Trans-boundary air pollution over remote islands in Japan: observed data and estimates from a numerical model

Observations of air pollutants were conducted in remote Japanese islands (Oki Island and Okinawa Island) in early spring to clarify the extent of trans-boundary air pollution from the Asian continent. A three-dimensional Eulerian model calculation, which included parameters on emission, transport and transformation of sulfur oxides, nitrogen oxides and ammonia, was performed to compile sulfate isosurface concentrations over the observational sites. Concentrations of non-sea-salt sulfate (nss-SO₄²⁻) of greater than 10 μg m⁻³ were observed at Oki after the northeastward passage of low-pressure systems in the Sea of Japan. At these times, the weather showed a typical winter pattern and air pollutants over China were transported southeastward to Japan with the northwesterly wind. The model calculation reproduced the observed variations of nss-SO₄²⁻ concentration well, except for one case in which the model calculation could not reproduce the extremely low nss-SO₄²⁻ concentration observed on 8 March. In Hedo (Okinawa Island), we observed long-lasting (3 days) medium concentrations of nss-SO₄²⁻ (approximately 5 μg m⁻³). Although the model reproduced these observed medium concentrations well, in general the observed results were reproduced better for Oki than for Hedo. Under the synoptic weather conditions of early spring, high concentrations of nss-sulfate were sometimes transported to these remote Japanese islands from areas of continental Asia with a strong outflow of air pollutants.     

Trace elements and stable isotopes (delta13C and delta15N) in shallow and deep-water organisms from the East China Sea

Trace elements (22) and stable isotope ratios (δ¹⁵N and δ¹³C) were analyzed in marine organisms from shallow (SW) and deep-water (DW) of the East China Sea to understand biomagnification and prey source of trace elements. In the benthic marine organisms from DW, δ¹⁵N values were negatively correlated with Ba, Cu, Ag, Mo, Sr, As, and Co concentrations. This may be due to the specific accumulation in lower trophic animals and/or the biodilution through the food web in DW. Relationships between δ¹⁵N and concentrations of Co, Cr, Bi, and Tl in fish and Ag, Bi, V, Hg, and Tl in crustaceans showed positive correlations, suggesting that trophic position was affecting the concentrations of those elements in phyla, with higher trophic animals retaining higher concentrations than the lower trophic animals. Positive correlations between δ¹³C and Rb were observed in marine organisms. Therefore, Rb may be a possible substitute of δ¹³C as tracer of prey source in the East China Sea although further investigation is required.     

Ionic imbalance due to hydrogen carbonate from Asian dust

In an attempt to identify the ionic imbalance, hydrogen carbonate, HCO₃⁻ (bicarbonate), was determined together with the commonly determined nine major ions because the imbalance was frequently encountered in the chemical analysis of samples with high pHs. Titration method was applied for the determination of the samples with pH higher than 5.6. These samples amounted to 102 of the 1536 samples collected in Hokkaido, Northern Japan, from April 1998 to December 2002. Of the 102 samples, 74 (Group A) showed an acceptable ion balance without including HCO₃⁻. In the other 28 (Group B), however, inclusion of HCO₃⁻ successfully improved the ion balance. These results suggested that hydrogen carbonate was a potential candidate for explaining the imbalance. The hydrogen carbonate concentrations showed a strong correlation with the corresponding non-sea salt calcium (nss-Ca²⁺) concentrations, which implied that hydrogen carbonate was derived from calcium carbonate particles incorporated into falling raindrops or cloud droplets. For Group A, the relationship between hydrogen carbonate and the nss-calcium ion concentration was very similar to that for commonly suspended particles in Hokkaido. On the other hand, Group B exhibited a stronger but significantly different correlation. To the samples of Group B, a back-trajectory analysis was applied to demonstrate that the samples were associated with aerosol travelling from Northern China or Mongolia, which indicated that alkaline aerosol affected the chemistry. In consideration of these findings, the current standard of the ion balance should be critically reviewed for modification in regard to the contribution of hydrogen carbonate not only in source areas but also in receptor areas of alkaline aerosol.     

太湖北部流域水化学特征及其控制因素

为了解太湖北部流域主要河网区水质受该流域地质状况、岩石和土壤的化学风化作用以及人类活动的影响等方面,对太湖北部流域河网区主要河道水体中的主要离子进行了采样研究。结果表明：太湖北部流域水体中的TDS平均值为355．74mg·L-1,变化范围为276．08--681．54mg·L-1,其中ca2＋和HCO3-是占绝对优势的离子,分别占阳离子和阴离子总量的46．2％和48．9％;其次是Na＋和SO42-,分别占阳离子和阴离子总量的35．9％和27．5％。进而判断出该流域水化学类型是以碳酸盐岩石和蒸发岩来源为主的HCO3-Ca2＋-Na＋型。再从离子的自然起源和人类活动角度分别对水化学类型的控制因素进行分析,一方面利用吉布斯分布模式投点作图得出结论：其离子自然起源的优势机制是岩石的风化作用,而蒸发一结晶和大气降水的输入作用十分微弱,这与该流域的水文、地理、地质背景相一致;另一方面通过SPSS软件的相关关系分析得出结论：NO3-、SO42-、心、ca2＋和Mg2＋的相关性较强,与cl‘也呈正相关,说明水体中这些主要离子都具有共同的来源,其中NO3-的较高含量（平均值为14．74mg·L-1）反映了该流域受人类影响较大。尤其是NO3-与sO42-的相关性达到0．83,再次说明氮污染对该流域水体的酸化和水质变化有较大影响。     

太湖水体中悬浮颗粒物的比吸收光谱特性及其参数化分析

通过对太湖水体的野外采样,利用定量滤膜技术测量了水体中浮游植物色素的吸收系数(aph(λ))和非色素颗粒物的吸收系数(aNAP(λ)),进而推算比吸收系数.同时,对浮游植物色素和非色素颗粒物的比吸收系数的时空变化特征进行了分析.结果表明,浮游植物色素的比吸收系数(aph*)在蓝光440nm的变化范围为0.008～0.268m2·mg-1,在红光670nm的变化范围为0.004～0.098m·2mg-1;通过K-Mean算法将浮游植物色素的比吸收光谱分成3种具有不同光谱特征的类型,类别1、2和3占总数的百分比分别为61.0%、12.2%和26.8%,表明太湖水体中浮游植物色素的比吸收光谱是以类别1为主;色素包裹效应因子Qa*(675)在Chla浓度<50mg·m-3时,随Chla浓度的增大迅速减小,而在Chla浓度>50mg·m-3时,其减小的趋势趋于缓慢,Qa*(675)与Chla浓度呈现出较好的幂函数关系.非色素颗粒物的比吸收系数(aNAP*)在蓝光440nm处的变化范围为0.012×10-3～0.143×10-3m2·mg-1,利用此处的比吸收系数建立的非色素颗粒物比吸收光谱的参数化模型,光谱曲线斜率S的变化范围为0.0049～0.0133nm-1,平均值为(0.0091±0.0029)nm-1.同时,建立的非色素颗粒物的比吸收系数与其浓度的指数函数模型,R2达到0.502.     

太湖草型湖区沉积物再悬浮对水体营养盐的影响

再悬浮过程中沉积物对水体营养盐的内源贡献是湖泊,特别是浅水湖泊富营养化研究中的重要问题.采用原位沉积物柱样和原状上覆水的Y型扰动装置,被用来研究常规风情下太湖草型湖区沉积物的再悬浮和沉降过程对水体营养盐负荷的影响.结果表明,小风和中风的再悬浮过程导致水体氨氮和磷酸根磷含量显著下降,单位面积水柱含量最大变化量分别为-0.140 g·m-2和-1.59 mg·m-2;大风条件下,水体氨氮含量下降幅度很小,磷酸盐则出现明显增加趋势,最大增量为0.81mg·m-2.再悬浮过程之后的沉降过程中,中、小风条件的水体氨氮含量变小,大风条件的含量没有明显变化.磷酸根磷含量在中、小风条件下与风浪前差别较小,大风条件的含量则明显增大,最大增量为1.36 mg·m-2.因此,沉积物的再悬浮过程和沉降过程对上覆水体的营养盐动态负荷都产生重要影响.与太湖无植被湖区的研究结果对比说明,水生植物的存在对风浪作用下沉积物与上覆水的物质交换有一定的抑制作用.     

两晋以来气候变化对太湖流域稻麦两熟复种的影响

太湖流域的稻麦两熟复种大约产生于东晋南朝时期（317～589年）,此后这一种植制度长期存在,并不断有所发展。考察发现,此一区域的稻麦两熟在历史上的大多数时候并无突出的季节矛盾,只是有两个时期例外。这两个时期一是明末清初,一是19世纪。太湖流域历史上突出的季节矛盾不由人口、品种等社会原因引起,而由气候变化这一自然因素导致。明末清初和19世纪分别是历史上最为寒冷的时期,是气候变冷造成了这一区域稻麦两熟突出的季节矛盾。     

太湖东北部沉积物理化特征及磷赋存形态研究

对太湖东部和北部8个沉积物样品进行了理化性质及磷赋存形态分析,在此基础上探讨了沉积物各理化性质与磷赋存形态间的相关关系。研究结果表明：太湖沉积物的总磷含量为307.43～1454.39 mg/kg,阳离子交换量为15.18～22.68 meq/100g土,有机质含量为1.66%～3.45%;颗粒组成以粉砂级和粘粒级为主,占总量的54.39%～76.83%;主要矿物组成为石英和长石,粘土矿物以伊利石/蒙脱石混层为主,其次是伊利石、绿泥石和高岭石;沉积物中氧化物以SiO2、Al2O3和TFe2O3为主,且它们的含量随沉积物中总磷含量的不同变化较大。磷的形态以无机磷为主,污染较重沉积物中铁/铝磷的含量明显升高,有机磷的比例降低,钙磷变化不大。沉积物的各理化性质与磷赋存形态间关系密切,随着沉积物中总磷含量的增加, 阳离子交换量和有机质的含量都逐渐升高,细颗粒含量（<2 μm）逐渐增多,铁/铝形态的磷在总磷中所占比例也逐渐增大。