Search

A potential control of downstream channel width variations on the structure and planform of pool–riffle sequence local bed topography is a key to the dynamics of gravel bed rivers. How established pool–riffle sequences respond to time-varying changes in channel width at specific locations, however, is largely unexplored and challenging to address with field-based study. Here, we report results of a flume experiment aimed at building understanding of how statistically steady pool–riffle sequence profiles adjust to spatially prescribed channel width changes. We find that local bed slopes near steady-state conditions inversely correlate with local downstream width gradients when the upstream sediment supply approximates the estimated transport capacity. This result constrains conditions prior to and following the imposed local width changes. Furthermore, this relationship between local channel bed slope and downstream width gradient is consistent with expectations from scaling theory and a broad set of field-based, numerical, and experimental studies (n=88). However, upstream disruptions to coarse sediment supply through actions such as dam removal can result in a transient flipping of the expected inverse correlation between bed slope and width gradient, collectively highlighting that understanding local conditions is critical before typically implemented spatial averaging schemes can be reliably applied.

DNA double-strand breaks (DSBs) are linked to neurodegeneration and senescence. However, it is not clear how DSB-bearing neurons influence neuroinflammation associated with neurodegeneration. Here, we characterize DSB-bearing neurons from the CK-p25 mouse model of neurodegeneration using single-nucleus, bulk, and spatial transcriptomic techniques. DSB-bearing neurons enter a late-stage DNA damage response marked by nuclear factor κB (NFκB)–activated senescent and antiviral immune pathways. In humans, Alzheimer’s disease pathology is closely associated with immune activation in excitatory neurons. Spatial transcriptomics reveal that regions of CK-p25 brain tissue dense with DSB-bearing neurons harbor signatures of inflammatory microglia, which is ameliorated by NFκB knockdown in neurons. Inhibition of NFκB in DSB-bearing neurons also reduces microglia activation in organotypic mouse brain slice culture. In conclusion, DSBs activate immune pathways in neurons, which in turn adopt a senescence-associated secretory phenotype to elicit microglia activation. These findings highlight a previously unidentified role for neurons in the mechanism of disease-associated neuroinflammation.

This is the peer reviewed version of the following article: [Hassan, M. A., Chartrand, S. M., Radić, V., Ferrer-Boix, C., Buckrell, E., & McDowell, C. (2022). Experiments on the sediment transport along pool-riffle unit. Water Resources Research, 58, e2022WR032796. https://doi.org/10.1029/2022WR032796], which has been published in final form at https://doi.org/10.1029/2022WR032796. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. This study examines channel dynamics and mixed-load bed load transport through a riffle and pool sequence forced by downstream channel width variations within an experimental flume. The experiment consisted of four runs across which we compare and contrast local and spatially-averaged bed surface texture and topography, sediment transport rates and sediment mobility at five locations across a pool-riffle pair. Sediment transport was measured using mini Helley-Smith (HS) samplers and particle tracers seeded in the monitored riffle and pool. In this study, “local” sediment transport rates were highly variable across the five monitoring locations. The lowest sediment transport rate was recorded at the riffle tail whereas the highest rates were measured at the riffle head and the pool centre. The texture of the bed surface and transported load do not explain measured bedload transport trends and depending on how the measurements are aggregated differing interpretations are supported. In general, the bed texture in the pool was finer than the texture in the riffle, however specific grain-size percentile classes derived from pooled population analysis suggests little to no difference between pool and riffle texture. The combined results highlight the importance of acknowledging and applying analysis techniques to better understand the inherent variability of bedload transport within channel reaches where morphology differs, such as pools and riffles.

A potential control of downstream channel width variations on the structure and planform of pool-riffle sequence local bed topography is a key to the dynamics of gravel-bed rivers. How established pool-riffle sequences respond to time-varying shifts in the channel width, however, is largely unexplored and challenging to address with field-based study. Accordingly, here we report results of a flume experiment aimed at building understanding of the response of statistically steady pool-riffle sequences to prescribed channel width adjustments. We find that local bed slopes near steady-state conditions inversely correlate with local width change dynamics, and agree with expectations from scaling theory and a broad set of field-based, numerical and experimental studies (n=88). We also find that coarse sediment release from dam removal can temporally flip the expected inverse correlation, collectively highlighting that local conditions are important for understanding river morphology, and would be overlooked if analysis instead emphasized spatial averaging.