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1.
In the under-ice period, gas exchange between Baikal and the atmosphere is taking place through a system of coastal and perennial fractures and airholes in the ice, as well as through the surface of the ice-free part of the lake at the Angara source [24]. The total area of the open water never exceeds 0.03% of lake water area. The emission of CO2 in the course of ice sublimation over the entire period is ≤0.02 g CO2 from 1 m2. The transport of dissolved gases from under-ice water into the atmosphere is limited by molecular diffusion in microfractions of ice cover. The narrow daily variations of CO2 in the air in lake coastal zone is due to the effect of populated localities on its coast and large coniferous forests, which serve as diffuse sources of CO2, as well as diurnal variations of the direction and velocity of air mass transport by local winds. 相似文献
2.
Urnersee and Gersauersee are two adjacent basins of Vierwaldstättersee (Lake Lucerne, Switzerland), seperated by a sill of 85 m depth, with similar topography (max. depth 195 and 213 m, respectively) but remarkably different exposure to “external forces”, such as wind and river input. Urnersee is exposed to diurnal winds and to occasional strong storms from the south (Föhn) whereas the wind over Gersauersee is moderate or weak. Two rivers, both having very large discharges during storms, replace the total water volume of Urnersee about once a year; in contrast, no large river flows directly into Gersauersee. Between March and October 1986, meteorological parameters, water temperatures and currents were measured quasi-continuously with the aim to quantify hypolimnic water exchange and mixing in Urnersee and to asses the relative importance of wind mixing versus river-induced water exchange for the renewal of the deep water layers. Three periods could be identified: (1) in April, weak stratification and strong episodic storms exchange about 50% of the deep hypolimnion (DH, defined as layer below 110 m depth) leading to a mean heat flux of 36 Wm2. Because of the large wind mixing the water of the exposed Urnersee below about 20 m depth becomes lighter than in the sheltered Gersauersee. (2) In May and June, the horizontal density gradient causes about 65% renewal of the Urnersee DH by the heavier Gersauersee intermediate water but does not affect the heart content. (3) Simultaneously with these processes are the episodic river floods adding another 20% to the DH water exchange and causing a heat flux of about 6 Wm2. During the rest of the summer, water exchange remains below 10% and is mainly due to episodic flood while wind mixing has little influence. Yet, during floods water input into the DH per unit time can still be very large and heat, fluxes reach 600 Wm2 or more. The influence of lateral density currents between the two adjacent basins on hypolimnic mixing is of great ecological significance and explains the oxygen saturation found in the deep water of Urnersee compared to Gersauersee. 相似文献
3.
Field observations of flow and sediment transport in a tributary channel through intertidal mudflats indicate that suspended sediment was closely linked to advection and dispersion of a tidal salinity front. During calm weather when tidal forcing was dominant, high concentrations of suspended sediment advected up the mudflat channel in the narrow region between salty water from San Francisco Bay and much fresher runoff from the small local watershed. Salinity and suspended sediment dispersed at similar rates through each tidal inundation, such that during receding ebbs the sediment pulse had spread spatially and maximum concentrations had decreased. Net sediment transport was moderately onshore during the calm weather, as asymmetries in stratification due to tidal straining of the salinity front enhanced deposition, particularly during weaker neap tidal forcing. Sediment transport by tidal forcing was periodically altered by winter storms. During storms, strong winds from the south generated wind waves and temporarily increased suspended sediment concentrations. Increased discharge down the tributary channels due to precipitation had more lasting impact on sediment transport, supplying both buoyancy and fine sediment to the system. Net sediment transport depended on the balance between calm weather tidal forcing and perturbations by episodic storms. Net transport in the tributary channel was generally off-shore during storms and during calm weather spring tides, and on-shore during calm weather neap tides. 相似文献
4.
Marcello G. Magaldi Tamay M. Özgökmen Annalisa Griffa Michel Rixen 《Ocean Dynamics》2010,60(1):93-122
This numerical study focuses on the response of the Western Adriatic Current to wind forcing. The turbulent buoyant surface
current is induced by the Po river outflow in the Adriatic Sea. Idealized and realistic wind conditions are considered by
retaining the complex geomorphology of the middle Adriatic basin. In the absence of wind, the Adriatic Promontories force
the current to separate from the coast and induce instabilities. Persistent 7-m s − 1 downwelling favorable northwesterly winds thicken and narrow the current. Instabilities whose size is ~10 km develop but
ultimately vanish, since there is not enough across-shore space to grow. On the contrary, 7-m s − 1 upwelling favorable southeasterly winds thin and widen the current, and instabilities can grow to form mesoscale (~35 km)
features. When realistic winds are considered, the same trends are observed, but the state of the sea set up by previous wind
events also plays a crucial role. The turbulent regimes set up by different winds affect mixing and the WAC meridional transport.
With downwelling winds, the transport is generally southward and mixing happens mostly between the fresher (S ≤ 38) salinity classes. With upwelling winds, the transport decreases and changes sign, and mixing mainly involves saltier
(S > 38) waters. In all cases, mixing is enhanced when a finer 0.5-km horizontal resolution is employed. 相似文献
5.
The sedimentology of proglacial Silt Lake was assessed by lake sediment coring and monitoring of lacustrine processes during a late‐summer period of high glacier melt to characterize sediment delivery from the heavily glacierized catchment and investigate the sediment trapping dynamics of this upland lake. A complete varve chronology was established for a distal basin of the lake which was exposed by Lillooet Glacier retreat between 1947 and 1962. The varve record showed decreasing sedimentation rates in the basin while the glacier retreated, and as the lake became free of ice contact in the early 1970s. Although recession has continued over recent decades, and glacier proximity to the lake has, therefore, continued decreasing, lacustrine sedimentation rates are now accelerating due to changing basin morphometry caused by delta progradation. Over shorter time scales, lake sedimentation patterns respond to changing runoff conditions, including late‐summer glacier melt intensity, intra‐annual flooding events, diumal runoff fluctuations, and within‐lake turbidity currents. Turbidity currents included quasi‐regular flows during high diurnal discharges and an episodic flushing of temporarily stored sediment from the sandur or delta at a time of low stage. Suspended sediment yield to Silt Lake is estimated to exceed 103 Mg km?2 a?1, a magnitude that surpasses previous local and regional yield estimates for the glacierized headwaters of the Lillooet River valley. Since Silt Lake currently traps a significant prooportion of that upland sediment supply, and the trapping efficiency of the basin has been variable at decadal time scales, the formation and continued development of Lilt Lake has likely had a significant influence on downstream sediment delivery. Lacustrine sediment‐based proxies of long‐term hydroclimatic variability being developed in glacially distal settings should include provisions for dynamic sediment trapping effects in upstream water bodies that often form in the active proglacial environment. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
6.
Nikolaos P. Nikolaidis Vicki S. Nikolaidis Jerald L. Schnoor 《Aquatic Sciences - Research Across Boundaries》1991,53(4):330-345
Monte-Carlo simulations were used to assess the extent of shortterm alkalinity depressions occuring in Sierra Nevada lakes due to acidic deposition events. The Episodic Event Model (EEM) was used to simulate spring snowmelt events. Snow course data, precipitation data and lake acidification surveys were used to derive values for the EEM parameters. Spring snowmelt events were shown to have great impacts on the water quality of Sierran lakes. Lakes are likely to be most affected by the early-spring snowmelt event because the epilimnion depth is at a minimum, which indicates minimum dilution. Under annual average loading conditions, no Sierran lake has been reported as acidic although 29% of the lakes have alkalinities less than 40 µeq/L indicating a sensitivity to acidification. In simulations of early-spring snowmelt events, using present-day acidic loading conditions, it was estimated 79% ± 9% of the lakes would experience shortterm lake alkalinity depressions to levels less than 40 µeq/L. The results provided by the model simulations are valuable in establishing upper and lower limits on the extent of possible episodic acidification to lake-resources-at-risk. The most critical parameters controlling the magnitude of lake alkalinity depressions during snowmelt episodic events are a) the lake area to watershed area ratio — a measure of input loading, and b) the epilimnion volume — a measure of dilution and mixing. 相似文献
7.
This study was motivated by an interest in understanding the potential effects of climate change and glacier retreat on late summer water temperatures in alpine areas. Fieldwork was carried out between July and September 2007 at Place Lake, located below Place Glacier in the southern Coast Mountains of British Columbia. Place Lake has an area of 72 000 m2, a single inlet and outlet channel, and an approximate residence time of 4 days. Warming between the inlet and outlet of the lake ranged up to 3 °C and averaged 1.8 °C, which exceeds the amount of warming that occurred over the 1 km reach of Place Creek between the lake outlet and tree line. Over a 23‐day period, net radiation totalled about 210 MJ·m–2, with sensible heat flux adding another 56 MJ m‐2. The latent heat flux consumed about 8% of the surface heat input. The dominant heat sink was the net horizontal advection associated with lake inflow and outflow. Early in the study period, temperatures between the surface and 6‐m depth were dominantly at or above 4 °C and were generally neutral to thermally stable, whereas temperatures decreased with depth below 6 m and exhibited irregular sub‐diurnal variations. The maximum outflow temperature of almost 7 °C occurred in this period. We hypothesize that turbidity currents associated with cold, sediment‐laden glacier discharge formed an underflow and influenced temperatures in the deeper portion of the lake but did not mix with the upper layers. Later in the study period, the lake was dominantly well mixed with some near‐surface stability associated with nocturnal cooling. Further research is required to examine the combined effects of sediment concentrations and thermal processes on mixing in small proglacial lakes to make projections of the consequences of glacier retreat on alpine lake and stream temperatures. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
8.
Analysis of the Pampa, Texas, multicell storms showed prestorm environmental conditions of a strong horizontal convergence
of moisture, mixing ratio 12 g/kg at the 850 mb level in the Texas Panhandle areas and strong winds with shear veering with
height. Rapid-scan satellite imagery showed that the clouds penetrated above the tropopause and cloud-top temperatures were
at least 4 to 9° C colder than the temperature of the tropopause. This formation and collapsing of high-mass-density overshooting
cloud tops above the tropopause is characteristic of tornadoes in the middle portion of the United States. 相似文献
9.
Glacier recessions caused by climate change may uncover pro‐glacial lakes that form important sedimentation basins regulating the downstream sediment delivery. The impact of modern pro‐glacial lakes on fluvial sediment transport from three different Norwegian glaciers: Nigardsbreen, Engabreen and Tunsbergdalsbreen, and their long‐term development has been studied. All of these lakes developed in modern times in overdeepened bedrock basins. The recession of Nigardsbreen uncovered a 1.8 km long and on average 15 m deep pro‐glacial lake basin during 1937 to 1968. Since then the glacier front has been situated entirely on land, and the sediment input and output of the lake has been measured. The suspended sediment transport into and out of the lake averaged 11 730 t yr?1 and 2340 t yr?1 respectively. Thus, 20% remained in suspension at the outlet. The measured mean annual bedload supplied to the lake was 11 800 t yr?1, giving a total transport of 23 530 t yr?1 which corresponds to a specific sediment yield of 561 t km?2 yr?1. A 1.9 km long and up to 90 m deep pro‐glacial lake basin downstream from Engabreen glacier was uncovered during 1890 to 1944. The average suspended sediment load delivered from the glacier during the years 1970–1981 amounted to 12 375 t yr?1and the transport out of the lake was 2021 t yr?1, giving an average of 16% remaining in suspension. The mean annual bedload was 8000 t yr?1, thus the total transport was 20 375 t yr?1, giving a specific sediment yield of 566 t km?2 yr?1. For Tunsbergdalsbreen glacier, measurements in the early 1970s indicated that the suspended sediment transport was on average 44 000 t yr?1. From 1987 to 1993 the recession of the glacier uncovered a small pro‐glacial lake, 0.3 km long and around 9 m deep. Downstream from this, the suspended sediment load measured in 2009 was 28 000 t yr?1, indicating that as much as 64% remained in suspension. Flow velocity, grain size of sediment, and morphology of the lake are important factors controlling the sedimentation rate in the pro‐glacial lakes. A survey of the sub‐glacial morphology of Tunsbergdalsbreen revealed that there are several overdeepened basins beneath the glacier. The largest is 4 km long and 100 m deep. When the glacier melts back they will become lakes and act as sedimentation basins. Despite an expected increase in sediment yield from the glacier, little sediment will pass these lakes and downstream sediment delivery will be reduced markedly. Beneath Nigardsbreen there was only a small depression that may form a lake and the sediment delivery will not be significantly affected. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
10.
