Nitrogen sources and exports in an agricultural watershed in Southeast China

The nitrogen (N) budget was developed for Jiulong River Watershed (JRW), an agricultural watershed in a warm and humid area of southeast China. Water quality monitoring, field surveys, modelling and GIS techniques were applied to estimate N flux of atmospheric deposition, mineralization, runoff, denitrification, and ammonia volatilization. Over the whole watershed, fertilizers, import of animal feeds, biotic fixation, mineralization and atmospheric deposition contributed 67.1%, 16.5%, 2.1%, 4.9% and 9.5%, respectively, of total N input (129.3 kg N ha⁻¹ year⁻¹). Runoff, sale of production, denitrification, and ammonia volatilization contributed 7.3%, 24.4%, 10.5% and 57.8% of total N output (72.9 kg N ha⁻¹ year⁻¹), respectively. The N budget for the JRW suggested that more than 50% of the N input was lost to the environment, and about 14% was discharged as riverine N, which indicated that agricultural and human activities in the watershed substantially impacted the estuary and coastal water quality, and so altered the N biogeochemistry process.     

Export of Nitrogen,Phosphorus, and Suspended Solids from a Southern New England Watershed to Little Narragansett Bay

The Pawcatuck River watershed (764 km²) is a mainly forested drainage basin with a low population density (80 people km⁻²) that discharges to a shallow estuary, Little Narragansett Bay (RI and CT, USA). In order to quantify the nitrogen (N) and phosphorus (P) flux to the estuary, we measured all forms of nitrogen and phosphorus, as well as suspended solids at the mouth of the river above tidal influence, on more than 80 occasions over an annual cycle. The annual export of total nitrogen, total phosphorus, and total suspended solids amounted to 16.0×10⁶ mol y⁻¹, 0.97×10⁶ mol y⁻¹, and 1.4×10⁶ kg y⁻¹, respectively. Nitrogen export was equally divided between dissolved inorganic (83% NO₃⁻) and organic forms, with particulate nitrogen comprising 17% of the total flux. Phosphorus export was dominated by particulate forms (67%), with dissolved inorganic phosphate contributing 30% and dissolved organic phosphorus contributing 8% of the annual flux. Preliminary nutrient budgets for the Pawcatuck watershed suggest that only about 10% of the nitrogen and phosphorus inputs are exported from the system. Strong regressions between water discharge and TN enabled us to extrapolate the data collected during the relatively dry study period to a long term average discharge year. Under normal river discharge conditions, the N flux would be approximately 26.0×10⁶ mol y⁻¹ or about 20% of the nitrogen inputs to the watershed. This value is very close to the N flux predicted by a regression developed by others from a wide range of larger watersheds. The relatively large size of the Pawcatuck watershed relative to the estuary (9.6 km²), makes Little Narragansett Bay one of the most intensively nitrogen loaded estuaries on the Atlantic coast in spite of the dominant forest cover of the watershed.     

Ecological research for the restoration and management of rivers and reservoirs in Japan

In Japan the River Law was amended in 1997 to expand the traditional roles of flood control and water supply in river management to include environmental conservation. Two major multidisciplinary research groups were also founded to address the environmental issues arising from the management of rivers and watershed areas in Japan. One called the River Ecology Research Group was formed in 1995 to search for an ideal dynamic state of rivers to be managed. Six case studies commenced involving measurements of natural and human impacts on representative rivers and their biota selected from different regions of the country. Restoration of natural rivers has also been attempted. The other, called the Watershed Ecology Research Group, was formed in 1998 to study the natural environment surrounding dams. It consists of four groups concerned with forest ecology in the headwaters, raptor management research, reservoir ecology, and flow regime research. The topics include modeling of regeneration dynamics of riparian forests, GIS mapping of endangered raptor habitats, developing measures to reduce eutrophication of reservoir water, and the use of biodiversity of benthic faunas as an indicator of environmental change in the downstream. In both groups, ecologists collaborate with engineers who are responsible for the river infrastructure, to predict future impacts and keep ecological perspectives for the maintenance of the healthy environment of rivers and reservoirs.     

Biological Image Segmentation Using Region-Scalable Fitting Energy with B-Spline Level Set Implementation and Watershed

ObjectivesImage segmentation plays an important role in the analysis and understanding of the cellular process. However, this task becomes difficult when there is intensity inhomogeneity between regions, and it is more challenging in the presence of the noise and clustered cells. The goal of the paper is propose an image segmentation framework that tackles the above cited problems.Material and methodsA new method composed of two steps is proposed: First, segment the image using B-spline level set with Region-Scalable Fitting (RSF) active contour model, second apply the Watershed algorithm based on new object markers to refine the segmentation and separate clustered cells. The major contributions of the paper are: 1) Use of a continuous formulation of the level set in the B-spline basis, 2) Develop the energy function and its derivative by introducing the RSF model to deal with intensity inhomogeneity, 3) For the Watershed, propose a relevant choice of markers that considers the cell properties.ResultsExperimental results are performed on widely used synthetic images, in addition to simulated and real biological images, without and with additive noise. They attest the high quality of segmentation of the proposed method in terms of quantitative and qualitative evaluation.ConclusionThe proposed method is able to tackle many difficulties at the same time: overlapped intensities, noise, different cell sizes and clustered cells. It provides an efficient tool for image segmentation especially biological ones.     

