Date of Award

Fall 12-2017

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Aria Amirbahman

Second Committee Member

Aram Calhoun

Third Committee Member

Stephen Norton

Abstract

Vernal pools are small seasonal wetlands that are a common landscape feature that contribute to biodiversity in northeastern North American forests. However, even basic information about their biogeochemical functions, such as carbon cycling, is limited. Dissolved gas concentrations (CH4, CO2) and other water chemistry parameters were monitored weekly at the bottom and surface of four vernal pools in central and eastern Maine, USA, from April to August 2016. The vernal pools were supersaturated with respect to CH4 and CO2 at all sampling dates and locations. Concentrations of dissolved CH4 and CO2 ranged from 0.4 to 2.1´102 μmol L-1 and 72 to 2.3´103 μmol L-1, respectively. Evaporative fluxes of CH4 and CO2 into the atmosphere ranged from 0.2 to 73 mmol m-2 d-1, and 30 to 5.9´102 mmol m-2 d-1, respectively. During the study period, the vernal pools emitted between 0.1 to 5.8 kgC m-2 and 9.6 to 1.2´102 kgC m-2 of CH4 and CO2, respectively. This is a carbon export of up to 2.4×102 kgC, which is less than the estimated carbon leaf litter input. The production rates of CH4 and CO2 ranged from -2.4×10-2 to 6.6×10-1 and 4.0×10-1 to 4.6 gC m-2 d-1, respectively, and increased significantly over the season. Concentrations of CH4 and CO2 covaried with alkalinity, temperature, and dissolved oxygen. Our study pools were characterized by large concentrations and effluxes of CH4 and CO2 with respect to other permanently inundated wetlands, indicating vernal pools may be important contributors to the global carbon budget and are metabolically active sites.

In addition to dissolved gas concentrations, temperature, dissolved oxygen, pH, ortho-P, NO3-, NH4+, Cl-, SO42-, Na+, K+, Mg2+, Ca2+, DOC, alkalinity, chlorophyll a, speciated Al, speciated Fe, speciated Mn, and speciated Si were monitored from April to August 2016 to establish general temporal trends in pool biogeochemistry. The pH in the vernal pools generally decreased over the study period. Dissolved oxygen concentrations fluctuated throughout the season but were generally lower in benthic samples than in surface. The nutrients ortho-P and NH4+ increased over the study period. Concentrations of NO3- were low throughout the study period, indicating denitrification was occurring. Dissolved organic carbon concentrations and alkalinity both increased over the study period. Concentrations of Cl-, and Na+ decreased over the season. Concentrations of K+ increased over the season. Concentrations of the metals Al, Fe, and Mn increased over the study period. The pools in this study are diverse in their biogeochemistry, but do exhibit trends in their aquatic chemistry during the open water season. These data can be used as a jumping off point for future studies on vernal pool biogeochemistry.

Share