沉水植物黑藻对沉积物有机、无机磷形态及潜在可交换性磷的影响

在室内模拟条件下研究了沉水植物黑藻对沉积物有机及无机磷形态及潜在可交换性磷的影响.结果表明:①黑藻可显著降低沉积物的有机质、阳离子代换量及总磷(p<0.05),对沉积物中的磷起到活化的作用.②黑藻对沉积物无机磷形态中的NaOH-P有极显著影响(p<0.01),对有机磷形态中的活性有机磷有一定影响(p<0.1),而对其他形态磷的影响没有达到显著水平.③有植物组沉积物的潜在可交换性磷的量增大了11.5%,而对照组沉积物的却减少了61.0%.两者变化的方向截然相反,而且变化的程度也存在较大差异.这说明黑藻的作用增大了沉积物中潜在可交换性磷的量.     

Phosphorus accumulation and eutrophication in feed-supply freshwater fishponds

The rapid growth and intensification of freshwater fishery can cause imbalances between phosphorus （P） input in feed and its output in produce. This aquaculture can result in enriching exogenous P in fishponds and, consequently, accelerates the process of eutrophication. To assess relations among input, accumulation, release of P and as a consequence degrading water quality in terms of chlorophyll-a （Chl-a） in freshwater fishponds, fourteen fishponds with feed supply, nine fishponds without feed supply, and five nonfish ponds in Shaoxing Plain, southeast China were selected for comparing P accumulation in their waters and surface sediments. Surface sediment samples were collected from each pond to evaluate their total P, water soluble P, Olsen P, algal available P, and P fractions. Water samples were also collected from the ponds to measure concentrations of dissolved P and Chl-a. Total P in the sediments ranged from 0.88 to 1.73 g/kg in the fishponds with feed supply, that in the non-fish ponds ranged from 0.47 to 0.86 g/kg. Organic P, accounted for 23% to 60% of total P in the sediments, was an important P fraction and increased linearly with increasing organic matter. Long-term application of feeds resulted in increased P availability in the bottom sediments and degradation of water quality in the freshwater fishponds. Compared with non-fish ponds, sediments from the feed-supplied fishponds contained considerably higher Olsen P, algal available P, and water soluble P. Higher proportions of the labile P （NH4Cl-P） and potentially labile P （NaOH-IP） were also found in the sediments from the fishponds. High solubility of P in the sediments resulted in elevation of P and chlorophyll-a concentration in the pond water. The dissolved P concentration in the pond water increased in the order of non-fish ponds （12μg/L） 〈 fishponds without feed supply （24 μg/L） 〈 fishponds with feed supply （66 μg/L）. Linear correlations between concentrations of total P, Olsen-P, algal available P, water-soluble P and P concentration in saturation extracts in the sediments and dissolved P in the pond water indicated that there was a buffering action of the sediment constituents on the dissolved P.     

Using NDVI to Assess Vegetative Land Cover Change in Central Puget Sound

We used the Normalized Difference Vegetation Index (NDVI) in the rapidly growing Puget Sound region over three 5-year time blocks between 1986–1999 at three spatial scales in 42 Watershed Administrative Units (WAUs) to assess changes in the amounts and patterns of green vegetation. On average, approximately 20% of the area in each WAU experienced significant NDVI change over each 5-year time block. Cumulative NDVI change over 15 years (summing change over each 5-year time block) was an average of approximately 60% of each WAU, but was as high as 100% in some. At the regional scale, seasonal weather patterns and green-up from logging were the primary drivers of observed increases in NDVI values. At the WAU scale, anthropogenic factors were important drivers of both positive and negative NDVI change. For example, population density was highly correlated with negative NDVI change over 15 years (r = 0.66, P < 0.01), as was road density (r = 0.71, P < 0.01). At the smallest scale (within 3 case study WAUs) land use differences such as preserving versus harvesting forest lands drove vegetation change. We conclude that large areas within most watersheds are continually and heavily impacted by the high levels of human use and development over short time periods. Our results indicate that varying patterns and processes can be detected at multiple scales using changes in NDVIa values.     

Mapping Invasive Aquatic Vegetation in the Sacramento-San Joaquin Delta using Hyperspectral Imagery

The ecological and economic impacts associated with invasive species are of critical concern to land managers. The ability to map the extent and severity of invasions would be a valuable contribution to management decisions relating to control and monitoring efforts. We investigated the use of hyperspectral imagery for mapping invasive aquatic plant species in the Sacramento-San Joaquin Delta in the Central Valley of California, at two spatial scales. Sixty-four flightlines of HyMap hyperspectral imagery were acquired over the study region covering an area of 2,139 km² and field work was conducted to acquire GPS locations of target invasive species. We used spectral mixture analysis to classify two target invasive species; Brazilian waterweed (Egeria densa), a submerged invasive, and water hyacinth (Eichhornia crassipes), a floating emergent invasive. At the relatively fine spatial scale for five sites within the Delta (average size 51 ha) average classification accuracies were 93% for Brazilian waterweed and 73% for water hyacinth. However, at the coarser, Delta-wide scale (177,000 ha) these accuracy results were 29% for Brazilian waterweed and 65% for water hyacinth. The difference in accuracy is likely accounted for by the broad range in water turbidity and tide heights encountered across the Delta. These findings illustrate that hyperspectral imagery is a promising tool for discriminating target invasive species within the Sacramento-San Joaquin Delta waterways although more work is needed to develop classification tools that function under changing environmental conditions.     

生态脆弱区输气管道沿线生态修复措施探讨--以西气东输宁夏段为例

西气东输宁夏段管道沿线区域为典型的生态脆弱区,管道建设施工过程中不可避免地会破坏生态环境,引发新的水土流失,造成环境进一步恶化.本文在实地调查的基础上,分析了沿线水文气象、土壤、植被状况等自然生态条件.依据"适地适树,适地适草"的原则,提出了风蚀防治区和水风蚀交错防治区等典型区植被恢复的树草种选择方案,并针对不同侵蚀区类型提出不同布设方案,最后对林草管护进行探讨.     

基于GIS的黄土高原植被生态信息系统研究

利用地理信息系统(GIS)技术在黄土高原地区植被与环境关系研究中开展了植被生态信息系统方面的应用研究,分析了植被生态信息系统的技术特征,并对建立黄土高原地区植被生态信息系统的一些问题进行了探讨,为西部大开发提供科学依据。     

雨水资源、土壤水资源与土壤水分植被承载力

在我国北方少雨地区开展雨水资源、土壤水资源与土壤水分植被承载力研究对于防治林草地土壤旱化和林草植被经营具有重要意义。2002年4月以来,在上黄生态实验站对多年生人工林林外和林内降水、地表径流、植物生长和土壤水分动态进行了定位观测,结果表明:次降雨林冠层截留量为0.2～6.47mm,为降水量的3.1%～53.3%,截留总量占降水量的16.9%;地表径流量为0.24～1.5mm,是降雨量的1.6%～6.8%;柠条林地土壤剖面水分垂直变化可分为活跃层、次活跃层和相对稳定层;年内土壤水分胁迫时,植物通过改变叶的颜色,降低自身的含水率、落叶或产生大量落叶来适应干旱的土壤水环境,但不会死亡。土壤水分植被承载力为土壤水分承载植物的最大负荷,是指在较长时期内,当根层土壤水分消耗量等于或小于降雨补给量时,所能维持特定植物群落健康生长的最大密度。     

酸沉降对重庆南山森林生态系统土壤和植被的影响

酸沉降现象在重庆南山地区已造成长期严重的环境污染.笔者根据东亚酸雨监测网土壤和植被监测技术规范方法,研究了酸沉降对森林生态系统土壤和植被的影响和危害.通过对土壤的分析表明:5个采样点的土壤pH值较低,A层均值为3.74,B层均值为4.20,盐基饱和度(BS)的均值小于10%,盐基离子交换量(CEC)A层为78.1~88.6 mmol/kg,B层为61.1~65.1 mmol/kg,土壤中含有较高的Al3+<\sup>可能与大气中S和N的输入有关,并导致了土壤酸化.土壤中C/N较低,A层接近12.0,并且随土层的加深而下降,说明在亚热带湿润气候条件下有机质层分解良好.通过对植被的分析表明,酸沉降可能对杉木和柳杉这两种酸敏感性植物有一定的危害作用.      

重庆酸雨地区森林生态系统土壤、植被与地表水现状分析

酸沉降现象在重庆已成为一个严重的长期环境污染问题，本文根据东亚酸雨监测网土壤、植被监测技术规范的方法-研究了酸沉降对森林生态系统土壤、地表水以及植被的影响和危害。通过对土壤的分析：3个采样点的土壤pH值较低，这可能与大气S和N的输入有关，导致了土壤酸化。而南山采样点的盐基饱和度(BS)均值少于10％，盐基离子交换量(CEC)也较低．土壤中Al^3 浓度相对较高，土壤中C／N较低，南山可能存在土壤酸度增加的危险，以及土壤中Al浓度增高并伴有S或N沉降增加的危险。对地表水分析结果表明，南山采样点地表水的酸中和能力(ANC)较大，但是该采样点土壤剖面的盐基饱和度并不高，由此可推测该地表水可能是经由盐基离子丰富的土壤或岩石径流而来。通过对植被的分析，酸雨可能对杉木和柳杉这两种酸敏感性植物有一定的危害作用。     

原生滩涂植被演替带土壤Cd形态分布及其生态风险评价

为了解原生滨海滩涂不同植被演替带土壤镉(Cd)的含量特征、赋存形态及生态风险,以盐城地区原生滨海滩涂为研究对象,利用BCR 3步提取法分析了不同植被演替带土壤Cd的含量及赋存形态,并采用平均沉积物质量基准系数法(SQG-Q)和风险评价准则(RAC)对Cd的潜在生态风险进行了初步评价。结果表明,原生滩涂土壤中总Cd(CdT)含量在2.21~3.61 mg·kg~(-1)之间,远高于江苏沿海土壤Cd背景值和国家土壤环境质量三级标准;不同植被演替带间,CdT含量表现为互花米草滩碱蓬滩芦苇滩光滩;SQG-Q系数显示该地区土壤CdT处于中等风险,互花米草滩风险相对较高;总体上原生滩涂土壤中可还原态Cd比例较低(12.8%),而酸溶态、可氧化态、残渣态三者差异不大(分别为28.2%、29.8%,29.2%);互花米草滩和芦苇滩酸溶态Cd比例(30.5%、37.0%)显著高于碱蓬滩和光滩(28.2%、20.6%),而残渣态Cd(21.5%、20.9%)则显著低于碱蓬滩和光滩(41.5%、45.6%);RAC评价结果显示,滩涂土壤Cd总体上呈现中等风险,而互花米草滩和芦苇滩达到高风险。以上结果显示,原生滨海滩涂土壤Cd已存在一定的生态风险,其中互花米草滩风险相对较高,随着互花米草的扩张及围垦面积的扩大,其重金属风险值得关注。