摘要:

The Tennessee Division of Water Pollution Control and the Tennessee Valley Authority (TVA) conducted a series of investigations from 1981 through 1983 to determine the extent of polychlorinated biphenyl (PCB) contamination of fish and sediment in Fort Loudoun Reservoir near Knoxville, Tenn. Fish and sediments from the Little River embayment had higher PCB concentrations than samples from other parts of the reservoir, and sediments contained up to 7 μg/g PCB near the mouth of the embayment. Little River embayment catfish contained up to 22 μg/g PCB in edible flesh, and over 60 percent exceeded the 5 μg/g Food and Drug Administration (FDA) limit for PCB. Sport fish and commercially important rough fish had PCB burdens below the 5 μg/g FDA limit. As a management response, a public advisory in April 1982 recommended against frequent consumption of catfish from Fort Loudoun Reservoir or consumption of any catfish from the Little River embayment. The Little River embayment was posted and closed to commercial catfishing. Active sources of PCB contamination were identified and eliminated. In August 1984 FDA revised the limit for PCB in edible fish flesh from 5 μg/g to 2 μg/g. As a public health precaution, Fort Loudoun Reservoir was closed to the taking of catfish for commercial resale and a public health advisory was issued against consumption of catfish by sport fishers. An extensive sampling program was designed and initiated to update the 1981–83 data base.

ISSN:1040-2381    

DOI:10.1080/07438148609354597

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

During June 1985 triploid grass carp (Ctenopharyngodon idellaVȧl.) were stocked in a large canal (2,000 cfs) to evaluate their potential for controlling hydrilla (Hydrilla verticillataL.F. Royle). Hydrilla biomass decreased from 9.1 kg/m2at the time of stocking to 0.12 kg/m2at the end of six weeks (includes effects of partial drawdown). Larger radio-tagged fish (1,000 g) had negotiated smaller canal culverts and siphons in previous studies, but the smaller fish of this stocking (120 g) have not traveled upstream past any structures with an elevation drop or turbulence. A canal drawdown one week after stocking removed aboveground biomass of plants in shallow water, but the reappearance of small plants in this area may indicate that the fish are less willing to feed in shallow water. Fish should be stocked between structures and at frequent intervals on long reaches of uninterrupted canal. Stocking prior to plant biomass buildup allows faster weed control.

ISSN:1040-2381    

DOI:10.1080/07438148609354598

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Grass carp have effectively controlled submergent aquatic macrophytes in large reservoirs when stocked at densities up to 75 fish per vegetated hectare. Large systems pose special concerns relative to decisions on whether to stock grass carp. Multiple use, multiple agency involvement, and interstate jurisdictions complicate decisionmaking. Complex vegetation communities of large systems make results less predictable. Grass carp movements not only allow impacts on nontarget areas but also may result in incomplete control. Grass carp biology is understood well enough to predict effects on vegetation, but vegetation responses to grass carp are not predictable enough for vegetation to be managed rather than controlled. This paper discusses the potentials and limitations for grass carp in large, open systems based principally upon studies in Lake Conroe, Tex., where 45 percent of the 8,000–hectare reservoir was infested by submergent macrophytes.

ISSN:1040-2381    

DOI:10.1080/07438148609354599

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Biomanipulation is a relatively new approach toward managing lakes. As a result, few data support its use, and many fisheries managers are reluctant to apply this technology. However, the results of biomanipulation and fisheries renovation programs are often the same: reduced populations of nuisance algae and improved water transparency. In this paper, the relative roles of rough fish elimination and restructuring the plankton–fish mix (biomanipulation) are compared as mechanisms in improving water transparency in lakes. Fisheries survey records from 13 renovated or winterkilled Indiana lakes are used to quantify these relationships. A statistically significant inverse relationship between Secchi disk transparency and percent of planktivorous fish exists for the lakes studied. Possible mechanisms for change are discussed, and recommendations for fisheries management are advanced.

ISSN:1040-2381    

DOI:10.1080/07438148609354600

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The biological structure of a 1.4 ha (3.5 acre) pond in Oldwick, N.J., was assessed during 1983 to facilitate improving swimming and fishing conditions. A biological management strategy, including reducing planktivore populations and restructuring of fish community size distribution, was employed in the spring of 1984. Although fish biomass was reduced, proportional stock density values indicated that fishing quality was substantially improved. Growth and recruitment of gamefish appeared to be minimally affected after one year of post-implementation monitoring. Reduced adult planktivore biomass lessened predation pressure on zooplankton stocks, which increased in both abundance and mean individual size. A resultant increase in grazing activity yielded reduced phytoplankton biomass through the summer and increased water clarity. Appeal and safety for contact recreation were noticably enhanced. The results suggest that managing fish populations can have cascading effects on other trophic levels to achieve a balance among desired water uses.

ISSN:1040-2381    

DOI:10.1080/07438148609354601

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Delaware Park Lake is an 11 ha lake located in Buffalo, N.Y. The average depth of the lake in 1975 was approximately 1.0 m. The lake suffered from eutrophication and associated problems including algal blooms, fishkills, odor, high turbidity, and bacterial contamination. In 1976 a four-part project to restore the lake was proposed under the federal Clean Lakes Program. The plan included isolating the lake from its inlet and outlet and diverting the inlet stream around the lake. The second project element rerouted storm sewers that had been entering the lake. The third involved involved draining and dry excavating 100,000 m3of bottom sediments. The final phase provided a makeup source and dilution water by way of a groundwater pumping system. Pre-restoration (April–August, 1979) water quality parameters indicated degraded conditions. Total phosphorus, chlorophylla, and Secchi transparency averaged 120 μg/L, 19.3 μg/L and 0.6 meter, respectively. Post-restoration quality (May–August, 1984) is improved with total phosphorus, chlorophylla, and Secchi transparency averaging 26 μg/L, 8.2 μg/L and 1.0 meter, respectively.

ISSN:1040-2381    

DOI:10.1080/07438148609354602

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A quantitative survey of the submersed aquatic macrophytes of Devils Lake, a 151 ha softwater seepage lake, was conducted July 30–August 1, 1984, in an effort to assess historical changes in the lake's macrophytes and water quality. Biomass (oven dry weight) and frequency of occurrence data were obtained from 28 transects spaced 200 m apart. Sample quadrats of 0.1 m2were collected at 5 m intervals along transects from shore to a water depth of 9 m. Eurasian watermilfoil,Myriophyllum spicatum, ranked second only toPotamogeton robbinsiiin importance, comprising 21 percent of total biomass and 35 percent frequency of occurrence. Milfoil was visually dominant, forming three distinctive surface canopy beds 25–50 m wide by 300 m long at water depths from 2–3 m. Total milfoil acreage (3 ha) represented 10 percent of the total vegetational cover in the lake. Average milfoil biomass within dense stands ranged from 160 to 183 g/m2between beds. Milfoil expansion within Devils Lake was accompanied by a decline inElodea canadensis. M. spicatummay be a disturbance indicator species (pioneer) rather than an aggressive invader.

ISSN:1040-2381    

DOI:10.1080/07438148609354603

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Between 1980 and 1983 dense beds of the macrophyteMyriophyllum spicatumL. became well established throughout Candlewood Lake, Conn., at the expense of a once diverse native flora. During 1983–84 and 1984–85 winter drawdowns of 2 and 2.7 m, respectively, were attempted to control the densities and further spread of theM. spicatum. After the initial drawdown, weed biomass was reduced by more than 90 percent in shallow sites; however, little change in densities occurred in deeper areas. The deeper drawdown resulted in a further reduction inM. spicatumdensities, although it remained the dominant plant at depths greater than 2.5 m.Najas minor allionibecame the dominant macrophyte in shallow areas, presumably developing from seeds.

ISSN:1040-2381    

DOI:10.1080/07438148609354604

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

In support of the U.S. Fish and Wildlife Service's Acid Precipitation Mitigation Program, International Science & Technology, Inc., and its subcontractors, AquaComp, Inc. and Svenska IS&T, developed a microcomputer-based decision model to assist water resource managers in selecting the most effective chemical neutralization strategy for renovating acid-stressed lakes and streams. The program can be used to establish proper dosages for a neutralization agent such as aglime through a dose calculation/dissolution subroutine. In addition, the program can assist in the selection of the most appropriate chemical agent, grain size (for neutralization agent), application technique, and reapplication rates to optimize costs and effectiveness for treating a particular system. The program also has subroutines that address dose calculations and effectiveness in meeting water quality objectives.

ISSN:1040-2381    

DOI:10.1080/07438148609354605

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

PHRED is a computer program written in C to run on the Radio Shack Tandy 6000 microcomputer. This program quantifies nonpoint source pollution in the form of sediment and phosphorus from cropland that is either in rotation or in continuous corn. It computes the production cost and net return to the farmer for existing conditions and for combinations of management practices. It also derives the corresponding dollar value benefit of pollutant reduction for each of the possible conservation practices and determines a benefit-to-cost ratio (B/C ratio). Conservation practices are incrementally applied to fields with excessive erosion rates in order of best B/C ratio until either an overall B/C ratio of 1 or an allowable erosion rate is achieved. Printouts of erosion rates, sediment delivery, phosphorus delivery, on and off site benefits, production costs, net returns, and conservation practices are available on a field by field basis and as aggregated totals for the farm and/or watershed.

ISSN:1040-2381    

DOI:10.1080/07438148609354606

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor