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USGS1983

Acoustic systems for the measurement of streamflow

The acoustic velocity meter (AVM), also referred to as an ultrasonic flowmeter, has been an operational tool for the measurement of streamflow since 1965. Very little information is available concerning AVM operation, performance, and limitations. The purpose of this report is to consolidate information in such a manner as to provide a better understanding about the application of this instrumentation to streamflow measurement. AVM instrumentation is highly accurate and nonmechanical. Most commercial AVM systems that measure streamflow use the time-of-travel method to determine a velocity between two points. The systems operate on the principle that point-to-point upstream travel-time of sound is longer than the downstream travel-time, and this difference can be monitored and measured accurately by electronics. AVM equipment has no practical upper limit of measurable velocity if sonic transducers are securely placed and adequately protected. AVM systems used in streamflow measurement generally operate with a resolution of ?0.01 meter per second but this is dependent on system frequency, path length, and signal attenuation. In some applications the performance of AVM equipment may be degraded by multipath interference, signal bending, signal attenuation, and variable streamline orientation. Presently used minicomputer systems, although expensive to purchase and maintain, perform well. Increased use of AVM systems probably will be realized as smaller, less expensive, and more conveniently operable microprocessor-based systems become readily available. Available AVM equipment should be capable of flow measurement in a wide variety of situations heretofore untried. New signal-detection techniques and communication linkages can provide additional flexibility to the systems so that operation is possible in more river and estuary situations.

Water Supply Paper↗
USGS1983

Estimating peak discharges of small, rural streams in Massachusetts

Floodflows on natural-flow streams in Massachusetts with drainage areas between 0.25 square miles and 260 square miles may be estimated from drainage area, main-channel slope, mean basin elevation, and the area of swamps, lakes, and ponds. Multiple-regression techniques were used to define the relationship between a suite of basin and climatic characteristics and flood peaks in three flood-frequency regions at a total of 95 sites. Station flood-frequency data were computed following guidelines in Bulletin 17A of the U.S. Water Resources Council. The frequency analyses are based upon weighted skew values, adjustments for high and low outliers, and historic peak data. Regression equations for estimation of peak discharges for 0.5, 0.2, 0.1, 0.04, 0.02, and 0.01 exceedance probabilities are provided for ungaged sites. An improved sample of flood peaks and gaging stations and the definition of three flood-frequency regions reduced the standard errors of estimate by about 5 percent over those for the 1977 relations. Included in this analysis were the synthetic flood-frequency data at 8 sites computed using historic climatic data and 10 parameters optimized by calibration of the U.S. Geological Survey's rainfall-runoff model with storm data observed over 11 years. The equations are applicable to streams unaffected by regulation where the usable manmade storage is less than 4.5 million cubic feet per square mile, or by diversions or urbanization. The equations are restricted to sites where the basin indices are within a specified range outside of eastern Plymouth, Barnstable, Dukes, or Nantucket Counties. In these areas, the available data do not adequately define the influence of high infiltration and storage capacities of drainage basins on floodflows.

Water Supply Paper↗
USGS1984

Availability and quality of water from the Dakota aquifer, northwest Iowa

The Dakota aquifer in northwest Iowa consists of sandstones in the Dakota Formation. It underlies most of the study area and is the most extensive source of ground water in the area. Individual sandstone beds are from less than 10 to more than 150 feet thick. The cumulative thickness of sandstone is more than 200 feet throughout much of the area. The aquifer is confined by overlying Cretaceous limestone and shale, Quaternary glacial deposits and loess. The underlying confining material is shale of the Dakota Formation, undifferentiated Paleozoic age rocks, or Precambrian crystalline rock. Water flows through the aquifer from the northcentral part of the study area to the east, south and southwest. Recharge is dominantly by infiltration from the land surface through the confining materials. Discharge is to underlying Paleozoic aquifers and to the alluvium and glacial outwash deposits along the Missouri and Big Sioux Rivers in the southwest part of the area. Flow components toward bedrock valleys may reflect discharge to Quaternary sand and gravel deposits in these valleys. Pumping tests conducted in the study area indicate a narrow" range of hydraulic conductivities of the Dakota aquifer, from 37 to 50 feet per day. Consequently, an average hydraulic conductivity of 40 feet per day was used to estimate the potential yield to wells completed in the aquifer. Yields of more than 250 gallons per minute can be expected throughout much of the study area and more than 1,000 gallons per minute could be produced in some areas. The quality of water from the Dakota is a calcium, magnesium, sulfate type. It is generally suitable for irrigation purposes, based on comparisons of sodium adsorption ratios and electrical conductivities. In some areas the aquifer has water with high salinity hazard that may restrict its use to irrigation of only well-drained types of soil. The concentration of radium-226 and other radionuclides exceeds recommended limits at several sites. The quality of water pumped from the aquifer may be altered by induced leakage from the underlying aquifers in Paleozoic age rocks if withdrawals reverse the pattern of natural flow from the Dakota into the Paleozoic aquifers. Evidence for such a reversal exists in the area around the city of LeMars.

Iowa↗
USGS1984

Sewage plume in a sand and gravel aquifer, Cape Cod, Massachusetts

Secondarily treated domestic sewage has been disposed of on surface sand beds at the sewage treatment facility at Otis Air Force Base, Massachusetts, since 1936. Infiltration of the sewage through the sand beds into the underlying unconfined sand and gravel aquifer has resulted in a plume of sewage-contaminated ground water that is 2,500 to 3,500 feet wide, 75 feet thick, and more than 11,000 feet long. The plume extends south and southwest of the sand beds in the same direction as the regional flow of ground water, and is overlain by 20 to 50 feet of ground water derived from precipitation that recharges the aquifer. The bottom of the plume generally coincides with the contact between the permeable sand and gravel and underlying finer grained sediments. The distributions in the aquifer of specific conductance, temperature, boron, chloride, sodium, phosphorus, nitrogen (total of all species), ammonia, nitrate, dissolved oxygen, and detergents are used to delineate the plume. In ground water outside the plume, the detergent concentration is less than 0.1 milligrams per liter as MBAS (methylene blue active substances), the ammonia-nitrogen concentration is less than 0.1 milligrams per liter, the boron concentration is less than 50 micrograms per liter, and specific conductance is less than 80 mircromhos per centimeter. In the center of the plume, detergent concentrations as high as 2.6 milligrams per liter as MBAS, ammonia-nitrogen concentrations as high as 20 milligrams per liter, boron concentrations as high as 400 micrograms per liter, and specific conductance as high as 405 micromhos per centimeter were measured. Chloride, sodium, and boron are transported by the southward-flowing ground water without significant retardation, and seem to be diluted only by hydrodynamic dispersion. The movement of phosphorus is greatly restricted by sorption. Phosphorus concentrations do not exceed 0.05 milligrams per liter farther than 2,500 feet from the sand beds. Detergent concentrations in the plume are highest between 3,000 and 10,000 feet from the sand beds and reflect the introduction of nonbiodegradable detergents in 1946 and the conversion to biodegradable detergents in 1964. The center of the plume as far as 5,000 feet from the sand beds contains nitrogen as ammonia, but no nitrate and no dissolved oxygen. Ammonia is gradually oxidized to nitrate between 5,000 and 8,000 feet from the sand beds, and at distances greater than 8,000 feet oxidation of ammonia is essentially complete. Ammonia also is oxidized to nitrate along the top and sides of the plume within 5,000 of the beds where the contaminated ground water mixes with uncontaminated ground water that contains up to 11 milligrams per liter dissolved oxygen.

