Impact of experimental warming on soil temperature and moisture of the shallow active layer of wet meadows on the Qinghai-Tibet Plateau

Climate change is now increasingly evident on the Qinghai–Tibet Plateau and has a strong impact on both the abiotic and biotic components of ecosystems, particularly on permafrost, active layer thickness, vegetation, and soil properties. Permafrost ecosystems are recognized to be sensitive to the influences of the changing climate, which may disturb the permafrost soil carbon (C) pool and lead to huge C emissions. To facilitate the assessment of warming effects on the temperature and moisture patterns in the shallow soil of the active layer of the wet meadows on the Qinghai–Tibet Plateau, near-surface air temperature was passively increased by using open-top chambers (OTCs) with two different temperature increments. Soil temperature and moisture were continuously monitored at depths of 5, 20, and 40 cm at hourly intervals in a wet meadow in the Beiluhe region on the Qinghai–Tibet Plateau from October 1, 2007 to June 24, 2009. When near-surface air temperature increased by 5.29 °C and 1.84 °C in the OTC2 and OTC1 plots, respectively, relative to the control plots, soil temperatures at depths of 5, 20, and 40 cm were seen to increase by 3.84°C, 2.23°C, and 1.42 °C, respectively, in the OTC2 plots and by 0.94°C, 0.27°C, and 0.25 °C, respectively, in the OTC1 plots. Soil moisture content at depths of 5, 20, and 40 cm declined by 8.04%, 1.79%, and 1.52%, respectively, in the OTC2 plots and by 5.33%, 0.69%, and 0.09%, respectively, in the OTC1 plots. Near-surface warming was found to extend the continuous thawing time of the shallow soil, delay the occurrence of the autumnal freezing process, and shorten the duration of continuous freezing. It was also seen to increase both the temperature of the shallow soil and the accumulated temperatures at different depths. Near-surface warming could be one of the main factors leading to the degradation of vegetation, thus threatening the stability of the soil C pool and the ecological safety of the Qinghai–Tibet Plateau.     

超高压处理对黑果枸杞汁贮藏及品质特性的影响

为开发黑果枸杞汁加工新技术,采用超高压处理(300、400、500 MPa/10 min)和巴氏杀菌(75℃,15 min)处理,分析处理前后及贮藏期(4和37℃,40 d)的微生物、活性成分、关键内源酶及抗氧化活性等品质的变化。结果表明,200 MPa以上高压处理和巴氏杀菌均能有效杀灭酵母菌和霉菌,300 MPa以上高压处理能使菌落总数降低到1个对数以下;300 MPa高压处理能使过氧化物酶(Peroxidase,POD)活性减少17.81 U/mL,但不能使多酚氧化酶(Polyphenol oxidase,PPO)酶活性显著降低;400 MPa以上及巴氏杀菌均能使POD酶和PPO酶活性降低至0.5 U/mL;超高压处理分别为300、400、500 MPa条件下,总酚含量分别为87.10、87.11、86.92 mg/100 g、总多糖含量分别为61.54、61.04、60.97 mg/mL、花青素含量分别为2.62、2.56、2.58 mg/mL;超高压处理的黑果枸杞汁对DPPH自由基清除率分别为86.82%、87.40%、86.60%,均高于巴氏杀菌处理的82.17%;超高压处理组对亚铁离子的还原能力分别为15.74、16.15、15.95 μg/100 mL DW,处理后直至贮藏结束,高压处理各活性物质均高于巴氏处理。超高压处理在有效灭活微生物、钝化酶的同时,极大程度保护活性物质不被破坏并保证了黑果枸杞汁的抗氧化能力,使得黑果枸杞汁得到了良好的贮藏品质。     

Additional deepwater sampling of prey fish in Lake Michigan annual bottom trawl survey reveals new insights for depth distribution dynamics

Beginning in 2013, sites at the 128-m bottom depth contour were added to the sampling design of the annual Lake Michigan bottom trawl survey for prey fish, which has been conducted by the U.S. Geological Survey Great Lakes Science Center (GLSC) each fall since 1973, to better assess fish depth distributions in a changing ecosystem. The standard sampling design included bottom depths from 9 to 110 m, although the GLSC also sporadically conducted bottom trawl tows at the 128-m bottom depth contour during 1973–1988. Enactment of this new sampling design in 2013 revealed that mean biomass density of deepwater sculpins (Myoxocephalus thompsonii) at the 128-m depth exceeded the sum of mean biomass densities at shallower depths, indicating that the bulk of the deepwater sculpin population is residing in waters deeper than 110 m. Thus, our findings supported the hypothesis that the depth distribution of the deepwater sculpin population had shifted to deeper waters beginning in 2007, thereby explaining, at least in part, the marked decline in deepwater sculpin abundance since 2006 based on the standard sampling design. In contrast, our results did not support the hypothesis that the slimy sculpin (Cottus cognatus) population had shifted to deeper waters sometime after 2000. A portion of the burbot (Lota lota) population may have also shifted in depth distribution to waters deeper than 110 m after 2007, based on our results. Our findings have served as an impetus to further expand the range of depths sampled in our bottom trawl survey.     

Analytical solution to one-dimensional mathematical model of flow and morphological evolution in open channels

Science China Technological Sciences - The evolution of open-channel flow and morphology can be simulated by one-dimensional (ID) mathematical models. These models are typically solved by numerical...     

Seventy years of food-web change in South Bay,Lake Huron

Though aquatic ecosystems (and the Laurentian Great Lakes in particular) have faced many stressors over the past century, including fisheries collapses and species invasions, rarely are data available to evaluate the long-term impacts of these stressors on food web structure. Stable isotopes of fish scales from the 1940s to the 2010s in South Bay, Lake Huron were used to quantify trophic position and resource utilization for fishes from offshore (alewife, cisco, lake trout, lake whitefish, rainbow smelt) and nearshore (rock bass, smallmouth bass, white sucker, yellow perch) habitats, providing one of the longest continuous characterizations of food webs in the Laurentian Great Lakes. Mean δ¹⁵N and δ¹³C values for each species were compared across twenty-year time periods. Using directional statistics, no significant community-wide changes were detected between time periods from 1947 to 1999. In contrast, a significant change was detected between 1980-1999 and 2000–2017, with all species showing increased reliance on nearshore resources. The increase in nearshore resource reliance for lake whitefish between these time periods was the greatest in magnitude compared with any other species between any two adjacent time periods. Besides lake whitefish, the increased reliance on nearshore resources was more pronounced for nearshore compared to offshore species. The timing of these shifts coincided with the invasion of dreissenid mussels and round goby, and declines in offshore productivity and prey densities. These results show the unprecedented magnitude of recent food-web change in Lake Huron after 50 years of relative stability.     

Seasonal fluctuations of organochlorine and triazines pesticides in the aquatic system of Ioannina basin (Greece)

For the period September 1984 to November 1985 water samples from the aquatic system of Ioannina basin were analyzed every second month for organochlorine and triazines pesticides. The detected compounds were found to follow a seasonal pattern, with an increment during summer followed by a decrease during winter and an increase again during late spring. This pattern was apparent for Ioannina lake as well as for the Kalamas river connected to it through the Lapsista's canal and tunnel. The results are discussed in terms of the amounts of the detected pesticides used for farming in the vicinity of the Ioannina basin and the seasonal rainfall.     

Dissolved and emitted methane in the Poyang Lake

Science China Technological Sciences - Lake waters often act as important methane sources for global greenhouse gas emission, but it would be more complex as lakes are regulated by rivers. In this...     

Modeling three-dimensional transport of microplastics and impacts of biofouling in Lake Erie and Lake Ontario

Studies in the oceans and The Great Lakes have found several orders of magnitude less plastic in surface samples than predicted by input estimates. Some plastic likely sinks after entering the water because it is naturally more dense than freshwater. For less dense particles, it has been proposed that biofouling, or the buildup of organic materials on the plastic, can cause them to become more dense and ultimately induce sinking. In this work we compare two different functional biofouling models: one basic algal growth population model and one model that assumes photosensitive defouling. We investigate the effects within the scope of a large-scale hydrodynamic model that includes advection, vertical diffusion, and sediment deposition applied to both Lake Erie and Lake Ontario. We find that deposition rates are dependent on the fouling method and lake depth. Lastly, we use the model to develop a first pass mass estimate for the sediment deposition rate in Lake Ontario.     

土石山区山坡壤中流汇流界面研究——以太行山崇陵流域为研究区

为促进山坡产汇流过程的精细化模拟,以河北省易县崇陵流域典型的土石山区不同坡位点(坡顶、坡中上、坡中、坡中下、坡脚)以及不同植被(油松和侧柏)为研究对象,采用亮蓝染色剂开展了野外双环入渗染色剂示踪试验,研究了山坡壤中流汇流界面的变化规律及其影响因子。结果表明:(1)山坡壤中流汇流界面埋深介于0. 6～1. 5 m之间,从坡顶到坡脚,汇流界面厚度逐渐减小;(2)植被覆盖对壤中流汇流界面的影响很大,在相同的坡位处,侧柏的壤中流汇流界面厚度大于油松的壤中流汇流界面厚度;(3)汇流界面的影响因素主要是土壤的结构和孔隙性、岩石风化层的层次结构,植被通过改变土壤的孔隙性引起汇流界面的变化。