摘要:

The purpose of this paper is to list known disturbances of Lake Washington, to describe the effect on the lake of several of them, and to discuss results in terms of whole-lake quasi-experiments. Eutrophication with treated sewage effluent and the diversion of effluent are treated as experiments, with nutrient manipulation, which change the phytoplankton community structure. A later unexpected increase in transparency is traced through a chain of predators to flood control measures in the largest inlet. An increase in alkalinity, accompanied by changes in phytoplankton, is attributed to real estate land development. The role of paleolimnological information is illustrated.

ISSN:1040-2381    

DOI:10.1080/07438149409354178

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We determined the pattern, rate, and extent of deposition of bulk sediments and sediment-bound phosphorus (P) in Black Lake. Vertical gradients in total phosphorus (TP) and137Cs often were irregular within cores and variable among cores, reflecting sediment disturbances including bioturbation, resuspension, and lateral transport. Surface sediments exhibited a horizontal spatial gradient in TP content, with P levels that declined downstream from the lake inlet, which reflected a large input of settleable P from the primary tributary. Sediment137Cs and TP data suggested an average lake-wide sediment accumulation rate of approximately 0.6 cm yr−1since the early 1960s and greater accumulation of TP in 1975–90 than during 1960–75. The mean depth of sediment accumulation over bedrock was estimated to be at least 3.6 m. These data indicate the contemporary rate of water depth decrease due to sediment accumulation in Black Lake is much greater than the lake's postglacial average, and the rate of sediment P accumulation may have increased recently.

ISSN:1040-2381    

DOI:10.1080/07438149409354179

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Sediment resuspension dynamics and discharge of sediment downstream in Marsh Lake (Minnesota) were examined during 1991 and 1992 under a variety of wind conditions. Based on a theoretical wave model, nearly the entire sediment surface area (81–100%) can be disturbed by wave activity at wind velocities as low as 15 km/h blowing from any direction. As an apparent result of dense submersed macrophyte beds that in 1991 covered nearly the entire lake, measured sediment resuspension was much less frequent than expected from wave theory in 1991 than in 1992. Critical thresholds of wind velocity required to resuspend sediment were much higher in 1991 (~ 20 km/h) than in 1992 (~ 12 km/h), resulting in a lower frequency of resuspension events in 1991 (5%) than in 1992 (32%). Discharge of resuspended sediment to downstream Lac Qui Parle Reservoir was much less in 1991 when submersed macrophytes were abundant than in 1992 when macrophytes were absent. These results suggest that the development and maintenance of stands of submersed aquatic macrophytes may be an effective management tool for limiting wind-driven sediment resuspension and sediment discharge in shallow impoundments and lakes.

ISSN:1040-2381    

DOI:10.1080/07438149409354180

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The first aluminum sulfate (alum) and sodium aluminate lake treatment in Washington State was performed in Green Lake, a shallow (mean depth = 3.9 m), highly eutrophic, polymictic lake in Seattle. During October 1991, 181 tons of alum and 76.5 tons of sodium aluminate were applied to attain a total aluminum dose of 8.6 mg L−1. The use of sodium aluminate as a buffering agent allowed a higher dose of alum to be used, and maintained lake pH (6.7) and alkalinity (28 mg CaCO3L−1) during treatment Secchi disk transparency increased from 1.9 to 6.1 m following treatment and remained higher throughout 1992 and 1993 than in pretreatment years with summer means of 3.5 and 2.9 m, respectively. Total phosphorus (TP) concentrations decreased from a mean of 40 μg L−1before treatment to 14 μg L−1immediately following treatment and remained below 29 μg L−1during 1992 and below 35 μg L−1during 1993. The 1992 and 1993 whole-lake, mean summer TP concentrations of 20 and 26 μg L−1. respectively, met the lake management goal of 30 μg L−1. Blue-green algal blooms were greatly reduced, despite the absence of summer dilution water inputs. Mean summer 1992 and 1993 chlorophyll a concentrations were 7.1 and 12.6 μg L−1; these concentrations were a marked improvement from the 1981 summer mean concentration of 28 μg L−1. The effectiveness of the alum/sodium aluminate treatment was critical in determining that the proposed $4.5 million, 11400 m3day−1water treatment plant, which would have provided low-nutrient dilution water to Green Lake, would not yield the desired improvement in lake water quality.

ISSN:1040-2381    

DOI:10.1080/07438149409354181

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Potamogeton crispus(Curlyleaf-pondweed) is an exotic macrophyte which has been introduced to the North American continent in the last century.P. crispusoften grows to nuisance proportions at the expense of native macrophyte communities. A summary of available literature onP. crispusplus original data are presented to improve the understanding of this exotic and and in lake improvement projects. Topics include the life cycle ofP. crispusis broken into sections covering the annual cycle of growth, reproduction, senescence and germination; environmental conditions associated with growth such as water quality, substrate characteristics and physical water conditions; nutrient dynamics ofP. crispuscovering the accumulation and concentration of nutrients found inP. crispustissue; growth rate and biomass production; and various macrophyte control measures.

