ISSN:1040-2381    

DOI:10.1080/07438140009354217

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Waldo Lake, Oregon, was described in 1970 as one of the most oligotrophic lakes in the world. But limnological data collected since then indicate that the lake has shifted toward a higher trophic status. This finding is based on three sets of evidence: (1) the spectral distribution of downward irradiance has changed, with blue light now being attenuated more rapidly, while the penetration of both green light and red light has increased; (2) phytoplankton primary production rates have increased 20-fold; and (3) zooplankton have become many times more abundant, and species composition has changed entirely. Although the cause of limnological change is uncertain, investigators believe that it has resulted largely from management and use of the lake. Accordingly, lake visitors have increased dramatically over the past 30 years, from a few hundred visits in 1967 to around 170,000 visits in 1994. Moreover, stocking the lake with 20 million fish between 1938 and 1990 may have disrupted the lake's seemingly fragile ecosystem. Remedial action to save the lake is now being proposed, including (1) repair or removal of sewage-disposal facilities that are possibly defective; (2) tighter restrictions on various lake and watershed uses, and (3) a permanent ban on fish stocking.

ISSN:1040-2381    

DOI:10.1080/07438140009354218

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Volcanism has been active in the central Oregon Cascade Range for at least the last 35 Ma. During that period interactions between the Pacific, North American, and Juan de Fuca plates have produced variations in the composition and rate of volcanism, the landward migration and narrowing of the axis of volcanism, and discreet deformational events. The result of these effects is widespread unconformities that have enabled Cascade Range workers to identify five mappable time-stratigraphic units. Waldo Lake occupies a position in the High Cascades physiographic province. The surrounding rocks are primarily very young (less than 1–2 Ma) basaltic andesite lava flows covered with a thin veneer of glacial drift. Waldo Lake was carved by a northward-moving glacier and is dammed on its southeast side by a lateral moraine. The location of the lake is probably controlled by a large north-south trending down-to-the-east normal fault.

ISSN:1040-2381    

DOI:10.1080/07438140009354219

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Waldo Lake and vicinity remained essentially an uncharted wilderness until the second half of the Nineteenth Century. The area was largely devoid of its aboriginal inhabitants when Judge John Breckenridge Waldo and his companions spent their summers recreating in the Cascades between 1880 and 1907. These Cascade Mountain respites ultimately led Waldo to call for the area's preservation. But Waldo Lake succumbed to another force in the history of the West, the reclamation movement. In 1905, promoters filed for water rights on Waldo for use as a natural reservoir. The first phase that began in 1905 was a failed attempt to develop the lake as a reservoir for power generation, ending in the mid-1930s as markets declined for hydroelectric power and irrigation water. Federal reclamation projects soon took up the slack, beginning in 1939 with a proposal to divert Waldo Lake out of the Willamette drainage entirely to the Upper Deschutes Project via canals and tunnels through the crest of the Oregon Cascades. Next, the Columbia River project of the U.S. Army Corps of Engineers proposed during the 1940s and 50s depicted Waldo Lake as a vital component of the Upper Willamette system of reclamation installations. By the mid-1950s the twin movements of recreation and wilderness preservation took root and renewed Judge Waldo's call for the protection of and recreation in such places as Waldo Lake. Initially, recreation development held sway, culminating in developed campground facilities in the 1960s. By 1984, the area surrounding Waldo Lake was officially designated as wilderness.

ISSN:1040-2381    

DOI:10.1080/07438140009354220

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Thermal and chemical profiles were obtained periodically in ultraoligotrophic Waldo Lake, Oregon during years 1986 through 1999. Profiling was done on a seasonal basis between May and October. During this period the lake becomes thermally well-stratified. Epilimnetic temperatures peak in August, then rapidly diminish in response to decreasing solar radiation. By October, the lake nears autumnal turnover. During winter, the lake freezes over. The lake features an orthograde oxygen profile, and is well-oxygenated to all depths. The lake is highly dilute, as indicated by extremely low values for specific conductance (2.9–5.2 μmhos cm−1) and alkalinity (0.39–0.71 mg·L−1as HCO3). pH readings were nearly all less than 7.0. Inorganic phosphorus and nitrogen concentrations were mostly less than the minimum detection limit of 1.0 μg·L−1. Dissolved silica concentrations ranged between 0.12 and 0.34 mg·L−1. TDS concentrations averaged 4.04 mg·L−1, with roughly 10% of all test results reported as 0.000 mg·L−1. The cause of the lake's extreme dilution is uncertain, but a major contributing factor may be the fact that the lake is fed entirely by direct precipitation and runoff, with no rivers or permanent streams entering the lake.