Massachusetts↗
USGS2004

Basic ground-water hydrology

Ground water is one of the Nation's most valuable natural resources. It is the source of about 40 percent of the water used for all purposes exclusive of hydropower generation and electric powerplant cooling. Surprisingly, for a resource that is so widely used and so important to the health and to the economy of the country, the occurrence of ground water is not only poorly understood but is also, in fact, the subject of many widespread misconceptions. Common misconceptions include the belief that ground water occurs in underground rivers resembling surface streams whose presence can be detected by certain individuals. These misconceptions and others have hampered the development and conservation of ground water and have adversely affected the protection of its quality. In order for the Nation to receive maximum benefit from its ground-water resource, it is essential that everyone, from the rural homeowner to managers of industrial and municipal water supplies to heads of Federal and State water-regulatory agencies, become more knowledgeable about the occurrence, development, and protection of ground water. This report has been prepared to help meet the needs of these groups, as well as the needs of hydrologists, well drillers, and others engaged in the study and development of ground-water supplies. It consists of 45 sections on the basic elements of ground-water hydrology, arranged in order from the most basic aspects of the subject through a discussion of the methods used to determine the yield of aquifers to a discussion of common problems encountered in the operation of ground-water supplies. Each section consists of a brief text and one or more drawings or maps that illustrate the main points covered in the text. Because the text is, in effect, an expanded discussion of the illustrations, most of the illustrations are not captioned. However, where more than one drawing is included in a section, each drawing is assigned a number, given in parentheses, and these numbers are inserted at places in the text where the reader should refer to the drawing. In accordance with U.S. Geological Survey policy to encourage the use of metric units, these units are used in most sections. In the sections dealing with the analysis of aquifer (pumping) test data, equations are given in both consistent units and in the inconsistent inch-pound units still in relatively common use among ground-water hydrologists and well drillers. As an aid to those who are not familiar with metric units and with the conversion of ground-water hydraulic units from inch-pound units to metric units, conversion tables are given on the inside back cover. Definitions of ground-water terms are given where the terms are first introduced. Because some of these terms will be new to many readers, abbreviated definitions are also given on the inside front cover for convenient reference by those who wish to review the definitions from time to time as they read the text. Finally, for those who need to review some of the simple mathematical operations that are used in ground-water hydrology, a section on numbers, equations, and conversions is included at the end of the text.

Water Supply Paper↗
USGS1984

Hydrologic characteristics of Nebraska soils

The influence of the physical characteristics of soil on hydrology is frequently neglected. In this report, the effects of five characteristics on the hydrologic responses of soils in Nebraska are evaluated quantitatively, soils are grouped through use of a simplified coding system according to similarities in hydrologic responses, and are mapped according to these responses. General soils maps of the U.S. Department of Agriculture Soil Conservation Service and data for the physical properties of the soils proved well-suited to hydrologic interpretation. This interpretation of the maps and data led to the selection of three characteristics as classification variables: Average permeability of the 60-inch soil profile, average maximum soil slope, and depth to the seasonal high water table. Permeability of the least permeable horizon and available water capacity, although not needed as classification variables, are useful in explaining some of the hydrologic responses of soils. The primary soil units used in groupings and interpretation of the soils for this study are the soil associations. A computer program is presented that sorts the soils into groups and calculates statistics for each group. The 147 soil associations in Nebraska were thus sorted into 29 hydrologic soil groups. The location and extent of these hydrologic soil groups are shown on maps at scales of 1:750,000 and 1:250,000 for the State.

Water Supply Paper↗
USGS1984

Floods of October 1977 in southern Arizona and March 1978 in central Arizona

Major floods occurred in October 1977 and March 1978 in Arizona. As much as 14 inches of rain fell during October 6-9, 1977, over the mountains of southern Arizona and northern Mexico resulting in the highest discharge since at least 1892 on the Santa Cruz River upstream from Tucson. The flood inundated areas as much as 4 miles wide, covered at least 16,000 acres of farmland, and caused $15.2 million in damage. Residential losses occurred at Nogales, Amado, Green Valley, and Sahuarita. Severe erosional damage occurred along the Santa Cruz River, Agua Fria Canyon, Potrero Creek, and many small drainages in the Sonoita Creek basin. The peak discharge in Agua Fria Canyon was the highest since before 1900. Less severe flooding occurred along the San Pedro River and the Gila River downstream from the San Pedro. Widespread rainfall of 3 to 6 inches and 9 to 14 inches in some areas in the central mountains during February 27 to March 3, 1978, caused the highest discharge since 1920 on the Salt River in Phoenix and resulted in three deaths. Flooding along the Salt and Gila Rivers and several lesser streams caused statewide damage totaling $65.9 million, of which about $37 million occurred in Maricopa County. Nine counties were declared disaster areas. During the flood of March 1978, moderate peak discharges and unusually high volumes of runoff occurred on tributaries to the Salt and Verde Rivers upstream from a system of reservoirs. Flood magnitudes were greater at the main-stem gaging stations than on the tributaries. The peak discharge into Theodore Roosevelt Lake, which was 21 percent full at the start of the flood, was about 155,000 cubic feet per second, the largest known from 1890 to 1978. The reservoirs stored large quantities of water and greatly reduced the magnitude of the flood. The peak discharge of the Salt River was 125,000 cubic feet per second below Granite Reef Dam and 122,000 cubic feet per second at Phoenix. Discharges in excess of 100,000 cubic feet per second occurred for 8 hours. Without the storage provided by the reservoirs, the peak discharge on the Salt River would have been 260,000 cubic feet per second, and the discharge would have exceeded 100,000 cubic feet per second for 66 hours. The Verde River was the principal flood source, but flows at the upstream gaging stations did not indicate the magnitude of the impending flood at Horseshoe Reservoir because large inflow from tributaries immediately upstream from the reservoir caused the river to rise at downstream stations before it rose at upstream stations. About 17 percent of the water entering the reach from Granite Reef Dam to Gillespie Dam went to recharge, temporary ground-water storage, or evapotranspiration losses. All water was stored at Painted Rock Reservoir and released at a low rate that prevented water from reaching the Gila River near Mohawk gaging station.

Water Supply Paper↗
USGS1984

Quantity and quality of streamflow in the southeastern Uinta Basin, Utah and Colorado

The southeastern Uinta Basin of Utah and Colorado includes an area of 3,000 square miles containing large oilshale deposits. Future mining and retorting of the oil shale in northeastern Utah is expected to impact the area's water resources. In order to determine premining conditions, streamflow and water-quality data were collected during 1974-79. These data plus all other available information were used to define baseline conditions for streamflow and water-quality characteristics. The data and interpretations will provide a basis for evaluating impacts of future mining. Areal and time variances in streamflow and waterquality characteristics were determined for the major rivers (Green and White) and the intra-area streams (streams that originate within the study area). The streamflow characteristics defined are average streamflow and low- and highflow extremes. Graphs of frequency curves, duration curves, and draft-storage relations are presented for selected gaging stations. Areal variances in average and peak flows are illustrated. Water-quality characteristics are summarized according to the following categories: general waterquality characteristics, major dissolved constituents, trace elements, nutrients, pesticides, and sediment, biological, organic, and radiochemical characteristics. The means and ranges in values are discussed for the major rivers and the intra-area streams. The water-quality constituents are compared to water-quality criteria of the Environmental Protection Agency. The major rivers flowing into the area convey an average of 5,900 cubic feet per second from a total drainage area of about 34,000 square miles. This is more than 100 times as much runoff as originates within the study area. The average flow for the major rivers is 0.17 cubic foot per second per square mile and does not vary significantly from one location to another within the study area. The flows of the intra-area streams vary from less than 0.001 to more than 0.10 cubic foot per second per square mile. Evapotranspiration losses can exceed inflow; thus average flows of some intra-area streams decrease in a downstream direction. The quality of streamflow varies considerably between the major rivers and the intra-area streams. In the major rivers, the concentrations vary seasonally but do not vary significantly from one location to another. In the intra-area streams, concentrations vary both seasonally and from one location to another. The water quality in the major rivers generally is better than that in the intra-area streams. Dissolved-solids concentrations average 572 milligrams per liter for the Green River and 500 milligrams per liter for the White River, whereas mean concentrations for the intraarea streams range from 549 milligrams per liter in ephemeral streams to 5,320 milligrams per liter in Bitter Creek. Concentrations of major constituents generally do not exceed water-quality criteria of the Environmental Protection Agency except for hardness and sulfate. Several trace elements exceed water-quality criteria in intra-area streams. Dissolved-solids concentrations in base flow in short reaches of Bitter Creek can exceed 10,000 milligrams per liter.

