城镇化过程中流域不透水面演变格局——以天津于桥水库流域为例

不透水面是衡量流域城镇化发展状况的一个关键指标,其扩展对流域生态水文过程产生重要影响.本文以天津于桥水库流域为例,在ENVI 5.1软件支持下,利用遥感影像获取1984、1994、2004和2013年4个时相的不透水面信息,采用修正后的归一化水体指数剔除水体信息,排除水体对不透水面提取精度的影响,运用线性光谱混合分析法生成流域不透水表面指数(ISA),并对其时空演变格局进行分析.结果表明: 模型均方根误差(RMSE)为0.005,像元精度为85.4%,试验结果准确可靠.1984—2013年,流域内不透水面覆盖度ISA平均值从0.16线性增长到0.23,在全流域范围内的不透水面面积增加了4.9%,其总不透水面面积增加近1倍.不透水面沿城镇区域呈现辐射式增长,沿子流域路网呈现填充式增长.不透水面覆盖度为中等等级的斑块形状不规则,破碎化程度最高.整个流域景观破碎化程度和多样性均逐年增高,人为干扰强度不断增大.     

洞庭湖区洪涝灾害形成机理与生态减灾和流域管理对策

洞庭湖是承纳湘,资,沅,澧四水和蚕吐长江的洪道型调蓄湖泊。湖区发展过程中忽视了环境整治与生态建设,没有协调好人地,人湖关系,中上游干支流水土流失加剧,湖泊泥沙 与过度围湖垦殖,高水位地段农业布局与种植制度不合理等人为因素导致湖区调蓄能力下降,洪水位抬升且历时持久;垸高田低,外洪内涝交织,灾害频率上升,灾情增大,为抗御洪水,堤防越筑越高,出现了“水涨－堤高－水再涨－堤再高”的恶性循环现象,造成抬高洪     

Remotely-sensed indicators for monitoring the general condition of “natural habitat” in watersheds: an application for Delaware’s Nanticoke River watershed

Over the past two decades there has been increasing interest in developing indicators to monitor environmental change. Remote sensing techniques have been primarily used to generate information on land use/land cover changes. The US Fish and Wildlife Service has used this technology to monitor wetland trends and recently developed a set of remotely-sensed indicators to characterize and assess trends in the integrity of natural habitat in watersheds. The indices largely focus on the extent of “natural” cover throughout a given watershed, with an emphasis on locations important to fish, wildlife, and water quality. Six indices address natural habitat extent and four deal with human-caused disturbance. A composite index of natural habitat integrity combining the habitat extent and habitat disturbance indices may be formulated to provide an overall numeric value for a watershed or subbasin. These indices facilitate comparison between watersheds (and subbasins) and assesssment of trends useful for environmental monitoring. This paper describes the indices and presents an example of their application for characterizing and assessing conditions of subbasins within Delaware’s Nanticoke River watershed.     

皇甫川流域几种主要植物水分生态特征

通过在丰水年 (1998年 )和欠水年 (1999年 )连续两个生长季对皇甫川流域几种主要植物 :沙棘 (H ippophae rhamnoides)、沙柳 (Salix psammophyla)、中间锦鸡儿 (Caragana intermedia)、杨树 (Populus simonii)、油松 (Pinus tabulaeformis)、沙打旺(Astragalus adsurgens cv.)、羊柴 (H edysarum leave)、玉米 (Zea mays)和百里香 (Thymus serpyllum)等植物生物学特性、蒸腾特征及土壤水分含量的测定及分析 ,得出以下结果 :几种主要植物蒸腾强度平均值由大到小的排列顺序是 :杨树 >沙柳 >沙打旺>羊柴 >中间锦鸡儿 >玉米 >百里香 >沙棘 >油松 ;在 1998年和 1999年 ,皇甫川流域主要植物蒸腾强度的季节动态基本相同 ,油松、沙棘、中间锦鸡儿以及百里香等植物年平均蒸腾强度较低。无论丰水年还是欠水年 ,生长季内皇甫川流域主要植物蒸腾系数均较高 ,表明了植物的生长是以消耗大量水分为代价 ,水分是其生长的主要限制因子 ;百里香蒸腾系数最小 ,其次是中间锦鸡儿 ,这反映了百里香和中间锦鸡儿能更有效地利用水分进行干物质积累 ;皇甫川流域乔木适宜种为油松、灌木种为中间锦鸡儿和沙棘、半灌木植物为百里香。主要植物群落地段的蒸散量与降雨量的比值在 1左右。但从土壤水分变化角度看 ,皇甫川流域主要植物群     

香溪河流域浮游植物调查与水质评价

报道了1996年10月～1997年7月和2003年对香溪河流域浮游植物2周年的调查结果。数据显示,香溪河流域的浮游植物主要由硅藻、绿藻和蓝藻组成。1996-1997年硅藻的种类最多,绿藻次之,蓝藻居第3位;2003年绿藻的种类数跃居首位,硅藻次之,其它藻类亦有不同程度的变化。藻类的细胞密度表现出明显的季节变化．最高、最低值分别出现在夏季和冬季。应用Margalef多样性指数和Menkinick多样性指数对香溪河流域的水质进行评价的结果显示：2003年该流域的水质营养等级为中一富营养型,水环境质量较6年前有所下降。     

The distribution of heath balds in the Great Smoky Mountains,North Carolina and Tennessee

Abstract. We used remote sensing and a geographic information system to model the distribution of evergreen shrub communities, called ‘heath balds’, in the Great Smoky Mountains, North Carolina and Tennessee, USA. The 421 heath balds averaged 1.8 ha in size and covered 0.3% of the landscape. They reached their greatest importance on upper slopes (92% had relative slope positions > 80), convex topography (82% occurred on sites with a curvature greater than 2.6), and elevations between 1100 and 1600 m (94% of the balds). Although heath balds were found in old‐growth watersheds, the two watersheds with the greatest number of balds burned extensively after logging in the early 1900s. Bald occurrence was positively correlated with burned sites, old growth condition, and a highly acidic rock type. Heath balds showed a striking geographic pattern, with 88.1% of the area of this community found in six watersheds comprising only 35.4% of the study area. Despite similar topography, geology, and history, the eleven other watersheds had only 11.9% of the bald area while comprising 64.4% of the study area. Multivariate models showed that this community occurs on only 0.4 to 9.0% of the seemingly appropriate sites. Once established, this shrub community, with its dense evergreen canopy and thick leaf litter, is resistant to tree invasion. Both forest and shrub communities are stable on sites that are seemingly ideal for heath bald occurrence.     

Changes in the character of DOC in streams during storms in two Midwestern watersheds with contrasting land uses

Dissolved organic carbon (DOC) dynamics in streams is important, yet few studies focus on DOC dynamics in Midwestern streams during storms. In this study, stream DOC dynamics during storms in two Midwestern watersheds with contrasting land uses, the change in character of stream DOC during storms, and the usability of DOC as a hydrologic tracer in artificially drained landscapes of the Midwest are investigated. Major cation/DOC concentrations, and DOC specific UV absorbance (SUVA) and fluorescence index (FI) were monitored at 2–4 h intervals during three spring storms. Although DOC is less aromatic in the mixed land use watershed than in the agricultural watershed, land use has little impact on stream DOC concentration during storms. For both watersheds, DOC concentration follows discharge, and SUVA and FI values indicate an increase in stream DOC aromaticity and lignin content during storms. The comparison of DOC/major cation flushing dynamics indicates that DOC is mainly exported via overland flow/macropore flow. In both watersheds, the increase in DOC concentration in the streams during storms corresponds to a shift in the source of DOC from DOC originating from mineral soil layers of the soil profile at baseflow, to DOC originating from surficial soil layers richer in aromatic substances and lignin during storms. Results also suggest that DOC, SUVA and FI could be used as hydrologic tracers in artificially drained landscapes of the Midwest. These results underscore the importance of sampling streams for DOC during high flow periods in order to understand the fate of DOC in streams.     

Total mercury and methylmercury dynamics in upland–peatland watersheds during snowmelt

Wetlands, and peatlands in particular, are important sources of methylmercury (MeHg) to susceptible downstream ecosystems and organisms, but very little work has addressed MeHg production and export from peatland-dominated watersheds during the spring snowmelt. Through intensive sampling, hydrograph separation, and mass balance, this study investigated the total mercury (THg) and MeHg fluxes from two upland–peatland watersheds in Minnesota, USA during the 2005 spring snowmelt and proportionally attributed these fluxes to either peatland runoff or upland runoff. Between 26% and 39% of the annual THg flux and 22–23% of the annual MeHg flux occurred during the 12-days snowmelt study period, demonstrating the importance of large hydrological inputs to the annual mercury flux from these watersheds. Upland and peatland runoff were both important sources of THg in watershed export. In contrast to other research, our data show that peatland pore waters were the principal source of MeHg to watershed export during snowmelt. Thus, despite cold and mostly frozen surface conditions during the snowmelt period, peatland pore waters continued to be an important source of MeHg to downstream ecosystems.     

The atmospheric deposition of phosphorus in Lake Victoria (East Africa)

Wet and dry atmospheric fluxes of total phosphorus (TP) and soluble reactive phosphorus (SRP) measured at four sites over a 12-month period were used to estimate lake-wide atmospheric phosphorus (P) deposition to Lake Victoria, East Africa. Atmospheric samples were collected in plastic buckets with top diameter of 25.5 cm by 30 cm deep. The highest P loading rates of 2.7 (TP) and 0.8 (SRP) kg ha^–2 year^–1 were measured at Mwanza compared to less than 1.9 (TP) and 0.65 (SRP) kg ha^–2 year^–1 measured in other three sites. By applying these loading rates to the lake surface, it was estimated that 13.5 ktons (13.5 × 10³ kg) of TP were deposited annually into the lake from the atmosphere. Thirty-two percent of the total was found to be in the SRP form. Dryfall, a component ignored in previous studies exceeded wet deposition by contributing 75% of the total P input. However, materials deposited by dryfall made a lesser contribution to soluble form of phosphorus, as SRP concentrations in the wet samples were 2–3 times higher than SRP concentrations in dry samples. The annual fluxes of phosphorus measured on the south and western shores of Lake Victoria (1.8–2.7 kg ha^–2 year^–1) are near the upper range of similar fluxes measured in the tropics. In comparison with the existing estimates of municipal and runoff P inputs from other studies, it is estimated that atmospheric deposition represent 55% of the total phosphorus input to the Lake Victoria. The four sampling sites were fairly clustered and wet and dry P deposition data were collected from shore/land stations and applied to open lake areas to estimate lake-wide P deposition. In this regard, the estimates determined here should be viewed as a first order approximation of actual P load deposited into the lake.     

新疆玛纳斯河流域冰川生态系统服务功能价值评估

冰川在干旱区内陆河流域中具有极其重要的生态作用,为流域发展提供着巨大的服务功能.然而,在全球气候变暖的影响下,冰川退缩将导致冰川生态系统服务功能降低.应用GIS空间分析技术分析了玛纳斯河流域从1964年至2006年冰川面积变化,并评估其生态系统服务功能价值变化.结果表明,在全球变暖的影响下,流域冰川生态系统服务功能总价值急剧下降.流域冰川面积从1964年557.1km2退缩到2006年的464.1km2,面积减少了16.7%.冰川生态系统服务功能价值从1964年的1228.5×108元下降到2006年的960.1×108元.冰川退缩改变了流域的水资源分布特征,导致冰川生态系统服务功能价值下降.在未来的流域发展规划中,应高度重视冰川变化产生的生态效应.