SPATIALLY EXPLICIT HYDROLOGIC MODELING OF LAND USE CHANGE1

ABSTRACT: Using a Geographic Information System (GIS), a method is presented to develop a spatially explicit time series of land use in an urbanizing watershed. The method is prefaced on the existence of independent observations of land use at different times and data that describes the spatial‐temporal land use transition characteristics of the watershed between these two points in time. A method is then presented to generalize the TR‐55 graphical method, a common lumped hydrologic model for estimating peak discharge, for use in a spatially explicit scheme. This scheme predicts peak discharge throughout a watershed, rather than at a single selected watershed outlet. Coupling these two methods allows the engineer to model both the temporal and spatial evolution of peak discharge for the watershed. An illustrative watershed in a suburban area of Washington, DC is selected to demonstrate the methods. The model results from these analyses are presented graphically to highlight the complex features in peak discharge behavior that exist both spatially, as a function of position within the watershed drainage network, and temporally, as the watershed undergoes urbanization. These features are not commonly noted in most hydrologic analyses but are captured in these analyses because of the high spatial and temporal resolution of the methods presented. The physical implications of the modeled results are discussed in the context of the information content of a stream gauge located at the overall outlet of the illustrative watershed. This work shows that the common practice of transposition of gauge information to locations internal to the watershed would neglect internal variability in peak discharge behavior, and could potentially lead to the determination of inappropriate design discharges.     

ESTIMATES OF MEAN CHLOROPHYLL-a CONCENTRATION: PRECISION,ACCURACY, AND SAMPLING DESIGN1

ABSTRACT: Data from 56 north-temperate lakes and reservoirs are used to develop models predicting temporal variance as a function of the mean chlorophyll-a concentration. Trophy, as estimated by mean chlorophyll-a concentration, is shown to have little effect on the sampling effort required to achieve a pre-determined level of precision for lakes sampled year-round. Collecting ten observations results in a coefficient of variation that averaged 20 percent; collecting more than ten observations yields increasingly marginal improvements in precision. The same guidelines apply to mesotrophic or eutrophic lakes sampled in the summer, whereas oligotrophic lakes sampled in the summer require fewer observations to achieve the same level of precision. The bias resulting from collecting too few observations is minimized if five or more observations are collected.     

STREAM NITRATE-N LOADS IN RELATION TO VARIATIONS IN ANNUAL AND SEASONAL RUNOFF REGIMES1

ABSTRACT: The calculation of stream nutrient loads from a sampling period of one year or, at most, a few years may provide an inaccurate estimate of average seasonal or annual loads due to considerable year-to-year variations in hydrological regime. The number of years of record required to give a reliable estimate of long-term average NO₃-N loads was analyzed for E. Duffin Creek and the Nottawasaga River in Ontario, Canada. Nitrate load rating relationships were used in combination with a continuous stream discharge record for 22 years (E. Duffin Creek) and 34 years (Nottawasaga River) to simulate long-term seasonal and annual variation in NO₃.N loads. The errors involved in calculating average loads were examined by comparing the loads derived from sampling periods of one or more consecutive years duration with the estimated long-term average load for the two rivers. Annual NO₃-N loads for a single year deviated from the long-term average load by ± 20 to 53 percent in 8 out of 22 years in E. Duffin Creek and in 13 of 34 years in the Nottawasaga River. Six consecutive years of record would be required for both rivers to ensure that an error of > ± 20 percent would occur in only 5 percent of these observation periods. February-April NO₃-N loads for a single year could deviate by up to +90 percent or -61 percent from the long-term average spring period load for the two rivers. A sampling period of at least 6–7 years would be needed to estimate average NO₃-N loads for the spring runoff season with an error <± 20 percent.     

SOURCES OF VARIABILITY IN PHOSPHORUS AND CHLOROPHYLL AND THEIR EFFECTS ON USE OF LAKE SURVEY DATA1

Summer lake survey measurements of total phosphorus (TP) and chlorophyll a (CHLa) from 188 reserviors and natural lakes in the midwest were analyzed to determine the magnitude of major sources of variability. Median variance among replicate samples collected at the same location and time was about 7-8 percent of the mean for both TP and CHLa. Median observed temporal variability within summers was 27 percent of the mean for TP and 45 percent of the mean for CHLa. Median values of year-to-year variance in average TP and CHLa were 22 percent and 31 percent of the mean, respectively. A range of approximately two orders of magnitude was observed among individual estimates of variance in each of these categories. The magnitude of observed temporal variability was affected only slightly by variance among replicate samples on individual days and was weakly correlated with the length of time during which samples were collected from individual lakes. Observed temporal variation was similar between reservoirs and natural lakes when variances were calculated with logtransformed data. The magnitude of temporal and year-to-year variance can severely limit the power of statistical comparisons of TP and CHLa means, but has less effect on establishing relative rankings of lake means, Sources and relative magnitude of variability are important in the use of TP and CHLa data in regression models and in the planning of lake surveys and subsequent data analysis.     

成渝经济区森林碳储量动态及空间格局特征

以GIS为支撑,以成渝经济区的空间关系、自然环境和社会环境为基础,分析2000—2007年森林碳储量的动态和空间格局.结果表明:①2000—2007年森林碳储量从3.39×108 t增至3.59×108 t,年均增长率为0.72%,区域碳汇能力逐渐增强.②各生态功能区森林碳储量变化不同,经济发达地区碳储量增长更为缓慢.③森林碳储量在各高程等级均有所增加,其中海拔在500～1 000 m的区域增长最快,海拔≥3 000 m的区域增长最慢;坡度为25～35°的区域增长最快,≥35°的区域增长最慢.④森林碳储量除在人口密度≥1 000人/km2的区域呈缓慢减少的趋势外,在其他区域均呈增加趋势,其中人口密度在250～500人/km2的区域增长最快.⑤同一年内森林碳储量呈现出随GDP增加而逐渐减少的趋势;年际间,各GDP等级内碳储量均呈增加趋势,其中在GDP为2.5×106～5.0×106元/km2的区域增长最快.     

Anatomical and physiological divergences and compensatory effects in two Leymus chinensis (Poaceae) ecotypes in Northeast China

The purpose of this study was to investigate the anatomical and physiological differences between two Leymus chinensis ecotypes coexisted in semi-humid meadow and semi-arid steppe. The study addressed the hypothesis that, at same habitat, the two ecotypes exhibit remarkable divergences in adaptive strategies under drought and salinity, and the function of these strategies is compensatory. Leaf samples were collected from each type at the two sites in field. Sections of 2 cm × 2 cm were cut from the middle of fully expanded leaves and fixed in FAA. Leaf anatomical traits (e.g. stomatal density, leaf thickness and vessel diameters) were examined, and leaf mass per area (LMA), relative water content (RWC), proline, K⁺ and Na⁺ were measured. Compared with the gray green type (GG), the yellow green type (YG) with relative greater LMA and leaf thickness, lower stomatal density and index exhibited more obvious xerophil-liked anatomical traits, while higher RWC, proline, K⁺ and K⁺/Na⁺ for the GG type suggested that the ability of osmotic adjustment and salt tolerance of the GG type were stronger than the YG type. Stronger xerophytic anatomical traits were the supplementary strategies of the YG type for its low ability of osmotic adjustment and salt tolerance to drought and salinity.Concluding, there exist significant differences in anatomical and physiological strategies between the two ecotypes and the compensatory effects of these strategies enable the two ecotypes coexist at similar habitat.     

黔中喀斯特石漠化地区土壤温室气体浓度的时空分布特征

2006~2007年对喀斯特石漠化地区土壤剖面中CO2、N2O和CH4的浓度分布进行观测.结果表明,土壤剖面中CO2、N2O和CH4浓度分别介于530.2~31512.6、0.27~0.67和0.1~3.5μL.L-1.总体上,自地表向下,CO2和N2O浓度逐渐增大,CH4浓度则为逐渐减小,但在阴冷潮湿的10、11月和1月,15cm以下土层中CO2和N2O浓度随着深度的增加逐渐减小,CH4浓度则明显增加.土壤温度、水分同时影响剖面中CO2、N2O和CH4的时空分布,但影响效应以及作用的土层深度有所不同.相关分析结果表明,土壤中CO2和N2O浓度的时空分布显著正相关(r为0.780~0.894,p0.05~0.01),相关关系受环境因子的影响;CO2和CH4的时空分布则呈显著负相关关系(r=330,p0.01);N2O和CH4的空间分布为互逆关系,但只在土壤水分较大月份达到显著水平(r为-0.829~-0.956,p0.05~0.01).     

基于15N 同位素示踪技术的地下河硝态氮来源时空变化特征分析

根据2007年10月至2008年10月每月对青木关地下河水的监测,利用~(15)N 同位素示踪技术并结合水化学指标,分析地下河硝态氮来源的时空变化特征.结果表明,地下河出口S2硝态氮浓度(20.35 mg/L)比入口D1(3.20 mg/L)高6倍多.受农业生产施肥和降雨冲刷稀释效应的影响,地下河水硝态氮浓度2007年10月至2008年3月较低且比较稳定,2008年4月至7月较高但受降雨冲刷稀释影响变化较大,2008年8月至9月随降雨减少,土壤中残留的化肥造成地下河水硝态氮浓度偏高.根据NO_3~--δ~(15)N 值识别出了地下河硝态氮来源变化特征为:D1处2007年10月至2008年3月以及2008年7月至10月NO_3~--δ~(15)N 值为-0.857‰±2.01‰(n=9),其硝态氮来源为稻田中残留的化肥;2008年4月、6月中下旬NO_3~--δ~(15)N 值为2.50‰±0.29‰(n=3),其来源为稻田中施用的化肥与土壤有机氮的混合;2008年5月下旬至6月上旬NO_3~--δ~(15)N 值分别为-3.74‰和0.52‰,其来源为稻田中施用的化肥.S2处硝态氮不仅来自上游的化肥,更主要的是来自中下游的耕地、林地土壤渗透水或侧向裂隙水带来的土壤有机氮与化肥,其中2007年10月至2008年3月以及2008年7月至10月NO_3~--δ~(15)N 值为4.77‰±0.73‰(n=9),其硝态氮主要来自于土壤有机氮;2008年4～6月NO_3~--δ～15N 值为3.16‰±0.39‰(n=5),其硝态氮来自于土壤有机氮与化肥的混合.     

珠江口广州海域叶绿素a分布特征及环境调控因素

于2009年5、8、10和12月对珠江口广州海域叶绿素a和环境相关因子进行了取样调查,分析了广州海域叶绿素a的时空变化特点及其分布的环境调控因素。结果表明,广州海域水体中叶绿素a变化范围为1.43～86.9μg/L,平均含量为20.7μg/L,最高值出现在夏季的N1站位,为86.9μg/L,最低值出现在春季的N8站位,为1.43μg/L。各站位叶绿素a年平均浓度从上游到下游表现出明显的递减趋势,以N1站位浓度最高(38.54μg/L),N7站位浓度最低(7.44μg/L),相差5.2倍。调查海域叶绿素a的季节变化明显,呈单峰型,总体上表现为夏季﹥秋季﹥冬季﹥春季。根据叶绿素a浓度对广州海域富营养化状态进行评价,15.6%的监测站位处于低度富营养化,50.0%处于中度富营养化,28.1%处于高度富营养化,6.3%处于过度富营养化,总的来讲,以中、高度富营养化状态为主体。叶绿素a浓度与NO3--N浓度、温度呈现出一定的正相关关系(分别为:r=0.374,p<0.05;r=0.502,p<0.01),与盐度、溶解氧呈现出一定的负相关关系(分别为:r=-0.433,p<0.05;r=0.455,p<0.01)。与国内其他近岸海域(河口)相比,珠江口广州海域叶绿素a浓度处于较高水平,仅低于深圳湾。     

滨海城市气溶胶中颗粒态汞的分布特征

与气溶胶颗粒相结合的汞,即颗粒态汞,不仅对人体健康及生态环境产生一定的危害,而且在汞的生物地球化学过程扮演重要角色.以我国东南滨海城市厦门市为研究对象,采集郊区、居民区、旅游区、工业区和背景区四季(2008年10月～2009年8月)的PM2.5、PM10和TSP样品,基于塞曼原子吸收法的俄罗斯LumexRA-915+汞分析仪对大气不同粒径颗粒物中颗粒态汞进行了测试.结果表明,厦门市大气不同粒径颗粒物中汞的含量均表现为冬、春两季的浓度明显高于夏、秋两季;春、夏、秋、冬四季细颗粒物(PM2.5)中的含量分别为(51.46±19.28)、(42.41±12.74)、(38.38±6.08)和(127.23±33.70)pg/m3.不同粒径颗粒物中汞主要分布在PM2.5中,占到颗粒物态汞的42.48%～67.87%,表明细粒子富集汞的能力较强.不同功能区颗粒态汞的浓度分布趋势为背景区居民区旅游区工业区郊区,说明颗粒态汞浓度的空间分布特征与采样点的环境功能密切相关.总体而言,滨海城市大气颗粒态汞含量较低;PM2.5对颗粒态汞的富集明显高于PM10和TSP,表明对颗粒态汞的控制应集中在细颗粒物污染上.