Grantee Research Project Results
1999 Progress Report: Lake Access: Making Water Quality Data Real and Relevantfor Minnesotans
EPA Grant Number: R827179Title: Lake Access: Making Water Quality Data Real and Relevantfor Minnesotans
Investigators: Barten, John , Host, George E.
Current Investigators: Barten, John
Institution: Suburban Hennepin Regional Park District, MN
EPA Project Officer: Packard, Benjamin H
Project Period: November 1, 1998 through October 31, 2000
Project Period Covered by this Report: November 1, 1998 through October 31,1999
Project Amount: $424,999
RFA: Environmental Monitoring for Public Access and Community Tracking (EMPACT) (1998) RFA Text | Recipients Lists
Research Category: Water , Sustainable and Healthy Communities , Air
Objective:
Lake Access will deliver real-time water quality information on Minneapolis metropolitan lakes to the public using advanced sensor technology and the internet. The project will provide an increased public understanding of factors affecting water quality in Minnesota lakes, along with information to make sound decisions on current regional issues.
Progress Summary:
Remote Underwater Sampling Stations (RUSS) were used to monitor changes in water quality for three lakes. Two RUSS units were deployed in Lake Minnetonka within West Upper and Halsted Bay on April 21, 1999; and another RUSS unit was deployed within Lake Independence on April 22, 1999. The RUSS units initiated automatic collection of water quality data at 1-meter depth intervals every six hours. A multi-probe water quality sonde, attached to a profiler device, monitored changes in the following water quality parameters: temperature, dissolved oxygen, pH, conductivity, and turbidity. Data was transmitted to a base station computer via cellular telephone modem, and was placed on the "Lake Access" Web-site (www.nrri.umn.edu/empact). The monitoring of these water quality parameters provided insight into the seasonal dynamics of Minneapolis metropolitan lakes.
Development of Stratification and Anoxic Conditions. Natural lakes located within temperature climates stratify as water temperature increases after ice-out. With the onset of stratification, the deepest and coldest layer of water, called the hypolimnion, within temperate productive lakes often becomes anoxic due to decomposition of organic matter. According to RUSS data, the development of anoxic conditions for Halsted Bay (approximately June 8, 1999) and Lake Independence (approximately May 11, 1999) coincided with the onset of stratification. However, the development of anoxic conditions within West Upper occurred substantially later than the onset of stratification (approximately April 30, 1999). Unexpectedly, we found that dissolved oxygen levels decreased below 8 m in depth, and then increased again as much as 2 mg/L at approximately 13 m in depth prior to decreasing again near the lake bottom (18 m in depth). This dissolved oxygen spike within the hypolimnion persisted until July 29, 1999. We are currently uncertain of the exact cause for the dissolved oxygen spike in the hypolimnion, and will be further investigated in the spring of 2000.
The development of anoxic conditions in the hypolimnion causes a nutrient (e.g. phosphorus and nitrogen) release from the bottom sediments. In relatively deep basins, these nutrients often become entrapped within the hypolimnion due to stratification, and most likely are not available for algae production. RUSS data indicated that there were no significant changes in stratification within West Upper and Lake Independence throughout the summer. However, nutrients released from the bottom sediments can become available to algae in relatively shallow basins due to wind mixing events that eventually degrade stratification (called internal loading). We found that the Halsted Bay RUSS unit recorded two unexpected incidences in which temperature and dissolved oxygen became uniform throughout the water column (August 29 and September 5, 1999). We speculate these mixing events within Halsted Bay were conducive to internal loading. Those nutrients that became available from mixing events resulted in algae blooms in Halsted Bay.
Algae Blooms. The lakes monitored with RUSS technology are highly productive eutrophic lakes, and experience periodic algae blooms. The RUSS units monitored changes in algae through turbidity measurements, which indicates the amount of particulate material suspended within the water column. We found that peaks in turbidity measurements near the surface corresponded with the presence of algae blooms. Changes in turbidity measurements suggested that Halsted Bay tended to be more conducive for algae blooms than West Upper and Lake Independence.
Excessive algae blooms can cause diel changes in dissolved oxygen due to photosynthetic activity. According to RUSS data, we observed diel changes in dissolved oxygen within Halsted Bay on July 30, 1999. Dissolved oxygen levels tended to increase during daytime hours due to plant photosynthesis, and decrease during the nighttime hours due to plant respiration.
Changes in pH and Conductivity relative to depth. Algae photosynthetic activity can also have an effect on pH and conductivity levels. During stratification, photosynthetic activity within the upper layers removes dissolved carbon dioxide from the water. Consequently, the amount of acid and ions within the water are reduced causing pH to increase and conductivity to decrease. In contrast, the cold dark lower layers are not conducive to photosynthetic activity, and carbon dioxide accumulates, causing pH to decrease and conductivity to increase. We observed similar changes in pH and conductivity levels relative to depth within Lake Minnetonka and Lake Independence.
Development of Lake "Turn Over." During the autumn, the water temperatures begin to decrease, which reduces the density differences between the upper and lower layers. Eventually, wind mixes the water column causing a gradual decrease in temperature. When surface and bottom waters approach the same temperature and density, autumn winds can mix the entire lake causing "turn over." After continuous mixing of the water column, dissolved oxygen levels also becomes uniform concurrently with temperature. We found that Halsted Bay "turned over" approximately September 7, 1999, which coincided with the time period of the second mixing event reference above (review development of lake stratification and anoxic conditions). Apparently, the shallow basin did not re-stratify because of continuous mixing. Lake Independence and West Upper did not turn over until much later because it requires more wind energy to mix these deeper basins. Unfortunately, we were uncertain of the exact time period that Lake Independence "turned over" because data was not collected continuously due to complications with the RUSS unit. However, non-continuous data suggested that "turn over" occurred between September 22 and October 1, 1999. Shortly after dissolved oxygen and temperature levels became uniform within Lake Independence, the thermocline began to gradually deepen for the West Upper basin, Lake Minnetonka. We found that the West Upper basin did not completely "turn over" until October 22, 1999.
Future Activities:
The following activities are anticipated:
1. Hennepin Parks currently is constructing three ice-houses to acquire continuous real-time RUSS data throughout the winter for Halsted Bay and West Upper, Lake Minnetonka, and Lake Independence. The RUSS deployment through the ice is scheduled to occur in early January 2000. After ice-out conditions, the three RUSS units will be re-deployed (late March or early April 2000) to continue time relevant data collection. The data will be available through the EMPACT "Lake Access" (www.nrri.umn.edu/empact) and "Water on the Web" (wow.nrri.umn.edu) Web sites.
2. The University of Minnesota Education Department at Duluth and the Minnesota Sea Grant have initiated a public out-reach program in which to educate the public about the "Lake Access" EMPACT project. A preliminary West Metro Lake Survey has been completed, and additional surveys are to be mailed to residents and specific interest groups throughout the Minneapolis/St. Paul metro area. To further increase public awareness about the "Lake Access" Web site, touch screen-based interactive kiosks that incorporate the EMPACT Web site will be strategically located at interpretive and community centers. Interpretive signs will also be developed and placed at boat access points on Lake Minnetonka and Lake Independence.
3. The University of Minnesota Education Department and NRRI will continue to develop and construct the "Lake Access" Web site. The "Lake Access" Web site will be integrated with the "Water on the Web" Web site. The real-time RUSS sensor data will be integrated with historical and current water quality monitoring data.
Supplemental Keywords:
water, watersheds, ecological effects, suspended particulates, ecosystem, indicators, innovative technology, conservation, environmental, environmental chemistry, biology, ecology, limnology, monitoring, analytical, central, midwest, Minnesota, MN, EPA Region 5., Scientific Discipline, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Hydrology, Environmental Chemistry, State, Monitoring/Modeling, Ecological Risk Assessment, aquatic ecosystem, EMPACT, environmental monitoring, lake access, Minnesota, MN, community-based approach, public information, remote underwater sampling, web site development, public access, water quality, public outreach, real-time monitoring, land managementProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.