In the News
Tribute to Dwight Brown. With sadness we note the passing of Dwight Brown, Professor Emeritus of Geography, University of Minnesota, and a long-time friend and colleague of our research group. Dwight was an early proponent of using Landsat imagery to assess lake water quality on a broad geographic scale, and did seminal work in the 1970s on classifying regional lakes according to water clarity (Secchi depth). This work led to the M.S. thesis by Leif Olmanson, which in turn led to a series of funded projects headed by Marvin Bauer and Patrick Brezonik to map lake water clarity of the seven-county Twin Cities Metropolitan Area and then the entire state. Our work on this topic continues to this day on an expanded set of water quality measures and with greatly improved technical capabilities. Professor Brown was an advocate of interdisciplinary graduate education and research in water resources, and was one of the faculty leaders who developed the interdisciplinary Water Resources Science graduate program in the 1990s.
Statewide classifications of CDOM are described in a recent paper by Leif Olmanson, Ben Page, Jacques Finlay, Patrick Brezonik, Marv Bauer, Claire Griffin, and Ray Hozalski in Science of the Total Environment. Its graphical abstract is below.
Chen, Y., R.M. Hozalski, L.G. Olmanson, B.P. Page, J.C. Finlay, P.L. Brezonik, and W.A. Arnold. 2020. Prediction of Photochemically Produced Reactive Intermediates in Surface Waters via Satellite Remote Sensing. Environmental Science & Technology 54: 11, 6671–6681.
High citation rates for our satellite image analysis papers
A recent review of Google Scholar for citations of our satellite image analysis publications shows that four of our early publications have been cited more than 200 times:
Sawaya, K.G., L.G. Olmanson, N.J. Heinert, P.L. Brezonik, M.E. Bauer. 2003. 460
Kloiber, S.M., P.L. Brezonik, L.G. Olmanson, M.E. Bauer. 2002. 358
Olmanson, LG., M.E. Bauer, P.L. Brezonik. 2008. 276
Brezonik, P.L., K.D. Menken, M.E. Bauer. 2005 228
Three have more than 100 citations:
Kloiber, S.M., P.L. Brezonik, M.E. Bauer. 2002 179
Brezonik, P.L., L.G. Olmanson, J.C. Finlay, M.E. Bauer. 2015. 143
Olmanson, L.G., P.L Brezonik, M.E. Bauer. 2013. 140
In addition, nine papers have more than 25 citations. Several of our recent papers also are being widely cited: Griffin, Finlay, et al. (2018) already has ten citations, and Brezonik, Bouchard, et al. (2019) has been cited nine times.
Revised/New LakeBrowser. The LakeBrowser has provided satellite-derived data on water clarity, an indicator of lake water quality, for over 10,000 Minnesota lakes since 2002. It was recently updated with lake clarity data for 2011 and 2015 and additional water quality properties (CDOM and chlorophyll). Additional capabilities for image and data display, geospatial analysis, and data access and download were added and now include summaries for the state, counties, ecoregions and watersheds, and display of high resolution imagery and land cover. An example for Lake Minnetonka is shown in the figure below. ArcGIS hosting and the application development was provided by U‑Spatial.
State Fair Exhibit and Demo. Ben Page and Leif Olmanson had an exhibit "Minnesota Water Quality: A View from Space" in the CFANS exhibit area at the Minnesota State Fair where they demonstrated the practical applications of how satellite imagery can be used to monitor the water quality of Minnesota's lakes. Some of the 400,000 attendees on the first Saturday and Sunday were delighted to learn about historical water quality trends of their lakes through visual animations and interacting with the online LakeBrowser. Ben and Leif met some of the citizen scientists who provide calibration data and interacted with many motivated students. They hope to return next year
Assessment of Surface Water Quality with Satellite Sensors. With support from the Environmental and Natural Resources Trust Fund through the LCCMR and many partners throughout the state, we recently completed a three-year project aimed at developing understanding necessary to apply new satellite capabilities to monitor surface water resources throughout Minnesota. Highlights of project achievements include: 1) Development of methods to measure algal abundance, colored dissolved organic matter, turbidity/suspended sediment, which are the three main drivers of water clarity in lakes and rivers; 2) Development of methods to predict contaminant behavior and water treatability for drinking water from remote-sensed properties of waterbodies; 3) Major expansion and enhancement of the LakeBrowser, a web portal for information on water quality of all Minnesota's lakes; 4) Revision of a website resource of remote sensing and water quality; and 5) Collaborations with state agencies to make water standards more accurate.
A major milestone for our NSF research project on colored dissolved organic matter (CDOM) was achieved recently by the publication in the International Journal Water Research of an article on the effects of CDOM on drinking water treatment processes. Authored by postdoc Yiling Chen, her mentor Ray Hozalski, and four other research group members, it describes relationships between CDOM levels and production of two major categories of toxic disinfection byproducts (trihalomethanes and haloacetic acids) and the effect of CDOM on increasing chlorine demand in treating water to standards of drinking water quality. In addition, it demonstrates the usefulness of satellite imagery in evaluating at regional scales the suitability of waters as drinking water sources.
New Brochures and Videos. As part of the outreach efforts on our NSF CDOM project, the group recently produced two brochures intended for use by extension educators and others in engaging with the public on lake water quality issues. One brochure deals with the ecological importance of CDOM and its roles in affecting human uses of lakes, and the other describes the many advantages and usefulness of satellite-based measurements to assess surface water quality.
In addition, we recently completed production of two videos that enhance capabilities for public education related to CDOM. “All about CDOM” describes the nature, sources and importance of CDOM in lakes, and the second, How to Measure CDOM,” describes various techniques for measuring CDOM, including regional-scale measurements by satellite imagery and the potential use of smartphones for CDOM measurements by citizen scientists. The videos are available on YouTube and can be accessed via this website’s CDOM page.
Research by Ben Page and Leif Olmanson on processing and atmospheric correction of Landsat 8 and Sentinel 2 data for monitoring lake clarity was published in Remote Sensing of Environment in September. The multi-sensor methodology can be used to expedite the pre-processing steps to retrieve lake information for resource management.
The LakeBrowser was updated recently with new statewide data on lake clarity for 2015, the distribution of CDOM in Minnesota lakes in 2015 and 2016-17, as well as summer chlorophyll-a concentrations for 2017-18. The graphic below shows the wide range of chlorophyll occurring in the many basins of Lake Minnetonka and in nearby lakes of the metro area west of Minneapolis. The search and display capabilities of the Browser currently are being expanded (expect more news on this in a few months), and new data will be added as they become available.
The LakeBrowser has provided satellite-derived data on water clarity, an indicator of lake water quality, for over 10,000 Minnesota lakes since 2002. It was recently updated with lake clarity data for 2011 and 2015 and additional water quality properties (CDOM and chlorophyll). Additional capabilities for image and data display, geospatial analysis, and data access and download were added and now include summaries for the state, counties, ecoregions and watersheds, and display of high resolution imagery and land cover. An example for Lake Minnetonka is shown in the figure below. ArcGIS hosting and the application development was provided by U‑Spatial.
Leif Olmanson and Ben Page presented papers at the European Space Agency, 2019 Living Planet Symposium in Milan, Italy in May. One paper described the group’s advances on lake water quality monitoring capabilities using Sentinel and Landsat imagery and automated high-performance computing, and the other described evaluation of atmospheric correction methods for inland water quality mapping. In collaboration with Chris Crawford from the USGS EROS Center, they also presented a poster on use of Sentinel-1 synthetic aperture radar remote sensing to characterize under-ice limnology and in-lake primary productivity. As part of their visit to Italy, they participated in a data collection campaign on Lake Garda with remote sensing scientist, Claudia Giardino, and visited the Lake Garda Experimental Station Eugenio Zilioli.
Jacques Finlayand his lab are collaborating with the newly formed Regional Monitoring Network for inland lakes to increase the integration of CDOM data into spatial and temporal analyses of water quality change. The RMN is a partnership among states, tribes and other groups to develop and integrate monitoring across thousands of lakes in the Northeast and Midwest US. Finlay’s lab is supporting interested RMN members through provision of information from our work, advice on methods, and in some cases analyses to allow expansion of CDOM data collection within the network. The RMN recently was described in a 2018 article by RMN coordinator Jen Stamp in the NALMS newsletter, Lakeline.
Patrick Brezonik is the lead author of two recently published articles that describe results from our CDOM work. A paper on the importance of CDOM in limiting Secchi depth (SD) in colored lakes and the implications for use of SD as a trophic state metric was published in Ecological Applications in March. This work was a collaboration between our group and scientists from the Minnesota Pollution Control Agency. Coauthors include Will Bouchard and Jesse Anderson from the MPCA, as well as Jacques Finlay, Claire Griffin, Leif Olmanson, Bill Arnold and Ray Hozalski. A paper that details findings on dissolved iron-CDOM interactions and the limited role of dissolved iron in affecting the color intensity of CDOM was published in PLOS ONE in February . Coauthors on the paper are Jacques Finlay, Claire Griffin, Bill Arnold, Evelyn Boardman, Noah Germolus, Ray Hozalski, and Leif Olmanson.
Claire Griffin began a new postdoc position at the University of Virginia in February, 2019, working on interactions between built and natural environments in the Arctic. Griffin will continue working with our group in writing several papers related to the CDOM work she did with us since 2016. Griffin also gave an oral presentation at the American Geophysical Union (AGU) fall meeting in Washington, DC, December 10-14, 2018 on regional-scale measurement of dissolved organic carbon pools in lakes using remote sensing techniques. Griffin and Patrick Brezonik also presented a poster in a session on citizen science at the fall AGU meeting on progress in developing a smartphone app to measure CDOM.
The Minnesota Lake Clarity Browser (water.rs.umn.edu/lakebrowser) with seven statewide classifications of lake clarity from 1975–2008 has been converted to ArcGIS Server with improved capability for search and display, additional basemaps, and data download. New classifications for 2010 and 2015 are underway and will be added as soon as they are available, along with capability to display temporal trends, geographic patterns and statistics by watershed, ecoregion and county.
Ray Hozalski presented a paper in mid-September on our CDOM work at the 19th conference of the International Humic Substances Society in Albena, Bulgaria.
Noah Germolus began his PhD studies in the joint MIT-Woods Hole Oceanographic Institute in Cambridge, MA, in September, 2018.
Leif Olmanson participated in an invitation-only workshop “A new paradigm in lake and reservoir research and management through global monitoring, modeling, and engaging and empowering people networks” in Alexandria, VA, Sept. 5-7, 2018. The workshop was sponsored by the Global Lake Ecological Observatory Network (GLEON); U.S. Geological Survey; UMN Dept. of Computer Science and Engineering; Center for Limnology, University of Wisconsin-Madison; and Cary Institute of Ecosystem Studies.
Leif Olmanson and Ben Page presented seminars "Near Real-Time System to Provide Critical Water Quality Information for Lake Management" to interest groups at the Minnesota Supercomputing Institute in August and April, 2018.
Jeff Peterson and Leif Olmanson were awarded a two-year grant starting July 1, 2018, from the Minnesota Environmental and Natural Resources Trust fund, as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR), to build a near real-time water quality monitoring system using satellite imagery. The new work is a collaborative effort of the Remote Sensing and Geospatial Analysis Laboratory (RSGAL), Minnesota Supercomputing Institute (MSI), and the Water Resources Center (WRC).
Noah Germolus, an undergraduate research assistant on the NSF CDOM study, completed his B.S. in Environmental Engineering with highest honors in May and continued to work on the citizen-science component of the study during summer. Noah completed an honors thesis under the direction of Professor Ray Hozalski and Professor Emeritus Patrick Brezonik on “Trends in Colored Organic Matter and River Flow in the Mississippi River 1944-2010” using a 66-year record of daily color measurements from the Minneapolis water utility.” Germolus and his former advisors currently are preparing a manuscript for journal publication based on his analysis.
Claire Griffin presented invited seminars related to our remote sensing studies at the Southwest Research Institute (San Antonio, May 9, 2018), the Kansas Biological Survey (Lawrence, KS, April 20, 2018), and the University of Minnesota Duluth Dept. of Chemistry (Feb. 23, 2018).
Benjamin Page was appointed as a research fellow in the WRC in March 2018 as part of the new Digital Water Initiative, which is a joint effort of the WRC and MSI, and has joined our research group. Page was hired to work with Leif Olmanson (RSGAL) and David Porter (MSI) on WRC-housed grants related to remote sensing and mapping of lake water quality and ice phenology. Page has a strong background in geospatial analysis and remote sensing of inland waters. After earning a B.S. in biology from UMD, he completed an M.S. at the University of Georgia in geography, where he developed algorithms for atmospheric correction and satellite techniques to assess cyanobacteria bloom phenology. He also worked on geospatial data projects for NASA's DEVELOP and SERVIR programs, with a recent focus on remote sensing to monitor inland water quality with applications to the African Great Lakes.
Research Associate Leif Olmanson (P.I.) has received a new two-year contract from the Minnesota Pollution Control Agency that will map lake water clarity statewide for two periods: 2010 and 2015. The project will enable updating our semi-decadal database that currently contains satellite-based water clarity results (reported as Secchi depth) for more than 10,000 Minnesota lakes in each of seven periods starting in 1975. The new grant also provides funds to update the LakeBrowser that is used to access the water clarity data.
This past summer was a very active time for our group gathering field data and water samples to calibrate statewide imagery for CDOM, chlorophyll, suspended solids, turbidity, and Secchi depth for our NSF and LCCMR projects. The 2017 field program was designed to collect samples within a few days following acquisitions of clear imagery by Sentinel-2.
We sampled 230 sites, from Hayes Lake in northwestern Minnesota and many lakes near Ely, MN to lakes within miles of the Iowa border. Claire Griffin, postdoctoral associate, led field coordination and sampling efforts with help from field teams that included three undergraduates, three technicians (recent graduates), two graduate students, and several Co-PIs. We also collaborated with researchers in the Cotner Lab at UMN, Lesley Knoll at the Itasca Biological Station, the Red Lake Nation DNR, Minneapolis Parks Board, Minnesota Science Museum St. Croix Research Lab, and volunteers from Brainerd and Lake Vermillion, who helped us obtain samples across a much larger area than we would have been able to do alone – many thanks to them! Despite cloudy conditions early in the summer, imagery from August and September provides clear data to map chlorophyll-a, suspended solids, and CDOM across the state. Some photos from the summer field work.
Professor Ray Hozalski (Department of Civil, Environmental, and Geo-Engineering), an international expert on drinking water treatment processes and P.I. of our NSF grant on CDOM, gave an invited talk titled “Remote Sensing for Source Water Characterization” at a Gordon Conference on Drinking Water Disinfection Byproducts in early August. The week-long conference was held at Mount Holyoke College in South Hadley, Massachusetts, and the talk covered a broad range of topics involved in the NSF grant. According to Prof. Hozalski, the presentation was received enthusiastically by conference participants.
Our ongoing work on satellite-based measurement of colored dissolved organic matter (CDOM) was described on NASA’s, Earth Observatory website, on October 25, 2016, in an article titled Minnesota: Land of the Many-Colored Lakes. The article provides maps of colored lakes in northern Minnesota and describes the state as “Minnesota, the land of 10,000 lakes,” might as well be called the “land of 10,000 shades of lakes,” stating that “many of them owe their color to CDOM: colored dissolved organic matter.” Comments by Leif Olmanson and Patrick Brezonik are included in the article, which can be viewed at: https://earthobservatory.nasa.gov/IOTD/view.php?id=88971
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