摘要:

An analysis of data from four turbid North Carolina reservoirs showed that both the summer mean biomass and relative biomass of planktonic blue-green algae (Cyanophyta/Cyanobacteria) are frequently lower than would be predicted by models developed from natural north temperate lakes. These results are consistent with the hypothesis that the growth of blue-green algae in these reservoirs is reduced in the presence of high concentrations of non-algal turbidity.

ISSN:1040-2381    

DOI:10.1080/07438149009354702

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Forty-six bird species were observed on 33 Florida lakes with some species occurring on only one lake and others on as many as 26 lakes. Average annual bird abundance ranged from seven to 750 bird/km2and total species richness ranged from two to 30 species per lake. Regression analyses were used to examine the effects of lake trophic status, aquatic macrophyte abundance, and lake morphology on average annual bird abundance and total species richness. All trophic state parameters (total phosphorus, total chlorophylla, etc.) accounted for significant portions of the variance in average annual bird abundance, but total chlorophyllaconcentrations (μg/L) accounted for the highest percentage (47 percent) of the variance. The best fit regression equation was: Log Bird Abundance = 1.35 + 0.56 Log Total Chlorophylla. Lake area, shoreline length, and all trophic state parameters accounted for significant portions of the variance in total species richness. Multiple regression analyses indicated that lake area (km2) and total chlorophylla(μg/L accounted for the highest percentage (87 percent) of the variance in total species richness (species/lake). The best-fit multiple regression equation was: Log Species Richness = 1.10 + 0.47 Log Lake Area + 0.17 Log Total Chlorophylla. After accounting for lake trophic status and lake area, neither aquatic macrophyte abundance nor lake morphology accounted for additional variances in average annual bird abundance or total species richness.

ISSN:1040-2381    

DOI:10.1080/07438149009354703

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

In summer 1988, Lake Taneycomo, Missouri, developed conspicuous algal blooms as a result of low inflow from an upstream hydropower reservoir and phosphorus loading from a point source. In multiple regression models, variation in total phosphorus concentration and an index of water residence time accounted for 78–85 percent of the variation in transparency, chlorophyll, and volatile suspended solids in surface water. Non-equilibrium conditions in this rapidly flushed lake led to rapid and predictable increases in algal standing crops during lulls in power generation.

ISSN:1040-2381    

DOI:10.1080/07438149009354704

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Three approaches to estimating fluvial mass transport to receiving waters are reviewed: concentration-discharge regressions, load-discharge regressions, and concentration discharge product methods. Concentration-discharge regressions are applied when constituent concentration (C) depends on river discharge. Several dilution, concentration and mixed-effects linear regression models are illustrated. The load (L)-discharge (Q) regression form: log L = a + b (log Q), where L = CQ, is widely used to estimate mass transport because it yields high coefficients of determination (R2) when concentration-discharge regressions do not. This is illustrated for Truckee River, Nevada, using eight years of monthly total nitrogen concentration ([TN]) and discharge data. However, the observed high R2(0.92) results from product spurious self correlation, where the discharge term appears on both sides of the regression equation, and is not due to a dependency of [TN] on discharge. When concentrations do not depend on discharge, constituent loadings should be estimated as the product of concentration and discharge. Several concentration-discharge product methods are given for fixed-time-interval or flow-interval sampling of concentration.

ISSN:1040-2381    

DOI:10.1080/07438149009354705

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

MINLAKE, a dynamic, one-dimensional, unsteady lake water stratification simulation model has been extended by a water jet mixing submodel (JETMIX). The model is intended primarily to evaluate lake management and control strategies. The extended model simulates the continuous change of lake stratification in response to artificial mixing induced by water jets and natural mixing by wind and cooling. Artificially forced summer destratification with a recirculating pump/jet discharge system, and a warm water jet discharged into an ice-covered lake were studied. Numerical results were obtained to predict the effect of jet mixing on the evolution of water temperature and dissolved oxygen profiles in time. The effect of the warm water jet discharge on the ice cover was of particular interest. The simulation model was verified with laboratory experimental data. The capabilities and applicability of the model were illustrated with simulations of a hypothetical summer destratification and a planned winter discharge. The results can be used to design a hydraulic jet-mixing system for a lake or reservoir in summer and a submerged thermal outfall for year-round conditions.

ISSN:1040-2381    

DOI:10.1080/07438149009354706

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Triploid grass carp (Ctenopharyngodon idella) were stocked at a mean length of 229 mm (total length) into two small South Dakota lakes in 1985.Charasp. was the predominant aquatic macrophyte in both lakes. Prior Lake contained a fish community in which the largemouth bass (Micropterus salmoides) was the only top-level predator. An introduction of 49 grass carp per hectare resulted in nearly complete elimination of vegetation within two years. Northern pike (Esox lucius) was the dominant predator in East Lake Eureka. Grass carp were introduced at a density of 61 per hectare, but no impact on aquatic vegetation was noted. We believe northern pike predation reduced grass carp numbers. Therefore, we suggest that further work is needed on size of grass carp stocked in waters containing northern pike.

