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951.
A River Water Quality Model for Chlorophyll and Dissolved Oxygen that Accommodates Zebra Mussel Metabolism 总被引:1,自引:0,他引:1
The development, testing and application of a dynamic two-dimensional (longitudinal-vertical) mass balance model for dissolved oxygen (DO) and chlorophyll (Chl) for rivers is documented that for the first time accommodates both the oxygen demand and filtering effects of zebra mussels. The test system is a phytoplankton-rich section ( 15 km long) of the Seneca River, NY, that is believed to represent an upper bound of the impact of this exotic invader. Changes in common measures of water quality of the river brought about by the zebra mussel invasion are reviewed and related longitudinal patterns in DO, Chl, and Secchi disc transparency are documented. Model testing is supported by comprehensive measurements of DO, Chl, and various forcing conditions over a three-month period, and independent determinations of several model coefficients. Wide variations in the areal consumption rate of DO (ZOD; g·m–2·d–1) and filtering rate (m3·m–2·d–1) of zebra mussels, as determined through model calibration, occurred over the study period. Values of ZOD in areas with dense zebra mussel populations at times (e.g., > 50 g·m–2·d–1) were an order of magnitude greater than the sediment oxygen demand associated with organically enriched deposits. The value of determinations of these fluxes from model calibration procedures is evaluated within the context of the limitations of protocols presently available to support independent specification of these rates. Model analyses are conducted to evaluate the relative magnitude of source and sink processes for DO and Chl, the potential operation and implications of feedback from low DO levels on oxygen consumption by zebra mussels, and the sensitivity of model simulations to selected sources of uncertainty and variability. Model projections of oxygen resources of the river are presented in a probabilistic format in evaluating reductions in zebra mussel biomass that would be necessary to eliminate violations of standards and regain assimilative capacity. 相似文献
952.
A. Sarkar R. Ramesh S. K. Bhattacharya N. B. Price 《Journal of Earth System Science》2000,109(1):157-169
δ18 O and δ13C of G.sacculifer have been measured in five cores from the northern Indian Ocean. In addition, high resolution analysis (1 to 2 cm) was performed
on one core (SK-20-185) for both δ18O and gd13C in five species of planktonic foraminifera. CaCO3 variation was measured in two cores. The results, presented here, show that
相似文献
– | • the summer monsoon was weaker during 18 ka and was stronger during 9 ka, relative to modern conditions; |
– | • δ13C variations are consistent with independent evidence that shows that during the last glacial maximum (LGM; 18 ka) the upwelling was reduced while during 9 ka it was vigorous; |
– | • calculation of CaCO3 flux shows that the LGM was characterized by low biogenic productivity in the Arabian Sea while during the Holocene productivity increased by ∼65%, as a direct consequence of the changes in upwelling. Similar changes (of lesser magnitude) are also seen in the equatorial Indian Ocean. The amount of terrigenous input into the Arabian Sea doubled during LGM possibly due to the higher erosion rate along the west coast. |
– | • δ18O values indicate that the Arabian Sea was saltier by 1 to 2%o during LGM. The northern part was dominated by evaporation while in the equatorial part there was an increased precipitation. |
953.
Deep saline aquifers are one of the most suitable geologic formations for carbon sequestration. The linear and global stability analysis of the time-dependent density-driven convection in deep saline aquifers is presented for long-term storage of carbon dioxide (CO2). The convective mixing that can greatly accelerate the CO2 dissolution into saline aquifers arises because the density of brine increases upon the dissolution of CO2 and such a density difference may induce instability. The effects of anisotropic permeability on the stability criteria, such as the critical time for the appearance of convective phenomena and the critical wavelength of the most unstable perturbation, are investigated with linear and global stability analysis. The linear stability analysis provides a sufficient condition for instability while the global stability analysis yields a sufficient condition for stability. The results obtained from these two approaches are not exactly the same but show a consistent trend, both indicating that the anisotropic system becomes more unstable when either the vertical or horizontal permeability increases. 相似文献
954.
From 1998 to 2002 investigations were carried out to estimate both the quantity and quality (heavy metal contents) of suspended matter loads discharged into a floodplain area measuring approx. 5 km2 of the Central German river Weiße Elster, a tributary of the river Saale in the Elbe river basin. Flood sediments, suspended particulate matter, and floodplain soils were investigated especially for the main pollutants Cd, Zn, Cu, Pb, Cr, and Hg. Supplementary gamma spectroscopy examinations were performed to help to identify the age of deposits in order to estimate sedimentation rates for last decades. The recent flood sediments are contaminated by up to 33 times the geogenic background (Cd). Up to 55% of the total annual SPM load of the river Weiße Elster is relocated into the investigated retention area in the flood‐stricken year 2002. The sedimentation rates for the last 50 years vary between 0.5 mm/a and 1 mm/a in far away and rarely flooded parts and between 1 mm/a and 2 mm/a in the frequently flooded parts of the inflow of the retention area. 相似文献
955.
The use of riparian vegetated filter strips to reduce river sediment loads: an overestimated control measure? 总被引:1,自引:0,他引:1
The spatially distributed soil erosion and sediment delivery model WATEM/SEDEM was used to simulate the impact of riparian vegetated filter strips (RVFSs) on river sediment delivery at different spatial scales. For a field plot with a straight slope, sediment reduction by the RVFSs is comparable to results obtained through experimental set‐ups elsewhere (i.e. >70%). However, at the scale of an entire catchment, sediment reduction is much less (i.e. ±20%) due to (1) overland flow convergence, which reduces the sediment trapping efficiency of an RVFS, and (2) because part of the sediment bypasses the RVFSs through ditches, sewers and road surfaces. These results suggest that, at the catchment scale, RVFSs should be accompanied with other conservation techniques that are more appropriate for reducing river sediment loads, and that also reduce on‐site soil erosion. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
956.