A modified landform development model for the topography of drained thermokarst lake basins in fine‐grained sediments 
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下载免费PDF全文 Permafrost degradation associated with the expansion of thermokarst lakes is commonly interrupted by catastrophic drainage. Subsequently, in tundra areas, permafrost aggradation in drained basins leads to uneven topography characterized by raised centres and wet, depressed margins. The genesis of such topography has been investigated in Old Crow Flats (OCF), a glaciolacustrine plain in the continuous permafrost of northern Yukon. The thermokarst lakes of OCF have a mean depth of only 1.5 m because excess ice is dominantly found only in the uppermost 10 m of the ground. Surface conditions were measured in three drained thermokarst lake basins, including relief, snow conditions, ground temperatures, near‐surface ground ice, and sediment stratigraphy. Four nearby lakes provided information on wave base, shore recession patterns, and bathymetry before drainage: the bottoms of these lakes were not raised in the centre. An elevation difference of up to 2 m was recorded between drained basin margins and centres but was not associated with variations in ice‐wedge density or segregated ice content. Hence basin topography was not controlled by differences in volumetric ground‐ice content between margins and centres. We propose that transport of fine sediment away from eroding lake margins during lake development is the primary mechanism for the genesis of depressed margins and raised centres in drained basins of OCF. Over time, the transport results in the deposition of more and finer sediment in the central parts of lakes, where the lake bottom has subsided below wave base, than at the shallow margins, where resuspension by wave action occurs frequently. This difference in sediment volume is revealed in the topography after drainage, when permafrost aggrades in the lake‐bottom sediment and underlying talik. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
11.
Robert Marsh 《Annales Geophysicae》1995,13(10):1027-1038
In the austral summer of 1992–1993 the passage of a storm system drove a strong upper ocean response at 45°S in the mid-South Atlantic. Good in situ observations were obtained. CTD casts revealed that the mixed layer deepened by \sim40 m over 4 days. Wind stirring dominated over buoyancy flux-driven mixing during the onset of high winds. Doppler shear currents further reveal this to be intimately related to inertial dynamics. The penetration depth of inertial currents, which are confined to the mixed layer, increases with time after a wind event, matched by a downward propagation of low values of the Richardson number. This suggests that inertial current shear is instrumental in producing turbulence at the base of the mixed layer. Evolution of inertial transport is simulated using a time series of ship-observed wind stress. Simulated transport is only 30-50% of the observed transport, suggesting that much of the observed inertial motion was forced by an earlier (possibly remote) storm. Close proximity of the subtropical front further complicates the upper ocean response to the storm. A simple heat balance for the upper 100 m reveals that surface cooling and mixing (during the storm) can account for only a small fraction of an apparent \sim1 °C mixed layer cooling. 相似文献
12.
Allen Gellis 《地球表面变化过程与地形》1993,18(6):505-517
Runoff generated from large storm events, such as hurricanes, is expected to transport large quantities of suspended sediment. Observations of suspended-sediment loads transported during Hurricane Hugo in the Lago Loìza (Lake Loiza) basin, Puerto Rico, indicate that loads were lower than expected. In the two main tributaries that enter Lago Loìza, Rio Grande de Loìza and Rio Gurabo, 99 600 tonnes of suspended sediment was transported by 58·2 × 106 m3 of runoff in a 48 h period. The storm-average suspended-sediment concentration in the Río Grande de Loìza for Hurricane Hugo was 2290 mgl−1, the second lowest for the 12 storms that have been monitored at this site. In Río Gurabo the storm-average suspended-sediment concentration was 1420 mgl−1, the sixth lowest recorded out of 15 monitored storms. In Quebrada Salvatierra, a small tributary to Río Grande de Loìza, suspended-sediment concentrations were as low as 33 mgl−1 during the peak runoff of 20 m3 s−1. Normally the suspended-sediment concentrations at this discharge are 3000 mgl−1. Hurricane force winds seem to be the most important factor contributing to the lower than expected suspended-sediment loads in the Lago Loìza basin. The high winds caused vegetation and debris to be dislodged and displaced. Debris accumulated on hillslopes and in small channels, blocked bridges and formed debris dams. These dams caused local backwater effects that reduced stream velocities and decreased suspended-sediment loads. 相似文献
13.
14.
1976-2015年柴达木盆地湖泊演变及其对气候变化和人类活动的响应 总被引：3，自引：0，他引：3
柴达木盆地众多的湖泊不仅对维持当地脆弱的生态环境具有极其重要的作用，而且中心盐湖也是重要的矿产资源.进入21世纪以来，受气候变化和人类活动的共同影响，盆地湖泊发生了一系列重大变化.为科学认识这一问题，选取了1976-2015年6期Landsat系列卫星影像，解译了该区域1 km2以上的湖泊水面，并分析了湖泊变化对气候和人类活动的响应.结果表明：柴达木盆地湖泊面积总体上存在扩张（1976-1990年）萎缩（1990-2000年）扩张（2000-2010年）萎缩（2010-2015年）4个阶段的变化过程，2010年湖泊面积最大，2015年湖泊又明显萎缩.就气候水文因素而言，湖泊面积变化主要受山区降水径流的影响.湖面变化与前3 a的降水径流关系最为密切.进入21世纪以来，气候变化与上游社会经济耗水、盐湖周边人为阻隔河湖连通、开采卤水、修建人工盐田、排放老卤等人类活动，对盆地中心湖泊的空间格局、面积都产生了显著影响，苦水沟、达布逊湖南部形成了新湖泊，鸦湖、团结湖面积显著扩大，东、西台吉乃尔湖逐渐萎缩、干涸，一里平湖由以前的干盐湖在2010年一跃成为盆地最大的湖泊.针对盐湖大规模开发产生的负面影响，提出了合理开发盐湖资源的建议. 相似文献
15.
Equatorial high mountain lakes are a special type of lake occurring mainly in the South American Andes as well as in Central Africa and Asia. They occur at altitudes of a few thousand meters above sea level and are cold-water lakes (<20 °C). Relatively little is known about them. A long-term limnological study was therefore undertaken at Lake Lago San Pablo, Ecuador to analyze the basic limnological processes of this lake, which has a tendency for eutrophication. Lago San Pablo is spread over an area of 668 hectares, has a maximum depth of 35 m, and is located 2660 m above sea level. Its thermal stratification is a monomictic one, with only 1–2 °C difference between the epi- and hypolimnion; overturn is achieved by strong winds during the dry summer period. The stratification phase is characterized by an oxygen deficit in the lower part of the hypolimnion. Besides, strong convective currents occur due to nocturnal cooling, and partial lake mixing was observed during the nocturnal period. This type of lake mixing is called atelomixis, which is characterized by the partial mixing of isolated layers (difference in temperature or ionic content) during stratification. The nutrient level of the lake is quite high: mean Ptotal concentration = 0.22 mg/l, mean Ntotal = 1.05 mg/l, soluble reactive phosphorus (SRP) > 0.01 mg/l, and soluble inorganic nitrogen > 0.2 mg/l. Nitrogen and phosphorus are available in the epilimnion all year round (Nsol. inorg·. = 0.3 to 1.7 mg/l N, SRP = 0.04 to 0.63 mg/l P). The N/P ratio is sometimes > 14, sometimes < 10, indicating a variability of the limiting nutrient factor. Considering the nutrient level, the phytoplankton biomass is quite low (about 4,000 cells per ml on average; maximum cell number: 13,000 in 1998 and 10,000 in 1999). The mean epilimnic chlorophyll content (Chl a was 10 mg/l in 1998 and 11 g/l in 1999, and the maximum Chl a content was 16 and 22 g/l in 1998 and 1999, respectively.Phytoplankton production can be limited by nutrients, mainly nitrogen, but convective currents can also cause a significant loss of biomass. The lake's euphotic zone is smaller than its epilimnic zone, indicating that light radiation is limiting in the deeper water body, this is caused by a weak thermocline due to destratification by nocturnal cooling, the atelomixis. 相似文献
16.
Pedro Walfir M. Souza-Filho Roberto Vizeu L. Pinheiro Francisco R. Costa José Tasso F. Guimarães Prafulla K. Sahoo Marcio S. Silva Cleverson G. Silva 《地球表面变化过程与地形》2020,45(14):3732-3746
This work details the role of fault reactivation in the development of tropical montane lakes by using basin morpho-structural analysis and seismostratigraphic studies. The upland lakes are severely faulted sinkholes, whose faults penetrate the Quaternary sedimentary units. Four main stages are related to the lake formation: (i) an Early Proterozoic tectonic deformation of the rocks along the southern border of the Carajás Structure, where the lake is placed; (ii) differential erosion by – and building of – the formation of the South Carajás Hill; (iii) Fe-rich crust formation by weathering and gravitational collapse faults following the E–W plateau border and the start of Violão Lake formation during the Pliocene–Pleistocene; and (iv) episodic fault-fracture reactivation by gravitational collapse causing pulses of subsidence in the lake and outlining its faulted borders. Dissolution of the lateritic crust and erosion by runoff drainage under wet climate conditions were coeval with fault activities, which allowed the deposition of relatively thick clastic deposits organized in three main seismostratigraphic units associated with major lake-level fluctuations. Initial fault reactivation under low-level water started lacustrine basin development with deposition of prograding fan deltas related to the main drainage. A second fault reactivation by gravitational collapse increased the lake accommodation space and resulted in the deposition of fine-grained sediments from dilute interflows or overflows until 36 000 cal year BP. At about 31 000 cal year BP, rapid decreases in the lake water level under redox conditions at the sediment/water interface allowed widespread siderite formation. A third gravitational collapse episode was responsible for the increase in the lake area and depth and the returning of clastic/organic deposition up to the present. This tropical montane lake can be seen as a representative example for understanding the formation of other upland lakes controlled by fault reactivation. © 2020 John Wiley & Sons, Ltd. 相似文献
17.
The rates of microbiological processes in CH4 cycling and organic matter destruction in the bottom sediment and water of different types of lakes in the Upper Volga basin and Baltic countries are determined. The rates of CH4 removal from silts and the peculiarities of its distribution in water mass as a function of the lake productivity and the character of water mixing in it are studied. The role of processes in CH4 cycling in destruction is shown to increase with increasing lake productivity. 相似文献
18.
Intensity of in‐lake processes in floodplain lakes within the Bug River zone of fluvial activity 下载免费PDF全文
下载免费PDF全文 The paper presents a new approach to calculating the erosion and deposition values of floodplain lake basins, the erosion–deposition index (EDI). The EDI is a sum of the basin geometry indices (BGIs), which can be calculated for a separate cross section of the lake. The distribution of processes within the basin was investigated in two selected floodplain lakes with the use of BGIs. Field research was carried out in the Bug River valley from 1 November 2006 to 31 October 2011. The highest erosion was observed in the lakes located close to the parent river. Deposition processes were observed in lakes with high inflow of groundwater. The results showed that EDI values of 48 out of the 71 floodplain lakes ranged from ?0.2 to 0.2. Spatial distribution of erosion and deposition processes within the lake basins resulted from a velocity of water inflowing or flowing through the basin. This was observed especially in contrafluent–confluent lake. Inflow of rivers water via upstream crevasse occurred later than via downstream one, but energy of flowing water was higher, which favoured erosion of this part of the lake basin. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
19.
Benthic diatoms of an Alpine stream/lake network in Switzerland 总被引：1，自引：0，他引：1
Christopher T. Robinson Barbara Kawecka 《Aquatic Sciences - Research Across Boundaries》2005,67(4):492-506
We compared the benthic diatom composition of lakes, and lake inlet and outlet streams in a high elevation catchment (∼2600
m a.s.l.) in the Swiss Alps. The catchment consisted of a southern basin mostly fed by glacial-melt water and a northern basin
fed by snowmelt and groundwater. Streams in both basins flowed through a series of small lakes before converging into a lake
with a primary outlet channel. The south basin had on average 4°C cooler water temperatures and 2× higher nitrate-N levels
(up to 300 μg/L) than the north basin. In contrast, the north basin had higher levels (2–4×) of particulate-P, particulate-N,
and particulate organic matter than the south basin. A total of 109 and 143 diatom species was identified in lakes and streams,
respectively, with a similar number of species found in each basin. Aulacoseira alpigena and Achnanthidium minutissimum were common benthic algae in north basin lakes, whereas Achnanthes subatomoides, Achnanthes marginulata, Pinnularia microstauron, and Psammothidium helveticum were most common in south basin lakes. One disconnected lake in the north basin had an assemblage dominated by Tabellaria flocculosa (66%) and Eunotia tenella (14%). Principal components analysis showed a clear separation between the north and south basins in lotic diatoms. Of the
10 most common species, streams in the south basin had greater abundances of Psammothidium helveticum, Achnanthes helvetica var. minor, Achnanthes marginulata, Achnanthes subatomoides, and Diatoma mesodon than the north basin, whereas north basin streams had higher abundances of Achnanthidium minutissimum, Aulacoseira alpigena, and Luticola goeppertiana. Lake outlet assemblages were similar to respective downstream lake inlet assemblages, and assemblages changed in composition
along each basins longitudinal flow path. However, Aulacoseira alpigena had higher average abundances in north basin outlets than inlets, and Achnanthidium minutissimum, Psammothidium helveticum, and Achnanthes helvetica var. minor had higher average abundances in south basin outlets than inlets. In contrast, Diatoma mesodon, Fragilaria capucina, and Gomphonema parvulum had higher average abundances in south basin inlets than outlets. The spatial patterns in species composition reflected the
hierarchical interaction of landscape features (geology, hydrology) on longitudinal gradients (lake position) in the stream/lake
network. 相似文献