Colorado, utah↗
USGS1984

Low-level radioactive-waste burial at the Palos Forest Preserve, Illinois: Geology and hydrology of the glacial drift, as related to the migration of tritium

A low-level radioactive-waste burial site is located in Palos Forest Preserve, about 22 kilometers southwest of Chicago, Illinois. Between 1943 and 1949 the site, named Plot M, was filled with radioactive waste from the first Argonne National Laboratory and from the University of Chicago Metallurgical Laboratory. Since 1973, tritium concentration levels up to 14 nanocuries per liter have been measured in water samples collected from a well 360 meters from the burial site. The U.S. Geological Survey is studying the geologic, hydrologic, and geochemical properties of the glacial drift and underlying bedrock at the Plot M site to determine the factors that control the movement of radionuclides. Test wells were drilled into the drift to collect water and core samples for laboratory analysis, to gather geologic and hydrologic data, and to conduct geophysical surveys. Plot M is located in drift that ranges in thickness from 25 to 45 meters. The drift is a stratified sequence of clay- and silt-rich sediments that contain thin, interstratified sand layers. The silt content of the drift increases with depth. The permeability of the drift, as indicated by field and laboratory hydraulic conductivity tests, ranges from 1.0 x 10 -6 to 1.0 ? 10 -8 centimeters per second. A tritium plume, the contaminated zone in the drift in which tritium concentration levels exceed 10 nanocuries per liter of water, extends horizontally northward from Plot M at least 50 meters and vertically downward to bedrock. The center of the plume, where tritium concentration levels are as high as 50,000 nanocuries per liter, is approximately 15 meters beneath the burial site. The size, shape, and 'bull's-eye' concentration pattern indicate that the plume is a single slug and that the site no longer releases tritium into the drift. The leading edge, or front, of the plume (the 10 nanocuries per liter boundary) left the burial site in either the late 1940's or the early 1950's and intersected the underlying bedrock surface before 1973. The calculated movement rate of the front is 6.3 x 10 -6 centimeters per second. Several key factors that control both the concentration level and the extent of migration of tritium in the drift at Plot M are 1. The limited amount of tritiated waste buried at Plot M. 2. The long period of time that has elapsed since the waste was buried (30-35 years) relative to the radioactive half-life of tritium (12.3 years). 3. The great thickness and low permeability of the glacial drift at the site.

Illinios↗
USGS1987

Water resources of the Zuni tribal lands, McKinley and Cibola Counties, New Mexico

