基于寒地特征的沈北蒲河生态城市规划思考

寒地城市因特殊的气候特征而给城镇居民生产、生活带来许多不便,极大地制约着区域协调可持续发展。针对寒地城市规划实践长期缺乏基础理论指导的现状,本文试图从地域功能综合体的视角引入生态城市理念——生态城市是一个基于"经济—社会—自然环境"的复合生态系统,一个"功能合理、结构明确、形态俱佳的有机协调统一体";并据此从复合生态系统视角分析寒地城市规划的内容组分,从有机协调统一体视角组织寒地城市规划功能结构和空间布局,以期为我国寒地城市规划实践提供一个系统的理论指导框架。最后以沈北蒲河新城为例,进行实证分析。

Impact of grazing on germination trait selection in an alpine grassland on the Tibet Plateau

Previous studies indicated that grazing can cause significant changes in abiotic and biotic environment in grassland.However,how these changes impact germination trait selection in grassland has not been well studied.Thus,we aimed to explore whether grazing can significantly change germination trait diversity and composition of grasslands community.We measured the germination traits of species in the laboratory,and compared their performance in grazed and nongrazed grasslands.Then,we compared the community-weighted means of germination traits and functional diversity of grazed and nongrazed grasslands based on these germination traits to know whether grazed and nongrazed grasslands differed in their germination trait structures.At the species level,we found that the changes of abundance in grazed and nongrazed grasslands were not related to species’germination traits.However,at the community level,compared with nongrazed grasslands,species in the grazed grasslands generally exhibited a higher seed germination percentage.Moreover,seed germination response in grazed grasslands was more positively related to alternating temperature than in nongrazed grasslands,and breadth of the germination temperature niche was narrower in grazed than in nongrazed grasslands.Compared with nongrazed grasslands,seed germination trait diversity was increased and germination trait evenness decreased in grazed grasslands.Grazing can change microhabitat conditions,thereby changing germination trait selection by environmental filtering,resulting in a significant difference in germinate trait composition at the community level.

Distribution of fatty acids in the alpine grassland soils of the Qinghai-Tibetan Plateau

As an important biomarker, fatty acids(FAs) have been extensively used to trace the origin of organic matter in sediments and soils. However, studies of the distribution and abundance of FAs in alpine grassland soils are still rare, especially on the Qinghai-Tibetan Plateau(QTP), the highest plateau in the world, which contributes sediments to many large rivers in Asia. This study investigates the composition, distribution and source of FAs with increasing soil depths from 17 typical alpine grassland sites in the QTP. The most abundant FAs included the ubiquitous C16 FA and even-numbered long-chain FAs(C20–C30), indicating mixed inputs from microbial and higher plant sources. Source apportionment showed that higher plants were the dominant contributor of FAs(approximately 40%) in QTP soils. The abundance of FAs decreased with soil depth, with the highest value(1.08±0.09 mg/g C) at a 0–10 cm depth and the lowest value(0.46±0.12 mg/g C) at a 50–70 cm depth, due to much lower plant inputs into the deeper horizons. The total concentration of FAs was negatively correlated to the mean annual temperature(MAT; P<0.05) and soil p H(P<0.01), suggesting that the preservation of FAs was favored in low-MAT and low-p H soils on the QTP. The abundance of fresh C source FAs increased significantly with the mean annual precipitation(MAP; P<0.05), indicating that high MAP facilitates the accumulation of fresh FAs in QTP soils. Other environmental parameters, such as the soil mineral content(aluminum and iron oxide), microbial community composition as well as litter quality and quantity, may also exert a strong control on the preservation of FAs in QTP soils and warrant further research to better understand the mechanisms responsible for the preservation of FAs in QTP soils.

Distribution and enrichment patterns of selenium in the Ediacaran and early Cambrian strata in the Yangtze Gorges area, South China

The distribution and enrichment patterns of selenium(Se) in the E-?1 strata in the Yangtze Gorges area of South China were obtained. The geochemical characteristics of the significantly and non-significantly enriched strata of Se were analyzed.The observed enrichment factor(EF, relative to the upper continental crust) and concentration coefficient(CC, relative to the similar lithology in Eastern China) both suggest that Se is the most enriched/concentrated(SeEF=26.97, SeCC=48.04) among the analyzed23 trace elements the E-?1 strata. The normalized enrichment factor(EF′, EF after Al or Th normalized) shows Se is secondly enriched(SeEF′=218.73), which is slightly lower than cadmium(CdEF′=288.46) but significantly higher than the third enriched trace element arsenic(AsEF′=97.49). Se concentrations in the E-?1 strata vary from <10.5 to 30.08 ppm with an arithmetic mean value of 1.35 ppm. Compared to the Nantuo Formation, Se increased 11.78 times in the whole E-?1 strata and the average EF values are displayed as Shuijingtuo(92.58)>Yanjiahe(54.45)>Doushantuo(24.72)>Dengying(2.48)>Shipai(1.95)>lower Tianheban(1.24)Formations. Se concentrations in the E-?1 strata are best displayed on natural logarithm normal quantile-quantile(Q-Q) plots and shown as a positive-skewed distribution pattern. The Se significantly enriched(EF>10) strata sequences mainly include the lower and upper Doushantuo member II(DST-II), top DST-III, DST-IV, the basal and upper Yanjiahe Formation, and lower and upper Shuijingtuo Formation. Geochemical characteristics indicate that Se concentrations in the significantly enriched strata were generally influenced by terrigenous detrital as well as the combined action of single or multiple factors, such as hydrotherm,volcanic debris and deep source. Moreover, pyrite and organic matter promoted the enrichment of Se in the upper DST-II, DST-IV,upper Shuijingtuo Formation and lower DST-II, upper Shuijingtuo Formation, respectively. The Se concentrations in the not significantly enriched strata(except for DST-I, middle Shuijingtuo Formation, Shipai Formation and lower Tianheban Formation)were also influenced by terrigenous detrital, but other enrichment activities(e.g., hydrothermal, volcanic debris, and deep source)were generally insignificant.