摘要:

A comprehensive rehabilitation plan was developed and implemented to shift Delavan Lake, Wisconsin, from a hypereutrophic to a mesotrophic condition. The plan was threefold: (1) reduce external phosphorus (P) loading by applying Best Management Practices in the watershed, enhance an existing wetland, and short-circuit the inflows through the lake, (2) reduce internal P loading by treating the sediments with alum and removing carp, and (3) rehabilitate the fishery by removing carp and bigmouth buffalo and adding piscivores (biomanipulation). The first and second parts of the plan met with only limited success. With only minor reductions in internal and external P loading, P concentrations in the lake returned to near pre-treatment concentrations. The intensive biomanipulation and resulting trophic cascade (increased piscivores, decreased planktivores, increased large zooplankton populations, and reduced phytoplankton populations) eliminated most of the original problems in the lake (blue-green algal blooms and limited water clarity). However, now there is extensive macrophyte growth and abundant filamentous algae. Without significantly reducing the sources of the problems (high P loading) in Delavan Lake, the increased water clarity may not last. With an improved understanding of the individual components of this rehabilitation program, better future management plans can be developed for Delavan Lake and other lakes and reservoirs with similar eutrophication problems.

ISSN:1040-2381    

DOI:10.1080/07438140009353961

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Total phosphorus, total nitrogen, total chlorophyll and Secchi visibility data from 127 Florida lakes across three time periods, Early (1967–1972), Middle (1979–1981), and Present (1996–1997) were compared using paired t tests and repeated measures analyses of variances. Although the population of Florida has increased 116% over the last 27 years, expected increases in lake concentrations of nutrients were not found. For this sample of lakes, total phosphorus concentrations decreased over a 30-year time period and total nitrogen concentrations showed no significant change. Secchi visibility, one of the simplest parameters to measure and easily understood by lake-users, also showed no significant change over time. The sample of lakes showed a significant but small increase in total chlorophyll concentrations. The increase was unexpected because total phosphorus concentrations decreased and total nitrogen concentrations stayed the same, suggesting that other factors were impacting total chlorophyll concentrations in this group of lakes. It is speculated that changes in color, fluctuating water levels, and increases in the amount of aquatic plant control over time may help explain some of the increases in total chlorophyll. Independent estimates of normal month-to-month and year-to-year temporal variance for Florida lakes were calculated using long-term Florida LAKEWATCH data (71 lakes, with greater than 4 years of monthly data) and compared to the variance among the Early, Middle, and Present time periods. Most of the differences detected among the time periods using statistical analyses were within calculated normal monthly temporal variance. Thus, increased nutrient concentrations or decreased water clarity, that is often speculated to occur with population growth and watershed development, have not been documented in this sample of Florida lakes.

ISSN:1040-2381    

DOI:10.1080/07438140009353962

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Nitrate [Ca(NO3)2] was added to the hypolimnion of eutrophic Lake Lyng (10 ha, maximum depth 7.6 m), Denmark, over a 2-year period to study the impact on sediment phosphorus release and to evaluate the potential of hypolimnetic nitrate dosing as a lake restoration method. Dissolved (1995) or granulated (1996) nitrate was added 10 to 11 times at a depth of 5 m during stratification. The total dose was 8 to 10 g N m−2yr−1. Hypolimnetic nitrate concentration was <0.01 mg N L−1in years without dosing (1994 and 1997), and reached 1.2 and 2.2 mg N·L−1in treatment years, respectively. Maximum concentrations of dissolved inorganic phosphorus (DIP) in the hypolimnion were 1.6 to 2.9 mg P·L−1in untreated years, but were reduced to 0.8 to 1.2 mg P·L−1in treatment years. Correspondingly, total phosphorus (TP) accumulation in treatment years was 48–77% that of non-treatment years. Dissolved nitrate seemed to reduce TP concentrations more efficiently than granulated nitrate, which sank partly into the loose sediment, and led to lower nitrate as well as lower iron concentrations in the hypolimnion. Lower iron release and/or lower nitrate concentrations resulted from the use of dissolved nitrate, which seemed to reduce precipitation of phosphate with iron and left a larger proportion of particulate phosphorus in the hypolimnion. Ammonia concentrations were higher with nitrate addition, probably due to enhanced mineralization of organic sediment and nitrate ammonification. The results from Lake Lyng suggest that the potential of using nitrate as a lake restoration method in deep lakes suffering from internal loading needs further investigation.

ISSN:1040-2381    

DOI:10.1080/07438140009353963

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We examine the idea that whenever high levels of planktonic algae impair a lake, nutrient control is the first step to be taken regardless of what other management actions might be contemplated. Our example is Lake Apopka, a 12,500 ha, shallow (1.7 m), polymictic lake in central Florida. Prior to 1947, the lake was dominated by macrophytes, was reputed to have clear waters, and had a national reputation for its largemouth bass fishery. Following a hurricane in 1947, the lake switched to a turbid, algal state and the bass fishery is all but gone. For over 30 years, it was either implied or stated directly that nutrient enrichment from anthropogenic activities, especially farms along the north shore, was to blame for this change and the lack of macrophyte recovery. The current management plan is to remove the farm nutrient supply by purchasing the farms under the theory that this will lower the total phosphorus concentration in the water and thus restore the lake. We have developed the most probable phosphorus budgets for the lake based on the studies of others and have determined that a fluid mud layer that is frequently resuspended by the wind will lead to high internal loading and slow the drop in phosphorus concentration. The equilibrium phosphorus concentration will lie between 52 and 88 mg·m−3, so the lake will remain in its eutrophic state. We propose an alternative management plan using artificial reefs that will focus on restoring the largemouth bass fishery in the immediate future. This idea is attractive because bass fishing was the dominant use of this lake in the past, it can be accomplished without waiting for a change in trophic state, and it can produce results in a relatively short period of time.

ISSN:1040-2381    

DOI:10.1080/07438140009353964

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An alternative method of preserving filtered chlorophyll samples allows immediate filtration of samples by professional lake managers and volunteer monitors with inexpensive transfer to a laboratory. Using a simple forced air-drying device, samples can be preserved for two weeks and, perhaps, as long as 1–1/2 months without significant change in pigment levels. Filters may be sent by first class mail to a laboratory after wrapping the filters in aluminum foil. A series of 5 experiments was conducted to explore the parameters for maximum extension of the holding time. Results suggest that preserving filters by forced air-drying may be equivalent to other methods such as immediate analysis or freezing, and may be better under many conditions common to field sampling.

ISSN:1040-2381    

DOI:10.1080/07438140009353965

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Agricultural Best Management Practices (BMPs) in the 290,000 ha Everglades Agricultural Area (EAA) resulted in a 55% reduction in phosphorus loading to the remnant Florida Everglades in 1996–98, exceeding the 25% load reduction mandated by law. Consonant with this, discharge total phosphorus concentrations (TP) declined from 173 ug·L−1in the 1980s to 103 ug·L−1during 1996–98. Although not mandatory until 1995, BMP activity started in the EAA in the mid-1980s. I analyzed 3,798 surface water TP samples collected from 1980 to 1999 in a 54,700 ha impounded Everglades marsh that received surface water inflows from the EAA to examine temporal changes in TP. A gradient of high (> 100 ug·L−1) to low (about 10 ug·L−1) TP existed from northern regions that received EAA discharge south to interior regions of the marsh. During the 1980s, higher TP concentrations extended further south into the marsh, but that process reversed in the 1990s. During the 1990s, wet climatic conditions occurred and TP was inversely correlated to water levels throughout the marsh. However in nearly all regions, TP declined between 1980 and 1999 after accounting for the effects of water levels. Marsh TP was correlated to inflow TP in the regions nearest to the discharge gates, and inflow TP declined from about 150 to 50 ug·L−1with the implementation of BMPs. In addition, this marsh was kept essentially flooded for 18 years to increase water supply, but a more normal “wet-dry” regulation schedule went into effect in late 1980 that permitted drying of the marsh. Three droughts followed by reflooding occurred during the 1980s that caused short-term “TP spikes” in the surface water. Lower inflow TP and possible stabilization of phosphorus between the sediment and the water in the marsh after being kept artificially flooded for so long appeared related to the decline in TP. The establishment of BMPs in the EAA have been successful to help in part to achieve phosphorus reduction goals throughout the remaining Everglades.

ISSN:1040-2381    

DOI:10.1080/07438140009353966

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1040-2381    

DOI:10.1080/07438140009353967

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor