Public Abstract

DE-SC0020309: Particulate Organic Matter (POM) Transport and Transformation at the Terrestrial-Aquatic Interface

Award Status: Expired

Institution: Board of Regents of the University of Wisconsin System, operating as University of Wisconsin-Madison, Madison, WI
UEI: LCLSJAGTNZQ7
DUNS: 161202122

Most Recent Award Date: 09/07/2022
Number of Support Periods: 3
PM: Swain, Amy

Current Budget Period: 09/15/2021 - 09/14/2023
Current Project Period: 09/15/2019 - 09/14/2023
PI: Ginder-Vogel, Matthew

Supplement Budget Period: N/A

Public Abstract

This project deals with the input and metabolism of particulate organic matter (POM) in near-surface riverbed sediments at the PNNL SFA Hanford 300 Area study site, where large fluctuations in water stage drive periodic fluid flow into or out of the hyporheic zone. It is increasingly recognized that rates of biogeochemical activity in riverbed sediments are much higher compared to those in the water column. This occurs because the concentrations of organic matter and associated microorganisms are several orders of magnitude higher than the corresponding concentrations in the water column. Thus, the riverbed represents a hot spot of biogeochemical cycling at the terrestrial-aquatic interface. Although in-river processing of organic matter and nutrients has been extensively studied, a comprehensive literature search reveals a paucity of information on the deposition, transport and processing of particulate organic matter into riverbed sediments, particularly in large river ecosystems. Such POM input has the potential to strongly impact the biogeochemistry of both the river itself as well as the hyporheic zone (or, more broadly, the hyporheic corridor) that is connected hydrologically to the river. Such dynamics have fundamental implications for organic carbon metabolism as well as retention and/or release of other nutrients (e.g., N, P) associated with POM decomposition. This application builds on a previously funded proposal entitled “Exploratory Research: Transport and Transformation of Particulate Organic Matter (POM) in Permeable Riverbed Sediments”, as well as prior PNNL SFA funded research at UW-Madison. The primary goal of these studies was to lay the foundation for future studies characterizing biogeochemical processes associated with POM accumulation and degradation in permeable riverbed sediments within the Hanford Reach of the Columbia River. Our experimental and modelling results revealed that POM does indeed accumulate in simulated riverbed sediment columns through a variety of velocity dependent mechanisms, including filtration, sorption to sediment, and sorption to previously retained POM. Additionally, upon flow reversal, POM can be readily mobilized leading to effluent concentrations above the initial input concentrations. The central hypothesis of our project is that advective introduction of POM into permeable riverbed sediments will result in its accumulation to levels much higher than the input concentration, which in turn will drive relatively rapid rates of microbial carbon and nutrient (N) metabolism. Additionally, we hypothesize that POM degradation may result in the export DOC and/or inorganic nitrogen into the underlying hyporheic zone. The following project objectives are based upon these hypotheses and will allow development of a quantitative model POM accumulation, transport, and metabolism that can be utilized in future studies, and in due course incorporated into the suite of modeling tools being developed within the PNNL SFA. (1): Investigate in situ POM dynamics and riverbed porewater chemistry (led by UW-Wisconsin in collaboration with PNNL SFA personnel); (2): Determine fresh POM degradation and transport parameters (led by U-Wisconsin). (3): Conduct large, flow-through sediment column experiments to gain insight into in situ riverbed POM processing (led by the Ecohydrology research group at U-Waterloo). (4): Develop reactive transport models of POM transport and metabolism in riverbed sediments (collaboration between U-Waterloo and U-Wisconsin). The proposed research directly addresses priority research objectives related to the need to quantify and predict how hydrology drives fine-scale biogeochemical processes in surface-subsurface systems, as well as quantifying how biological, abiotic-biotic interactions and molecular transformations control the mobility of nutrients and critical biogeochemical elements. Additionally, the proposed research will develop computational models that will aid in translating biogeochemical behavior across scales to predict flows of water, carbon, and nutrients in large river hyporheic corridors. These models will also in due course be useful in quantifying and predicting watershed responses to natural and anthropogenic perturbations and shifts to new states and translating predictive understanding of watershed system function and evolution into near- and long-term environmental and energy strategies.

This project deals with the input and metabolism of particulate organic matter (POM) in near-surface riverbed sediments at the PNNL SFA Hanford 300 Area study site, where large fluctuations in water stage drive periodic fluid flow into or out of the hyporheic zone. It is increasingly recognized that rates of biogeochemical activity in riverbed sediments are much higher compared to those in the water column. This occurs because the concentrations of organic matter and associated microorganisms are several orders of magnitude higher than the corresponding concentrations in the water column. Thus, the riverbed represents a hot spot of biogeochemical cycling at the terrestrial-aquatic interface. Although in-river processing of organic matter and nutrients has been extensively studied, a comprehensive literature search reveals a paucity of information on the deposition, transport and processing of particulate organic matter into riverbed sediments, particularly in large river ecosystems. Such POM input has the potential to strongly impact the biogeochemistry of both the river itself as well as the hyporheic zone (or, more broadly, the hyporheic corridor) that is connected hydrologically to the river. Such dynamics have fundamental implications for organic carbon metabolism as well as retention and/or release of other nutrients (e.g., N, P) associated with POM decomposition.

This application builds on a previously funded proposal entitled “Exploratory Research: Transport and Transformation of Particulate Organic Matter (POM) in Permeable Riverbed Sediments”, as well as prior PNNL SFA funded research at UW-Madison. The primary goal of these studies was to lay the foundation for future studies characterizing biogeochemical processes associated with POM accumulation and degradation in permeable riverbed sediments within the Hanford Reach of the Columbia River. Our experimental and modelling results revealed that POM does indeed accumulate in simulated riverbed sediment columns through a variety of velocity dependent mechanisms, including filtration, sorption to sediment, and sorption to previously retained POM. Additionally, upon flow reversal, POM can be readily mobilized leading to effluent concentrations above the initial input concentrations.

The central hypothesis of our project is that advective introduction of POM into permeable riverbed sediments will result in its accumulation to levels much higher than the input concentration, which in turn will drive relatively rapid rates of microbial carbon and nutrient (N) metabolism. Additionally, we hypothesize that POM degradation may result in the export DOC and/or inorganic nitrogen into the underlying hyporheic zone. The following project objectives are based upon these hypotheses and will allow development of a quantitative model POM accumulation, transport, and metabolism that can be utilized in future studies, and in due course incorporated into the suite of modeling tools being developed within the PNNL SFA. (1): Investigate in situ POM dynamics and riverbed porewater chemistry (led by UW-Wisconsin in collaboration with PNNL SFA personnel); (2): Determine fresh POM degradation and transport parameters (led by U-Wisconsin). (3): Conduct large, flow-through sediment column experiments to gain insight into in situ riverbed POM processing (led by the Ecohydrology research group at U-Waterloo). (4): Develop reactive transport models of POM transport and metabolism in riverbed sediments (collaboration between U-Waterloo and U-Wisconsin).

The proposed research directly addresses priority research objectives related to the need to quantify and predict how hydrology drives fine-scale biogeochemical processes in surface-subsurface systems, as well as quantifying how biological, abiotic-biotic interactions and molecular transformations control the mobility of nutrients and critical biogeochemical elements. Additionally, the proposed research will develop computational models that will aid in translating biogeochemical behavior across scales to predict flows of water, carbon, and nutrients in large river hyporheic corridors. These models will also in due course be useful in quantifying and predicting watershed responses to natural and anthropogenic perturbations and shifts to new states and translating predictive understanding of watershed system function and evolution into near- and long-term environmental and energy strategies.