摘要:

In response to a growing need for statistically sound information on status and trends in the condition of the nation's ecosystems, the U.S. Environmental Protection Agency is developing and implementing the Environmental Monitoring and Assessment Program (EMAP). One component, EMAP-Surface Waters, will concentrate on lakes and streams. In its focus on lake condition at the regional and national scale, EMAP-Surface Waters will address concerns about the present extent and geographical distribution of lakes, their current ecological condition, the proportion that is degrading or improving, where, and at what rate, and the likely causes of adverse effects. The national design is based on a systematic grid of randomly placed points, so that conditions and trends can be estimated with known uncertainty. Lake condition will be assessed primarily through biological measurements; physical, chemical, and landscape information will be used to support and interpret conditions estimated by the biological indicators. In late summer of 1991, EMAP-Surface Waters will conduct a pilot lake assessment in the northeastern United States. This paper describes the EMAP design and indicators strategy tailored for lakes, with examples showing how these indicators can describe condition and trends at national and regional scales.

ISSN:1040-2381    

DOI:10.1080/07438149109354249

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The Trophic Status Model of Ontario's Lakeshore Capacity Study is a refinement of the Dillon-Rigler (1975) model for predicting total phosphorus concentration and several trophic status indicators in lakes. A recent version of this model allows the modeling of watersheds, extending 3 lakes upstream for up to 15 catchments of a study lake. This feature enables lake managers to predict the effect of lakeshore development throughout an entire watershed, including downstream lakes. Differences between modeled and measured concentrations of total phosphorus for the ice-free period were less than 20% in 11 of a set of 15 lakes in a south-central Ontario watershed. Annual, seasonal and long-term coefficients of variation for measured phosphorus concentrations were 19–22% over a 9-year period in an intensively studied lake. Assumptions and sources of error in modeled and measured phosphorus concentrations are discussed. The ability of the Trophic Status Model to predict phosphorus concentrations in the absence of development is discussed and used to establish water quality objectives for total phosphorus on an individual lake basis.

ISSN:1040-2381    

DOI:10.1080/07438149109354250

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Total fish standing crop data from 79 North American streams located in Wyoming (N = 20), Vermont (N = 19), Florida (N = 15), Iowa (N = 12), Ontario (N = 10), Washington (N = 2), and Missouri (N = 1) were used to test the hypothesis that stream fertility as indexed by total phosphorus concentrations is an important environmental factor influencing fish standing crop. Total fish standing crop among the different geographical regions was not related to differences in latitude, but regional estimates of average fish standing crop were significantly correlated to total phosphorus concentrations (r = 0.79, p < 0.05, n=7). The best-fit empirical regression model for these data was:

ISSN:1040-2381    

DOI:10.1080/07438149109354251

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Enhanced growth of periphyton (primarily attached algae) is an early indicator of nutrient enrichment in lakes. Periphyton abundance, composition, and spatial distribution were examined in ultra-oligotrophic Lake Chelan, Washington to characterize relationships to nutrient inputs. The wide range in the nutrient content of tributaries discharging to Lake Chelan provided a unique opportunity to evaluate nearshore periphyton development in relation to nutrient concentration while minimizing the interference of other potentially controlling factors (e.g., light, temperature, substrate, wave energy). Periphyton samples were quantitatively collected during summer 1987 from rocks located in nearshore areas at discrete distances from five tributaries. The distribution of tributary waters was assessed using specific conductance as a tracer. Compared to stations distant from the nutrient-rich tributaries, high periphyton biomass (50–216 mg chlorophylla/m2) with a greater proportion of filamentous algae was generally found at stations influenced by the tributary plumes.

ISSN:1040-2381    

DOI:10.1080/07438149109354252

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This preliminary study evaluates the ability of the widespread, exotic clamCorbicula flumineato influence the characteristics of plankton in eutrophic Florida lakes. Effective clam densities of 1310 m−2and 2621 m−2reduced chlorophyllaconcentrations in hypereutrophic lake water > 60 per cent over 7 days. Clam filtration rates were estimated to be approximately 500 ml hr−1clam−1. Zooplankton communities shifted to dominance by copepods in all treatments, although rotifer populations declined more rapidly in clam treatments. Although clams stimulated dissolved nitrogen concentrations, phytoplankton populations were reduced. Potential effects ofCorbicula flumineaon plankton characteristics of subtropical lakes are discussed.

ISSN:1040-2381    

DOI:10.1080/07438149109354253

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Spillways at lake outlets are commonly employed to reduce water level fluctuations and promote year-round lake access. However, stabilized water levels may cause accelerated accumulation of sediment on the lake bottom. This can change aquatic plant communities, cloud the water, and eliminate hard-bottom nesting areas for many sportfish. These effects may be particularly pronounced when spillway design does not allow for bottom water drainage and outflow is restricted to less turbid surface waters. Such a structure controls the single surface-outflow of shallow, algal-dominated Newnans Lake, Florida. A 90-day removal of this spillway flushed 60 metric tons (dry weight) of sediment (containing 15% total Kjeldahl nitrogen and 0.5% total phosphorus) from the lake. This quantity was small compared to the likely stores in the lake, but the removal was accomplished at no cost. Data suggest low lake stage at the start of dewatering, resulting in small hydraulic head and low flow through the lake system depressed removal rates. Elevated concentrations of particulate organic matter (POM), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) were noted during the first month of dewatering when adequate head differential was still present. Storms stirred the water column and promoted flushing of resuspended matter.In situand laboratory tests did not demonstrate net oxidative removal of organic matter from exposed areas of the lake bottom. Production of organic matter under high solar radiation and nutrient availability likely replaced material lost through oxidation. Consolidated sediments remained firm after reflooding, providing improved habitat for rooted macrophytes and fish spawning. Short-term partial drawdowns are inexpensive and effective in flushing organic matter and nutrients when they are initiated at high lake stage and coincide with frequent storm events. Routine application of this management technique may produce a periodic rejuvenation of the lake ecosystem.

ISSN:1040-2381    

DOI:10.1080/07438149109354254

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Dense surface canopies of aquatic macrophytes were associated with significant changes in the physical and chemical water quality of two shallow Pacific Northwest lakes. Internal loading of phosphorus (P) was observed at the sediment-water interface beneath canopies ofCeratophyllum demersumL. andMyriophtllum exalbescens(Fern.) Jeps. and in deep open-water areas when dissolved oxygen (DO) concentrations were ≤0.4 mg/L. Aerobic release of P was observed at sites with surface covers of the green filamentous algaePithophorasp. where concentrations of DO were >20 mg/L and pH >9. An increase in surface P concentrations was also observed in sites dominated by the floating leafedBrasenia schreberiGmel., and appeared to be associated with leaf decay within the surface canopy. There was an apparent net loss of phosphorus to the sediments beneath both submergent and floating leafed canopies when DO concentrations were ≥0.4 mg/L. The removal or reduction of the plant canopies could simultaneously reduce anoxic P release, while increasing aerobic P release. These P cycling mechanisms should be considered in the management of aquatic macrophytes.

ISSN:1040-2381    

DOI:10.1080/07438149109354255

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A flow-through, water quality monitoring system, designed to evaluate the spatial heterogeneity of water quality in reservoirs (Grimshaw, 1987), was used to sample Lake Thunderbird, a reservoir near Norman, Oklahoma. Field testing was conducted to evaluate the operational feasibility of monitoring several water quality parameters along multiple transects, in a real-time manner. Results were processed and interpolated using two computer mapping systems and synoptic maps were generated. Qualitative and quantitative comparisons of the two mapping techniques were made. A synoptic map of turbidity, generated from Landsat Multispectral Scanner Band 3 (700–800 nm) data was compared to results obtained from both computer mapping techniques. With the exception of pH and turbidity, the synoptic maps provided similar estimates of lake area within selected intervals, but differed in the degree of detail revealed. Landsat-based turbidity estimates were higher than those measured directly in the littoral zone.

ISSN:1040-2381    

DOI:10.1080/07438149109354256

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Lake Thunderbird, a 2428 hectare reservoir located in Norman, Oklahoma, was studied along with 15 other lakes in south central Oklahoma over a two year period. An objective of this study was continued development and testing of satellite-based capabilities to assess the water quality variations within reservoirs. To accomplish this goal, lake measurements and water samples were obtained on each day of Landsat overpass. A mathematical model of the relationship between suspended sediment and reflectance measured by the satellite was calibrated to the 16 south central Oklahoma lakes. A series of multi-date suspended sediment maps was generated for Lake Thunderbird with this model using Landsat MSS near infrared (Band 3) data. These maps were used to quantitatively evaluate the geographic extent of suspended sediment on each date investigated. The results demonstrate the feasibility of using Landsat data to routinely monitor and assess surface water bodies impacted by suspended sediment.

ISSN:1040-2381    

DOI:10.1080/07438149109354257

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Systematic variations in methods for the storage, digestion and measurement of lake water samples for phosphorus determinations show that these methods are very robust. Frozen samples can be kept for at least one year without any detectable change in total phosphorus, [TP], but the concentrations of P subfractions may change. Variations in the amount of oxidant (0.05 to 0.8 g potassium persulphate/40 ml sample), in the duration (10–90 min), or pressure (100 vs 200 k Pa) of oxidation, and in the amount of sample lost in autoclaving had no effect on estimated [TP]. The exact composition of acid molybdate “mixed reagent” also proved not to be critical, for when each of the components was varied in turn, similar results were obtained with 5 to 10 g ammonium molybdate, 2.5 to 20 g ascorbic acid, 0.025 to 0.4 g potassium antimony tartrate and 55 to 100 ml sulphuric acid per liter of mixed reagent. No significant difference was obtained by varying the amount of mixed reagent from 1 to 7.5 ml/40 ml sample, so some economy may be achieved by reductions in the amount of reagent used. Colour development was stable for up to 8 hours after reagent addition. Refrigerated mixed reagent was stable for up to 48 h, and ascorbic acid solution for 72 h, although storage appeared to increase variation. The insensitivity of this analysis to substantial variations no doubt contributes greatly to the method's success.

ISSN:1040-2381    

DOI:10.1080/07438149109354258

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor