Hydrologic exchange flows (HEFs) across the river‐aquifer interface have important implications for biogeochemical processes and contaminant plume migration in the river corridor, yet little is known about the hydrogeomorphic factors that control HEFs dynamics under dynamic flow conditions. Here, we developed a 3‐D numerical model for a large regulated river corridor along the Columbia River to study how HEFs are controlled by the interplays between dam‐regulated flow conditions and hydrogeomorphic features of such river corridor system. Our results revealed highly variable intra‐annual spatiotemporal patterns in HEFs along the 75‐km river reach, as well as strong interannual variability with larger exchange volumes in wet years than dry years. In general, the river was losing during late spring to early summer when the river stage was high, and river was gaining in fall and winter when river stage was low. The magnitude and timing of river stage fluctuations controlled the timing of high exchange rates. Both river channel geomorphology and the thickness of a highly permeable river bank geologic layer controlled the locations of exchange hot spots, while the latter played a dominant role. Dam‐induced, subdaily to daily river stage fluctuations drove high‐frequency variations in HEFs across the river‐aquifer interfaces, resulting in greater overall exchange volumes as compared to the case without high‐frequency flows. Our results demonstrated that upstream dam operations enhanced the exchange between river water and groundwater with strong potential influence on the associated biogeochemical processes and on the fate and transport of groundwater contaminant plumes in such river corridors.

Chicken-pathogenic Escherichia coli is severely endangering the poultry industry in China and worldwide, and antibiotic therapy is facing an increasing problem of antibiotic resistance. Bacteriophages can kill bacteria with no known activity in human or animal cells, making them an attractive alternative to antibiotics. In this study, we present the characteristics of a novel virulent bacteriophage, Bp7, specifically infecting pathogenic multidrug-resistant E. coli. Phage Bp7 was isolated from chicken feces. Bp7 belongs to the family Myoviridae, possessing an elongated icosahedral head and contractile sheathed tail. It has a 168-kb doublestranded DNA genome. For larger yields, its optimal multiplicity of infection (MOI) to infect E. coli was about 0.001. The latent period was 10 to 15 min, and the burst size was 90 PFU/infected cell. It was stable both at pH 5.0 to 10.0 and at 40°C or 50°C for at least 1 h. Bp7 could infect 46% of pathogenic clinical E. coli strains. Bp7 harbored 791 open reading frames (ORFs) and 263 possible genes. Among the 263 genes, 199 possessed amino acid sequence identities with ORFs of phage T4, 62 had identities with other T4-like phages, and only one lacked any database match. The genome of Bp7 manifested obvious division and rearrangement compared to phages T4, JS98, and IME08. Bp7 is a new member of the "T4-like" genus, family Myoviridae. Its wide host range, strong cell-killing activity, and high stability to pH make it an alternative to antimicrobials for controlling drug-resistant E. coli in chickens. Chicken colibacillosis is one of the main bacterial diseases and severely endangers the poultry industry in China and worldwide. Escherichia coli has been identified as a major pathogen (1). Antibiotics are widely used to control chicken colibacillosis, but it is very common for E. coli to be resistant to antibiotics (2, 3). In recent years, nearly 80% of E. coli isolates from diseased animals have manifested severe resistance to antimicrobial drugs (4, 5), so antibiotic therapy is facing an increasing problem of antibiotic resistance. Bacteriophages are now considered a good alternative to antibiotics (6, 7).However, there are many problems with phage therapy, and not every phage strain is appropriate for such therapy. Based upon their replication methods, phages are classified as either virulent or lysogenic. Virulent phages replicate in their bacterial hosts and destroy them in the process, but lysogenic phages insert their genomes into their hosts' genomes (8). As it has turned out, both lysogenic and virulent bacteriophages are actively involved in the evolution of bacteria, including pathogens (9). A troubling possibility is that there are virulence genes in some phages and these genes can change the pathogenicity of their host bacteria. Lysogenic phages transfer genes that express toxin proteins or pathogenic factors among bacterial species (8, 10). For safety reasons, lysogenic phages are not allowed to be used in phage therapy, and if a phage is permitted to be an alternati...

The Community Land Model (CLM) represents physical, chemical, and biological processes of the terrestrial ecosystems that interact with climate across a range of spatial and temporal scales. As CLM includes numerous sub-models and associated parameters, the high-dimensional parameter space presents a formidable challenge for quantifying uncertainty and improving Earth system predictions needed to assess environmental changes and risks. This study aims to evaluate the potential of transferring hydrologic model parameters in CLM through sensitivity analyses and classification across watersheds from the Model Parameter Estimation Experiment (MOPEX) in the United States. The sensitivity of CLM-simulated water and energy fluxes to hydrological parameters across 431 MOPEX basins are first examined using an efficient stochastic sampling-based sensitivity analysis approach. Linear, interaction, and high-order nonlinear impacts are all identified via statistical tests and stepwise backward removal parameter screening. The basins are then classified according to their parameter sensitivity patterns (internal attributes), as well as their hydrologic indices/attributes (external hydrologic factors) separately, using Principal component analysis (PCA) and expectation-maximization (EM)based clustering approach. Similarities and differences among the parameter sensitivity-based classification system (S-Class), the hydrologic indices-based classification (H-Class), and the Koppen climate classification systems (K-Class) are discussed. Within each parameter sensitivity-based classification system (S-Class) with similar parameter sensitivity characteristics, similar inversion modeling setups can be used for parameter calibration, and the parameters and their contribution or significance to water and energy cycling may also be more transferrable. This classification study provides guidance on identifiable parameters, and on parameterization and inverse model design for CLM but the methodology is applicable to other models. A set of 3 experiments of model calibration were conducted to evaluate the transferability of model calibration strategies and parameter values within and between the classes. It was demonstrated that inverting parameters at representative sites belonging to the same class can significantly reduce parameter calibration efforts.

The present work explores the impact of the roughness on the turbulent boundary layers over forward-facing steps. The roughness topography on the top surface of the rough step is replicated from a realistic turbine blade and embodies three-dimensional and highly irregular topographical features. High spatial resolution particle image velocimetry measurements are performed in the x−y planes at two different spanwise positions in turbulent boundary layers over both smooth and rough steps of the same mean heights at Reh=3450 and δ/h=8. Comparison of mean flow structures, Reynolds normal and shear stresses, quadrant analysis of instantaneous shear stress contributing events, and average spanwise vorticity reveals that the separated flow after the step is weakened by the surface roughness on top of the step while the flow ahead of the step is invariant to the surface conditions. The characteristics of the coherent spanwise vortices such as the numbers, size, and circulation distributions are also found to be significantly modified by the roughness topography.

Semiarid ecosystems play a critical role in determining the interannual variability of the global terrestrial carbon sink. Water availability is a critical driver of productivity in semiarid ecosystems, which often alternate between carbon sink/source functioning during wet/dry years. In this study, we investigate how groundwater availability resulting from groundwater‐river water exchange influences net ecosystem exchange of CO2 (NEE), evapotranspiration (ET), and the surface energy balance at two semiarid ecosystems along the Columbia River in central Washington, USA. We examined 1 year of eddy covariance measurements from an upland sagebrush ecosystem primarily fed by rainfall without groundwater access and a riparian grassland ecosystem with groundwater access during the dry season due to lateral groundwater‐river water exchange. The two sites had distinct seasonal patterns of NEE and ET, driven by differences in water availability. While NEE at the upland sagebrush site was strongly constrained by water availability during the dry months, access to groundwater allowed the riparian site to maintain high NEE magnitude and ET during the same dry months. The riparian site had larger annual gross primary productivity than the upland site (612 vs. 424 gC/m2), which was offset by higher ecosystem respiration (558 vs. 363 gC/m2). Thus, the magnitude of the annual NEE at the upland site was larger than that at the riparian site (−62 vs. −54 gC/m2). Our results demonstrate that groundwater access determined by connectivity between groundwater and surface water can be a critical driver of carbon uptake and ET in semiarid ecosystems.