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2014 Temperature Monitoring Project Report

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2014 Temperature Monitoring Project Report 2014 Temperature Monitoring Project Report January 13, 2015 Lakes Environmental Association 230 Main Street Bridgton, ME 04009 207-647-8580 [email protected] Project Summary LEA began using in-lake data loggers to acquire high resolution temperature measure- ments in 2013. We expanded in 2014 to include 15 basins on 12 lakes and ponds in the Lakes Region of Western Maine. The loggers, also known as HOBO temperature sensors, allow us to obtain important information that was previously out of reach because of the high cost of man- ual sampling. Using digital loggers to record temperature gives us both a more detailed and longer record of temperature fluctuations. This information will help us better understand the physical structure, water quality, and extent and impact of climate change on the waterbody tested. Most of the lakes tested reached their maximum temperature on July 23rd. Surface tem- perature patterns were similar across all basins. The date of complete lake mixing varied con- siderably, with shallower lakes destratifying in September and others not fully mixed until No- vember. Differences in yearly stratification were seen in lakes with HOBO sensor chain data from 2013 and 2014. A comparison with routine water testing data confirmed the accuracy of the HOBO sensors throughout the season. A month-by-month comparison of temperature pro- files in each lake showed the strongest stratification around the time of maximum temperature, in late July. In addition, August stratification was stronger than June and early July stratifica- tion. Shallow sensors showed similar average temperatures between 2013 and 2014. Deployment of temperature sensors on Trickey Pond. 2 Introduction and Background Because of its role in physical, chemical, and biological processes, temperature is an important and in- formative lake measurement. In order to get a better idea of temperature patterns in and between lakes, LEA began monitoring lake temperature using in-lake digital data loggers in 2013. These loggers, also known as HOBO sensors, are programmed to record temperature readings every 15 minutes. The sensors are deployed in the spring and the data is stored on the sensors until they are retrieved in the mid to late fall. LEA serves six towns in western Maine, providing comprehensive lake monitoring for 40 lakes and ponds. This comprehensive testing includes meas- urements of temperature profiles using a handheld “The data collected by these temperature YSI meter. This method is time consuming, resulting sensors provides much greater detail and in at best 8 temperature profiles per year. Using clarity than the traditional method ever could. HOBO sensors there is an initial time investment, Daily temperature fluctuations, brief mixing but once deployed, the sensors record over 12,000 events caused by storms, the date and time of profiles before they are removed in the fall. stratification set up and breakdown, and the This wealth of data provides much greater timing of seasonal high temperatures are all detail and clarity than the traditional method ever valuable and informative events that could. Daily temperature fluctuations, brief mixing traditional sampling can’t measure.” events caused by storms, the date and time of strati- fication set up and breakdown, and the timing of seasonal high temperatures are all valuable and informative events that traditional sampling can’t measure. The measurements these sensors record allow us to infer the effect of temperature on diverse lake char- acteristics such as stratification (lake layering), ecology, habitat, and nutrient loading. In addition, comparing temperature data over a number of years allows us to make observations about climate change in our region. During the first season of testing in 2013, four basins on three lakes (Highland Lake, Moose Pond, and 2 sites on Long Lake) contained sensors at 2 meter intervals measuring the entire water column. Nine addi- tional lakes contained one sensor in a shallow (littoral) area. All sensors were attached to a rope held in place by an anchor and a sub-surface buoy. For the second season of testing in 2014, a total of 16 sites were tested (figure 1, next page). Thirteen basins at ten lakes and ponds contained sensors measuring the entire water column (table 1, page 5). Three ad- ditional sensors measured shallow temperature on two ponds. The locations of deep water sensors were clearly marked by regulatory-style buoys. Lake Stratification Most of the lakes LEA tests become stratified in the summer. This means that the lake separates into dis- tinct layers – the epilimnion, metalimnion and hypolimnion – based on temperature and water density. The top layer, the epilimnion, is the warmest. Somewhere in the middle, there will be a large temperature and density shift. This is known as the metalimnion and it defines the location of the thermocline. The hypolimnion contains the cold- est water and reaches from the bottom of the metalimnion to the bottom of the lake. Each lake’s stratification is unique and is affected by weather, as well as the lake’s size, depth, and shape. Stratification sets up in the Spring and breaks down in the Fall. “Lake turnover” refers to the destratification of a lake, when the water completely mixes and the temperature becomes uniform from top to bottom. 3 Figure 1. Map of temperature sensor sites. Yellow circles indicate shallow sensor placement; green squares show the location of multi-sensor temperature buoys. 4 Sampling Methods Thirteen sites on ten lakes were outfitted with a marked, Table 1. Details of HOBO temperature data logger deployment, including lake/pond name, location of sensor string, type of deployment, and number regulatory-style buoy attached by of sensors per string. rope to an anchor (figure 2). The Name Midas # Location Type # sensors HOBO sensors (figure 3) were Back Pond 3199 Main basin Deep 5 attached to the rope at 2 meter in- Hancock Pond 3132 Main basin Deep 9 tervals, beginning 1 meter from Island Pond 3448 Main basin Deep 6 the bottom and ending approxi- Keoka Lake 3416 Main basin Deep 6 mately 1 meter from the top. Each Long Lake 5780 North basin Deep 9 buoy apparatus was deployed at Long Lake 5780 Middle basin Deep 9 the deepest point of the lake or McWain Pond 3418 Main basin Deep 6 basin it monitored. The setup re- Moose Pond 3134 North basin Deep 3 sults in the sensors being located Moose Pond 3134 Middle basin Deep 11 at odd numbered depths through- Moose Pond 3134 South basin Deep 6 out the water column (the shal- Peabody Pond 3374 Western shore Shallow 1 lowest sensor is 1 meter deep, the Peabody Pond 3374 Outlet Shallow 1 next is 3 meters, etc.). Sand Pond 3130 Main basin Deep 7 Two additional ponds, Pea- Stearns Pond 3234 Western shore Shallow 1 body and Stearns, contained tem- Trickey Pond 3382 Main basin Deep 8 perature sensors at shallow loca- Woods Pond 3456 Main basin Deep 4 tions. These were attached to a small mooring buoy and deployed so that they were located approxi- Figure 2. (Left) Diagram mately 1 meter below the surface showing the buoy apparatus of the water, at a total depth of with temperature sensors approximately 3 meters. attached. Temperature sensors were de- ployed between June 6th and July 9th, 2014 and collected between th th Figure 3. (Below) A HOBO October 30 and November 25 , temperature sensor. 2014. Each sensor was configured to take temperature readings at 15 minute intervals. This results in 96 readings from each sensor every day, and thousands of readings during the course of deployment. 5 Results and Discussion General Patterns in 2014 Out of a total of 92 sensors deployed, only four were unable to provide data. Two sensors failed due to water intrusion, one was dislodged from the buoy line and lost, and a fourth sensor re- corded faulty data. This section will compare data from a variety of lakes. For a report focusing on temperature data from a specific lake, please see the Lake Informa- tion page on our website, www.mainelakes.org, and click on the lake Individual reports for you want to know more about. each lake can be found There were a few temperature patterns that were common across all basins in 2014, although they varied in intensity. This simi- on the Lake Information larity makes sense because surface temperature is affected strongly page of our website, by the weather, and these lakes and ponds have similar weather pat- www.mainelakes.org terns due to their proximity to one another. Figure 4 (next page) shows the complete dataset for Hancock Pond, with each sensor’s data graphed in a different color. It labels the common patterns seen across most of the lakes. Figure 5 is a more visual representation of the same data from McWain Pond, showing the thermal dynamics of the lake over time. A sharp spike in surface temperature was seen on all basins on July 2nd and/or 3rd. This was, in most cases, the second highest temperature reading for the season. The spike occurred around the time of heavy storms on the 3rd, so it is reasonable to assume the storm caused the subsequent cooling of water temperatures. Another sharp spike in temperature was not seen, though temperatures did gradu- ally increase over the month of July. The data showed that most basins reached their maximum tem- perature on or around the same date, which was July 23rd. The beginning of seasonal temperature decline across all basins occurred around the 8th and 9th of September. This date marked the beginning of a steady drop in temperature leading to lake turn- over. There were two brief warm periods where calm conditions allowed for slight water restratifica- tion, these being between the 27th and 29th of September and the 17th and 18th of October.
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