共查询到20条相似文献，搜索用时 906 毫秒
1.
D. Degobbis N. Smodlaka I. Pojed A. Škrivanić R. Precali 《Marine pollution bulletin》1979,10(10):298-301
The Northern Adriatic is one of the most productive regions of the Mediterranean, primarily due to the eutrophicating influence of Italian rivers, in particular the Po. In June 1977 unusually high phytoplankton standing crops (13 μg Chl a l.?1) occurred, together with extremely low dissolved oxygen concentrations in bottom waters (to 13%) which persisted for 4–6 months. Such conditions were associated with unusual climatic conditions creating increased discharge from the Po.The data indicate long term meteorological changes which may alter the biological characteristics of the region to a degree equal to, or exceeding, those created by anthropomorphic eutrophication.The 1977 data are presented, discussed, and contrasted with a 10 year data series. 相似文献
2.
黄河干流浮游植物群落特征及其对水质的指示作用 总被引：1，自引：0，他引：1
2008年5-6月和9-10月对黄河干流13个河段和4座水库的浮游植物群落及其环境进行了全面调查.共鉴定浮游植物8门83属150种,其中有硅藻59种,绿藻55种,蓝藻24种,甲藻4种,裸藻4种,金藻2种,黄藻1种和隐藻1种,平均细胞密度和生物量分别为126.90×104cells/L和0.940mg/L.从大的格局上看,浮游植物群落在种类数、种类组成和现存量上均存在较明显的空间分异,这种分异性可从河流流速、泥沙含量和受污染程度得到解释.根据浮游植物污染指示种和Shannon-Wiener多样性指数分析,黄河干流各河段多受到不同程度的污染.与1986年的资料相比,黄河干流浮游植物组成发生了明显变化,属数下降了9.8%,而平均生物量升高了128.7%,且在种类组成上也发生了明显的变化,表明河流污染程度的加剧. 相似文献
3.
4.
5.
湖北浮桥河水库底栖动物的群落结构及生物多样性 总被引：9，自引：3，他引：6
1997年 4月至 1998年 1月 ,在浮桥河水库 14个采样点调查底栖动物 ,共获 4 7种 .其优势种类为霍甫水丝蚓 (Limnodrilushoffmeisteri)、中国长足摇蚊 (Tanypuschinensis)、前突摇蚊属 (Procladiussp .)和摇蚊属 (Chironomussp .) .水库底栖动物的Shannon指数和Margalef指数偏低 ,上游的指数值最高 .从种类相似性来看 ,底栖动物的季节变化不明显 ;在水平分布上 ,上游与库汊的种类相似性最低 ,库汊与下游的种类相似性最高 .浮桥河水库底栖动物的平均密度为5 2 9.1ind/m2 ,平均生物量为 35 34.1mg/m2 ,均以水生昆虫占优 ,其时空变化主要受水生昆虫控制 .能量估算法估算出浮桥河水库底栖动物的渔产潜力为 1.5× 10 4 kg/a . 相似文献
6.
L.R. Pomeroy L.P. Atkinson J.O. Blanton W.B. Campbell T.R. Jacobsen K.H. Kerrick A.M. Wood 《Continental Shelf Research》1983,2(1):1-20
The distribution and abundance of bacteria and phytoplankton on the continental shelf of the southeastern United States were observed in relation to physical processes. Phytoplankton production was influenced by inputs of water of reduced salinity from the estuaries and by inputs of high salinity, low-temperature water from the west front of the Gulf Stream. The distribution of chlorophyll suggests that in each case production is influenced both by inputs of nutrients and by the enhanced vertical stability associated with the stratification of waters of different densities. The standing stock of bacteria on the inner shelf, 106 ml?1, is little changed by the influx of water of reduced salinity. On the outer shelf, where the usual standing stock of bacteria is 105 ml?1, the numbers increase to 106 ml?1 in and above intrusions of Gulf Stream water in which phytoplankton blooms have developed, suggesting that the bacteria respond to products of both phytoplankton and zooplankton production. Adenylate energy charge values in the waters of the southeastern shelf are variable and volatile. At times values of 0.7 to 0.8 are widespread over most of the shelf, while at other times values <0.6 are common, with localized patches of high values. Both autotroph-dominated and heterotroph-dominated microbial communities show these variations. 相似文献
7.
