摘要:

Water supply reservoirs in urban areas need protection from potential loading of toxic chemicals associated with industrial and commercial land uses, as well as transportation spills. As it is infeasible to eliminate all uses of toxic chemicals from developed watersheds, management strategies attempt to eliminate potential sources from the most sensitive areas. In many jurisdictions this goal is implemented through zoning restrictions which prohibit commercial/industrial activities within a certain fixed distance of the reservoir pool. This simple approach, however, often imposes unnecessary restrictions on some landowners, while failing to provide uniform protection to the water supply. Land use restrictions are never popular, and should be targeted toward the most sensitive potential source areas. A quantitative, geographic assessment of relative risk from all points within the watershed can be used to maximize protection from zoning while minimizing restrictions on economic growth. A steady-state modeling approach, as presented here, provides a rational basis for developing zoning restrictions for source water protection.

ISSN:1040-2381    

DOI:10.1080/07438149709354319

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

An empirical phosphorus (P) loading model modified from the original Vollenweider formulation has been used since the late 1970s to track progress toward a legally mandated P loading target for Lake Okeechobee, Florida. The loading target is designed to achieve, as an annual average for the pelagic region, a total P (TP) concentration of 40 μg L−1. This TP goal is not based on historic data from the lake, nor on how certain levels of TP might cause use-impairment or ecological harm. Nevertheless, our retrospective analyses indicate that the goal falls within a range of TP concentrations (26 to 92 μg L−1) derived from historical data, pelagic TP-algal bloom relationships, pelagic TP-chlorophyllarelationships, and a Florida lake regression model. When first applied to Lake Okeechobee, the modified Vollenweider model gave accurate estimates of pelagic TP, but now it under-predicts TP by nearly 50 percent. This may reflect time lags in lake responses to recent reductions in P loads, an increase in the relative magnitude of internal vs. external P loads, or a change of in-lake processing of P. The lake's P budget shows a decline over time in the net sedimentation of P. The Vollenweider model estimates P sedimentation based on a fixed empirical relationship using water residence time (τw), a parameter that has not displayed a significant historical trend. Given these issues, it is important to consider whether the existing model is an effective management tool for Lake Okeechobee. Our results indicate that the modified Vollenweider model may suffice as a coarse-scale tool for tracking progress in the eutrophication management program, with a major caveat: model predictions of pelagic TP at any given external loading rate may reflect what ispotentiallyattainable, if internal loading rates decrease to their previous lower levels. A more complex dynamic model is being developed, which accounts for sediment-water P exchanges. The new model should provide more accurate estimates of pelagic TP, as well as estimates of recovery time and predictions of short-term responses to management actions.

ISSN:1040-2381    

DOI:10.1080/07438149709354320

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The drainage from a wetland was diverted in fall 1988 from eutrophic Pine Lake, a small (36-ha), thermally stratified (maximum depth 11.9 m) lake in the Puget Sound region. Although the wetland contributed only 20% of the lake's annual phosphorus loading, 90% of the phosphorus was soluble and entered the lake's lighted zone during winter-spring. Furthermore, the wetland drainage fueled a spring blue-green algal bloom, which was the lake's principal water quality problem. The diversion resulted in a reduction of 36-kg TP loading (86% of total external) and greatly improved lake water quality during spring. The spring blue-greenal gal bloom was eliminated in 1989 and 1990. Spring epilimnetic mean TP declined from 27 μg· L−1in 1980 to 16 μg · L−Jin 1990 and mean chladecreased from 18 to 6 μg· L−1, while transparency increased from 1.9 to 4.5 m. However, lake quality during late summer and fall worsened from 1980 to 1990 concomitant with a doubling in hypolimnetic TP. Metalimnetic populations of blue-green algae (AphanizomenonandAnabaena) formed surface scums following lake turnover in the late summer and fall of 1989 and 1990. Increasing development in the watershed (from 9% to >50% residential since 1976) probably contributed increased P loading to the lake and possibly increased hypolimnetic P and fall algal blooms.

