摘要:

Eau Galle Reservoir, located in west central Wisconsin, is a small eutrophic flood control impoundment. The reservoir sustains high sediment and associated nutrient loadings from its agricultural watershed. Despite this system's riverine nature, much of the phosphorus accumulated in the water column during the summer derives typically from internal loading. Entrainment of phosphorus in the epilimnion from hypolimnetic sources during weather-induced partial mixing events has encouraged the development of large phytoplankton blooms. In 1986 internal phosphorus loading was substantially reduced by applying alum to profundal sediments. However, this effect was short-lived (< 1 year) because of high rates of sedimentation with probable burial of alum. Phytoplankton production was not diminished by alum treatment, partly because of high rates of external phosphorus loading during the unusually wet summer of 1986. In addition to inputs from the anaerobic hypolimnion, phosphorus is also transported to surface waters from the littoral zone by convective exchange flows driven by diel changes in water temperature. Phosphorus release from littoral sediments is enhanced at elevated values of pH, induced by macrophyte and phytoplankton photosynthesis. Groundwater discharge may provide another source of phosphorus to the epilimnion of Eau Galle Reservoir.Ceratium hirundinellaand other dominant phytoplankton species (blue-green algae) possess significant vertical migrational capabilities, and are thus able to maximize phosphorus uptake whether from the hypolimnion, the littoral zone, or directly from riverine inputs. As with many other eutrophic reservoirs, it is difficult to control nutrient inputs from external sources in Eau Galle Reservoir. Control of internal sources of phosphorus loading to this reservoir appears to be equally difficult.

ISSN:1040-2381    

DOI:10.1080/07438149009354690

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Lake Morey, Vermont provides a case history of a successful lake restoration effort. Decades of algal blooms and a major summer fish kill preceded a hypolimnetic alum and sodium aluminate treatment in 1986. Earlier diagnostic studies with paleolimnological analyses and a detailed phosphorus budget revealed the cause to be internal phosphorus loading from anoxic hypolimnetic sediments. The aluminum treatment of these sediments resulted in sharp declines in total phosphorus and chlorophyllaconcentrations, and increased Secchi transparency. The dose rate of 44 g Al/m2appears to have been sufficient to form an effective barrier to sediment phosphorus release, and improved conditions continue to persist after four years. Elevated dissolved aluminum levels and some possible adverse effects on the benthic invertebrates and the yellow perch population were temporarily observed following the treatment. The apparent success of the project in controlling phosphorus concentrations is the result of an accurate diagnosis of sediment release as the dominant source of phosphorus and the appropriate use of aluminum treatment to inhibit release.

ISSN:1040-2381    

DOI:10.1080/07438149009354691

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Smith Mountain Lake, an 8,300 ha hydroelectric impoundment in south-central Virginia, experienced a sharp decline in its sport fishery beginning in the late 1970s. Potential causes were investigated over a three-year period and included: (1) increased hydroelectric pumpback operations; (2) reduced nutrient loading; and (3) trophic interactions between native and introduced fishes. Expanded hydroelectric operations did not substantially affect littoral and pelagic fish habitat. However, fish standing stock was highly correlated with total phosphorus concentration; both declined by over 75 percent between 1975 and 1984. Predation and competition of introduced and native fishes were minimized by habitat segregation, but forage fish production was inadequate to sustain a high abundance of piscivorous sport fishes. Restorative measures should focus on reduced piscivore stocking, increased harvest of juvenile sport fish, habitat enhancement, and adjustment of angler expectations to match the limits on fishery productivity imposed by other uses of the reservoir. This case study illustrates the need for effective planning in the management of reservoir fisheries, including consideration of issues at the design stage, frequent assessment, establishment of a protocol for introduction, new species, and compromise among users with different goals.

