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Washington State University (2020)

Impacts of Varying Climate Conditions and Groundwater Accessibility on Semiarid Ecosystem Fluxes

Missik, Justine Emilia.

Titre : Impacts of Varying Climate Conditions and Groundwater Accessibility on Semiarid Ecosystem Fluxes

Auteur : Missik, Justine Emilia.

Université de soutenance  : Washington State University

Grade : Doctor of Philosophy (PhD) 2020

Résumé
Semiarid ecosystems are an important component of Earth’s carbon, water and energy budgets, and changes in hydroclimatic conditions could significantly alter fluxes of carbon, water, and energy over these ecosystems. This dissertation examines the impacts of meteorological and groundwater conditions on carbon, water, and energy fluxes over semiarid ecosystems. The first study used one year of eddy covariance data from paired upland and riparian sites to examine the impacts of groundwater availability on ecosystem fluxes. Despite being subjected to similar meteorological conditions, the two sites had distinct seasonal patterns of net ecosystem productivity (NEP) and evapotranspiration (ET). While NEP at the upland site was strongly constrained by water availability during the dry months, groundwater access sustained large NEP and ET at the riparian site during the dry months. The riparian site had larger annual gross primary productivity (GPP) than the upland site (612 versus 424 gC m-2 ), which was offset by higher ecosystem respiration (Reco, 558 versus 363 gC m-2 ). Thus, the upland site had larger annual NEP than the riparian site (62 versus 54 gC m-2 ). The second study used data from the same upland and riparian sites during two years with contrasting river flow conditions to examine the interactions among river stage conditions, meteorological drivers, and ecosystem fluxes. At the upland site, the mean latent heat flux (LE) during the dry season differed by less than 2% between the two years, but at the riparian site contrasting river flow conditions resulted in a 41% difference in peak monthly LE between the two years. The third study investigated the response of Reco to precipitation events and soil moisture conditions in semiarid ecosystems using soil chamber and eddy covariance measurements. Precipitation events triggered large pulses in soil respiration (Rsoil), and the temperature sensitivity of Rsoil was strongly controlled by soil moisture. These processes were captured by eddy covariance measurements of NEP, but not by partitioning algorithms for Reco. The results in this dissertation indicate that better representation of groundwater dynamics and respiratory processes in Earth system models would improve prediction of semiarid ecosystem fluxes under future climate conditions.

Présentation (ProQuest)

Page publiée le 20 mai 2021