RECENT RIVERINE CARBON OF THE YELLOW RIVER: FLUXES, OUTGASSING AND BURIAL

Ph.DDOCTOR OF PHILOSOPH

Long-term spatial and temporal variation of CO2 partial pressure in the Yellow River, China

10.5194/bg-12-921-2015Biogeosciences124921-93

METTL14 Is a Chromatin Regulator Independent of Its RNA N6-Methyladenosine Methyltransferase Activity

METTL3 and METTL14 are two components that form the core heterodimer of the main RNA m6A methyltransferase complex (MTC) that installs m6A. Surprisingly, depletion of METTL3 or METTL14 displayed distinct effects on stemness maintenance of mouse embryonic stem cell (mESC). While comparable global hypo-methylation in RNA m6A was observed in Mettl3 or Mettl14 knockout mESCs, respectively. Mettl14 knockout led to a globally decreased nascent RNA synthesis, whereas Mettl3 depletion resulted in transcription upregulation, suggesting that METTL14 might possess an m6A-independent role in gene regulation. We found that METTL14 colocalizes with the repressive H3K27me3 modification. Mechanistically, METTL14, but not METTL3, binds H3K27me3 and recruits KDM6B to induce H3K27me3 demethylation independent of METTL3. Depletion of METTL14 thus led to a global increase in H3K27me3 level along with a global gene suppression. The effects of METTL14 on regulation of H3K27me3 is essential for the transition from self-renewal to differentiation of mESCs. This work reveals a regulatory mechanism on heterochromatin by METTL14 in a manner distinct from METTL3 and independently of m6A, and critically impacts transcriptional regulation, stemness maintenance, and differentiation of mESCs

Substantial increase of organic carbon storage in Chinese lakes

Previous studies typically assumed a constant total organic carbon (OC) storage in the lake water column, neglecting its significant variability within a changing world. Based on extensive field data and satellite monitoring techniques, we demonstrate considerable spatiotemporal variability in OC concentration and storage for 24,366 Chinese lakes during 1984–2023. Here we show that dissolved OC concentration is high in northwest saline lakes and particulate OC concentration is high in southeast eutrophic lakes. Along with increasing OC concentration and water volume, dissolved and particulate OC storage increase by 44.6% and 33.5%, respectively. Intensified human activities, water input, and wind disturbance are the key drivers for increasing OC storage. Moreover, higher OC storage further leads to an 11.0% increase in nationwide OC burial and a decrease in carbon emissions from 71.1% of northwest lakes. Similar changes are occurring globally, which suggests that lakes are playing an increasingly important role in carbon sequestration

Global carbon dioxide efflux from rivers enhanced by high nocturnal emissions

Carbon dioxide (CO2) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO2 concentrations. Using a global compilation of high-frequency CO2 measurements, we demonstrate that nocturnal CO2 emissions are on average 27% (0.9 gC m−2 d−1) greater than those estimated from diurnal concentrations alone. Constraints on light availability due to canopy shading or water colour are the principal controls on observed diel (24 hour) variation, suggesting this nocturnal increase arises from daytime fixation of CO2 by photosynthesis. Because current global estimates of CO2 emissions to the atmosphere from running waters (0.65–1.8 PgC yr−1) rely primarily on discrete measurements of dissolved CO2 obtained during the day, they substantially underestimate the magnitude of this flux. Accounting for night-time CO2 emissions may elevate global estimates from running waters to the atmosphere by 0.20–0.55 PgC yr−1

Estimating sediment trapping efficiency from Landsat images: A case study of the Yellow River basin

This paper is concerned with the man-made reservoirs constructed in the Yellow River basin. Given the shortcomings of conventional approaches to assessing reservoirs constructed in large river basins, remote sensing techniques offer several benefits. Remote sensing data can provide high-resolution synoptic and repetitive information at short time intervals. Based on the results of reservoir delineation and storage capacity estimation, in this study the Yellow River basin was divided into 12 sub-basins for which the water residence time and potential sediment trapping efficiency were explored. Water cycling in the basin has been greatly regulated and its residence time increased to 3.97 years during 2006-2009. The basin-wide sediment trapping efficiency is 95.2%, indicating that most sediment entering the channels would be trapped by the reservoirs. With more reservoirs to be completed, it is expected that flow regulation will become much more important and that the sediment flux reaching the ocean will further decrease. Copyright © 2012 IAHS Press.Link_to_subscribed_fulltex

Delineation of China's reservoirs and lakes using remote sensing techniques

We used remote sensing images to provide the first complete picture of the reservoirs and lakes located within China. We extracted 89 691 reservoirs, covering about 26 755 km2 of the land surface. By applying an empirical formula relating reservoir storage capacity and surface area, we estimated the total storage capacity to be about 770 km3. Also, we delineated more than 180 000 lakes and ponds, with a total surface area of about 79 767 km2. These include 2721 lakes larger than 1 km2. Through comparison with previous studies, we found that dramatic changes have occurred over the past decades. Reservoir construction and water diversion have changed the spatial distribution and seasonal variation of water resources and have made the river systems fragmented. Additionally, this study found that more than 200 lakes of >1 km2 on the Mongolia-Xinjiang Plateau and the Eastern Plain have disappeared, but about 50 lakes >1 km2 have appeared on the Tibetan Plateau. The disappearing lakes on the Mongolia-Xinjiang Plateau and the newly appearing lakes on the Tibetan Plateau could be a result of climate change; whereas the disappearance of lakes on the Eastern Plain, especially in the middle-lower reaches of the Yangtze and Huaihe River basin, reflect the impact of human activities, such as land reclamation and urbanization. The database of delineated reservoirs will be employed to estimate the total amount of sediment trapped behind dams. Copyright © 2012 IAHS Press.Link_to_subscribed_fulltex