Lakes as Sentinels- Using buoys and advanced sensors to study lakes
As the lowest point in the surrounding terrestrial catchment, lakes serve as indicators or sentinels of change in the landscape. To better understand the role of lakes as sentinels, scientists are identifying the key lake variables that respond to changes in the watershed both seasonally and over the long term.
GLEON (Global Lakes Ecological Observatory Network) engages limnologists and information scientists in a global network of lake sensors to document signals that lakes give as they respond to changes in the surrounding watershed and climate. In this spirit, the Global Change Limnology Laboratory has deployed buoys in several regions of North America, including the Rocky Mountains (Heart and Beartooth lakes in the Beartooth Mountains of Montana and Wyoming; Lake Oesa in Yoho National Park, Canada) and the Poconos (lakes Giles and Lacawac in eastern Pennsylvania), as well as in an Arctic lake in Greenland.
The remote location of many of our study lakes challenged lab members to think creatively about the design of the buoys as all of the equipment is carried in backpacks by only a few individuals (images left). With the help of Fondriest Environmental, graduate students in the IGERT-EARS program designed a buoy that was lightweight and able to sample 10 water and 6 weather parameters. This "mobile" buoy weighs a mere 30 lbs without sensors and is fairly inconspicuous (see Images of mobile buoy), an important consideration for an instrument deployed in a remote pristine landscapes.
A second, "profiling" buoy was designed to measure changes in lakes by sampling at different depths. A suite of sensors including CDOM, chlorophyll-a, phycocyanin, dissolved oxygen, pH, turbidity, and underwater PAR collected data at hourly intervals at the surface of the lake and performed automated profiles to the maximum depth of the lake every four hours. With the recent increase in extreme events such as episodic storm events or severe drought that strongly affect the vertical zonation of lakes, the profiling buoy will improve our understanding of the effects of climate change on aquatic ecosystems.
With the help of the sensors on these buoys, we hope to better understand how changes in the watershed affect variables such as lake transparency, dissolved organic carbon (DOC), and chlorophyll. With these data, we can track how lakes change seasonally as well as ask questions about the ecological consequences of these changes including the timing, causes, and consequences of harmful algal blooms and oxygen depletion (hypoxia, anoxia).
Below are data collected from the mobile buoy deployed in Heart Lake (2010) following ice-out. These data revealed that there was a spike in chlorophyll after the ice melted and then a drop in concentration to a level comparable to other lakes in the region. High resolution data from this buoy also enabled us to track the establishment of thermal stratification in Heart Lake as well as seasonal changes in CDOM (chromophoric dissolved organic matter).
The use of a portable buoy sensor system provides the unique opportunity to explore the idea of lakes as sentinels in remote locations, while a profiling buoy facilitates our understanding by collecting data throughout the water column. Integration and collaboration with programs such as IGERT-EARS and GLEON enable us to employ advanced sensor tools and compare our suite of lakes to changes observed across the continent and globe.
One of the major projects ongoing in the Global Change Limnology Lab is assessing the role of vertical temperature profiles in lakes as sentinels of both air temperature and precipitation components of climate change.
Pocono Lakes- Lacawac Sanctuary as a "Hub for EONS" (Ecological Observatory Networks)
This work is centered at the Lacawac Sanctuary and Biological Field Station where a new NSF-funded field laboratory combines with a recent NSF Long Term Research in Environmental Biology grant to support a "Hub for EONS" (ecological observatory networks) at Lake Lacawac. For over 30 years, we have collected limnological data from three lakes in the region, a green lake, a brown lake, and a blue lake in eastern Pennsylvania. During this time, the lab has compiled a large data set, including information about
- Vertical profiles across depth of light (PAR and UV), temperature, and dissolved oxygen
- The quantity and quality of dissolved organic matter (DOM) and chlorophyll
- Phytoplankton community composition
- Zooplankton community composition and vertical distribution
- The relative abundance of young-of-year fish
In collaboration with Kevin Rose at Rensselaer Polytechnic Institute, our active NSF LTREB grant is continuing this long-term sampling as well as supporting experiments to better understand the mechanisms that underlie the long-term trends that have been observed in the study lakes (Williamson et al. 2015, Pilla et al. 2018, Knoll et al. 2018).
Lake Giles and Lake Lacawac were the home of the UV Lakes project. From 2002-2009, 10 researchers from eight institutions worked to investigate the interactive effects of UV and temperature on pelagic food webs.
Lake Giles (above, left) is a transparent, low DOM lake. In contrast, Lake Lacawac (above, right), which is part of the Lacawac Field Station, is characterized by higher DOM. Because DOM is one of the main factors controlling UV transparency, these striking differences provide a unique opportunity to investigate the effects of UV on the aquatic community. Nearby Lake Waynewood, a more productive lake very similar in size to Lacawac, completes an interesting set of lakes that vary in their trophic status from oligotrophic, blue-water Lake Giles to mesotrophic/dystrophic, brown-water Lake Lacawac, to more eutrophic, green-water Lake Waynewood. Numerous experiments have been conducted at these sites by collaborating researchers, as well as graduate and undergraduate students through the years.
Our collaborative research in these two study lakes has shown substantial increases in DOM associated with decreases in UV transparency, depth of the thermocline, and increases in oxygen depletion. These changes in UV are important because UV drives the vertical migration of some zooplankton species in transparent lakes. Yellow perch spawn their egg masses at deeper depths in the more transparent Lake Giles. Experiments have shown that if perch spawned at shallower depths their eggs would perish due to the high UV levels. Dramatic changes in UV transparency have been observed in Lake Giles during the summer. UV used to penetrate to depths of over 15 m in July, but now the 1% attenuation (of 320nm UV surface irradiance) depths are closer to 2-4 m. This decrease in transparency in Lake Giles is likely due largely to increases in precipitation in the region and hence greater terrestrial DOM inputs. Recovery from acid deposition related to the Clean Air Act Amendments may also be involved. Research continues in these lakes, and with the building of a new laboratory, hiring of a new Director of Research and Education, new collaborations, and development of the programs at the Field Station, exciting opportunities exist.