Extensive reservoir construction has fragmented more than 70% of the world's rivers, significantly impacting river connectivity and carbon cycling. However, the response of riverine dissolved organic matter (DOM) to reservoir influence and its potential downstream effects remains unclear. In this study, we employed multiple analytical techniques, including Fourier transform ion cyclotron resonance mass spectrometry, radiocarbon dating, and environmental factor analysis, to investigate the dynamic changes in DOM and its controlling factors under different hydrological management regimes in the LongTan Reservoir, the largest reservoir in the Pearl River, which is the second largest river in China by water discharge. Our results indicate that the molecular diversity of riverine DOM is reduced in the reservoir. Oxygen-rich and heteroatomic compounds, such as those containing nitrogen, sulfur, and phosphorus, are preferentially removed through enhanced photo- and biodegradation processes in the reservoir, particularly during the storage period. This leads to DOM that is enriched with oxygen-poor compounds and shows a biodegraded Delta 14C value downstream. This study highlights that the composition of riverine DOM is significantly altered by the reservoir, but these effects could potentially be mitigated by optimizing the outlet location.

Planets between the sizes of Earth and Neptune are the most common in the Galaxy, bridging the gap between the terrestrial and giant planets in our solar system. Now that we are firmly in the era of JWST, we can begin to measure, in more detail, the atmospheres of these ubiquitous planets to better understand their evolutionary trajectories. The two planets in the TOI-836 system are ideal candidates for such a study, as they fall on either side of the radius valley, allowing for direct comparisons of the present-day atmospheres of planets that formed in the same environment but had different ultimate end states. We present results from the JWST NIRSpec G395H transit observation of the larger and outer of the planets in this system, TOI-836c (2.587 R-circle plus, 9.6 M-circle plus, T-eq similar to 665 K). While we measure average 30-pixel binned precisions of similar to 24 ppm for NRS1 and similar to 43 ppm for NRS2 per spectral bin, we do find residual correlated noise in the data, which we attempt to correct using the JWST Engineering Database. We find a featureless transmission spectrum for this sub-Neptune planet and are able to rule out atmospheric metallicities <175x solar in the absence of aerosols at less than or similar to 1 mbar. We leverage microphysical models to determine that aerosols at such low pressures are physically plausible. The results presented herein represent the first observation from the COMPASS (Compositions of Mini-Planet Atmospheres for Statistical Study) JWST program, which also includes TOI-836b and will ultimately compare the presence and compositions of atmospheres for 12 super-Earths/sub-Neptunes.

Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations of protoplanetary disks in the millimeter continuum have shown a variety of radial gaps, cavities, and spiral features. These substructures may be signposts for ongoing planet formation, and therefore these systems are promising targets for direct imaging planet searches in the near-infrared. To this end, we present results from a deep imaging survey in the L ' band (3.8 mu m) with the Keck/NIRC2 vortex coronagraph to search for young planets in 43 disks with resolved features in the millimeter continuum or evidence for gaps/central cavities from their spectral energy distributions. Although we do not detect any new point sources, using the vortex coronagraph allows for high sensitivity to faint sources at small angular separations (down to similar to 0.'' 1), allowing us to place strong upper limits on the masses of potential gas giant planets. We compare our mass sensitivities to the masses of planets derived using ALMA observations, and while we are sensitive to similar to 1 M Jup planets in the gaps in some of our systems, we are generally not sensitive to planets of the masses expected from the ALMA observations. In addition to placing upper limits on the masses of gas giant planets that could be interacting with the dust in the disks to form the observed millimeter substructures, we are also able to map the micron-sized dust as seen in scattered light for 8 of these systems. Our large sample of systems also allows us to investigate limits on planetary accretion rates and disk viscosities.

Shock experiments are widely used to understand the mechanical and electronic properties of matter under extreme conditions. However, after shock loading to a Hugoniot state, a clear description of the post-shock thermal state and its impacts on materials is still lacking. We used diffraction patterns from 100-fs x-ray pulses to investigate the temperature evolution of laser-shocked Al-Zr metal film composites at time delays ranging from 5 to 75 ns driven by a 120-ps short-pulse laser. We found significant heating of both Al and Zr after shock release, which can be attributed to heat generated by inelastic deformation. A conventional hydrodynamic model that employs (i) typical descriptions of Al and Zr mechanical strength and (ii) elevated strength responses (which might be attributed to an unknown strain rate dependence) did not fully account for the measured temperature increase, which suggests that other strength-related mechanisms (such as fine-scale void growth) could play an important role in thermal responses under shock wave loading/unloading cycles. Our results suggest that a significant portion of the total shock energy delivered by lasers becomes heat due to defect-facilitated plastic work, leaving less converted to kinetic energy. This heating effect may be common in laser-shocked experiments but has not been well acknowledged. High post-shock temperatures may induce phase transformation of materials during shock release. Another implication for the study is the preservability of magnetic records from planetary surfaces that have a shock history from frequent impact events.

Hydrogen will play a key role in decarbonizing economies. Here, we quantify the costs and environmental impacts of possible large-scale hydrogen economies, using four prospective hydrogen demand scenarios for 2050 ranging from 111-614 megatonne H2 year-1. Our findings confirm that renewable (solar photovoltaic and wind) electrolytic hydrogen production generates at least 50-90% fewer greenhouse gas emissions than fossil-fuel-based counterparts without carbon capture and storage. However, electrolytic hydrogen production could still result in considerable environmental burdens, which requires reassessing the concept of green hydrogen. Our global analysis highlights a few salient points: (i) a mismatch between economical hydrogen production and hydrogen demand across continents seems likely; (ii) region-specific limitations are inevitable since possibly more than 60% of large hydrogen production potentials are concentrated in water-scarce regions; and (iii) upscaling electrolytic hydrogen production could be limited by renewable power generation and natural resource potentials.

This second paper presents an in-depth analysis of the composition of the planetary material that has been accreted on to seven white dwarfs with circumstellar dust and gas emission discs with abundances reported in Rogers et al. The white dwarfs are accreting planetary bodies with a wide range of oxygen, carbon, and sulphur volatile contents, including one white dwarf that shows the most enhanced sulphur abundance seen to date. Three white dwarfs show tentative evidence (2-3 sigma) of accreting oxygen-rich material, potentially from water-rich bodies, whilst two others are accreting dry, rocky material. One white dwarf is accreting a mantle-rich fragment of a larger differentiated body, whilst two white dwarfs show an enhancement in their iron abundance and could be accreting core-rich fragments. Whilst most planetary material accreted by white dwarfs display chondritic or bulk Earth-like compositions, these observations demonstrate that core-mantle differentiation, disruptive collisions, and the accretion of core-mantle differentiated material are important. Less than 1 per cent of polluted white dwarfs host both observable circumstellar gas and dust. It is unknown whether these systems are experiencing an early phase in the disruption and accretion of planetary bodies, or alternatively if they are accreting larger planetary bodies. From this work there is no substantial evidence for significant differences in the accreted refractory abundance ratios for those white dwarfs with or without circumstellar gas, but there is tentative evidence for those with circumstellar gas discs to be accreting more water rich material which may suggest that volatiles accrete earlier in a gas-rich phase.