Takesi Yukutake 《Physics of the Earth and Planetary Interiors》1981,24(4):253-258
An examination of the westward drift of the geomagnetic field indicates that the drift velocity is almost independent of latitude, suggesting a uniform rigid rotation of spherical shape. When the geomagnetic field is separated into standing and drifting components and expressed in a spherical harmonic series, a lack of sectorial terms is noted in the standing field. It is shown that these features are well explained by a stratified core model.The core is supposed to be stratified near the surface where toroidal fluid motions are predominant. In the deeper part, the fluid motion is two-dimensional, forming Taylor columns. A simplified core model is assumed to represent these features, in which the core is divided into two parts, an outer spherical shell that rotates westwards at a uniform rate of 0.3° y?1 and a central sphere in which the two-dimensional columnar motions reside. The toroidal motions in the outer spherical interact with the dipole field to induce the drifting field, whereas the columnar motions generate the standing field through interaction with a toroidal field. It follows that a small velocity as 5 × 10?3 cm s?1 for the stratified motion is sufficient to create the observed drifting field. 相似文献
8.
Land use changes due to energy policy as a determining factor for morphological processes in fluvial systems in São Paulo State,Brazil 
下载免费PDF全文
下载免费PDF全文 Cenira Maria Lupinacci Fabiano Tomazini da Conceição Adriano Luis Heck Simon Archimedes Perez Filho 《地球表面变化过程与地形》2017,42(14):2402-2413
The number of hydroelectric dams used for energy production and the cultivation of sugar cane crops for ethanol production have increased significantly in the southeastern region of Brazil. These land use/land cover changes (LULCC) associated with energy policy can affect landscape changes over a range of temporal and spatial scales. This article focuses on how human–landscape interactions have influenced geomorphological dynamics in the lower course of the Piracicaba River for two different scenarios that represent pre‐dam and post‐dam conditions in 1962 and 2007, respectively, and the expansion of sugar cane crops after 1975. This assessment was performed by mapping land use and geomorphological changes in the study area in the 1962 and 2007 scenarios, in addition to quantifying the sedimentation rates upstream from the Barra Bonita Reservoir using 210Pb. The main land uses identified for the 1962 scenario were pastures, meadows, annual crops and forests. However, the main land use change was the expansion of sugar cane cropland from 4 to 39%. In the 1962 scenario, the lower course of the Piracicaba River had a predominantly meandering pattern, and there were pronounced alluvial plains in the region. In the 2007 scenario, oxbow lakes were not mapped, and the river terraces were reduced in area due to construction of the Barra Bonita Reservoir. The changes in the sedimentation rates indicate an association between the construction of the Barra Bonita Reservoir and the expansion of sugar cane crops. It was therefore not possible to assess the specific influences of each anthropogenic change on the sedimentation processes, reinforcing that the human–landscape systems in São Paulo State associated with energy policy are complex. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
9.
三道河水库浮游生物现状及其鱼产力的估算 总被引：1，自引：0，他引：1
本文报道1990年对三道河水库浮游生物现存量和浮游植物初级生产量的凋查结果。经初步鉴定,该水库浮蝣植物有8门39属,其中以绿藻门种类最多,占总属数的49％,其次为蓝藻和硅藻;浮游动物为37属,其中原生动物12属,轮虫13属,枝角类7属,桡足类5属。经测算,三道河水库1990年4—10月浮游植物数量和生物量分别为1139ind./L和2.085mg/L,浮游动物数量和生物量则分别为1253ind./L和1.327mg/L。浮游植物初级毛生产量平均为3.950g O_2/m~2·d。根据估算,该水库鲢鳙鱼产力为15×10~4kg左右。 相似文献
10.
Erik Oerter Eric Slessarev Ate Visser Kyungjin Min Megan Kan Karis J. McFarlane Malay C. Saha Asmeret Asefaw Berhe Jennifer Pett-Ridge Erin Nuccio 《水文研究》2021,35(9):e14366
Perennial bioenergy crops with deep (>1 m) rooting systems, such as switchgrass (Panicum virgatum L.), are hypothesized to increase carbon storage in deep soil. Deeply rooted plants may also affect soil hydrology by accessing deep soil water for transpiration, which can affect soil water content and infiltration in deep soil layers, thereby affecting groundwater recharge. Using stable H and O isotope (δ2H and δ18O) and 3H values, we studied the soil water conditions at 20–30 cm intervals to depths of 2.4–3.6 m in paired fields of switchgrass and shallow rooted crops at three sites in the southern Great Plains of North America. We found that soil under switchgrass had consistently higher soil water content than nearby soil under shallow-rooted annual crops by a margin of 15%–100%. Soil water content and isotopic depth profiles indicated that hydraulic redistribution of deep soil water by switchgrass roots explained these observed soil water differences. To our knowledge, these are the first observations of hydraulic redistribution in deeply rooted grasses, and complement earlier observations of dynamic soil water fluxes under shallow-rooted grasses. Hydraulic redistribution by switchgrass may be a strategy for drought avoidance, wherein the plant may actively prevent water limitation. This raises the possibility that deeply rooted grasses may be used to passively subsidize soil water to more shallow-rooted species in inter-cropping arrangements. 相似文献
11.
Seasonal evolution of runoff generation on agricultural land in the Belgian loess belt and implications for muddy flood triggering 总被引：1，自引：0，他引：1
Muddy floods due to agricultural runoff are a widespread and frequent phenomenon in the European loess belt, and particularly in central Belgium. These floods are triggered when high quantities of runoff are generated on cropland and cause severe erosion. Three soil surface characteristics are relevant to determine the runoff potential of cultivated soils: soil cover by crops and residues, soil surface crusting and roughness. These characteristics have been observed on 65 cultivated fields throughout 2005. A heavy rainfall event representative for events triggering muddy floods in the region (60 mm h?1 during 30 minutes) has been simulated using a 0·5 m2 simulator on fields with the 17 most observed combinations of soil surface characteristics in central Belgium. Runoff is not observed in the case of (ploughed) bare uncrusted soils, nor in the case of soils covered by crops showing a transitional crust and a moderate roughness (1–2 cm). In the cases where runoff has been observed, mean runoff coefficients ranged from 13% (wheat in July) to 58% (sugar beet or maize in May and June). Grassed buffer strips (GBSs) and grassed waterways (GWWs) show a higher runoff coefficient (62% for GBSs and 73% for GWWs) than most cultivated soils (13–58%). Furthermore, it is demonstrated that small plot measurements can be used to estimate runoff generation at the field scale. A classification of runoff generation risk based on the surveys of soil surface characteristics has been applied to common crops of central Belgium. February as well as the period between May and September are the most critical for runoff at the field scale. However, it appears from monitoring of a 16 ha catchment that the highest runoff volumes and peak discharges are recorded between May and August after heavy rainfall, explaining why 85% of muddy floods are recorded during this period in central Belgium. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
12.
In this study, the impacts of climate change on crop water requirements and irrigation water requirements on the regional cropping pattern were evaluated using two climate change scenarios and combinations of 20 GCM models. Different models including CROPWAT, MODFLOW, and statistical models were used to evaluate the climate change impacts. The results showed that in the future period (2017 to 2046) the temperature in all months of the year will increase at all stations. The average annual precipitation decline in Isfahan, Tiran, Flavarjan, and Lenj stations for RCP 4.5 and RCP 8.5 scenarios are 18.6 and 27.6%, 15.2 and 18%, 22.5 and 31.5%, and 10.5 and 12.1%, respectively. The average increase in the evapotranspiration for RCP 4.5 and RCP 8.5 scenarios are about 2.5 and 4.1%, respectively. The irrigation water demands increases considerably and for some crops, on average 18%. Among the existing crops in the cropping pattern, barley, cumin, onion, wheat, and forage crops are more sensitive and their water demand will increase significantly. Results indicate that climate change could have a significant impact on water resources consumption. By considering irrigation efficiency in the region, climate change impacts will result in about 35 to 50 million m3/year, over-extraction from the aquifer. This additional exploitation causes an extra drop of 0.4 to 0.8 m in groundwater table per year in the aquifer. Therefore, with regard to the critical condition of the aquifer, management and preventive measures to deal with climate change in the future is absolutely necessary. 相似文献
13.
T. Berman Y. Z. Yacobi U. Pollingher 《Aquatic Sciences - Research Across Boundaries》1992,54(2):104-127
The general features of phytoplankton seasonal succession, abundance and distribution in Lake Kinneret, as based on observations from 1970 through 1989, are summarised. Throughout this period of observation, the large, thecate dinoflagellatePeridinium gatunense formed an annual, late winter to early spring bloom resulting in very high standing stock levels. The dominance of these dinoflagellates has a profound impact upon the lake ecosystem. In the summer and fall the phytoplankton assemblage consisted mainly of nanoplanktonic green and blue-green algae and diatoms. Picophytoplankton, mainly picocyanobacteria, were present in low numbers during the dinoflagellate bloom but reached maximum abundance (105 cells · ml–1) in the epilimnion during the summer and fall. Within a given year, chlorophyll concentrations correlated well with estimates of wet weight biomass, derived from microscope counts. However, interannual averages of chlorophyll did not correlate closely with those for wet weight biomass. Both wet weight biomass and chlorophyll standing stocks fluctuated more than 2 fold from 1970 through 1989 but no extreme, long-term, continuous trend of increase or decrease was observed. Thus, phytoplankton has remained relatively stable although there has been a significant rise in the levels of summer-fall biomass since 1981. The main factor responsible for this may have been increased available phosphorus; the abundance of phytoplankton did not show any clear, long-term relation to that of herbivorous zooplankton. 相似文献
14.
Changes in the soluble sugar, starch, total non-structural carbohydrate (TNC) and nutrient (N, P, K) concentration in the reed rhizome were investigated in different reed habitat types in Lake Fertõ/Neusiedlersee during the vegetation period in 1993 to 94. Three die-back and four vigorous reed stands were monitored.For biomass estimations rhizomes were collected twice, in early summer and in autumn. They were calculated to be 1.9 to 2.7 kg/m2 at die-back and 3.1 to 6.1 kg/m2 at vigorous sites.The carbohydrate and nutrient concentrations of the reed rhizomes were high at the beginning of the vegetation period; they reached their minima in May–June, which was followed by a gradual increase until the end of the vegetation period. From autumn to spring the concentrations decreased, e.g. TNC concentration by 15 to 40% at vigorous, 50 to 70% at die-back sites.In both years the lowest carbohydrate concentrations were recorded at the end of May, a month before the inflorescence developed (vigorous sites: 50–70 mg TNC/g, die-back sites: 70–120 mg TNC/g). In that period the standing stock of the TNC in the rhizome did not separate the sites clearly, and the smallest carbohydrate standing stock was measured at a vigorous site with a high water cover.At the beginning of summer and in autumn the soluble sugar, TNC and N concentration values were higher at the die-back than at the vigorous sites but the standing stock was higher at the vigorous sites. In autumn the TNC standing stock of the rhizomes was between 780 and 1200 g/m2 at vigorous, between 380 and 690 g/m2 at die-back sites. This is especially important for the reactions and resistance of die-back reed stands to unfavourable conditions. 相似文献
15.
Temporal sequential analyses of the hydrological observational data in the Tarim Basin over the last forty years revealed an annual increase of 2× 107m3 in the water quantities at the three headstreams of the upper courses and an annual decrease of 3 × 107m3 in the water flow from Alaer, which is on the upper main stream. A prediction of the trends indicates that there can be severe situations under which intermittent water interceptions occur. By means of approximate estimations on vegetative water consumption through phreatic evaporation combined with a quota assessment, the ecological water demands required to maintain the ecological environment in the mainstream area over the three different targeted years of 2005, 2010 and 2030 are defined as standing at 31.86 × 108m3, 36.27 × 108m3 and 41.04 × 108m3 respectively. Ecological fragility indexes are established on the basis of the selection of environmental sensitivity factors. Rational evaluations give proof that the lower reaches of the mainstream have already turned into zones where their ecological environments are gravely damaged. Multi-objective optimization should be conducted and protective schemes be framed within the threshold limits of the bearing capacities of water resources and the environment 相似文献
16.
The accumulation of debris is an insidious problem throughout the world’s oceans. Here we document 234.24 items of macro-debris/km2 in the shallow populated parts of Majuro lagoon (Republic of the Marshall Islands) which is the second highest standing stock of macro-debris recorded to date in any benthic marine habitat in the world. The majority of macro-debris was from household sources (78.7%) with the peak abundance recorded in areas of medium affluence. Marine debris causes suffocation, shading, tissue abrasion and mortality of corals and we show a significant negative correlation exists between the level of hard coral cover and coverage of marine debris. Given long decomposition times, even if the input of rubbish to Majuro lagoon is stopped immediately, the standing stock of debris will persist for centuries. Multiple new initiatives are needed to curtail the direct and indirect dumping of waste in Majuro lagoon. 相似文献
17.
丹江口水库的浮游甲壳动物 总被引：10，自引：2，他引：8
为了合理开发利用丹江口水库的渔业资源,1992年12月至1993年9月对丹江口水库的浮游甲壳动物进行了四次调查。结果显示丹江口水库浮游甲壳动物有26属36种,其中枝角类11属17种,桡足类15属19种。浮游甲壳动物年平均数量为31.0个/L,年平均生物量为0.6311mg/L,水库每年可提供浮游动物食性鱼类的年生产潜力为5.87×10~5kg。 相似文献
18.
Analytical and numerical analysis of tides and salinities in estuaries; part I: tidal wave propagation in convergent estuaries 总被引：2，自引：2，他引：0
Leo C. van Rijn 《Ocean Dynamics》2011,61(11):1719-1741
Analytical solutions of the momentum and energy equations for tidal flow are studied. Analytical solutions are well known
for prismatic channels but are less well known for converging channels. As most estuaries have a planform with converging
channels, the attention in this paper is fully focused on converging tidal channels. It will be shown that the tidal range
along converging channels can be described by relatively simple expressions solving the energy and momentum equations (new
approaches). The semi-analytical solution of the energy equation includes quadratic (nonlinear) bottom friction. The analytical
solution of the continuity and momentum equations is only possible for linearized bottom friction. The linearized analytical
solution is presented for sinusoidal tidal waves with and without reflection in strongly convergent (funnel type) channels.
Using these approaches, simple and powerful tools (spreadsheet models) for tidal analysis of amplified and damped tidal wave
propagation in converging estuaries have been developed. The analytical solutions are compared with the results of numerical
solutions and with measured data of the Western Scheldt Estuary in the Netherlands, the Hooghly Estuary in India and the Delaware
Estuary in the USA. The analytical solutions show surprisingly good agreement with measured tidal ranges in these large-scale
tidal systems. Convergence is found to be dominant in long and deep-converging channels resulting in an amplified tidal range,
whereas bottom friction is generally dominant in shallow converging channels resulting in a damped tidal range. Reflection
in closed-end channels is important in the most landward 1/3 length of the total channel length. In strongly convergent channels
with a single forward propagating tidal wave, there is a phase lead of the horizontal and vertical tide close to 90o, mimicking a standing wave system (apparent standing wave). 相似文献
19.
《Continental Shelf Research》1987,7(9):1049-1062
Water column primary production was measured 43 times over a 3-year period (1983–1985) on the outer shelf of the central Great Barrier Reef province and in the adjacent East Australian Current. No seasonal production cycle could be established. Estimated daily production rates in shelf and offshore waters ranged between 0.1 and 1.5 g C m−2, with most between 0.2 and 0.7 g C m−2. Annual primary production during 1983 in mid-shelf, shelf break and offshore zones was estimated to be 183, 167 and 211 g C m−2, respectively. Annual production by the<10μm size fraction at the same sites was 114, 94 and 127 g C m−2, 62, 56 and 60% of total production, respectively. Corresponding proportions of chlorophyll standing crop in the<10μm fraction were 65, 85 and 79%. In a subset of the above experiments, picoplankton (<2μm size fraction) accounted for 37–99% of total water column production and 32–85% of the chlorophyll standing crop. At first order, annual phytoplankton plus coral reef primary production on the outer shelf in the central GBR is estimated to be 404 g C m−2, with phytoplankton contributing 37%. 相似文献
20.
富营养深水水库底栖动物群落与浮游生物相关性分析 总被引：1，自引：0，他引：1
底栖动物和浮游生物通过食物网发生复杂的交互作用,是水库生态系统物质循环的重要组分.南湾水库和汤浦水库均为存在富营养化现象的深水水库,具有较长时间的水温分层期.本文选取这两座供水水库为对象,比较其水体营养状态、底栖动物的群落结构、现存量和多样性.通过群落状态指数(IICS)定量评估底栖动物群落状态,并采用PLS模型、Spearman秩相关以及回归图探讨浮游生物各类群密度与IICS的关系.研究结果显示,南湾水库富营养程度高于汤浦水库,寡毛类在南湾水库占据优势地位,摇蚊类在汤浦水库数量上占优.南湾水库以收集者为主,其数量占比远高于汤浦水库.深水水库通常存在较强的热分层,富营养化会加重水库底部的缺氧或厌氧状态,导致底栖动物遭受周期性的缺氧扰动,影响种类多样性和现存量,改变浮游生物类群与底栖动物群落的相关性,因此底栖动物群落与浮游生物的相关性能够提供判断水库富营养化程度的重要信号,进而为水库管理方提供更多有价值的参考信息. 相似文献