ISSN:1040-2381    

DOI:10.1080/07438149009354692

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Mesotrophic and eutrophic lakes have been treated with aluminum salts (alum) to lower phosphorus concentrations and inhibit phosphorus recycling from the sediment. Changes in the profundal benthic and merobenthic fauna of five selected lakes were assessed, revealing increases in faunal density and diversity in nearly all treated lakes. The dominant organisms wereChaoborus punctipennis(Say) andChironomusspp. Sediment cores used to evaluate the presence of an aluminum hydroxide floc layer showed aluminum concentrations above extrapolated background levels in most cores within the top 20 cm of substrate. Increased chironomid density resulting from such treatments might reduce the expected benefit from the alum addition. To assess the effect of sediment bioturbation, a bioassay withChironomus tentansF. larvae was carried out to determine if translocation of phosphorus across the flocculent barrier is dependent on floc thickness or chironomid density. In the absence of a floc layer, chironomid activity generated higher concentrations of soluble reactive phosphorus (SRP) than when a floc layer was present. Even with a floc layer of 0.5–2.0 cm thickness, chironomids were able to increase soluble reactive phosphorus concentrations. Soluble reactive phosphorus concentrations in assays with alum and no insects were at or below the detectable limit of 4 μg/L. Alum toxicity to insects was not apparent in the lake treatment part of this assessment. An indirect toxicity was observed in the bioassays when alum dosages greater than 75 mg Al+3/L were used. The absence of toxicity in bioassays at lower treatment rates, which are more indicative of normal aluminum salt usage, indicates that this phosphorus reduction technique is relatively safe toChironomus tentans.

ISSN:1040-2381    

DOI:10.1080/07438149009354693

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Rooted, submersed macrophytes, primarilyElodea densa, have apparently served to restrict internal phosphorus loading during the summer in shallow Long Lake, Washington, instead of contributing phosphorus through senescence (process of aging). Internal loading was consistently controlled for five years by treatment by drawdown and alum, and mean, whole-lake macrophyte biomass ranged from about 30 to 250 g/m2during the 12 study years. Instead of the positive relationship between macrophyte biomass and lake phosphorus content during the summer that has been observed by others, the two variables had an inverse relationship. Gross internal loading (before and after alum control), estimated by a nonsteady-state model, was greater during years when low winds (< 10 km/h) were frequently followed by high winds (> 16 km/h). This indicates the importance of stability in creating an anoxic layer over the sediment, followed by wind mixing to entrain it into the water column. Thus, rather than serving as a direct source in summer through senescence, a dense cover of macrophytes in this lake may impede sediment release of phosphorus by creating a barrier to wind mixing. Late fall and winter senescence may, however, facilitate sediment phosphorus release by the iron-redox mechanism through organic enrichment of the sediment surface. The varied role of macrophytes since treatment suggests that partial alum control may have persisted for at least nine years.

ISSN:1040-2381    

DOI:10.1080/07438149009354694

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This study was undertaken to assess the effectiveness of alternative water quality monitoring programs in detecting water quality trends over time, identifying differences in water quality between water bodies, and examining spatial variability in water quality within a single water body. Monthly historical data on phosphorus, nitrogen, and specific conductance from the North Carolina Division of Environmental Management and the U.S. Army Corps of Engineers were analyzed. The historical data on nutrients and specific conductance were first examined for deterministic patterns. In most cases, the concentration varied seasonally according to a cyclical pattern that repeated each year. In addition, concentration at riverine sampling sites was often inversely related to streamflow. Following removal of the deterministic patterns from the data, autocorrelation was found in a few cases. Once it was concluded that only white noise remained in residuals for a particular data series, the required sample size for a given power and significance was calculated. In many instances, a large number of samples were required to detect changes of 25 percent or less with low error rates, because of the high level of background variability.

ISSN:1040-2381    

DOI:10.1080/07438149009354695

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Forty-five percent of the water from the river supplying Lake Chapala has been diverted in the past 10 years. The water quality consequences of this change in water quantity are numerous. In this period, the lake volume has declined by 50 percent. Because of the reduced flushing and the corresponding relative increase in outputs via evaporation more than twofold, the lake's total dissolved solids content has increased. A second consequence, and one of great importance to the ecology of the lake, is the increase in water turbidity. With a reduction in lake mean depth from 7.2 m to 4.5 m, wind-driven resuspension of the inorganic sediments has increased. This has caused light limitation of phytoplankton production to the extent that nutrient loading models to predict production of biomass fail when applied to this lake. Reduction in turbidity by increased flocculation could significantly speed up the eutrophication process, because high concentrations of nutrients are present in the system (total inorganic phosphorus = 520 μg/L and total inorganic nitrogen = 512 μg/L). Because of the importance of this lake as a water supply resource and the unique nature of the water quality problems, a special set of water quality criteria appropriate to Lake Chapala is presented. To avoid further reduction in the water supplied to Lake Chapala from the River Lerma, its principal influent, consumptive water use in the River Lerma cannot increase. Further increases in the irrigated areas should come only from other water sources (e.g., wastewater reuse) or more efficent irrigation.

