Program: FRAGILE ENVIRONMENTS
Project Title: DETERMINATION OF NUTRIENT LOADS TO EAST COAST CANALS
Location of Study Area: SOUTH FLORIDA
Project Start Date: OCTOBER 1995
Project End Date: SEPTEMBER 1999 (under extension request)
Project Number: 4598-61300
Project Chief: Arthur C. Lietz
Region/Division/Team/Section:
South-East Region/WRD/FL District/Miami Subdistrict
E-mail:alietz@usgs.gov
Phone:
Commercial 305-594-0655
305-526-2895
Fax: 305-526-2881
Mailing Address:
U.S. Geological Survey-Water Resources Division
9100 NW 36th St., Miami, FL., 33178
Program Element(s)/Task(s)
ELEMENT 2 - MODELING AND SUPPORT STUDIES FOR SOUTHERN INLAND COASTAL SYSTEMS OF EASTERN DADE COUNTY AND BISCAYNE BAY
TASK 2.3 -WATER QUALITY - DETERMINATION OF NUTRIENT LOADS TO EAST COAST CANALS
Panel:
Collaborators, Clients:
During the duration of the project close collaboration and exchange of technical information will be maintained with other projects of the South Florida Ecosystem Restoration Initiative, particularly the Fresh Surface Water Discharge to the East Coast project which is using the Acoustic Doppler Current Profiler to develop discharge ratings for the east coast canals. Also close collaboration with the south Florida NAWQA program and other agencies such as the U.S. Army Corps of Engineers will be maintained. This investigation will interface closely with the south Florida NAVVQA program in that it will contribute to the process of defining the relationship between land use and water quality conditions and help identify water quality trends in south Florida. Coordination of sampling efforts and exchange of information will also be maintained with DERM's Biscayne Bay monitoring program. Determination of nutrient loads to Biscayne Bay and long-term trends at NASQAN stations will aid regulatory agencies such as SFWMD and DERM in water resource management particularly with proposed plans to redirect flow from the urban/agricultural corridor to Everglades National Park. Logistical support in gaining access to control structures during sampling events is provided by the SFWMD field offices.

BACKGROUND NARRATIVES

Project Summary: The ecological health of bays and estuaries has become a matter of concern throughout the country. Biscayne Bay, which is a shallow, oligotrophic, subtropical estuary along the southeastern coast of Florida has been adversely impacted in certain locations by the increase in nutrient loads from tributary canals that have resulted from agricultural, urban, commercial an-d industrial processes. The ecological health of the Bay, as well as development of restoration efforts is dependent in part on understanding loads to the bay. This project will attempt to quantify nitrogen and phosphorus loads to the Bay based upon models developed from ordinary least squares regression techniques. It will also examine which historical methods of sampling accurately represent nutrient concentrations in the water column of south Florida canals and can be used to calculate past nutrient loading. Also, water-quality trend analysis will be conducted on data from two former National Stream Quality Accounting Network (NASQAN) sites that have a direct impact on the south Florida ecosystem.

Project Justification: The ecological health of Biscayne Bay is dependent on nutrient loads and understanding the hydrologic processes that control nutrient loading to the Bay is necessary in order to properly develop restoration efforts. In order to accomplish this, reliable estimates of loads to the Bay are necessary. Much of the nutrient data that have been collected historically has been from point samples by the Dade County Department of Environmental Resource Management. The degree to which these samples adequately represent nutrient concentrations within the water column of the canals of south Florida is presently unknown and limits confidence in loading estimates. Furthermore, the relationship between flow and concentration that occurs in natural, uncontrolled streams in other parts of the country may not apply to the artificially controlled canals of south Florida. Both of these issues need to be addressed in order to develop nutrient budgets and to plan effective restoration strategies now and in the future. Also, water-quality trend analysis on data collected at two former NASQAN sites will provide insight into processes that have affected nutrient and pollutant loading to the Bay as well as the south Florida ecosystem as a whole.

Project Objectives: This objectives of this project are threefold: 1. To determine if point samples collected from 1979 to the present at one meter below the surface near the centroid of flow adequately represent stream cross-sectional chemistry, and 2. To develop reliable estimates of nitrogen and phosphorus loads for east coast canals based upon statistical models developed from concentration/discharge relations, and 3. To summarize water-quality data and determine temporal trends for water-quality constituents at two sites that contribute to Biscayne Bay and the south Florida ecosystem.

Overall Strategy, Study Design, and Planned Major Products: During Phase I of the project an intensive field sampling and data collection effort will be undertaken. This will consist of the collection of water samples for nitrogen and phosphorus species upstream of discharge points for selected coastal canals during various seasons and flow conditions in order to obtain samples truly representative of the hydrologic cycle. Depth-integrated and point samples will be collected at each canal during Phase 1. Temporal water quality trends at two former NASQAN sites will also be determined. During Phase 11 of the investigation data analysis and report preparation will be undertaken. This will entail using statistical procedures to compare the two sampling methods and regression analysis will be utilized in order to develop load models for nitrogen and phosphorus species for each site,

WORK PLAN

Overall: During Phase 1, water samples will be collected upstream of the canal discharge points during various hydrologic flow regimes and during various hydrologic conditions during the year. Water quality data collection and discharge computation was accomplished at 5 sites during the 1996 water year and is beginning at 10 sites during the 1997 water year. Because the number of verticals sampled at a site should be based on the need to collect a sample representative of cross-sectional chemistry, at each sampling location upstream of the canal discharge point a water quality cross-section survey will be done during various seasons and during various periods of flow in order to document horizontal and vertical variability within the water column. Parameters measured will be specific conductance, pH, temperature and dissolved oxygen. Based upon these surveys, depth-integrated water samples will be collected according to the EWI (equal-width-increment) method. This consists of dividing the stream cross-section into equal width intervals and raising and lowering the sampler through the vertical in each interval. In this method, a constant transit rate is established in the vertical with the greatest stream velocity and this rate for raising and lowering the sampler is used in all verticals so that the bottle is never overfilled when returned to the surface. Samples from each vertical are composited in a churn splitter prior to processing for analysis. Since stream velocities in south Florida are almost always less than 2 ft/s and canal depths 15 ft or less, a weighted bottle can be used to collect samples. A 1-liter polyethylene bottle will be housed in a stainless steel basket sampler coated with plastidip to prevent contamination from the sampler surface. Parts per billion procedures employed in the NAWQA program for cleaning, preparation and sampling will be adhered to, including the 'clean hands' and 'dirty hands' requirement. A point sample at one meter below the surface of the stream near the centroid of flow will be collected concurrently with the depth -integrated sample by using a Niskin bottle. Quality assurance procedures will include field blanks, equipment blanks and duplicate samples. Samples will be chilled immediately following collection and shipped within 48 hours to the USGS Water Quality Service Unit in Ocala, Fla. for analysis of total ammonia (NH₄), total organic nitrogen, total nitrate(N0₃), total nitrite(N0₂), total ortho-phosphorus (P0₄), and total phosphorus. During each sampling event the upstream and downstream stages and gate openings will be recorded in order to compute the instantaneous discharge. Discharge coefficients have been determined by another ecosystem project entitled 'Fresh Surface Water Discharge to the East Coast.' Phase 11 will involve data analysis and report preparation. The paired sample approach will be used to statistically compare depth-integrated and point samples either using the paired t-test or the Wilcoxson signed rank test. Simple linear and multiple linear regression analysis will be utilized to develop load models for nitrogen and phosphorus species. Extensive use will be made of regression diagnostics such as leverage, influence, prediction error sum of squares (PRESS) and residual analysis in order to develop the best fit equation. Both classical and distribution-free tests will be used to analyze data from two NASQAN sites. The data will be described using box plots, histograms, Piper diagrams and statistical tables. The Seasonal Kendall trend test which is a distribution-free test will be used to determine temporal trends in censored and uncensored data and a maximum likelihood estimator called Tobit will be used to determine trends for data containing multiple detection levels. Depending on the degree to which discharge data exists concurrently with water-quality data, the Seasonal Kendall t

Timeline:

    MAJOR TASKS:   1996: Data collection and instantaneous discharge computation

                   from 5 sites.

                   1997: Data collection and instantaneous discharge computation

                   from 10 sites. 

                   1998: Report preparation and publishing of nutrient load report. (A.

                   C. Lietz, project chief ) Data review and data interpretation of two

                   former NASQAN sites, Miami canal and Tamiami trail. Also,

                   literature search for report on trends.

    

    DELIVERABLES:  1998 and 1999: Quarterly progress reports- October, January, April

                   and July

                   1998 and 1999: Draft report- October to March

                   1998 and 1999: Report review- April to June

                   1998 and 1999: Report approval- July to August

                   1998 and 1999: Report published and distributed- September



    PRODUCTS:      1998: Water Resources Investigative Report entitled, 'Estimation of

                   Nitrogen and Phosphorus Loads to East Coast Canals based upon

                   Regression Models and Statistical Comparison of Sampling

                   Methods, Dade County, 1997-1998.'

                   1999: Trend analysis report on two former NASQAN sites.