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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.
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Responses by benthic invertebrate community composition to dissolved organic matter in lakes decline substantially above a threshold concentration
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.
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- Award ID(s):
- 2048031
- PAR ID:
- 10499032
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Freshwater Biology
- Volume:
- 69
- Issue:
- 2
- ISSN:
- 0046-5070
- Page Range / eLocation ID:
- 288 to 299
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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This dataset includes (1) original data from a dissolved organic carbon (DOC) incubation experiment and (2) a data synthesis of the DOC incubation experiment literature. Study component (1) was a factorial lab experiment crossing varying dissolved organic matter (DOM) sources (Suwannee River Fulvic Acid, Elliott soil leachate, Chlorella leachate) with varying microbial communities. The objective of this study component was to test the interacting effects of microbial community composition and DOM characteristics on carbon (C) biodegradation. We used a Micro-Oxymax Respirometer (Columbus Instruments, Columbus, Ohio) to measure carbon dioxide and oxygen accumulation at two hour intervals for a period of two weeks, and quantified the initial and final concentrations of dissolved organic carbon and total dissolved nitrogen of each experimental unit. To verify that the three DOM source solutions had differing chemical compositions and potential bioreactivity, we optically characterized each DOM source using mass spectra analysis and excitation-emission matrices (EEMs). Study component (2) is a synthesis of DOC concentrations from the C degradation experiment literature. The criteria for including a study in this synthesis was that (a) incubation DOM was sourced from a river, lake, marine, estuary, or marsh, and (b) that C concentrations were measured at least twice throughout the incubation in addition to an initial measurement. For each study, we extracted initial DOC values, elapsed incubation time, and reported DOC concentrations during the incubation period for each experimental treatment. This data package is completed.more » « less
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Abstract Coastal ecosystems are rapidly shifting due to changes in hydrologic presses (e.g., sea‐level rise) and pulses (e.g., seasonal hydrology, disturbances, and restoration of degraded wetlands). Changing water levels and sources are master variables in coastal wetlands that can alter carbon concentrations, sources, processing, and export. Yet, how long‐term increases in water levels from marine and freshwater sources influence dissolved organic carbon (DOC) concentrations and dissolved organic matter (DOM) composition is uncertain. We quantified how long‐term changes in water levels are affecting DOC concentration (2001–2021) and DOM composition (2011–2021) differently across the Florida Everglades. DOC concentrations decreased with high water depths in peat marshes and increased with high water levels in marl marshes and across mangroves, and these relationships were reproduced in freshwater peat marshes and shrub mangroves. In the highly productive riverine mangroves, cross‐wavelet analysis highlighted variable relationships between DOC and water level were largely modulated by hurricane disturbances. By comparing relationships between water level and DOC concentrations with carbon sources from DOM fluorescence indices, we found that changing water sources between the dry and wet season shift DOM from algal to detrital sources in freshwater marshes, from detrital marsh to detrital mangrove sources in the brackish water ecotone, and from detrital mangrove to algal marine sources in downstream mangroves. As climate change and anthropogenic drivers continue to alter water levels in coastal wetlands, integrating spatial and temporal measurements of DOC concentrations and DOM compositions is essential to better constrain the transformation and export of carbon across these coastal ecosystems.more » « less
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/fwb.14211
