摘要:

Although science has grown faster than its resources for over 300 years, this situation is unstable. Eventually, the growth of science must slow to match that of its base, and researchers will have to compete harder. Verbal models of ecological competition provide scenarios of the likely conditions in the competitive science of the future. Individual researchers can expect to be more stressed and less productive. The scientific population will be more stable, reducing the youthfulness and immediacy of contemporary science, allowing the dominant individuals who succeed in fierce competition greater opportunity to impose theirviews. Science as a whole should expect more interdisciplinary infighting for available funds, and the largest subdisciplines will likely win even larger shares of the available pie. In a recent reallocation in Canada, aquatic sciences and related areas lost funds to supposedly more industrially and economically relevant fields, even though Canadian aquatic scientists outperform those competitors in terms of refereed publication and citation. Since the dominance of the USA is less marked in aquatic sciences, American aquatic scientists could find themselves competitively weak in funding reevaluations. A consequent reduction in American support would be a serious blow to the entire field. Researchers can compete by accepting the new conditions in science and using them to their advantage while applying their skills to the world's immediate problems. On the other hand, researchers can redimension their expectations to their resources.

ISSN:1040-2381    

DOI:10.1080/07438149609354281

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

One goal for eutrophication research is to predict lake trophic state without extensive field programs. However, existing comparisons of predicted:observed TP (total phosphorus) concentration calculate the former from measured watershed characteristics that require field sampling. Predictions of lake TP based on estimated rather than measured components are probably much less powerful, but this possibility should be quantitatively assessed. To assess the predictive power of current mass-balance models of eutrophication, measured estimates of volumetric water discharge (Qobs: m3·yr−1, n=110) and phosphorus load (Lobs: mg·m−2·yr−1, n=96) from lakes in the OECD (Organization for Economic and Cooperative Development) eutrophication data set were compared to calculated values of Q (Qcal) and 16 different variants of calculated phosphorus loading (Lcal, respectively. For the entire data set, Qcalwas unbiased and strongly correlated with Qobs. In regional comparisons, some Lcalvariants correlated well with Lobs, but others did not, and no single variant was significantly better than all of the others. In these comparisons, up to 95% of the variance in Lobswas explained by a single regional Lcalvariant, but the best regression of a single variant against Lobsfor the entire data set explained only 58% of its variance. Stepwise multiple regression to improve prediction of Lobsproduced the following model; Log Lobs= 1.23 + 0.81 (log Lbest) + 0.19(G) − 0.42(%F) − 0.38(%U)− 0.11 (log Ad); R2= 0.75,Sxy= 0.37, P < 0.001

ISSN:1040-2381    

DOI:10.1080/07438149609354282

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Idiosyncrasies, erroneous assumptions and gaps are still hampering lake evaluations, despite several decades of defining the trophic state of lakes. I reevaluated nutrient and algal biomass limits that group lakes into oligo-, meso-, eu- and hyper eutrophic lakes at transition concentrations of 10, 30 and 100 μg · L−1average total phosphorus concentration of the summer epilimnion. I investigated the direct and indirect effects of general lake characteristics like morphometry and geochemistry (water hardness and color) on lake trophic state and formulated models to deal with their significant influences. Nutrient and biomass concentrations as well as quantitative measures of anoxia were used to determine the trophic state. I demonstrated that the number of coldwater fish species may be used to classify the lower trophic levels in geographically constraint areas. Limits and models were established with data from well-studied lakes and verified with literature data from worldwide lakes. Trophic state limits were set for oligo-, meso-, eu- and hypereutrophic lakes at transition concentrations for average total nitrogen of 350, 650 and 1,200 μg·L−1, for summer chlorophyll of 3.5, 9 and 25 μg·L−1, for summer transparency (Secchi disk depth) of 4, 2 and 1 m, for die anoxic factor of 20, 40 and 60 d·summer−1, and for the areal oxygen depletion rate of 250, 400 and 550 mg·m−2·d−1.

ISSN:1040-2381    

DOI:10.1080/07438149609354283

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Upper Rideau Lake is a major lake in the Rideau Canal system; a waterway constructed in 1832 to link Kingston with Ottawa. The lake is currently borderline eutrophic, and local residents are concerned about its water quality. Long-term water chemistry data, however, are not available, and so we used diatom-based paleolimnological techniques to reconstruct the lake's development over the last two centuries. Our data indicate that Upper Rideau Lake was moderately productive even before European settlers began to affect this part of Ontario. The construction of the Rideau Canal, the first major anthropogenic disturbance in this system, greatly affected water quality. During the construction of the canal, the water level in Upper Rideau Lake was raised 1.5 m, resulting in increased nutrient and sediment loading, and an enlarged littoral zone. Deforestation associated with timber harvesting and agricultural activities maintained higher nutrient levels between ca. 1830 and the 1940s. Nutrient levels increased again over the last 40 years, with increased cultural activities in the drainage basin. Notwithstanding these more recent disturbances, the construction of the Rideau Canal in the early part of the 19th century had the largest impact on this lake.

ISSN:1040-2381    

DOI:10.1080/07438149609354284

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The effects of harvesting floating plant tussock communities by mechanical methods on selected water quality parameters in Lake Istokpoga, Florida were examined. Dissolved oxygen, temperature, pH, conductivity, turbidity, chlorophylla, and nutrients (nitrogen and phosphorus) were compared under pre-harvest, harvest and post-harvest conditions. Water quality data were compared between one tussock harvest site and three reference sites (30 m, 61 m, and 91 m away from the harvested plot). Very minor, although statistically detectable (p < 0.05), DO differences occurred at harvest site. Chlorophylla, total nitrogen and total phosphorus concentrations decreased significantly during the harvest. Loadings of total nitrogen concentrations in Lake Istokpoga could be reduced by harvesting of floating plant communities in the littoral areas. A significant increase in turbidity and dissolved solids occurred during mechanical harvesting in both the harvested plot and the reference site 30 m away.

ISSN:1040-2381    

DOI:10.1080/07438149609354285

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Oxygen demand and anoxic factor values were calculated for Garner Lake, a 96-ha reservoir in Shelby County, Tennessee during 1994 and 1995. This physically unique reservoir of the West Tennessee Plain physiographic region has a mean depth of 5.5 m and very high total phosphorus concentrations (concentrations often above 100 μg · L−1and a maximum value of 1510 (μg · L−1). Areal hypolimnetic oxygen deficit (AHOD) values were 234 and 182 mg · m−2· day−1, and anoxic factors (AF) were 17.7 and 13.0 days · year−1in 1994 and 1995, respectively. AHOD and AF values predicted from phosphorus and lake morphometry are much higher than observed values. Several causes could explain Garner Lake's lower than expected AHOD and AF values: 1) it is a southern reservoir and may function differently from more northern, dimictic lakes upon which the models are based, 2) it had been fertilized in 1993.

ISSN:1040-2381    

DOI:10.1080/07438149609354286

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Microporous, hollow fiber membranes have potential for use as a lake hypolimnetic aerator because oxygen is transferred without bubble formation. Thus, the large capital costs of traditional hypolimnetic aerators can be avoided. Two hollow fiber aerator designs are considered for application to hypolimnion aeration. The first was a passive design that required no external energy input other than a pressurized oxygen supply. This approach was dismissed, however, because the low velocities which exist in lake hypolimnia result in oxygen transfer rates that are too small to provide cost-effective aeration. An alternative design, in which membrane modules were rotated through the water by a mechanical motor, was also examined. Experiments were conducted to characterize fiber performance for this design as a function of relative water velocity, and examine the effects of fouling on membrane performance. The experimental results were used to assess capital and operating and maintenance (O&M) costs of a rotating membrane aerator. The estimated costs compare favorably with the known costs of conventional lake aerators, indicating that this is a potentially viable new technology.

ISSN:1040-2381    

DOI:10.1080/07438149609354287

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

This paper reviews some of the major aquatic weeds in New Zealand lakes and discusses some of the problems they cause. Approaches to the management of nuisance weed beds are also discussed. New Zealand's indigenous aquatic flora has proved susceptible to invasion with many of our marginal and submerged species being replaced by dense, tall-growing weed species. A variety of management approaches are discussed including ‘leave alone’ strategies and targeted control of nuisance weed beds. Mechanical control of nuisance weeds has tended to focus on problems associated with strandings (e.g., removal of shoreline strandings and at hydroelectric station intakes), but refinement of removal methods at their source is continuing. Chemical control of aquatic weeds is an effective option for target weeds of national importance (e.g., water hyacinth and salvinia) and for specific waterbodies where an acceptable degree of selective control can be achieved. Research results using grass carp have confirmed eradication ofEgeriais possible in small waterbodies and this may be followed by native plant recovery; while similar trials onHydrillahave achieved effective control, but the question of eradication is still unresolved on account of continuing tuber viability within lake sediments.

ISSN:1040-2381    

DOI:10.1080/07438149609354288

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Pretty Lake is a 64 acre, sandy-bottomed groundwater flow-through lake that has a history of hydrologic disturbance. Residents and regulators require a better understanding of lake-groundwater interaction to develop measures to protect the lake's hydrologic system and water quality. A groundwater flow model was constructed as a tool to synthesize field data collected at the site, delineate recharge areas that supply groundwater to the lake, and predict die effect of dredging an adjacent drainage ditch. The one layer, two-dimensional steady-state areal model used analytic element (AE) methods because they are quick to apply and include sophisticated simulation of groundwater-surface water interaction. The model calibrated well to groundwater heads (mean absolute difference = 0.05 m), lake stage (within 0.05 m) and ditch fluxes (mean absolute difference = 0.0023 m3·s−1). Model results showed that a single 1000 m wide recharge area supplies all the groundwater inflow to the lake. In addition, the model predicted that dredging an adjacent ditch by 3.0 m would lower the lake level by 0.31 m. The analytic element model was verified using a widely accepted finite-difference (FD) code; differences were less than ±0.015 m near die lake area and reached a maximum of 0.08 m at far corners of the FD grid. These differences are likely a result of die nodal interpolation inherent to FD techniques and error associated with applying a discrete boundary to die AE infinite aquifer. Although developed recently, AE methods have great potential to aid characterizations of groundwater-lake systems.

ISSN:1040-2381    

DOI:10.1080/07438149609354289

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor