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The objectives of the sub-basin-scale monitoring, to be conducted by the USGS over 10 years at 17 sites in the LOWP area, are as follows:
1. Compute loads for phosphorus, nitrogen, and total suspended solids in selected sub-basins with no current load monitoring.
2. Characterize spatial distribution of loads across the LOWP area.
3. Establish a baseline of water quality and streamflow information at the sub-basin level.
4. Provide data to cooperators for planning activities for restoration of Lake Okeechobee.
5. Provide data for evaluating changes in the watershed, particularly the cumulative effect of restoration activities at the sub-basin level.
Agricultural development in the drainage area and construction of the Central and South Florida (C&SF) project during the last century has resulted in excess nutrients inputs and more efficient delivery of stormwater to the lake. As a result, in-lake phosphorus concentrations have doubled since 1970. This increase in phosphorus has shifted the natural balance of nutrients in the lake, led to conditions that are favorable for blue-green algal blooms, and contributed to the accumulation of phosphorus-rich bed sediments over an extensive area of the lake. Operation of the C&SF project for regional flood control has resulted in prolonged periods of high water levels in the lake. This situation has exacerbated the lake’s phosphorus problems and has contributed to a decline in health of the lake’s littoral zone. The C&SF project canals that discharge excess floodwaters to the St. Lucie and Caloosahatchee estuaries from Lake Okeechobee have severely impacted both estuaries. The USACE re-evaluated the C&SF project in the mid-1990s and developed the Comprehensive Everglades Restoration Plan (CERP) in 1999 for the restoration, protection, and preservation of water resources of central and southern Florida. This Plan received overwhelming bipartisan support and was signed into law by President Clinton in December 2000. The LOW Project incorporates 4 of the 68 major components of the CERP and has 3 major objectives: 1) to improve water quality in tributaries and discharges to Lake Okeechobee, 2) to increase storage capacity for watershed runoff and lake water, and 3) to enhance and restore wetlands in the watershed.
Somers, W. P.
Novak, C. E.
Nguyen, H. T.; Ross, J. H.
Two types of samples were collected as part of the monitoring network:
1. Flow-weighted composite samples collected using an unrefrigerated autosampler 2. Manual samples collected from multiple transects in the stream and composited in a churn splitter
Both types of samples were collected weekly, provided that there was sufficient flow throughout the week. The term ‘sufficient flow’ means that enough flow has passed the site during the week in order to collect a minimum sample volume in the autosampler. At an absolute minimum, enough volume must be collected for the total phosphorus sample, since phosphorus is the most critical analyte in this monitoring program. Manual samples were collected only if the autosampler had collected the minimum required sample volume AND stream water around the site is not stagnant or pooled at the time of the visit.
All sites have Daily Average Flow and Stage except for C-41 Canal near Brighton, FL which has only Daily Average Flow.
Data for all sites were revised between 5/12/2008 and 5/19/2008.
Phase 2 started April 1, 2003. Construction of 3 monitoring stations was completed on June 12; construction of remaining 14 stations will commence mid-July. Streamflow monitoring will begin in August.
The basis for inclusion of water quality constituents is whether construction of Storm water Treatment Areas (STAs) and other management measures in the basin are designed to control concentrations and loads of that constituent or if performance of these projects will be directly affected by concentrations of the constituent.
Throughout the proposal, the term "total" refers to unfiltered samples, and the term "dissolved" refers to samples filtered through a 0.45- micron encapsulated filter.
The following parameters are planned for the sub-basin-scale monitoring network: Total phosphorus Dissolved phosphorus Dissolved ortho-phosphate phosphorus Total organic + ammonia nitrogen Total nitrite + nitrate nitrogen Dissolved ammonia nitrogen Total suspended solids
Weekly field measurements of water temperature, specific conductance, pH, and dissolved oxygen concentration also will be made.
The water quality sub-team of the LOW PDT developed the following list of selection criteria for sites in order to meet the monitoring objectives: Emphasis on priority basins (S-191, S-154, S-65D, S-65E) Network to provide project area-wide coverage Selection of sites meeting accessibility and other logistic requirements Selection of several basins with one or more of the following planned activities: a. homogeneous land use b. expected land use shifts c. expected land use intensification d. urban land use (1-2 sites) e. pristine basins where little activity is expected, to be used as control sites on hydrologic variability (1-2 sites)
Under these guidelines, the sub-team developed a list of 27 potential sites. USGS personnel investigated these sites during a field reconnaissance of the LOW Project area in the spring and summer of 2002. The following site characteristics were recorded:
Site accessibility Site description for construction and instrumentation needs Hydraulic characteristics including channel geometry and flow components (depth and velocity) Description of bottom sediments Description of drainage/discharge features immediately upstream and downstream of site Land use information Description of existing contaminant discharge points adjacent to site Other relevant site conditions
Of the 27 potential sites, 6 were eliminated due to access, safety, or extremely difficult flow measurement conditions, and 4 were eliminated due to budget constraints and lower priority. The original numbering scheme has been retained to show that 27 sites were considered. Sites 1 and 2, Lettuce Creek and Henry Creek, respectively, were replaced by downstream site 1A, L-63S Interceptor. Site 12 Gore Sough at CR724 near Basinger, FL) will be monitored for streamflow only because it is considered a relatively small contributor to nutrient loading in LOW. Site 12 will serve as a control site on hydrologic variability.
Ten sites coincide with existing SFWMD tributary monitoring sites. The SFWMD collects data at these sites to support general trend monitoring within the basins. The USGS will collect data at these stations regardless of whether the SFWMD continues their current collection scheme. SFWMD collects bi-weekly, monthly, or quarterly water samples for nutrients (plus additional parameters at site 18 Arbuckle Creek at Highway 98 near De Soto City, FL). Streamflow monitoring is not conducted by SFWMD at these sites.
Sample Collection Two types of samples will be collected as part of the monitoring network, as follows: 1. Flow-weighted composite samples collected using an unrefrigerated autosampler 2. Manual samples collected from multiple transects in the stream and composited in a churn splitter
Both types of samples will be collected weekly, provided that there is sufficient flow throughout the week. The term ‘sufficient flow’ means that enough flow has passed the site during the week in order to collect a minimum sample volume in the autosampler. At an absolute minimum, enough volume must be collected for the total phosphorus sample, since phosphorus is the most critical analyte in this monitoring program. Manual samples will be collected only if the autosampler has collected the minimum required sample volume AND stream water around the site is not stagnant or pooled at the time of the visit.
For autosampled constituents, concentrations determined from the weekly flow proportional composite samples will be used as the primary source of data for load computations. The sample volume collected from the autosampler will be split; one half of the sample will be submitted for analysis and the other half will be archived at 4 degrees Celsius. If the original sample is rejected at the laboratory due to bottle breakage, erroneous result, etc., the archived sample will be submitted in its place. However, if the original sample is analyzed successfully and results are received from the laboratory, the archived sample will be destroyed. If both autosampler samples are rejected, results from the manual sample will be used to compute an instantaneous load. Dissolved phosphorus, dissolved ortho-phosphate phosphorus, dissolved ammonia nitrogen, and total suspended solids concentrations will be determined solely from weekly manual samples.
Automatic sampler lines will be positioned in a representative location in the stream cross-section. The best placement of the autosampler intake will be determined through examination of flow profiles, collection and analysis of point samples using field HACH kits, and collection of quality control samples. Each automatic sampler will be triggered to collect a 100- milliliter aliquot of stream water after a set volume of streamflow has passed the site. Data collected from stage sensing equipment and an acoustic Doppler velocity meter will be used to trigger the autosampler. The volume of streamflow required to trigger the automatic sampler will be set to collect stream-water samples as frequently as possible without filling all the automatic sampler bottles before the site is serviced. The trigger volume will be small enough to permit resolution during storm events but large enough to represent diurnal fluctuations in water quality constituents.
The USGS will use one or a combination of the three following methods, depending on the particular site and the data available, to choose an appropriate trigger volume for the autosampler: 1. The USGS will try to establish preliminary discharge ratings prior to operation of the autosamplers. 2. Historical USGS and SFWMD streamflow data will be gathered from current and discontinued streamflow monitoring sites near the sub-basin sites. Statistical analysis will be conducted on those data in order to roughly estimate expected streamflow at sub-basin sites. Preliminary high- and low- flow trigger volumes will be selected using procedures outlined in "Flow-Proportional Sampling from Variable Flow Canals" (Abtew et al., 1997). 3. The USGS will consult with developers of the LOW Project WAMVIEW model to obtain predictions of streamflow data at the sub-basin level. The selection of the proper trigger volume will, of course, be an iterative process. Since both positive and negative flows are expected at many sites, the net positive (downstream) flow will be used when calculating the cumulative flow volume. Flow-weighted composite samples will be preserved with sulfuric acid to prevent changes in nitrogen and phosphorus concentrations due to biological activity. Each autosampler bottle will be pre-acidified with 1 milliliter of 50% (by volume) ACS-grade sulfuric acid per 1 liter of sample water. Research by the SFWMD (Burke and others, 2002) has shown no significant difference in total phosphorus, total nitrite plus nitrate nitrogen, and total organic plus ammonia nitrogen determined from unrefrigerated automatic samples collected using this method of pre-preservation compared to those determined from automatic samples collected under refrigerated conditions. During each site visit, stream-water samples contained in each autosampler bottle will be composited in a decontaminated plastic churn splitter. Sub-samples will then be withdrawn for analysis of total phosphorus, total nitrite plus nitrate nitrogen, and total organic plus ammonia nitrogen. Autosampler bottles will then be replaced with a set of decontaminated bottles.
Weekly manual samples will be collected according to USGS techniques (USGS, 1997 to present). Following the Equal-Width-Increment (EWI) method, a sampling cross-section will be marked using a tag line or by placing marks on a bridge. Approximately 10 points along the cross section will be sampled using a hand-held or weighted bottle sampler because stream velocities are anticipated to be below the operating threshold of standard USGS isokinetic water quality samplers. All samples taken from the cross section will be composited in a decontaminated plastic churn splitter. Sub-samples will then be withdrawn from the churn splitter. Total phosphorus and total organic plus ammonia nitrogen samples will be preserved with 1 milliliter of 1:7 sulfuric acid. Manual samples collected for total suspended solids analysis will not be acidified. The remaining water in the churn splitter will be filtered through a pre-cleaned 0.45- micron encapsulated filter for analysis of dissolved phosphorus, dissolved ortho-phosphate phosphorus, and dissolved ammonia nitrogen. All samples will be kept at a temperature of 4 degrees Celsius and will be analyzed within 28 days at the laboratory. One site (Site 20, Fisheating Creek at Palmdale) has an overflow channel that may divert water from the main channel during high stage events. The channel will be checked weekly and if flowing, additional manual samples will be collected according to techniques described in the previous paragraph. These manual samples will then be compared to manual samples collected from the main channel. If the overflow channel flows frequently and contributes a large percentage of the total streamflow, and constituent concentrations in the two sample sets are significantly different, installation of automatic sampling equipment or construction of a separate gage may be necessary, and future costs for operation of the network will have to be adjusted.
During each site visit, field readings of water temperature, specific conductance, dissolved-oxygen concentration, and pH will be made using calibrated instruments. Field meters will be calibrated according to USGS techniques (USGS, 1997 to present). A record of field meter calibration, calibration verification, and maintenance will be kept in accordance with USGS procedures (USGS, 1997 to present).
To minimize contamination of water quality samples, clean sampling techniques will be used. In these techniques, one person is designated to perform all activities involving contact with the sample water and another person is designated to perform all activities involving contact with sample collection equipment, such as bridge cranes, boat motors, and pumps.
All water quality sampling equipment will be decontaminated according to standard USGS techniques (USGS, 1997 to present). Sampling equipment will be soaked in a 2 percent solution of a non-phosphate detergent, such as Liquinox, scrubbed with nonmetallic brushes, rinsed with tap water, then rinsed with de- ionized water. The clean equipment will then be air-dried and stored inside double plastic bags. Sample bottles will be cleaned prior to use by rinsing twice with de-ionized water, and encapsulated filters will be cleaned prior to use by pumping 1 liter of de- ionized water through the filter.
Water quality samples will be submitted to the USGS Ocala Water Quality and Research Laboratory (OWQRL) in Ocala, Florida, for analysis. Total suspended solids, nitrogen, and phosphorus concentrations will be analyzed using USGS analytical methods, except total organic plus ammonia nitrogen, which will be analyzed using U.S. Environmental Protection Agency (EPA) method 351.2. The SFWMD has requested low- level analyses on all phosphorus species, total nitrite plus nitrate nitrogen, and dissolved ammonia nitrogen, to be consistent with other water quality monitoring projects in the area. Low- level analyses are not currently available for total organic plus ammonia nitrogen or total suspended solids.
The USGS methods are based on the EPA methods, but with slight modifications (e.g., a different color reagent or slightly less acid is used in the analysis). These methods are approved by the EPA under CFR-136 and are directly comparable to the EPA methods. The USGS OWQRL is certified to use these methods by the Florida Department of Health Environmental Laboratory Certification project (certification number E63507) and the U.S. EPA. USGS analytical methods are described in detail in Fishman and Friedman (1989). Total suspended solids concentrations will be determined gravimetrically. Nitrogen and phosphorus concentrations will be determined using colorimetry.
Quality Assurance/Quality Control
Nine types of QC samples will be collected to document that the project is meeting QC requirements. Collecting a representative sample is crucial to obtaining accurate concentration data and load estimates. Therefore, the QC effort to verify that the stream is well- mixed and that the location of the autosampler intake is representative will be intensified early in the monitoring effort (during the first 1-2 years). Note that 'Year 2' is considered the first year of water quality sampling. 'Year 1' of the project is considered to be April - October, 2003 (1/2 year), during which no water quality samples will be collected. The use of multiple autosampler intake ports may be investigated at a site if QC sampling shows that a single sampling port will not generate representative samples.
A blank is a sample that is intended to be free of the analytes of interest. Autosampler blanks and field equipment blanks will be prepared by rinsing the equipment with inorganic blank water (water certified to be free of nutrients and other inorganic species). A sample of blank water will be collected, composited in a plastic churn splitter, and filtered as if a routine environmental sample were being collected. Replicate samples are two or more samples collected so that the samples are considered to be essentially identical in composition. Split replicate samples will be prepared by dividing a single volume of water into two samples, which will be processed separately.
In the laboratory, samples are identified by a unique site name and number, date and time of collection, and a bottle type code, which indicates the general type of analyses to be performed. Laboratory personnel check the condition of all sample containers to determine if any bottles are cracked or broken, check the completeness of the sample documentation, and verify the sample preservation method. After these initial checks are complete, the sample information is entered into the laboratory database. Chilled samples are then placed in refrigerators dedicated to the storage of specific sample types, such as nutrients. Non-chilled samples are sorted by bottle code in the incoming sample storage room. Access to sample storage areas is restricted to laboratory personnel.
The OWQRL database is called the Laboratory Information Management System (LIMS), which is located on a UNIX file server located in a locked computer room. Access to the computer room is restricted to the chief of the OWQRL, computer administrator, and computer staff. Nutrient data entry into the LIMS is automated. A designated individual in each USGS office typically retrieves data from the LIMS. Each USGS office is assigned a unique user code. Only the office assigned to the user code may retrieve data for samples tagged with that user code. After retrieval from LIMS, the data are uploaded into the USGS National Water Information System (NWIS). Laboratory notebooks, worksheets, calibration logs, and field notes are considered original data. These are retained permanently by the USGS.
The assistant laboratory chief and laboratory QA/QC officer check analytical data prior to release. The assistant laboratory chief is responsible for checking raw data entries, calculations, and extraction logs. The QA/QC officer is responsible for checking instrument analytical logs, calibration integrity, and all data entry into the LIMS. A daily report is generated and provided to the laboratory chief and analyst on all QC data that exceed upper and lower warning limits. A report generated from the LIMS is sent to laboratory management whenever over one- half of a parameter's holding time has expired.
Any use of trade, product, or firm names is for descriptive purposes only and does not constitute endorsement by the U.S. Government
Data Collection In the last decade, techniques for continuous streamflow monitoring have evolved from the more traditional "stage-discharge" approach, in which discharge is computed as a function of stream stage, into the area of hydroacoustics, which require greater technical skills for measurements and for data processing. Hydroacoustic velocity meters provide continuous "index" velocity measurements, which can be used to develop discharge ratings at sites where traditional stage-discharge relationships alone are inadequate. Both stage-discharge and index-velocity approaches are planned for the LOW monitoring network. In general, the index-velocity approach will be used when the relation of stage and discharge is unstable due to backwater effects, reverse flows, and changes in channel roughness (Laenen, 1985). All sites will initially be instrumented as index-velocity sites until the hydraulics are better understood.
Continuous index-velocity measurements will be made using Acoustic Doppler Velocity Meters (ADVMs). The type of ADVM to be used may vary based on stream width, depth, expected velocity, and amount of vegetation present. To obtain accurate velocity measurements, ADVM technology requires that a sufficient amount of suspended particles be present in the stream to reflect the emitted acoustic signal (see Morlock, 2002, for more information on ADVM technology). To test this requirement, during the field reconnaissance in spring 2002, USGS personnel measured stream velocity at proposed monitoring sites with a small point-velocity ADVM in low-flow conditions, when the least amount of suspended particles is expected in the stream. At all sites tested in this manner, stream water contained enough suspended particles to adequately reflect the acoustic signal.
At each site, stage, index velocity, standard deviation, and signal strength will be recorded on a 15- minute basis. A data collection platform (DCP) will store these data in a datalogger and transmit data through satellite transmission every 1 to 4 hours. When the data are transmitted, they will automatically be stored in the USGS database as raw data and then processed to compute discharge (when a rating has been established for the site). Data will be reviewed daily in the office by USGS personnel to detect problems with equipment and determine whether a field crew should be dispatched to make necessary repairs or corrections.
During the first 2 years, 10 to 12 discharge measurements will be made per year to develop each site's rating curve. The method of discharge measurement may also change depending on site conditions.
The USGS will use standard procedures presented in Buchanan and Somers (1969) to measure discharge at each site. The stream cross-section will be divided into 20 to 30 increments, and ideally, no one increment should contain more than 5% of the total discharge. For each increment, the increment width, stream depth, and average velocity will be measured. After measurements are made for all increments, the total discharge for the cross-section will be calculated using equations presented in Rantz and others (1983b).
Sites will be surveyed every 3 years for datum corrections that may be required if the walkway or platform (on which equipment is mounted) settles.
Any mechanical equipment used to measure velocity during periodic discharge measurements, such as Price AA and Pygmy meters, will be calibrated according to USGS techniques presented in Smoot and Novak (1968). A record of meter calibration, calibration verification, and maintenance will be kept in accordance with USGS procedures. A staff gage reading will be recorded weekly to verify the float gage reading in the stilling well. Non-mechanical ADVMs are "calibrated" initially by the manufacturer and need no further calibration for the remainder of their operational life.
Stream temperature will be measured weekly and compared to the temperature measured by a probe inside the ADVM, as signal "drift" can occur if actual stream temperature is significantly different from internally- measured temperature (J. Shelton, USGS, personal communication). In addition, velocity measured during periodic discharge measurements will be compared to ADVM readings at the time of the measurement in order to detect any problems or signal "drift" in the ADVM. Continuous monitoring of index-velocity standard deviation and signal strength also will permit troubleshooting of the ADVM. All equipment will be checked weekly for vegetal growth and malfunction and will be cleaned and repaired as appropriate. If major repairs are needed, a separate field crew will be dispatched to repair and/or replace the equipment.
Data Processing, Storage, and Review Discharge measurements made at the site are computed in the field, when practical, and compared with the rating (if one exists yet). The measurements are checked by another individual in the office to ensure that all data are complete and that no errors have been made in the calculations. The hydrographer responsible for the discharge at each site then stores the discrete (verification) discharge measurements in the USGS Automated Data and Processing System (ADAPS) database. Data that are continuously transmitted through telemetry are automatically stored in the USGS ADAPS database and processed to compute other parameters (such as discharge) based on the recorded data and mathematical relationships stored within ADAPS. Discharge measurements made at the site and stored within ADAPS are plotted on a ‘shift diagram’, and any necessary adjustments to the discharge calculations are made by applying shifts.
Quality Assurance/Quality Control A number of mechanisms are in place to ensure quality of the flow data collected by the USGS.
Load Calculation Procedures Weekly loads for total phosphorus, total organic plus ammonia nitrogen, and total nitrite plus nitrate nitrogen will be calculated from the flow-weighted composite concentration data.
The Vertical Datum Control Surveys PDT of CERP has drafted technical specifications for horizontal and vertical datum control and associated QC requirements. In accordance with these draft requirements, a monument will be set at each monitoring site, such as a stainless steel rod inserted to refusal or a class C monument set 30 inches deep. The monument will then be leveled to National Geodetic Survey Third Order accuracy for both the North American Vertical Datum of 1988 and National Geodetic Vertical Datum of 1929. Topographic survey data will be processed to both the 1929 and 1988 datums; however, monitored data (such as stage) will initially be processed only to the 1929 datum because all current SFWMD and USGS data are processed to the 1929 datum.
Load summary includes Date of Site Visit/Sample, Primary Load in metric tons (TKN, NO2+NO3, and Total P), and Secondary Loads in metric tons (Diss P, Diss o-PO4, NH3, and TSS). TKN = Total Kjeldahl Nitrogen, Diss P = Dissolved Phosphorus, NOx = Nitrate+Nitrite Nitrogen, NH3 = Ammonia Nitrogen, TP = Total Phosphorus, TSS = Total Suspended Solids, and o-PO4 = Dissolved Ortho-Phosphate
Manual Samples and Autosampler Samples data include USGS Sample ID; Date and Time collected; USGS Station ID; USGS Station Name; Sample Type; Date Shipped; Date received by Lab; NWIS Record Number; pH (std units); Specific Conductance (micro-siemens per centimeter); Dissolved Oxygen/DO (mg/L); Stream Width (feet); Water Temp (degrees Celsius); Starting and Ending Water Level (feet); Starting and Ending Index Velocity (feet per second); mg/L, Lab Qualifier, and MDL for TSS, Diss NH3 as N, TKN, NO2+NO3, TP, Diss P, Diss o-PO4; Inter-parameter checks; Weekly Representative Flow Volume; and Weekly Loads (metric tons) for TSS, Diss NH3, TKN, NO2+NO3, Total P, Diss P, and Diss o-PO4. MDL = Method Detection Limit.
Daily Avg Flow includes Year, Month, Day, Date, Mean Daily Streamflow (cubic ft per second), and Mean Daily Gage Height (ft above datum)
Code Key contains definitions for the General acronyms and Lab Qualifiers.
The statistical summary of data collected 2003-2006 includes a summary of data (Flow, Mean Daily in cubic feet per second (cfs); Gage Height, Mean Daily in feet above datum; Manual Sample Concentrations in mg/L for TP, DP, o-PO4. TKN, NOx, NH3, and TSS; Flow-Weighted Composite Sample Concentrations in mg/L for TP, TKN and NOx; and Calculated Loads in metric tons for TP, DP, o-PO4, TKN, NOx, NH3, and TSS) for all sites by Station No., Map No., and Station Name. Also included are the Load Summary data for each site.
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