Evaluation of the storage of diffuse sources of salinity in the Upper Colorado River Basin

OWRT project no. B-121-COL

Microbial and Chemical Characterization of Underwater Fresh Water Springs in the Dead Sea

Due to its extreme salinity and high Mg concentration the Dead Sea is characterized by a very low density of cells most of which are Archaea. We discovered several underwater fresh to brackish water springs in the Dead Sea harboring dense microbial communities. We provide the first characterization of these communities, discuss their possible origin, hydrochemical environment, energetic resources and the putative biogeochemical pathways they are mediating. Pyrosequencing of the 16S rRNA gene and community fingerprinting methods showed that the spring community originates from the Dead Sea sediments and not from the aquifer. Furthermore, it suggested that there is a dense Archaeal community in the shoreline pore water of the lake. Sequences of bacterial sulfate reducers, nitrifiers iron oxidizers and iron reducers were identified as well. Analysis of white and green biofilms suggested that sulfide oxidation through chemolitotrophy and phototrophy is highly significant. Hyperspectral analysis showed a tight association between abundant green sulfur bacteria and cyanobacteria in the green biofilms. Together, our findings show that the Dead Sea floor harbors diverse microbial communities, part of which is not known from other hypersaline environments. Analysis of the water’s chemistry shows evidence of microbial activity along the path and suggests that the springs supply nitrogen, phosphorus and organic matter to the microbial communities in the Dead Sea. The underwater springs are a newly recognized water source for the Dead Sea. Their input of microorganisms and nutrients needs to be considered in the assessment of possible impact of dilution events of the lake surface waters, such as those that will occur in the future due to the intended establishment of the Red Sea−Dead Sea water conduit

Suspended sediment transport in flash floods of the semiarid northern Negev

Abstract Our aim is to provide insight into various suspended sediment transport phenomena of upland ephemeral streams in a semiarid environment. Information about suspended sediment concentration is derived with the help of a programmable pump sampler and the continuous record of a turbidity sensor. Suspended sediment concentrations are high; the mean during six years of measurements was 34 000 mg 1"' and regression of suspended sediment concentration on water discharge takes the form SSC = 10 4 ' 1 Q 0A1 . During individual flash floods, the suspended sediment-water discharge relation may be hysteretic (clockwise or counterclockwise) and/or monotonie. In spite of complicated intra-event behaviour, there is a good, deterministic (R~ > 0.9) relation between total suspended sediment yield and flood volume

Grain‐Size Distribution and Propagation Effects on Seismic Signals Generated by Bedload Transport

Bedload transport is a key process in fluvial morphodynamics, but difficult to measure. The advent of seismic monitoring techniques has provided an alternative to in‐stream monitoring, which is often costly and cannot be utilized during large floods. Seismic monitoring is a method requiring several steps to convert seismic data into bedload flux data. State‐of‐the‐art conversion approaches exploit physical models predicting the seismic signal generated by bedload transport. However, due to a lack of well‐constrained validation data, the accuracy of the resulting inversions is unknown. We use field experiments to constrain a seismic bedload model and compare the results to high‐quality independent bedload measurements. Constraining the Green's function (i.e., seismic ground properties) with an active seismic survey resulted in an average absolute difference between modeled and empirically measured seismic bedload power of 11 dB in the relevant frequency band. Using generically estimated Green's function parameters resulted in a difference of 20 dB, thus highlighting the importance of using actual field parameters. Water turbulence and grain hiding are unlikely to be the cause of differences between field observations and our analysis. Rather, they may be either due to the inverted model being particularly sensitive to the coarse tail of the grain‐size distribution, which is least well constrained from field observations, or due to the seismic model underestimating effects of the largest grains.Key Points: Constrained seismic model inversion reveals dominant control of largest grain size on bedload flux estimates Measuring ground properties from a seismic experiment allows improving spectrogram fit by an order of magnitude in seismic power Considering all field‐constrained parameters results in bedload flux overestimation by two orders of magnitudeIsrael Science Foundation (ISF) http://dx.doi.org/10.13039/501100003977Israel Science Foundation (ISF) http://dx.doi.org/10.13039/501100003977NSF‐BS

Influence of Rarely Mobile Boulders on Channel Width and Slope: Theory and Field Application

Large, rarely mobile boulders are observed globally in mountainous bedrock channels. Recent studies suggest that high concentrations of boulders could be associated with channel morphological adjustment. However, a process‐based understanding of large boulder effects on channel morphology is limited, and data are scarce and ambiguous. Here, we develop a theory of steady‐state channel width and slope as a function of boulder concentration. Our theory assumes that channel morphology adjusts to maintain two fundamental mass balances: (a) grade, in which the channel transports the same sediment flux downstream despite boulders acting as roughness elements and (b) bedrock erosion, by which the channel erodes at the background tectonic uplift rate. Model predictions are normalized by a reference, boulder‐free channel width and slope, accounting for variations due to sediment supply, discharge, and lithology. Models are tested against a new data set from the Liwu River, Taiwan, showing steepening and widening with increasing boulder concentration. Whereas one of the explored mechanisms successfully explains the observed steepening trend, none of the models accuratly account for the observed width variability. We propose that this contrast arises from different adjustment timescales: while sediment bed slope adjusts within a few floods, width adjustment takes a much longer time. Overall, we find that boulders represent a significant perturbation to fluvial landscapes. Channels tend to respond by forming a new morphology that differs from boulder‐free channels. The general approach presented here can be further expanded to explore the role of other hydrodynamic effects associated with large, rarely mobile boulders.Plain Language Summary: Large boulders are a significant feature in mountainous landscapes. Recent studies suggested that boulders residing in rivers interfere with the flow and sediment transport, forcing their geometry, specifically width and slope, to change. Our ability to understand and predict such changes is challenged by scarce field data and a general lack of models capable of explaining the processes underlying channel geometry adjustment in the presence of boulders. Here, we develop a theory and several models for the variation of channel width and slope as with channel boulder coverage. Our theory builds on the assumption that the geometry of boulder‐bed channels evolves to a new configuration to maintain steadiness of erosion rate and sediment transport. Predictions from the various models are tested against data from the steep Liwu River in Taiwan. These data show that width and slope increase with more boulders. We find that channel slope increases to overcome the greater resistance to sediment transport due to the boulders. In contrast, the scattered nature of the width data and the overall models inability to explain width variability likely reflect a longer adjustment period for width than for slope. This study demonstrates the important role of boulders in shaping landscapes.Key Points: We develop a theory for steady‐state reach‐scale channel morphology responding to large, rarely mobile boulders in bedrock rivers. Predictions of boulder‐bed channel width and slope are derived based on grade equilibrium and bedrock erosional balance. Theory is tested against new data from the Liwu River, Taiwan, showing steepening and widening with increasing boulder concentration.Israel Science Foundation http://dx.doi.org/10.13039/501100003977NSF‐BSFhttps://zenodo.org/record/6371224#.YjdBkOpByU

Water stage and turbidity data of the Lower Jordan River 2010-2012

In February 2010, a hydrometric station was installed at the ''Qasser al-Yahud'' baptism site (740992E, 3525198N UTM Z36) at the Lower Jordan River, including a pressure sensors (Waterpilot FMX21, Schlumberger) and a turbidity sensor (TurbiMax WCUS41)