摘要:

Excluding motor boats from small experimental plots in a lake with heavy boat traffic significantly increased macrophyte biomass, coverage, and shoot height compared to impacted areas. Lakes across the country are increasingly threatened by overuse, particularly involving more and larger motor boats. In recent years, Lake Ripley, located in Jefferson County in southern Wisconsin, has exhibited a decline in macrophyte abundance along with increased motor boat activity. To examine the possible connections between these two events, a study on the effects of motor boats on submerged aquatic macrophytes was conducted during the summer of 1995. Four enclosures, two of solid plastic and two of mesh fencing, were built in each of two areas in about 1 m of water adjacent to high boat traffic areas. These enclosures were intended to exclude motor boat access and, in the solid-walled enclosures, to block the turbidity generated by boat-induced sediment resuspension. Weekly water samples were collected for turbidity, suspended solids, dissolved oxygen, and temperature. At the end of the study, plant biomass, height and percent cover were measured inside the enclosures and in control plots. Our hypothesis was that motor boats limit macrophyte growth either directly by physical disturbance or more indirectly by generating turbidity which decreases light availability and therefore limits production and biomass. Results indicated that motor boats reduced plant biomass quite dramatically, primarily through scouring of the sediment substrate and direct cutting, but not through turbidity generation.

ISSN:1040-2381    

DOI:10.1080/07438149709354290

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

All state licensed commercial fisheries taking lake whitefish (Coregonus clupeaformis) in Michigan waters of Lake Superior have been required to use trap nets since 1974. Trap nets are fished with pot depths (≤27.4 m (90 ft), which is within easy reach of deep diving common loons (Gavia immer). In 1993, some commercial fisheries began to modify (increase) the mesh size on the top of the net heart from 20.4 cm (8 in) stretched mesh to 30.4 cm (12 in) stretched mesh to allow loons to escape. In 1995, 3 fisheries were monitored to estimate catch and mortality of common loons. These samples represented 9% of the total annual trap net effort by these fisheries. Seven dead loons were found entangled both in the pots and in the hearts. None was caught in the heart of modified nets. The extrapolated annual catch of common loons was 77, with 43% of these caught in the hearts of unmodified nets, compared to 86% in unmodified nets before conversion. It appears that stretched mesh size of 30.4 cm reduces catch and mortality of common loons, thus a recommendation to convert tops of nets to large mesh is appropriate.

ISSN:1040-2381    

DOI:10.1080/07438149709354291

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Pelagic total phosphorus (TP) concentrations in Lake Okeechobee were shown previously to be correlated with lake water levels, possibly due to littoral flooding and subsequent P release from vegetation (Canfield and Hoyer 1988). The present paper reviews the research to test this and other hypotheses to explain the water level – TP relationship. Research in the littoral region indicates that during low to intermediate water levels, there is little water or nutrient exchange between the pelagic and littoral regions, and that under high water levels, the littoral is a P sink. These findings lead to a rejection of the littoral flooding hypothesis. Alternative hypotheses, concerning internal loading from pelagic sediments, have been suggested. Maceina and Soballe (1990) proposed that wind, rather that water level, controls TP – in windy years, there is frequent resuspension of P-rich sediments into the water column. This hypothesis is supported by results of hydrodynamic model simulations, and by studies of sediment composition and sediment-water P transport. Also, there is evidence that horizontal P transport is enhanced by a combination of high wind and high water levels (Maceina 1993). There is an additional effect of high water levels that could increase TP concentrations – a greater thermal stability of the water column during summer could result in anoxic bottom waters and subsequent P release. Research results showing that Fe regulates soluble P transport between sediments and water in Lake Okeechobee, and findings that this process is a key one affecting internal loading in other shallow lakes, are supportive of this hypothesis.

ISSN:1040-2381    

DOI:10.1080/07438149709354292

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Lake Okeechobee experiences blooms of cyanobacteria, perhaps due in part to the low nitrogen:phosphorus (N:P) ratios found in the water column, which may favor cyanobacteria over other phytoplankton taxa. The current strategy for managing the lake is to reduce external P loads. Some have recommended that pumping of N-rich water from the Everglades Agricultural Area (EAA), located adjacent to the south end of the lake, into Lake Okeechobee could increase N:P ratios and reduce cyanobacterial blooms until P loads are reduced. We conducted experiments to assess potential impacts of that strategy on phytoplankton in the lake's south pelagic region. Threein situexperiments were conducted during July 1994, with triplicated treatments (P, N, N+P, or EAA canal water additions) applied to 20-L clear plastic carboys, which were incubated in the lake for 3 days. In the first experiment, additions of P (50 μg · L−1) did not stimulate chlorophyllaor net primary productivity. Additions of N (500 μg · L−1) led to significant increases in both parameters. The greatest biomass and productivity increases (5-fold) occurred when the N and P were added together. In the second experiment, additions of N at 1X, 2X, and 4X the concentrations utilized in experiment 1 caused 3-fold increases in chlorophyllaand primary productivity. Nearly the same results were obtained in the third experiment, where EAA canal water was added to lake water in a 1:10 or 1:5 ratio, increasing soluble reactive P (SRP) by 17 and 34 μ · L−1, and dissolved inorganic nitrogen (DIN) by 175 and 350 μg · L−1, respectively. Although agricultural canal water often has been shown to contain herbicides which can suppress algal growth, no such effect was observed here. The yields of chlorophyllaper unit SRP or DIN in experiment 3, where canal water was added, were nearly identical to those in experiments 1 and 2, where N or N+P were added. In none of the experiments was there a shift from cyanobacteria to other algal taxa, despite the presence of small rapidly-growing chlorophytes in the lake water inoculum. The phytoplankton was dominated by cyanobacteria (70 to 81% of total phytoplankton densities), especiallyLyngbya, Oscillatoria, Chroococcus, andAphanocapsa, in all treatments, which encompassed DIN:SRP ratios from below 1:1 to over 140:1. From a management standpoint, these results indicate a potential for increased biomass of cyanobacteria in this N-limited lake if water pumping from the EAA were to be substantially increased.

ISSN:1040-2381    

DOI:10.1080/07438149709354293

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The South Florida Water Management District (SFWMD), like many environmental management programs, is faced with complex decisions about research and management. These decisions incorporate both qualitative and quantitative information, are often characterized by uncertainty, and usually involve multiple decision makers. A decision analysis system has been suggested to help the SFWMD make such complex decisions. Through a case study, this paper explores the potential of the Analytic Hierarchy Process (AHP) as a decision analysis tool. The AHP is applied to the selection by the SFWMD Research Department of a water quality model for blue-green algal blooms in Lake Okeechobee. The three models under consideration were Eutromod, Expert Elicitation (structured scientific judgment), and WASP4. In the case study of model selection, four respondents were interviewed using the AHP. Three of the four respondents chose WASP4 as the favored model; this was an unexpected result for two of the respondents. WASP4's success was largely due to the emphasis the respondents placed on accuracy and the high accuracy rating this model received. The AHP was shown to be useful in finding the sources of differences in opinion. Thus, the AHP results appeared to be a useful basis for group communication and decision making. Based on the case study experience, it seems likely that the AHP has the potential to aid numerous types of complex environmental management decisions.

ISSN:1040-2381    

DOI:10.1080/07438149709354294

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A decision analytic framework and the USEPA mechanistic water quality model WASP4 were used to prioritize research and monitoring needs to address the water quality management objective,reduce algal blooms to an acceptable levelin Lake Okeechobee. With the WASP4 model as a scientific assessment framework, proposed research and monitoring projects should be evaluated for their effectiveness in reducing WASP4 prediction uncertainty. Sensitivity analysis based on either model calculations or expert judgment may be used to estimate the reduction in prediction uncertainty associated with proposed projects. A utility-based approach can then be developed to select from among proposed research and monitoring projects. Selected projects may be expected to provide scientific information to reduce model prediction uncertainty for the use of the model in decision making.

ISSN:1040-2381    

DOI:10.1080/07438149709354295

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Decision analysis provides an organized, logical frame work for decision making under uncertainty. In brief, decision analysis should begin with thorough identification of objectives, attributes, and feasible management actions, followed by development of a probability model to characterize uncertain science and a utility or net benefits function to represent value. This approach results in an analytic framework that may be used to guide decision making and to answer questions such as: (1) is scientific understanding sufficient to act now, or should additional information be obtained? (2) if additional information is needed, what scientific research and monitoring should be undertaken to provide this information? (3) what, if any, simulation model should be used to evaluate and present scientific information for decision support? These research and modeling issues are explored in an application of decision analysis to guide research planning for the management of eutrophication in Lake Okeechobee, Florida. This paper describes decision analysis, outlines the Lake Okeechobee eutrophication problem, and explains the importance of the simulation model in research prioritization.

ISSN:1040-2381    

DOI:10.1080/07438149709354296

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Phytoplankton biomass, composition, and size structure were examined in oligotrophic Kootenay Lake, British Columbia, during two years of a fertilization program aimed at enhancing declining stocks of kokanee salmon. Phosphorus (47.1 metric tonnes per year) and nitrogen (206.7 metric tonnes per year) were added to the northern end of this long, narrow lake. Comparisons were made between the fertilized North Arm and unfertilized South Arm of the lake. The two arms did not indicate any significant differences in water chemistry prior to fertilization. Algal biomass was highest at the fertilized sites during the spring bloom (June) but did not differ between fertilized and unfertilized regions during the summer months (June 21 – September 21). There was an overall increase in biomass from 1992 (the first season of experimental nutrient loading) to 1993. Algal composition at the division level did not change between fertilized and unfertilized sites, except in 1993 when an increase in summer Chlorophyta was seen at the fertilization area relative to the unfertilized area. Diatoms dominated the phytoplankton community followed by Cryptophyta and Chrysophyta. The biomass of the nanoplankton (2 to 20 μm) and microplankton (20 to 64 μm) size fractions was not altered between fertilized and unfertilized sites in 1992, but there was an increase in net plankton (> 64 um) at the fertilized sites. In 1993, the average biomass of the nanoplankton had decreased at both sites while average microplankton biomass was significandy higher than in 1992. Photosynthetic picoplankton (0.2 to 2 μm) biomass was lower in the fertilized than in die unfertilized area on the one date of assessment in the summer of 1993, suggesting that fertilization may be shifting die energy flow in Kootenay Lake towards a more efficient classical food chain.

ISSN:1040-2381    

DOI:10.1080/07438149709354297

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Due to prolonged drought conditions in the Upper Colorado River Basin, Lake Powell's water surface elevation declined steadily from 1988 to an early 1993 level approximately 27 m below the full pool level of 1130 m above MSL, resulting in a 60% reduction in reservoir storage. Associated with this drawdown was the exposure and resuspension of over 100 channel kilometers of deltaic deposits in the combined major tributary arms of the reservoir. This resuspension process maybe a significant source of nutrient and trace element loading to the reservoir due to the release of substances associated with these sediments. This may have implications to productivity processes and bioaccumulation of heavy metals in the aquatic ecosystem.

ISSN:1040-2381    

DOI:10.1080/07438149709354298

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Previous research has suggested thatEuhrychiopsis lecontei, an aquatic weevil native to North America, may act as a biological control for Eurasian watermilfoil. To be able to predict which lakes weevils are likely to be effective in laboratory and field studies were carried out under a range of conditions. In the laboratory, weevils survived and reproduced in water up to 31°C, but not at 34°C. Weevils preferred Eurasian watermilfoil plants with no marl, but ate and laid eggs on marl-covered plants. The weevils preferred plants grown in richer sediment, but did eat and lay eggs on plants grown in poorer sediment After open water releases of weevils in three lakes, weevil populations were established and had a negative impact on Eurasian watermilfoil. We have followed a Eurasian watermilfoil decline from 1990–1995. Plant and weevil abundance have varied over the years; however, Eurasian watermilfoil has never regained its former dominance. Based on these trials, it appears thatE. leconteican survive and cause damage over a range of temperatures and plant conditions. Wider scale introductions would help determine the conditions under which this weevil is successful, and its limitations as a biological control for Eurasian watermilfoil.

ISSN:1040-2381    

DOI:10.1080/07438149709354299

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor