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1.
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
2.
Mark B. Edlund Daniel R. Engstrom Laura D. Triplett Brenda Moraska Lafrancois Peter R. Leavitt 《Journal of Paleolimnology》2009,41(4):641-657
Evaluation of land-use effects on coastal and marine ecosystems requires better understanding of the role of rivers in regulating
mass transport from terrestrial to oceanic environments. Here we take advantage of the presence of a riverine lake to use
paleoecological techniques to quantify impacts of logging, European-style agriculture, urbanization and continued terrestrial
disturbance on mass transport and water quality in the northern drainage of the Mississippi River. Two 2-m sediment-cores
recovered in 1999 from Lake St. Croix, a natural impoundment of the St. Croix River, were dated using 210Pb and 137Cs, and analyzed for historical changes (c. 1840–present) in sediment magnetic susceptibility, inorganic and organic matter
content, biogenic silica, fossil pigments, and diatom microfossils. Inorganic sediment accumulation increased threefold between
the mid-1800s and present, whereas clear signs of eutrophication were only evident after the mid-twentieth century when biogenic
silica accumulation increased sixfold, diatom accumulation rates increased 20- to 50- fold, and the diatom community shifted
from predominantly benthic species to assemblages composed mainly of planktonic taxa. Similarly, fossil pigment concentrations
increased during the 1960s, and diatom-inferred total phosphorus (DI-TP) increased from ~30 μg TP l−1 c. 1910 to ~60 μg l−1 since 1990, similar to historical records since 1980. Together, these patterns demonstrate that initial land clearance did
not result in substantive declines in water quality or nutrient mass transport, instead, substantial degradation of downstream
environments was restricted to the latter half of the twentieth century.
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
3.
Lake St. Croix is a natural impoundment of the lowermost 37 km of the St. Croix River in Minnesota and Wisconsin, making this
one of a few large river systems in the world possessing a long-term depositional basin at its terminus. The river’s relatively
pristine condition led to its designation as a National Scenic Riverway in 1968, but increasing urbanization in its lower
reaches has raised concerns about impacts on water quality. This study was initiated to reconstruct historical loadings of
suspended sediment and phosphorus (P) from the sediment record in Lake St. Croix. Twenty-four piston cores, with an average
length of 2 m, were collected along eight transects of the lake. Dated chronologies from 210Pb, 137Cs and 14C were used to calculate the rate of sediment accumulation in the lake over the past 100+ years. Diatom microfossil analysis
was used to reconstruct historical lakewater P concentrations over the same time period, and sediment P analysis quantified
the amount of P trapped in lake sediments. Using a whole-lake mass balance approach, the loading of sediment and P to Lake
St. Croix over the last 100+ years was calculated. Beginning in 1850, sediment accumulation increased dramatically to a peak
in 1950–1960 of eight times background rates prior to European settlement. The peak is driven largely by sediment contributions
from small side-valley catchment tributaries to the downstream half of the lake. The total P load to the lake increased sharply
after 1940 and remains high, at around four times the level of pre-European settlement conditions. The timing of peak sediment
and P loading to the lake shows that early settlement activities, such as logging and the conversion of forest and prairie
to agricultural land between 1850 and 1890, had only modest impacts on the lake. By contrast, the mid-1900s brought major
increases in sediment and P loading to the lake, suggesting that relatively recent activities on the landscape and changes
to nutrient balances in the watershed have caused the current eutrophic condition of this important recreational and natural
resource.
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
4.
Historical trace metal loading to a large river recorded in the sediments of Lake St. Croix,USA 总被引:1,自引:0,他引:1
Steven J. Balogh Laura D. Triplett Daniel R. Engstrom Yabing H. Nollet 《Journal of Paleolimnology》2010,44(2):517-530
The global cycling of anthropogenic trace metals intensified during the twentieth century, impacting aquatic systems throughout
the world. There are, however, few quantitative records showing the history of this contamination in large rivers. Here we
present a well-dated sedimentary record of trace metal accumulation in Lake St. Croix, a natural riverine lake on the St.
Croix River (Minnesota and Wisconsin, USA), revealing the history of heavy metal inputs to the river over the past 200 years.