ISSN:1040-2381    

DOI:10.1080/07438149709354321

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Concentrations of 12 trace elements (Hg, Cd, Be, Co, As, V, Pb, Cu, Ni, Zn, Ba, Mn) were determined for different organs of 6 dominant macrophytes of the Novosibirsk Reservoir (Phragmites australis (Cav.) Trin. ex Steud., Typha angustifolia L., Nymphoides peltata (S.G. Gmel) O. Kuntze, Potamogeton lucens L., Potamogeton perfoliatus L., Salvinia natans (L.) All.). This investigation showed: 1) concentrations of trace elements (excepting Mn) in roots and rootstocks were greater than in organs above the sediment surface, 2) maximum trace element concentrations were observed inSalvinia natansr, Nymphoides peltataandPotamogetonspecies accumulated lesser amounts thanSalvinia natans; Phragmites australisandTypha angustifoliaalways showed the lowest concentrations of all elements in both above- and underground organs, and 3) because of their greater biomass, communities ofPhragmites australisaccounted for greater total amounts of trace elements than other macrophyte communities of Novosibirsk Reservoir. These communities contained 57% of Cd, 52% of As, 42% of Pb, 54% of Cu, 57% of Ni, 66% of Zn, 32% of Mn accumulated in the six studied macrophyte communities of Novosibirsk Reservoir.

ISSN:1040-2381    

DOI:10.1080/07438149709354322

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Osgood (1988) proposed a morphometric index, mean depth over square root of surface area ([zbar] / √ A0), to estimate the probability of partial or complete mixing of lakes during summer storms. Such mixing could introduce phosphorus (P)-rich waters to the entire water column (polymictic lakes) or to the epilimnion, and could delay lake recovery following abatement of allochthonous P loading. Cooke et al. (1993) hypothesized that aluminum sulfate (alum) applications to control internal P loading would be most effective in lakes with an Osgood Index less than 6 and significant diversion of external loading. We tested the hypothesis that vertical P transport is higher in lakes with the lowest Osgood Index numbers by estimating transport in four northeastern Ohio lakes with Osgood numbers of 2.9, 7.4, 9.7, and 26.3 during Summer 1992. The hypothesis was rejected. Although the lake with the lowest number most often had the highest vertical P transport rate, transport was not significantly different between lakes. The qualitative trends among lakes corresponded with their relative differences in P concentration gradients. Lakes with a high Osgood Index could have significant vertical P transport if there is a steep P gradient in the water column. The results suggest that alum applications have the potential to decrease trophic state in lakes with a high Osgood Index value.

ISSN:1040-2381    

DOI:10.1080/07438149709354323

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Field vegetation surveys were used to evaluate some of the target and nontarget impacts associated with whole-lake applications of Sonar®*1A.S. aquatic herbicide (active ingredient, fluridone) applied to Michigan lakes between 1990 and 1996. The applications analyzed were made in the spring to control Eurasian watermilfoil (Myriophyllum spicatumL.) and/ or curly leaf pondweed (Potamogeton crispusL.). Dose-rate response curves for the control of individual aquatic plant species were constructed from plant species lists compiled before and after treatment. Plant species varied considerably in their response to Sonar. Eurasian watermilf oil, curly leaf pondweed, elodea (Ehdea canadensisMichaux.), naiads (Najas sp.), and coontail (Ceratophyllum demersum L.) were highly susceptible; bladderwort (Utricularia sp.) and water stargrass (Heteranthera dubia(Jacq.) MacM.) were very tolerant; and large-leaf pondweeds (Potamogeton sp.), wild celery (Vallisneria americanaMichaux.), narrow-leaf pondweeds (Potamogeton sp.), medium-leaf pondweeds (Potamogeton sp.), and flatstem pondweed (Potamogeton zosteriformisFern.) exhibited intermediate susceptibility. Sonar A.S. impacts on plant cover and diversity were highly dose dependent. Both cover and diversity usually declined during the year of treatment following applications at dose rates above 10 ppb (calculated on the volume of the top 10-ft layer of the lake). Cover and diversity typically recovered within 1 to 3 years following applications at these rates. Applications at dose rates of 10 ppb or less were typically much more selective. Impacts of low-dose rate treatments on total and native plant cover depended on the abundance of highly sensitive plant species, including Eurasian watermilfoil, curly leaf pondweed, elodea, coontail, naiad, and native watermilfoil. Where these species constituted a small part of the community, total native plant cover often increased following treatment. Low-dose rate (<10 ppb) Sonar applications are an effective method for controlling Eurasian watermilfoil and curly leaf pondweed with minimal impact on many native plant species.

ISSN:1040-2381    

DOI:10.1080/07438149709354324

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor