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Grazing impact of Daphnia longispina on phytoplankton and bacteria in Lake Paione Superiore (Northern Italy) was evaluated using fluorescently labeled cells in short-term in situ experiments. Structure and size distribution of Daphnia were studied weekly from its appearance in July to its decline in September. Relative importance of algae and bacteria in the diet varied over time, as did consequently the relative impact of Daphnia on the phytoplankton and bacteria populations. Biomass of bacteria in the diet of Daphnia varied from 1 to 42%, and was highest at the beginning of population development when young individuals dominated. The percent biomass of algae in the diet increased with population development, ranging from 58 to 99%. Daphnia population consumed per hour 0.04–1.8% of bacteria and 0.3–17.6% of phytoplankton abundances. 相似文献
995.
Mercury Loading and Methylmercury Production and Cycling in High-Altitude Lakes from the Western United States 总被引:1,自引:0,他引:1
Krabbenhoft David P. Olson Mark L. Dewild John F. Clow David W. Striegl Robert G. Dornblaser Mark M. VanMetre Peter 《Water, Air, & Soil Pollution: Focus》2002,2(2):233-249
Studies worldwide have shown that mercury (Hg) is a ubiquitouscontaminant, reaching even the most remote environments such ashigh-altitude lakes via atmospheric pathways. However, very fewstudies have been conducted to assess Hg contamination levels ofthese systems. We sampled 90 mid-latitude, high-altitude lakes from seven national parks in the western United States during afour-week period in September 1999. In addition to the synoptic survey, routine monitoring and experimental studies were conducted at one of the lakes (Mills Lake) to quantify MeHg fluxrates and important process rates such as photo-demethylation. Results show that overall, high-altitude lakes have low total mercury (HgT) and methylmercury (MeHg) levels (1.07 and 0.05 ng L-1, respectively), but a very good correlation of Hg to MeHg (r2= 0.82) suggests inorganic Hg(II) loading is a primary controlling factor of MeHg levels in dilute mountain lakes. Positive correlations were also observed for dissolved organic carbon (DOC) and both Hg and MeHg, although to a much lesser degree. Levels of MeHg were similar among the seven national parks, with the exception of Glacier National Park where lowerconcentrations were observed (0.02 ng L-1), and appear to berelated to naturally elevated pH values there. Measured rates ofMeHg photo-degradation at Mills Lake were quite fast, and thisprocess was of equal importance to sedimentation and stream flowfor removing MeHg. Enhanced rates of photo-demethylation are likely an important reason why high-altitude lakes, with typically high water clarity and sunlight exposure, are low in MeHg. 相似文献
996.
Previous research has established clear relationshipsbetween the chemical composition of surface waters andthe nature of their contributing catchments. Theserelationships are particularly strong when broadenvironmental gradients are considered. However, forfreshwaters at higher altitudes, some of the catchmentprocesses that mediate chemical composition are lessinfluential than those at lower altitudes. The waterchemistry of 85 upland lochs in Scotland, U.K. is examinedto assess differences in chemical composition along arelatively short altitude gradient. Principal componentsanalysis identifies the main gradients of variationwithin the dataset. A series of digital datasets is usedto characterise the catchments according to a range ofattributes including soils and landcover. Multivariatestatistical analysis is undertaken to examine the extentto which the catchment attributes can explain variationin surface water chemistry in upland systems. Theseempirical relationships may be used in the development ofregionalisation procedures, which will allow upscaling ofknowledge from individual sites to regions. 相似文献
997.
The natural Park of Peñalara consists of a small mountainousarea near Madrid and includes a series of water bodies (fromsmall mountain lakes to temporary ponds and peat bogs), the mostknown of them being the so-called `Laguna Grande dePeñalara'. Due to growing numbers of visitors theenvironmental conditions of this lake started to decline in theearly 1970s because of: (1) the start of severe soil erosionprocesses; (2) the increase of nutrient load; and (3) theintroduction of a non-native fish species. Since the area wasprotected in 1990, several conservation and restoration projectsincluded in an integrated management plan have been developed. Here we summarise some of the results of these efforts: (1) controlled access of livestock and visitors to the area; (2) palaeolimnology studies aimed at inferring recent changes in thewatershed; and (3) monitoring of the limnological features of thesystem. Restoration of this lake and its watershed is intendedto serve as a model for the management of other severely alteredhigh mountain lakes. 相似文献
998.
UV/Fenton法处理高浓度香料废水的试验研究 总被引:6,自引:1,他引:6
研究了UV/Fenton法处理高浓度废水的新技术以及有关影响因素。试验:pH在2-4,COD/H2O2=1:1.5,Fe^2 浓度为1.7g/L的条件下,反应时间90min,COD去除率可达99.6%。 相似文献
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A three-year study of Connecticut, USA, salt-marsh vegetation was undertaken to determine the relationship of its distribution on the marsh surface to tidal levels, particularly mean high water (MHW) as measured on each of three sites representing different tidal amplitudes. Elevations and species present were measured on 1-m2 grids in 10x 70-m belt transects at each site. After the data were subjected to discriminant analysis and other standard statistical procedures, the results showed that 98.4% of all observations ofSpartina alterniflora Loisel. occurred at or below MHW. The data can aid in salt-marsh restoration by offering a reliable indicator of what species should be planted when restored elevations and on-site MHW are known. 相似文献