ISSN:1040-2381    

DOI:10.1080/07438148409354523

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Phytoplankton productivity and biomass fluctuations are controlled by the same energy and nutrient inputs and the same balance of gain and loss factors in natural and manmade lakes. However, some significant physical and hydrodynamic differences between lakes and reservoirs do exist which influence (1) the relative contributions of various primary producers to their food-webs, (2) the relative importance of certain limiting factors to primary production (e.g., turbidity, nutrient availability, flushing rate), (3) the spatial variability of primary production within reservoirs, and (4) the applicability of lake-based classifications and empirical relationships to reservoirs. An important distinction between most natural and manmade lakes is that reservoirs are semi-fluvial environments that fall between rivers and lakes on a continuum of aquatic ecosystems. A wider recognition of the riverine influences on reservoir ecosystems will enhance our understanding of the spatial and temporal heterogeneity associated with manmade impoundments and, thereby, permit more effective management of reservoir resources.

ISSN:1040-2381    

DOI:10.1080/07438148409354524

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The estimation of annual organic matter budgets for lakes and reservoirs can be an important initial step in investigating aquatic ecosystem structure and function. Comparison of organic matter budgets for a number of aquatic systems indicates that hydraulic retention time exerts a critical influence on the efficiency with which those systems process and trap their organic matter inputs. Generally, lakes or reservoirs with short retention times have high drainage basin area: water surface area ratios, and receive large quantities of allochthonous organic matter. These rapidly flushed ecosystems are relatively inefficient in retaining and processing their inputs and transport large quantities of organic matter downstream. Lakes or reservoirs with long retention times have low drainage basin area: water surface area ratios and are dominated by autochthonous inputs. These ecosystems are considerably more efficient in retaining and processing their inputs, and lose little organic matter downstream. Lakes and reservoirs with similar retention times and drainage basin area: water surface area ratios tend to behave similarly, both in the relative importance of allochthonous inputs and in the efficiency with which organic matter inputs are processed and trapped within the ecosystem.

ISSN:1040-2381    

DOI:10.1080/07438148409354525

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Eau Galle Lake (Spring Valley, Wis.), a U.S. Army Engineers reservoir, is more susceptible to weather-related mixing events than most north temperate lakes. Bottom withdrawal at Eau Galle leads to considerable heat storage in the hypolimnion and by late summer there is only 6–8° C difference between surface and bottom temperatures. Steep metalimnetic gradients never develop and as a result the reservoir has a relatively low thermal stability, which implies a susceptibility to weather-induced (i.e., wind or cold front passage) mixing events. Two types of mixing events were observed in Eau Galle Lake in the summers of 1981 and 1982: (1) Small scale mixes similar to those observed in lakes. These events lead to net movement of nutrients into the epilimnion and a resultant increase in chlorophyll a concentrations. (2) Large scale mixes that function essentially as short-lived turnovers. These large scale mixes are preceded by a cooling trend in air temperature which results in heat loss from the surface of the reservoir. Surface cooling reduces the already small temperature differences between surface and bottom and sufficient wind can produce considerable mixing. These events lead to the introduction of oxygen into the previously anoxic hypolimnion and rather than increasing epilimnetic concentrations of nutrients, there is a general loss throughout the water column. Low thermal stability and susceptibility to mixing may be a common feature of bottom withdrawal reservoirs and may exert a considerable influence on nutrient and phytoplankton dynamics.

ISSN:1040-2381    

DOI:10.1080/07438148409354526

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The use of nutrient loading models for predicting the trophic status of lakes and reservoirs is based partially upon empirical phosphorus/chlorophyll relationships which were originally developed using data from northern natural lakes. Recently, increased attention has been given to the effects of other potentially limiting factors, including nitrogen, light, and flushing rate, on the performance of empirical chlorophyll models. This paper describes a study of these relationships in reservoirs and is derived from a nationwide research project conducted for the U.S. Army Corps of Engineers. Effects of N/P ratios, flushing rate, turbidity, and impoundment morphometry on phosphorus/chlorophyll relationships are systematically evaluated. Apparent lake/reservoir differences in average chlorophyll response to phosphorus are related more to the limited generality of phosphorus/chlorophyll regression models and to regional factors than to effects of impoundment type. The analysis has led to the development of a more general model which explicitly accounts for effects of algal growth limitation by phosphorus, nitrogen, light, and flushing rate.

ISSN:1040-2381    

DOI:10.1080/07438148409354527

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A creel survey was conducted in 1980 on Norris Reservoir, Tenn., from March through October to assess the effects of artificial fish attractors (also known as hides, havens, shelters, or reefs) on fisherman success. An average of 9.8 brush-pile attractors was installed in each of 259 coves in the lake by TVA/CETA between 1978 and 1980. The 7.5-month creel survey yielded 1,435 party interviews, separating those fishermen who had fished only attractor areas (115 individuals) from those who had fished other areas exclusively (2,582), and those who had fished both attractor and nonattractor sites. Ten species of fish were caught by attractor fishermen, whereas nonattractor fishermen caught specimens of 19 species, and those who had fished both area types on the same day accounted for 15 species. Comparisons of attractor and nonattractor creels indicated that percent successful, mean number of fish caught, mean fish per man/hour, and mean kilograms per man/hour were all significantly higher for attractor fisherman. Analysis of variance showed that those fishermen angling primarily for crappie (Pomoxisspp.) caught significantly more fish per man/hour and kilograms per man/hour, contributing most to the higher overall success rates for attractor fishermen.

ISSN:1040-2381    

DOI:10.1080/07438148409354528

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Since 1969, the authors have been involved in over 200 hydroacoustic surveys of fish populations in more than 25 lakes. These studies have included a variety of different species assemblages and objectives, although most, such as Lakes Washington and Ozette in Washington and Tustumena in Alaska, are sockeye salmon nursery lakes. The objectives of these studies have included fisheries management, evaluation of lake enhancement programs, or environmental impact. During the 14 years of these investigations, both the equipment and procedures have evolved and improved considerably. Earlier techniques were very limited in their ability to detect fish near surface or in shallow water and had very limited capabilty for size discrimination. Current technology has solved most of these problems. These developments and their capabilities are presented along with the results of surveys on lakes with a variety of biological and physical characteristics. The results include a considerable amount of “ground truth” data from other assessment techniques. In many cases these data are obtained from various net sampling techniques. However, some comparisons have revealed considerable biases with net sampling techniques which are associated with changes in light intensity, turbidity, or fish behavior.

ISSN:1040-2381    

DOI:10.1080/07438148409354529

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Historical early life history patterns of fall Chinook salmon have been altered by impoundment of the Columbia River. While growth rates remain high, riverine survival has been reduced by impoundment, passage mortality at dams, predation, disease, thermal stress, and possibly, late ocean entry. Late ocean entry may reduce fall Chinook salmon survival by delaying passage through a sequence of habitats (spatial windows) at a time, size, or physiological state (temporal windows) when they are best adapted to that habitat. Extended freshwater residence retards higher growth rates normally associated with entry into the estuary and ocean, and reduces the higher survival associated with increased size. Managers of hatchery and wild stocks must take these spatio-temporal windows into account when evaluating management techniques such as flow manipulation or transportation.

ISSN:1040-2381    

DOI:10.1080/07438148409354530

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The expansion of the white perch,Morone americana, population in Lake Anna Reservoir, Va., is documented by examining data resulting from several collection methods. White perch data were derived from annual cove rotenone studies, bimonthly gill net and shoreline electroshock surveys, semiweekly intake screen impingement studies and seasonal entrainment and ichthyoplankton tow surveys. The length of the sampling period ranged from 2 to 7 years depending on how long each method had been employed on the Reservoir and when white perch appeared in each collection. An attempt is made to determine the impact of this expansion upon other species of fish in the reservoir and to address future implications.

ISSN:1040-2381    

DOI:10.1080/07438148409354531

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

From June 1980 through March 1983, 528 hoop nets fished in Lake George, Little Lake George and Crescent Lake, Fla. were observed, representing 4,356 net-days of fishing. Commercially important species comprised 66.1 percent of the total catch by number while game fish species represented 7.7 percent of the total catch and 23.1 percent of all game fish caught. Initial mortality for all game fish caught in lake hoop nets was 0.4 percent. Hoop nets baited with blueback herring,Alosa aestivalis, or soybean chips caught more commercially important species (4.5/net-day) than unbaited nets (2.3/net-day) and fewer game fish species (0.5/net-day) than unbaited nets (1.6/net-day). Commercially important species comprised 57.7 percent of the total catch in unbaited nets and 89.3 percent of the catch in baited nets. Game fish species comprised 41.5 percent of the catch in unbaited nets and 10.5 percent of the total catch in baited nets. Juvenile black crappiePomoxis nigromaculatus(< 22.9 cm) comprised 83.0 percent of all game fish caught in unbaited hoop nets while bluegill comprised 74.6 percent in baited nets. The catch rate of all sizes of game fish caught in baited and unbaited nets combined was 1.4/net-day. An estimated 10–20 game fish/hectare/year were caught in commercial nets during the study. Based on our knowledge of standing crop data from Florida lakes, legally fished hoop nets set for catfish apparently had little impact on the game fish populations of these lakes.

ISSN:1040-2381    

DOI:10.1080/07438148409354532

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor