Amount and reactivity of dissolved organic matter export are affected by land cover change from old-growth to second-growth forests in headwater ecosystems     

Timothy S. Fegel  Claudia M. Boot  Timothy P. Covino  Kelly Elder  Edward K. Hall  Banning Starr  James Stegen  Charles C. Rhoades 《水文研究》2021,35(8):e14343

Headwater forest ecosystems of the western USA generate a large portion of the dissolved organic matter (DOM) transported in streams across North America. Land cover changes that alter forest structure and species composition affect the quantity and composition of DOM transferred to aquatic ecosystems. Clear-cut harvesting affects ~1% of the forest area of North America annually, leaving most western forests in varying stages of regrowth and the total area of old-growth forest is decreasing. The consequences of this widespread management practice on watershed carbon cycling remain unknown. We investigated the role of land cover change, because of clear-cut harvesting, from mixed-species old-growth to lodgepole pine-dominated second-growth forest on the character and reactivity of hillslope DOM exports. We evaluated inputs of DOM from litter leachates and export of DOM collected at the base of trenched hillslopes during a 3-year period (2016–2018) at the Fraser Experimental Forest in north-central Colorado, USA. Dissolved organic carbon and total dissolved nitrogen were higher in lateral subsurface flow draining old- versus second-growth forest. Fluorescence spectroscopy showed that the DOM exported from the old-growth forest was more heterogeneous and aromatic and that proteinaceous, microbially processed DOM components were more prevalent in the second-growth forest. Biological oxygen demand assays revealed much lower microbial metabolism of DOM in litter leachate and subsurface exports from the old-growth forest relative to second growth. Old-growth and second-growth forests are co-mingled in managed ecosystems, and our findings demonstrate that land cover change from a mixture of conifer species to lodgepole pine dominance influences DOM inputs that can increase the reactivity of DOM transferred from terrestrial to aquatic ecosystems.  相似文献   

EFFECTS OF HARVEST STAGE ON THE TOTAL LIPID AND FATTY ACID COMPOSITION OF FOUR CYLINDROTHECA STRAINS     

梁英  麦康森  孙世春 《中国海洋湖沼学报》2002,(2)

ＩＮＴＲＯＤＵＣＴＩＯＮＰｅｏｐｌｅｓｈｏｗｅｄｇｒｅａｔｉｎｔｅｒｅｓｔｓｉｎｍｉｃｒｏａｌｇａｅｄｕｅｔｏｔｈｅｉｒｇｏｏｄｃｈａｒａｃｔｅｒｉｓｔｉｃｓ,ｓｕｃｈａｓｈｉｇｈｅｆｆｉ ｃｉｅｎｃｙｏｆｕｓｉｎｇｓｏｌａｒｅｎｅｒｇｙ,ｓｍａｌｌｓｉｚｅ ,ｎｕｔｒｉｔｉｏｎａｌｖａｌｕｅ ,ｒａｐｉｄｇｒｏｗｔｈａｎｄｍｕｌｔｉｐｌｉｃａｔｉｏｎｒａｔｅ .Ｍｉ ｃｒｏａｌｇａｅｈａｖｅａｎｉｍｐｏｒｔａｎｔｒｏｌｅｉｎｍａｒｉｃｕｌｔｕｒｅａｓｆｏｏｄｆｏｒｌａｒｖａｌｓｔａｇｅｓｏｆｃｒｕｓｔａ…  相似文献   

采伐剩余物管理方式对人工林土壤黑碳和黑氮的影响     

姜丹  何宗明  尹云锋  范少辉  黄志群  万晓华 《亚热带资源与环境学报》2014,(3):68-74

黑碳（Black carbon,BC）是土壤惰性碳库的重要组成部分,在土壤碳循环中发挥着关键作用,而黑氮（Black nitrogen,BN）同样对碳封存具有重要作用。本研究以15年生杉木人工林为对象,采用化学氧化法研究2种采伐剩余物管理方式（炼山和保留采伐剩余物）对杉木人工林表层土壤（0~10 cm）BC和BN含量及储量的影响。结果表明,5次采样年份,炼山和保留采伐剩余物的BC平均含量分别为2.99~3.70 g/kg和3.52~4.36 g/kg,储量分别为3.24 t/hm^2和3.87 t/hm^2;炼山和保留采伐剩余物的BN平均含量均为0.12 g/kg,储量分别为0.12 t/hm2和0.11 t/hm^2。方差分析表明,2种采伐剩余物管理方式下的土壤BC和BN含量以及储量年际差异均不显著（P〉0.05）。由此可见,采伐剩余物管理方式对杉木人工林土壤BC和BN的长期效应并不显著。  相似文献   

Natural and anthropogenic controls on sediment rating curves in northern California coastal watersheds     

Adam Fisher  Patrick Belmont  Brendan P. Murphy  Lee MacDonald  Ken L. Ferrier  Kai Hu 《地球表面变化过程与地形》2021,46(8):1610-1628

The watersheds along the north coast of California span a wide range of geologic settings, tectonic uplift rates, and historic timber harvest activity. Known trends in how each of these factors influence erosion rates provides an opportunity to examine their relative importance. We analyzed 71 watersheds within nine larger river basins, investigated the factors influencing suspended sediment rating curves (SRCs), investigated how SRCs varied among our study watersheds, and used Random Forest modeling (RFM) to determine which environmental characteristics and land management metrics influence SRC shapes, vertical offsets, and slopes. While SRCs typically take the form of a power function, they also can exhibit threshold or peak relationships. First, we found both power and threshold relationships for the SRCs within our study watersheds. Second, the SRC offsets and slopes systematically varied with regional tectonic uplift. Third, SRC offsets increased in several watersheds following intensive timber harvest events and SRC slopes decreased due to a greater relative increase in suspended sediment concentration at lower flows than higher flows. Our RFM correctly classified 96% of the SRC shapes using two near-channel metrics; near-channel precipitation-sensitive deep-seated landslide susceptibility and near-channel soil erodibility. Our RFM models also showed that timber harvest activity and near-channel local relief can explain 40% of the variability in SRC offsets, whereas tectonic uplift rates, millennial-scale erosion rates, and precipitation patterns explain 40% of the variability in SRC slopes.  相似文献   

全国晚稻气候年景评价方法研究   总被引：1，自引：0，他引：1       下载免费PDF全文

娄秀荣  侯英雨 《气象》2003,29(2):21-25

通过对晚稻产量和气象资料的处理，划分出全国晚稻主产区的丰歉年型及其主要气象要素的特征等级。在不同区域气候年景特征等级分析的基础上，建立了晚稻气候年景综合评价模型，并在2001年农业气象业务服务中的丰歉年型评价中取得了较好的效果。  相似文献   

Routes to illegal residence: A case study of immigration detainees in the United Kingdom     

Richard Black  Ronald Skeldon 《Geoforum》2006,37(4):552-564

This paper investigates the various ways in which migrants to the United Kingdom become illegally resident. Drawing on findings from a pilot study of undocumented migrants held in detention centres in the United Kingdom, it explores why respondents had chosen to come to the United Kingdom, how they came, and how they ended up residing illegally. In contrast to common assumptions about ‘illegal immigrants’, the present study reveals the diversity of paths into illegal residence, and stresses the importance of perceived safety, both from ‘persecution’ and more generalised violence, as well as the ease of finding work in a strong economy. The sample included both those who had knowingly come to the United Kingdom to live and work illegally, and those who had become illegal during their stay.  相似文献   

棉花年景评价方法          下载免费PDF全文

王建林  太华杰 《气象》1997,23(4):24-27

文章介绍两种棉花年景评价方法：综合气象要素评价法和相似分析评价法。前者是将ＡＢ报收到的旬平均气温、旬降水量和旬日照时数按照一定的原则组合成为综合气象要素，分析历史综合气象要素和棉花产量丰歉，得出其评价指标，依据指标，进行实时棉花年景评价；后者是根据历史资料，确定丰歉年型，利用相似分析原理，得出相似分析评价指标，根据指标，判断棉花产量的丰歉。结果表明，这两种评价方法在棉花产量丰歉评价中，准确率都在９０％以上。  相似文献   

甘肃省服务干旱指标的初步研究   总被引：6，自引：1，他引：5  

刘德祥  王宝灵  瞿汶 《干旱气象》1998,(3)

利用前期底墒降水和当时降水、气温,确定了适合甘肃的干旱指数,提出了用干旱指数划分服务干旱等级的指标和气候年景划分标准。用该等级和标准与降水量、土壤湿度比较分析,能较客观地反映旱涝实际情况。  相似文献   

An evaluation of the implicit management procedure used for some ICES roundfish stocks   总被引：1，自引：5，他引：1  

Kell  L.T.; Pilling  G.M.; Kirkwood  G.P.; Pastoors  M.; Mesnil  B.; Korsbrekke  K.; Abaunza  P.; Aps  R.; Biseau  A.; Kunzlik  P.; Needle  C.; Roel  B.A.; Ulrich-Rescan  C. 《ICES Journal of Marine Science》2005,62(4):750-759

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Institutional designs to face the dark side of total allowable catches     

del Valle  Ikerne; Astorkiza  Kepa 《ICES Journal of Marine Science》2007,64(4):851-857

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