for the period 2071â2100. Hydrological models vary in their spatial distribution and process representations of unsaturated and saturated zones. Very good performance is achieved for 1975â1999 (NSE: 0.65â0.8; r: 0.79â0.93). GCM-related uncertainty dominates variability in projections of high and mean discharges (mean: â34% to +55% for RCP4.5,â2% to +195% for RCP8.5). Although GCMs dominate uncertainty in projected low flows, inter-hydrological model uncertainty is considerable (RCP4.5: â60% to +228%, RCP8.5: â86% to +337%). Analysis of variance uncertainty attribution reveals that GCM-related uncertainty occupies, on average, 68% of total uncertainty for median and high flows and hydrological models no more than 1%. For low flows, hydrological model uncertainty occupies, on average, 18% of total uncertainty; GCM-related uncertainty remains substantial (average: 28%)
The role of superficial geology in controlling groundwater recharge in the weathered crystalline basement of semi-arid Tanzania
Study region: Little Kinyasungwe River Catchment, central semi-arid Tanzania. Study focus: The structure and hydraulic properties of superficial geology can play a crucial role in controlling groundwater recharge in drylands. However, the pathways by which groundwater recharge occurs and their sensitivity to environmental change remain poorly resolved. Geophysical surveys using Electrical Resistivity Tomography (ERT) were conducted in the study region and used to delineate shallow subsurface stratigraphy in conjunction with borehole logs. Based on these results, a series of local-scale conceptual hydrogeological models was produced and collated to generate a 3D conceptual model of groundwater recharge to the wellfield. New hydrological insights for the region: We propose that configurations of superficial geology control groundwater recharge in dryland settings as follows: 1) superficial sand deposits act as collectors and stores that slowly feed recharge into zones of active faulting; 2) these fault zones provide permeable pathways enabling greater recharge to occur; 3) âwindowsâ within layers of smectitic clay that underlie ephemeral streams may provide pathways for focused recharge via transmission losses; and 4) overbank flooding during high intensity precipitation events increases the probability of activating such permeable pathways. These conceptual models provide a physical basis to improve numerical models of groundwater recharge in drylands, and a conceptual framework to evaluate strategies (e.g., Managed Aquifer Recharge) to artificially enhance the availability of groundwater resources in these regions
Effects of Antiepileptic Drugs on GABA Responses and on Reduction of GABA Responses by PTZ and DMCM on Mouse Neurons in Cell Culture
The mechanisms of action of antiepileptic drugs effective against generalized absence seizures (antiabsence AEDs) remain uncertain. Antiabsence AEDs are generally effective against seizures induced in experimental animals by pentylenĂtĂtrazol (PTZ) and methyl-6,7-dimethoxy-4-ethyl-Î-carboline-3-carboxylate (DMCM), drugs which reduce GABAergic inhibition. Thus, antiabsence AEDs have been suggested to enhance GABAergic inhibition. We studied the effects of several AEDs on GABA responses recorded from mouse spinal cord neurons grown in primary dissociated cell culture. Four antiabsence AEDs were included: ethosuximide (ESM), dimethadione (DMO), sodium valproate (VPA), and diazepam (DZP). Two experimental AEDs, CGS 9896 and ZK 91296, with anticonvulsant action against PTZ- or DMCM-induced seizures were