Ecological parameter reductions, environmental regimes, and characteristic process diagram of carbon dioxide fluxes in coastal salt marshes

Khandker S Ishtiaq,Omar I Abdul-Aziz

doi:10.1038/s41598-020-72066-8

Abstract

We investigated the ecological parameter reductions (termed “similitudes”) and characteristic patterns of the net uptake fluxes of carbon dioxide (CO2) in coastal salt marshes using dimensional analysis method from fluid mechanics and hydraulic engineering. Data collected during May–October, 2013 from four salt marshes in Waquoit Bay and adjacent estuary, Massachusetts, USA were utilized to evaluate the theoretically-derived dimensionless flux and various ecological driver numbers. Two meaningful dimensionless groups were discovered as the light use efficiency number (LUE = CO2 normalized by photosynthetically active radiation) and the biogeochemical number (combination of soil temperature, porewater salinity, and atmospheric pressure). A semi-logarithmic plot of the dimensionless numbers indicated the emergence of a characteristic diagram represented by three distinct LUE regimes (high, transitional, and low). The high regime corresponded to the most favorable (high temperature and low salinity) condition for CO2 uptake, whereas the low regime represented an unfavorable condition (low temperature and high salinity). The analysis identified two environmental thresholds (soil temperature ~ 17 °C and salinity ~ 30 ppt), which dictated the regime transitions of CO2 uptake. The process diagram and critical thresholds provide important insights into the CO2 uptake potential of coastal wetlands in response to changes in key environmental drivers.

Highlights

Reduces the CO2 uptake rates and overall productivity in tidal wetlands by influencing the plants’ physiological responses to available light[11, 12]
Based sented on the existing salt marsh C O2 literature, uptake relative to the was termed the “light use efficiency” (LUE) number, which repreavailable sunlight (PAR)[42,43,44]
The nearly orthogonal (90°) orientations of LUE with these other environmental driver numbers indicated their lack of linkages with the C O2 flux number

Summary

Introduction

Reduces the CO2 uptake rates and overall productivity in tidal wetlands by influencing the plants’ physiological responses to available light[11, 12]. Similitude represents the parametric reduction of a physical system by developing independent dimensionless groups or pi (Π) numbers, which functionally defines the mechanistic process of the s ystem[18]. In “Moody Diagram”, seven original process variables of pipe flow were reduced to three process-based dimensionless groups using dimensional analysis, representing pipe friction and roughness across laminar, transitional, and turbulent flow regimes. This study tests a fundamental hypothesis that the net C O2 uptake fluxes in coastal salt marshes follow emergent ecological parameter reductions (i.e., similitudes) and distinct environmental regimes. The hypothesis was evaluated by formulating meaningful dimensionless numbers and defining different process regimes of salt marsh CO2 uptake fluxes, leading to a characteristics process diagram. The field data collected from four salt marshes on the southern shore of Cape Cod, MA, USA were used to examine the hypothesis

Methods

Results

Discussion

Conclusion