Influence Of Cascade Hydropower Development On Fluvial Morphology And Fish Diversigy In The Mainstream Of The Yellow River Source Zone

As a concentrated distribution area of the Qinghai-Tibet plateau fishes in the Yellow River, the source region of the Yellow River is a key area for aquatic ecosystem protection. At the same time, fulvial morphology in here has received more attention for its unique diversity. However, the focus of hydropower development in the upstream of the Yellow River gradually transferred to the mainstream of the Yellow River Source Zone (YRSZ). So the study on fluvial morphology, fish diversity and the relationship between them, predicted the influence of cascade hydropower development on them in this area, has its important significance.8 indicators were adopted to establish an index system reflecting the spatial, inter-channel lands and boundary features of fluvial morphology. Based on field survey, analysis of remote sensing images and DEM, collection of literature, characteristics of river morphology were analyzed. Fluvial morphology diversity of each reach were evaluated through the method of factor analysis. The diversity and the spatial distribution of fish species in the study area was presented via literature search and data organization. Then we discussed the relationship between fluvial morphology and fish species diversity in the mainstream of the YRSZ. Besides, DEM data, the location of dams and their storage levels were used to simulate the flooding impacts on fluvial morphology and connectivity of river. Finally, based on fish characteristics and the change of river morphology, the possible influence of cascade hydropower development on fish diversity were predicted. Results are as follows:1. Features of river morphologyBased on river patterns, the mainstream of the YRSZ between the tail area of the Longyangxia Reservoir and the Huangheyuan Reservoir was divided into 14 sections.Spatial features:In terms of spatial-longitudinal features, most of sections in the mainstream are meandering reaches. The longitudinal profile in the reach from the tail area of the Longyangxia Reservoir to Zequ and the reach from Awancang to Youerqu rise far more steeply than other reaches, and the rest of the reaches rise slower. River bed gradient in the multiple channels section are less than the following downstream single channel section. In terms of spatial-horizontal features, the average value of river width in the trunk stream between the tail area of the Longyangxia Reservoir and the Huangheyuan Reservoir is 428m. The average value of river width in single and multiple channels sections have a trend of rise first then fall, and reached the maximum at the first bend of the Yellow River. River width within every reach are quite difference. The diversity of cross sections’shape in the mainstream of the YRSZ are relatively high.In-channel lands’ features:The total area, the area ratio and the ratio of in-channel lands’ area and reach’s length in single channel sections are far less than multiple channels sections. Area ratio in multiple channels sections near the first bend of the Yellow River, the Gangnagemacuo Lake and Maduo County are relatively high. River pattern in every multiple channels section is reflected by the ratio of in-channel lands’ area and reach’s length, and the ratio of in-channel lands’ area and reach’s length in anastomosing, braided, anabranching pattern reaches reduce in turn.Boundary feature:Boundaries of multiple channels sections are more gentle than single channel sections generally. More than 90% of the slope of border in multiple channels sections are within 0-25°. In single channel sections, the boundary of the reach from Wutuo to Kaerge and the reach from Awancang Yellow River Bridge to Longka (near Mengtang Town) are relatively steep.River morphology diversity:From downstream to upstream, the fluvial morphological diversity of the reach from Wutuo to Kaerge is relatively low, the reach from Kaerge to Tangke is meduim, the reach from Awancang Yellow River Bridge to Youyun Town is relatively high, the reach from Tangke to Awancang Yellow River Bridge and the reach from Youyun Town to Huangheyuan reservoir are high. The fluvial morphological diversity in the reach near the Gangnagemacuo Lake gets the maximum.2. The diversity and the spatial distribution of fish speciesFish species diversity and major habits:There are a total of 32 species including 24 native species and 8 exotic species in the YRSZ (above Longyangxia). The proportion of endemic and endangered species is high, accounting for about 41.7% of total native species. Most of the native fishes belong to the Central Asia plateau mountain area complex. The breeding season of major fishes in the YRSZ comes from Apirl to August. They spawn the demersal eggs, with low reproduction capacity and slow growth, and they live in the middle and lower layers. Less carnivorous fishes.Spatial distribution of fish species:For the spatial distributions of fishes in the YRSZ, Gymnocypris eckloni, Gymnodiptychus pachycheilus, Platypharodon extremus, Schizopygopsis pylzovi, Triplophysa siluroides and Triplophysa pappenheimi are widespread across the YRSZ. Triplophysa scleroptera mainly distributed in the Zalinghu Lake, Xinxinhai Lake and the lower reaches following Maqu. Chuanchia labiosa mainly distributed in the Zalinghu Lake and the lower reaches following Maqu. Triplophysa pseudoscleroptera mainly distributed in the lower reaches following Maqu. The distribution of Acanthogobio guentheri is relatively limited and mainly distributed in the reach from Jungong to Longyangxia. The diversity of fish species along the mainstream of the reach from Tehetu to Longyangxia goes up from upstream to downstream, and gets the maximum in the reach from Jungong to Yangqu.3. Relationship between fish species distribution and fluvial morphologyRelationship between fish species distribution and fluvial morphology was analyzed. Results show that the range of mainly fluvial morphology indicator values between reaches in which fish sampling points exist and all reaches are similar, that is to say, fluvial morphology of reaches in which fish sampling points exist are not special.In general, there is no significant relevance between fluvial morphology diversity and fish species diversity in the YRSZ. As fish diversity is influenced by many factors, fluvial morphology isn’t the dominant factor driving fish species diversity pattern in the mainstream of the YRSZ.4. Influence of cascade hydropower developmentChanges of fluvial morphology:Results document a huge change of fluvial morphology between pre- and post- dam construction. The length ratio of unnatural, multiple and single channels will be altered from 1:6:8 (now) to 9:5:1, with a greater rate of decrease (87%) of single channels than multiple channels (20%). The unnatural channels will account for 60% of the reach between the Longyangxia and Huangheyuan Reservoir. The sinuosity of the flooded sections will decline, and more than 50 km2 of in-channel lands will be submerged.Changes of river connectivity:With the number of hydropower stations in the YRSZ increase, the river connectivity will gradually decline, but the falling will get smaller.In the present case, if another one hydropower stations was constructed, the location will make a great difference. The degree of impacts are the stream above Shaqu River (changes little within it)> the stream between Maqu to Jungong (more upstream more impact)>the stream below Jungong (changes little within it). Our study shows that the construction of the planning dams above the first great bend of Yellow River will influence the connectivity greatly.Possible influence of hydropower development on fish species diversity: Based on the spatial distribution, the sensitivity to the hydropower development, the condition of artificial propagation and releasing of fish species, all the fishes which directly affected by cascade hydropower development in the YRSZ were divided into 4 groups. The degree of impacts on them are Acanthogobio guentheri>Chuanchia labiosa and Triplophysa siluroides> Platypharodon extremus, Gymnodiptychus pachycheilus, Triplophysa pappenheimi> Gymnocypris eckloni, Schizopygopsis pylzovi, Triplophysa scleroptera, Triplophysa pseudoscleroptera.5. Suggestions on hydropower development based on the protection of fish resourcesFirst, planning dams in the national nature reserve of endemic fish in the Yellow River upstream area and above the first great bend of Yellow River should be cautiously constructed. Second, small hydropower stations in main branches of the downstream of the first great bend of Yellow River should be demolished to lessen the impacts of cascade hydropower development in the mainstream.