also included. Possible effects of the antiabsence and experimental AEDS on PTZ- and DMCM-induced inhibition of GABA responses were also evaluated. PTZ and DMCM revers-ibly reduced GABA responses in a concentration-dependent manner. PTZ complĂtĂly inhibited GABA responses at 10 mM (IC 50 of 1.1 mM), whereas DMCM-induced inhibition of GABA responses reached a plateau level of 39% of control values at 1 p.M (IC 50 of 33 nM). ESM (1,200 ÎM), DMO (6 mM), VPA (200 u.M), CGS 9896 (2 ÎM), and ZK 98% (2 Î M ) did not alter GABA responses. DZP enhanced GABA responses in a concentration-dependent manner. The inhibition of GABA responses produced by PTZ 1 mM was unaltered by ESM (600 Î M ), DMO (6 mM), CGS 9896 (1 Î M), or ZK 9896 (1 ÎM)- Coapplication of VPA (200 ÎM) and PTZ (1 mM) slightly enhanced the PTZ effect. DZP (> 10 nM), however, reversed the PTZ-induced reduction of GABA responses. The DMCM (250 nM) inhibition of GABA-responses was unaltered by ESM (600 Î.M), DMO (2 mM), or VPA (200 ÎM). CGS 9896 (2 Î M ) and ZK 91296 (2 ÎM), however, antagonized the DMCM effect. DZP (> 10 nM) significantly reversed the DMCM-induced inhibition of GABA responses. The lack of effect of VPA, ESM, and DMO on postsynaptic GABA responses suggests that direct enhancement of postsynaptic GABA action is not a common mechanism of action of antiabsence AEDs. The AEDs DZP, CGS 98%, and ZK 912% all reversed DMCM, but not PTZ, reduction of GABA responses, suggesting that these AEDs blocked DMCM seizures by acting at benzodiazepine receptors. However, since only DZP enhanced GABA responses, it is unclear how CGS 98% and ZK 912% blocked PTZ seizures. Key Words: AnticonvulsantsâGABAâNeuron cultureâCell cultureâSpinal cord neuronsâConvulsants. RESUMEN Los mecanismos de accidn de las medicaciones antiepilĂpticas eficaces contra los ataques generalizados de ausencia (AEDs antiausencia) permanecen inciertos. Los AEDs antiausencia son, generalmente, eficaces contra ataques experimentales inducidos por el pentilentetrazol (PTZ) y el metil-6,7-dimetoxy-4-etil-Pcarbolina-3-carboxilato (DMCM) en animates, medicaciones que reducen la inhibiciĂn GABAĂrgica. Hemos estudiado los efectos de varios AEDs sobre respuestas-GABA registradas en las neuronas de la mĂdula espinal de ratones que habian crecido en cultivos de cĂlulas primarieas disociadas. Cuatro AEDs antiausencia fueron incluidos: etoxusimida (ESM), dimetadiona (DMO), valproato sĂdico (VPA) y diazepan (DZP). TambtĂn se incluyeron dos AEDs experimentales, CGS 9896 y ZK 912%, con acciĂn anticonvulsiva contra los ataques inducidos por PTZ o DMCM. TambiĂn se valoraron los posibles efectos de los AEDs antiausencia y experimentales sobre el PTZ y la inhibiciĂn de las respuestas-GABA inducidas por el DMCM. El PTZ y el DMCM redujeron las respuestas-GABA de modo reversible y dependiendo de sus concentraciones. El PTZ inhibiĂ cmpleta-mente las respuestas-GABA a 10 mM (IC 50 de 1.1 mM) mientras que la inhibitiĂn de las respuestas GABA inducida por el DMCM alcanzĂ un nivel estable del 39% de los valores control con 1 Î. M (IC 50 de 33 mM). La ESM (1200 Î.M), la DMO (6 mM), el VPA (200 Î M ), el CGS 98% (2 Î M) y el ZK 98% (2 Î M) no alteraron las respuestas-GABA. El DZP aumentĂ las respuestas GABA de una manera concentraciĂn-dependiente. La inhibition de las respuestas-GABA producidas por el PTZ (1 mM), no se altero con las ESM (600 Î M), la DMO (6 mM), el CGS 98% (1 Î M) o el ZK 98% (1 Î .M). La co-aplicacion de VPA (200 Î M) y el PTZ (1 mM) aument6 ligeramente los efectos del PTZ. Sin embargo el DZP (10 nM) revirtiĂ significativamente la inhibition de las respuestas GABA inducidas por el DMCM. La falta de efectos de CPA, ESM y DMO sobre las respuestas GABA post-sinĂpticas sugiere que el incremento de la acciĂn GABA post-sinĂptica no es un mecanismo comĂn de actuatiĂn de las AEDs antiausencia. Todas las AEDs DZP, CGS 98% y ZK 912% revirtieron la reduction de las respuestas GABA producidas por el DMCM pero no las inducidas por el PTZ lo que sugiere que estos AEDs bloquean los ataques DMCM actuando sobre los receptores de la benzodiazepina. Sin embargo, puesto que el incremento de las respuestas GABA sĂlĂ se produce por el DZP, permanece todavia sin aclarar el por quĂ el CGS 98% y el ZK 912% bloquean los ataques producidos por el PTZ. ZUSAMMENFASSUNG Der Wirkmechansimus von Antiepileptika gegen generalisierte Absencen ist unklar. Antiabsencemittel sind generell wirkungs-voll gegen PTZ- und Methyl-6,7-Dimethoxy-4-Ăthyl-P-Carbolin-Î-Carboxylat (DMCM) induzierte tierexperimentelle AnfĂlle, also von Medikamenten, die die GABA-erge Inhibition reduzieren. Es wurde vermutet, daĂ Antiabsencemittel die GABA-erge Inhibition verstĂrken. Wir untersuchten die Wirkung von verschiedenen Antiepileptika auf GABA-Antworten in spinalen MĂuseneuronen, die in Zellkulturen gew-achsen waren. Es wurden 4 Absencemittel untersucht: Ethosux-imid (ESM), Dimethadion (DMD), Sodium Valproat (VPA) und Diazepam (DZP). ZusĂtzlich wurden 2 experimentelle Antiepileptika, CGS 98% und ZK 912%, die gegen PTZ0 oder DMCM-induzierte AnfĂlle wirkungsvoll sind, eingeschlossen. Mogliche Wirkungen der Antiabsence- und experimentellen Antiepileptika auf PTZ- und DMCM-induzierte Hemmung der GABA-Antworten wurden ebenfalls ausgewertet. PTZ und DMCM zeigten eine konzentrationsabhĂngige reversible Reduktion der GABA-Antworten. PTZ zeigte eine komplette Hemmung der GABA-Antworten bei 10 mM (IC 50 1,1 mM), DMCM-Hemmung der GABA-Antworten zeigte ein Plateau von 39% der Kontroll-werte bei 1 uJtf (ICJO von 33 mAfl. ESM (1200 uJtf), DMD (6 mM), VPA (200 Î M), CGS 98% (2 Î M) und ZK 98% (2 Î M) anderten nicht die GABA-Antworten. DZP verstarkte die GABA-Antworten konzentrationsabhangig. Die durch PTZ (1 mM) hervorgerufene Hemmung der GABA-Antworten war bei ESM (600 Î M), DMD (6 mM), CGS 98% (1 mAO und ZK 3836 (1 mM) unverĂndert. ZusĂtliche Anwendung von VPA (200 mM) und PTZ (1 mM) verstĂrkten geringfĂgig den PTZ-Effekt. DZP (10 nM) kehrte die durch PTZ hervorgerufene Reduktion der GABA-Antworten um. Die durch DMCM (250 nM) hervorgerufene Hemmung der GABA-Antworten war durch ESM (600 Î .M), DMD (2 mM) und VPA (200 Î M ) unbeeinflusst. CGS 98% (2 Î M) und ZK 912% (2 Î M ) antagonisierten die DMCM-Wirkung. DZP (>10 nM) kehrte die durch DMCM-induzierte Hemmung der GABA-Antworten um. Das Fehlen einer Wirkung von VPA. ESM und DMD auf die postsynaptischen GABA-Antworten legen nahe, daĂ eine direkte VerstĂrkung der postsynaptischen GABA-Aktion kein gemeinsamer Mechanis-mus der Antiabsencemittel darstellt. Die Antiepileptika DZP, CGS 98% und ZK 912% kehrten die DMCM-Wirkung auf die GABA-Antworten um, jedoch nicht die von PTZ, was vermuten lapt, daĂ diese Antiepileptika die DMCM-AnfĂlle Ăber die Wirkung an den Benzodiazipin-Rezeptoren verhinderte. Da jedoch nur DZP GABA-Antworten verstarkte, ist unklar, in welcher Weise CGS 98% und ZK 912% die PTZ-AnfaUe ver-hinderten.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65188/1/j.1528-1157.1989.tb05275.x.pd
Linkages between GRACE water storage, hydrologic extremes, and climate teleconnections in major African aquifers
Water resources management is a critical issue in Africa where many regions are subjected to sequential droughts and floods. The objective of our work was to assess spatiotemporal variability in water storage and related controls (climate, human intervention) in major African aquifers and consider approaches toward more sustainable development. Different approaches were used to track water storage, including GRACE/GRACE Follow On satellites for Total Water Storage (TWS); satellite altimetry for reservoir storage, MODIS satellites for vegetation indices, and limited ground-based monitoring. Results show that declining trends in TWS (60â73 km3 over the 18 yr GRACE record) were restricted to aquifers in northern Africa, controlled primarily by irrigation water use in the Nubian and NW Saharan aquifers. Rising TWS trends were found in aquifers in western Africa (23â49 km3), attributed to increased recharge from land use change and cropland expansion. Interannual variability dominated TWS variability in eastern and southern Africa, controlled primarily by climate extremes. Climate teleconnections, particularly El Nino Southern Oscillation and Indian Ocean Dipole, strongly controlled droughts and floods in eastern and southern Africa. Huge aquifer storage in northern Africa suggests that the recent decadal storage declines should not impact the regional aquifers but may affect local conditions. Increasing groundwater levels in western Africa will need to be managed because of locally rising groundwater flooding. More climate resilient water management can be accomplished in eastern and southern Africa by storing water from wet to dry climate cycles. Accessing the natural water storage provided by aquifers in Africa is the obvious way to manage the variability between droughts and floods
In-situ fluorescence spectroscopy is a more rapid and resilient indicator of faecal contamination risk in drinking water than faecal indicator organisms
Faecal indicator organisms (FIOs) are limited in their ability to protect public health from the microbial contamination of drinking water because of their transience and time required to deliver a result. We evaluated alternative rapid, and potentially more resilient, approaches against a benchmark FIO of thermotolerant coliforms (TTCs) to characterise faecal contamination over 14 months at 40 groundwater sources in a Ugandan town. Rapid approaches included: in-situ tryptophan-like fluorescence (TLF), humic-like fluorescence (HLF), turbidity; sanitary inspections; and total bacterial cells by flow cytometry. TTCs varied widely in six sampling visits: a third of sources tested both positive and negative, 50% of sources had a range of at least 720 cfu/100 mL, and a two-day heavy rainfall event increased median TTCs five-fold. Using source medians, TLF was the best predictor in logistic regression models of TTCs â„10 cfu/100 mL (AUC 0.88) and best correlated to TTC enumeration (Ïs 0.81), with HLF performing similarly. Relationships between TLF or HLF and TTCs were stronger in the wet season than the dry season, when TLF and HLF were instead more associated with total bacterial cells. Source rank-order between sampling rounds was considerably more consistent, according to cross-correlations, using TLF or HLF (min Ïs 0.81) than TTCs (min Ïs 0.34). Furthermore, dry season TLF and HLF cross-correlated more strongly (Ïs 0.68) than dry season TTCs (Ïs 0.50) with wet season TTCs, when TTCs were elevated. In-situ TLF or HLF are more rapid and resilient indicators of faecal contamination risk than TTCs
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