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Urban lakes are heavily impacted by human activities and climate variability, and they provide many ecosystem services to residents. The MSP LTER program is studying long term changes in urban lake water quality, ecology and management as part of our long term studies of urban environments. The goal of this dataset is to understand how land-use change, management, and climate have impacted urban lake biogeochemistry over time. This dataset includes parameters characterizing the long term (> 5 years) surface water quality and chemistry of 294 lakes and ponds in the Minneapolis-Saint Paul Seven County Metropolitan Area, Minnesota, USA. The dataset draws from data publicly available through the Minnesota Pollution Control Agency and data provided by individual agencies, park districts and cities. The dataset is distinct from other lake datasets because it is curated to only report a single value per lake x date x parameter, minimizing the amount of data manipulation needed before use in statistical analyses. All data come from the top two meters of the water column. In the case of multiple spatial measurements on a single lake or multiple agencies sampling the same lake on the same day, chemistry data were averaged to generate a single value. For Secchi data, the deepest reported observation on a given lake x date was used. Parameters: total phosphorus, total nitrogen, total Kjeldahl nitrogen, nitrate, nitrite, nitrate + nitrite (NOx), ammonium, chlorophyll a (corrected and not corrected for pheophytin), specific conductivity, chloride, and Secchi depth. These waterbodies are identified by their DNR Division of Water (DOW) number with minor alterations for subbasin identification. This dataset does not comprehensively represent all lentic waterbodies that have substantial water quality data in the metro area, and some included waterbodies may be considered wetlands according to state classifications. The data brought together in this database has undergone QAQC by the organizations that originally collected it, as well as a screening process during data harmonization. While we believe that the resulting dataset is robust, we cannot guarantee that it is free of errors or inaccuracies. 

Sunlight breaks down dissolved organic matter (DOM) in lakes and streams to produce carbon dioxide (a greenhouse gas). The efficiency of this process depends on light exposure, the aromatic content of DOM (i.e., Ar–C), and dissolved iron (Fe). 

In Lake Erie, toxin-forming harmful algal blooms (HABs) occur following high concentrations of hydrogen peroxide (H 2 O 2 ). Correlation between H 2 O 2 concentrations and HABs revealed knowledge gaps on the controls of H 2 O 2 production in Lake Erie. One way H 2 O 2 is produced is upon absorption of sunlight by the chromophoric fraction of dissolved organic matter (CDOM). Rates of this photochemical production of H 2 O 2 may increase in proportion to the apparent quantum yield of H 2 O 2 ( Φ H 2 O 2 ,λ ) from CDOM. However, the Φ H 2 O 2 ,λ for H 2 O 2 production from CDOM remains too poorly constrained to predict the magnitude and range of photochemically produced H 2 O 2 , particularly in freshwaters like Lake Erie. To address this knowledge gap, the Φ H 2 O 2 ,λ was measured approximately biweekly from June–September 2019 in the western basin of Lake Erie along with supporting analyses ( e.g. , CDOM concentration and composition). The average Φ H 2 O 2 ,λ in Lake Erie was within previously reported ranges. However, the Φ H 2 O 2 ,λ varied 5-fold in space and time. The highest Φ H 2 O 2 ,λ was observed in the Maumee River, a tributary of Lake Erie. In nearshore waters of Lake Erie, the Φ H 2 O 2 ,λ decreased about five-fold from June through September. Integration of the controls of photochemical production of H 2 O 2 in Lake Erie show that the variability in rates of photochemical H 2 O 2 production was predominantly due to the Φ H 2 O 2 ,λ . In offshore waters, CDOM concentration also strongly influenced photochemical H 2 O 2 production. Together, the results confirm prior work suggesting that photochemical production of H 2 O 2 contributes but likely cannot account for all the H 2 O 2 associated with HABs in Lake Erie. 

Methane (CH4) concentrations were measured in dissolved organic carbon (DOC) leachates of permafrost soils collected from the frozen permafrost layer at five sites underlying tussock tundra or wet sedge vegetation on the North Slope of Alaska during the summers of 2018 and 2019. 

Leachates of dissolved organic carbon (DOC) from permafrost soils were prepared from soils collected from the North Slope of Alaska in 2018 and 2022. Soil leachates were then either kept in the dark or exposed to light from LEDs at 305 nm (UV) and 405 nm (visible), and then inoculated with native microbial communities and incubated. At the start of the biological incubations, single replicates of the DOC after dark or light treatment and inoculation were assigned accession numbers and analyzed for 14C and 13C at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility. At the end of the biological incubations, duplicates of the dissolved inorganic carbon (DIC) in those waters were assigned accession numbers and analyzed for 14C and 13C at the NOSAMS facility. 

Dissolved organic carbon (DOC) was leached from permafrost soils near the Toolik Field Station in the Alaskan Arctic. Daily rates of sunlight absorption by chromophoric dissolved organic matter (CDOM) from the permafrost soil leachates over the water column depth of an arctic headwater stream were quantified. 

Dissolved organic carbon (DOC) was leached from permafrost soils near the Toolik Field Station in the Alaskan Arctic, either kept in the dark or exposed to light treatments, and then incubated with native permafrost microbial communities. The radiocarbon (14C) and stable carbon (13C) isotopic compositions of the initial DOC present in the dark or light-exposed permafrost soil leachates and the carbon dioxide (CO2) produced by microbial respiration of dark or light-exposed permafrost DOC were quantified. 

Dissolved organic carbon (DOC) was leached from permafrost soils collected from the frozen permafrost layer at four sites underlying tussock tundra or wet sedge tundra vegetation and from both undisturbed soil and a thermokarst failure on the North Slope of Alaska during the summers of 2018 and 2022.