ISSN:1040-2381    

DOI:10.1080/07438149009354696

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The impact of silt and clay loading from an agricultural watershed on zooplankton abundance and several physical, chemical, and biological measures of water quality was assessed during stormflow and baseflow flow regimes in Tuttle Creek Reservoir, near Manhattan, Kansas. Bacteria and suspended solids increased during the stormflow period, while water transparency, chlorophylla, dissolved solids, and zooplankton declined. The abundance and reproductive performance ofDaphnia parvulaandDaphnia pulexin predator-free enclosures incubated along the longitudinal axis of the reservoir also decreased significantly during the stormflow period. Chlorophylla, suspended solids, and dissolved solids were spatially distributed during the sampling period with highest concentrations at the riverine end of the reservoir where water transparency was lowest.Diaphanosomasp. and calanoid copepods exhibited high abundances at the riverine end of the reservoir whileDaphniasp.,Bosminasp., and cyclopoid copepods exhibited low abundances there. The reproductive performance ofDaphnia parvulain enclosures, however, was significantly greater at the riverine end, where silts and clays are most abundant. These spatial and temporal patterns in water quality, zooplankton abundance, andDaphniareproductive performance demonstrate the importance of flow regime and the magnitude of its associated suspended sediment load from agricultural runoff on reservoir water quality and zooplankton dynamics.

ISSN:1040-2381    

DOI:10.1080/07438149009354697

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This paper describes a geographic information system (GIS) approach to modeling the effects of distance to water and slope angle on external phosphorus loading to lakes. A raster GIS database was created that included land use, topography, soils, and watershed boundaries for three Indiana reservoirs (Lakes Kickapoo, Lenape, and Shakamak). Three sets of phosphorus export coefficients were selected and assigned to each cell according to land use. Linear filters were designed and applied to the export coefficients such that areas nearest the water and with the steepest slopes would contribute the greatest amount of phosphorus relative to the initial phosphorus export coefficient. These filtered coefficients were used to calculate aerial phosphorus loading and in-lake phosphorus concentrations. The predicted concentrations were within 5 μg/L of the observed phosphorus concentration in Lake Shakamak for three modeling scenarios, and within 22 μg/L of the observed concentration in Lake Lenape for three scenarios. Predictions of phosphorus concentrations in Lake Kickapoo were consistently low (35 percent to 95 percent). This may have resulted from the complex hydrology of Lake Kickapoo or the inability to accurately model the physical processes as intended. The GIS system was useful for modeling the effects of distance and slope on phosphorus loading and for providing data highlighting critical management areas.

ISSN:1040-2381    

DOI:10.1080/07438149009354698

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Lake Okeechobee, Florida, is large (1730 km2) and shallow (Zx= 2.7 m) with 44 percent of the bottom covered by flocculent, unconsolidated mud. Consequently, wind resuspension of sediments was an important determinant of limnological conditions between 1975 and 1988. Higher wind speeds occurred between October and May, and calmer conditions were prevalent during the summer months (June–September). Monthly averages of soluble reactive phosphorus, total phosphorus, nitrate-nitrite, total nitrogen, silica, total suspended solids concentrations, and turbidity were positively correlated with average monthly wind speed (r = 0.66 to 0.90, P <0.05). Annual total wind speed was correlated with average annual total phosphorus (r = 0.78, P <0.01) and soluble reactive phosphorus (r = 0.67, P <0.05) concentrations. From 1950 to present, greater wind speed was also associated with higher lake stages. Wind speed, rainfall on the lake, tributary inflow, and lake levels appeared to be interrelated parameters on Lake Okeechobee.

ISSN:1040-2381    

DOI:10.1080/07438149009354699

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor