生态系统结构对太湖有机聚集体理化性质的影响

2007年1~12月对太湖4个不同生态类型湖区水体中有机聚集体(organic aggregates,OA)的丰度、有机质含量和营养盐(N、P)含量及其它水环境因子进行了同步监测.结果表明,①OA是太湖水体中营养盐的一个重要来源,其N、P含量分别占水体中TN、TP的16.5%及43.3%;②水体中OA的丰度与水体的富营养化程度密切相关,随着水体富营养化水平的提高和浮游植物生物量的增加,OA丰度及其中有机质的含量也呈现逐渐上升的趋势;③风浪扰动对太湖水体中OA的理化性质影响较大.OA作为营养盐的一个重要载体,可能是浅水湖泊营养盐循环中的一个关键点.     

Managing erosion and water quality in agricultural watersheds by small detention ponds

Terrace-contouring systems with on-site water detention cannot be installed in areas of complex topography, small parceling and multi-blade moldboard plow use. However, field borders at the downslope end may be raised at the deepest part where runoff overtops to create detention ponds, which can be drained by subsurface tile outlets and act similar to terrace-contouring systems. Four of such detention ponds were monitored over 8 years. Monitored effects included the prevention of linear erosion down slope, the sediment trapping from upslope, the enrichment of major nutrients in the trapped and delivered sediments, the amount of runoff retained temporarily, the amount of runoff reduced by infiltration, the decrease in peak runoff rate and the decrease in peak concentrations of agrochemicals due to the mixing of different volumes of water within the detention ponds. The detention ponds had a volume of 30–260 m³ ha⁻¹ and trapped 54–85% of the incoming sediment, which was insignificantly to slightly depleted (5–25%) in organic carbon, phosphorus, nitrogen and clay as compared to the eroding topsoil, while the delivered sediment was strongly enriched (+70–270%) but part of this enrichment already resulted from the enrichment of soil loss. The detention ponds temporarily stored 200–500 m³ of runoff. A failure was never experienced. Due to the siltation of the pond bottom, the short filled time (1–5 days) and the small water covered area, infiltration and evaporation reduced runoff by less than 10% for large events. Peak runoff during heavy rains was lowered by a factor of three. Peak concentrations of agrochemicals (Terbutylazin) were lowered by a factor of two. The detention ponds created by raising the downslope field borders at the pour point efficiently reduced adverse erosion effects downslope the eroding site. They are cheap and can easily be created with on-farm machinery. Their efficiency is improved where they are combined with an on-site erosion control like mulch tillage because sediment and runoff input are reduced. Ponds had to be dredged only after the first year when on-site erosion control was not fully effective.     

Nitrogen cycling of atmosphere-plant-soft system in the typical Calamagrostis angustifolia wetland in the Sanjiang Plain,Northeast China

The nitrogen(N)distribution and cycling of atmosphere-plant-soil system in the typical meadow Calamagrostis angustifolia wetland (TMCW)and marsh meadow Calamagrostis angustifolia wetland(MMCW)in the Sanjiang plain were studied by a compartment model.The results showed that the N wet deposition amount was 0.757 gN/(m~2.a),and total inorganic N(TIN)was the main body (0.640 gN/(m~2.a)).The ammonia volatilization amounts of TMCW and MMCW soils in growing season were 0.635 and 0.687 gN/m~2, and the denitrification gaseous lost amounts were 0.617 and 0.405 gN/m~2,respectively.In plant subsystem,the N was mainly stored in root and litter.Soil organic N was the main N storage of the two plant-soil systems and the proportions of it were 93.98% and 92.16%, respectively.The calculation results of N turnovers among compartments of TMCW and MMCW showed that the uptake amounts of root were 23.02 and 28.18 gN/(m~2.a)and the values of aboveground were 11.31 and 6.08 gN/(m~2.a),the re-translocation amounts from aboveground to root were 5.96 and 2.70 gN/(m~2.a),the translocation amounts from aboveground living body to litter were 5.35 and 3.38 gN/(m~2.a),the translocation amounts from litter to soil were larger than 1.55 and 3.01 gN/(m~2.a),the translocation amounts from root to soil were 14.90 and 13.17 gN/(m~2.a),and the soil(0-15 cm)N net mineralization amounts were 1.94 and 0.55 gN/(m~2.a), respectively.The study of N balance indicated that the two plant-soil systems might be situated in the status of lacking N,and the status might induce the degradation of C.angustifolia wetland.     

Characteristics of plankton Hg bioaccumulations based on a global data set and the implications for aquatic systems with aggravating nutrient imbalance

• Hg bioaccumulation by phytoplankton varies among aquatic ecosystems. • Active Hg uptake may exist for the phytoplankton in aquatic ecosystems. • Impacts of nutrient imbalance on food chain Hg transfer should be addressed. The bioaccumulation of mercury (Hg) in aquatic ecosystem poses a potential health risk to human being and aquatic organism. Bioaccumulations by plankton represent a crucial process of Hg transfer from water to aquatic food chain. However, the current understanding of major factors affecting Hg accumulation by plankton is inadequate. In this study, a data set of 89 aquatic ecosystems worldwide, including inland water, nearshore water and open sea, was established. Key factors influencing plankton Hg bioaccumulation (i.e., plankton species, cell sizes and biomasses) were discussed. The results indicated that total Hg (THg) and methylmercury (MeHg) concentrations in plankton in inland waters were significantly higher than those in nearshore waters and open seas. Bioaccumulation factors for the logarithm of THg and MeHg of phytoplankton were 2.4–6.0 and 2.6–6.7 L/kg, respectively, in all aquatic ecosystems. They could be further biomagnified by a factor of 2.1–15.1 and 5.3–28.2 from phytoplankton to zooplankton. Higher MeHg concentrations were observed with the increases of cell size for both phyto- and zooplankton. A contrasting trend was observed between the plankton biomasses and BAF_MeHg, with a positive relationship for zooplankton and a negative relationship for phytoplankton. Plankton physiologic traits impose constraints on the rates of nutrients and contaminants obtaining process from water. Nowadays, many aquatic ecosystems are facing rapid shifts in nutrient compositions. We suggested that these potential influences on the growth and composition of plankton should be incorporated in future aquatic Hg modeling and ecological risk assessments.     

Elimination of Methanol and Ethanol by Biofiltration: An Experimental Study

This study presents the experimental results obtained during long-term operation of two biofilters treating two alcohols: methanol and ethanol. The biofilters used for this purpose were previously packed with a compost material made from tobacco processing residues. The alcohols concentrations tested lay between 0.40 and 3.20 g/m³ for methanol, and 0.55 and 5.05 g/m³ for ethanol. The empty bed residence time in each biofilter was 60 s. Biofilter inlet loads of less than 190 and 300 g/m³/h for the methanol and ethanol additions respectively, were thereafter evaluated. In addition, the concentrations of nutrient nitrogen were also varied, from 0.1 to 2.0 g-N/l and from 0.3 to 11.3 g-N/l for the ethanol and the methanol, respectively. The results thus obtained have made it possible to select the optimal nitrogen concentrations which, for the cases examined, turn out to be 0.3 g-N/l and between 2 and 3.8 g-N/l for the ethanol and methanol substrates, respectively. The maximum elimination capacities obtained in this study were 82 and 150 g/m³/h, respectively for the methanol and ethanol cases. It was therefore concluded that, for a readily biodegradable compound such as ethanol, the nitrogen requirement is substantially lower than that needed for the methanol degradation, the latter appearing to be more difficult to degrade biologically under similar operating conditions. The production rate of the co-product carbon dioxide during methanol and ethanol biofiltration was also investigated. Also, a good correlation was found to exist between the temperature and the conversion achieved in the biofilter.     

典型喀斯特城市湖库溶解性有机质成分特征及来源解析

为探索喀斯特城市湖库溶解性有机质（DOM）成分特征及来源信息,以我国贵阳市重要喀斯特湖库——红枫湖、百花湖、松柏山水库和阿哈水库为研究对象,分析了表层水体溶解性有机碳（DOC）、叶绿素a（Chla）和DOM光学参数(a₂₅₄、a₂₈₀、a₃₅₀、 E2∶E3、S_275-295、 FI、β:α、 BIX、 HIX)的空间差异,同时利用荧光吸收峰（B、 T、 A、 M、 C、 D、 N）和三维荧光平行因子分析（EEM-PARAFAC）解释DOM各成分丰度及占比状况,并运用Spearman相关分析及主成分分析（PCA）揭示DOM参数的相关性和主要环境过程.结果表明,喀斯特城市湖库ρ（DOC）和ρ（Chla）范围分别为4.24～11.9 mg·L^-1和0.32～19.7μg·L^-1,松柏山水库腐殖质(a₂₅₄)和芳香类蛋白质(a₂₈₀)较高,导致相对分子质量(E2∶E3和S_275-295)高于其它湖...     

磷化氢在湖泊磷生物地球化学循环中的作用

重点介绍磷化氢对湖泊富营养化和在湖泊磷的生物地球化学循环中的作用，并探讨其形成机理。     

气候变暖背景下森林土壤碳循环研究进展

由人类活动引起的温室效应以及由此造成的气候变暖对森林牛态系统的影响已引起人们的普遍关注.森林土壤碳循环作为全球碳循环的重要组成部分,是决定未来陆地牛物嘲表现为碳源/碳汇的关键环节,揭示这一作用对于准确理解全球变化背景下陆地生态系统碳循环过程具有重要的指导意义.本文主要通过论述影响土壤碳循环过程的5个方面(土壤呼吸、土壤微生物、土壤酶活性、凋落物输入与分解、土壤碳库),综述了近10 a来全球气候变暖对土壤碳循环过程的影响.近年来,尽管已开展了大量有关土壤碳循环对气候变暖的响应及反馈机制的研究,并取得了一定的成果,但研究结果仍然存在很大的不确定性.整合各种密切关联的全球变化现象,完善研究方法和实验手段,加强根际微生态系统碳循环过程与机理研究将是下一步研究的方向和重点.参70     

Nitrogen cycling of atmosphere-plant-soil system in the typical Calamagrostis angustifolia wetland in the Sanjiang Plain, Northeast China

The nitrogen (N) distribution and cycling of atmosphere-plant-soil system in the typical meadow Calamagrostis angustifolia wetland (TMCW) and marsh meadow Calamagrostis angustifolia wetland (MMCW) in the Sanjiang plain were studied by a compartment model. The results showed that the N wet deposition amount was 0.757 gN/(m2·a), and total inorganic N (TIN) was the main body (0.640 gN/(m2·a)). The ammonia volatilization amounts of TMCW and MMCW soils in growing season were 0.635 and 0.687 gN/m2, and the denitrification gaseous lost amounts were 0.617 and 0.405 gN/m2, respectively. In plant subsystem, the N was mainly stored in root and litter. Soil organic N was the main N storage of the two plant-soil systems and the proportions of it were 93.98% and 92.16%, respectively. The calculation results of N turnovers among compartments of TMCW and MMCW showed that the uptake amounts of root were 23.02 and 28.18 gN/(m2·a) and the values of aboveground were 11.31 and 6.08 gN/(m2·a), the re-translocation amounts from aboveground to root were 5.96 and 2.70 gN/(m2·a), the translocation amounts from aboveground living body to litter were 5.35 and 3.38 gN/(m2·a), the translocation amounts from litter to soil were larger than 1.55 and 3.01 gN/(m2·a), the translocation amounts from root to soil were 14.90 and 13.17 gN/(m2·a), and the soil (0-15cm) N net mineralization amounts were 1.94 and 0.55 gN/(m2·a), respectively. The study of N balance indicated that the two plant-soil systems might be situated in the status of lacking N, and the status might induce the degradation of C. angustifolia wetland.     

Social environment versus cycling competency predicting risk-taking in 11- to 13-year-old cyclists in The Netherlands

Abstract

Objectives: From age 12 onwards, cycling injuries begin rising in The Netherlands. A known contributing factor is younger children’s underdeveloped competency to deal with complex and hazardous traffic situations, and their exposure to such situations strongly increases after transitioning to secondary school. Little is known about intentional risk-taking as a contributing factor. In this developmental stage, children become increasingly vulnerable because of intentional risk-taking, affecting their safety and health. The incidence, predictors in the child’s social environment, and trends of such risks are systematically monitored; for instance, for alcohol use, smoking, and cyber bullying. Such monitors do not include risky road behavior. This exploratory field study examined the frequency of intentional risky cycling, its relationship with the perceived social environment, and relative to cycling competency measured as the ability to detect emerging hazards quickly.

Methods: Three hundred thirty-five students between 11 and 13 years of age (51% male) completed computerized tests of hazard perception skill and surveys on crashes, risk-taking, peer pressure, perceived risk-taking by parents or friends, and exposure to risky driving as passenger.

Results: Frequent risk-taking was associated with higher crash frequency. Stepwise regression confirmed that children who more often took risks on the road were also more sensitive to peer pressure, had more often been passengers of risky drivers, had parents and friends who exhibited risky behaviors in traffic more often, and perceived hazards as less dangerous but, in contrast to expectations, did not do worse on the detection of hazards. The predictors explained 28% of the variance in total risk-taking but varied from 6 to 20% depending on the specific risk-taking behavior concerned.

Conclusions: At least 20% of children sometimes or more often take risks in traffic. Children who feel peer pressure to behave in a risky manner, observe parents and friends behaving in a risky manner in traffic, and have been exposed as passengers to risky driving more often take risks in traffic themselves. These results provide support for including items on risky road behavior in health monitors and to design interventions that address the risk factors in the child’s perceived social environment.