Effects of Physical Forcing on Summertime Hypoxia and Oxygen Dynamics in the Pearl River Estuary

A validated hydrodynamic-biogeochemical model was applied to investigate the effects of physical forcing (i.e., river discharge, winds, and tides) on the summertime dissolved oxygen (DO) dynamics and hypoxia (DO < 3 mg L−1) in the Pearl River estuary (PRE), based on a suite of model sensitivity experiments. Compared with the base model run in 2006 (a wet year), the simulated hypoxic area in the moderate year (with 75% of river discharge of the base run) and the dry year scenario (with 50% of river discharge of the base run) was reduced by ~30% and ~60%, respectively. This is because under the lower river discharge levels, less particulate organic matter was delivered to the estuary that subsequently alleviated the oxygen demand at the water–sediment interface, and in the meantime, the water stratification strength was decreased, which facilitated the vertical diffusion of DO. Regarding the effect of winds, the highly varying and intermittent strong winds had a significant impact on the replenishment of bottom DO by disrupting water stratification and thus inhibiting the development of hypoxia. Sensitivity experiments showed that the hypoxic area and volume were both remarkably increased in the low wind scenario (with a bottom hypoxic zone extending from the Modaomen sub-estuary to the western shoal in Lingdingyang Bay), whereas hypoxia was almost absent in the strong wind scenario. The DO budget indicated that winds altered the bottom DO mostly by affecting the DO flux due to vertical diffusion and horizontal advection, and had a limited influence on the DO consumption processes. Moreover, the DO concentration exhibited remarkable fluctuations over the spring-neap tidal cycles due to the significant differences in vertical diffusion. The results of a tide-sensitivity experiment indicated that without tide forcing, most of the shallow areas (average water depth < 5 m) in the PRE experienced severe and persistent hypoxia. The tides mainly enhanced mixing in the shallow areas, which led to higher vertical diffusion and enhanced replenishment of bottom DO

Spatiotemporal variations and controlling mechanism of low dissolved oxygen in a highly urbanized complex river system

Study region: Dongjiang River Network (DJRN), a complex urbanized river network in the Pearl River Basin, China. Study focus: Low-oxygen conditions have been expanding in urbanized river systems, whereas a clear and quantitative understanding on the deoxygenation processes is still lacking. This study utilized a well-validated physical-biogeochemical model to investigate the oxygen dynamics combined with river ecosystem metabolisms over an annual cycle and explicitly quantify the contribution of major oxygen-depleting substances from different sources to low-oxygen conditions. New hydrological insight for the region: Our results showed significant spatiotemporal variations in low-oxygen extents and oxygen source-sink patterns in the DJRN, where the underlying control mechanisms varied across stream order due to the intricate geographic and hydrological regime shifts in conjunction with diverse pollution stressors. Ascribed to the seasonal variations in anthropogenic pollution and water temperature, the entire DJRN shifted to a completely heterotrophic system with severe oxygen deficits during the late summer and early autumn. Scenario simulations indicated that in line with the substantial wastewater control in the DJRN region, local pollutant loads played a trivial role in the low-oxygen generation, which instead was primarily fueled by organic matter from transboundary delivery and in-situ primary production. Our findings underscored the necessity of co-regional collaborative management on pollutant emissions and the importance of eutrophication mitigation for the sake of oxygen recovery in the urbanized river network

Ni dispersed ultrathin carbon nanosheets as bi-functional oxygen electrocatalyst induced from graphite-like porous supramolecule

Excellent porosity and accessibility are key requirements during carbon-based materials design for energy conversion applications. Herein, a Ni-based porous supramolecular framework with graphite-like morphology (Ni-SOF) was rationally designed as a carbon precursor. Ultrathin carbon nanosheets dispersed with Ni nanoparticles and Ni-Nx sites (Ni@NiNx-N-C) were obtained via in-situ exfoliation during pyrolysis. Due to the hetero-porous structure succeeding from Ni-SOF, the Ni@NiNx-N-C catalyst showed outstanding bifunctional oxygen electrocatalytic activity with a narrow gap of 0.69 V between potential to deliver 10 mA cm−2 oxygen evolution and half-wave potential of oxygen reduction reaction, which even surpassed the Pt/C + IrO2 pair. Therefore, the corresponding zinc-air battery exhibited excellent power output and stability. The multiple Ni-based active sites, the unique 2D structure with a high graphitization degree and large specific surface area synergistically contributed to the excellent bifunctional electrocatalytic activity of Ni@NiNx-N-C. This work provided a novel viewpoint for the development of carbon-based electrocatalyst