云南纳板河保护区蕨类植物区系地理研究

通过多次野外调查及资料整理,对纳板河流域国家级自然保护区蕨类植物的区系组成、地理成分、区系联系、性质及起源等方面进行了分析研究。结果显示:(1)纳板河保护区共有蕨类植物43科90属239种,优势科为水龙骨科、金星蕨科、凤尾蕨科、蹄盖蕨科、三叉蕨科,优势属为凤尾蕨属、鳞盖蕨属、毛蕨属、石韦属。(2)纳板河保护区蕨类植物区系具有明显的热带向亚热带过渡的性质,当属热带亚洲蕨类植物区系,但在一定程度上受到中国-喜马拉雅蕨类植物区系的影响。(3)纳板河保护区在地理亲缘关系上与云南大围山最为密切,与海南岛、哀牢山保护区的关系次之,与苍山、轿子雪山及雕林山保护区的联系较为疏远。     

黄土高原沟壑区小流域水分环境演变研究

以南小河沟为例,评价了水土保持工程措施、生物措施和生产力水平提高过程对流域水分环境条件的影响．结果发现南小河沟流域水环境在近５０年内发生了很大变化,坡面年总汇流量由治理前的１５．８３ｍｍ逐步减小为５．１６ｍｍ和现在的３．６６ｍｍ,未来１０年可能减到２．８６ｍｍ;塬面产流量却因庭院和道路面积增加以及建筑风格提高而逐步增大;坡地和沟谷的产流量逐步减小．同时生产力水平的提高进一步加强了水分小循环,削弱了水文大循环,改变了流域水均衡要素的定量分配     

松辽流域河流表层沉积物中有机氯农药的分布特征

利用气相色谱-电子捕获检测器(gas chromatography-electron capture detector,GC-ECD)对松辽流域重点污染河流22个表层沉积物样品的13种有机氯农药进行了分析.结果表明,大辽河流域有机氯农药含量为3.06～23.24 ng·g^-1,松花江流域为4.26～18.45 ng·g^-1.松辽流域沉积物中主要有机氯农药为六六六(HCH),松花江流域和大辽河流域表现出了不同的污染趋势.松花江沉积物中也有较高的滴滴涕(DDT)残留量.整个松辽流域都有较高含量的丙体六六六(γ-HCH),超过了其初始效应浓度,可能对该地区水生生物产生毒性效应.     

鄱阳湖流域泥沙流失及吸附态氮磷输出负荷评估

水土流失是吸附态氮磷输出负荷的主要方式,也是非点源污染评估的重要环节。鄱阳湖流域水土流失及其所带来的泥沙和吸附态氮磷等营养盐将直接影响到鄱阳湖的生态功能,进而影响着长江中下游水环境安全。科学估算鄱阳湖赣江、抚河、信江、饶河、修河等五大流域的土壤侵蚀量和吸附态氮、磷的输出负荷,将为鄱阳湖流域农业非点源污染控制及鄱阳湖生态建设和环境保护提供理论依据。以2007年全国第一次农业污染源普查数据和2007年江西省土壤质量调查数据为基础,利用RUSLE方程和GIS的空间统计功能,对江西省境内鄱阳湖流域的土壤侵蚀量和吸附态氮、吸附态磷的输出负荷进行估算。结果表明：基于RUSLE得到的2007年鄱阳湖五大流域输沙模数比较可信,鄱阳湖流域内泥沙、吸附态氮、吸附态磷的年输出负荷分别为1245183t、3383t和73t,其中赣江流域吸附态氮磷的年输出负荷最大,占鄱阳湖全流域的58.1%,抚河、饶河、信江、修河等分别占11.2%、7.2%、11.3%和12.2%。与流域内农业污染源总氮、总磷排放量相比较,尽管流域尺度内泥沙的输出负荷相对较大,但吸附态氮、磷的输出负荷较小,应该不是鄱阳湖水污染中总氮和总磷等营养盐的主要来源。     

东江流域森林水源涵养功能空间格局评价

东江流域森林水源涵养功能对于保障流域可持续发展具有重要作用。应用In VEST模型,结合东江流域土地覆盖分类数据、气候数据、土壤数据评估了东江流域森林水源涵养功能的空间分布。结果表明:东江流域森林生态系统水源涵养总量为47.29×10~8m~3,水源涵养功能最高为572.6 mm,平均水源涵养功能为204.15 mm。东江流域森林水源涵养功能在空间上呈现出不同的分布特征,流域内森林水源涵养功能随海拔升高呈现先上升后降低的趋势,在海拔900—1200 m范围,水源涵养功能平均值达到最大值270 mm;流域内森林水源涵养功能随坡度升高呈增加趋势,在坡度大于50°的区域,森林水源涵养功能平均值增加到327.2 mm,高于流域平均水平60%。流域水源涵养功能呈现中游下游上游的空间格局,流域上、中、下游地区的水源涵养总量占流域的比例分别为11%、72%、17%。     

城镇化过程中流域不透水面演变格局——以天津于桥水库流域为例

不透水面是衡量流域城镇化发展状况的一个关键指标,其扩展对流域生态水文过程产生重要影响.本文以天津于桥水库流域为例,在ENVI 5.1软件支持下,利用遥感影像获取1984、1994、2004和2013年4个时相的不透水面信息,采用修正后的归一化水体指数剔除水体信息,排除水体对不透水面提取精度的影响,运用线性光谱混合分析法生成流域不透水表面指数(ISA),并对其时空演变格局进行分析.结果表明: 模型均方根误差(RMSE)为0.005,像元精度为85.4%,试验结果准确可靠.1984—2013年,流域内不透水面覆盖度ISA平均值从0.16线性增长到0.23,在全流域范围内的不透水面面积增加了4.9%,其总不透水面面积增加近1倍.不透水面沿城镇区域呈现辐射式增长,沿子流域路网呈现填充式增长.不透水面覆盖度为中等等级的斑块形状不规则,破碎化程度最高.整个流域景观破碎化程度和多样性均逐年增高,人为干扰强度不断增大.