ISSN:1040-2381    

DOI:10.1080/07438140009354221

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Previous limnological investigations have identified Waldo Lake as one of the most pristine and chemically dilute lakes in the world. This study focusing on the major ion chemistry of Waldo Lake has confirmed this status. Situated at a topographical divide in the central Oregon Cascades, with a very small watershed (watershed area to lake area ratio = 2) and shallow, porous soils, Waldo Lake chemistry is dominated by precipitation input with relatively less influence from watershed processes. Based on median values, conductivity for Waldo Lake is 3.4 μS·cm−1, while the cation and anion sums are 39 and 29 μeq·L−1, respectively. Acid neutralizing capacity (ANC, also total alkalinity) is 17 μeq·L−1(0.85 mg·L−1as CaCO3), indicating that Waldo Lake is very weakly buffered and highly susceptible to acidification from acidic deposition, although there is no evidence that this has occurred. Chloride (14 μeq·L−1) and sulfate (2.1 μeq·L−1) are derived mainly from precipitation (wet and dry deposition), ANC is derived mainly from weathering of watershed base minerals, and base cations (Ca+Mg+Na+K) are derived from both precipitation (two-thirds) and weathering reactions (one-third). Waldo Lake has been classified as ultraoligotrophic based on the extraordinarily low values of primary productivity and nutrient concentrations. Reported nutrient concentrations vary widely due to the extremely low concentrations and insensitivity of methods employed. However, phosphorus has been identified as the limiting nutrient based on algal bioassay methods. Best estimates based on literature data are total P < 3 ug·L−1, about 50% as inorganic P, and total N < 100 to 200 ug·L−1, more than 90% as organic N. There is a net removal of most inorganic N and P from precipitation in the watershed and lake, but watershed and internal lake processes affecting N and P are not well understood. Estimated total phosphorus loading to the lake is 620 kg y−1and estimated total phosphorus loss from the lake is 81 kg y−1, with about 85% of P retained in the sediments. Waste disposal facilities installed within the last 30 years could substantially increase phosphorus loading and thus alter the ecology of the lake, although remediation measures are now under consideration.

ISSN:1040-2381    

DOI:10.1080/07438140009354222

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The phytoplankton community in Waldo Lake, Oregon is unusual for several reasons, including: (1) phytoplankton diversity is extremely low, with the dinoflagellateGlenodinium neglectumcomprising more than 75% of the total phytoplankton; (2) phytoplankton densities are extremely small, with total density and total biovolume averaging 57 algal units ml−1and 18.5 X 103μm3ml−1, respectively; (3) phytoplankton abundance and species composition are nearly uniform throughout the water column, surface to 120 m; (4) several phytoplankton taxa are rare, and some may be new species that have not yet been identified; and (5) picoplankton, which are abundantly present, may be important contributors to the lake's primary production.

ISSN:1040-2381    

DOI:10.1080/07438140009354223

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Waldo Lake is located in the Willamette National Forest along the west side of Oregon's Cascade Mountain Range. The lake is regarded as one of the most oligotrophic lakes in the world, chemically similar to distilled water, with very low rates of phytoplankton primary production and concentrations of chlorophylla. Historically, vertical light transmission was considerable, with 1% of the lake's incident solar radiation penetrating to depths greater than 60 m.

ISSN:1040-2381    

DOI:10.1080/07438140009354224

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Cyanobacteria (blue-green algae) dominate the benthic habitats of Waldo Lake. These photosynthetic microorganisms may be the principal contributors to overall primary production in the lake, although hard data are not yet available. The main biomass of cyanobacteria consists of filamentous, nitrogen-fixing forms, which also produce a yellow-brown, UV-screening pigment (scytonemin) in their extracellular sheaths. This pigment is probably a necessity under these conditions of extreme water clarity in which UV radiation penetrates well. In addition, a conspicuous feature at 1 m to 5 m depths, along much of the shoreline, are living “stromatolites” which resemble shelf-like rock formations, and appear to be formed primarily by the growth of cyanobacteria. Further studies are underway.

ISSN:1040-2381    

DOI:10.1080/07438140009354225

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

At least thirteen taxa of bryophytes occur between 40 and 128 m depth in Waldo Lake, Oregon. Many taxa exhibit morphological modification precluding positive identification below the level of genus. Liverworts comprise about 98% of the bryomass, the balance being pleurocarpous mosses with trace representation of acrocarps. Predominance of liverworts at extreme depth suggests that they are more viable than mosses under attenuated blue light. All liverworts except one are apparently aquatic forms of upland species. Two mosses are normally upland species, the rest aquatic. Red pigments in some liverwort taxa were maintained as deep as 70 m, but most lost pigment below 40 to 50 m.Sphagnummaintained red pigment as deep as 100 m. Although production of benthic plants would be expected to be exceedingly slow under conditions of low light, low temperatures, limited nutrient availability, and considerable hydrostatic pressure, new growth of 1.5 to 3 cm on liverwort stems approximates annual growth increments observed on upland plants.

ISSN:1040-2381    

DOI:10.1080/07438140009354226

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor