P. Brezonik - Academia.edu (original) (raw)

Papers by P. Brezonik

Advances in Chemistry, 1994

International Journal of Geosciences, 2011

Changes in land use and land cover (LULC) in the drainage basin of Lake Malawi over the period 19... more Changes in land use and land cover (LULC) in the drainage basin of Lake Malawi over the period 1982-2005 were estimated from satellite imagery, and possible relationships were evaluated among the four major land-cover classes: cropland, forest, water, and savanna/shrub/woodland. AVHRR and MODIS sensors gave different values of areal extent of the four classes, limiting the feasibility of establishing consistent temporal trends over the entire period of the study, but forest land showed the least change among three land cover types, and extent of water bodies remained virtually unaltered over the period. AVHRR results show that cropland was mainly derived from savanna/shrub/woodland, which declined by almost 90% over the period 1982-1995.

Biogeochemistry, 2007

Storages and cycling of total mercury (Hg T), methylmercury (MeHg), and Hg 0 are described for Sp... more Storages and cycling of total mercury (Hg T), methylmercury (MeHg), and Hg 0 are described for Spring Lake, a small bog lake in the Marcell Experimental Forest in north-central Minnesota. We quantified photoredox transformations, MeHg photolysis, burial to the sediments, and internal and external loadings of Hg T and MeHg. Atmospheric deposition was the main input of Hg T ; MeHg was supplied by a combination of atmospheric, near-shore wetland, and biotic (methylation) sources. Hg T outputs were dominated by burial (67%), and Hg 0 evasion accounted for 26% of Hg T outputs. The watershed of Spring Lake is small (3.7• lake surface area), and accordingly, bog and upland runoff were minor contributors to both Hg T and MeHg inputs. Wet deposition was *9% of total MeHg input, and other external inputs (runoff, sediment porewater) provided only an additional 7%, indicating that internal production of MeHg was occurring in the lake. Photolysis of MeHg, measured in the field and laboratory, removed *3• the lake mass of MeHg (20 mg) annually, and was the dominant sink for MeHg. Residence times of MeHg and Hg T in the lake were 48 and 61 days, respectively, during the open-water season, compared with only 8 days for the residence time of MeHg on settling particles (seston). Photoreduction of Hg 2+ to Hg 0 was greater than the reverse reaction (Hg 0 photooxidation), and the residence time of Hg 0 in the photic zone was short (hours). Data from this study show active cycling of all the measured species of mercury (Hg T , MeHg, and Hg 0) and the importance of MeHg photolysis and photo-redox processes.

JAWRA Journal of the American Water Resources Association, 2013

ABSTRACT A large 20‐year database on water clarity for all Minnesota lakes ≥8 ha was analyzed sta... more ABSTRACT A large 20‐year database on water clarity for all Minnesota lakes ≥8 ha was analyzed statistically for spatial distributions, temporal trends, and relationships with in‐lake and watershed factors that potentially affect lake clarity. The database includes Landsat‐based water clarity estimates expressed in terms of Secchi depth (SDLandsat), an integrative measure of water quality, for more than 10,500 lakes for time periods centered around 1985, 1990, 1995, 2000, and 2005. Minnesota lake clarity is lower (more turbid) in the south and southwest and clearer in the north and northeast; this pattern is evident at the levels of individual lakes and ecoregions. Temporal trends in clarity were detected in ~11% of the lakes: 4.6% had improving clarity and 6.2% had decreasing clarity. Ecoregions in southern and western Minnesota, where agriculture is the predominant land use, had higher percentages of lakes with decreasing clarity than the rest of the state, and small and shallow lakes had higher percentages of decreasing clarity trends than large and deep lakes. The mean SDLandsat statewide remained stable from 1985 to 2005 but decreased in ecoregions dominated by agricultural land use. Deep lakes had higher clarity than shallow lakes statewide and for lakes grouped by land cover. SDLandsat decreased as the percentage of agriculture and/or urban area increased at county and catchment levels and it increased with increasing forested land.

The Handbook of Environmental Chemistry, 2015

Remote, satellite-based sensing is a cost-effective way to gather information needed for regional... more Remote, satellite-based sensing is a cost-effective way to gather information needed for regional water quality assessments in lake-rich areas. A major advantage is that it enables retrieval of current and historic information on lakes that were not part of ground-based sampling programs. Advances over the past decade have enabled the use of satellite imagery for regional-scale measurement of lake characteristics, such as clarity and chlorophyll. For example, in the Midwest USA, historic and recent Landsat water clarity assessments have been conducted on more than 20,000 lakes to investigate spatial and temporal patterns and explore factors that affect water quality. The spatial characteristics of Landsat imagery allow for the assessment of all lakes larger than ~4 ha, but the broad nature and placement of its spectral bands have limited assessments largely for water clarity. European Space Agency (ESA) MERIS imagery with spectral bands that were selected for water has been used to assess chlorophyll for about 900 of Minnesota’s large lakes (those > 150 ha). Improvements of the recently launched Landsat 8 and upcoming ESA Sentinel-2 satellites will expand our capabilities further enabling assessment of other optically related water quality characteristics, such as chlorophyll, colored dissolved organic matter (CDOM), and mineral suspended solids for all lakes, and upcoming Sentinel-3 will continue these capabilities for large lakes.

Marine Chemistry, 2004

ABSTRACT Mercury speciation at a small seepage lake in Northern Minnesota was shown to be influen... more ABSTRACT Mercury speciation at a small seepage lake in Northern Minnesota was shown to be influenced by photoreduction and photooxidation. Fluxes of Hg0 from water to air were greatest in the warmer, sunnier months in 2001 to 2002; however,
correlation with solar radiation was weak. The daytime evasional loss was generally from water to air and was estimated at 5.3 pmol m^-2 h^-1 for 2001 and 6.2 pmol m^-2 h^-1 for 2002 using a two-layer gas transfer model. Losses of Hg0(aq) in the dark over 10 days were observed in lake water (0.02 h^-1), Milli-Q water, and HPLC grade water (0.002 h^-1) and agreed with reported pseudo-first-order loss rates in the dark in other freshwaters. Using a mercury arc lamp, the pseudo-first-order loss rate of Hg0 in
water from Spring Lake was found to range from 0.39 to 0.76 h^-1. Other sinks for Hg0 exist through reaction with ozone, hydroxyl radical, and possibly singlet oxygen. A second-order reaction rate constant for Hg0(aq) and OH of 1.0x109 M^-1 s^-1
was estimated based on data from experiments and the literature. Although less reactive, there is a higher steady state concentration of ozone in lake water compared to hydroxyl radical. Consequently, loss of Hg0(aq) by ozone may predominate.
Potential oxidation of Hg0(aq) by singlet oxygen using rose bengal as a sensitizer could not distinguish between oxidation by rose bengal and by singlet oxygen itself. Chloride enhanced the oxidation of Hg0(aq) and should be considered in the mercury cycle in the ocean.

Water research, 2018

Colored dissolved organic matter (CDOM) has been widely studied as part of efforts to improve und... more Colored dissolved organic matter (CDOM) has been widely studied as part of efforts to improve understanding of the aquatic carbon cycle, by laboratory, in situ, and remote sensing methods. We studied ecoregion-scale differences in CDOM and dissolved organic carbon (DOC) to understand variability in organic matter composition and the use of CDOM as a proxy for DOC. Data from 299 lakes across the U.S. Upper Midwest showed that CDOM, measured as absorptivity at 440 nm (a), correlated strongly with DOC (R = 0.81, n = 412). Colored lakes in the Northern Lakes and Forests (NLF) ecoregion drove this relationship. Lakes in the North Central Hardwood Forests (NCHF) had low color (most had a < 3 m) and weaker CDOM-DOC relationships (R = 0.47). Spectral slopes and specific ultraviolet absorbance (SUVA), indicated relatively low aromaticity and non-terrestrial DOM sources in low color lakes. Multiple regression analyses that included total dissolved nitrogen (TDN) and CDOM, but not chlorophy...

Remote Sensing of Environment, 2015

A combination of new measurements and analysis of historical data from several geographic regions... more A combination of new measurements and analysis of historical data from several geographic regions was used to address four issues that affect the reliability and interpretation of colored dissolved organic matter (CDOM) measured by remote sensing of inland waters. First, high variability of CDOM levels in lakes and rivers was found at seasonal and multi-year time scales and at shorter intervals in some rivers and lakes. Coefficients of variation (CVs) of 30%-50% for absorptivity at 440 nm (a 440) were common in historical and new data sets we examined. CDOM values used to calibrate imagery thus should be measured close to the image acquisition date, preferably within 1-2 months in lakes and a few days in large rivers, unless it can be shown that CDOM levels are temporally stable over longer (or shorter) time periods in a given aquatic system. Second, spectral slopes (S) for CDOM in the visible range vary little over time (even over multi-year periods) within sites. Substantial variation was found between sites, however, and most spectra showed a change in slope near 460 nm. Values of S 400-460 for waters with moderate to high CDOM levels generally were within a narrow range (~0.014-0.018) and similar to reported S values in the near UV. Values of S 400-460 for waters with low CDOM generally were smaller and more variable, as were values for S 460-650 for all waters. Overall, the variability of spectral slopes in the visible range should not have a large effect on the reliability of a 440 estimates made from remote sensing, which in many models involve reflectance measurements at wavelengths N 500 nm. Third, although a strong correlation (r 2 = 0.925) was found between CDOM levels and DOC concentrations in 34 surface waters sampled in 2013, the standard error of estimate suggests an uncertainty of~±20% in predicting DOC at a 440 = 5 m −1 (a moderate CDOM level). Moreover, CDOM-DOC relationships for unpublished data sets we analyzed and those reported in the literature indicate that both the fraction of DOC that is colored and slopes of regressions between CDOM and DOC are highly variable in space and time. Prediction of DOC concentrations in water bodies from CDOM levels (whether measured in the laboratory or by remote sensing) thus is associated with considerable uncertainty. For the present, this implies that field sampling is required to verify DOC concentrations predicted from remotely sensed CDOM measurements until we have a better understanding of variations in DOC-CDOM relationships. Fourth, shapes of reflectance spectra for CDOM-rich waters varied greatly depending on the concentrations of other constituents (suspended solids and chlorophyll) that affect the optical properties of water. Nonetheless, it is not obvious from our results for several predictive models that different remote sensing algorithms are needed to calculate CDOM levels accurately for waters where CDOM is the only variable affecting reflectance versus waters where other constituents also affect the spectra. The best band or band ratio models for simulated Landsat 8, Sentinel-2 and Sentinel-3 bands from field measured reflectance spectra yielded high r 2 values (0.84-0.86) for a 440. The broader Landsat 8 bands worked nearly as well for a 440 as the narrower Sentinel band sets and hyperspectral bands, probably because CDOM is characterized by a broad exponential increase in absorbance with decreasing wavelength rather than specific peaks or troughs in absorbance or reflectance.

In keeping with the Americans with Disabilities Act, this material is available in other formats ... more In keeping with the Americans with Disabilities Act, this material is available in other formats upon request. Call the University of Minnesota Water Resources Center at 612/624-9282.

Journal of Great Lakes Research, 1976

Sources and factors affecting the concentrations of biologically active compounds in atmospheric ... more Sources and factors affecting the concentrations of biologically active compounds in atmospheric precipitation are reviewed with primary emphasis on nitrogen and phosphorus. Rainfall concentrations of these constituents are highly variable and accurate flux measurements are correspondingly difficult. High N and P loadings are associated with agricultural activity, especially feed-lot and barnyard operations. Total atmospheric P loadings are in the range 0.01 to 0.10 g/m2-yr while nitrogen loadings generally range from 0.5 to 3.0 g/m2-yr. While these values are generally insufficient to cause lake eutrophication by themselves, the upper ranges approach the critical loading rates. The atmosphere represents a significant component for the total nutrient loadings to many lakes.

The technical program for the workshop on metropolitan water supply issues was planned by the com... more The technical program for the workshop on metropolitan water supply issues was planned by the committee listed at the bottom of this page. Special thanks are extended to the panel chairs for helping to organize the topics of their panels, preparing the issue statements, and arranging panel membership. The cooperation of Jack Ditmore, Chair of the Metropolitan Water Supply Task Force, and all members of the task force in planning and participating in the workshop is gratefully acknowledged. Editorial assistance in preparing the proceedings was provided by Liz Espointour and Alice Tibbetts. Support for the workshop and publication of the proceedings was provided by the Water Resources Research Center through the University of Minnesota Graduate School.

The Integrated Ocean Observing System (IOOS), established through the efforts of the National Off... more The Integrated Ocean Observing System (IOOS), established through the efforts of the National Office for Integrated and Sustained Ocean Observations (Oceans.US) provides quality controlled data and information on a routine and continuous basis regarding current and future states of the oceans and Great Lakes at scales from global ocean basins to coastal ecosystems. The seven societal goals of IOOS are outlined in this paper. The Engineering and Geosciences Directorates at the National Science Foundation (NSF) are collaborating in planning the WATERS (WATer Environmental Research System) Network, an outgrowth of earlier, separate initiatives of the two directorates: CLEANER (Collaborative Large-scale Engineering Analysis Network for Environmental Research) and Hydrologic Observatories. WATERS Network is being developed by engineers and scientists in the academic community who recognize the need for an observation and research network to enable better understanding of human-dominated ...

Environmental Science & Technology, 2010

Peatland Biogeochemistry and Watershed Hydrology at the Marcell Experimental Forest, 2011

Lake and Reservoir Management, 2006

Menken, K., P. Brezonik and M. Bauer. 2006. Influence of chlorophyll and colored dissolved organi... more Menken, K., P. Brezonik and M. Bauer. 2006. Influence of chlorophyll and colored dissolved organic matter (CDOM) on lake reflectance spectra: Implications for measuring lake properties by remote sensing. Lake and Reserv. Manage. 22(3):179-190. Light reflected from lake surfaces can convey much information about water quality, especially algal abundance, humic content, turbidity and suspended solids. Light reflectance from lakes is complicated, and detailed spectra are needed for analysis of controlling factors. We obtained detailed reflectance spectra from the water surfaces of 15 lakes in east-central Minnesota and found patterns related to chlorophyll a (chl a), turbidity and humic matter (colored dissolved organic matter, CDOM). Increasing chl a and turbidity generally resulted in higher reflectance across the visible and near-infrared spectrum. Increasing CDOM led to low reflectance, especially below ~500 nm. Spectra of lakes with high chl a were distinguishable from those of lakes low in chl a, and lakes with low or high CDOM had readily distinguishable spectra. Several optical characteristics of lake water can be estimated from reflectance intensities measured over narrow wavelength bands. The ratio of reflectance at 700 nm to that at 670 nm was the best predictor of chl a over a wide range of conditions, including high turbidity and CDOM. Several relationships involving reflectance at 412, 443, 488, and 551 nm, the wavelengths used to calculate oceanic chl a from MODIS satellite data, also yielded a high R 2. The ratio of reflectance at 670 nm to 571 nm provided the best estimates of humic color despite the low absorbance of CDOM at these wavelengths. Relationships involving reflectance for all 15 lakes in the range 400-500 nm, where CDOM absorbs light, had low r 2 values; none was high enough for reliable estimates of lake color. For 10 lakes with low to medium chl a levels (≤10 mg m-3), regressions involving 412 and 443 nm yielded moderately good relationships. Airborne and satellite remote sensing thus might be used to identify lakes high in CDOM, and may provide reasonable estimates of humic color in lakes with low chl a levels.

Geochmica et Cosmochimica Acta

Air and water pollution, 1966

Water Science and Technology, 1999

The Minnesota River (Minnesota, USA) receives large non-point source pollutant loads. Complex int... more The Minnesota River (Minnesota, USA) receives large non-point source pollutant loads. Complex interactions between agricultural, state agency, environmental groups, and issues of scale make watershed management difficult. Subdividing the basin's 12 major watersheds into agro-ecoregions based on soil type, geology, steepness, and climate enhances predictability of stream water quality parameters. An eight-step framework for agricultural watershed management is presented.