Lake Water Quality Data Management, Analysis and Reporting (FY06-07)

Lake Water Quality Data Management, Analysis and Reporting (FY07-08) SWIM Phase 1, Part 2

Background

The Mecklenburg County Water Quality Program (MCWQP) has an ongoing program to monitor the water quality in the three Catawba Lakes bordering the county: Lake Norman, Mountain Island Lake and Lake Wylie. Data collected from all lake sites are used to screen for environmental problems using MCWQP Action and Watch levels for various pollutants and also to rate the overall water quality at sampling locations in the lakes using a water quality index. Additional objectives are to describe seasonal trends and address spatial variability in the data

Sampling Program

Regular monthly lake sampling is conducted at seven locations in Lake Norman and one location each on Lake Cornelius and Lake Davidson , eight locations in Mountain Island Lake and thirteen sampling locations in Lake Wylie (see Lake SAP) . Sample collection at Lakes Cornelius and Davidson was changed in 2005 from 3 sites at each lake quarterly to one site per lake monthly from May through September. All other lakes were sampled monthly from May through September and every other month during the rest of the year, i.e. January, March and November. During the summer months extra sites were monitored for fecal coliform bacteria on all lakes (see Lake SAP).

Depth profiles of various physical-chemical measurements (temperature, dissolved oxygen, pH and conductivity, turbidity and chlorophyll) are collected in the field during lake runs using a calibrated YSI 6600 multiprobe. Water transparency is measured in the field using a Secchi disk. Water samples are collected using a composite sampler to a depth of twice the Secchi depth. During the summer months (May through September) a discrete bottom sample is collected about 1.5 m off the bottom at forebay locations near the dams of all three lakes: LN1, MI1 and LW1. Water samples collected for laboratory analysis are placed on ice and transported back to the Charlotte Mecklenburg Utilities (CMU) Hal Marshall Laboratory where they are analyzed by standard methods. Water chemistry samples collected at all sites are analyzed for the following parameters: nutrients (total phosphorus, TKN, NH3, NO3, NO2), chlorophyll a, total suspended solids, total solids, turbidity, alkalinity and fecal coliform bacteria. In March 2005, a separate analysis for NO3 and NO2 was discontinued and was replaced by a combined NO3-NO2 (or NOX) analysis. This was based on historical data showing that a separate NO2 analysis was found to be below the detection limit in lake samples most of the time. During one summer sampling run volatile organic compound (VOC) samples are collected at selected sites in all three lakes. Metals are collected at both surface and bottom samples at forebay locations from May through September and at all sites in August.

All data is entered into the EPIC database system at MCWQP by LUESA personnel and reviewed by a designated Environmental Specialist for QA/QC purposes. The Lake Water Quality Index (Fusilier 1982) was calculated for each location and date using EPIC. Fusilier’s Lake Water Quality Index (LWQI) is an opinion-based index that uses scores from nine water quality parameters (temperature, dissolved oxygen, chlorophyll a, Secchi disk depth, nitrate, total alkalinity, pH, specific conductivity and total phosphorus) to calculate an overall score rated from Very Poor to Excellent. In addition, the North Carolina Trophic State Index (NCTSI) was calculated using total phosphorus, Secchi depth and organic nitrogen using a formula developed as part of North Carolina’s original Clean Lakes Classification Survey (NCDNRCD 1982). Lakewide means through the growing season (May through September) were used to produce the NCTSI score for each lake.

Data Management

Data handling and management for the Mecklenburg County Water Quality Program (MCWQP) Lake program is handled in much the same way as the Fixed Interval, Stormwater, BMP and Fecal Monitoring programs.

Field Data

Field data collected during lake runs consists of YSI multiprobe data an Secchi depth data. Secchi depth data are hand written into the lake log at each site when the measurements are taken. This data must then be hand entered into the database.

YSI multiprobe data is stored to the YSI 650 datalogger in the field. This data in .DAT format is uploaded into YSI’s Ecowatch software by serial cable to a PC. The .DAT file is then opened in EcoWatch and exported as a .CDF file to the storage directory. It is given a filename descriptive of the sampling run and date. The .CDF file is then opened in EXCEL and stored again as an .XLS file.

EXCEL files with YSI depth profile data are opened and reviewed in EXCEL by the Lake Coordinator. The Lake Coordinator will delete extraneous depth records and generally “clean up” the data file. After the data file has been reviewed and scrubbed it will be uploaded into the Water Quality Program Data Repository.

Laboratory Data

Laboratory Data is handled in the same manner as other lab data submitted by MCWQP.

Calculations

Lake Water Quality Index

Fusilier’s (1982) Lake Water Quality Index (LWQI) is calculated for each location and date. The LWQI is an opinion-based index that uses scores from nine water quality parameters (temperature, dissolved oxygen, chlorophyll a, Secchi disk depth, nitrate (NOX) , total alkalinity, pH, specific conductivity and total phosphorus) to calculate an overall score rated from Very Poor to Excellent.

2 North Carolina Trophic State Index

The North Carolina Trophic State Index (NCTSI) is calculated for each site using using a formula developed as part of North Carolina’s original Clean Lakes Classification Survey (NCDNRCD 1982). Parameters used in the NCTSI are total phosphorus, Secchi depth and organic nitrogen Lakewide means through the growing season (May through September) are used to produce the NCTSI score for each lake. The NCTSI is calculated based on summer data collections and data from different locations is usually combined to obtain a lakewide average. Chlorophyll a and nutrient concentrations are measured in the trophic zone (twice the Secchi depth).

The EXCEL spreadsheet containing the NCTSI calculations are located in: ENV\XFER\buetodh\data\TSIcalc.xls The following are the formulas in the spreadsheet used to calculate the NCTSI:

Secchi Depth Score = -0.82*((LOG(C5*39.3701))-1.73)/0.35 Chlorophyll Score = 0.83*((LOG(D5))-1)/0.43 Total Organic Nitrogen Score = 0.9*((LOG(F5-E5))+0.45)/0.24 Total Phosphorus Score = 0.92*((LOG(G5))+1.55)/0.35

Secchi Depth units are entered as meters and converted to inches in the formula. Chlorophyll a units are in ppb Total Organic Nitrogen = TKN (Column F) - ammonia (Column E), units are in ppm. Total Phosphorus units are in ppm Once data has been input into the EXCEL spreadsheet the NCTSI will automatically be calculated and displayed.

The trophic classification based on NCTSI is interpreted as follows:

NCTSI Classification < -2.0 Oligotrophic -2.0 to 0 Mesotrophic 0 to 5.0 Eutrophic > 5.0 Hypereutrophic

3 Reports

Lakes Program Measure WQI Reports will lag one quarter behind. In other words, the report for the first quarter will be for the last quarter of the previous fiscal year, etc. The average WQI value is calculated quarterly using 11 sites, including LN2, 5 and 6 on Lake Norman, MI2, 3 and 5 on Mountain Island Lake and BC2, PALC1, PALC10, LW4 and LW10 on Lake Wylie. This quarterly average WQI value will be presented graphically as points connected by a blue line. The blue line will show each average annual WQI lake value back to FY97-98 (S.W.I.M. initiation date). The graphic will also include a line representing the Threshold (red), Successful (yellow) and Exemplary (green). At the end of the fiscal year, the annual average WQI for all four (4) quarters will be calculated and shown as a straight, dashed blue line on the graph.

Lake Water Quality Index (LWQI)

82.69 82.71

x Exemplary at 79.7 e 80.52

d 80 n I

y 78.62

t 78.53 i l 77.98 77.73

a 77.65

u 76.68 76.99 Q

r Successful at 77.7 75.75 e

t 75 75.04 a W

a 72.12 L

a Threshold at 71.7 r 70 e v A

LWQI - 8 sites near Mecklenburg County 65

60 FY 99-00 FY 00-01 FY 01-02 FY 02-03 FY 03-04 FY 04-05 FY 04-05 FY 04-05 FY 04-05 FY 05-06 FY 05-06 FY 05-06 FY 05-06 1st Qtr 2nd Qtr 3rd Qtr 4th Qtr 1st Qtr 2nd Qtr 3rd Qtr 4th Qtr Sam pling Period

Preparation of LWQI Maps to present to Marine Commissions

LWQI and fecal coliform maps are presented to the Lake Norman, Mountain Island Lake and Lake Wylie Marine Commissions as soon as practicable when the data is available. The maps are prepared as follows:

4 LWQI Maps

The LWQI maps consist of three elements: 1) a map of the lake showing the LWQI as a color coded circle at each site location, 2) a line graph showing historical trends in the LWQI with the lake wide average and 2 year trailing average going back about 10 years and 3) a table listing the current LWQI values for each site for the month sampled compared with those observed the previous year.

Parts 2 and 3 of above are performed in EPIC on a spreadsheet named: G:\Prot\WQ\WQ- Data\LAKE\WQI 2007.

A. Long term trend graphs 1. Enter LWQI values generated in EPIC onto the bottom of the Data worksheet for the month sampled. 2. Find the long term graph for the lake sampled on the Graphs worksheet. 3. Update the source data range to include the most recent LWQI data added and save the EXCEL spreadsheet. 4. Open the Paint accessory software and copy the updated graph into it. 5. Save the graph to a .BMP file.

B. Comparison table with previous year 1. Locate the comparison table for the previous year in one of the Tables worksheets. 2. Copy the previous year’s table to the bottom of the spreadsheet. 3. Move the previous year’s data left one column. 4. Rename the right hand data column to the current year. 5. Copy the range of new LWQI data from step A1 above and transpose it into the current year data range (or hand enter). 6. Differences with previous year will automatically populate the appropriate column. 7. Open the Paint accessory software and copy the updated table into it. 8. Save the table to a .BMP file

C. ArcView Graph 1. Open the appropriate ArcView project file for either Lake Norman/Mt. Island Lake or Lake Wylie. 2. Open the View for LWQI. 3. Enter new LWQI values into the appropriate ArcView table and double check for accuracy. 4. In View load the legend for LWQI, choose the current data and apply to the map. The colored dots should now reflect the current data. 5. In Layouts choose the generic LWQI layout for the lake sampled. 6. Change the Title to reflect the current month. 7. Long term trend graph and comparison table will automatically be placed on the graph page. 8. Print requested number of copies, usually 10 to 12.

5 Example Lake Water Quality Index Map

Fecal Maps

1. In the ArcView project file open the appropriate view for the lake sampled. 2. Enter new fecal coliform data into the appropriate ArcView table and double check for accuracy. 3. Apply fecal coliform legend to map to change dot color if necessary. 4. Remove data labels from previous months fecal map. 5. Change Label Field under Theme Properties to point to the new data added. 6. Autolabel data points on the map with the new fecal data. 7. In Layouts choose the generic fecal map layout for the lake sampled. 8. Change the Title to reflect the current month. 9. Print requested number of copies, usually 10 to 12.

6 Example Lake Fecal Coliform Map