Influences of carbonate weathering and hyporheic exchange on carbon fluxes in Pearl River Basin, China.

Deciphering riverine dissolved carbon dynamics is pivotal for a comprehensive picture of the global carbon cycle. Through rigorous in-situ sampling across the Pearl River Basin (PRB), our investigation reveals the Pearl River networks function as a significant carbon source, with the annual carbon dioxide (CO2) emission of 2.57 ± 1.94 Tg C, which offsets 10 ± 8 % of the forest carbon sequestration or 65 ± 49 % carbon sink via chemical weathering in the PRB. Based on the mass balance of 222Rn, we initially reveal that the contributions of water flux from the hyporheic zone increased with the river orders (Hack Order) across both dry and wet seasons. Conversely, the evasion rates of dissolved CO2 (CO2*) and dissolved inorganic carbon (DIC) from the hyporheic zone into river channels exhibited a decline with the increasing river orders. The hyporheic exchange contributes 4 - 11 % of the lateral and vertical DIC losses, thereby is a key mechanism in the riverine carbon cycle. Furthermore, CO2* derived from the hyporheic zone was ∼4 times of riverine CO2 emissions and this CO2* flux from the hyporheic zone was buffered into carbonates/bicarbonates in river channels, due to the high riverine pH resulted from carbonate weathering in the basin. These results not only highlight the substantial role of carbonates and hyporheic processes in modulating riverine carbon fluxes but also signify their broader implications on understanding riverine carbon dynamics at both regional and global scales.

Large lateral photovoltaic effect with ultrafast optical relaxation time in SnS2/n-Si junctions.

A large lateral photovoltaic effect (LPE) with a fast optical response time is necessary to develop high-performance position-sensitive detectors. In this paper, we report an LPE with a high self-powered position sensitivity and ultrafast optical relaxation time in S n S 2/n-S i junctions prepared using pulsed laser deposition. A large built-in electric field was generated at the S n S 2/S i interface, which resulted in a large LPE with a positional sensitivity of up to 116 mV/mm. Furthermore, the measurement circuit with multiple parallel resistors had a strong influence on the ultrafast optical response time of the LPE and the fastest optical relaxation time observed was ∼0.44µs. Our results suggest that the S n S 2/S i junction would be a promising candidate for a wide range of optoelectronic device applications.

Nitrogen removal through denitrification in China's aquatic system.

Investigating aquatic denitrification is essential for understanding nitrogen (N) removal in ecosystems, especially in China, the largest N fertilizer producer and consumer globally. In this study, we examined benthic denitrification rates (DNR) in China's aquatic ecosystems with 989 data over two decades to overview the long-term trend and spatial and system differences of DNR. Rivers have the highest DNR among the studied aquatic ecosystems (rivers, lakes, estuaries & coasts, and continental shelves) due to high hyporheic exchange, the fast nutrient supply, and more suspended particles. The average DNR in China's aquatic ecosystems is much higher than that of the global average, indicating an effect of higher N inputs and lower N use efficiency. Spatially, DNR increases from west to east in China, and DNR hotspots are on coasts, estuaries, and downstream of rivers. Temporally, DNR shows a slight decline regardless of system differences, owing to national-scale water quality recovery. Human activities indeed impact denitrification, where N fertilization intensity strongly correlates with DNR, and higher population density and human-dominated land may enhance DNR by increasing C and N loadings to the aquatic system. The total N removal via denitrification in China's aquatic systems is roughly estimated to be 12.3 ± 5 Tg N yr-1. Based on the overview of previous studies, we suggest conducting investigations with larger spatial scales and long-term denitrification measurements in the future to better understand the mechanism and hotspots in N removal in the context of climate change.

Modeling Phosphorus Losses through Surface Runoff and Subsurface Drainage Using ICECREAM.

Modeling soil phosphorus (P) losses by surface and subsurface flow pathways is essential in developing successful strategies for P pollution control. We used the ICECREAM model to simultaneously simulate P losses in surface and subsurface flow, as well as to assess effectiveness of field practices in reducing P losses. Monitoring data from a mineral-P-fertilized clay loam field in southwestern Ontario, Canada, were used for calibration and validation. After careful adjustment of model parameters, ICECREAM was shown to satisfactorily simulate all major processes of surface and subsurface P losses. When the calibrated model was used to assess tillage and fertilizer management scenarios, results point to a 10% reduction in total P losses by shifting autumn tillage to spring, and a 25.4% reduction in total P losses by injecting fertilizer rather than broadcasting. Although the ICECREAM model was effective in simulating surface and subsurface P losses when thoroughly calibrated, further testing is needed to confirm these results with manure P application. As illustrated here, successful use of simulation models requires careful verification of model routines and comprehensive calibration to ensure that site-specific processes are accurately represented.