共查询到20条相似文献,搜索用时 468 毫秒
1.
We studied the effect of calcite encrustation in stoneworts (Chara spp.) on P cycling in an aquatic ecosystem. Sequential fractionation was performed to quantify P fractions of the internodes of calcified (Ca-CF) and uncalcified (UCa-CF) Chara fibrosa Agardh ex Bruzelius. Our results showed that Ca-CF was able to store more P and about 14 to 23% of total P in Ca-CF was co-precipitated with encrusted calcite, while only 2 to 3% was found in UCa-CF. Furthermore, in Ca-CF, an increased amount of total P did not result in a higher release of bioavailable water-soluble and sodium hydroxide-extractable P. Extracellular calcification in Chara enhanced nutrient sink for P, provided a further bottom-up control of phytoplankton, and should be regarded as a positive feedback in stabilizing Chara dominance in lakes. 相似文献
2.
Data from the Woburn Erosion Reference Experiment (Bedfordshire, UK) were used to test the hypothesis that losses of phosphorus (P) in small erosion events are as great as those in infrequent large events, and to examine the effect of storm characteristics on the selective enrichment of P in eroded sediment. For almost every plot event in the period 1988 to 1994, the clay-sized fraction of the sediment was enriched compared with the soil of the plots. There was more variation in clay enrichment for smaller erosion events than for larger ones. The clay and P contents of the sediment were strongly correlated (p < 0.01), and there was a wider range of P concentrations in the sediment derived from small events than in that from large events. However, individual events resulting in small soil losses (< 100 kg) did not account for greater P losses than larger events (> 100 kg). The greater frequency of smaller events, combined with the likelihood of higher P concentrations in the sediment, therefore accounted for a greater proportion of the P lost over the 6-yr period than the infrequent large events. Phosphorus concentrations generally increased with increasing peak discharge and decreased with increasing event duration. For the same return period, P losses were generally greater from plots cultivated up and down the slope than from those cultivated across the slope. Overall, our results suggest that small erosion events should be controlled to prevent P contamination of surface waters and that the most effective means of doing this are by the introduction of minimal tillage techniques and across-slope cultivations. 相似文献
3.
Amending poultry litter with Al sulfate (alum) has proven effective in reducing water-soluble P in the litter and in runoff from fields that have received litter applications. Although its effectiveness has been demonstrated on a macroscopic scale in the field or in the poultry houses, little is known about P speciation in either alum-amended or unamended litter. This knowledge is important for the evaluation of long-term stability and bioavailability of P, which is a necessary prerequisite for the assessment of the sustainability of intensive poultry operations. Here we report results from an investigation of alum-amended poultry litter (PL) that combined a chemical extraction sequence with solid-state 31P nuclear magnetic resonance (NMR) spectroscopic analysis of the residues. Aluminum is predominantly found in the fine size separate (<125 microm), indicating that the alum added to the poultry houses hydrolyzed without being completely dispersed in the litter. The NMR spectra confirmed the hypothesis that calcium phosphate phases are only dissolved during extraction with dilute acid and phosphate associated with Al is mainly dissolved during extraction with NaOH. Extraction of phosphate associated with Al was incomplete, however, as evidenced by 31P NMR spectroscopy. It could also be demonstrated that the extraction sequence overestimates the calcium phosphate fraction by an order of magnitude in this particular sample. Results from sequential chemical extraction should therefore be used with caution when assessing the magnitude of different phosphate pools in poultry litter. 相似文献
4.
Braskerud BC Tonderski KS Wedding B Bakke R Blankenberg AG Ulén B Koskiaho J 《Journal of environmental quality》2005,34(6):2145-2155
Construction of wetlands is a possible supplement to best management practices (BMP) at the field level to mitigate phosphorus (P) pollution from agricultural areas. In this paper, annual results from 17 intensively studied wetlands in the cold temperate or boreal climatic zone are reported and analyzed. Surface areas varied from 0.007 to 8.7% of the catchment area. The average total phosphorus (TP) retention varied from 1 to 88%, and the dissolved reactive phosphorus (DRP) retention from -19 to 89%. Retention varied substantially from site to site, indicating the existence of site-specific factors in the catchment and wetlands that influenced the P removal. Factors important for P retention in wetlands were evaluated through multiple statistical analyses by dividing P into two fractions: particulate phosphorus (PP) and DRP. Both relative (%) PP and DRP retention increased with wetland surface area. However, PP retention was not as sensitive as DRP in terms of wetland size and retention: specific PP retention (gram P retention per m(2) and year) decreased as wetland area (A(w)) increased, suggesting the existence of a site-specific optimal wetland to catchment area (A(c)) ratio. Particulate P retention decreased with increasing DRP to TP ratio, while the opposite was found for DRP. Dissolved reactive P retention was higher in new than in old wetlands, while increasing age did not influence PP retention negatively. Effective BMP in the catchment is important to keep the P loss low, because the outlet concentration of P from wetlands is often positively correlated to the input concentration. However, wetlands act as the last buffer in a catchment, since the retention often increases as the P concentration in streams increases. 相似文献
5.
底泥中微量元素的含量水平,是衡量环境质量的一个重要指标。应用粉末发射光谱法测定,可以克服化学法、原子吸收法和溶液发射光谱等方法存在的溶样困难,操作步骤复杂,周期长,一些元素易被污染的缺点,分析成本低,简便、快速,能同时测定多种元素,是一种行之有 相似文献
6.
7.
9.
10.
陕,甘,宁,青干旱序列年表及其气候特征 总被引:5,自引:0,他引:5
根据历史文献记载和气象观测资料,事理了近200年西北上省(区)旱涝连年表,并对近200年的旱涝进行了气候统计分析,结果表明:近200年以来出现过三个干旱时期,三个多雨时期,平均10.3年发生一次大旱,4.3年发生一次一般干旱,1991年开始可能进入一个新的干旱时期。 相似文献
11.
我局以淮河流域污染整治为总方针,把污染综合防治作为企业的“生命工程”来抓,连环推出了五大举措,9月底已初见成效,与去年同期相比,采油污水回注率提高了3.5%,年底可实现采油污水全部回注及其它工业污水达标排放,部分污染防治工程已通过江苏省环保局的初验收... 相似文献
12.
利用曲线补偿,变时溶出示差技术提高了测定铜、铅、锌、镉的灵敏度、精密度和准确度,进一步改变了谱图的分辨率,避免了O2波的干扰。 相似文献
13.
随着世界人口的增加,陆地资源日趋减少.开发利用海洋,向海洋进军,已被很多国家和地区作为解决人口、资源和环境危机的重要之路。但是,迄今为止.人们对海洋的了解甚少,海洋生态意识淡薄,所以在开发利用海洋的过程中,违反海洋生态规律,污染海洋环境.破坏海洋资源的情况屡屡发生,并且随着对海洋开发强度的加大已导致海洋资源锐减,海洋生态环境污染和破坏口愈严重。因此,了解海洋,关心海洋,规范人们的海洋开发利用活动与行为,努力去保护海洋,应当是人类的共同使命。一、海洋在全球环境及人类生存发展中的地位和作用1、海洋是… 相似文献
14.
15.
16.
水中Cu,Zn,Pb,Cd的量浓度变化范围较大,可能从痕量到很高的含量,但大多数水样中Cu,Zn,Pb,Cd含量都在痕量水平。采用原子吸收分光光度法测定元素含量时,常受到试样中共存元素的干扰,影响测定准确度,另外因含量甚 相似文献
17.
18.
19.