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1.
The Delaware River Estuary (DRE) is a cornerstone of industrialization, shipping, and urban usage, and has a long history of human impact on pollution and recovery. Mercury (Hg) is a contaminant of concern in the DRE based upon concentrations in some fish samples that were found to exceed State and Federal fish tissue criteria. Methylation of Hg often follows a seasonal pattern as its production is biologically mediated. Surveys were conducted in November 2011, April 2012, and July 2012 to assess this effect. We sampled surface and bottom water at six sites spanning the estuarine turbidity maximum (ETM) in the main channel of the river, plus three sediment sites at shallow, subtidal locations. Our results indicate there is a clear seasonal increase in both water column and sediment methylmercury (MeHg) and %MeHg concentrations in the ETM during July. Water-column-filtered total mercury (HgT), suspended particle HgT, and MeHg concentrations were found to fluctuate little with location or season in the ETM. In contrast, sediment MeHg, water-column-filtered MeHg, and pore water HgT varied seasonally. Furthermore, pore water MeHg levels were elevated in concert with increased k meth rates in July. Estimated river input and sediment and atmospheric depositional MeHg flux were compared seasonally. River flux was more than an order of magnitude higher than sediment flux in April, coinciding with higher fluvial transport. However, during July, river flux decreases and sediment flux becomes a larger relative source. This trend has potential implications for fish and other biota residing in the DRE during summer.  相似文献   

2.
Redox transformations of iron in the surface waters of the Gulf of Aqaba, Red Sea, were studied on recurrent cruises from September 2006 to May 2007. Fe(II) concentrations and oxidation kinetics were measured in situ using luminol chemiluminescence. High Fe(II) concentrations of 200-400 pM were recorded in the autumn, followed by low concentrations of 20-130 pM in the winter-spring. A distinct diurnal pattern in Fe(II) concentrations was observed in the autumn with maximum values coinciding with maximum solar irradiance. In situ and in vitro Fe(II) oxidation rates showed temporal and spatial variability that was accounted for by changes in water temperature and pH. Dissolved oxygen was found to be the dominant oxidant in all but one cruise. In situ photoreduction rates (deduced from oxidation rates) were linearly correlated with solar irradiance during the autumn, suggesting that the reducible iron pool was not exhausted even at the strongest irradiances and that it was kept constant throughout the season. Phytoplankton had no discernible influence on Fe(II) production, consumption, or oxidation kinetics. Given the fast oxidation and photoreduction rates of up to 180 pM min−1, the turn-over rates of iron were estimated at 10-30 per day. Such a dynamic Fe redox cycle probably influences the chemical reactivity and bioavailability of iron and may enhance the solubility of the abundant aerosol dust.  相似文献   

3.
Plankton metabolism andRuppia maritima biomass were measured seasonally during 1982–83 in El Verde Lagoon, a small coastal lagoon with an ephemeral inlet on the Pacific Coast of Mexico. Total net aquatic primary production was 521 g C m?2 y?1. The water column was slightly heterotrophic, with an annual P/R ratio of 0.89. Our analysis indicates that tropical and subtropical coastal lagoons with restricted or seasonal inlets have generally higher net aquatic primary productivity levels than lagoons with permanently open inlets. We hypothesize that this is due to retention of nutrients and plankton stocks during the dry season. The seasonal pattern of water column metabolism was related to rainfall and riverflow, with higher values generally occurring during the wet season. Net production and respiration were about three times lower during the 1982 dry season as compared to the 1983 dry season which received considerable rains due to abnormal climatic conditions. The biomass ofR. maritima ranged from zero to 620 g dry wt m?2. Growth occurred only during the dry season and there were two distinct biomass peaks representing two separate crops. The second crop was heavily epiphytized with nitrogen-fixing algae. There was an apparent succession in dominance of water column productivity over the year, withRuppia dominating during the dry season and phytoplankton more important during the wet season.  相似文献   

4.
During 1995 the phytoplankton in the Swan River were intensively sampled to assess biomass and species composition. Continuous measurements of fluorescence, salinity, and temperature were made weekly during 40 km sampling trips along the estuary and used to map the seasonal progression of the algal biomass. Weekly measurements of primary production were made and used to model net primary production from the vertical distribution of biomass, irradiance, and phytoplankton species composition. Potential nutrient limitation was assessed with “all but one” nutrient bioassays. The results indicate a complex mixture of potentially limiting factors, which vary in time and space. Although the data sequence is short, it suggests a annual succession pattern of diatoms, chlorophytes, diatoms, and finally dinoflagellates and cryptophytes in late summer-autumn. Peak seasonal biomass was observed during January to April. Mean annual chlorophylla biomass was greatest in upstream stations (5–9), where estimates of net primary production rates averaged 1.55 g C m?2 d?1 and gross primary production was 800–1000 g C m?2 yr?1. Potential nutrient limitation was most severe from November to May, although not during January 1995. Based on bioassay results, during the period of greatest potential for nutrient limitation, nitrogen was 15 to 30 times more limiting to biomass development than phosphate. Runoff due to consistent rainfall during winter eventually breaks down stratification and flushes the estuary with low-salinity, nutrient-rich water, producing, a light-limited, nutrient-rich aquatic ecosystem. Timing and magnitude of physical forcing events, mainly rainfall, appear critical in determining the susceptibility of this ecosystem to summer and autumn algal blooms.  相似文献   

5.
A 2-year (October 2003–October 2005) high-resolution sediment trap study was conducted in Sacrower See, a dimictic hardwater lake in northeastern Germany. Geochemical and diatom data from sediment trap samples were compared with a broad range of limnological and meteorological parameters to quantify the impact of single parameters on biochemical calcite precipitation and organic matter production. Our goals were to disentangle how carbonaceous varves and their sublaminae form during the annual cycle to better understand the palaeorecords and to detect influences of dissolution, resuspension as well as of global radiation and stratification on lake internal particle formation. Total particle fluxes in both investigated years were highest during spring and summer. Sedimentation was dominated by autochthonous organic matter and biochemically precipitated calcite. Main calcite precipitation occurred between April and July and was preceded and followed by smaller flux peaks caused by resuspension during winter and blooms of the calcified green algae Phacotus lenticularis during summer. In some of the trap intervals during summer up to 100% of the precipitated calcite was dissolved in the hypolimnion. High primary production due to stable insolation conditions in epilimnic waters began with stratification of the water column. Start and development of stratification is closely related to air and water surface temperatures. It is assumed that global radiation influences the onset and stability of water column stratification and thereby determining the intensity of primary production and consequently of timing and amount of calcite precipitation which is triggered by phytoplanktonic CO2 consumption. Sediment fluxes of organic matter and calcite are also related to the winter NAO-Index. Therefore these fluxes will be used as a proxy for ongoing reconstruction of Holocene climate conditions.  相似文献   

6.
邹全  王国亚  贺斌  沈永平 《冰川冻土》2013,35(3):733-740
利用玛纳斯河流域肯斯瓦特站1957-2010年的气温、 降水和洪水径流等资料, 分析了该流域自1957年以来的气候变化以及夏季洪水径流过程对极端气候的响应. 结果表明: 玛纳斯河流域自1957年以来平均气温呈明显的上升趋势, 1979年是年均温由下降趋势转为上升的转折点, 并且1978年之后极端高温天气增多, 主要出现在7月份.玛纳斯河年降水量总的变化趋势是波动减少的, 1986年以后降水有所增加, 但只是恢复到多年平均降水量水平的上下波动.降水主要集中在4-8月, 约占年降水量的70%.气温高的月份与降水量多的月份并不完全对应, 如5月份气温较低, 但降水较大; 7月气温最高, 但6月降水量最大; 8月气温较高, 但降水量较少.玛纳斯河年径流主要集中在6-9月, 4个月的总径流量约占全年总径流量的80%, 7月份径流量最大, 约占全年总径流量的28.8%.历年最大洪峰流量呈显著增加趋势, 1993年是最大洪峰流量由下降变为增多的转折点, 而1994-2010年最大洪峰流量基本保持在高位上下波动.最大15日洪量占年径流量的比例较大, 说明洪水过程持续时间较长, 汛期水量较为集中.最大洪峰流量出现时间基本都在7月和8月上旬.玛纳斯河夏季月径流与夏季月气温和降水的关系并不密切, 低度相关, 说明玛纳斯河流域自1993年以来夏季洪水频繁发生, 尤其超标准洪水次数增多、 量级增大主要是由于夏季极端高温和极端降水天气增多引起的.  相似文献   

7.
祁连山区黑河流域季节冻土时空变化研究   总被引：3，自引：0，他引：3  
季节冻土的时空变化对地—气水热交换、地表能量平衡、地表水文过程、生态系统及碳循环等有着非常重要的影响.利用黑河流域11个气象站40多年的气温数据和5 cm深度处的土壤温度数据,建立了月平均气温与土壤冻结天数之间的关系.同时应用月平均气温与冻结天数的相关关系和5 km网格化月平均气温及30 m分辨率的DEM数据,编制了黑河流域逐月季节冻土分布图,并按其空间分布特征,将逐月地表冻融状态划分为:完全冻结、不完全冻结和不冻结3种.系统研究了黑河流域2000-2009年逐月季节冻土分布及冻结概率的时空变化特征.在季节分配上,黑河流域完全冻结面积最大值出现在1月;不完全冻结面积最大值在11月;而不冻结面积最大值在6月和7月.在年际变化上,完全冻结状态的离差值在冷季变化大,暖季变化小;不完全冻结状态在一年的回暖期和降温初期,年际变化较大;不冻结状态分别在4月和10月变化较大.冻结概率在1月达到最大值,6月和7月降低到最小值.在空间分布上,黑河流域季节冻土的逐月分布与变化和冻结概率主要受海拔高度控制,纬度的影响次之.  相似文献   

8.
Ten detailed vertical water column profiles were taken between April and November, 1979, in Esthwaite Water (English Lake district), a lake with high biological productivity and a seasonally anoxic hypolimnion. Measurements of the major-element particle composition (organic C, P, S, Si, Al, Ti, K, Mg, Ca, Fe, Mn, and Ba) and hydrochemical constituents (temperature, pH, dissolved oxygen, total suspended load, dissolved Fe, Mn, P, and Ba) were carried out. These have revealed new information about the mechanisms and kinetics of biogeochemical cycles in a lake.Pronounced seasonal cycles exist in which large excess concentrations (those unsupported by detrital components) of particulate organic C, Fe, Mn, P, S, Mg, K, Ba, and Ca are being generated and lost in situ in the water column (15m deep). In the epilimnion these elements (excepting Fe and Mn) are incorporated into the organic components of growing phytoplankton during the spring and summer. Simultaneously, in the hypolimnion there is a build-up and then a decrease in the excess concentrations of particulate C, P, S, Mg, K, Ba and Ca; this cycle is due to the indirect involvement of these elements with the iron redox cycle. As the hypolimnion becomes anoxic, dissolved ferrous Fe is released from the sediments and large concentrations of excess particulate iron (III) oxides accumulate; these oxides act as adsorbing substrates for the above mentioned elements. As conditions become more reducing, these same elements are solubilized as the iron (III) oxide particles are reduced to dissolved ferrous iron.Adsorption equations are derived from the field data which relate the concentration of excess particulate Fe to those of POC, P, S, Ca, Mg, Ba, and K. At the last stages of anoxia (before the lake overturns) large populations of bacteria and the formation of iron sulfide particles control the concentrations of excess particulate C, S, P, Mg, K, and Ca.  相似文献   

9.
We investigated spatial and temporal changes in spectral irradiance, phytoplankton community composition, and primary productivity in North Inlet Estuary, South Carolina, USA. High concentrations of colored dissolved organic matter (CDOM) were responsible for up to 84 % of the attenuation of photosynthetically available radiation (PAR). Green-yellow wavelengths were the predominant colors of light available at the two sampling sites: Clam Bank Creek and Oyster Landing. Vertical attenuation coefficients of PAR were 0.7–2.1 m?1 with corresponding euphotic zone depths of 1.5–6.7 m. Phytoplankton biomass (as chlorophyll a [chl a]) varied seasonally with a summer maximum of 16 μg chl a l?1 and a winter minimum of 1.4 μg chl a l?1. The phytoplankton community consisted mainly of diatoms, prasinophytes, cryptophytes and haptophytes, with diatoms and prasinophytes accounting for up to 67 % of total chl a. Changes in phytoplankton community composition showed strongest correlations with temperature. Light-saturated chl a-specific rates of photosynthesis and daily primary productivity varied with season and ranged from 1.6 to 14 mg C (mg chl a) ?1?h?1 (32–803 mg C m?3?day?1). Calculated daily rates added up to an annual carbon fixation rate of 84 g C m?3?year?1. Overall, changes in phytoplankton community composition and primary productivity in North Inlet showed a strong dependence on temperature, with PAR and spectral irradiance playing a relatively minor role due to short residence times, strong tidal forcing and vertical mixing.  相似文献   

10.
胡政  陈再谦 《中国岩溶》2018,37(2):245-253
以贵阳市地铁2号线三桥站主体结构基坑抗浮为研究对象,根据长观孔3~5年地下水位与降雨量关系对地下水位动态变化进行分析,提出一种定量计算抗浮水位的取值方法:抗浮水位值包括三个部分,勘察期间场区地下水最高水位（Hkmax）、可能的意外补给造成该层地下水位的上升值（ΔH0）及该层地下水相对勘察时的最大变幅值（ΔHe）;长观孔地下水位呈雨季升高、枯季下降的变化规律,最高水位出现在6、7月份;通过对4、5、6月份的降雨量与观测孔水位进行线性拟合,得到地下水位变化量与月降雨量变化量的线性变化关系;结合历史降雨量推测场区地下水位的最大升幅为2.26 m,进而计算场区的抗浮水位为1 128.46 m。   相似文献   

11.
Organic ligands, especially oxalate, play an important role in iron dissolution from iron-containing minerals. To study the effects of organic acid ligands on the dissolution of iron-containing minerals, the dissolution kinetics of hematite in the presence of oxalate, acetate, and formate were studied under ultraviolet radiation with varying ligand concentrations (10–3 mM). The results indicate that for adsorption dissolution, oxalate is the dominating ligand for producing soluble iron (III) from hematite; for photoreductive dissolution under ultraviolet radiation and in oxic conditions, the production of iron (II) is highly proportional to the concentrations of oxalate, whereas the effects of varying concentrations of formate and acetate are not significant. At low oxalate concentrations (10–500 µM), the photoreductive dissolution of iron (II) is substantially low, while at high oxalate concentrations (3 mM), oxalate is equally effective as formate and acetate for producing photoreduced iron (II) from hematite. Combining with field data from other works, it is likely that the ratios of oxalate to total iron need to be higher than a threshold range of ~1.2–5.5 in order for oxalate to effectively produce photoreduced iron (II) from hematite. This study demonstrates that the iron (II) yield from photoreduction of hematite is significantly lower when the hematite surface is pre-coated with organic ligands versus when it is exposed to ultraviolet radiation instantaneously.  相似文献   

12.
黑河流域上游融雪径流时间变化特征及成因分析   总被引：4，自引：3，他引：1  
以黑河流域上游莺落峡水文站和札马什克水文站1959-2008年及祁连水文站1967-2008年的天然径流序列为基础数据, 通过计算水文站的流量质心时间来表示融雪径流时间, 研究了黑河流域上游融雪径流时间变化的特征. 结果表明: 莺落峡站和札马什克站自20世纪70年代起, 融雪径流时间表现为提前的趋势, 祁连站自20世纪80年代起融雪径流时间提前.野牛沟站和祁连站10月至次年4月降水量增加或4-7月气温升高, 会使得莺落峡站融雪径流时间提前, 札马什克站融雪径流时间的提前与野牛沟站10月至次年4月降水量的增加具有较高的相关性, 祁连站融雪径流的提前与祁连气象站4-7月气温升高的相关性较强.通过分析莺落峡站融雪径流时间与年径流及各季节径流的相关性, 可知如果融雪径流时间提前, 莺落峡站观测到的年径流量和夏秋季的径流量均会减少, 而同时冬春季的径流量会增加, 这对合理安排流域水资源配置和管理具有重要的指导意义.  相似文献   

13.
长江源区高寒退化湿地地表蒸散特征研究   总被引：1，自引：0，他引：1  
青藏高原作为“亚洲水塔”,对东亚乃至全球大气水分循环都有非常显著的影响.高寒退化湿地是高原上生态多样性的保证,也是水汽循环和地表径流的重要源地,其地气之间水分交换不但可以反映气候变化,而且也对生态环境保护具有重要意义.以长江源区隆宝滩湿地连续一年、每10分钟一次的观测资料为基础,利用FAO Penman-Monteith方法分析了长江源区高寒退化湿地蒸散量的变化特征及其与环境因子之间的关系.结果表明：1）牧草生长期,潜在蒸散量日、月变化特征显著;实际蒸散量整体表现为冬小、夏大,夏季蒸散贡献最大.2）观测期间,蒸散量远大于降水量,水分亏损严重,局地蒸散对降水的贡献较高.3）土壤温度对蒸散发过程影响显著,尤其是表层5 cm地温与蒸散发相关性较好,土壤湿度变化表明其为蒸散发过程提供了充足的水分.4）全年变化中,气温是影响蒸散的主要因素.晴天中,高寒退化湿地实际蒸散量与辐射具有几乎相同的变化趋势,气温对蒸散量影响较小,蒸散量与相对湿度呈现显著的反相关.  相似文献   

14.
Eight meadows of the seagrassThalassia testudinum Banks ex König representing a gradient of freshwater influence in Charlotte Harbor, Florida (United States), were sampled on a bimonthly basis from April 1995 to August 1996. Spatial and temporal variation in the density, biomass, productivity, and epiphyte loads of short shoots were determined. Physical factors such as water temperature, salinity, and light extinction coefficients were also measured. Areal blade production (g dw m?2 d?1) ofT. testudinum was not strongly associated with water temperature, salinity, or the amount of subsurface irradiance reaching the bottom at each station. Variation in production could be described by a linear combination of the independent variables water temperature and salinity. Water clarity (expressed as the percent of subsurface irradiance reaching the bottom) was positively related to salinity. The lack of a clear relationship between water clarity and areal production was probably due to water clarity being highest during times of the year when water temperatures were too cold to support growth ofT. testudinum. Our results suggest that seagrass light requirements determined by averaging irradiance levels measured during the growing season might be more relevant than those established by averaging light measurements collected throughout the year. The use of field studies for estimating lower salinity tolerances of seagrasses might be inappropriate for those systems where water clarity is positively associated with salinity.  相似文献   

