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ERIC N. POWELL JOHN M. KLINCK EILEEN E. HOFMANN MARGARET A. McMANUS 《Environmental management》2003,31(1):0100-0121
A hydrodynamic–oyster population model was developed to assess the effect of changes in freshwater inflow on oyster populations
in Galveston Bay, Texas, USA. The population model includes the effects of environmental conditions, predators, and the oyster
parasite, Perkinsus marinus, on oyster populations. The hydrodynamic model includes the effects of wind stress, river runoff, tides, and oceanic exchange
on the circulation of the bay. Simulations were run for low, mean, and high freshwater inflow conditions under the present
(1993) hydrology and predicted hydrologies for 2024 and 2049 that include both changes in total freshwater inflow and diversions
of freshwater from one primary drainage basin to another.
Freshwater diversion to supply the Houston metropolitan area is predicted to negatively impact oyster production in Galveston
Bay. Fecundity and larval survivorship both decline. Mortality from Perkinsus marinus increases, but to a lesser extent. A larger negative impact in 2049 relative to 2024 originates from the larger drop in fecundity
under that hydrology. Changes in recruitment and mortality, resulting in lowered oyster abundance, occur because the bay volume
available for mixing freshwater input from the San Jacinto and Buffalo Bayou drainage basins that drain metropolitan Houston
is small in comparison to the volume of Trinity Bay that presently receives the bulk of the bay's freshwater inflow. A smaller
volume for mixing results in salinities that decline more rapidly and to a greater extent under conditions of high freshwater
discharge.
Thus, the decline in oyster abundance results from a disequilibrium between geography and salinity brought about by freshwater
diversion. Although the bay hydrology shifts, available hard substrate does not. The simulations stress the fact that it is
not just the well-appreciated reduction in freshwater inflow that can result in decreased oyster production. Changing the
location of freshwater inflow can also significantly impact the bay environment, even if the total amount of freshwater inflow
does not change. 相似文献
2.
Rosanna L. Mattingly Edwin E. Herricks Douglas M. Johnston 《Environmental management》1993,17(6):781-795
The environmental impact of loss of natural stream and riparian habitat is of concern throughout the United States and Europe.
Environmental impacts related to such activities as channelization of and levee construction along streams and rivers are
particularly apparent in the Midwestern United States. The objective of the research presented here was to delineate the extent,
relative degree of impact, and implications for management of channelization and levee construction along watercourses located
in the state of Illinois. According to records maintained through the Illinois Streams Information System data base (Illinois
Department of Conservation), nearly 25% of surface water resources in the state have been modified directly by channelization
and/or levee construction. Reviews of agency records, elaboration of case histories, interviews with agency personnel, and
inspections of impacted sites indicated that these alterations have occurred without the benefit of effective mitigation.
Although permit records may provide suggestions for mitigation to be incorporated in the design of a particular project, permits
issued generally do not require even minimal instream habitat and bank stabilization efforts in conjunction with channel alteration.
Information derived from policy and case study analyses suggests that institutional constraints, rather than lack of particular
understanding about mitigation, provide major barriers to protecting the state's surface water resources in terms of regulatory
review, policy interpretation and implementation, and project evaluation. Recommendations for environmental management efforts
regarding these and similar channel alterations are elaborated from these findings. 相似文献
3.
Effects of stream channelization on exports of nitrogen and phosphorus from north Carolina coastal plain watersheds 总被引:1,自引:0,他引:1
Laura A. Yarbro Edward J. Kuenzler Patrick J. Mulholland Robert P. Sniffen 《Environmental management》1984,8(2):151-160
Nitrogen and phosphorus exports from channelizedstream watersheds were elevated over those from nearby natural swamp-stream watersheds. Nitrate exports were significantly greater from channelized-stream watersheds, and higher exports were attributed to faster groundwater drawdown, continual streamflow, and transformation of former floodplain to croplands following channelization. Exports of total organic nitrogen and total nitrogen were also significantly greater from channelized-stream watersheds. Differences in the exports of ammonium, filterable reactive phosphorus, and filterable unreactive phosphorus between the two watershed types were not detectable. Particulate phosphorus exports were significantly higher from channelized-stream watersheds, presumably because of greater erosion potential of nearby croplands and steep channel banks in the altered watersheds. The presence of nonpoint sources of pollution increased watershed exports of nutrients regardless of stream morphology. Examination of nutrient budgets for a portion of swamp floodplain at the base of one natural-stream watershed revealed that changes in local groundwater hydrology and stream morphology associated with channelization appeared to have greater effect on nutrient exports than simply the loss of bordering forested floodplain. 相似文献
4.
Wyzga B 《Environmental management》2001,28(3):341-358
River engineers use sediment transport formulas to design regulated channels in which the river's ability to transport bedload
would remain in equilibrium with the delivery of materials from upstream. In gravel-bed rivers, a number of factors distort
the simple relationship between particle size and hydraulic parameters at the threshold of sediment motion, inherent in the
formulas. This may lead to significant errors in predicting the bedload transport rates in such streams and hence to instability
of their regulated channels. The failure to recognize a nonstationary river regime may also result in unsuccessful channelization.
Rapid channel incision has followed channelization of the main rivers of the Polish Carpathians in the 20th century. A case
study of the Raba River shows that incision has resulted from the increase in stream power caused by channelization and the
simultaneous reduction in sediment supply due to variations in basin management and a change in flood hydrographs. Calculations
of bedload transport in the river by the Meyer-Peter and Müller formula are shown to have resulted in unrealistic estimates,
perhaps because the different degree of bed armoring in particular cross-sections was neglected. It would have been possible
to avoid improper channelization if the decreasing trend in sediment load of the Carpathian rivers had been recognized on
the basis of geomorphological and sedimentological studies. Allowing the rivers to increase their sinuosity, wherever possible
without an erosional threat to property and infrastructure, and preventing further in-stream gravel mining are postulated
in order to arrest channel incision and reestablish the conditions for water and sediment storage on the floodplains. 相似文献
5.
Changes in vegetation and land use since 1826 were evaluated along the 800 kilometer portion of the Missouri River flood-plain that extends across the State of Missouri using County Land Office Survey records for 1826 and aerial photos for 1937, 1958, and 1972. The combined results show a decline in flood-plain forest coverage from 76% in 1826 to 13% in 1972; cultivated land increased from 18% to 83% during the same time. Uncultivated-unforested areas increased from 6% in 1826 to 27% in 1937, then declined to 1% in 1972; these changes occurred coincident with extensive bank-stabilization and channelization activities initiated in 1912 by the U.S. Army Corps of Engineers. Riverbank stabilization activity since that time may account for the increased rate of decline in flood-plain forests from 0.25% per year between 1826 and 1937 to 1.6% per year between 1937 and 1972.The overall species composition of the 1826 flood-plain forests was found to be most similar to mature forest stands evaluated in 1972; similar frequencies in 1826 and 1972 occurred for hackberry (Celtis occidentalis; 80% in 1826, 83% in 1972), elm (Ulmus spp.; 80% and 83%), and sycamore (Platanus occidentalis; 57% and 50%). Pawpaw (Asimina triloba), found only in mature flood-plain forests in 1972, was recorded along 54% of the 1826 section lines.These combined data indicate (1) that pre-settlement flood-plain forests were extensive and included frequent, mature stands, (2) that in certain areas substantial portions of the flood-plain were in cultivation prior to extensive riverbank stabilization and channelization, and (3) that increased flood-plain forest clearing occurred coincident with increased bank-stabilization activities. 相似文献
6.
Thompson DM 《Environmental management》2003,31(3):0385-0400
The Veteran's Fishing section of the Blackledge River in central Connecticut was relocated in the late 1950s. The relocation
resulted in an unstable channel despite extensive efforts to prevent erosion. Overbank erosion and meander cutoffs were investigated
using detailed survey data, characterizations of sediment deposits, flow modeling, and a moment-stability analysis. Limited
reworking of revetment boulders indicate that riprap bank material was immobile during a 1979 flood event responsible for
the formation of the cutoff channel. A moment-stability analysis factor-of-safety value of 1.1 supports the conclusion that
riprap was not directly eroded from the banks. Alluvial particles with d95 values ranging up to 120 mm were deposited along a bar downstream from the cutoff channel at flows estimated to be below
a 1.5-year recurrence interval flow. Development of the bar deposit resulted in locally elevated water surfaces at high flow.
The resulting overbank flow across the meander neck to the adjacent downstream bend led to the creation of an upstream migrating
knickpoint, the erosion of approximately 16,000-year-old sediments, and the subsequent meander cutoff. The results of the
study indicate that traditional erosion-control measures cannot prevent extreme channel adjustments if the geomorphic processes
that control sediment continuity also are not considered. 相似文献
7.
The choice of spatial and temporal scale used in environmental assessments may influence the observed results. One method
of assessing the impact of stream habitat alterations involves the comparison of response variables among treatment categories
(i.e., impacted and unimpacted sites). The influence of spatial resolution on patterns of response variables among treatment
categories in assessments of stream channelization and other types of habitat alterations has not been evaluated. We examined
how patterns of 10 community response variables among channel types and our interpretations of channelization impacts on fish
and macroinvertebrate communities differed among three spatial resolutions in a warmwater stream in Mississippi and Alabama.
Four fish and three macroinvertebrate community response variables exhibited different patterns among channel types at different
spatial resolutions. Our interpretations of the impacts of channelization on fish and macroinvertebrate communities differed
among spatial resolutions. Channelization had a negative influence on fish communities either with or without evidence of
potential community recovery in one channel type. Channelization impacts on macroinvertebrate communities ranged from a negative
influence to no effect. Our results suggest that spatial resolution can influence the observed results and interpretations
derived from assessments of stream habitat alterations. 相似文献
8.
Nelson R. Nunnally 《Environmental management》1978,2(5):403-411
Channelization is one of the most common solutions to urban drainage problems, despite the fact that channelized streams are frequently morphologically unstable, biologically unproductive, and aesthetically displeasing. There is increasing empirical and theoretical evidence to suggest that channelization may be counterproductive unless channels are designed to prevent the bank erosion and channel silting that often accompanies stream dredging. Many of the detrimental effects of channelization can be avoided, with little compromise in channel efficiency, by employing channel design guidelines that do not destroy the hydraulic and morphologic equilibria that natural streams possess. These guidelines include minimal straightening; promoting bank stability by leaving trees, minimizing channel reshaping, and employing bank stabilization techniques; and, emulating the morphology of natural stream channels. This approach, called stream restoration or stream renovation, is being successfully employed to reduce flooding and control erosion and sedimentation problems on streams in Charlotte, North Carolina. 相似文献
9.
Nelson R. Nunnally 《Environmental management》1985,9(5):417-425
Many of the environmental problems associated with channel modifications can be anticipated if known fluvial relationships are considered early in the planning process. Plan modifications or corrective measures can be employed to prevent environmental degradation and improve project performance. The fluvial system is reviewed from a geomorphic perspective. Functional fluvial relationships are described and their use in planning and design of flood channels is demonstrated. 相似文献
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