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261.
In a recent paper, Nof et al. (J Paleolimnol 35:417–439, 2006) suggest a physical mechanism which could account for the formation
of ice on Lake Kinneret (Sea of Galilee) in northern Israel. Based on the sea surface temperature record of sediment cores
from the Mediterranean Sea the authors argue that centennial-scale cold events had the potential to trigger local ‘springs
ice’ formation on the lake in the past. Here, we demonstrate that a closer inspection of the paleoceanographic record in combination
with correlation and regression analyses of meteorological data provides no evidence for such cold events in the lake region
during the last 10,000 years. Thus, the formation of ‘springs ice’ on Lake Kinneret was unlikely at least since the beginning
of the Neolithic. 相似文献
262.
K. W. Keatings I. Hawkes J. A. Holmes R. J. Flower M. J. Leng R. H. Abu-Zied A. R. Lord 《Journal of Paleolimnology》2007,38(2):261-283
The utility of ostracod-based palaeoenvironmental reconstruction was evaluated using instrumental data for Lake Qarun, Egypt.
The euryhaline ostracod Cyprideis torosa was the only species found in the lake’s recent sediment record. This species is known to tolerate salinity levels and water
solute compositions that may prevent colonisation by other species. Oxygen and carbon isotope ratios of ostracod carbonate
from lake sediments covary with changes in instrumental values for lake level and salinity for the period 1890–1974. δ13C-values correlate negatively with lake water salinity (r
2 = 0.87) and δ18O-values correlate negatively with measured lake level changes (r
2 = 0.41). Other ostracod proxy data provide qualitative information on lake level trends. Fossil assemblage data (juvenile/adult
and valve/carapace ratios and valve preservation) provide information on wave energy. Ecophenotypic variation of C. torosa valves provided some useful palaeolimnological information. Sr/Ca and Mg/Ca ratios in ostracods were not found to reflect
water composition, due to the uncoupling of these ratios with salinity in Lake Qarun. Overall, our results highlight the need
to calibrate ostracod proxy data in modern systems prior to their use for palaeoenvironmental reconstruction. 相似文献
263.
Francine M. G. McCarthy John H. McAndrews Steve M. Blasco Sarah H. Tiffin 《Journal of Paleolimnology》2007,37(3):453-470
High-resolution seismic reflection profile data show that the modern sediment cover (over the last 150 years) in Georgian
Bay is thin and spatially discontinuous. Sediments rich in ragweed pollen, largely derived from siltation linked to land clearing
and European settlement, form a thin, discontinuous veneer on the lakebed. Much of the lakebed consists of exposed sediments
deposited during the late glacial or early postglacial. Accumulation rates of modern sediments range from < 0 mm/year (net
erosion) to ∼3.2 mm/year, often within a few hundred metres spatially. These rates are much lower than those reported for
the main basin of Lake Huron and the other Great Lakes, and are attributed to the low sediment supply. Only a few small rivers
flow into Georgian Bay, and most of the basin is surrounded by bedrock of Precambrian gneiss and granite to the east, and
Silurian dolostone, limestone and shale to the west. Thick deposits of Pleistocene drift, found on the Georgian Bay shoreline
only between Meaford and Port Severn, are the main sediment source for the entire basin at present. Holocene to modern sediments
are even absent from some deep basins of Georgian Bay. These findings have implications for the ultimate fate of anthropogenic
contaminants in Georgian Bay. While microfossil assemblages in the ragweed-rich sediments record increased eutrophication
over the last 150 years, most pollutants generated in the Georgian Bay catchment are not accumulating on the lakebed and are
probably exported from the Bay. 相似文献
264.
Diatoms were identified and enumerated from a surface sediment calibration set of 50 lakes in northwestern Québec. The relationship
between species composition and environmental variables was examined using canonical correspondence analysis (CCA). Forward
selection and Monte Carlo permutation tests in CCA indicated that diatom species distributions in the data set are most strongly
correlated to lakewater pH. A strong (r
2
boot = 0.83) weighted averaging calibration model, that includes bootstrapped error estimates, was developed for inferring past
lakewater pH. Using this model, temporal changes in pH were reconstructed for two kettle lakes, Lac de la Pépinière and Lac
Perron. Based on limnological data, both the study lakes were expected to have recently acidified due to increased acidic
precipitation and increases in anthropogenic metal loading. However, our long-term pH inference data indicate that these lakes
were naturally acidic during pre-industrial times. Nonetheless, the rate of acidification, particularly in Lac de la Pépinière,
has accelerated in the last ∼75 years. These long-term pH records developed for the dilute lakes in northwestern Québec suggest
that the region has received increased atmospheric pollutants from the nearby Horne smelter in Rouyn-Noranda. The pH inference
profiles are markedly different from many other paleolimnological studies in acid-sensitive regions of Canada that have become
acidic primarily as a result of industrial activities.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献
265.
洞庭湖流域水生态系统服务功能经济价值研究 总被引:9,自引:2,他引:9
以洞庭湖流域水生态系统为例,在明确河湖库塘生态系统服务功能内涵的基础上,运用生态学与生态经济学方法对洞庭湖流域各类水生态系统服务功能经济价值进行了评估。结果表明,全流域河湖库塘水生态系统服务功能总价值量为1106.19亿元,约占湖南省2004年GDP(5612.26亿元)的19.7%,其中,城镇和农村生活供水、工农业生产供水、水力发电、内陆航运等直接利用价值为415.698亿元;调洪、输沙、水资源贮存等间接利用价值为690.492亿元。可以认为,流域水生态系统服务功能对湖南省工农业生产的持续发展,维系生态环境健康和人民生命财产安全起到了不可替代的支撑和保障作用。 相似文献
266.
青海湖是我国内陆最大的闭流型水体,地处东亚季风和西风的交汇影响区,对区域降水的改变等气候变化反应敏感,其水位变化历史是研究区域季风环境演变极其宝贵和重要的环境档案。青海湖Q14B孔岩芯介壳δ18Oc变化曲线自1991年发表以来,受到国内外同行的广泛关注和继续探讨。依据近年来青海湖气候与环境演变研究的最新研究结果和个人对闭流型湖泊同位素地球化学的认识,对介壳δ18Oc变化曲线进行了重新判读并得出以下结论:14.5~10.5 ka B.P.,青海湖区气候已逐渐从干冷向温湿过渡,季风降水逐渐增加;10.8~10.5 ka B.P.,青海湖处于碳酸盐滩湖环境,湖水深度从几米演变到接近干涸;10.5~9.5 kaB.P.,季风降水增加;9.5~8 ka B.P,湖水位从此前的接近干涸演变到此间的2~8 m,δ18Oc值跌落到一个较低的位置;8~3.5ka B.P,气候条件相对稳定,湖水不断蒸发引起重同位素的富集;3.5~0ka B.P,湖水处于同位素稳定阶段。研究结果还显示,δ18Oc值的短期波动与湖泊水位短期变化关系密切且明显,即水位高低分别对应δ18Oc的低值与高值。δ18Oc值的长期变化与湖泊水位长期变化关系不明显,水位较浅时,二者几乎无关联;水位较深时,水位的长期缓慢下降自然会导致δ18Oc逐渐攀升,而水位的长期缓慢上升也可以伴随δ18Oc逐渐攀升。 相似文献
267.
268.
269.
