Carbon fixed by plants in soft tissues is nearly quantitatively released back to the atmosphere in a matter of years, and yet the paths, processes, and timelines by which leafy organic matter (OM) is eventually remineralized has a profound impact on the biosphere, including soils, water, and biota. Organic matter leached from soft tissues contributes to soil OM and fertility, enters water bodies and shapes the light field, fuels microbial foodwebs, exerts strong controls on photochemistry, and functions as the electron donor in countless redox reactions. Release of nutrients drives fertility in soils, spurs primary productivity in waters, fuels denitrification in combination with released organic matter, and functions as an electron acceptor in countless redox reactions in anoxic environments. In this session, we invite primary research that quantifies the breakdown and loss of OM and nutrients from leaves, needles, and grasses as well as more persistent barks and woods through a variety of natural processes, and investigates the processes and fates of these released materials throughout the biosphere. We also welcome secondary analyses of existing literature that defines or clarifies conceptual models. Submissions to this session are great candidates for a special issue in the Journal of Geophysical Research - Biogeosciences with the same title as this session. In addition to process-based studies, we are also interested in the topic of how to conduct simple laboratory leaching and incubation experiments that are still relevant to complex environmental systems.
Lead Organizer: Peter Hernes, University of California, Davis (pjhernes@ucdavis.edu)
Co-organizers:
Juliana D'Andrilli, University of North Texas (juliana.d'andrilli@unt.edu)
Klaus Kaiser, Martin Luther University Halle-Wittenberg (klaus.kaiser@landw.uni-halle.de)
Presentations
09:00 AM
ORGANIC MATTER IN LEAF LITTER LEACHATE IMPACTS CYANOBACTERIAL BLOOMS BOTH POSITIVELY AND NEGATIVELY (9093)
Primary Presenter: Michele Burford, griffith university (M.Burford@griffith.edu.au)
Much of our understanding of the links between biogeochemical processes and freshwater cyanobacterial blooms has focussed on nutrient concentrations and loads. However, the impact of other terrestrial compounds on cyanobacterial growth is less well studied. Our research focussed on characterizing tDOM and determining the effect of tDOM leachate from leaf litter and terrestrial soil on growth of a toxic cyanobacterial species. Chemical studies, Using 1H-NMR, showed that the leachate contained a complex mixture of dissolved organic compounds, with the amino acid, proline, as well as gallic acid and polyphenols had the greatest inhibitory effect on cyanobacterial photosynthesis. In a mesocosm study, the concentration of leaf leachate additions impacted the scale of suppression of a toxic cyanobacterial bloom. Light availability was not the primary driver. By contrast, at lower concentrations, leachate from soil and leaves were shown to stimulate growth of algae, either directly from increased dissolved inorganic nutrient concentrations, or indirectly via microbially-mediated transformation of organic nutrients into inorganic nutrients. Our research shows the important role that tDOM plays in freshwater systems, both directly on cyanobacterial growth, and indirectly via the impact on the microbial community. With DOM concentrations increasing globally, the ultimate impact on the ecosystem health of freshwaters warrants further investigation.
09:15 AM
VARIABILITY IN DISSOLVED ORGANIC MATTER ACROSS SOURCES WITHIN FORESTED WETLANDS OF THE SOUTHEASTERN COASTAL PLAIN (8856)
Primary Presenter: Cameron Stacey, Texas A&M University (cameron.a.stacey@gmail.com)
Forested wetlands as headwaters for organic-rich ‘blackwater’ rivers. The sources of carbon in these areas generating the intense blackwater color are poorly resolved. A study conducted from May to late July 2024 examined the optical characteristics (absorbance) and DOC content of throughfall, surface water, groundwater, and soil leachate of wetlands on Hobcaw Barony (South Carolina Coastline). To highlight DOC differences between forests, 4 sites were chosen: two upland forests, one dominated by long-leaf pine (Pinus palustris) and the other by laurel oak (Quercus laurifolia), and two forested wetlands, one dominated by swamp cypress (Taxodium distichum) and the other by swamp tupelo (Nyssa biflora). DOC concentration and variability of throughfall was considerable (2-45 mg/L), but there was no significant DOC concentration difference in throughfall between tree species. Surface and groundwater were enriched with DOC (avg 24 mg/L and 74 mg/L, respectively), were variable over time and significantly different between sites. This suggests seasonality and unresolved mechanisms controlling DOC concentration between forest sites. Carbon-specific absorbance values (SUVA₂₅₄) of surface water (avg 10.3) were significantly higher than throughfall (avg 4.4), groundwater (avg 5.8), and soil leachate (avg 4.5), indicating processes alter the source’s DOC characteristic once it enters surface water. Results suggest forested wetlands contribute large volumes of colored carbon to the watershed, and further testing should examine degradation mechanisms altering carbon sources properties.
09:30 AM
From Canopies to Creeks: Chasing Dissolved Organic Matter Through the Storm with High Resolution Mass Spectrometry (9549)
Primary Presenter: Hollis Harrington, SUNY ESF (hcharrin@syr.edu)
Throughfall dissolved organic matter (DOM) is an important, yet understudied, component of forest organic matter dynamics. Previous studies have focused primarily on bulk DOM characteristics, such as DOM concentrations and optical properties, with few studies exploring the detailed chemical composition of throughfall DOM. Moreover, previous researchers have often limited their scope to bulk precipitation samples on a per storm basis. No known research has examined intra-storm variations in throughfall DOM composition at the molecular level. To address this gap, the presented study analyzes intra-storm variations in throughfall DOM via high-frequency sampling during a precipitation event. Stream and throughfall samples were collected over 36 hours at the Arbutus Pond inlet, a long-term ecological monitoring site in the Adirondack region of New York State. Dissolved organic carbon and total nitrogen concentrations were obtained for each sample, along with excitation-emission matrix spectra, and single and tandem mass spectrometry analyses using HPLC-Orbitrap. The resulting analysis yielded molecular formula assignments for thousands of masses in both stream and throughfall DOM. Temporal dynamics in DOM composition highlight the importance of intra-storm analyses of throughfall DOM. Additionally, the presence of throughfall DOM in streams was examined to identify potential tracers for DOM transport from canopies to streams during precipitation events. This work lays the foundation for future intra-storm molecular characterization studies of throughfall DOM.
09:45 AM
POLLEN MINERALIZATION RATES: IS POLLEN A SUBSTANTIAL SOURCE OF CARBON AND NUTRIENTS INTO THE LAURENTIAN GREAT LAKES? (9215)
Primary Presenter: Jake Zunker, University of Minnesota Duluth (zunke018@d.umn.edu)
Pollen is a ubiquitous particulate regarded as recalcitrant organic matter (OM) in aquatic environments, seasonally introducing undetermined quantities of terrigenous OM to inland lakes, a fraction of which survives water column settling and sediment burial. Carbon (C) and nutrients have been shown to rapidly leach from pollen after aquatic deposition, ranging from a few days to weeks, with upwards of 50% carbon by weight leached into surrounding waters. The role of pollen as a carbon and nutrient delivery mechanism for Laurentian Great Lake (LGL) Superior has not been explored. Our recent study, as a part of the Great Lakes Sediment Surveillance Project, suggests that conifer pollen accounts for delivery of up to 0.19 Tg C to LGL Superior sediments annually. In this study, we examined the effects of pollen mineralization on organic C and nutrient availability in waters of LGL Superior to evaluate its potential as an unquantified perennial source of C, nitrogen (N), and phosphorus (P). Pollen standards were added to water collected from LGL Superior, incubated for up to 30 days, and measured for dissolved and particulate fractions of C, N, and P. Preliminary results show a 33% increase in dissolved organic carbon concentration within the first week of incubation, with subsequent nine-fold and two-fold increases in ammonium and phosphate concentrations, respectively. These results suggest pollen contains a labile fraction of OM that is a substantial source of C, N, and P that must be integrated into nutrient budgets of LGL Superior and, more broadly, low nutrient lakes.
10:00 AM
BLACK CARBON AND MOLECULAR COMPOSITION OF THROUGHFALL DISSOLVED ORGANIC MATTER FROM 36 TREE SPECIES IN AN URBAN FOREST (9334)
Primary Presenter: Patrick Milne, Northeastern University (milne.pa@northeastern.edu)
Most rain that falls on land is intercepted by a tree canopy, making leaves the first source of dissolved organic matter (DOM) to this water, which mainly drips to the ground as throughfall. While throughfall has been well studied in rural forests, less research has focused on the throughfall of urban trees. This study collected throughfall samples from thirty-six tree species on Northeastern University’s urban campus arboretum in Boston, Massachusetts. The DOM was solid phase extracted and analyzed via Fourier transform ion cyclotron resonance mass spectrometry to define molecular composition and also analyzed for the amount and composition of black carbon using high pressure liquid chromatography. How throughfall black carbon and molecular composition vary with tree species and aspects of the urban environment (e.g., proximity to roads and buildings) are explored. Since some throughfall components are readily consumed by microorganisms, while others, including black carbon, can be stable in the environment for millennia, results will enlighten the downstream effects of trees on urban carbon cycling and water quality. This will enable stakeholders to manage tree planting and maintenance, runoff management, and water quality protection in ways that account for the impacts of trees on the urban environment.
SS23 - What Leaves Leave When Leaves Leave Trees?
Description
Time: 9:00 AM
Date: 29/3/2025
Room: W201CD