Ni dispersed ultrathin carbon nanosheets as bi-functional oxygen electrocatalyst induced from graphite-like porous supramolecule

Excellent porosity and accessibility are key requirements during carbon-based materials design for energy conversion applications. Herein, a Ni-based porous supramolecular framework with graphite-like morphology (Ni-SOF) was rationally designed as a carbon precursor. Ultrathin carbon nanosheets dispersed with Ni nanoparticles and Ni-Nx sites (Ni@NiNx-N-C) were obtained via in-situ exfoliation during pyrolysis. Due to the hetero-porous structure succeeding from Ni-SOF, the Ni@NiNx-N-C catalyst showed outstanding bifunctional oxygen electrocatalytic activity with a narrow gap of 0.69 V between potential to deliver 10 mA cm−2 oxygen evolution and half-wave potential of oxygen reduction reaction, which even surpassed the Pt/C + IrO2 pair. Therefore, the corresponding zinc-air battery exhibited excellent power output and stability. The multiple Ni-based active sites, the unique 2D structure with a high graphitization degree and large specific surface area synergistically contributed to the excellent bifunctional electrocatalytic activity of Ni@NiNx-N-C. This work provided a novel viewpoint for the development of carbon-based electrocatalyst

Predicted current and future (2080) suitable habitats for five woody oil plants (<i>Pistacia chinensis</i>, <i>Cornus wilsoniana</i>, <i>Xanthoceras sorbifolia</i>, <i>Vernicia fordii</i> and <i>Sapium sebiferum</i>).

<p>Predicted current and future (2080) suitable habitats for five woody oil plants (<i>Pistacia chinensis</i>, <i>Cornus wilsoniana</i>, <i>Xanthoceras sorbifolia</i>, <i>Vernicia fordii</i> and <i>Sapium sebiferum</i>).</p

Percent contributions of the bioclimatic variables in the MaxEnt models for the nine target bioenergy plants.

<p>Percent contributions of the bioclimatic variables in the MaxEnt models for the nine target bioenergy plants.</p

Predicted current and future (2080) suitable habitats for four bioenergy grasses (<i>Miscanthus sinensis</i>, <i>M. floridulus</i>, <i>M. sacchariflorus</i> and <i>Arundo donax</i>).

<p>Predicted current and future (2080) suitable habitats for four bioenergy grasses (<i>Miscanthus sinensis</i>, <i>M. floridulus</i>, <i>M. sacchariflorus</i> and <i>Arundo donax</i>).</p

Predicting the Impacts of Climate Change on the Potential Distribution of Major Native Non-Food Bioenergy Plants in China

<div><p>Planting non-food bioenergy crops on marginal lands is an alternative bioenergy development solution in China. Native non-food bioenergy plants are also considered to be a wise choice to reduce the threat of invasive plants. In this study, the impacts of climate change (a consensus of IPCC scenarios A2a for 2080) on the potential distribution of nine non-food bioenergy plants native to China (<i>viz.</i>, <i>Pistacia chinensis</i>, <i>Cornus wilsoniana</i>, <i>Xanthoceras sorbifolia</i>, <i>Vernicia fordii</i>, <i>Sapium sebiferum</i>, <i>Miscanthus sinensis</i>, <i>M. floridulus</i>, <i>M. sacchariflorus</i> and <i>Arundo donax</i>) were analyzed using a MaxEnt species distribution model. The suitable habitats of the nine non-food plants were distributed in the regions east of the Mongolian Plateau and the Tibetan Plateau, where the arable land is primarily used for food production. Thus, the large-scale cultivation of those plants for energy production will have to rely on the marginal lands. The variables of “precipitation of the warmest quarter” and “annual mean temperature” were the most important bioclimatic variables for most of the nine plants according to the MaxEnt modeling results. Global warming in coming decades may result in a decrease in the extent of suitable habitat in the tropics but will have little effect on the total distribution area of each plant. The results indicated that it will be possible to grow these plants on marginal lands within these areas in the future. This work should be beneficial for the domestication and cultivation of those bioenergy plants and should facilitate land-use planning for bioenergy crops in China.</p></div

The area under receiver operating curve (AUC) score of MaxEnt models for each of the nine bioenergy plants.

<p>The area under receiver operating curve (AUC) score of MaxEnt models for each of the nine bioenergy plants.</p