15.
Little is known about the response of terrestrial East Antarctica to climate changes during the last glacial-interglacial cycle. Here we present a continuous sediment record from a lake in the Larsemann Hills, situated on a peninsula believed to have been ice-free for at least 40,000 yr. A mutli-proxy data set including geochronology, diatoms, pigments and carbonate stable isotopes indicates warmer and wetter conditions than present in the early part of the record. We interpret this as Marine Isotope Stage 5e after application of a chronological age-depth model and similar ice core evidence. Dry and cold conditions are inferred during the last glacial, with lake-level minima, floristic changes towards a shallow water algal community, and a greater biological receipt of ultraviolet radiation. During the Last Glacial Maximum and Termination I the lake was perennially ice-covered, with minimal snowmelt in the catchment. After ca. 10,500 cal yr B.P., the lake became seasonally moated or ice-free during summer. Despite a low accumulation rate, the sediments document some Holocene environmental changes including neoglacial cooling after ca. 2450 cal yr B.P., and a gradual increase in aridity and salinity to the present.  相似文献   

16.
The redox cycle of iron and manganese is a major geochemica process at the boundary layers of lake sediments.Lake Aha,which lies in the suburbs of Guiyang City,Guizhou Province,China,is a medium-sized artificial reservoir with seasonally anoxic hypolimnion,Long-term sedimentary accumulation of iron and manganese resulted in their enrichment in the upper sediments,In the anoxic season,Fe^2 and Mn^2 ,formed by diological oxidation,would diffuse up to overlying waters from sediments.However,the concentration of oxidation,would diffuse up to overlying waters from sediments,However,the concentration of Fe^2 increased later and decreased earlier than that of Mn^2 .Generally,sulfate reduction occurred at 6 cm below the sediment-water interface.Whereas,in the anoxic season.the reduction reached upper sediments,inhibiting the release of Fe^2 ,The Fe concentration of anoxic water is quickly decreased from high to low as a result of reduction of the suplhur system.  相似文献   

17.
Physical and chemical characteristics of the Hooghly estuary during winter (December 1997–January 1998), summer (May 1998) and post-monsoon (November 1998) seasons have been studied. Salinity varied spatially and temporally and seasonally during ebb and flood tide conditions. Water temperature showed a difference of 10‡C in winter to summer. Temperature did not vary much vertically as it is a well-mixed estuary. Strong currents exceeding 100 cm S-1 were observed during peak ebb and flood tide conditions irrespective of the season. Longitudinal eddy diffusion coefficient (K x ) was estimated as 757m S-1 and 811m2 S-1 during summer and post-monsoon seasons, respectively. The vertical eddy diffusion coefficient (εv) was estimated as 0.0337 m2 S-1 during post-monsoon season. The salinity and current observations are compared with those obtained from models reported earlier. Values of pH, Dissolved Oxygen and Biological Oxygen Demand are within the threshold limits of the estuarine environment. Nutrients show seasonal variation in the estuarine environment. High values (160-2686 mg l-1) of total suspended matter were noticed both at surface and bottom in the study region showing the impact of fresh water and sediment transportation.  相似文献   

18.
The origin and environmental dependencies of lamination in stalagmites from Katerloch, common in speleothems from other cave sites, are examined in detail. Petrographic observations and chemical analyses (including isotopes) of stalagmites and modern calcite were combined with multi‐annual cave monitoring. All investigated stalagmites are composed of low‐Mg calcite and show white, porous laminae and typically thinner, translucent dense laminae. The binary lamination pattern results from changes in the calcite fabric: white, porous laminae are characterized by a high porosity and abundant fluid inclusions and also by enhanced vertical growth and thinning towards the flanks. Translucent, dense laminae exhibit a compact fabric and constant thickness of individual growth layers. U‐Th dating supports an annual origin of the lamination and the seasonally changing intensity of cave ventilation provides a robust explanation for the observed relationships between lamination, stable C isotopic compositions and trace elements (Mg, Sr and Ba). The seasonally variable air exchange, driven by temperature contrasts between the cave interior and outside atmosphere, modulates the rate and amount of CO2 degassing from the drip water and affects the hydrochemistry and consequently the fabric of the precipitating calcite. Although cave air composition and drip rate are both major variables in controlling CO2 degassing from the drip water, the seasonally changing ventilation in Katerloch exerts the primary control and the results suggest a secondary (amplifying/attenuating) influence of the drip rate. Drip rate, however, might be the controlling parameter for lamina development at cave sites experiencing only small seasonal cave air exchange. Importantly, the seasonally variable composition of drip water does not reflect the seasonal cycle of processes in the soil zone, but results from exchange with the cave atmosphere. The alternating porous and dense calcite fabric is the expression of a variable degree of lateral coalescence of smaller crystallites forming large columnar crystals. The white, porous laminae represent partial coalescence and form during the warm season: low calcite δ13C values are linked to low δ13C values of cave air and drip water during that time. This observation corresponds to times of reduced cave ventilation, high pCO2 of cave air, low drip water pH, lower calcite supersaturation and typically high drip rates. In contrast, the translucent, dense laminae represent more or less complete lateral coalescence (inclusion‐free) during the cold season (high calcite, drip water and cave air δ13C values), i.e. times of enhanced cave ventilation, low cave air pCO2, increased drip water pH, relatively high calcite supersaturation and typically low drip rates. In essence, the relative development of the two lamina types reflects changes in the seasonality of external air temperature and precipitation, with a strong control of the winter air temperature on the intensity of cave‐air exchange. Thick translucent, dense laminae are favoured by long, cold and wet winters and such conditions may be related closely to the North Atlantic Oscillation mode (weak westerlies) and enhanced Mediterranean cyclone activity during the cold season. Studies of speleothem lamination can thus help to better understand (and quantify) the role of seasonality changes, for example, during rapid climate events.  相似文献   

19.
Using the Eddy Covariance (EC) technique, we analyzed temporal variation in net ecosystem CO2 exchange (NEE) and determined the effects of environmental factors on the balance between ecosystem photosynthesis and respiration in a reed (Phragmites australis) wetland in the Yellow River Delta, China. Our results indicated that diurnal and seasonal patterns of NEE and its components (ecosystem respiration (R eco), gross primary production (GPP)) varied markedly among months for the growing season (May to October). The cumulative CO2 emission was 1,657 g CO2 m?2, while 2,612 g CO2 m?2 was approximately accumulated as GPP, which resulted in the reed wetland being a net sink of 956 g CO2 m?2. The ratio of R eco to GPP in reed wetland was 0.68, which was close to other temperate wetlands. Soil temperature and soil moisture exerted the primary controls on R eco during the growing season. Daytime NEE values during the growing season were strongly correlated with photosynthetically active radiation. Aboveground biomass showed significant linear relationships with 24-h average NEE, daytime GPP, and R eco, respectively. Thus, we conclude that the coastal wetland acted as a carbon sink during the growing season despite the variations in environmental conditions, and long-term flux measurements over these ecosystems are undoubtedly necessary.  相似文献   

20.
利用清政府布设在黄河中游三门峡万锦滩、沁河下游木栾店以及永定河下游石景山、卢沟桥的志桩水位记录,以首次涨水超过0.64m作为汛期建立的标志,在候尺度下恢复了其汛期建立时间距平序列。黄河中游、沁河下游和永定河下游序列分别开始于1766年、1736年和1761年。研究时段内,黄河中游和沁河下游平均在7月6~10日入汛、永定河则在7月16~20日。永定河相对较为稳定,显示出其上游雨季开始时间基本维持在7月初,而黄河中游和沁河却波动较大,早晚相差达3个月;黄河中游与沁河入汛距平波动的同相位现象在19世纪中期之后比较明显。1870~1900年代黄河中游、沁河和永定河入汛普遍延迟1个候左右,对应于黄土高原夏温偏低的时期;1820~1860年代黄河中游、沁河入汛偏早,则对应了黄土高原夏温偏高。  相似文献   

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