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Date Permissions Signed

11-3-2011

Date of Award

2011

Document Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Environmental Sciences

First Advisor

Rybczyk, John M.

Second Advisor

Bunn, Andrew Godard

Third Advisor

Bulthuis, Douglas A.

Abstract

As sea level rise (SLR) accelerates in response to climate change, coastal wetlands must accrete vertically to prevent submergence and habitat loss. Padilla Bay, an estuary in the Puget Sound containing an expansive eelgrass meadow, has been hydrologically altered such that insufficient sedimentation may now prevent vertical accretion, potentially affecting the long-term survival of the eelgrass meadow. The objective of this study was to quantify trends in surface elevation change throughout Padilla Bay. To this end, our research group monitored surface elevation change at 19 sites from 2002-2010 using sediment elevation tables (SET's). Additionally, I explored potential ecogeomorphic relationships between surface elevation change and selected physical (elevation, sediment characteristics) and biological (eelgrass biomass) variables. Only 1 of 19 study sites exhibited significant surface elevation gain, whereas, 9 sites exhibited significant elevation loss. The mean rate of surface elevation change throughout Padilla Bay was -0.22 ± 0.27 cm yr-¹, values ranged from -0.80 cm yr-¹ to 0.22 cm yr-¹. Accounting for surface elevation change, eustatic SLR (0.33 cm yr-¹), and regional geologic uplift (0.09 cm yr-¹), I calculated a mean surface elevation deficit of -0.46 ± 0.27 cm yr-¹. These findings indicate that surface elevation change in Padilla Bay is not keeping pace with the current rate of SLR. A negative relationship between surface elevation change and elevation, and a positive relationship between surface elevation change and eelgrass biomass were apparent, although correlations were non-significant. There was a significant negative correlation between elevation and eelgrass biomass. Surface elevation change did not correlate with the sediment properties measured (bulk density, mineral matter, organic matter). Although some ecogeomorphic patterns were detected, relationships remained indistinct and require further study. Sediment scour, induced by the SET benchmark, was observed at several SET sites in Padilla Bay, particularly un-vegetated and high elevation sites. Addressing potential bias introduced by sediment scour required a supplementary analysis providing both a detailed description of scour and the development of an analytical method for removing scour bias. This assessment provided a precise determination of when scour began to impact the SET data, indicated a specific location for truncating impacted datasets, and allowed scour bias in surface elevation change measurements to be removed. Scour was an unforeseen and undocumented byproduct of surface elevation monitoring, this study provides the first indication that alternative SET designs are necessary for use in macro-tidal mudflat habitats.

Type

Text

Publisher

Western Washington University

OCLC Number

761319517

Digital Format

application/pdf

Geographic Coverage

Padilla Bay (Wash.)

Genre/Form

Academic theses

Language

English

Rights

Copying of this thesis in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.

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