摘要:

Water quality variability can be examined to estimate the magnitude of changes in water quality needed to detect significant differences over time. Adjustments can be made to reduce the estimate of variability, thereby decreasing the water quality change required for statistical significance. These adjustments include: accounting for changes in meteorologic and hydrologic conditions through covariate variables in trend analyses; changing the sampling frequency; increasing the number of years in the monitoring scheme; and use of other statistical trend analyses, such as t-tests, linear regression, and time series analyses. Water quality monitoring data was examined from the Idaho Rural Clean Water Program (RCWP) project. Generally, a 30 to 60 percent change in unadjusted geometric mean concentrations is required to document a significant change in water quality. However, adjustments that reduce the estimate of variability can be used to reduce the required concentration change to 20 to 40 percent.

ISSN:1040-2381    

DOI:10.1080/07438148709354775

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Procedures are described for establishing mean chlorophyllawater quality standards based on the probability and frequency that any specified “maximum” chlorophyllaconcentration will be exceeded by a given mean chlorophyllaconcentration. The models developed employ frequency distribution relationships and provide a means through which water quality standards can be established for mean chlorophyllaconcentrations while accounting for the impacts of peak algal growths. This is felt to be a more appropriate approach than establishing arbitrary maximum chlorophyll a standards. The relationships developed can be used in conjunction with other models to predict the effect that remedial programs could have on the probabilities that chlorophyll a concentrations would exceed desired levels. The procedures permit the establishment of rational sampling programs for compliance/ enforcement monitoring. These models are calibrated on data for North Carolina lakes. The complications arising from the dependency of “maximum” chlorophyllaon sample size is accounted for by these models. A linear regression model is developed for predicting the largest expected chlorophyllaconcentration from the mean chlorophyllaconcentration, and is compared with the model based upon frequency distribution relationships.

ISSN:1040-2381    

DOI:10.1080/07438148709354776

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

During the summer months of 1982 and 1983, aninvivo, flow-through, fluorometric method was used to obtain chlorophyllaestimates on a synoptic basis from the upper euphotic zones of two Oklahoma reservoirs (Grimshaw et al. 1985). SYMAP, a computer-based mapping routine was used to generate a total of 73 synoptic chlorophyll isopleth (chloropleth) maps for these reservoirs, and reservoir areas containing persistently high chlorophyll concentrations were delineated statistically. Serial chlorophyll mapping was effective in delineating sources of nutrient pollution, and proved useful in the development of efficient, cost-effective, sampling programs. The greatest strength of the method lies in its suitability for use on water bodies which have not been previously characterized limnologically. Its use permits a rapid transition from descriptive to experimental limnology for water bodies lacking a history of limnological research.

ISSN:1040-2381    

DOI:10.1080/07438148709354777

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Underwater macrophytes can influence fish diet and growth by restricting access inshore. The movements of largemouth bass (Microptemssalmoides) and biuegills (Lepomismacrochirus) were followed in a shallow Wisconsin impoundment nearly one-half covered with potamogetons and other macrophytes. Plant density averaged 130–200 g/m2(dry weight) from May through August during the six-year study. Fish activity was observed from a still boat or by diving. Stomach samples of fishes were obtained on 55 dates by boom shocking. Submerged macrophytes at a density above 90 g/m2functioned as a screen to selectively restrict fish movements. Bass and bluegills under age III were mostly confined to plant beds, where they grazed chironomid larvae and other aquatic insects on the plants and lake bottom. Bluegills shifted to zooplankton and finally plant tissue as summer progressed, while bass turned increasingly to fish as prey. Older bass had difficulty in penetrating the plant beds until openings appeared from plant decay or were created by a mechanical harvester. Slow growth of bass after age II was also reported in other Midwestern lakes with dense vegetation and is attributed to their difficulty in foraging on young fishes inshore. Selectively channelizing macrophyte beds with bottom screens or a mechanical harvester can be an effective management strategy to enhance fish growth in densely-planted lakes.

ISSN:1040-2381    

DOI:10.1080/07438148709354778

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Littoral zones are centers of community life in shallow lakes and reservoirs. Invertebrates and young fishes forage and seek cover among the bottom and plant habitats found inshore. Because boaters and swimmers scorn dense vegetation, lake shallows are defoliated with chemical herbicides or mechanical harvesters. Such wanton destruction of animal and plant life can be avoided by restructuring littoral zones. This architectural approach views lakes as aquascapes that can be improved for both recreation and biological diversity. A lake use plan is first developed from a hydrographic map depicting summer macrophyte growth and patterns of lake use. The lake is next zoned into areas of similar function. A management strategy is then tailored to each zone. Some lakes are managed for specific functions; others for multiple use. Intensive management is applied to open space zones for swimmers and boaters. Posting speed or time restrictions on power boating in these zones can reduce user conflicts. Prime angling habitat is constructed in other areas by channelization or transplantation. Quiet zones of dense foliage are reserved for waterfowl. Emergent cover is planted on shore for birds and small mammals. Restructuring littoral zones ultimately provides a balanced and integrated approach to enhancing lake recreation without needless loss of community life.

ISSN:1040-2381    

DOI:10.1080/07438148709354779

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Factors influencing the growth and distribution of submersed aquatic macrophytes in two South Carolina reservoirs were investigated through the statistical analysis of chemical, physical and biological data obtained throughout the 1984, 1985 and 1986 growing seasons. Comparisons of parameter means between areas with and without plants identified significant differences for depth, Secchi depth, light penetration, dissolved oxygen. Comparisons of parameter and means between areas with and without plants identified significant differences for depth, Secchi depth, light penetration, dissolved oxygen, pH, nitrate-nitrogen, and fetch (exposure). Through logistic multiple regression techniques, Secchi depth, light penetration, surface, dissolved oxygen, and fetch were determined to be important in predicting the presence of submersed aquatic macrophytes. Of the parameters examined, light penetration and fetch appear to have the strongest influence on macrophyte distribution. Light penetration most likely limits macrophyte distribution in the shallow sheltered areas of upper Lake Marion, which experience high suspended solids loadings, and in pelagic regions where the effects of surface waves generally would not reach the bottom. In the shallow, open areas of lower Lake Marion and Lake Moultrie, fetch appears to be the most influential factor.

ISSN:1040-2381    

DOI:10.1080/07438148709354780

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Aluminum sulfate was injected directly into lake sediments in an attempt to create a phosphorus-limiting environment to control macrophyte growth. The experimental site was located in a shallow lagoon off Lake Wingra, Wisconsin, which historically supports a dense, monotypic stand ofMyriophyllumspicatum. A pump and probe mechanism was developed for sediment injection and alum was injected into experimental plots in late May 1986 at a dosage of 200 mg Al3+/L. Following injection, total dissolved phosphorus was reduced to a mean of 70 μg/L in interstitial Water at 13 cm sediment depth, compared to a mean of 460 μg/L in control plots at the same sediment depth. Phosphorus remained significantly lower in treated plots for at least 2 months. Alkalinity and pH were not significantly reduced; dissolved aluminum levels increased immediately following injection, but only in sediment-surface samples in harvested plots. No reduction in biomass attributable to alum treatment was observed during the 1986 growing season. No differences were seen in the percent phosphorus by dry weight in plant vegetation but lower percent phosphorus in root tissue was attributable to the alum treatment. Phosphorus mobilization from sediments and incorporation in plant tissue appears to have been more rapid in alum treated plots compared to controls.

ISSN:1040-2381    

DOI:10.1080/07438148709354781

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Recent hatchery advances producing sterile triploid grass carp and the relaxing of state and federal restrictions on their distribution are expected to result in widespread use of these fish for aquatic plant management in North America. This large Asian cyprinid is a voracious herbivore and must be used properly to avoid major reductions in desirable aquatic vegetation. Grass carp exhibit strong food preferences and should only be used to manage plants that they prefer. Their use to manage plants that they do not prefer can result in expansion of the target plant and severe reductions in non-target species. Food preferences must be verified regionally. For best results, plant biomass should first be reduced and then grass carp should be stocked at 2 fish per metric ton of remaining vegetation. Grass carp should not be used to control aquatic plants in waterfowl management areas. Because grass carp are very difficult to recapture, overstocking should be avoided. Overstocking grass carp has resulted in near complete elimination of submersed plants and severe reductions in many emersed species for periods greater than 10 years. Use of grass carp can increase turbidity, phytoplankton, and nutrient concentrations in the water column but to a lesser degree than can occur using most aquatic herbicides. Provided that they are not overstocked, triploid grass carp appear compatible for use in fisheries management areas.

ISSN:1040-2381    

DOI:10.1080/07438148709354782

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Grass carp (CtenopharynqodonidellaVal.) were introduced to McNeely Lake in August 1985 in an attempt to control nuisance growths of duckweed on the lake surface. Complete control of duckweed was achieved within nine months of the stocking date. No significant changes in nutrient concentrations, dissolved oxygen levels, or general water quality parameters have been observed. Although phytoplankton standing crop, as estimated by chlorophyll a levels remained unchanged, there appears to have been a shift in algal populations toward smaller species and diatoms.

ISSN:1040-2381    

DOI:10.1080/07438148709354783

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The effects of insect and mite herbivores and plant pathogens on waterhyacinth leaf and ramet mortality were studied at Canal-M, Palm Beach Co., Florida, from December 1981 to January 1983. Individual ramets were tagged in December 1981 and again in May 1982, then monitored to determine rates of leaf production, proportional amounts of damage by various organisms, and ultimate causes of leaf and ramet mortality. Only the mothSameodesalbiguttalis(Warren) and the weevils,NeochetinabruchiHustache andN.eichhorniaeWarner, caused reduced leaf longevity. Other organisms were sporadic or restricted to old leaves. About 74 percent of the first group of tagged ramets were killed.S.albiguttaliskilled 31 percent by late April, then ceased to be effective due to changing plant morphology.Neochetinaspp. killed 42 percent, and mortality was relatively constant.Neochetinaspp. killed about 33 percent of the shoots tagged in May. We conclude thatS.albiguttalisis effective for control of waterhyacinth in only very restrictive circumstances. The weevilN.eichhorniae, and to a lesser extentN.bruchi. are more effective biocontrol agents. The demise of the waterhyacinth population was predictable from a comparison of leaf production and leaf mortality rates. The relationship between herbivore persistence and the plants' ability to replace damaged tissue mediates the resiliency of waterhyacinth populations.

ISSN:1040-2381    

DOI:10.1080/07438148709354784

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor