Blue Carbon and Darcy's Law: exploring the role of porewater transport in coastal carbon dynamics
Abstract
Tidal wetlands, with their daily-to-monthly three-dimensional advective flows and global distribution, are ideal to test the role of porewater transport in soil organic matter (SOM) stabilization. Improved observations and reaction models in upland soils show that microbial degradation of SOM is enhanced where advection supplies reactants, and is limited where diffusion dominates material exchange. This transport-limitation of SOM degradation, while described mostly for preferential flowpaths in well-drained soils, also occurs in saturated soils. Soil cores across tidal wetlands, globally, provide a strong case for a shift from advective processes to diffusive processes in soil cohorts as they age. Because organic particles contribute substantially to tidal wetland soil volume, SOM decomposition promotes soil compaction, which in turn, reduces advective porewater flows and thus reduces microbial activity. This sequence has depth and landscape implications for carbon cycling patterns in tidal wetland soils, which endure large hydrologic pulses and yet maintain globally similar carbon stocks for centuries to millenia. In addition to identifying a protection mechanism that supports a universal "protection paradigm" for SOM preservation across the soil-sediment continuum, the decomposition-protection feedback conceptual model can improve predictive modeling of carbon dynamics in tidal wetlands, and potentially other aquatic ecosystems. Geomorphic constraints on the specific terms in Darcy's Law (Equation 1; hydraulic head, path length, hydraulic conductivity as a function of permeability and porosity) may provide a new metric for predicting soil carbon stock vulnerability, carbon burial rates (accretion), lateral flux within estuaries, and methane emissions.
Equation 1 (Darcy's Law): Q = KA * (Dh/DL) Q = total discharge in m3/s K = hydraulic conductivity in m/s a = cross sectional areas of flow in m2 Dh = difference in hydraulic head in m DL = path length in m- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B43G2926W
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0428 Carbon cycling;
- BIOGEOSCIENCESDE: 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCESDE: 0442 Estuarine and nearshore processes;
- BIOGEOSCIENCES