共查询到11条相似文献，搜索用时 31 毫秒
1.
Riverine ecosystems have been altered in many large catchments by dam development to provide water, power, flood control and navigational benefits to humans. Conservation actions in these river ecosystems are commonly focused on minimum releases of water to downstream ecosystems. Increasingly minimum release approaches are being replaced with ‘experimental’ flows that mimic natural conditions in order to benefit riverine ecosystems. While these new policies are intuitive in their design, there is limited data of how riverine ecosystems actually respond to more natural flows. A test of more natural steady‐flow water release was compared with typical fluctuating hydropower flows in the adaptive management programme at Glen Canyon Dam, Arizona, during 2008–2011 to assess growth improvements of endangered juvenile humpback chub Gila cypha. Our results are counterintuitive and show that more natural steady flows reduced growth rates of juvenile humpback chub compared with fluctuating flows when both treatments occurred within the same year. Daily growth rates during steady flows of 2009 and 2010 were 0.05 and 0.07 mm day?1 slower, respectively, than fluctuating flows those same years, despite similar water temperatures. Juvenile humpback chub also grew more slowly during steady flows that occurred in the same season. During the summer, juvenile humpback chub grew 0.12 and 0.16 mm day?1 in fluctuating flow regimes in 2009 and 2010, respectively, and only 0.07 mm day?1 in the experimental steady flow regime in 2011, despite higher water temperatures. Our results suggest that optimal conservation management policies for endangered species in regulated rivers may not always be achieved with more natural flows. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
2.
W. D. Hintz A. P. Porreca J. E. Garvey Q. E. Phelps S. J. Tripp R. A. Hrabik D. P. Herzog 《河流研究与利用》2015,31(10):1218-1226
Identifying the appropriate scale at which habitat is biologically relevant to riverine fishes in large, sand‐dominated rivers is a challenge. Alluvial islands are important to several of these fishes throughout the central USA, but there is a paucity of information on island habitat features that restoration efforts should try to replicate. We determined the physical characteristics of two island complexes in the middle Mississippi River that facilitate the settlement and survival of age‐0 shovelnose sturgeon Scaphirhynchus platorynchus at relatively large (mean 39,000 m2) and small (mean 320 m2) scales. Depth (m), flow rate (m s?1), substrate (sand, rock, silt) and vegetation were quantified at these two scales using hydroacoustic techniques (split‐beam sonar and acoustic Doppler current profiler). Abiotic attributes in the surrounding littoral zone of the island complexes were highly correlated but differed depending on location. At the coarse spatial scale, vegetation was positively related to shovelnose sturgeon abundance. At the fine spatial scale, age‐0 shovelnose sturgeon were restricted to flow rates < 0.89 m s?1, with abundance peaking at about 0.40 m s?1. However, heterogeneity in depth and flow was important, and sturgeon abundance peaked at intermediate variability in these two abiotic attributes. A computer‐generated model of the habitat surrounding islands suggests that these habitats are diverse and may provide flow refugia and foraging patches for shovelnose sturgeon. We submit the results presented here that can contribute to a hierarchical model for island restoration in large rivers. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
3.
Loren W. Stearman;Franklin T. Heitmuller; 《河流研究与利用》2024,40(5):693-707
Channel incision in rivers can cause marked ecological and economic damages. This phenomenon is abundant and generally well documented along impacted streams in the loess hills adjacent to the Lower Mississippi River valley. Bayou Pierre, an ecologically important small tributary of the Mississippi River, is currently incising but causes are not well understood. In this study, we examine diverse data sources to: (1) reconstruct a history of erosional stimuli and possible origins and (2) examine effects of contemporary controls. Review of long-term planform and land use data for the Mississippi River revealed episodic foreshortening events followed by episodic deforestation and reforestation. Hydrologic data suggest an increase in rainfall over the last few decades. Estimates of knickpoint retreat place origins prior to Mississippi River channel straightening (1929–1944). Planform analysis in three focal reaches of Bayou Pierre demonstrates slow change prior to 1982, but accelerated changes after those periods. Mean rainfall and 3-day storm intensity correlate to some planform changes; however, the storm of 1983 may be a better explanation of sudden planform change. We found some evidence of potential internal feedback loops in patterns of bar growth. Together, our analyses provide a synthesis of stimuli experienced by Bayou Pierre over the last ~200 years and suggest both channel migration events before straightening of the Mississippi River and more recent hydrologic events have influenced patterns of geomorphic change in Bayou Pierre. 相似文献
4.
