共查询到7条相似文献,搜索用时 15 毫秒
1.
Chapman Lauren J. Chapman Colin A. Crisman Thomas L. Nordlie Frank G. 《Hydrobiologia》1998,385(1-3):201-211
This paper quantifies the temporal pattern of thermal stratification and deoxygenation in Lake Nkuruba, a small (3 ha), deep
(maximum depth = 38 m) crater lake in western Uganda. Dissolved oxygen penetrated to an average depth of 9 m and a maximum
depth of 15 m below which the lake was permanently anoxic over the 2 years of study. Although surface oxygen levels were correlated
with both surface water temperature and rainfall, seasonal cycles of dissolved oxygen were not well-defined and may have been
obscured by the high frequency of short-term fluctuations and by inter-annual variations caused by shifts in rainfall.
Surface water temperature averaged 23.3±0.7 °C (S.D.) and varied directly with air temperature. Both diurnal changes and top-bottom
temperature differentials were small averaging 1.7±0.7 °C and 1.6±0.8 °C, respectively. Thermal stability ranged from 101.3
to 499.9 g-cm cm-2 and was positively related to surface water temperature suggesting that this small protected lake responds rapidly to short-term
meteorological changes. Because contribution to the annual heat exchange cycle was confined to upper waters, the lake's annual
heat budget was low, 1,073.8 cal cm-2 yr-1. However, net primary productivity was relatively high averaging 1.3 g C m-2d-1.
The region where Lake Nkuruba is situated experienced a very strong earthquake (6.2 on the Richter scale) on 4 February, 1994.
Subsequently, water levels dropped markedly in the lake, falling 3.14 m over a 5-month period.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
2.
The relationship between mercury content in fish (pike and perch), the different fractions of mercury in lake water and water color was investigated in 76, mainly oligotrophic lakes distributed over a large part of Sweden. The lakes were classified in terms of drainage area characteristics, lake morphometry and water chemistry. The dominant fraction of mercury in lake water was RIHg (fraction reducible to elemental mercury by NaBH4). RIHg and water color were strongly positively correlated. Water color (determined by the comparative method using colored disks) was used as a surrogate for the amount of humic matter in the water. Thus, humic matter appears to be acting as an important carrier of mercury. A positive relationship between mercury content in fish and water color was found only in deep lakes (average depth > 5 m). It is suggested that the bioavailability of mercury attached to humic matter increases due to anoxic conditions, common in the hypolimnion of deep lakes. 相似文献
3.
Dipesh Rupakheti Lekhendra Tripathee Chhatra Mani Sharma Rukumesh Paudyal Mika Sillanpää 《人类与生态风险评估》2017,23(5):959-973
The concentration of 13 metals (Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Pb, and Hg) and their associated health risk assessment was performed for two Himalayan lakes, urban Phewa and remote Gosainkunda, from Nepal. Water Quality Index (WQI), Metal Index (MI), Hazard Quotient (HQ), Hazard Index, and Cancer Risk were calculated in order to evaluate the water quality of these lakes. Correlation analysis revealed that Mn and Fe were derived from natural geological weathering processes and Pb, V, Cr, Co, Ni, Cu, Zn, and Cd might have originated from anthropogenic sources. The results revealed that WQI of the remote lake fell into excellent water quality and urban lake fell into poor water quality, which is also supported by the MI calculation. Moreover, the HQ of Mn in urban lake showed values greater than unity suggesting its health risk to the local inhabitants. The cancer index values indicated “high” risk due to Cr, whereas Cd possesses “very low” cancer risk on local population residing nearby areas. This study provides the useful database and suggests for the regular assessment and policy formulation for safeguarding the natural water bodies in the region. 相似文献
4.
E. S. EUSKIRCHEN A. D. McGUIRE† D. W. KICKLIGHTER‡ Q. ZHUANG§ J. S. CLEIN R. J. DARGAVILLE¶ D. G. DYE J. S. KIMBALL K. C. McDONALD†† J. M. MELILLO‡ V. E. ROMANOVSKY‡‡ N. V. SMITH§§ 《Global Change Biology》2006,12(4):731-750
In terrestrial high‐latitude regions, observations indicate recent changes in snow cover, permafrost, and soil freeze–thaw transitions due to climate change. These modifications may result in temporal shifts in the growing season and the associated rates of terrestrial productivity. Changes in productivity will influence the ability of these ecosystems to sequester atmospheric CO2. We use the terrestrial ecosystem model (TEM), which simulates the soil thermal regime, in addition to terrestrial carbon (C), nitrogen and water dynamics, to explore these issues over the years 1960–2100 in extratropical regions (30–90°N). Our model simulations show decreases in snow cover and permafrost stability from 1960 to 2100. Decreases in snow cover agree well with National Oceanic and Atmospheric Administration satellite observations collected between the years 1972 and 2000, with Pearson rank correlation coefficients between 0.58 and 0.65. Model analyses also indicate a trend towards an earlier thaw date of frozen soils and the onset of the growing season in the spring by approximately 2–4 days from 1988 to 2000. Between 1988 and 2000, satellite records yield a slightly stronger trend in thaw and the onset of the growing season, averaging between 5 and 8 days earlier. In both, the TEM simulations and satellite records, trends in day of freeze in the autumn are weaker, such that overall increases in growing season length are due primarily to earlier thaw. Although regions with the longest snow cover duration displayed the greatest increase in growing season length, these regions maintained smaller increases in productivity and heterotrophic respiration than those regions with shorter duration of snow cover and less of an increase in growing season length. Concurrent with increases in growing season length, we found a reduction in soil C and increases in vegetation C, with greatest losses of soil C occurring in those areas with more vegetation, but simulations also suggest that this trend could reverse in the future. Our results reveal noteworthy changes in snow, permafrost, growing season length, productivity, and net C uptake, indicating that prediction of terrestrial C dynamics from one decade to the next will require that large‐scale models adequately take into account the corresponding changes in soil thermal regimes. 相似文献
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