Geology topics

V. A. Levesque

Publications and source records attributed to V. A. Levesque.

5 recordsLinked to original sources

USGS2004

Water flow and nutrient flux from five estuarine rivers along the southwest coast of the Everglades National Park, Florida, 1997-2001

Discharge and nutrient fluxes for five tidally affected streams were monitored and evaluated as a part of the U.S. Geological Survey Place-Based Studies Initiative and the U.S. Department of the Interior Critical Ecosystem Studies Initiative. Locations on Lostmans Creek, and Broad, Harney, Shark, and North Rivers were selected using the criterion that a large amount of the water that flows through Shark River Slough must pass these sites. Discharge and nutrient-concentration data collection started at the Broad, Harney, and Shark River stations in January 1997 and ended in early 2001. Discharge and nutrient-concentration data collection started at the Lostmans Creek and North River stations in April 1999 and ended in early 2001. Each station was equipped with a vertically oriented acoustic-velocity sensor, water-level pressure transducer, bottom water-temperature thermistor, and specific conductance four-electrode sensor. Data collected using a vessel-mounted acoustic discharge measurement system were used to calibrate regression models of the mean river velocities and the in-situ index velocities. Information from these stations, in conjunction with data from other ongoing studies, will help to determine environmental effects on the southwest coast estuaries as changes in water management of the Everglades National Park continue. Discharges from the Lostmans Creek, and Broad, Harney, Shark, and North River stations are influenced by semidiurnal tides, meteorological events, and surface- and ground-water inflow. Each of the five rivers is usually well mixed, having no greater than 500 microSiemens per centimeter at 25? Celsius difference in specific conductance from top to bottom during flood and ebb tides. Instantaneous flood discharges (water moving upstream) are typically of greater magnitude and shorter duration than instantaneous ebb discharges (water moving downstream). Instantaneous discharge data were filtered using a low-pass filter to remove predominant tidal frequencies, and the filtered data were used to compute daily mean and monthly mean residual discharges. Lostmans Creek, and Broad, Harney and Shark Rivers each contributed from 20 to 27 percent of the total measured discharge to the Gulf of Mexico, whereas North River contributed approximately 4 percent. The main discharge region of the Shark River Slough extends from as far north as Lostmans Creek to as far south as North River. North River discharge has similar response characteristics to the other four rivers measured, but with a lesser magnitude of discharge. Comparisons of monthly mean discharges from the Tamiami Canal flow control structures S-12-A, B, C, and D located on U.S. Highway 41 (Tamiami Trail) to the five station total monthly mean discharges indicate that the discharges from the five rivers are approximately 2 to 3 times the S-12-A, B, C, D discharges, and that the measured southwest coast discharge peaks lead the S-12-A, B, C, D discharge peaks by approximately 1 month. Residual total nitrogen and total phosphorus fluxes were estimated using linear regression models of discharge and flux. Monthly mean total nitrogen residual fluxes for the five southwest coast rivers ranged from approximately 0 to 390 short tons, whereas monthly mean total phosphorus residual fluxes ranged from approximately 0 to 6 short tons. Total nitrogen and total phosphorus residual fluxes at Lostmans Creek, and Broad, Harney, and Shark Rivers were similar in magnitude, each accounting for between 20 to 29 percent of the total measured residual flux. North River contributed between 3 to 4 percent of the total nitrogen and total phosphorus residual flux from the five rivers.

Florida↗

USGS1997

Comparison of two methods for estimating discharge and nutrient loads from tidally affected reaches of the Myakka and Peace Rivers, west-central Florida

The Myakka and Peace River Basins constitute more than 60 percent of the total inflow area and contribute more than half the total tributary inflow to the Charlotte Harbor estuarine system. Water discharge and nutrient enrichment have been identified as significant concerns in the estuary, and consequently, it is important to accurately estimate the magnitude of discharges and nutrient loads transported by inflows from both rivers. Two methods for estimating discharge and nutrient loads from tidally affected reaches of the Myakka and Peace Rivers were compared. The first method was a tidal-estimation method, in which discharge and nutrient loads were estimated based on stage, water-velocity, discharge, and water-quality data collected near the mouths of the rivers. The second method was a traditional basin-ratio method in which discharge and nutrient loads at the mouths were estimated from discharge and loads measured at upstream stations. Stage and water-velocity data were collected near the river mouths by submersible instruments, deployed in situ, and discharge measurements were made with an acoustic Doppler current profiler. The data collected near the mouths of the Myakka River and Peace River were filtered, using a low-pass filter, to remove daily mixed-tide effects with periods less than about 2 days. The filtered data from near the river mouths were used to calculate daily mean discharge and nutrient loads. These tidal-estimation-method values were then compared to the basin-ratio-method values. Four separate 30-day periods of differing streamflow conditions were chosen for monitoring and comparison. Discharge and nutrient load estimates computed from the tidal-estimation and basin-ratio methods were most similar during high-flow periods. However, during high flow, the values computed from the tidal-estimation method for the Myakka and Peace Rivers were consistently lower than the values computed from the basin-ratio method. There were substantial differences between discharges and nutrient loads computed from the tidal-estimation and basin-ratio methods during low-flow periods. Furthermore, the differences between the methods were not consistent. Discharges and nutrient loads computed from the tidal-estimation method for the Myakka River were higher than those computed from the basin-ratio method, whereas discharges and nutrients loads computed by the tidal-estimation method for the Peace River were not only lower than those computed from the basin-ratio method, but they actually reflected a negative, or upstream, net movement. Short-term tidal measurement results should be used with caution, because antecedent conditions can influence the discharge and nutrient loads. Continuous tidal data collected over a 1- or 2-year period would be necessary to more accurately estimate the tidally affected discharge and nutrient loads for the Myakka and Peace River Basins.

Florida↗

USGS1996

The effect of discharge and water quality of the Alafia River, Hillsborough River, and the Tampa Bypass Canal on nutrient loading to Hillsborough Bay, Florida

Techniques to measure discharge and nutrient loads in the tidally affected portions of two major rivers tributary to Tampa Bay, the Alafia River and the Hillsborough River, were developed and tested. Discharge, water quality, and total phosphorus and total nitrogen loads for the period April 1, 1991, through March 31, 1992, were evaluated and compared with discharge,water quality, and loads at long-term, nontidal gages in the basins. Long-term discharge and water-quality characteristics at selected sites in the Alafia river and Hillsborough River basins were evaluated. A long-term, decreasing trend in annual-mean discharge was observed for discharges at the Alafia River, Sulphur Springs, and Hillsborough River. Low-flow and high-flow characteristics in the Alafia River and Hillsborough River have changed as well. The decreasing trend in the Alafia River discharges is not due to deficient rainfall but probably is due to decreased ground-water inflow to the river because of long-term declines in the potentiometric surface of the Upper Floridan aquifer. Daily-mean discharges at the mouth of the Alafia River were more variable than discharges at the long-term gage upstream. Daily-mean discharge near the mouth of the river was negative at times, indicating a net loss of water from the river. Daily-mean discharge from the Hillsborough River was minimal from Apil to May 1991, and from late September 1991 to March 1992. During these periods, discharge from Sulphur Springs was a major source of freshwater to the tidally affected reach of the river. Concentrations of total phosphorus and orthophosphorus in the Alafia River above Lithia Springs were the greatest in the 1960's and have generally declined since then. Total nitrogen concentrations have been declining since about 1981. However, increases in nitrate plus nitrite nitrogen concentrations are occurring in Lithia Springs, a second-magnitude spring that flows into the Alafia River. Specific conductance of water discharging from Sulphur Springs to the Hillsborough River has increased from about 124 to more than 2,000 microsiemens per centimeter since 1945. Water quality at the mouth of the Alafia River and Hillsborough River is the result of mixing of freshwater and estuarine water from Hillsborough Bay. Large daily variations in water quality occur at these site because of tidal currents, and vertical stratification of specific conductance is a common feature. Concentrations of phosphorus, nitrate plus nitrite nitrogen, organic carbon, and silica are inversely related to specific conductance at the mouth of the Alafia River. Constituent concentration and discharge data were used to compute loads during the study period. Average daily phosphorus loads were 2.4 tons per day at the mouth of the Alafia River; 0.35 ton per day at the mouth of the Hillsborough River; and 0.06 ton per day at the Tampa Bypass Canal. Average daily nitrogen loads were 1.7 tons per day at the mouth of the Alafia River; 0.86 ton per day at the mouth of the Hillsborough River; and 0.26 ton per day at the Tampa Bypass Canal. The greatest annual loads of phosphorus and nitrogen from the major tributaries to Hillsborough Bay are from the Alafia River, with the greatest loads at the river mouth. Total phosphorus load from the Alafia River was about 894 tons during April 1991 through March 1992, more than six times greater than phosphorus loads form the Hillsborough River. Annual total nitrogen load at the mouth of the Alafia River was about 630 tons, two times greater than at the mouth of the Hillsborough River and more than six times greater than loads from the Tampa Bypass Canal. Basinwide yields of total phosphorus during April 1991 through March 1992 were about 2 tons per square mile at the mouth of the Alafia river basin and were about 0.2 ton per square mile at the mouth of the Hillsborough River. Total nitrogen yield was about 1.5 tons per square mile at the mouth of the Alafia River and about 0.5 ton per s

Water-Resources Investigations Report↗

USGS1996

Discharge, water-quality characteristics, and nutrient loads from McKay Bay, Delaney Creek, and East Bay, Tampa, Florida, 1991-1993

Nutrient enrichment in Tampa Bay has caused a decline in water quality in the estuary. Efforts to reduce the nutrient loading to Tampa Bay have resulted in improvement in water quality from 1981 to 1991. However, Tampa Bay still is onsidered enriched with nutrients. Water quality in East Bay (located at the northeastern part of Hillsborough Bay, which is an embayment in Tampa Bay) is not improving at the same rate as the rest of the bay. East Bay is the center of shipping activity in Tampa Bay and the seventh largest port in the United States. One of the primary cargoes is phosphate ore and related products such as fertilizer. The potential for nutrient loading to East Bay from shipping activities is high and has not previously been measured. Nitrogen and phosphorus loads from East Bay to Hillsborough Bay were measured during selected time periods during June 1992 through May 1993; these data were used to estimate seasonal and annual loads. These loads were evaluated to determine whether the loss of fertilizer products from shipping activities resulted in increased nutrient loading to Hillsborough Bay. Discharge was measured, and water-quality samples were collected at the head of East Bay (exiting McKay Bay), and at the mouth of East Bay. Discharge and nitrogen and phosphorus concentrations for the period June 1992 through May 1993 were used to compute loads. Discharges from McKay Bay, Delaney Creek, and East Bay are highly variable because of the effect of tide. Flow patterns during discharge measurements generally were unidirectional in McKay Bay and Delaney Creek, but more complex, bidirectional patterns were observed at the mouth of East Bay. Tidally affected discharge data were digitally filtered with the Godin filter to remove the effects of tide so that residual, or net, discharge could be determined. Daily mean discharge from McKay Bay ranged from -1,900 to 2,420 cubic feet per second; from Delaney Creek, -3.8 to 162 cubic feet per second; and from East Bay, -437 to 3,780 cubic feet per second. Water quality in McKay Bay, Delaney Creek, and East Bay varies vertically, areally, and seasonally. Specific conductance and concentrations of phosphorus and ammonia nitrogen were greater near the bottom than near the surface at the head and mouth of East Bay. Concentrations of total nitrogen and ammonia plus organic nitrogen generally were greater at the head of East Bay than at the mouth, indicating that McKay Bay is the primary source of nitrogen to East Bay. Concentrations of total ammonia nitrogen, nitrite plus nitrate nitrogen, phosphorus, orthophosphorus, and suspended solids and values of turbidity and specific conductance generally were greater at the mouth of East Bay than at the head. The greatest concentrations of nitrogen and phosphorus were measured in Delaney Creek. In East Bay and McKay Bay, the greatest concentrations of nitrogen, phosphorus, and ammonia plus organic nitrogen occurred in summer, whereas turbidity, specific conductance, and concentrations of suspended solids were greater in winter. The greatest daily mean loads from McKay Bay and East Bay occurred in late June 1992 and April and May 1993 and coincided with periods of daily mean discharge greater than about 2,000 cubic feet per second. Although concentrations of nitrogen and phosphorus were greater in Delaney Creek than in McKay Bay and East Bay, loads were minimal because of minimal discharges from Delaney Creek. Monthly loads of total nitrogen ranged from about 20 tons to about 83 tons at McKay Bay; from about 1 ton to 4.2 tons at Delaney Creek; and from about 17 tons to 76 tons at the mouth of East Bay. Monthly loads of phosphorus ranged from about 11 tons to about 45 tons at McKay Bay; from about 0.62 ton to 2.6 tons at Delaney Creek; and from about 10 tons to about 45 tons at the mouth of East Bay. The results of this study indicate that nitrogen and phosphorus loads from the basin draining directly to East Bay (excluding loads from the McKa

Water-Resources Investigations Report↗

USGS1995

Summary of sediment resuspension monitoring activities, Old Tampa Bay and Hillsborough Bay, Florida, 1988-91

Sediment resuspension was studied in Old Tampa BaY, the northwestern subembayment of Tampa Bay, and in Hillsborough Bay, the northeastern subembayment of Tampa Bay located along the coast of west-central Florida. Electromagnetic current meters, optical backscatterance sensors, and water samples were used to collect sediment resuspension data at several study sites in the two bays. This report describes the data-collection methods and summaries sediment resuspension data collected intermittently from October 1988 through December 1990 in Old Tampa Bay and from March 1990 through September 1991 in Hillsborough Bay. Example data are presented for selected monitoring events.

Water-Resources Investigations Report↗