Recent water quality trends and a comparison to sediment-core records for two riverine lakes of the Upper Mississippi River basin: Lake St. Croix and Lake Pepin     

Brenda Moraska Lafrancois  Suzanne Magdalene  D. Kent Johnson 《Journal of Paleolimnology》2009,41(4):603-622

Long-term water quality monitoring data from two riverine lakes in the Upper Mississippi River basin, Lakes St. Croix and Pepin, were analyzed to compare the long-term average water quality conditions and land use distributions, water quality trends and loads at lake inlets and outlets, trends from long-term versus short-term monitoring records, and the ability of paleolimnological cores to accurately infer lake water quality conditions. During the 1976–2004 period, the long-term average concentrations of nutrients, suspended solids, and chlorophyll-a were consistently lower at the Lake St. Croix inlet versus the Lake Pepin inlet, which drains a greater proportion of urban and agricultural runoff. Despite these differences, nutrient trends were similar at the inlets to both lakes; reductions in total phosphorus and ammonium concentrations were attributed to improvements in point source technologies, whereas increasing nitrate concentrations were attributed to both point source changes and nonpoint source increases. Despite improvements in several water quality variables, nitrate concentrations are increasing in both lakes, sediment trends indicate persistent nonpoint source inputs to Lake Pepin, and current total phosphorus concentrations remain well above pre-1950s levels in both lakes. Since urban development and agriculture are increasing in the Lake St. Croix and Lake Pepin Watersheds, continued point source regulation and additional nonpoint source control efforts will be needed to further improve water quality in these lakes. The 1976–2004 trends for most water quality variables were similar at inlet versus outlet sites on Lake St. Croix. Trends at Lake Pepin inlet versus outlet sites were less similar, but data availability limited the comparison to the 1993–2003 period. While the truncated data record highlighted short-term trends in both lakes, the full data record was most useful for exploring general patterns in water quality. Length of monitoring record affected our ability to detect trends at the inlets to both lakes, and altered the magnitude of detected trends. During the two decades of the 1980s and 1990s, paleolimnological estimates of retained phosphorus loads were similar to those estimated from recent water quality monitoring. These similarities support the use of paleolimnological approaches to infer past water quality conditions in Lakes St. Croix and Pepin. This is one of eight papers dedicated to the “Recent Environmental History of the Upper Mississippi River” published in this special issue of the Journal of Paleolimnology. D. R. Engstrom served as guest editor of the special issue.  相似文献   

地下流体长趋势异常变化与强震预测的初步研究   总被引：2，自引：0，他引：2  

陆明勇  刘耀炜  范雪芳  曹玲玲  高小其  官致君  张素欣  刘翔  李民  牛安福  丁风和  朱自强  房宗绯  赵丽葵 《地震研究》2009,32(4)

以华北、川滇、青藏东北缘、新疆及邻区等重点地区的地下流体观测点为基础,选择水位、水氡、水温、汞等长期观测资料,进行了历史强震震例的地下流体长趋势资料处理、干扰排除和异常提取的方法和技术的研究,初步建立了分区的强地震地下流体长期预测指标并探讨其异同。  相似文献   

Stream Temperature Trends in Turkey     

Mine Albek  Erdem Albek 《洁净——土壤、空气、水》2009,37(2):142-149

Stream temperature is an important property of water and affects most other water quality constituents. It is also a property which is very much influenced by exogenous factors like air temperature and stream flow. This study investigates long‐term trends in stream temperatures measured at various stream monitoring stations in Turkey to better understand links with climate change. It was found by statistical trend analysis that more streams have experienced decreasing trends than increasing ones. Moreover, stream temperatures show a rising tendency in most stations over Turkey. Flow‐adjusted temperatures were computed to eliminate flow dependency and these show more positive than negative trends. Management plans of streams and watersheds need to take this into account and incorporate the implications into plans.  相似文献   

中国西北地区降水的演变趋势和年际变化   总被引：32，自引：2，他引：30  

韦志刚  董文杰  惠小英 《气象学报》2000,58(2):234-243

将 PCA和 SSA相结合 ,分析了中国西北地区降水量的演变趋势和年际变化 ,结果表明 :西北地区的降水变化的主要趋势是 1 960年代初多雨 ,到 1 970年代初演变为少雨 ,1 980年代又多雨 ,1 990年代少雨。这种趋势在陇南和陕西中南部是最显著的 ,天山北麓区也是相对显著区。西北地区降水主要存在准 8.5a、准 3～ 4a和准 5.1 a的甚低频振荡。甚低频振荡在降水中的重要性依次为准 8.5a、准 3～ 4a和准 5.1 a。准 8.5a振荡的振幅要比准 3～ 4a和准5.1 a振荡的振幅变化大。振荡位相在空间的分布并不完全一致。  相似文献   

广西芒场锡-多金属矿田叠加褶皱构造及趋势面分析研究          下载免费PDF全文

沈镭  池三川  王思源  杨海明 《地质科学》1992,(1):44

 本文利用传统构造地质学中小构造要素统计方法,从空间上恢复并确定了芒场锡-多金属矿田内印支早期北北西向芒场复背斜和燕山晚期北北东向褶皱;利用趋势面分析方法给出了两期褶皱的叠加部位及其控矿模型。根据叠加褶皱具等距性控矿特点,笔者预测了已知矿床外围的两个未知矿点,经野外验证和工程揭露表明,上述矿点均见有锑、银矿化。  相似文献   

我国海洋溢油事故特征与趋势分析          下载免费PDF全文

宫云飞  赵鹏飞  兰冬东  朱容娟  许妍  鲍晨光  于春艳 《海洋开发与管理》2018,35(11):42-45

文章通过对1971—2011年期间发生在我国沿海海域内溢油量在50t以上的海洋溢油事故数据的收集调查,分析了海洋溢油事故的年际变化、事故原因、油品种类、事故发生地区、事故等级等的统计特征。结果表明:1971—2011年我国50t以上海洋溢油事故共发生81起,溢油总量为49 667t;碰撞是造成海洋溢油事故的最主要原因,占总溢油次数的48.2%;污染物类型主要为燃油、原油和柴油;广东省和山东省是发生溢油事故的大省;特别重大溢油事故发生频率为0.32次/a。  相似文献   

近60年中国探空观测气温变化趋势及不确定性研究     

郭艳君  王国复 《气象学报》2019,77(6):1073-1085

基于118站探空资料研究了近60年中国850—100 hPa气温变化趋势及季节和区域特征,并通过与1979—2017年卫星微波气温的对比研究了中国探空气温均一化的不确定性。研究表明,1958—2017年中国平均对流层气温呈上升趋势,300 hPa升温最为显著,平流层下层（100 hPa）为降温趋势。冬季对流层上层升温趋势和夏季平流层下层降温趋势较强。1979—2017年较整个时段对流层升温趋势较强,平流层下层降温趋势较弱。青藏高原和西北地区对流层上层升温趋势较强。通过与卫星微波气温和邻近探空站探空气温的对比以及均一化前后日夜气温差值检测出中国探空均一化气温仍残存非均一性问题。由于参照序列的局限性,均一化未能完全去除21世纪最初10年中国探空系统变化造成的对流层中、上层至平流层下层气温系统性下降的影响,导致中国对流层上层升温趋势被低估和平流层下层降温趋势被高估。未来可通过参考卫星微波气温和邻近探空站序列调整非均一性订正顺序并增加合理性检验等方法改进中国探空气温均一化方案。   相似文献   

张家口地震台连续重力异常分析     

屈曼  侯晓真  陈建国  王曰风  朱振兴  周亚  刘仲韬 《山西地震》2021,(1):26-29,49

张家口地震台gPhone连续重力观测仪潮汐因子自2016年6月出现持续下降的趋势变化,累计变化量达到7×10-3。分析重力残差曲线,异常出现时同期残差数据未出现同步变化;将去零漂前后潮汐因子的变化情况进行对比分析,发现潮汐因子变化趋势一致,排除仪器调零影响;针对新建楼房可能引起的重力变化,建立了重力正演模型,计算结果显示,新建楼房的荷载变化仅能引起0.31微伽的重力变化,表明新建楼房对重力观测的影响较弱。综合分析认为,此次出现的重力潮汐因子下降趋势异常可能为前兆异常,需加强跟踪分析。  相似文献   

Temporal trends of hydro-climatic variables and their relevance in water resource management     

Karim Solaimani  Mahmoud Habaibnejad  Abdollah Pirnia 《国际泥沙研究》2021,36(1):63-75

Identification of temporal changes in hydrological regimes of river basins is an important topic in contemporary hydrology because of the potential impacts of climate change on river flow regimes.For this purpose,long-term historical records of rainfall(P),runoff(Q)and other climatic factors were used to investigate hydrological variability and trends in the Tajan River Basin over the period 1969e1998.Actual evaporation(E),rainfall variability index(d),evaporation ratio(CE)and runoff ratio(CQ)were estimated from the available hydroclimatological records.Mann-Kendall trend analysis and nonparametric Sen's slope estimates were performed on the respective time series variables to detect monotonic trend direction and magnitude of change over time.Rainfall variability index showed that 1973 was the wettest year(δ=+2.039)while 1985 was the driest(δ=-1.584).Also,decades 69e78 and 89e98 were recognized as the wettest and driest decades respectively.The gradient of variation of climatological parameters showed that during the study period,all three parameters of rainfall,evaporation and runoff have decreased and the variations of rainfall and evaporation were significant at the 95%level.Investigation of hydrological changes due of dam construction(1999)showed that the amount and annual distribution of discharge were completely different pre and post-dam construction.Discharge decreased in high water months and increased in low water months to meet water supply demands,especially for agriculture.The relationship between temperature and rainfall trends is compared for three stations in Mazandaran Province(Gorgan,Babolsar and Ramsar)from 1956 to 2003 and nine other stations with different statistical periods of 19e36 years,relating trends to northern hemisphere and global trends.Decreases in temperature were accompanied by decreases in rainfall,and vice versa.These trends were not observed in northern hemisphere and world scales,where temperature increases are accompanied by decreases in rainfall.These variations of hydroclimatological parameters show undesirable water resources situations during the statistical periods if the trend continues severe water resource crises.  相似文献   

中国55年来地面水汽压网格数据集的建立及精度评价   总被引：5，自引：0，他引：5  

沈艳  熊安元  施晓晖  刘小宁 《气象学报》2008,66(2):283-291

对气象要素网格化是气候变化研究中避免空间抽样误差的有效方法之一.文中采用薄盘光滑样条插值法(ANUSPLIN),在考虑站点经度、纬度和海拔高度的基础上,对中国55年来地面水汽压站点资料进行空间插值,得到了中国陆地水汽压年和月平均值1°×1°网格数据集.精度检验表明:中国年水汽压插值误差普遍小于0.3 hPa;而月水汽压的插值误差由于受水汽压周期变化的影响,表现出周期性变化的特点.一般夏季较大,最大误差在0.5 hPa左右,冬季较小,约为0.2 hPa.在考虑站点海拔与对应网格DEM差值大小的基础上,建立实测水汽压值与对应网格水汽压值年序列,并进一步分析二者的相关关系,表明:(1)二者具有很好的相关性,相关系数为0.88-0.96;(2) 能很好地模拟地形影响,得到的网格水汽压可以较好地代表实测水汽压的变化趋势.由此建立了中国近55年来地面水汽压的年序列.其趋势表明:近55年来中国年平均水汽压呈增加趋势,其线性趋势为0.52 hPa/(100 a),其中西部增加趋势大于东部,且以夏季的增大趋势最为显著.结合近50年来气温的变化趋势说明:在中国,气温每增加1 ℃,大气中年平均水汽含量约增加3.15%.  相似文献