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Excessive human disturbance (e.g., overgrazing, deforestation) has degraded the environment in the Qilian Mountains in China. Vegetative restoration is likely to be a crucial tool to restore these biologically significant habitats, but it is impossible to achieve this goal if the baseline plant community composition and its variation with local environmental conditions were not understood fully. To assess plant community composition by slope aspect, four different aspects – south-facing slope (SF), southwest-facing slope (SW), northwest-facing slope (NW), and north-facing slope (NF) – were surveyed on three almost non-degraded mountains. The results showed that each slope aspect has different abiotic environments. From SF to NF, soil water content has an increasing trend, but it shows no difference between SF and SW; and daily soil temperature and pH have a decreasing trend, while the former shows no difference between SF and SW, and SW and NW; and the latter shows no difference between SW and NW; and soil organic carbon was significantly increased, but soil bulk density was significantly decreased. Herbaceous plants were dominant on SF, SW, and NW, and trees (Picea crassifolia) were dominant on NF. From SF to NW, the dominant herbaceous plants were Agropyron cristatum and Stipa grandis, Agropyron cristatum and Carex aridula, and Kobresia humilis and Carex crebra, respectively, while on NF they were Carex spp. and Polygonum macrophyllum. The baseline survey points to the need to consider underlying patterns in abiotic conditions when planning restoration programs in these degraded mountain habitats, and to select native plants similar to the original vegetation. The survey provides a vital milestone for the development of policy-based funding initiatives and for ongoing vegetation monitoring during restoration to assess if these vegetative targets have been met.
Hydrological and nitrate pollution processes are important parts of aquatic ecosystems. For this study we collected samples of river water, reservoir water, shallow groundwater, deep groundwater, and precipitation in the Fenhe River Basin. δD and δ¹⁸O were used to identify the hydrological process. δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻ were used to identify the sources and pollution process of NO₃⁻. The results show that precipitation is the main source of water in the study area, and there is an obvious isotopic fractionation caused by evaporation. The reservoir water, river water, soil water, and shallow groundwater had a mutual recharge and discharge association. Deep groundwater is recharged by archaic groundwater and less affected by evaporation and human activity. NO₃⁻ is the main N species in the study area, nitrification is the main source of NO₃⁻, and denitrification is also found in some river branches. 46.2% of NO₃⁻-N concentrations exceeded the drinking water standard of China. NO₃⁻ Sources are mainly controlled by land use type. Nitrogen in precipitation and soil organic N are the major sources of NO₃⁻ in the upstream. The midstream area is mainly polluted by manure and sewage, while the downstream area is polluted by a mixture of soil organic N and fertilizers.
We investigated the Cr(VI) adsorption characteristics of bentonite under different modifi cation patterns by using a mixture of BS-12 (dodecyl dimethyl betaine) and DTAB (dodecyl trimethyl ammonium bromide). DTAB was used to compositely modify 25%, 50%, and 100% BS-12-modifi ed bentonite (three modifi ed modes of bentonite with BS-12). In addition to these modifi cation modes, variations as functions of pH value, temperature, and ionic strength were compared. Results showed: 1. Cr(VI) adsorption capacity of bentonite compositely modifi ed with BS (short for BS-12) + DT (short for DTAB) rapidly increased compared with that of BS-modifi ed bentonite, and the adsorption capacity of 100%BS+100%DT-modifi ed bentonite was the highest among the samples surveyed and 23-fold higher than that of CK (raw bentonite). 2. Cr(VI) adsorption on bentonite exhibited saturated adsorption in ion exchange (IE) mode, distributive adsorption in ion exchange and hydrophobic bond coexisting (IE+HB) pattern, and synergistic adsorption in the hydrophobic bond (HB) pattern. 3. Effects of rising temperature on Cr(VI) adsorption appeared in the IE mode, while negative temperature effect was observed in the HB mode. Higher pH value and ionic strength were unfavorable for Cr(VI) adsorption. 100%BS+100%DT compositely modifi ed bentonite exhibited the optimal adsorption of Cr(VI) at 10ºC, pH = 4, and ionic strength of 0.01 mol L⁻¹.
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