2004年3月至2005年7月对古尔班通古特沙漠南部典型半固定沙垄土壤水分进行了系统监测,结合气象资料,特别是对冬季积雪和冻土资料的分析,认为该沙漠沙丘土壤水分时空变化规律在很大程度上受积雪融化和季节性冻土的影响.由于冬季稳定存在20~30 cm的积雪于春季融化,使得春季沙丘土壤含水率成为全年最高的季节,从而为早春植物的萌发生长创造了有利的条件.冬季1 m多深的冻土于早春时节由表及里开始消融,沙丘表面融化的雪水在坡面重力作用下,沿难以透水的冻土层上界自坡上向坡下发生迁移,在春夏季形成了垄间最高、坡部次之和垄顶最少的土壤水分空间格局.该研究具有生态学意义,可为古尔班通古特沙漠特殊环境条件下植被恢复与重建提供依据. 相似文献
957.
柴达木盆地天然气的碳同位素地球化学特征及成因分析 总被引:4,自引:0,他引:4
依据天然气碳同位素中δ13C1、δ13C2、δ13C3的组成与划分标准,将柴达木盆地天然气划分为煤型气、裂解气、油型气与生物气四种类型,通过对天然气同位素中的δ13C1、δ13C2-δ13C1、δ13C3-δ13C2值的差异分析以及与对应的烃源岩干酪根碳同位素进行对比分析,探讨了柴达木盆地不同地区天然气的成因以及影响因素,这对于探索柴达木盆地的成气规律以及在不同地区天然气勘探的目标选择都有着现实意义。 相似文献
958.
959.
植物化石和土壤中的有机质碳同位素指标常用来反映古气候的变化,然而碳同位素这个指标在特定地区反映气候的定量关系缺乏检验。研究剖面选择自中国的秦岭(34°14'24″N,106°55'30″E)到蒙古人民共和国北部,接近贝加尔湖地区(51°35'08″N, 100°45'49″E)的研究剖面线,选择了3种C3植物(Artemisia scoparia, Ajania achilleides 和 Artemisia frigida),在剖面线上沿南北方向上每隔4'到5'采取一个样点,共选取161个C3植物茎叶样品进行了δ13 C值测定。同时收集了剖面线附近气象站的降水、气温等资料,用插值方法得到每个采样点的气温、降水数据。分析表明:C3植物的δ13 C值分布范围为-30 ‰ ~-22 ‰ ,其平均值为-26.81 ‰ ,该平均值较全球C3植物δ13 C平均值偏正。通过对比C3植物δ13 C与年均温、年均降水量、生长季节的干燥度等随纬度的变化规律,发现C3植物δ13 C、年均降水量、生长季节的干燥度有非常一致的变化趋势,而C3植物δ13 C和年均温不具有一致性。通过一元回归分析也同样发现C3植物δ13 C与年均降水量呈线性负相关关系(y=-0.0077x-24.838,n=161,R2=0.4418,p=0.01),与生长季节的干燥度呈线性正相关关系(y=0.7328x-28.806,n=161,R2=0.3685,p=0.01),而与年均温度没有明显的相关关系(y=-0.0461x-26.756,n=161,R2=0.0232,p=0.01)。在本研究区C3植物δ13 C对年均降水量和生长季节的干燥度响应十分显著,而对温度的响应不明显。研究区具有明显的降水和温度的梯度分布特征,是验证植物碳同位素与气候关系的理想场所,而土壤中的有机质碳同位素与其地面上的植物碳同位素息息相关。研究也说明,在本研究区或其他气候植物组合相似的地区可以利用古土壤中的有机质碳同位素来定量或半定量地反映古气候的变化。 相似文献
960.
耕作措施对陕西耕作土壤碳储量的影响模拟* 总被引:6,自引:0,他引:6
鉴于农业生态系统土壤有机碳(SOC)平衡对中国农业可持续发展的重要性,文章以陕西农业生态系统为对象,整合农业生物地球化学模型(DNDC)与陕西农业地理信息系统数据库,利用陕西地区气象和作物资料,对陕西省2000年作物生长发育和土壤碳循环进行了模型模拟,实例探讨了耕作管理对土壤碳储量的影响,并由此评价生物地球化学模型在气候变化、土壤性质及农业耕作管理措施对土壤碳含量影响方面的预测能力。敏感性分析表明土壤性状,尤其是初始有机碳含量是影响模型区域尺度模拟的最主要敏感因素。区域模拟使用灵敏系数分析法,分别采用敏感因子的最大、最小值驱动模型在每一模拟单元内的运算,以产生一个土壤有机碳变化的范围值,土壤有机碳变化的真实值应以较大机率包含在这一范围内。分析模拟结果可以得出3点结论: 1)2000年陕西耕作土壤总有机碳储量约为103TgC,是一个大气CO2源,向大气释放碳0.5TgC; 2)提高作物秸秆还田率是提高陕西农田碳库储量的有效可行措施,将作物秸秆还田率从当前的15 % 提高到50 % 或90 % 会使陕西农田土壤从大气CO2源转变为汇,每年分别增加土壤有机碳库储量0.7TgC或2.1TgC; 3)施用有机农肥(500kg/hm2)也会增加土壤碳输入,从而提高土壤碳储量,使陕西农田系统转变为较弱的碳(C)源,每年可多固定0.2TgC。 相似文献