ISSN:1040-2381    

DOI:10.1080/07438149009354707

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Offset reservoirs deserve study because of their importance in water supply systems, yet little information is available about how these lakes process nutrients. To close this gap the water, nitrogen and phosphorus budgets were determined for an offset reservoir, Lake Hefner, Oklahoma. During 1981, about 87 percent of the water and 88 percent and 97 percent of the nitrogen and phosphorus entered the lake via a canal connecting the North Canadian River to the lake. The lake accumulated both nitrogen and phosphorus. The sedimentation coefficient (R) for phosphorus was 0.86 yr−1. Loading models developed for artificial lakes predicted roughly the same total phosphorus concentrations as were observed in the lake, although not precisely. Apparently, offset reservoirs are not special cases of artificial lakes. These conclusions were based upon a data set for only one year and do not reflect year-to-year variability. An empirical monitoring approach is suggested for management of offset reservoirs.

ISSN:1040-2381    

DOI:10.1080/07438149009354708

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Variations in the concentrations of total and particulate organic matter were estimated from 1979 through 1988 in natural and simulated runoff events to improve estimates of reservoir gross organic loading from intermittent flows. Total organic matter concentrations in natural runoff from pinyon-juniper watersheds and particulate organic matter concentrations in runoff from creosote bush watersheds increased as a natural logarithmic function of discharge. Total organic matter and particulate organic matter discharge-weighted concentrations in natural runoff events were related to measurements of instantaneous discharge and total organic matter and particulate organic matter concentrations, and to estimates of the maximum discharge of total organic matter and particulate organic matter concentrations that occurred in the event. In rainfall simulations conducted in watersheds of creosote bush, desert grass, pinyon-juniper, ponderosa pine, and spruce meadow, only particulate organic matter concentrations in ponderosa pine differed significantly (P ≤ 0.05) from the other sites; there, concentrations were lower. The percentage of organic matter in the total suspended solids eroded during simulated runoff events decreased as vegetation cover decreased and bare soil area increased. Estimates of gross annual total organic matter loading revealed large annual variations at specific reservoirs and large variations of mean annual loading among reservoirs. These results suggest that intermittent runoff has a significant potential impact on reservoir trophic states in arid and semi-arid regions.

ISSN:1040-2381    

DOI:10.1080/07438149009354709

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Eighty-four percent of Ohio's lakes and reservoirs are eutrophic. Significant reductions in nutrient loading are usually the object of lake restoration projects. However, variations in attainable nutrient concentrations, based on regional differences in watershed characteristics and land use, often are not considered. The purpose of this project was to evaluate the “ecoregion” concept for estimating which surveyed Ohio reservoirs might have the greatest potential for reduction in phosphorus concentrations. Ecoregional watershed characteristics dictate the practical lower or attainable limits of stream nutrient concentrations that can be reached. Attainable reservoir phosphorus concentrations were estimated from stream phosphorus concentration data that represent the best water quality in each Ohio ecoregion and by the use of a loading model. The reservoirs with actual summer 1989 phosphorus concentrations that exceeded predicted attainable concentrations by the greatest amounts were considered to have the greatest potential for restoration. These were not reservoirs with the worst trophic states. Similar findings have been reported for Minnesota (Heiskary et al. 1987). The method proposed here could be used statewide to establish water quality standards, provide a rational way to establish a priority program for lake restoration, and develop lake improvement and protection goals.

ISSN:1040-2381    

DOI:10.1080/07438149009354710

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

During the last decade Swedish agriculture has modernized considerably, as evidenced by increasing crop yields and declines in the amount of arable land and number of farmers. Two results of this agricultural modernization have been declining air and water quality. This paper summarizes what Swedish researchers have learned from long-term measurements of nutrient losses from agriculture and the subsequent effects on the surrounding environment. The results presented here are a collection of important findings from many Swedish research teams, including some work carried out by the authors. The conclusions can be summarized briefly as follows:•Swedish agriculture contributes about one-third of the total nitrogen emissions to air through evaporation of ammonia from the handling of manure, with subsequent effects on vegetation and acidification of soils and waters.•More than half of the ammonia deposited in Sweden originates from other northern European countries.•A complex pattern, including background and human factors, influences the leaching of nitrogen and phosphorus to water. Leaching has increased since the 1950s, although atmospheric conditions also play an important role.•Agricultural activities are only one reason for the pollution of coastal waters and the open sea surrounding Sweden. Other sources of significant pollution are atmospheric deposits, forestry, households, and urban stormwater. International understanding of the environmental problems caused by agriculture is urgently needed to ensure successful management of eutrophication. About 9 percent of the total nitrogen load and 5 percent of the total phosphorus load on the surrounding seas originate from Sweden.•There are many ways to reduce the pollution caused by agriculture. The cost-effective options include tailoring fertilizer application to soil content and crop requirements, redistributing excess manure to manure-deficient farms in other areas, and introducing “wintergreen” plants.•Before pollution from agriculture can be controlled, pollution must be understood. Without that understanding, efforts to prevent pollution may be neither helpful nor cost effective.

ISSN:1040-2381    

DOI:10.1080/07438149009354711

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor