中国水产科学  2021, Vol. 28 Issue (12): 1602-1611  DOI: 10.12264/JFSC2021-0055
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引用本文 

马宝珊, 魏开金, 徐进, 卢建超, 徐滨, 朱祥云. 雅砻江下游及其主要支流安宁河着生藻类多样性与空间分布[J]. 中国水产科学, 2021, 28(12): 1602-1611. DOI: 10.12264/JFSC2021-0055.
MA Baoshan, WEI Kaijin, XU Jin, LU Jianchao, XU Bin, ZHU Xiangyun. Diversity and spatial distribution of periphytic algae in the lower reaches of the Yalong River and its main tributary, the Anning River[J]. Journal of Fishery Sciences of China, 2021, 28(12): 1602-1611. DOI: 10.12264/JFSC2021-0055.

基金项目

国家自然科学基金项目(51809280).

作者简介

马宝珊(1983–),女,博士,副研究员,研究领域为水域生态及鱼类生态学研究. E-mail: baoshanma@yfi.ac.cn

通信作者

魏开金,研究员. E-mail: weikj@yfi.ac.cn

文章历史

收稿日期:2021-02-02
修改日期:2021-02-24
雅砻江下游及其主要支流安宁河着生藻类多样性与空间分布
马宝珊1,魏开金1,徐进1,卢建超1,徐滨1,朱祥云1,     
1. 中国水产科学研究院长江水产研究所,湖北 武汉 430223
摘要:于2018年6–8月对雅砻江下游干支流的着生藻类进行调查,并以其主要支流安宁河为代表,重点研究河流纵向梯度下着生藻类的空间分布格局(102°6′6″E, 28°46′21″N~101°49′22″E, 26°38′38″N)。结果显示:雅砻江下游共鉴定着生藻类95种,以硅藻(Bacillariophyta)、绿藻(Chlorophyta)和蓝藻(Cyanophyts)为主。雅砻江干流物种数最多,优势种为曲壳藻属未定种 (Achnanthes sp.)、异极藻属未定种 (Gomphonema sp.)和胶质细鞘丝藻(Leptolyngbya gelatinosa)等;其次为安宁河干流,优势种为曲壳藻属未定种和细小隐球藻(Aphanocapsa elachist);安宁河支流物种丰富度最低,优势种主要为曲壳藻属未定种、胶质细鞘丝藻和异极藻属未定种等。着生藻类平均密度呈雅砻江干流<安宁河支流<安宁河干流趋势。沿着河流纵向梯度,安宁河干流物种丰富度逐渐增加,硅藻密度比例渐趋下降,而绿藻和蓝藻的比例却逐渐升高。水温、浊度和底质类型与雅砻江下游流域着生藻类多样性和空间分布格局密切相关;流速和海拔是影响纵向梯度下安宁河着生藻类分布的主要环境因子。本研究旨在为高原山区河流的水生生物多样性保护提供依据,并为该流域食物网构建提供基础资料。
关键词雅砻江下游    安宁河    着生藻类    纵向梯度    环境因子    
Diversity and spatial distribution of periphytic algae in the lower reaches of the Yalong River and its main tributary, the Anning River
MA Baoshan1,WEI Kaijin,1,XU Jin1,LU Jianchao1,XU Bin1,ZHU Xiangyun1    
1. Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Wuhan 430223, China
Abstract:The Yalong River is the biggest tributary of the Jinsha River. Periphytic algae are an important component of the aquatic ecosystem, playing an important role in the energy flow and matter cycling of river food chains. To understand the community structure of periphytic algae and its relation to the environmental conditions, surveys were conducted in the lower Yalong River and its tributaries between June and August 2018 (102°6′6″E, 28°46′21″N–101°49′22″E, 26°38′38″N). A total of 95 species of periphytic algae belonging to 49 genera of five phyla were identified, among which Bacillariophyta (57 species) were the dominant taxa, followed by Chlorophyta (20 species) and Cyanophyta (14 species). The species richness was highest in the Yalong River, followed by the Anning River, and lowest in the Anning River tributaries. The dominant species in the lower Yalong River were Achnanthes sp., Gomphonema sp., Leptolyngbya gelatinosa, Synedra sp., Navicula sp., Oocystis naegelii, and Cymbella sp.; the dominant species in the Anning River were Achnanthes sp. and Aphanocapsa elachista; and the dominant species in the tributaries of the Anning River were Achnanthes sp., L. gelatinosa, Gomphonema sp., Navicula sp., and Cocconeis placentula. The algal density in the Yalong River was significantly lower than that in the Anning River and its tributaries. The algal density in the Anning River was higher than that in the tributaries. Upstream to downstream, the species richness in the Anning River increased under a longitudinal gradient, the proportion of Bacillariophyta in the Anning River decreased gradually, while the proportion of Chlorophyta and Cyanophyta increased gradually. Redundancy analysis indicated that the periphytic algae structure in the lower Yalong River was relative to the ecological factors, such as water temperature, turbidity, and substrate type. Current velocity and altitude were the main environmental factors affecting the distribution of periphytic algae in the Anning River under a longitudinal gradient. This study provides a scientific basis for the research on and conservation of biodiversity in high-altitude areas.
Key wordslower reaches of Yalong River    Anning River    periphytic algae    longitudinal gradient    environmental factors    

着生藻类又称为周丛藻类或底栖藻类,生长于水中各种基质表面,其物种数较多,群落结构复杂,是河流生态系统中重要的生物类群之一[1-2]。着生藻类是水域生态系统重要的初级生产者,在维持生态系统多样性、能量流动和物质传递方面起着重要作用。在一些流速适宜的河流中,该类群所固定的初级生产力远比浮游植物和水生维管植物高[3]。随着社会经济的发展,水质恶化、梯级水电站建设、岸坡硬化护砌、采石挖沙等人为干扰显著改变了河流环境,导致着生藻类多样性和群落结构发生变化[4-6]。由于着生藻类具有营固着生活、繁殖迅速和生命周期较短等特性,其数量和种类组成对环境变化和各种干扰较为敏感,对水体富营养化、水文变化以及其他污染物都有较快的响应,进而在河流生物多样性监测与健康评价中应用广泛[6-7]

通常,着生藻类的分布格局受到河流等级、河流纵向环境梯度等因素的影响,从而具有明显的空间异质性。环境因子与着生藻类的关系非常密切,已有研究表明,水温、水深、流速和营养盐等环境因子对河流着生藻类群落结构有着重要影响[8-11]。而山区河流中流速和底质类型等环境因子对着生藻类多样性的影响研究较少[12-13],纵向梯度下河流环境与着生藻类空间分布格局的研究则更为少见。

雅砻江是金沙江最大的一级支流,水电资源丰富。目前雅砻江下游规划的5座梯级(即锦屏一级、锦屏二级、官地、二滩和桐子林)已全部建成,河流环境明显改变。作为雅砻江下游的最大支流,安宁河水生生物多样性对维持雅砻江水域生态系统结构和功能具有重要意义。而目前有关雅砻江下游及安宁河水生生物群落的研究报道较少,仅见于吴乃成等[12]和渠晓东等[14]对雅砻江锦屏段着生藻类和底栖动物的多样性分析,以及马宝珊等[15-18]对安宁河中游水生生物群落结构及其关键环境因子的分析。在此背景下,为理解河流环境变化下水生生物多样性格局及关键因子,本研究对雅砻江下游及支流安宁河的着生藻类多样性及空间格局进行研究,并以安宁河为代表,着重分析河流纵向梯度下着生藻类的空间格局,以期为高原山区河流的水生生物多样性保护提供依据,并为该流域食物网构建提供基础资料。

1 材料与方法 1.1 采样时间和地点

2018年6–8月在雅砻江下游干支流共设置31个样点进行调查采样,其中雅砻江干流采样点10个,一级支流安宁河干流采样点14个,二级支流安宁河支流采样点7个(图1)。

图1  雅砻江下游着生藻类调查样点分布示意图雅砻江下游干流10个样点(Y1~Y10),安宁河干流14个样点(A1~A14),安宁河支流7个样点(Z1~Z7). 安宁河干流A1~A4为上游,A5~A10为中游,A11~A14为下游. Fig. 1  Sampling sites for periphytic algae in the lower Yalong RiverThe Yalong River, 10 sites (Y1–Y10); the Anning River, 14 sites (A1–A14); the tributaries of the Anning River, 7 sites (Z1–Z7). The upper Anning River, A1–A4; the middle Anning River, A5–A10; the lower Anning River, A11–A14.
1.2 环境参数的测定

采样期间,对采样点的河流环境进行了现场记录:经纬度、海拔、河宽、水深、透明度、流速、水温、溶氧、pH、电导率和浊度等。将每个调查河段分为3个等距的断面,在每个断面上测量河宽。在每个断面上选取3个等距截点,在每个截点处测量水深(Peedtech SM-5)和透明度,并在每个截点60%水深处测量流速(Global Water FP-311)。水温、溶氧、pH、电导率和浊度指标通过YSI-EXO2便携式多参数水质分析仪获取[19]。将底质类型分为5类:(1)淤泥和黏土(粒径<0.06 mm); (2)沙(粒径0.06~2 mm); (3)砾石(粒径2~64 mm); (4)卵石(粒径64~256 mm); (5)大石(粒径>256 mm)[20]。经现场目测后,计算各个样点各底质类型的百分比[21]

1.3 样本的采集和鉴定

在采样河段上下范围100 m内,依据河流生境不同(水深和流速等),挑选 3块石头,每块石头选取约9 cm2 (3 cm×3 cm的方形塑料片)的平面,用硬毛牙刷反复刷取后装入50 mL样本瓶中,鲁哥氏液固定[22]

参考胡鸿钧等[23]以及朱蕙忠等[24]进行着生藻类的种类鉴定和数据记录。每个样品计数2片(0.1 mL浮游植物计数框),每片100个小格,再取其平均值。

1.4 数据分析

优势度计算公式:Y=(Ni /N)Fi,式中,Fi为物种i的出现率,Ni为物种i的密度,N为总密度。本研究将Y≥0.02 的物种定为优势种[25]

着生藻类物种多样性指数计算如下:

Margalef’s richness指数(D): D=(S–1)/lnN

Shannon–Wiener指数(H′): H=–ΣPi (lnPi)

Pielou’s evenness指数(J): J=H′/lnS

式中,Pi为物种i的个数百分比,N为总个数,S为群落总物种数[26]

采用Canoco 4.5分析着生藻类群落结构与环境因子的相关性。分析前,先对环境因子(除pH)和密度数据进行对数化处理,使数据呈正态分布;再采用除趋势对应分析(DCA)对着生藻类密度数据进行排序,依据排序轴长度决定哪种模型更为合适。由于排序轴长度小于3.0,故采用冗余分析(RDA)解析着生藻类密度与环境因子的关系。RDA分析中通过前选法和蒙特卡罗检验排除贡献较小的环境因子[27]。本研究选取优势度>0.001的物种进行RDA分析。

采用SPSS16.0中的方差分析(ANOVA)和Tukey’s post hoc test检验不同河流及不同河段间环境因子和着生藻类多样性指数的差异性,显著水平为0.05。文章作图采用Origin2016。

2 结果与分析 2.1 环境参数

雅砻江下游干流、安宁河干流及安宁河支流的环境参数见表1。调查显示,随着河流级别的升高,海拔和流速呈下降趋势,水深、河宽、水温和电导率呈上升趋势。雅砻江干流的水深、河宽、溶氧和电导均高于安宁河干支流。浊度以安宁河干流最大,其次为安宁河支流,雅砻江干流最低。不同河流之间的水温差异不大。雅砻江干流透明度较大,安宁河干流水较浑浊,而安宁河支流大部分为清澈见底的溪流。

沿“上游–下游”纵向梯度,随着安宁河海拔的下降,水深、河宽、水温和电导率呈上升趋势。安宁河干流不同河段之间的海拔和水温相差很大,中下游的水深、河宽和电导率均高于上游。不同河段之间的流速、溶氧和浊度无明显差异(表2)。

表1  雅砻江下游及其一级、二级支流环境参数 Tab. 1  Environmental parameters of the lower Yalong River and its tributaries
表2  安宁河干流环境参数 Tab. 2  Environmental parameters in the mainstream of the Anning River
2.2 着生藻类群落结构 2.2.1 着生藻类物种丰富度及组成

本研究共采集着生藻类95种,隶属于5门49属。其中硅藻门(Bacillariophyta) 24属57种,绿藻门(Chlorophyta)15属20种,蓝藻门(Cyanophyta)7属14种,甲藻门(Dinophyta) 1属2种,裸藻门(Euglenophyta) 2属2种。其中雅砻江干流物种丰富度最高(57种),安宁河干流次之(52种),安宁河支流最低(49种,表3)。物种组成上,雅砻江干流中除了蓝藻、硅藻和绿藻种类以外,还有少量甲藻和裸藻种类;而安宁河干支流中仅采集到蓝藻、硅藻和绿藻。

雅砻江干流优势种为曲壳藻属未定种(Achnanthes sp.)、异极藻属未定种(Gomphonema sp.)、胶质细鞘丝藻(Leptolyngbya gelatinosa)、针杆藻属未定种(Synedra sp.)、舟形藻属未定种(Navicula sp.)、大卵囊藻(Oocystis naegelii)和桥弯藻属未定种(Cymbella sp.),安宁河干流优势种为曲壳藻属未定种和细小隐球藻(Aphanocapsa elachist),安宁河支流流优势种为曲壳藻属未定种、胶质细鞘丝藻、异极藻属、舟形藻属和扁圆卵形藻(Cocconeis placentula)(表3)。

沿“上游–下游”纵向梯度,安宁河干流藻类物种丰富度呈上升趋势(表3);安宁河上游全部为硅藻,中游为硅藻和绿藻,下游则蓝藻、硅藻和绿藻均有。安宁河中上游的优势种与下游差异明显,中上游优势种全部为硅藻种类(舟形藻属未定种、桥弯藻属未定种、异极藻属未定种、扁圆卵形藻和曲壳藻属未定种),而下游的优势种仅有蓝藻门一种(细小隐球藻)。

2.2.2 着生藻类密度

雅砻江干流着生藻类平均密度为12.67×108 ind/m2,安宁河干流为72.91×108 ind/m2,安宁河支流为30.96×108 ind/m2。雅砻江干流着生藻类密度低于安宁河干支流,安宁河干流着生藻类密度高于支流。安宁河干流密度以蓝藻占优势,支流密度以硅藻占据优势(图2)。

安宁河上游着生藻类平均密度为2.72×108 ind/m2,中游为17.25×108 ind/m2,下游为226.59× 108 ind/m2。沿着河流纵向梯度,由上游至下游,安宁河干流硅藻比例渐趋下降,而绿藻和蓝藻的比例却逐渐升高,下游密度以蓝藻占据绝对优势(99.20%) (图2)。

2.2.3 着生藻类多样性

丰富度指数(D)以雅砻江干流最高,其次为安宁河支流,安宁河干流最低。多样性指数(H′)以雅砻江干流最高,其次为安宁河干流,安宁河支流最低。均匀度指数(J)以安宁河干流最高,其次为雅砻江干流,安宁河支流最低(图3a)。但从方差分析结果来看,雅砻江下游不同河流等级的着生藻类丰富度指数(D)、多样性指数(H′)和均匀度指数(J)均无显著性差异。

纵向梯度下安宁河干流着生藻类丰富度指数(D)呈上升趋势。而多样性指数(H′)和均匀度指数(J)却以中游最高,其次为下游,上游最低(图3b)。安宁河不同河段着生藻类的多样性指数均无显著性差异。

表3  雅砻江下游着生藻类种类数、主要优势种及优势度 Tab. 3  Species number and dominant periphytic algae and their dominance in the lower Yalong River
图2  雅砻江下游着生藻类的密度DA:安宁河下游,MA:安宁河干流,MA′:安宁河中游,MY:雅砻江干流,TA:安宁河支流,UA:安宁河上游. Fig. 2  Density of periphytic algae from the lower Yalong RiverDA: downstream of the Anning River; MA: the mainstream of the Anning River; MA′: midstream of the Anning River; MY: the mainstream of the Yalong River; TA: the tributaries of the Anning River; UA: upstream of the Anning River.
图3  雅砻江下游流域着生藻类的物种多样性MY:雅砻江干流;MA:安宁河干流;TA:安宁河支流;DA:安宁河下游;MA′:安宁河中游;UA:安宁河上游. Fig. 3  Species diversity of periphytic algae in the lower Yalong River basinMY: the mainstream of the Yalong River; MA: the mainstream of the Anning River; TA: the tributaries of the Anning River; DA: downstream of the Anning River; MA′: midstream of the Anning River; UA: upstream of the Anning River.
2.3 着生藻类与环境因子的关系

冗余分析结果显示,雅砻江下游流域着生藻类密度与水温、浊度和底质类型(砾石)显著相关(P<0.05, 表4, 图4a)。第一和第二排序轴所反映的物种信息量共计53.4%。水温与第一排序轴的正相关性最高,其次为砾石;浊度与第一排序轴呈负相关。砾石与第二排序轴呈正相关,水温和浊度与第二排序轴呈负相关。绝大部分藻类密度与砾石比例呈正相关,与浊度呈负相关。细小隐球藻、多形眉藻(Calothrix polymorpha)、大卵囊藻(Oocystis naegelii)和双对栅藻(Scenedesmus bijuga)等蓝绿藻密度与水温呈正相关,扁圆卵形藻、偏肿桥弯藻(Cymbella ventricosa)、优美桥弯藻(Cymbella delicatula)和冬生等片藻中型变种(Diatoma hiemale var. mesodon)等大部分硅藻密度与水温呈负相关。

表4  雅砻江下游着生藻类密度与环境因子关系的RDA分析结果 Tab. 4  RDA results relating densities of periphytic algaeto environmental factors in the lower Yalong River

RDA结果显示,安宁河着生藻类密度与流速显著相关(P<0.05),与海拔相关性较高,但并不显著(P=0.059, 表5, 图4b)。第一和第二排序轴所反映的物种信息量共计69.7%。流速和海拔与第一排序轴呈负相关;流速与第二排序轴呈正相关,海拔与第二排序轴呈负相关。绝大部分藻类密度与流速呈负相关。桥弯藻、曲壳藻、扁圆卵形藻和异极藻等硅藻密度与海拔呈正相关,而细小隐球藻和大卵囊藻等藻类则与海拔呈负相关。

图4  着生藻类群落结构与环境因子的RDA排序图a:雅砻江不同河流等级;b:安宁河不同河段;APH:细小隐球藻;OSC1:钻头颤藻;OSC2:颤藻属未定种;LYN:近稀疏鞘丝藻,PSE:链状假鱼腥藻,LEP1:胶质细鞘丝藻,LEP2:浮游细鞘丝藻,LEP3:细鞘丝藻藻属未定种,CAL:多形眉藻;CYC:小环藻属未定种;DIA:冬生等片藻中型变种;FRA:钝脆杆藻;SYN:针杆藻属未定种;NAV:舟形藻属未定种;CYM1:近缘桥弯藻;CYM2:膨胀桥弯藻;CYM3:偏肿桥弯藻;CYM4:优美桥弯藻;CYM5:桥弯藻属未定种;GOM:异极藻属未定种;COC:扁圆卵形藻;ACH:曲壳藻属未定种;OOC:大卵囊藻;SCE:双对栅藻. Fig. 4  RDA diagram of periphytic algae community and environmental factorsa: different river grades of the Yalong River; b: different sections of the Anning River; APH: Aphanocapsa elachista; OSC1: Oscillatoria terebriformis; OSC2: Oscillatoria sp.; LYN: Lyngbya subconfervoides; PSE: Pseudanabaena catenate; LEP1: Leptolyngbya gelatinosa; LEP2: Leptolyngbya planktonica; LEP3: Leptolyngbya sp.; CAL: Calothrix polymorpha; CYC: Cyclotella sp.; DIA: Diatoma hiemale var. mesodon; FRA: Fragilaria capucina; SYN: Synedra sp.; NAV: Navicula sp.; CYM1: Cymbella affinis; CYM2: Cymbella tumida; CYM3: Cymbella ventricosa; CYM4: Cymbella delicatula; CYM5: Cymbella sp.; GOM, Gomphonema sp.; COC: Cocconeis placentula; ACH: Achnanthes sp.; OOC: Oocystis naegelii; SCE: Scenedesmus bijuga.
表5  安宁河着生藻类密度与环境因子关系的RDA分析结果 Tab. 5  RDA results relating densities of periphytic algae to environmental factors in Anning River
3 讨论 3.1 梯级电站对雅砻江下游着生藻类空间分布格局的影响

本研究结果表明,雅砻江下游干流着生藻类密度低于安宁河干支流分析其主要原因可能如下:(1)自然状态下,雅砻江下游干流着生藻类的密度便低于支流,比如,在梯级电站建成前,雅砻江锦屏江段干流着生藻类的密度远低于支流[12]; (2)梯级电站的建设,导致水位升高,流速降低,原有的流水生境丧失,底质类型发生改变,着生藻类缺乏适宜的栖息生境,故其密度显著下降[18]; (3)雅砻江干支流底质组成存在较大差异,雅砻江干流生境以高坝深库为主,库区环境不利于着生藻类的生长,故雅砻江干流的密度及优势种等与安宁河差异较大,而安宁河干支流底质以大石和卵石为主,比较适合着生藻类的生长发育。

此外,梯级电站建成前,雅砻江锦屏江段物种组成以硅藻占据绝对优势,不管丰水期还是枯水期优势种都全部由硅藻组成[12]。本次调查中锦屏江段(Y1~Y4)仍以流水为主,其着生藻类优势类群主要以硅藻为主;但随河流梯度往下,雅砻江干流出现较大量的蓝藻和绿藻,而且蓝绿藻的比例呈上升趋势,这与雅砻江下游梯级电站的建成运行有一定关系。电站建成后,雅砻江下游干流大部分江段形成库区,其水位高,流速低,原有的流水生境丧失,底质类型发生改变,导致库区的藻类群落呈现蓝藻和绿藻种类和密度增加的趋势,蓝藻和绿藻种类也逐渐成为优势种[4]。陈家厚等[4]指出,大顶子山航电枢纽蓄水运行后,水环境变化导致松花江哈尔滨段着生藻类中蓝绿藻比例升高。吴乃成[28]对香溪河水电站建设前后进行对比,结果表明,电站蓄水运行后,下游流速、水深和河宽等主要水文指标显著改变,进而导致着生硅藻总密度、桥弯藻密度、直立型硅藻相对含量、物种丰富度以及Margalef多样性指数等显著下降。Jansen等[29]对加利福尼亚州鳗鱼河建坝干流和未建坝支流着生藻类的比较,也表明建坝蓄水会影响着生藻类和底栖动物的群落结构组成及其密度,进而影响整个食物网的能量传输。综上所述,梯级电站的建设对水环境将产生累积效应,最终导致下游水体蓝绿藻比例升高,硅藻密度、物种丰富度和生物多样性等呈下降趋势。

3.2 河流纵向梯度下着生藻类空间分布格局及其主要环境因子

河流可被视为一个由上游至下游的线性等级结构,沿着这一纵向梯度,许多非生物因子呈现出连续性的空间变化,并对水生生物的空间分布产生重要影响[30]。河流连续统及相关理论认为,河流的环境特征沿水流方向呈现一定的规律性,如海拔降低、水温升高、流速变缓、水深增加等[31]。Jiang等[21]对尼洋河的调查结果也显示,沿着河流纵向梯度,尼洋河水深和水温逐渐升高,流速逐渐降低。本研究中,纵向梯度下安宁河干流的海拔和流速呈下降趋势,水深、河宽、水温和电导率呈上升趋势;沿着河流纵向梯度,安宁河干流中上游水深较浅,流速非常快,底质主要由大石、卵石和砾石组成,着生藻类主要以硅藻为主,下游水深较深,流速较缓,底质虽然也以大石、卵石和砾石为主,但沙粒和黏土占据一定比例,绿藻和蓝藻的比例相对较高。

纵向梯度下安宁河干流的物种多样性指数(Shannon–Wiener指数,H′)呈现出一定的规律,符合中间高度膨胀(mid-altitude bulge)理论,即安宁河中游着生藻类多样性指数最大,上游河段和下游河段相对较低。中间高度膨胀理论指出,在中间海拔区域内物种的多样性指数最高,而在高海拔或低海拔区域内物种的多样性指数呈下降趋势[18]。刘海平等[13]也指出尼洋河着生藻类Shannon– Wiener指数在中游最大,中上游河段和中下游河段呈下降趋势。

海拔与物种分布存在一定相关性。海拔高度决定了一个地区的水温和光照强度等环境条件的变化,对河流着生藻类的群落结构组成的影响较大[5,13]。肖妮娜等[5]指出,海拔对赣江中游着生藻类群落结构有显著影响,海拔越高,着生藻类物种数、密度和多样性指数越低。本研究结果表明,纵向梯度下安宁河着生藻类物种数、总密度及丰富度指数(D)均呈上升趋势。刘海平等[13]研究西藏尼洋河着生藻类时也有相似结果。此外,本研究中部分硅藻种类密度与海拔呈正相关,由于海拔提升,水温降低,喜低温的硅藻成为优势种,因此中上游主要以硅藻为主,下游海拔低,水温高,喜高温的蓝绿藻比例显著上升。

水温影响着生藻类细胞代谢、酶活性及繁殖生长等生物特性。在适度范围内,水温上升有利于藻类的生长繁殖[9]。已有研究表明,藻类最适生长水温也依种类不同而有所差异,例如,绿藻和蓝藻喜高温,硅藻喜低温[17]。本研究中沿着河流纵向梯度,安宁河干流水温逐渐升高,硅藻比例渐趋下降,而绿藻和蓝藻的比例却逐渐升高,这对解释上述现象提供了佐证。本研究RDA结果也显示细小隐球藻等蓝藻的密度以及大卵囊藻等绿藻的密度与水温呈正相关,而扁圆卵形藻和桥弯藻等大部分硅藻的密度与水温呈负相关。

流速也是影响着生藻类分布的重要环境因子[32]。韦丽丽等[33]指出,新疆伊犁河着生藻类的生物量与流速呈极显著的负相关。安宁河上游流速较高,水流对石块上附着藻类的冲刷,导致着生藻类密度下降[13]。下游流速较缓,着生藻类的适宜生境较多,有利于其生长繁殖。本研究RDA结果表明大部分藻类密度与流速呈负相关。另外流速与河床底质类型存在一定的相关性[13],马宝珊等[18]对安宁河中游着生藻类的调查也表明流速和底质类型共同影响丰水期着生藻类的群落结构。

自然状态下,在雅砻江这种高海拔山区河流中,着生藻类往往是鱼类及其他水生动物主要的饵料来源[34-35]。因此,着生藻类多样性及现存量对于维持雅砻江水生生物多样性及河流生态功能具有重要作用。然而,随着雅砻江下游水电梯级的全面实施,水域生态环境和鱼类群落结构已发生明显变化[36-37]。分析区域内着生藻类的空间分布格局,有利于理解流域水生态系统结构和功能的变化。在干流梯级开发加速推进的背景下,加强支流水生态环境的保护显得尤为重要。

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