ISSN:1040-2381    

DOI:10.1080/07438149409354182

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The ability of the crayfishOrconectes immunisto graze submersed aquatic macrophytes was evaluated experimentally. Crayfish at a biomass greater than 140–150 g m−2(fresh weight) significantly decreased macrophyte biomass in all experiments. The rate of crayfish grazing in cages where significant decreases in macrophyte biomass occurred averaged 0.012 g m−2day−1crayfish−1(ash-free dry weight) of macrophytes.

ISSN:1040-2381    

DOI:10.1080/07438149409354183

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Fifteen years of historical data from Lake Okeechobee, Florida, were used to quantify relationships between annual mean and extreme values of algal biomass, measured as chlorophyllaYearly chlorophyllamaxima and algal bloom frequencies (the percent of samples during a year containing >40 μg L−1chlorophylla) increased approximately 2-fold for each unit increase in the annual chlorophyllamean, although there was some variation in these relationships among different regions of the lake. Threshold chlorophyllaconcentrations (15–21 μg L−1) were also identified, below which bloom frequencies were reduced to near zero. Results indicate that if nutrient diversion strategies are successful in reducing annual mean chlorophyllaconcentrations in Lake Okeechobee, even more pronounced reductions in algal blooms will occur. Reductions of lake-wide chlorophyllameans to early 1980s levels might nearly eliminate algal blooms as defined here.

ISSN:1040-2381    

DOI:10.1080/07438149409354184

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This study quantified the seasonal and spatial distribution of algal blooms (defined as chlorophylla>40 μg L−1) in Lake Okeechobee, based on 13 years of data collected from eight pelagic monitoring stations by the South Florida Water Management District Relationships between bloom frequencies and limnological parameters, including nutrient (nitrogen and phosphorus) loading rates, in-lake nutrient concentrations, Secchi transparencies, lake stage, and wind velocities, were investigated by rank correlation analyses. Blooms were found to vary both seasonally and spatially; they were most frequent during late spring and autumn, and they generally occurred in the northern and western regions of the pelagic zone. Blooms were least frequent in a central pelagic region where resuspension of soft mud sediments by wind produces frequent light limitation. Lake-wide bloom frequencies were uncorrelated with external loads of phosphorus and nitrogen, but were positively correlated with water temperatures (r = 0.19, p = 0.009) and Secchi transparencies (r = 0.22, p = 0.003). Blooms were negatively correlated with both wind velocity (r = −0.45, p = 0.05) and total phosphorus (r = −0.30, p < 0.001). The latter reflects a wind-driven resuspension of phosphorus-containing sediment particles, which produces low light availability and a subsequent decoupling of total phosphorus and algal blooms in this shallow lake ecosystem.

ISSN:1040-2381    

DOI:10.1080/07438149409354185

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Excessive atmospheric H2S (hydrogen sulfide) emissions from large salt evaporation ponds in San Francisco Bay, California, and the effectiveness of possible remedies have been studied since 1989. These emissions are caused by filamentous algae (Cladophoraspp.,Enteromorphaspp.) which accumulate on the downwind shores, and decay under anoxic conditions. On-site pilot experiments were used to test the effectiveness of two methods of controlling H2S emissions: harvesting the shoreline accumulation of filamentous algae and the use of a barrier (“phytofence”) to prevent accumulation of algae onshore. Replicate experimental plots were set up along a portion of the downwind (east) shore. Atmospheric H2S concentrations above the phytofence plots were significantly lower than above both control and harvest plots. In addition, total dissolved sulfide was significantly lower and dissolved oxygen significantly higher in the phytofence plots than in control and harvest plots. Thus, a phytofence may be a viable method for reducing H2S emissions. Harvest plot H2S emissions, total dissolved sulfide, and dissolved oxygen concentrations were not significantly different from control plots. Removal of filamentous algae to significantly reduce the H2S emissions is impractical early in the season due to large amounts of algae involved and the difficulty of harvesting; it is impossible later in the season because of the decomposed state of the algae. Harvesting is not a viable method for reducing H2S emissions from these evaporation ponds.

ISSN:1040-2381    

DOI:10.1080/07438149409354186

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Although most authors accept that trophic status and angler effort affect fish yield, few predictive relationships use both variables because both are rarely available in the same data set. To fill this lacuna, we have developed a data set representing lakes of various trophic levels lying on both igneous and sedimentary drainage basins in Ontario. These data include estimates of sport fish yield, lake morphometry, lake chemistry, and fishing effort. With these data, we developed five models. None of these models were significantly better than the rest but all predicted sport fish harvest effectively despite the presence of ratios in three of the models. The model that is most attractive because it contains no ratios, explains 86% of the variation in sport fish catch, and uses manipulable variables, is: log10catch (kgseason−1) = 0.685 log10angler hours (hoursseason−1) + 0.366 log10TP (total phosphorus)-area (mg m−1) – 0.124 (log10mean depth)3(m) −1.028.

ISSN:1040-2381    

DOI:10.1080/07438149409354187

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor