Antimicrobial Resistance in Escherichia coli and Enterococcal Isolates From Irrigation Return Flows in a High-Desert Watershed

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.

Environmental effects of irrigation modernization in The Violada District (Spain)

<p>The comparative environmental studies on the modernization of irrigation systems are generally based on different areas with different characteristics (soil, dominant crops, crop management, or even weather conditions), not allowing for comparing the environmental effects in the same pre- and post-modernized irrigation district. Thus, there is a need to analyze the effect of the modernization process through the use of actual, detailed data from the same irrigation district.</p><p>The Violada Irrigation District (VID; 5234 ha, widely studied since the 1980s), with  92% of the surface modernized in 2008-09 form gravity to pressurized irrigation, offers an ideal scenario to evaluate the environmental implications of irrigation modernization.</p><p>The main tools for this evaluation have been (i) the water balance in the VID, to characterize the main irrigation water flows and their concentrations in salts and N, (ii) the soil water balance, to determine the main crops consumption [corn, alfalfa and cereal actual evapotranspiration (ETa)]; and (iii) the farmers surveys to establish fertilization and cropping practices. With all this information under both systems, the differences between the water and nitrogen use efficiencies for the main crops have been established for surface and sprinkler irrigation.</p><p>Comparing periods with similar crop patterns, dominated by corn, the modernization reduced the water abstraction for irrigation, decreased irrigation return flows and increased the consumptive use by the crops. Altogether, the modernization left more high-quality water available for other uses in the basin.</p><p>The irrigation and fertilization management also changed considerably with the modernization, allowing for lower doses with higher frequencies, and increasing the crop yields. Corn (the main crop in VID) showed the highest decrease in nitrogen fertilization. Nevertheless, the total nitrogen inputs to the system slightly increased due to the introduction of double crops. Thus, the corn increased water use efficiency and the nitrogen use efficiency.</p><p>The salt and nitrogen loads exported decreased after modernization, due to the reduced irrigation return flows. Under surface irrigation, the salts leaching was mainly produced during the irrigation season while under sprinkler irrigation, it took place all the year-round, avoiding the higher salt loads to the water bodies during the period of lower flow, when their environmental impact would be higher.</p><p>On the basis of the results obtained, it can be concluded that the modernization of the irrigation system caused a decrease in the flow restored to the basin, reduced the irrigation water depletion and preserved water quality globally. In this way, modernization leaves more water available for further uses and reduces the irrigation return flows and the pollutant loads associated with them. Finally, it was inferred that the salt and nitrogen loads emitted from the VID depend mainly on the irrigation system, and secondly, in regard to nitrogen only, on the prevailing crops.</p>

Groundwater natural background quality in transboundary aquifers

The Groundwater Natural Background Quality indicators stands for the percentage of the transboundary aquifer (TBA) area where groundwater natural quality satisfies local drinking water standards. In north-eastern Africa, parts of the Middle East and Northern India and Pakistan, low recharge values in TBAs are combined with high population densities. In these areas, return flows from irrigation and other human induced recharge appear to play a major role in the sustainability of groundwater resource utilization. Very low natural quality (less than 20 per cent of the aquifer area) coincides with TBAs highly impacted by irrigation return flows in densely populated areas with low to medium natural recharge, like the Nubian, Indus, Pre Caspian TBAs. For more information, visit: https://ggis.un-igrac.org/ggis-viewer/viewer/twap/public/default Drinking water Quality Transboundary