Concentrations of Hg, Pb, Ag, Cd, Cr and Zn and stable Pb isotopes were measured in eight 210Pb-dated sediment cores collected from profundal depositional areas throughout the lake. Time trends of trace metal concentrations
and accumulation rates differed greatly between the upper lake (above Valley Creek) and the lower lake, reflecting contrasting
sediment sources along the flow axis of the lake. For most of the study period (1800–2000 AD), sediment deposited throughout
the lake derived almost exclusively from the suspended sediment load carried by the main-stem river into the lake. From 1910
through 1970, however, large inputs of eroded soils and stream channel sediments from side-valley tributaries resulted in
greatly increased sediment and trace metal accumulation in the lower lake. Anthropogenic accumulation rates of Hg, Pb, Cd,
Zn, and Ag in the upper lake correlate well with those from Square Lake, a small, relatively undisturbed nearby lake that
has received trace metal inputs almost exclusively via atmospheric deposition. The similarity of these records suggests that
atmospheric deposition was primarily responsible for trace metal accumulation trends in upper Lake St. Croix. Trace metal
accumulation in the lower lake was also strongly influenced by atmospherically derived inputs, but metal contributions from
native soils were important, as well, during the period of elevated sediment inputs from side-valley tributaries. Concentrations
and accumulation rates of trace metals in both upper and lower lake sediments have decreased substantially since the 1970s
due to decreased atmospheric inputs and sediment loadings, but accumulation rates remain well above pre-settlement values.
Metal inputs to Lake St. Croix have been far lower than those to nearby Lake Pepin, located on the Mississippi River downstream
of the Minneapolis-St. Paul metropolitan area, but there nevertheless remains a clear record of anthropogenic impact on the
relatively pristine St. Croix River. 相似文献
5.
We used 210Pb-dated sediment cores from wetlands and Blue Cypress Lake, in the Upper St. Johns River Basin (USJRB), Florida, USA, to measure historical accumulation rates of bulk sediment, total carbon (C), total nitrogen (N), and total phosphorus (P). Marsh cores displayed similar stratigraphies with respect to physical properties and nutrient content. Wetland sediments typically contained > 900 mg organic matter (OM) g–1 dry mass, > 500 mg C g–1, and 30–40 mg N g–1. OM, C, and N concentrations were slightly lower in uppermost sediments of most cores, but displayed no strong stratigraphic trends. Total P concentrations were relatively low in bottommost deposits (0.01–0.11 mg g–1), but ranged from 0.38–2.67 mg g–1 in surface sediments. The mean sediment accretion rate in the marsh since ~ 1900, 0.33 ± 0.05 cm yr–1, was calculated from ten 210Pb-dated cores. All sites displayed increases in accumulation rates of bulk sediment, C, N, and P since the early part of the 20th century. These trends are attributed to recent hydrologic modifications in the basin combined with high nutrient loading from agricultural, residential, and urban sources. 相似文献
6.
Trace metals and polycyclic aromatic hydrocarbons (PAH) were analyzed in sediment cores from three central Alberta lakes to
determine the contributions of local coal-fired power plants to contaminant loadings. In Wabamun Lake, with four power plants
built since 1950 within a 35-km radius, sediment concentrations of mercury, copper, lead, arsenic and selenium have increased
by 1.2- to 4-fold. Trace metal enrichments were less pronounced in Lac Ste. Anne and Pigeon Lake, situated 20 km north and
70 km south of Wabamun Lake, respectively. Total Hg flux to Wabamun Lake sediments (21–32μg m−2 yr−1) has increased 6-fold since 1950, compared to 2- and 1.5-fold increases in Lac Ste. Anne and Pigeon Lake, respectively, since
circa 1900. Total PAH flux to surface sediments was 730–1100μg m−2 yr−1 in Wabamun Lake, 290–420μg m−2 yr−1 in Lac Ste. Anne, and 140–240μg m−2 yr−1 in Pigeon Lake. Without adoption of pollution-abatement technology that compensates for increases in generating capacity,
continued expansion of coal-burning industry in Alberta will result in increased contaminant deposition, primarily from local
sources. 相似文献
7.
Dylan J. Blumentritt Herbert E. WrightJr. Vania Stefanova 《Journal of Paleolimnology》2009,41(4):545-562
Study of Lake Pepin and Lake St. Croix began more than a century ago, but new information has permitted a closer look at the
geologic history of these two riverine lakes located on the upper Mississippi River system. Drainages from large proglacial
lakes Agassiz and Duluth at the end of the last glaciation helped shape the current valleys. As high-discharge outlet waters
receded, tributary streams deposited fans of sediment in the incised river valleys. These tributary fans dammed the main river,
forming riverine lakes. Lake Pepin was previously thought to be a single long continuous lake, extending for 80 km from its
dam at the Chippewa River fan all the way up to St. Paul, with an arm extending up the St. Croix valley. Recent borings taken
at bridge and dam locations show more than a single section of lake sediments, indicating a more complex history. The Minnesota
and Mississippi Rivers did not always follow their current paths. Valleys cut into bedrock but now buried by glacial sediment
indicate former river courses, with the most recent of these from the last interglacial period marked at the surface by chains
of lakes. The morphology of the Mississippi valley bottom, and thus the morphology of Lake Pepin as it filled the valley,
is reflect in part by the existence of these old valleys but also by the presence of glacial outwash terraces and the alluvial
fans of tributary streams. A sediment core taken in Lake Pepin near Lake City had a piece of wood in gravels just below lake
sediments that dated to 10.3 ka cal. BP, indicating that the lake formed as the Chippewa River fan grew shortly after the
floodwaters of Lakes Agassiz and Duluth receded. Data from new borings indicate small lakes were dammed behind several tributary
fans in the Mississippi River valley between the modern Lake Pepin and St. Paul. One tributary lake, here called Early Lake
Vermillion, may have hydraulically dammed the St. Croix River, creating an incipient Lake St. Croix. The tributary fans from
the Vermillion River, the Cannon River, and the Chippewa River all served to segment the main river valley into a series of
riverine lakes. Later the growth of the Chippewa fan surpassed that of the Vermillion and Cannon fans to create a single large
lake, here called late Lake Pepin, which extended upstream to St. Paul. Sediment cores taken from Lake Pepin did not have
significant organic matter to develop a chronology from radiocarbon dating. Rather, magnetic features were matched with those
from a Lake St. Croix core, which did have a known radiocarbon chronology. The Pepin delta migration rate was then estimated
by projecting the elevations of the top of the buried lake sediments to the dated Lake Pepin core, using an estimated slope
of 10 cm/km, the current slope of Lake Pepin sediment surface. By these approximations, the Lake Pepin delta prograded past
Hastings 6.0 ka cal BP and Red Wing 1.4 ka cal BP.
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
8.
This study used the Water Quality Analysis Simulation Program (WASP) to simulate nutrients, dissolved oxygen (DO), and chlorophyll-a dynamics in the Shenandoah River basin and performed an uncertainty analysis to examine the complexity of these variables in water quality estimation and their influence on the Shenandoah River. Significant progress has been made; however, nutrient loads emitted into the Shenandoah River from nonpoint sources remain high. Modeling of three points on the Shenandoah River in Virginia and West Virginia provides an ideal case study since the river is classified by the Virginia Department of Environmental Quality as being impaired. The results of a sensitivity test show that model error decreases with increasing model complexity and sensitivity. The model predicted DO values that tended to be close to the measured data, while total nitrogen and phosphorus tended to be overemphasized. Our results examine the importance of temperature, stream flow, and velocity in influencing water quality between seasons and levels on the different sections of the watershed. 相似文献
9.
Enfeng Liu Ji Shen Gavin F. Birch Xiangdong Yang Yanhong Wu Bin Xue 《Journal of Paleolimnology》2012,47(4):677-691
We present a sedimentary geochemical record of human perturbation in the watershed and related changes in trace metals (Cr,
Ni, Zn and Pb), phosphorus and abundant rock-forming elements (Al, Fe, K, Mg, etc.) in Chaohu Lake over the past 500 years,
a period spanning historical agricultural expansion and modern economic development. The record exhibited a stable terrestrial
detrital input to Chaohu Lake before ca. 1540 AD, a period with less human perturbation of the watershed, which resulted in
low and constant values of trace metals and phosphorus (TP) concentrations as well as Al, Fe, K, Mg, fine silt (<16 μm), the
chemical index of alteration (CIA) and K/Na ratio. Two periods of successive marked increases in Al, Fe, K, Mg, fine silt,
chemical index of alteration (CIA) and K/Na ratio occurred after ca. 1540 AD and 1950 AD. The former period apparently resulted
from enhanced well-weathered topsoil erosion in the watershed related to the expansion of arable land, and the latter resulted
from further enhancement of human perturbation in the watershed during the modern period. Concentrations of trace metals and
TP were positively correlated with that of the rock-forming elements and fine silt. Trace metal pollution was limited during
1540–1950 AD, according to the low enrichment factors (EFs = 0.8–1.1), when an increase in trace metal concentrations was
also linked to changes in detrital input. In addition to detrital regulation, pollution also contributed to an increase in
TP concentrations (average EF 1.4) during 1540–1950 AD and the average accumulation rate of anthropogenic phosphorus was 87.3 mg m−2 a−1. Anthropogenic phosphorus increased further and Pb and Zn pollution also occurred after 1950 AD, reaching maximum values
after 1980 AD, when the average accumulation rates of anthropogenic Zn, Pb and phosphorus (mainly in the form of NaOH-P) were
242.2, 43.3 and 811.8 mg m−2 a−1, respectively. The increase in phosphorus pollution in recent decades is probably from the domestic sewage sources of Hefei
City and non-point sources related to agricultural utilization of commercial fertilizer, whereas Zn and Pb pollution is probably
derived mainly from industrial sources of Hefei City, as deduced from their spatial variations in the sediments of the river
mouths. 相似文献
10.
Assessment of nutrient sources and paleoproductivity during the past century in Longgan Lake,middle reaches of the Yangtze River,China 总被引:3,自引:0,他引:3
Total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) were determined in combination with stable isotope
ratios of carbon and nitrogen (δ13COrg, δ15N) in a 63 cm sediment core from Longgan Lake, located in the middle reaches of the Yangtze River, China. These geochemical
and isotopic records provide a continuous history of lake productivity and trophic state of Longgan Lake since 1890. Variations
of δ13COrg, TOC, TN and TP indicate that primary productivity of Longgan Lake increased continuously during the last century and that
the trophic state of the lake shifted from oligotrophic to mestrotrophic conditions accordingly. Anthropogenic sources of
organic carbon (OC), nitrogen (N) and phosphorus (P) were distinguished from their natural background in the sediments using
mass accumulation rates. Element mass accumulation rates suggested increased human activities in the lake’s catchment since
1950s, were especially the utilization of artificial fertilizers amplified the anthropogenic input of N and P into the lake.
In the course of the improved availability of dissolved nutrients also primary productivity of Longgan Lake increased, resulting
in an increase of the Suess-effect corrected organic carbon isotope ratios. δ15N of bulk sediments show a marked shift towards lower values around 1950 that has been attributed to the input of nitrogen
from chemical fertilizers characterized by relatively depleted isotopic signatures into the lake. 相似文献
11.
非点源营养负荷泥沙关系的建立及其应用 总被引:19,自引:2,他引:17
为满足水污染控制规划和流域水资源保护工作的需要,以几个流域的非点源污染监测资料为基础,建立了TP、TN等营养物的非点源污染负荷—泥沙定量关系,相关系数高达0.9以上。以渭河的支流黑河和陕南的汉江流域为例,具体说明了污染负荷—泥沙关系法的应用步骤和预测结果,并与水质水量相关法的结果进行了对照。结果表明,该方法可用于次暴雨及不同频率代表年的非点源营养负荷量预测。 相似文献
12.
Mary Beth Day David A. Hodell Mark Brenner Jason H. Curtis George D. Kamenov Thomas P. Guilderson Larry C. Peterson William F. Kenney Alan L. Kolata 《Journal of Paleolimnology》2011,45(1):85-99
Tonle Sap Lake, Cambodia, possesses one of the most productive inland fisheries in the world and is a vital natural resource
for the country. The lake is connected to the Mekong River via the Tonle Sap River. Flow in the Tonle Sap River reverses seasonally,
with water exiting the lake in the dry season and entering the lake during the summer monsoon. This flood pulse drives the
lake’s biological productivity. We used Sr, Nd, and Pb isotopes and elemental concentrations in lake sediment cores to track
changes in the provenance of deposits in Tonle Sap Lake. We sought to determine when the lake first began to receive water
and sediment input via the Mekong River, which initiated flood pulse processes. The transition from a non-pulsing lake to
the Mekong-connected system is marked by shifts to values of 87Sr/86Sr, εNd, and 207Pb/204Pb that are characteristic of Mekong River sediments. In addition, magnetic susceptibility increased and sediment elemental
composition changed. Elemental (P) measures point to enhanced phosphorus loading and C/N and isotope ratios of bulk organic
matter indicate a shift to greater relative contribution of organic material from aquatic versus terrestrial environments,
coinciding with the initiation of flood pulse processes. On the basis of radiocarbon dating in two cores, we estimate the
initiation of the annual flood pulse occurred between ~4,450 and 3,910 cal year BP. 相似文献
13.
Georg Schettler Jens Mingram Jörg F. W. Negendank Liu Jiaqi 《Journal of Paleolimnology》2006,35(2):271-288
Palaeovariations of the atmospheric 210Pb flux in Northeast China (Long Gang area, Jilin province), quantified by high resolution 210Pb measurements on seasonally laminated sediments of Lake Sihailongwan are presented on decadal scale. The mean flux of unsupported
210Pb between 1790 and 1970 for the centre of the lake basin is 517 Bq m−2 yr−1 with maximum deviations between −23% and +27% of this value. Flux rates above this average were found between 1783 and 1813,
around 1836, and between 1860 and 1901. The mean 210Pbexc flux rates derived were clearly lower around 1821, 1908, 1930, and 1953. The 210Pbexc flux reached its minimum of 344 Bq m−2 yr−1 during the period 1977–1982. The atmospheric flux of unsupported 210Pb is correlated with the precipitation frequency during the summer monsoon and shows coinciding variability with geochemical
proxies that document the groundwater inflow into the lake. Al2O3-rich dust of remote provenance scavenged by wet-deposition in the rainy season is the major carrier of the atmospheric 210Pbexc flux. 相似文献
14.
Daniel R. Engstrom James E. Almendinger Julie A. Wolin 《Journal of Paleolimnology》2009,41(4):563-588
Long-term changes in sediment and phosphorus loading to the upper Mississippi River were quantified from an array of 25 sediment
cores from Lake Pepin, a large natural impoundment downstream of the Minneapolis-St Paul metropolitan area. Cores were dated
and stratigraphically correlated using 210Pb, 137Cs, 14C, magnetic susceptibility, pollen analysis, and loss-on-ignition. All cores show a dramatic increase in sediment accumulation
beginning with European settlement in 1830. Accumulation rates are highest and show the greatest post-settlement increases
in the upper end of the lake. Present-day sediment-phosphorus concentrations are roughly twice those of pre-settlement times,
and the Fe/Al-bound fraction makes up a greater portion of the total. Diatom assemblages record a marked increase in nutrient
availability over the last 200 years, changing from clear-water benthic forms and mesotrophic planktonic taxa in pre-settlement
times to exclusively planktonic assemblages characteristic of highly eutrophic conditions today. Lake-water total-phosphorus
concentrations, estimated by weighted averaging regression and calibration, increased from 50 to 200 μg l−1 during this period. Sediment loading to Lake Pepin from the Mississippi River has increased by an order of magnitude since
1830. Modern fluxes are about 900,000 metric tons annually, and are more than 80% detrital mineral matter. About 17% of the
lake’s volume in 1830 has been replaced by sediment, and at current accumulation rates the remainder will be filled in another
340 years. Phosphorus accumulation in Lake Pepin sediments has increased 15-fold since 1830, rising from 60 to 900 metric
tons annually. This rise represents a sevenfold increase in phosphorus loading from the Mississippi River coupled with more
efficient retention of phosphorus inflows by bottom sediments. More efficient trapping of phosphorus in Lake Pepin over the
last century resulted from higher rates of sediment burial. The most dramatic changes in nutrient and sediment inputs to Lake
Pepin have occurred since 1940, although gradual increases began shortly following European settlement. Sediment accumulation
rates rose sharply between 1940 and 1970 and then leveled off, while phosphorus inflows record their largest increases after
1970.
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
15.
Elva Escobar Briones Javier Alcocer Edith Cienfuegos Pedro Morales 《International Journal of Salt Lake Research》1998,7(4):345-355
Carbon stable isotope ratios were determined in dominant biotic components of pelagic and littoral systems in Alchichica crater-lake.
Results showed that carbon signatures were significantly different between both systems. The pelagic environment was more
depleted (−26.15 to −15.14 per mille) than the littoral zone (−21.03 to −17.91 per mille). The potential source end-point
in the simplified pelagic community was established to be diatomaceous phytoplankton; its predicted value was −21.7 per mille.
There is a clear evidence thatNodularia does not sustain the pelagic food chain. In contrast, the highly diverse littoral community was sustained by epiphytes. No
allochthonous sources seemed to influence this food web.13C enrichment was observed along the components of both systems with fractionations of 0.8 to 1.4 per mille. The contribution
of the seagrassRuppia maritima is probably associated with the detritus pathway. Carbon source partitioning between both systems was not recorded. The δ13C in Alchichica crater-lake was more enriched than in other saline lakes and could be attributed to different salinity and
CO2 concentrations among lakes. 相似文献
16.
Supriyo Kumar Das Joyanto Routh Alakendra N. Roychoudhury J. Val Klump 《Journal of Paleolimnology》2008,39(3):349-360
We used elemental carbon, nitrogen, phosphorus and hydrogen ratios (C/N, N/P and H/C) with total organic carbon (TOC) and
total phosphorus (TP) as well as stable carbon and nitrogen isotopes (δ13C and δ15N) to investigate the source and depositional conditions of organic matter in sediments from Zeekoevlei, the largest freshwater
lake in South Africa. Typical C/N (10–12), H/C ratios (≥1.7) and δ13Corganic values (−22 to −19‰) together with the increase in TOC concentration indicate elevated primary productivity in lower middle
(18–22 cm) and top (0–8 cm) sections of the sediment cores. Seepage of nutrients from a nearby waste water treatment plant,
rapid urbanization and heavily fertilized farming in the catchments are responsible for the increased productivity. Consistent
with this, measured δ15Norganic values (∼11‰) indicate increased raw sewage input towards the top-section of the core. Although cyanobacterial blooms are
evident from the low δ15N values (∼3‰) in mid-section of the core, they did not outnumber the phytoplankton population. Low N/P ratio (∼0) and high
TP (100–2,200 mg l−1) support cyanobacterial growth under N limited condition, and insignificant input of macrophytes towards the organic matter
pool. Dredging in 1983, caused sub-aerial exposure of the suspended and surface sediments, and affected organic matter preservation
in the upper mid-section (12–14 cm) of the core. 相似文献
17.
Neil L. Rose David Morley Peter G. Appleby Richard W. Battarbee Tiiu Alliksaar Piero Guilizzoni Erik Jeppesen Atte Korhola Jaan-Mati Punning 《Journal of Paleolimnology》2011,45(4):447-468
Sediment accumulation rate (SAR) is an important physical parameter in all lakes and increases have been observed in many
over the last c.100 years. This has been ascribed to changes in land-use and land-management causing accelerated catchment
soil erosion and an increase in autochthonous organic matter production. The EU Water Framework Directive requires that assessment
of biological, hydromorphological and chemical elements of water quality should be based on the degree to which present day
conditions deviate from those expected in the absence of significant anthropogenic influence, termed reference conditions.
Currently however, the reference condition for sediment accumulation rate for lakes of different types is undefined. To improve
our understanding of the controls on SARs we compiled SAR and lake typology data for 207 European lakes derived from 210Pb dated cores to assess how rates have changed through time (in 25 year classes) both overall and for lakes of different
types. Seventy-one percent of these sediment cores showed surface SARs higher than “basal” (mainly nineteenth century) rates,
11% showed no change while 18% showed a decline. Lakes were then classified into lake-types using four variables: alkalinity
(3 classes), altitude (3 classes), maximum depth (2 classes) and lake area (2 classes). This generated a possible 36 lake
classes of which 25 were represented in the dataset. Nine lake-types contained >10 lakes. Little change in SAR occurred prior
to 1900 and most increases occurred in more recent periods, in particular 1950–1975 and post-1975. This indicates a general
acceleration in SAR in European lakes during the second half of the twentieth century. Reference SARs were estimated for six
lake-types with the highest number of sites. European mountain lakes had the lowest reference SAR (0.005 ± 0.003 g cm−2 yr−1) while lowland, high alkalinity sites had the highest (0.03–0.04 g cm−2 yr−1). SARs for other lake-types ranged between 0.012 and 0.024 g cm−2 yr−1. Using the mountain lake-type as an example, the 1850 reference SAR appears to show good agreement with available data for
lakes beyond Europe indicating these values may be more broadly applicable. Contemporary SARs in lakes of all classes showed
exceedence over their defined reference SAR. This may be partly due to diagenetic processes. Greatest exceedences were found
in shallow, low altitude lakes and these are considered to be the ones under the greatest threat from continued elevation
of SAR. It is considered that climate change may play a progressively more important role in driving SAR in the future. 相似文献
18.
Namakan Lake, located in shared border waters in northeastern Minnesota and northwestern Ontario, was subjected to several
anthropogenic impacts including logging, damming, water-level manipulations, and perhaps climate change. We used paleolimnology
to determine how these stressors impacted Namakan Lake in comparison to a control lake (Lac La Croix) that was not subject
to damming and hydromanagement. One core was retrieved from each lake for 210Pb dating and analysis of loss-on-ignition and diatom composition. 210Pb-derived chronologies from the cores indicated that sediment accumulation increased after logging and damming in Namakan
Lake; Lac La Croix showed no significant change. Loss-on-ignition analysis also showed an increase in concentration and accumulation
of inorganic material after damming in Namakan Lake; again, minimal changes were observed in Lac La Croix. Diatom communities
in both lakes displayed community shifts at the peak of logging. Simultaneous, post-1970s diatom community changes may reflect
regional climate warming. Taxonomic richness in Namakan Lake decreased sharply after damming and the peak of logging, and
was followed by a slow recovery to taxonomic richness similar to that prior to damming. Ecological variability among post-damming
diatom communities, however, was greater in Namakan Lake than in Lac La Croix. A diatom calibration set was used to reconstruct
historical conductivity and total phosphorus (TP). Lac La Croix showed little historical change in conductivity and TP. In
contrast, conductivity increased for several decades in Namakan Lake after damming, possibly in relation to several large
fires and flooding. Total phosphorus also increased in Namakan Lake after damming, with a possible decrease in the last decade
to pre-damming TP levels. 相似文献
19.
Macroinvertebrate communities were studied in two saline tributaries of the Hopkins River, western Victoria. Monthly sampling
from May to August, 1990, showed the mean salinity of Bushy Creek was 5 g L−1 while in Back Creek mean salinity varied from 9 to 20 g L−1 between sites. Macroinvertebrate species richness and relative abundance were measured on each sampling occasion. Cluster
analysis showed that community composition varied between creeks and between sites within a creek. Bushy Creek sites were
more similar to each other than to Back Creek sites. A negative relationship was found between site salinity and species richness
over the range 4 to 26 g L−1, although there was a wide range of salinity (up to 12 g L−1) over which the relationship of species richness to salinity was not clear cut.
The effects of salinity on species richness in stream communities appear to be similar to that described elsewhere in salt
lakes. 相似文献
20.
Kathleen R. Stoof-Leichsenring Annett Junginger Lydia A. Olaka Ralph Tiedemann Martin H. Trauth 《Journal of Paleolimnology》2011,45(3):353-367
Lake Naivasha, Kenya, is one of a number of freshwater lakes in the East African Rift System. Since the beginning of the twentieth
century, it has experienced greater anthropogenic influence as a result of increasingly intensive farming of coffee, tea,
flowers, and other horticultural crops within its catchment. The water-level history of Lake Naivasha over the past 200 years
was derived from a combination of instrumental records and sediment data. In this study, we analysed diatoms in a lake sediment
core to infer past lacustrine conductivity and total phosphorus concentrations. We also measured total nitrogen and carbon
concentrations in the sediments. Core chronology was established by 210Pb dating and covered a ~186-year history of natural (climatic) and human-induced environmental changes. Three stratigraphic
zones in the core were identified using diatom assemblages. There was a change from littoral/epiphytic diatoms such as Gomphonema gracile and Cymbella muelleri, which occurred during a prolonged dry period from ca. 1820 to 1896 AD, through a transition period, to the present planktonic Aulacoseira sp. that favors nutrient-rich waters. This marked change in the diatom assemblage was caused by climate change, and later
a strong anthropogenic overprint on the lake system. Increases in sediment accumulation rates since 1928, from 0.01 to 0.08 g cm−2 year−1 correlate with an increase in diatom-inferred total phosphorus concentrations since the beginning of the twentieth century.
The increase in phosphorus accumulation suggests increasing eutrophication of freshwater Lake Naivasha. This study identified
two major periods in the lake’s history: (1) the period from 1820 to 1950 AD, during which the lake was affected mainly by
natural climate variations, and (2) the period since 1950, during which the effects of anthropogenic activity overprinted
those of natural climate variation. 相似文献