Introduction

The lake volunteer monitoring program is split into two levels of data collection, Level I and Level II. The Level I program measures surface water temperature, precipitation, lake level, color, and Secchi depth. The Level II program includes: (1) the collection of water samples for laboratory analysis of total phosphorus (TP), total nitrogen (TN), chlorophyll a, and phytoplankton; (2) the measurement of Secchi depth and water temperature; and (3) the measurement of alkalinity, dissolved oxygen, and hardness using CHEMetrics Titrets® kits.

Level I Data Collection

The water year is generally defined as a hydrologic or precipitation year rather than the standard calendar year. Level I data collection begins at the start of the water year which runs from October through the following September in this region.

For the 1993-1994 water year, 23 lakes participated in the Level I program. During the 1994-1995 water year, 33 lakes participated in the program. Table 1 highlights the participating lakes for these two water years and level of data collection completed for each lake. For many of the lakes, volunteers were able to gather data for the entire season. For several lakes, however, volunteers were not able to complete this commitment or were recruited later during the monitoring year and thus collected only a partial data set. Anomalies in individual lake data collection efforts are noted in the results sections where individual lakes are discussed.

Volunteer lake monitors measured lake level and precipitation daily and recorded them on a daily data sheet. Lake level was measured from a gauge (an aluminum or steel metric ruler) attached to a dock, post, or other permanent fixture in the lake adjacent to the volunteer’s home. Precipitation was collected in a plastic rain gauge which was installed in an area exposed to precipitation and away from overhanging trees or buildings. Precipitation totals were collected in the gauge and emptied daily. Monitors recorded the time of their observations on the data sheets.

Monitors measured Secchi depth, surface water temperature, and lake color on a weekly basis. Secchi depth was measured at the lake’s deepest point which was located using bathymetric maps (Wolcott, 1961 and USGS, 1976). Volunteers measured Secchi depth by lowering the disk over the shady side of the boat (if the sun was shining) until the disk disappeared. The depth of the disk in the water was marked at the water surface and noted. The disk was then raised until it became visible again, and this distance noted. The average between these two measurements to the nearest 0.25 meter was then recorded as the Secchi depth on the field sheet.

Water temperature was measured at the same location as Secchi depth by submerging a Celsius thermometer in the water to approximately one foot below the water surface for one minute. Water temperature was then recorded on the field sheet. The weekly data summaries for individual lakes that participated in Level I data collection are found in Appendix A. Daily precipitation and lake level data are available upon request from the SWM Division.

Level II Data Collection

Twenty-five lakes participated in the Level II program in 1994 and 23 lakes participated during 1995. Table 1 highlights the participating lakes for the past two years. For most participating lakes, volunteers were able to successfully monitor data for the entire growing season (May through October). Anomalies in individual lake data collection efforts are noted in the result sections where lake results are individu ally discussed.

Level II volunteer monitoring activities were performed twice monthly beginning in May and ending in October. Volunteers measured Secchi depth or transparency, water temperature, alkalinity, dissolved oxygen, and total hardness on-site. Alkalinity, dissolved oxygen, and total hardness were determined using CHEMetrics Titrets® kits per manufacturers directions. Volunteers also collected water samples for laboratory analysis of total phosphorus, total nitrogen, chlorophyll a, and phytoplankton.

Volunteers performed their measurements and collected water samples while anchored at their lake’s deepest point. For each sample date, volunteers would indicate time and date of sampling, weather conditions, and air temperature on their field sheet prior to beginning measurements and water sample collection.

After determining Secchi depth transparency (as described for Level I), water samples were collected using a vertical Van Dorn-type water sampler at one meter and at the measured Secchi depth, and composited for the laboratory analyses. Water collected at one meter was used to fill a composite container to the 500 mL fill line before pouring into a 1000 mL sample container. A second portion of water was used to fill the composite container to the 250 mL level before pouring it into the designated 500 mL sample bottle. A third portion of water was placed in a plastic cup for determining dissolved oxygen, alkalinity and total hardness. A second water sample was collected at the Secchi depth and the sample compositing procedure repeated. The caps for the 500 mL and 1000 mL bottles were attached and the contents of the two bottles mixed. After mixing, a small portion of the sample from the 1000 mL sample container was poured into a small bottle (containing iodine preservative) for phytoplankton analysis.

Appendix B contains the raw data from the Level II lake monitoring effort. All additional depths at which water samples were collected for temperature, dissolved oxygen, alkalinity and total hardness determination are included in Appendix B. Detailed Level II volunteer monitoring sampling methods are described in the Draft 1995 Training Manual for Volunteers (Brenner, 1995).

Data Analysis

Average values for temperature and Secchi depth were determined for Level I volunteer monitoring data. Annual lake level range and precipitation totals were also determined for each participating lake. Daily or weekly values for lake level, precipitation, temperature, and Secchi depth were also displayed graphically. Data were illustrated on a two year time scale for the monitoring period beginning October 1993 and ending September 1995, for all Level I lakes. This allowed a comparable time scale for all participating lakes including those where data were only partially collected during this two-year monitoring period.

For the Level II measured parameters, average values were determined for the summer data only (May through October 1994 and May through October 1995 data). The winter data were not included in these summer value calculations to simplify the data discussion and presentation and for calculating trophic state. Peak winter values of notable interest, however, were included in the discussion of an individual lake. For each Level II lake, the bimonthly monitoring data were plotted in contrast with one standard deviation about the median value of the combined data (for each date). Thus, each lake’s data could be compared with the average data values of all lakes monitored.

Seasonal data trends and a relative comparison between lakes was performed using Secchi depth, lake level, and precipitation data collected from the Level I volunteers. Carlson trophic state index (TSI), and nitrogen to phosphorus ratios were also determined for all Level II volunteer monitoring data. The TSI is a lake productivity scale which can be used to compare and contrast individual lake water quality. Nitrogen to phosphorus ratios were also used to identify the limiting nutrient for algal growth for the participating Level II lakes.

Source: King County Lake Volunteer Monitoring Report 1993-1995. King County Water and Land Resources Division, Seattle, WA, May 1996.