RESUMEN

Geologically "saline" zones with scarce pluviometry, which are already susceptible to the salinization of natural drainage, can experience the acceleration of the salinization of the receiving water systems with the implementation of irrigation. The main objective of this paper is to analyze the geochemical processes that control the variations of the hydrosaline balance due to the implementation of irrigation of the Lerma basin (Spain) from the beginning of its transformation into irrigation land (2004) until the consolidation of irrigation (2020). The results of this study evidence the dissolution of some mineral phases, such as halite, gypsum, and dolomite, and the precipitation of others, such as calcite. Additionally, the final composition of the irrigation return flows cannot be explained without consideration of the NaCa exchange. Part of the dissolved Ca2+ is deposited in the soil, which, in turn, contributes with Na+ to the solution. These natural processes are accelerated with irrigation but progressively slow down as the soil salts are washed with time. Although less evident, there is an additional negative agroenvironmental effect associated with the precipitation of calcite and the possible formation of petrocalcic horizons in the soil. The results obtained herein indicate that studies focusing on the salinity of irrigated zones should go a step further and include the geochemical processes in quantifying the global mass of exported salts.

RESUMEN

The intensive agricultural expansion and rapid urban development in Abu Dhabi Emirate, United Arab Emirates (UAE) have resulted in a major decline in local and regional groundwater levels. By using the latest release (RL06) of Gravity Recovery and Climate Experiment (GRACE) satellite measurements and Global Land Data Assimilation System (GLDAS) products, the groundwater storage change was computed and compared with the time series of in-situ monitoring wells over the period of 2010-2016. The RL06 GRACE products from Jet Propulsion Laboratory (JPL), University of Texas Center for Space Research (CSR), German Research Center for Geosciences (GFZ), and JPL mass concentrations (MASCON) were assessed and have shown satisfactory agreements with the monitoring wells. The JPL MASCON reflected the in-situ groundwater storage change better than the other GRACE products (R = 0.5, lag =1 month, RMSE = 13 mm). The groundwater recharge is estimated for the study area and compared with the in-situ recharge method that considers multi recharge components from the rainfall, irrigation return flow and internal fluxes. The results show that the agreements between in-situ and GRACE-derived recharge estimates are highly agreeable (e.g., R2 = 0.91, RMSE = 1.5 Mm3 to 7.8 Mm3, and Nash-Sutcliff Efficiency = 0.7). Using the Mann-Kendall trend test and Sen's slope, the analyses of policies, number of wells, and farm areal expansion with groundwater time series derived from GRACE helped to validate GRACE and emphasize the importance of regulations for sustainable development of groundwater resources. The impacts of subsidy cuts after 2010 can be captured from the GRACE data in the eastern region of Abu Dhabi Emirate. The linear trend of groundwater storage anomaly obtained from GRACE over the period from 2003 to 2010 is -6.36 ± 0.6 mm/year while it showed a decline trend of -1.2 ± 0.6 mm/year after the subsidy cut. The proposed approach has a potential application for estimating groundwater recharge in other arid regions where in-situ monitoring wells are limited or absent.

RESUMEN

Irrigation return flows (IRFs) collect surface runoff and subsurface drainage, causing them to have elevated contaminant and bacterial levels, and making them a potential source of pollutants. The purpose of this study was to determine antimicrobial susceptibility among Escherichia coli and enterococcal isolates that were collected from IRFs in a south-central Idaho watershed. Environmental isolates can be a potentially important source of antimicrobial resistance (AMR) and IRFs may be one way resistance genes are transported out of agroecosystems. Water samples were collected from nine IRFs and one background site (canal water from Snake River) on a biweekly basis during 2018. Escherichia coli and enterococci were enumerated via a most probable number (MPN) technique, then subsamples were plated on selective media to obtain isolates. Isolates of E. coli (187) or enterococci (185) were tested for antimicrobial susceptibility using Sensititre broth microdilution plates. For E. coli, 13% (25/187) of isolates were resistant to tetracycline, with fewer numbers being resistant to 13 other antimicrobials, with none resistant to gentamicin. While 75% (141/187) of the E. coli isolates were pan-susceptible, 12 multidrug resistance (MDR) patterns with 17 isolates exhibiting resistance to up to seven drug classes (10 antimicrobials). For the enterococcal species, only 9% (16/185) of isolates were pan-susceptible and the single highest resistance was to lincomycin (138/185; 75%) followed by nitrofurantoin (56/185; 30%) and quinupristin/dalfopristin (34/185; 18%). In addition, 13 enterococcal isolates belonging to Enterococcus faecalis, Enterococcus faecium, Enterococcus casseliflavus, and Enterococcus thailandicus, were determined to be MDR to up to six different antimicrobial drug classes. None of the enterococcal isolates were resistant to gentamycin, linezolid, tigecycline, and vancomycin.

RESUMEN

Surface waters could be a dominant route by which antibiotic resistance genes (ARGs) are disseminated. In the present study we explored the prevalence and abundance of ARGs [blaCTX-M-1, erm(B), sul1, tet(B), tet(M), and tet(X)], class 1 integron-integrase gene (intI1), and IncP-1 and IncQ-1 plasmids in eight irrigation return flows (IRFs) and a background site (Main Line Canal, MLC) in the Upper Snake Rock watershed in southern Idaho. Grab samples were collected on a monthly basis for a calendar year, which were processed to extract microbial DNA, followed by droplet digital PCR to quantify the gene copies on an absolute (per 100 mL) and relative (per 16S rRNA gene copies) basis. The antibiotic resistance and intI1 genes and IncP-1/IncQ-1 plasmids were recovered at all IRF sampling sites with detections ranging from 55 to 81 out of 81 water sampling events. The blaCTX-M-1 gene was detected the least frequently (68%), while the other genes were detected more frequently (88-100%). All of the genes were also detected at MLC from April to Oct when water was present in the canal. The genes from lowest to greatest relative abundance in the IRFs were: blaCTX-M-1 < erm(B) < tet(B) < IncQ-1 < tet(M) < sul1 < intI1 = IncP-1 < tet(X). When compared to the average annual relative gene abundances in MLC water samples, they were found to be at statistically greater levels (P ≤ 0.008) except that of the IncP-1 and IncQ-1 plasmids (P = 0.8 and 0.08, respectively). The fact that most IRFs contained higher levels than found in the canal water, indicates that IRFs can be a point source of ARGs that ultimately discharge into surface waters.

Asunto(s)

Farmacorresistencia Microbiana/genética , Monitoreo del Ambiente , Genes Microbianos , Riego Agrícola , Genes Bacterianos , Integrones/genética , Plásmidos , ARN Ribosómico 16S/genética

RESUMEN

Irrigation return flow can include contaminants derived from agricultural practices, and then deteriorate the quality of surface and subsurface water within the watershed. Thus, it is important to estimate the effect of irrigation return flow on water chemistry/quality. To do that water samples were collected between November 2004 and December 2005 from stream and groundwater in a small watershed that contains extensive rice paddy fields. The water isotopic compositions represented seasonal variation, particularly in downstream of main channel and the tributary. In April and May, water samples in the downstream and tributary could not be explained by three-component (soil water, groundwater and rainfall) hydrograph separation models (THSM). These results indicated that the stream water was affected by high evaporation and that another water body (e.g. quick return flow) impacted on THSM. Plot of Cl/NO3 and NO3/HCO3 showed that the water chemistry of all water samples was mainly regulated by soil water and groundwater. In addition, the water chemistry was related to water derived from rice paddy fields (WR) and manure. Manure impacted the water chemistry in tributary, one of the shallow groundwaters and the deep groundwaters, whereas that water in downstream was affected by WR. On a plot of δ15NNO3 and δ18ONO3 values, many samples were in a cluster indicative of manure and on a denitrification line. These imply that irrigation return flow characterized by denitrification processes was involved in determining the water chemistry. We suggest that chemical and multi-isotopes approach combined with the THSM is useful to elucidate the sources and processes controlling water chemistry in stream associated with rice paddy fields.