An evaluation of the water resources of the Zuni tribal lands in west-central New Mexico was made to determine the yield, variability, and quality of water available to the Pueblo of Zuni. This study is needed to aid in orderly development of these resources. Rocks of Permian to Quaternary age supply stock, irrigation, and domestic water to the Zuni Indians. The Glorieta Sandstone and San Andres Limestone (Glorieta-San Andres aquifer) of Permian age and sandstones in the Chinle Formation of Triassic age provide most of this water supply. Water in the Glorieta-San Andres aquifer is confined by minimal-permeability shales and is transmitted through the aquifer along interconnected solution channels and fractures. Water-level and water-quality information indicate greater hydraulic conductivities along the southern boundaries of Zuni tribal lands. Well yields from the Glorieta-San Andres aquifer are as much as 150 gallons per minute, and aquifer transmissivity ranges from 30 to 1,400 feet squared per day. Longterm, water-level declines of as much as 29 feet have been measured near pumping centers at Black Rock. Multiple-well aquifer tests are needed to further define aquifer properties (storage, transmissivity, and leakage from confining units) and the effects of well design on well yields. Dissolved-solids concentrations in water from the aquifer range from 331 to 1,068 milligrams per liter. Calcium and sulfate are the predominant ions. Water in sandstones of the Chinle Formation is confined by adjacent shales and is transmitted along interconnected fractures. Well yields range from 5 to 125 gallons per minute, and aquifer transmissivity ranges from 40 to 1,400 feet squared per day. Water-level declines of as much as 27 feet have been measured near Zuni Village. Dissolved-solids concentrations in water from the aquifer range from 215 to 1,980 milligrams per liter. Sodium and bicarbonate are the predominant ions. Other sources of ground water are used primarily for livestock watering by means of windmills, with the exception of buried alluvial channel deposits along the Rio Pescado. These deposits provide domestic and irrigation water through springs and wells to Pescado and Black Rock. The Bidahochi Formation of Miocene and Pliocene age could potentially provide an additional supply of water chemically suitable for most uses. Seismic-reflection techniques are being used to locate buried channels eroded in the rocks underlying the Bidahochi Formation. These buried channels may contain thicker sections of saturated sands and gravels that could be developed for stock and domestic use.

Water Supply Paper↗
USGS1984

Evaluation of environmental factors affecting yields of major dissolved ions of streams in the United States

The seven major dissolved ions in streams-sodium, potassium, magnesium, calcium, chloride, sulfate, and bicarbonate and their sum dissolved solids from 56 basins in the conterminous United States and Hawaii were correlated with bedrock type, annual precipitation, population density, and average stream temperature of their respective basins through multiple linear-regression equations to predict annual yields. The study was restricted to basins underlain by limestone, sandstone, or crystalline rock. Depending on the constituent, yields ranged from about 10 to 100,000 kilograms per square kilometer. Predicted yields were within 1 order of magnitude of measured yields. The most important factor in yield prediction was annual precipitation, which accounted for 58 to 71 percent of all yields. Rock type was second in importance. Yields of magnesium, calcium, bicarbonate, and dissolved solids from limestone basins were 4 to 10 times larger than those from sandstone or crystalline basins as a result of carbonate weathering. Population density was an ineffective indicator of all constituents except sodium and chloride; it accounted for 13 percent of the annual sodium yield and 20 percent of the annual chloride yield. Average stream temperature was significant only for calcium and bicarbonate in limestone basins. Its relationship with yields was consistently negative. Either carbonate dissolution increases at low temperatures, or weathering in northern basins, which contain glacial deposits and have the lowest stream temperatures, is greater than in southern basins. Average ion contributions from atmospheric deposition accounted for 30 percent of the sodium and chloride and 60 percent of the sulfate in annual yields. The amount of sulfate derived from atmospheric contributions was higher in sandstone and crystalline basins (65 and 80 percent, respectively) than limestone basins (38 percent). This disparity is attributed to the lack of available sulfate in crystalline rock and the chemical precipitation of sulfate in the sandstone basins, most of which are in semi-arid or arid areas.

Water Supply Paper↗
USGS1984

A filtration and column-adsorption system for onsite concentration and fractionation of organic substances from large volumes of water

A portable filtration and column-adsorption system which can concentrate suspended sediment and dissolved-aqueous organic substances onsite was developed. Organic solutes also are fractionated into hydrophobic- and hydrophilic-acid, base, and neutral fractions. Subsequent isolation of organic solutes from fraction concentrates and extraction of organic constituents in suspended sediment entrained on filter tubes is performed by a variety of procedures in the laboratory. Three surface-water samples and one ground-water sample ranging in volume from 300 to 1,100 liters were processed through the filtration and column-adsorption system, yielding from about 0.8 to 3.0 grams of recovered organic carbon per sample.

Water Supply Paper↗
USGS1985

Controls on phosphorus mobility in the Potomac River near the Blue Plains wastewater treatment plant

The Blue Plains wastewater treatment plant is the largest point source of phosphorus in the Potomac River basin, discharging an average of 2 metric tons of phosphorus into the river each day in 1980. An intensive study of the water and sediments in the vicinity of the treatment plant was conducted in 1979-80 in order to characterize the major factors controlling the mobility of effluent-derived phosphorus in the area. The transport of phosphorus near the treatment plant was found to be affected by the circulation regime, by inorganic adsorption reactions with sediments, and by metabolic uptake and release by phytoplankton. The effect of river discharge on the convective transport of phosphorus near the outfall is significantly reduced by a mid-river shoal area, which confines the flow path of the effluent to an embayment on the eastern side of the river for a distance of 4 kilometers below the outfall. This embayment appears to serve as a sediment trap, where protection from bottom scour during high-flow events has permitted fine-grained sediments to accumulate. Measurements of mean residence time indicate that the effluent leaves the embayment area 21? days after being discharged from the outfall. Measurements of the linear decay constant for the removal of dissolved phosphorus from the water column reveal a diurnal cycle corresponding to the metabolic utilization of phosphorus by phytoplankton. This cyclic removal is superimposed on a constant and noncyclic adsorption of phosphorus by inorganic phases. Forty-eight hour average values of the linear decay constant for dissolved phosphorus in the area range from 0.4 to 1.1 per day. Analyses of bottom sediments indicate that approximately 13 percent of the phosphorus discharged between September 1977 and August 1980 has been retained in the embayment. The primary inorganic phase responsible for phosphorus adsorption is amorphous iron (ferric oxy-hydroxides); amorphous aluminum and clay minerals appear to play secondary roles. The accumulation of sorbed phosphorus in the embayment has been promoted by the deposition of fine-grained sediments enriched in ferric oxy-hydroxides. Conversely, the absence of ferric oxy-hydroxides in coarse-grained sediments near the outfall has facilitated the precipitation of the ferrous phosphate mineral vivianite.

District of Columbia, Maryland, Virginia↗
USGS1988

Phytoplankton dynamics of the fresh, tidal Potomac River, Maryland, for the summers of 1979 to 1981

The distribution and abundance of phytoplankton in the fresh, tidal Potomac River, Md., was different during 1979-81 from that observed in the 1960's and 1970's. Concentrations of phytoplankton in the 1960's and 1970's reached maximum attainable levels that were limited only by self-shading. A sag in phytoplankton abundance, apparent during the summers of 1980 and 1981 between Rosier Bluff and Marshall Hall, appears to have been caused by the Asiatic clam, Corbicula fluminea. Reduced abundance of phytoplankton throughout the entire fresh, tidal river during the summers of 1980 and 1981 may have been due to grazing by Corbicula, high discharge, and perhaps phosphorus limitation in late August at and downstream of Hallowing Point. Phytoplankton growth rates and chlorophyll-to-cell ratios were highest at Hatton Point and Marshall Hall (the sag reach). A model was constructed that predicted phytoplankton growth rates by varying only chlorophyll a concentration and light penetration. Nutrient concentrations were not required to make the model fit the data. Primary productivity was highest for the year during August 1980 and August 1981. Productivity-per-unit chlorophyll was highest at Hatton Point, where reduced concentrations of phytoplankton permitted the deepest light penetration in the fresh, tidal river.

Maryland↗