A. M. F. Lagmay K. S. Rodolfo F. P. Siringan H. Uy C. Remotigue P. Zamora M. Lapus R. Rodolfo J. Ong 《Bulletin of Volcanology》2007,69(7):797-809
The 1991 Pinatubo eruption left 5–6 km3 of debris on the volcano slopes, much of which has been mobilized into large lahars in the following rainy seasons. Also
during the eruption, collapse, localized in part along preexisting faults, left a caldera 2.5 km in diameter that almost immediately
began to accumulate a 1.6 × 108 m3 lake. By 2001, the water had risen to the fault-controlled Maraunot Notch, the lowest, northwestern portion of the caldera
rim comprising the physiographic sill of the Caldera Lake. That year, a narrow artificial canal dug into an old volcanic breccia
underlying the outlet channel failed to induce a deliberate lake breakout, but discharge from heavy rains in July 2002 rapidly
deepened the notch by 23 m, releasing an estimated 6.5 × 107 m3 of lake water that bulked up into lahars with a volume well in excess of 1.6 × 108 m3. Lakes in other volcanoes have experienced multiple breakouts, providing practical motivation for this study. Fieldwork and
high-resolution digital elevation models reveal andesites and ancient lacustrine deposits, strongly fractured and deformed
along a segment of the Maraunot Fault, a prominent, steeply dipping, left-lateral fault zone that trends N35°–40°W within
and parallel to the notch. Seismicity in 1991 demonstrated that the Maraunot Fault is still active. The fault zone appears
to have previously been the erosional locus for a large channel, filled with avalanche or landslide deposits of an earlier
eruption that were exhumed by the 2002 breakout floods. The deformed lacustrine sediments, with an uncalibrated 14C age of 14,760 ± 40 year BP from a single charcoal sample, attest to the existence of an earlier lake, possibly within the
Tayawan Caldera, rim remnants of which survive as arcuate escarpments. That lake may well have experienced one or more ancient
breakouts as well. The 2002 event greatly reduced the possibility of another such event by scouring away the erodible breccia,
leaving less erodible fractured andesites and lacustrine rocks, and by enlarging the outlet channel and its discharge capacity.
Several lines of evidence indicate, however, that future lahar-generating lake breakouts at the notch may keep populations
of Botolan municipality downstream at risk: (1) a volume of 9.5 × 107 m3 of lake water remains perched 0.8 km above sea level; (2) seismicity in 1991 demonstrated that the Maraunot Fault is still
active and movements of sufficient magnitude could enlarge the outlet and the discharge through it; (3) more likely, however,
with or without earthquake activity, landslides from the steep to overhanging channel walls could block the channel again,
and a major rainstorm could then cause a rise in lake level and sudden breakouts; (4) intrusion of a new dome into the bottom
of the lake, possibly accompanied by phreatic explosions, could expel large volumes of lahar-generating water. 相似文献
270.
The abundance and preferences of individual invertebrate populations (including zooplankton) closely associated with the substrates provided by aquatic plant structures and open-water areas of Lake Nasser were quantified in this study in order to gain understanding of the importance of submerged macrophyte for invertebrate diversity, and their relation to water properties. The following water parameters were measured: temperature, pH, dissolved oxygen (DO), total dissolved salts, electrical conductivity, turbidity, total suspended solids, carbonate, bicarbonate, nitrate, nitrite, phosphate, sulphate, silica, potassium, total hardness, calcium and magnesium.Five macrophyte species were recorded: Myriopyllum spicatum, Najas horrida, Potamogeton schweinfurthii, Potamogeton pectinatus and Vallisneria spiralis. In total 67 invertebrate species were recorded, comprising 39 Rotifera, 12 Cladocera, 4 Copepoda, 4 Insecta, 2 Protozoa, 2 Ostracoda and one species of Turbellaria, Tardigrada, Annelida and Nematoda. Thirty-seven species were exclusively epiphytic, 11 species were collectively planktonic and 19 species were found in both habitats. The greatest abundance of epiphytic invertebrates occurred in association with N. horrida-P. schweinfurthii community.The results indicated that total suspended solids (TSS), TH and NO2 are the most influential water variables on the distribution of the aquatic macrophyte samples and their invertebrate communities. Also, the study indicates that water variables have a higher impact on the aquatic macrophytes than on the associated invertebrate populations. P, NO3, K, Na, Mg, Cl and DO were the most influential water variables that dictate the distribution of invertebrate groups recorded in the open-water zone. Water temperature, electric conductivity, pH, NO2, SO4−−, SiO3−, CO3−− and turbidity have a lesser influence of the distribution of the invertebrates recorded in this zone. 相似文献