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1.
The serial discontinuity concept (SDC; Ward and Stanford, in Ecology of River Systems, 1983) predicts that recovery of large regulated rivers over distance downstream from a dam is limited by relative tributary size; however, channel geomorphology may also influence the recovery process. We examined the spatial variation in water quality, benthic composition and ash-free dry standing biomass (AFDM) among the bedrock-defined geomorphological reaches in three turbidity segments of the Colorado River between Glen Canyon Dam and Diamond Creek, Arizona, including most of the Grand Canyon. This 387-km long study area supported virtually no Ephemeroptera, Plecoptera or Trichoptera, probably because cold, stenothermic, hypolimnetic releases limited maximum aestival warming to 17·1°C. The benthos displayed abrupt, physically related decreases in AFDM over distance from the dam and in the varial zone. The 26-km long clear water segment between the dam and the Paria River supported a depauperate Cladophora glomerata/epiphyte/chironomid/Gammarus lacustris/lumbricine/Physella sp. assemblage, and ooze-dwelling oligochaetes. This segment contained 6·9% of the aquatic habitat below the 140 m3/s (normal minimum) discharge stage of the Colorado River study area, but supported 63·5% of the benthic primary producer AFDM and 87% of the benthic consumer AFDM in the entire study area. Turbidity increased and light penetration decreased immediately downstream from the confluence of the small, turbid Paria River, and further downstream from the Little Colorado River confluence. The benthos downstream from the Paria River was abruptly replaced by an Oscillatoria/Simuliium assemblage with a mean AFDM of <0·12 g C/m2. Dam-related effects on water clarity, varial flow and water temperature overrode geomorphological influences on habitat availability. These results generally support the SDC, in that recovery of the benthos did not take place over distance in this large river ecosystem; however, geomorphological differences in substratum availability between reaches mediated dam and tributary effects on water clarity and benthic AFDM. Interactions between flow regulation and geomorphology produce a pattern of circuitous recovery of some physical river ecosystem characteristics over distance from the dam, but not of the benthos. Improving discharge management for endangered native fish populations requires detailed understanding of existing and potential benthic development, and trophic interactions, throughout the geomorphological reaches and turbidity segments in this river. © 1997 John Wiley & Sons, Ltd. 相似文献
2.
A two‐dimensional hydrodynamic model was applied to seven study reaches in the Colorado River within Grand Canyon to examine how operation of Glen Canyon Dam has affected availability of suitable shoreline habitat and dispersal of juvenile humpback chub (Gila cypha). Suitable shoreline habitat typically declined with increasing discharges above 226–425 m3/ s, although the response varied among modelled reaches and was strongly dependent on local morphology. The area of suitable shoreline habitat over cover types that are preferred by juvenile humpback chub, however, stayed constant, and in some reaches, actually increased with discharge. In general, changes in discharge caused by impoundment tended to decrease availability of suitable shoreline habitat from September to February, but increased habitat availability in spring (May–June). Hourly variation in discharge from Glen Canyon Dam substantially reduced the amount of persistent shoreline habitat at all reaches. Changes in suitable shoreline habitat with discharge were shown to potentially bias historical catch per unit effort indices of native fish abundance up to fourfold. Physical retention of randomly placed particles simulating the movement of juvenile humpback chub in the study reaches tended to decline with increasing discharge, but the pattern varied considerably due to differences in the local morphology among reaches and the type of swimming behaviour modelled. Implications of these results to current hypotheses about the effects of Glen Canyon Dam on juvenile humpback chub survival in the mainstem Colorado River are discussed. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
3.
We examined subadult humpback chub densities along 24 kms of the Colorado River in the Grand Canyon to: (1) identify geomorphic conditions in the study area; (2) determine associations between subadult humpback chub (<200 mm TL) habitat use and geomorphic differences; and (3) determine how discharge, during base flow conditions, was related to subadult humpback chub habitat conditions. Habitat was categorized at two nested spatial scales: geomorphic reach and shoreline type. Within reaches, shoreline types were categorized according to geomorphology. We measured water depth, velocity and cover attributes along all shoreline types over a range of discharges to determine if habitat quality of reaches and shoreline types varied with discharge. Reaches 1 and 3 had narrow, deep corridors, whereas Reach 2 was a wide, shallow reach. Among shoreline types, depth, velocity and cover varied; however, differences were not consistent between reaches. Fish densities also varied among shoreline types and reaches. Vegetation, talus and debris fan shorelines had the highest densities of subadult humpback chub in a pattern similar to that of cover. In addition, subadult humpback chub presence was associated with a high frequency of cover regardless of shoreline designation. However, these relationships explained little of the overall variation in subadult densities. Lack of a strong association between fish density and geomorphology may be partially due to effects of discharge on habitat quality. The overall trend among shorelines (without regard to type) showed that cover decreased with increasing discharge, whereas depth and velocity increased. However, no consistent pattern between discharge and depth, velocity and cover among individual shoreline types was evident. Vegetated shorelines, consisting mainly of non-native tamarisk (Tamarix chinensis), had nearly twice the fish densities of talus and debris fan. Reasons are discussed as to why subadult humpback chub occupy naturalized habitat like vegetated shorelines in greater densities than natural habitats. The relationships observed in this study have important implications for humpback chub recovery and management of the Colorado River through Grand Canyon. © 1998 John Wiley & Sons, Ltd. 相似文献
4.
Glen Canyon Dam, located on the Colorado River 24km upstream from Grand Canyon National Park, has affected downstream alluvial sand deposits which are used as campsites by recreational boaters. Inventories of campsite numbers and sizes conducted in 1973, 1983 and 1991, and comparison of aerial photograph series taken in 1965, 1973, 1984 and 1990 show that there has been a system-wide decrease in the number and size of campsites. Campsites are unevenly distributed along the river, and availability is regarded as ‘critical’ along reaches comprising 45% of the river, based on interviews with river guides. During the first 10 years of Glen Canyon Dam operations, at least 30% of all campsites decreased in size. During the next 18 years, between 1973 and 1991, 32% of all campsites decreased in size, and campsite capacity decreased by 44%. High annual dam releases in excess of power plant capacity in 1983 caused a net system-wide increase in the number of campsites, but decreased campsite capacity in two critical reaches. The ‘benefit’ of sand aggradation due to the 1983 high flow was short-lived, and by 1991 only a few campsites were larger than they had been in 1973. In contrast, other sites, especially in critical reaches, were eroded by the 1983 high flows and have not recovered in size. Options for future dam management must consider the variable response of campsites to high flows in critical and non-critical reaches and the duration over which ‘beneficial’ high flow effects persist. 相似文献