大沙河水库主要入库河流氮磷营养输入分析

为了解大沙河水库流域内营养盐输入对水库水质的影响,以 2011年3月~2012年2月大沙河水库5条主要入库河流(大沙河、白沙河、双石河、富食河和沃江河)的水文水质监测数据为依据,分析了这些入库河流的流量和氮磷营养盐浓度,并估算了外源负荷总量,旨在为水库进行高效和合理的流域规划以及水质保护方案的制定提供科学依据。结果表明:位于西南方向的白沙河年平均流量最大(1.01 m³·s^-1),西北部富食河流量最小(0.23 m³·s^-1)。各入库河流总氮平均浓度变化范围为1.62~4.37 mg·L^-1,总磷平均浓度范围为0.08~0.36 mg·L^-1,其中富食河氮和磷营养盐的浓度最高,大沙河总氮浓度最低,白沙河总磷浓度最低,总体上西北部河流的氮磷浓度高于西南部河流。全年大沙河水库总氮输入量为176.7 t,总磷输入量为13.7 t。在所有入库河流中,位于水库北部的沃江河对水库营养盐输入量贡献最大,氮、磷负荷分别占总输入量的33%和32%,位于西部的双石河氮负荷最小(12%),西南方向大沙河磷负荷最小(9%)。     

流溪河水库水动力学对营养盐和浮游植物分布的影响

流溪河水库2001年年降雨量2250mm,其中79％来自4月至9月的丰水期。入库流量变幅4．25～414．00m^3／s,近60％的入库水量流来自吕田河。流域营养盐输送量取决于流域降雨径流强度,吕田河高于玉溪河。由于营养盐被泥沙吸附沉积,丰水期湖泊区营养盐浓度明显低于河流区。浮游植物密度为17～1245cells／ml,以硅藻为主要优势种群。硅藻密度分布与水流流速和透明度的相关程度明显高于与营养盐和温度的相关程度。在丰水期,由于受水流和透明度的强烈控制,尽管营养盐供应比较充足,硅藻密度处于比较低的水平。丰水期硅藻密度稍低于枯水期,河流区明显低于大坝处。浮游植物香农-威纳多样性指数为0．97～2．75。受水库水动力学(水位波动等因素)的影响,最大浮游植物多样性出现于水位波动比较大的8月份,最小值则出现于水位波动最小的6月份。     

不同尺度景观空间分异特征对水体质量的影响——以深圳市西丽水库流域为例

由于景观格局对水体质量的影响是依赖于研究尺度、并且随着时间尺度和空间尺度的变化而变化的,因此探讨不同尺度上景观格局变化对水质的影响程度具有重要的研究价值。从深圳市水库流域水环境保护的需求出发,选择西丽水库及其汇水子流域为研究对象,以陈利顶等提出的景观空间负荷对比指数分析方法为基础,区分高度、坡度和距离3个空间要素计算了分区和累积景观空间负荷对比指数,继而利用该指数对比分析了不同时空尺度上“源”“汇”景观空间分异特征变化对水质的影响程度。研究结果表明,不同尺度上的景观空间分异特征可以显著影响“源”“汇”景观在非点源污染输出和削减方面贡献程度的对比关系,从而影响水体质量。由于不同尺度上景观空间分异特征的复杂性以及“源”“汇”景观在数量和类型方面差异的显著性,景观空间负荷对比指数的对比关系并不能良好地反映不同空间尺度上景观空间分异特征对水质影响的差异状况,因此必须 针对不同的研究尺度有选择的应用该方法来探讨景观空间分异特征对水质的影响程度。     

高州水库氮磷营养盐变化特征及水质管理对策

通过2012-2013 年对广东省高州水库氮磷营养盐的趋势变化进行分析, 探讨了水库中氮磷浓度的变化特征,并从水库管理与水动力学两方面对水库水质管理对策进行了讨论。研究结果表明: 高州水库总氮、总磷浓度均表现为丰水期高, 说明受强降雨的影响, 农业面源污染携带大量的氮磷随地表径流进入库区, 致使库区氮磷营养盐含量升高。其次, 入库河流是库区氮磷营养盐的主要来源。氮磷比分析结果表明, 高州水库流域内部分水体在时空上处于氮限制与磷限制交替出现的状态, 且氮磷比与总磷呈现显著地正相关, 进一步反应了高州水库水体主要处于磷素限制状态。水库上游集雨区人口分布集中, 大量的生活排污与农业面源污染的输入是库区营养盐的主要来源; 合理处理上游居民生活垃圾并严格控制工业污染, 是降低库区营养盐的主要途径。此外, 人为改变高州水库的出流方式, 可以抑制浮游植物及藻类的生长, 从而减少水库富营养化的可能。     

乌江中上游梯级水库氮磷滞留效应

目前世界河流普遍面临大规模筑坝拦截现状,原有河流自然形态逐渐向湖泊化转变,研究河流中氮磷营养盐物质的输送通量与滞留效应成了评价水坝水环境情况的关键问题。本研究详细调查了位于乌江流域中上游的洪家渡、东风和乌江渡3座水库的氮磷营养盐分布特征、输送通量及滞留效应。结果表明,洪家渡、东风和乌江渡3座水库TN年平均实际滞留率分别为20.2%、36.0%和-21.1%,TP年平均实际滞留率分别为5.4%、56.5%和-84.9%。3座水库因受到水文条件的不同、建库时间的长短和人为输入等因素影响,氮磷营养盐表现出不同的滞留现象及时空差异性。乌江渡水库氮磷营养盐的年平均滞留率因网箱养鱼的影响表现为负值。东风水库存在明显的氮磷滞留效应。洪家渡水库因受早期淹没植被再降解过程的影响,氮磷营养盐实际滞留效应弱于东风水库。     

漳泽水库主要入库河流氮、磷营养盐特征

以2006—2007年的漳泽水库3条入库河流(南漳河、石子河、绛河)的水文、水质调查数据为依据,研究了漳泽水库入库河流的主要水文变化特征、氮磷营养盐浓度及其通量的逐月动态。3条入库河流水体流速缓慢,水温适宜,年平均值在12.5℃～15.1℃。3—5月水温回升较快,夏季水温高,光照充足,易发生水华。3条入库河流中总氮含量年平均值在1.75～8.90mg·mL-1,总磷含量平均值在0.005～3.760mg·mL-1,氮磷营养盐浓度总体偏高,其中石子河贡献了48.3%的总氮和77.3%的总磷。溶解态无机氮(DIN)是氮的主要存在形式,而其中又以硝酸盐氮(NO3--N)为主,平均占到DIN的60%以上。氮磷通量季节性变化规律不明显,且月均波动较为平缓。点源污染是氮磷进入南漳河、石子河的主要途径,而绛河的氮主要来自面源污染。从保护漳泽水库的角度考虑,应重点控制南漳河和石子河的点源污染。     

广州流溪河氮磷浓度的季节变化和空间分布特征

广州市流溪河横跨北回归线,是典型的热带-亚热带过渡区河流。为了解该河流的营养盐分布特征,设置了20个采样点,于2015年2月至2017年2月进行季节性采样,共开展了8次水质监测,利用多元统计方法分析了主要营养盐(氮和磷)的季节动态和空间分布,并探讨影响营养盐时空分布的主要因素。结果表明:TN和TP的浓度范围分别为0.29~11.88 mg·L~(-1)与0.01~0.59 mg·L~(-1),TN浓度枯水期高于丰水期,总体上受降雨量的调节和河水稀释效应的影响; TP浓度丰水期高于枯水期,总体上受降雨量的调节及外源输入的影响; TN与TP在枯水期具有相似的季节变化特征,而在丰水期季节变化特征差异大;NO_3~--N和TN浓度的空间变化趋势相似,分为三个区段:流溪河水库上游的中值区河段,流溪河水库下游到街口大桥处的低值区河段和街口大桥下游的高值区河段,流溪河上游的两座大型水库对营养盐的滞留是导致其空间差异的主要因素之一; NH_4~+-N和TP浓度沿流域上游至下游总体上呈上升的趋势;三级河流氮和磷浓度显著高于一级河流和二级河流,河流氮、磷浓度与土地利用类型显著相关,建筑用地、裸露地和耕地所占比例的扩大会增加水体中TP、NH_4~+-N和NO_3~--N的浓度,而增加林地面积有助于水土保持和减少水体中氮、磷浓度。因此,上游水库的调节和下游城镇地区增加林地面积等方式对改善流溪河水质具有积极作用。     

不同时间尺度下基于绿量的草地水土保持效应研究

基于福建省长汀县河田镇土壤侵蚀试验小区连续四年的自然降雨、植被、产流和产沙观测数据, 分析了次降雨、月、季和年这四种时间尺度下草地植被绿量、降雨指标和保水、保土效应的变化特征及其相互关系。结果表明, 随着时间尺度的增大, 降雨和植被参数呈现或增或减的变化特征, 保水效应值(RE)变幅较小, 而保土效应值(SE)的变幅则缓慢降低。各时间尺度RE 的均值呈约10%-20%幅度的变化, RE 表征的草地保水效应以季尺度最好, 年尺度最差,而SE 表征的草地保土效应以月尺度最好, 季和次降雨尺度最差且接近。草地植被的保水效应多受制于降雨因素, 次降雨尺度下, RE 与降雨历时和降雨量关系密切, 较长时间尺度下最大30 分钟雨强是主要的控制因子。而保土效应则多受制于植被因素, 在次降雨尺度下, 贴近地表的枯叶层对保土效应的贡献值得重视, 在中等的月和季尺度保土效应同时受降雨和植被的影响, 而在较大的年时间尺度下, 草本植被绿量参数可有效表征植被的保土效应。可见, 在不同的时间尺度, 影响水土保持的诸要素呈现不同的变化和耦合特征, 水土保持效应亦存在差异, 因而在水土保持的研究和管理工作中应关注时间尺度的影响。     

3座南亚热带串联调水水库浮游植物群落的CCA分析

蛇地坑水库、南屏水库、竹仙洞水库是珠海市对澳门供水的3座串联水库,平均每天对澳门和拱北水厂供水2.2×10⁵m³。但水库自身流域集水难以满足水量需求,从广昌和平岗泵站从磨刀门水道抽水通过管道输入南屏水库,再进入竹仙洞水库或由洪湾泵站由洪湾水道抽水先进入蛇地坑水库后再进入竹仙洞水库。当竹仙洞水库供水不足时,蛇地坑水库泄水向竹仙洞水库输水洪湾泵站取水点位于磨刀门水道的下游,水质较差,长期调水入库增加了水库的营养盐负荷。蛇地坑水库的调水主要发生在1月份和3月份,水力滞留时间较长;南屏和竹仙洞水库的调水入库频繁,水体水力滞留时间短,平均为23.5和10天。2006年对3座水库进行了富营养化和浮游植物调查,营养盐浓度较低的蛇地坑水库4月份发生了蓝藻水华,而营养盐浓度较高的南屏和竹仙洞水库的蓝藻的生物量均很低,前者以硅藻为主要浮游植物类群,后者以绿藻为主。是什么原因导致这3座水库浮游植物群落结构的差异?蛇地坑水库的浮游植物以微囊藻、卷曲鱼腥藻、蓝纤维藻、小球藻和小环藻为优势;南屏水库浮游植物主要以假鱼腥藻、小环藻、针杆藻和微小多甲藻为优势种;竹仙洞水库浮游植物主要以衣藻、小环藻、游丝藻和隐藻等为优势种。三个水库相比较,蛇地坑水库4月份蓝藻占优势,其后主要以绿藻占优势,12月份是硅藻占优势;南屏水库4月份以绿藻为优势类群,随后的三个月以硅藻为优势类群,蓝藻在6月和8月为次优势类群,绿藻门的实球藻是12月份的优势种;竹仙洞水库浮游植物4月份丰度最高,绿藻门的四鞭藻是该时期的优势种,6月份竹仙洞水库浮游植物优势类群和4月份类似,但生物量明显下降,随后的三次采样,优势种更替较频繁,硅藻、绿藻、蓝藻和裸藻先后成为优势门类。应用典范对应分析(CCA) 对3座水库的浮游植物与环境因子关系分析:pH值、水位库容、正磷和水力滞留时间与浮游植物的分布关系最为直接;而透明度和降雨量对其也有一定的影响。在蛇地坑水库中,总磷、正磷酸盐浓度是影响蓝藻丰度的主要因子,硅藻则与库容和透明度有关。在南屏水库中,硅藻在短水力滞留时间期间丰度高,微小多甲藻的丰度主要出现在丰水期。竹仙洞水库的绿藻分成两个集群:四鞭藻、游丝藻等大型绿藻在低温、低水位和较长水力滞留时间的4月份较高;小球藻、栅藻、月牙藻等小型种类则与较高的水位和正磷酸盐浓度呈正相关。南屏水库与竹仙洞水库的浮游植物优势种类相似,蛇地坑水库的优势种则与它们存在较为明显的差异。从生物量上看丰水期南屏水库的硅藻为优势,而竹仙洞水库以绿藻为优势,主要是南屏水库截留了河流中含硅丰富的泥沙,且水体动荡更大的原因。影响这3座水库浮游植物群落组成的主要因素是水力滞留时间,短水力滞留时间抑制了南屏和竹仙洞水库中的蓝藻成为优势类群。     

基于SPI的石羊河流域气候干湿变化及干旱事件的时空格局特征研究

利用石羊河流域4个气象站1960—2013年逐月降水量资料,应用标准化降水指数(SPI)、游程理论等方法,分析石羊河流域近54年的气候干湿变化及不同时间尺度干旱事件时空演变特征。结果表明:1不同时间尺度SPI对降水量变化的敏感程度存在较大差异,时间尺度越小,SPI对一次降水的反应越明显。2石羊河流域年代际、年际和季的SPI在波动中均呈增加趋势,其中,冬季湿润化速度最快,对年湿润化过程的贡献最显著。31960—2013年,石羊河流域不同时间尺度干旱事件持续时间、干旱程度和干旱强度均呈减少趋势,且波动渐趋平缓;石羊河流域农业干旱和水文干旱最严重的时期分别为1964—1965年和1962—1964年。4两种时间尺度干旱事件持续时间的减少速度从上游至下游均逐渐变慢,上游乌鞘岭地区是农业干旱持续时间最长区域,永昌和下游民勤地区是水文干旱持续时间较长区域;两种时间尺度干旱事件干旱程度减少速度最快区域均在上游乌鞘岭地区;武威和民勤地区3月尺度干旱强度稍有上升,其它地区不同时间尺度干旱事件干旱强度均呈下降趋势,永昌地区是多尺度干旱事件干旱强度较大区域。     

流域非点源氮素流失空间分异特征的多时间尺度分析

流域非点源污染关键源区的定位是控制和治理流域非点源污染的重要问题,为进一步揭示时间尺度对流域非点源氮素流失空间分异特征的影响,通过构建山美水库流域SWAT模型,在对各个子流域的总氮(TN)流失强度进行模拟的基础上,从多年平均、多年月平均、场次暴雨洪水过程等3种时间尺度,对氮素流失的空间分异特征和关键源区进行分析,并通过多元线性相关分析,对自然和人为因素的影响进行研究.结果表明： 不同时间尺度下流域氮素流失空间差异均十分显著,氮素流失空间分异程度以多年月平均最高,场次暴雨洪水过程最低;桃溪亚流域氮素流失量最大,是非点源氮污染关键源区.不同时间尺度下,土地利用类型均是影响流域非点源氮素流失空间分布的主要因素,而降雨、径流等自然因子对氮素流失空间分异的影响仅表现在不施肥月份和部分不施肥场次的暴雨洪水过程,这种规律与土地利用及施肥具有显著空间变化、而降雨径流的空间变异程度低有关.     

Analyses of landuse change impacts on catchment runoff using different time indicators based on SWAT model

Previous researches mainly focused on the runoff responses to landuse change based on annual, seasonal or monthly time scales, there are few studies based on daily scale. We conducted a comprehensive investigation into runoff responses on the daily scale as well as annual and monthly time scales using SWAT, and compared the impacts of time scales with different time indicators quantitatively. Jinjiang, a coastal catchment of southeast China with a humid sub-tropical climate, was used for simulations. A calibrated SWAT model produced satisfactory reproduction of annual, monthly and daily runoff processes over a nine-year (2002–2010) period at three gauging stations. Runoff was then simulated and compared using the same meteorological input but two different landuse scenarios (1985 and 2006, with reduced forest and increased cropland and urbanized area). The results showed varying change in runoff among three time scales and three catchments. The annual runoff had the smallest increase between two scenarios, monthly runoffs had medium rates (increasing in all months except October–November), and daily runoff had the largest rates with the increase in flood peaks but decrease in drought flows, because of the variable influence on interception/evapotranspiration loss, percolation and antecedent soil water storage. Indicators of different time scales (annual runoff, monthly runoff, maximum 1-day and 5-day flood runoff, minimum 1-day and 7-day runoff) proved appropriate for analysing landuse change impacts.     

Silica retention in the Three Gorges Reservoir

A mass balance of dissolved silica (DSi) based on daily measurements at the inflow and outflow of the Three Gorges Reservoir (TGR) in 2007 and a more precise budget, with inflow, outflow, primary production, biogenic silica (BSi) settlement, dissolution of BSi in the water column and flux of DSi at the sediment–water interface in the dry season (April) of 2007 were developed. We address the following question: How much does the Three Gorges Dam (TGD) affect silica transport in the TGR of the Changjiang River (Yangtze River)? The DSi varied from 71.1 to 141 μmol/l with an average of 108 μmol/l, and it ranged between 68.1 and 136 μmol/l, with an average of 107 μmol/l in inflow and outflow, respectively, in the TGR in 2007. The linear relationship of DSi between inflow and outflow water is significant (r = 0.87, n = 362, p < 0.01). Along the main stream of the TGR, the DSi concentration decreases with an average concentration of 84.0 μmol/l in the dry season. However, the stratification of DSi was not obvious in the main channel of the TGR in the dry season. The BSi is within the range of 0.04–5.00 μmol/l, with an average concentration of 2.1 μmol/l in the main channel of the TGR, while it is much higher in Xiangxi Bay (1.30–47.7 μmol/l, 13.1 μmol/l) than in the main stream of the TGR and the other bays. After the third filling of the TGR, approximately 3.8% of the DSi was retained by the TGR based on a 12-month monitoring scheme in 2007, which would slightly reduce nutrient fluxes of the Changjiang River to the East China Sea (2%). DSi was lost during January to June and November, whereas the additions of DSi were found during the other months in 2007. The budget results also indicate that there is a slight retention of DSi. The retention of DSi in the reservoir is approximately 2.9%, while BSi is approximately 44%. Compared with the total silica load, the retention of DSi and BSi in the reservoir is only 5.0% in the dry season. With its present storage capacity, the reservoir does not play an important role as a silica sink in the channel of the TGR. The DSi load is significantly related to discharge both in inflow and outflow waters (p < 0.01). DSi retention, to some extent, is the runoff change due to impoundment.     

Phytoplankton strategies and time scales in a eutrophic reservoir

Phytoplankton species groups were studied in a eutrophic reservoir at different time scales (daily, weekly, monthly and yearly). Four strategic groups along the r-K continuum were defined and their seasonal time courses were followed. Their temporal distribution of relative biomass reflected resource partitioning because each strategic group dominated the phytoplankton community at different times in the year. However, the relationships between strategic groups changed with the time scale involved. At the daily scale an inverse relationship between r- and K-groups occurred whereas at supradaily scales such relationships did not hold. Species groups reflected strategic groups. No relationship between population growth and losses was found, suggesting that both were not counterbalanced. In the long term (supraannual) the phytoplankton community changed very much in this reservoir, its ecological memory being small as compared with that of lakes.     

辽河流域丰枯遭遇下水库调度

利用Copula函数分析辽河流域水库入库流量边缘分布及其生态径流量,得出水库可调水范围,在满足生态流量基础上,保障辽河流域城市供水。研究表明:(1)英那河与张家堡水库入库流量以对数正态分布为最佳边缘分布,其余水库入库流量最佳边缘分布均为广义极值分布,同时,Gumbel Copula与Frank Copula函数对水库入库流量拟合效果最优;(2)7组水库组合中有3组水库组合入库流量(白石与锦凌、白石与青山、张家堡与碧流河)丰枯异步概率高于丰枯同步概率,且枯枯遭遇概率较低,分别为13%,12%以及13%。其余4组水库组合枯枯遭遇概率皆高于27%,水库间入库水文过程发生同枯概率可能性较大;(3)使用90%保证率逐月频率计算法所求流量是辽河流域9个水库的最佳生态径流量。(4)枯水月水库间易发生枯枯遭遇,当水库间入库径流皆低于最小生态径流标准,水库无法对各自调水城市进行供水调度,其中,大伙房与桓仁、白石与锦凌、白石与青山主要在1、2月无法对沈阳、凌海和绥中县进行输水,桓仁与清河水库仅在2002年5月无法对开原进行供水,此时需考虑水库提前蓄水以满足城市用水需求。碧流河、英那河和张家堡水库虽两两存在无法输水情况,但可三者联动对大连进行联合调度,缓解无法输水问题。     

Collection strategies for quantifying protist assemblages in temperate headwater streams

We aimed at indicating some regularities of a constructed wetland treating agricultural runoff in China. The regularities, including the nitrogen removal capacity all year round, the nitrogen distribution pathways, and the nitrogen species removal kinetics, of a free water surface constructed wetland (2,800 m²) in the Dianchi Valley, which has been in operation for 27 months, were studied. The planted Phragmites australis and Zizania caduciflora were harvested biannually. The average inflow rate was recorded by an ultrasonic flow instrument, and then the hydraulic loading rate (HLR) and hydraulic retention time (HRT) were calculated. The average inflow and outflow concentrations of total nitrogen (TN), ammonia, and nitrate were measured, while the corresponding removal rates were calculated, showing better results than other constructed wetlands. Then the distribution pathways of nitrogen were analyzed, which indicated that plant harvesting was more important in wetland-treated agricultural runoff than in domestic wastewater. The reason for a good nitrogen removal capability and the obvious function of plants in the present wetland is the sound climate and intermittent inflow in the wetland. Results showed that inflow load had significant correction with both TN and ammonia removal efficiency. HLR, inflow rate, inflow nitrogen concentration, and temperature had significant and positive correction with both TN and ammonia removal. However, HRT had negative correction with both TN and ammonia removal, and the nitrate removal efficiency and parameters mentioned earlier were not significantly correlated. The rate constant values for nitrate and ammonia in summer were obviously larger than in winter. It is possible that bacterial and microbial activities were more active in summer than winter, and more conducive to bacterial and vegetative growth in summer than winter. Since this study was a pioneer for the implementation of constructed wetlands in China treating agricultural runoff, it has proved that this eco-technology could be used effectively for water quality enhancement in China and other areas with a similar climate.     

Phytoplankton structure in two contrasting cascade reservoirs (Paranapanema River,Southeast Brazil)

A series of eleven reservoirs was constructed in the Paranapanema River, southeast Brazil, for hydropower production. The phytoplankton structure and its relations with the environmental variables were studied in two of these reservoirs: a large upstream located storage system (high water retention time) and a small run-of-river system (short water retention time). The samples were collected quarterly for two consecutive years, at four sampling stations in each reservoir. Higher phytoplankton richness was observed in the semi-lotic compartments. Higher values of diversities were observed in the upper region of the run-of-river reservoir, under the influence of the larger storage reservoir discharges, and lower values were observed in deeper layers of this same reservoir. The pronounced variation on seasonal rain precipitation and operational water releases, retention time and quota had major influence in the phytoplankton assemblages. The influence of other environmental variables was also indicated by a canonical correlation analysis. Chlamydophyceae, Dinophyceae, Zygnemaphyceae, Chrysophyceae, Chlorophyceae, Bacillariophyceae and Cyanobacteria were positively correlated with higher transparency and depth; Euglenophyceae with temperature and Cryptophyceae with total phosphorus, dissolved oxygen, conductivity, turbidity, total nitrogen and total suspended solids. The influence of the storage reservoir on the phytoplankton of the downstream run-of-river reservoir was more evident in the dry period. During the rainy period the lateral tributaries effects seems to have a higher influence, especially on the smaller studied reservoir.     

Impact of migratory snow geese on nitrogen and phosphorus dynamics in a freshwater reservoir

1. We examined impacts of nutrient loading, particularly of nitrogen and phosphorus, from greater snow geese (Chen caerulescens atlantica) on a reservoir in south‐eastern Pennsylvania, U.S.A. Approximately 100 000 geese use the reservoir for 2–6 weeks prior to their spring migration northward. 2. We estimated the magnitude of nutrient loading by geese during their presence and compared that to surface input and output rates. We also conducted nutrient limitation bioassay experiments to examine patterns of algal nutrient limitation upstream and downstream of the reservoir. 3. During their presence from 1 February to 27 March 2001, snow geese contributed 85–93% of the phosphorus and 33–44% of the nitrogen loaded to the reservoir. Both nutrients were exported from the reservoir slowly rather than as a quick pulse. Consequently, phosphorus concentrations in the outflow were higher than in the inflow from February to the end of July. However, nitrogen concentrations were consistently lower in the outflow than the inflow. 4. Nutrient limitation bioassays conducted in June and July indicated that primary production in the outflow was limited by nitrogen whereas the inflow was co‐limited by nitrogen and phosphorus. Further downstream from the reservoir, primary production was consistently phosphorus limited. Therefore, nitrogen limitation persisted long after the geese had left, but was relatively localised.     

不同尺度流域日径流分形特征

基于分形理论和实测流域日径流长序列资料,研究了中尺度流域（武水流域）和小尺度流域（贞福流域和双溪流域）日径流的分形特征.结果表明：相同时间尺度和不同日径流门限值条件下,相同空间尺度流域间和不同空间尺度流域间日径流均具有显著的分形特征,具有自相似性.随着门限值的增大,不同空间尺度流域间日径流的分形盒维数均逐步减小;当时间尺度在120～150 d时,不同空间尺度流域日径流的分形维数点集均逐渐趋向饱和,当时间尺度大于该值时,就有出现一定门限值径流的可能性.