An official website of the United States government
This dataset includes chlorophyll-a concentrations, periphyton biomass estimates, water quality measurements, and qualitative observations from a large-scale mesocosm experiment conducted in the Green Lakes Watershed, Colorado. The experiment was designed to test how earlier lake ice-off and increased dissolved organic material (DOM), associated with terrestrial plant encroachment in alpine watersheds, interactively influence aquatic food webs. In fall 2019, twenty 2600L “megacosms” were established at Sandy Corner (3300 m ASL; 40.042289, -105.584006), left to fill with snowmelt, and maintained throughout the 2020 open water season. The experiment followed a 2 × 2 randomized block design manipulating ice-off timing (via black vs. beige tank coloration) and DOM inputs (presence/absence of willow leaf packs), with five replicates per treatment. All tanks were seeded with sediments and zooplankton from both alpine and montane lakes (Green Lake 1 and Green Lake 4), and instrumented with thermistors recording surface and hypolimnion temperature every two hours year-round. Periphyton growth was monitored using clay tiles, sampled across five time points. Chlorophyll-a concentrations were extracted from filtered water samples and analyzed spectrophotometrically. Periphyton biomass was estimated via ash-free dry mass (AFDM) determinations, based on the mass lost on combustion of material scraped from tiles. Water quality was measured 1–2 times weekly using a YSI ProPlus multiprobe and Li-Cor quantum sensor, and snow/ice cover was qualitatively assessed monthly during winter.
more »
« less
Spatial and Temporal Variability of Dissolved Organic Matter Molecular Composition in a Stratified Eutrophic Lake
Abstract Dissolved organic matter (DOM) is an intermediate between organic carbon formed by primary producers and carbon dioxide (CO2) produced through respiration, making it a key component of the carbon cycle in aquatic ecosystems. Its composition influences the routes of mineralization. Here, we evaluate DOM composition as a function of time and depth in Lake Mendota, a highly productive eutrophic lake that stratifies in warm months and is located in Madison, Wisconsin, USA. Dissolved organic carbon concentrations and optical properties are presented for 73 samples collected at a single location at varying depths within the water column from June to November. A subset of samples is analyzed by Fourier transform‐ion cyclotron resonance mass spectrometry (FT‐ICR MS) to investigate DOM composition at the molecular level. Temporally, increases in more oxidized formulas are observed in both the epilimnion and hypolimnion. At the surface, correlations between DOM formulas and both chlorophyll concentrations and light intensity show that photochemical reactions contribute to DOM oxidation. In the hypolimnion, redox conditions and interactions with sediments likely influence temporal compositional change. Our results show DOM composition varies with depth with more highly oxidized formulas identified deeper in the water column. However, DOM composition varies more temporally than by location within the water column. This work has implications for climate change as DOM photooxidation in lakes represents an understudied flux of CO2to the atmosphere. Additionally, lake eutrophication is increasing due to warming temperatures and this data set yields detailed molecular information about DOM composition and processing in such lakes.
more »
« less
- PAR ID:
- 10363489
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 127
- Issue:
- 1
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Dissolved organic matter (DOM), often measured as dissolved organic carbon (DOC), plays a fundamental role in influencing the structure and function of lake ecosystems. Due to the myriad ecosystem effects of DOM, widespread observations of long‐term increasing DOM concentrations have received much attention from ecologists. DOM positively influences primary production and consumer production at low concentrations due to the fertilising influence of bound nutrients. However, beyond a unimodal peak in production, a reduced light environment may result in a negative effect on production. This unimodal model has been largely developed and tested in lakes with low to moderate DOM concentrations (i.e., typically ≤10 mg/L DOC).To understand ecological responses in lakes across a larger range in DOM concentrations, we examined the response of benthic invertebrate communities in 148 Swedish lakes with DOM concentrations ranging between 0.67 and 32.77 mg/L DOC.We found that increasing DOM concentrations had a strong effect on invertebrate community composition belowc.10 mg/L. Across this range, abundances of individual taxa both increased and decreased, probably in response to environmental change induced by DOM. However, in lakes above this concentration, increasing DOM had minimal influence on community composition.As DOM concentrations continue to increase, faunal communities in lakes below this 10 mg/L DOC threshold are likely to undergo substantial change whereas those above this threshold are likely to be minimally impacted.more » « less
-
Several areas around the world rely on seawater desalination to meet drinking water needs, but a detailed analysis of dissolved organic matter (DOM) changes and disinfection by-product (DBP) formation due to chlorination during the desalination processes has yet to be evaluated. To that end, DOM composition was analyzed in samples collected from a desalination plant using bulk measurements ( e.g. dissolved organic carbon, total dissolved nitrogen, total organic bromine), absorbance and fluorescence spectroscopy, and ultrahigh resolution mass spectrometry (HRMS). Water samples collected after chlorination ( e.g. post pretreatment (PT), reverse osmosis (RO) reject (brine wastewater) (BW), RO permeate (ROP), and drinking water (DW)), revealed that chlorination resulted in decreases in absorbance and increases in fluorescence apparent quantum yield spectra. All parameters measured were low or below detection in ROP and in DW. However, total solid phase extractable (Bond Elut Priority PolLutant (PPL) cartridges) organic bromine concentrations increased significantly in PT and BW samples and HRMS analysis revealed 392 molecular ions containing carbon, hydrogen, oxygen, bromine (CHOBr) and 107 molecular ions containing CHOBr + sulfur (CHOSBr) in BW PPL extracts. A network analysis between supposed DBP precursors suggested that the formation of CHOBr formulas could be explained largely by electrophilic substitution reactions, but also HOBr addition reactions. The reactions of sulfur containing compounds are more complex, and CHOSBr could possibly be due to the bromination of surfactant degradation products like sulfophenyl carboxylic acids (SPC) or even hydroxylated SPCs. Despite the identification of hundreds of DBPs, BW did not show any acute or chronic toxicity to mysid shrimp. High resolution MS/MS analysis was used to propose structures for highly abundant bromine-containing molecular formulas but given the complexity of DOM and DBPs found in this study, future work analyzing desalination samples during different times of year ( e.g. during algal blooms) and during different treatments is warranted.more » « less
-
Dissolved organic matter (DOM) plays an important role in carbon cycling in natural waters. The processing of DOM in these waters can occur via photooxidation, or interaction with sunlight. This processing can lead to the production of CO2, and also the alteration of organic compounds that make up DOM. It is likely that the extent of photooxidation is at least partially determined by the chemical composition of DOM. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to characterize the dissolved organic matter at the molecular level for all water samples, both before and after light exposure to better understand the photooxidation of DOM. Chemical formulas were assigned to mass to generated mass to charge ratios using a custom script in R, resulting in a list of chemical formula assignments for each DOM sample, at multiple light exposure time points.more » « less
-
Dissolved organic matter (DOM) drives biogeochemical processes in aquatic ecosystems. Yet, how hydrologic restoration in nutrient‐enriched ecosystems changes DOM and the consequences of those changes for the carbon cycle remain unclear. To predict the consequences of hydrologic restoration on carbon cycling in restored wetlands, we need to understand how local environmental factors influence production, processing, and transport of DOM. We collected surface water samples along transects in restored peat (organic‐rich, macrophyte‐dominated) and marl (carbonate, periphyton‐dominated) freshwater marshes in the Everglades (Florida, U.S.A.) that varied in environmental factors (water depth, phosphorus [P] concentrations [water, macrophytes, periphyton, and soil], and primary producer biomass) to understand drivers of dissolved organic carbon (DOC) concentrations and DOM composition. Higher water depths led to a “greening” of DOM, due to increasing algal contributions, with decreasing concentrations of DOC in peat wetlands, and a “browning” of DOM, due to increasing humic contributions, with increasing DOC concentrations in marl wetlands. Soil total P was positively correlated with DOC concentrations and microbial contributions to DOM in peat wetlands, and periphyton total P was positively correlated with algal contributions to DOM in marl wetlands. Despite large variations in both vegetation biomass and periphyton biovolume across transects and sites, neither were predictors of DOC concentrations or DOM composition. Hydrologic restoration differentially alters DOM in peat and marl marshes and interacts with nutrient enrichment to shift proportions of green and brown contributions to surface water chemistry, which has the potential to modify wetland food webs, as well as the processing of carbon by micro‐organisms.more » « less
