Geology Reports⌕ Search

Geology topics

Robert C. Averett

Publications and source records attributed to Robert C. Averett.

5 recordsLinked to original sources
USGS2007

Comparison of four artificial substrates and the Ponar grab for benthic invertebrate collection

Four different bottom‐placed artificial substrates were compared with the Ponar grab for collecting benthic invertebrates. Artificial substrate samples of organisms were larger and more diverse than those of the grab. Barbeque Basket samplers caught the most taxa and individuals and Beak Trays caught the least. Chironomids and crustaceans were dominant in artificial substrate samples. Exposure habitat (left or right bank) determined taxa availability, whereas sampler design determined suitability for colonization by the taxa. Diversity for Beak Tray samples was lower than that for other artificial substrates but higher than for Ponar samples. The Barbeque Basket, Bull Basket, and Multiple Plate samples were taxonomically similar. Ponar samples were different, and Beak Trays were of intermediate similarity. As qualitative samplers, Barbeque Baskets were 63 percent efficient, followed by Bull Baskets (55 percent), Multiple Plates (48 percent), Beak Trays (38 percent), and Ponar Grabs (6–10 percent). Bull Baskets required the least and Beak Trays the most replicates to be within a preselected percentage error of the mean at the 95 percent probability level for numbers of taxa and individuals, and for diversity. Under conditions of the study, Bull Baskets ranked highest, followed by Barbeque Baskets and Multiple Plates, in selected performance criteria. Differences between grab and artificial substrate samples are explainable in terms of major riverine habitats and characteristics of the collection methods.

Journal of the American Water Resources Associatio↗
USGS1977

Phytoplankton distribution and primary productivity in Donner Lake, California

Donner Lake is an unenriched system in the Lake Tahoe basin of the Sierra Nevada of California. The lake has a surface area of 1.5 square miles (3.9 square kilometres) and a drainage area of 14 mi 2 (36 km 2 ). The maximum depth is about 200 feet (60 metres). Between May and December 1973, the phytoplankton in Donner Lake was represented by 6 classes and at least 25 genera. The dominant green alga was the desmid Cosmarium staurastroides , which comprised about 25 percent of the total phytoplankton collected. The dominant diatom was Asterionella formosa , which comprised about 13 percent of the total phytoplankton. Blue-green algae were represented by Chroococcus sp., but were never abundant and constituted only 1.5 percent of the total organisms sampled. The depth of the euphotic zone from May through September ranged from 35 to 93 feet (11 to 28 metres). Thermal stratification was strong throughout the summer with a maximum temperature difference between the surface and bottom water of 17° Celsius in July. Average phytoplankton concentrations were often greater below the euphotic zone than in the euphotic zone. This pattern of phytoplankton distribution is similar to nearby Lake Tahoe and other oligotrophic lakes. Three primary productivity measurements were made during the study using the carbon-14 method. The primary productivity values were 93, 64, and 56 milligrams of carbon per cubic metre per day for May 17, August 13, and October 16, respectively. The productivity profile in May was shallow and unimodal, whereas the August and October profiles were deeper and biomodal. Dissolved-oxygen concentrations were maximum at the same depths as maximum primary productivity. On the basis of phytoplankton types and their vertical distribution patterns, and upon primary productivity measurements, Donner Lake is considered oligotrophic.

California↗
USGS1974

Limnological data from selected lakes in the San Francisco Bay region, California

Limnological data were compiled on 21 lakes in the San Francisco Bay area. The data were obtained from regulating agencies and from recent surveys made by the U.S. Geological Survey. The history of each lake and of its respective regulating agency is presented, along with methods used for data collection and analyses. The largest reservoir, Lake Berryessa, has a volume of 1,600,000 acre-ft (1,975 hm 3 ), with a drainage. area of 576 mi 2 (1,490 km 2 ). Pilarcitos Lake is one of the smallest reservoirs, with a volume of 3,100 acre-ft (3. 8 hm 3 ) and a drainage area of 3. 80 mi 2 (9.84km 2 ). Eleven of the 21 reservoirs are open to the public for recreation. The most intensive shoreline development and use is at Lake Berryessa and Lake Merced. All but three of the 21 reservoirs (not including Upper Crystal Springs Reservoir) were thermally stratified during the summer. Eight of the reservoirs showed evidence of dissolvedoxygen depletion during the summer. Lafayette Reservoir and Loch Lomond are mechanically aerated in order to increase the dissolved-oxygen concentration and lower the surface water temperature. The lake waters ranged from the hard (320 mg/1 CaC0 3 ) of Calero Reservoir, to the soft (27 mg/1 CaC0 3 ) of Upper Crystal Springs Reservoir. Drainage from abandoned mercury mines in Santa Clara County has resulted in mercury concentrations in Calero and Lexington Reservoir fish which exceed U.S. Food and Drug limitations (0.5 μ /g) for acceptability of mercury in fish used for human food. In Loch Lomond, four major production periods of the blue-green algae, Anabaena sp . , occurred from May to October, 1967-69. Blue-green algae were the most numerous algae in Lake Del Valle from March through July 1971, with 5,400 blue-green algal organisms per millilitre collected in April.

California↗
USGS1974

Limnological study of Lake Shastina, Siskiyou County, California

Lake Shastina provides water for irrigation in Shasta Valley, as well as recreation. Presently, its shoreline is being developed for summer homes. Surface water constituted more than 90 percent of the approximately 50,000 acre-foot (62-cubic hectometre) inflow to Lake Shastina in the 1972 water year. Controlled outflow is via the Montague Main Canal; however, leakage from the lake through volcanic rocks to the northwest was estimated to be greater than the measured outflow. Appreciable annual changes in the quantity of water in storage in the lake are related mainly to variations in annual inflow. From June through August the lake was thermally stratified. In the spring and summer the epilimnion was often supersaturated with oxygen, while at the same time the hypolimnion was undersaturated and 'often devoid of dissolved oxygen. Vertical stratification of carbon dioxide, carbonate, bicarbonate, hydrogen ion, nitrogen, and phosphorus was also recorded during the spring and summer. Orthophosphate, total phosphorus, and total nitrogen concentrations (organic, ammonium, and nitrate) were highest in the hypolimnion during the period of thermal stratification. Ten-inch (25-centimetre) core samples from the reservoir bottom were chemically analyzed at 0.8-inch (2-centimetre) intervals. The concentrations ranged from 6.3 to 28.9 milligrams per gram of iron, 0.07 to 0.43 milligrams per gram of manganese, 0.4 to 2.7 milligrams per gram of organic nitrogen plus ammonium, and 0.06 to 1.3 milligrams per gram of total phosphorus. Organic matter in the cores ranged from 4 to 14 percent. Green algae and diatoms were the dominant algal types, reaching maximum concentrations of about 7 and 30 million cells per litre, respectively. These phytoplankton occurred near the surface during thermally stratified periods, but were distributed at greater depths during nonthermally stratified periods. Blue-green algae were present only in the spring samples, and reached a maximum concentration of about 5 million cells per litre. Zooplankton numbers were greatest in March, July, and September, with lesser concentrations in June. Three major zooplankton groups, Cladocera, Copepoda, and Rotifera, were present. The major groups of benthic organisms were Oligochaeta, Chironomidae, and Chaoborus, with numbers ranging from 3350, 890, and 8450 per square metre, respectively. A discussion on algal control is included.

California↗