The planimetric shifts in channel location of large alluvial rivers are a critical component in the creation of diverse structures and functions in riverine habitats. Engineered management schemes must also compensate for this type of channel change to protect resources and maintain navigation channels. The stability of the Lower Mississippi River channel was assessed through an analysis of historical records of channel position produced and archived by the United States Army Corps of Engineers. Channel location was recorded for the years 1765, 1820, 1881, 1915, 1930, 1937, 1960 and 1970. Channel stability was measured by two introduced metrics on a cell‐by‐cell basis: (1) the standard deviation of Euclidean distance to a channel cell for the entire period of record, and (2) the rate of Euclidean distance change between years in the period of record. At a coarse spatial scale, channel instability increased in the downstream direction. The variability of channel stability also increased in the downstream direction. Analysis of this variability identified alternating areas of high and low stability occurring with greater frequency as distance downstream increased. These findings are validated by past studies of channel stability along the Lower Mississippi River. As a result, the proposed metrics provide a consistent, quantitative, efficient and cost‐effective means of identifying areas of channel instability at several spatial scales. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
5.
Audrey B. Harrison Amanda J. Oliver William T. Slack Nicky M. Faucheux K. Jack Killgore Clifford A. Ochs 《河流研究与利用》2023,39(6):1084-1093
In large rivers, secondary channels occur where the main channel is divided by an instream island, forming one or multiple smaller channels outside the main channel. Secondary channels are highly variable in morphometry, flow characteristics, and degree of connectivity to the main channel. Engineered closing structures at the upstream end of most secondary channels restrict inflow from the main channel, resulting in gradients of flow connectivity among secondary channels that vary with river stage. We investigated the relationship of flow connectivity to benthic macroinvertebrate assemblage richness and structure among a series of secondary channels of the Lower Mississippi River. Samples were collected over 2 years at times of high and low river stages. We discovered (1) macroinvertebrate assemblage structure and taxonomic richness varied along the flow connectivity gradient, and (2) there was a legacy effect of prior connection on assemblage structure that lasted up to a year. We contend that for management and restoration planning aimed at conservation of large river biological diversity, an important consideration are the life history requirements of animals utilizing secondary channel habitats. 相似文献
6.
System-wide spatial patterns of ichthyoplankton abundance and variability were assessed in the upper Mississippi and lower Illinois rivers to address the experimental design and statistical confidence in density estimates. Ichthyoplankton was sampled from June to August 1989 in primary milieus (vegetated and non-vegated backwaters and impounded areas, main channels and main channel borders) in three navigation pools (8, 13 and 26) of the upper Mississippi River and in a downstream reach of the Illinois River. Ichthyoplankton densities varied among stations of similar aquatic landscapes (milieus) more than among subsamples within a station. An analysis of sampling effort indicated that the collection of single samples at many stations in a given milieu type is statistically and economically preferable to the collection of multiple subsamples at fewer stations. Cluster analyses also revealed that stations only generally grouped by their preassigned milieu types. Pilot studies such as this can define station groupings and sources of variation beyond an a priori habitat classification. Thus the minimum intensity of sampling required to achieve a desired statistical confidence can be identified before implementing monitoring efforts. 相似文献
7.
Magnitude-frequency analysis of gauging station records (1950-1982) on the Lower Mississippi shows that there is a clearly defined dominant flow of about 30000 m3 /s. This lies within an effective range of channel-forming flows between 17000 and 40000 m3 /s, which are responsible for transporting a disproportionately large percentage of the sediment load. The 33 year period of record is sufficiently long that the occurrence of an extreme high flow event does not significantly change these results. Hydrographic survey data, long-profile records and stage-discharge relationships from calibrated one-dimensional flow models indicate that the dominant discharge corresponds to ‘bar-full’ discharge on the Lower Mississippi and that the effective range of flows occurs between the stage that just tops mid-channel bars and that which significantly overtops the banks. Historical trends in bar growth suggest that bar-top elevations have generally risen to the dominant flow elevation over the last 30 years. In this trained river, where most of the banks are protected by revetments and the alignment is fixed by groynes and spurs, the mid-channel bars represent the major, contemporary morphological feature of the alluvial river. 相似文献
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In nutrient-rich systems, phytoplankton production is frequently light-limited and light attenuation can become a critical factor controlling the rates of production, especially in shallow systems subject to wind resuspension of sediments. This study examined the relation between light availability and primary production in Lake Onalaska, a shallow, nutrient-rich impoundment of the Upper Mississippi River. Continuous water quality monitors recorded dissolved oxygen, temperature and light flux at a network of sites from July to September 1990 and these data were used to estimate the primary production, light availability and light attenuation coefficients. The gross primary production averaged 2·2gCm?2 day?1 and was due almost entirely to phytoplankton. Production was strongly light-limited, with most of the light attenuation due to non-algal components, possibly related to wind resuspension in this shallow system. Regression analyses revealed significant effects of wind speed and direction on light attenuation. 相似文献
10.
Oliver P. Harmar Nicholas J. Clifford Colin R. Thorne David S. Biedenharn 《河流研究与利用》2005,21(10):1107-1131
During the twentieth century, the planform and profile of the Lower Mississippi River from Cairo, Illinois, to New Orleans, Louisiana, have been transformed by a series of engineering modifications. These include steepening of the long profile by removal of the most sinuous bends, extensive bank stabilization, and regulating sediment movement by dyke field construction. Prior to these modifications, the Lower Mississippi River adjusted its morphology in the planform, long profile and cross‐section. Planform adjustment has, however, effectively been negated and other adjustments are now constrained. Nevertheless, analysis of hydrographic surveys between 1949 and 1989 demonstrates that geomorphological response during the post‐cutoff period remained complex. Morphological adjustments involved phased patterns of aggradation and degradation, together with changes in cross‐sectional form, and in the number, size, location and shape of pools and crossings. Greatest changes occurred in the early post‐cutoff period (1949–64) upstream from Vicksburg, Mississippi, but were accompanied by complementary changes elsewhere which propagated downstream. The combined set of responses may be interpreted with respect to a dynamic equilibrium in which the river responded to additional energy created by the cutoffs by increasing and adapting flow resistance over various scales and time periods. This study helps resolve paradoxes from previous analyses, and has significance for interpreting past engineering impacts and for suggesting future management strategies for the Lower Mississippi River. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
11.
T. M. Jicha L. B. Johnson B. H. Hill R. R. Regal C. M. Elonen M. S. Pearson 《河流研究与利用》2014,30(5):650-662
Overbank flooding is thought to be a critical process controlling nitrogen retention and cycling. Yet, studies aimed at quantifying these effects, specifically nitrification, are relatively few. In this study, we investigated the effects of season and flood frequency on soil nitrification rates in forested floodplains of Upper Mississippi River, Pool 8. Samples were collected from three plots within each site in April, August and November 2006. Plots were equally divided among three flood frequency categories as follows: rare, moderate and frequent based on elevation and flood probability model. We found a significant difference in nitrification rates among flood frequency categories as follows: rare > moderate > frequent (F = 4.49, p < 0.01) and over season: spring > summer > autumn (F = 8.88, p < 0.01). Regression for all samples showed that elevation, NH4‐N, bulk density and soil temperature explained a moderate amount of variation in nitrification rates (R2 = 0.29, p < 0.01). Models for moderately flooded, spring, summer and autumn samples improved when analysed individually. The absence of a correlation between nitrification rates and hydrology limits our ability to predict rates based on hydrology alone. The model based on elevation and season allows us to estimate nitrification rates with moderate confidence (R2 = 0.27, p < 0.01). A rough calculation of forest floodplain nitrification rates suggests that 473 mt of NO3‐N are produced annually, about 0.5% of Pool 8 total annual NO3‐N budget. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献