Sea level rise and sediment elevation dynamics in a hydrologically altered Puget Sound estuary

145 Pages·2016·1.52 MB·English

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WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship
2011
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Kara D. Kuhlman
Western Washington University
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Kuhlman, Kara D., "Sea level rise and sediment elevation dynamics in a hydrologically altered Puget Sound
estuary" (2011). WWU Graduate School Collection. 167.
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SEA LEVEL RISE AND SEDIMENT ELEVATION DYNAMICS
IN A HYDROLOGICALLY ALTERED
PUGET SOUND ESTUARY

By

Kara D. Kuhlman

Accepted in Partial Completion
Of the Requirements for the Degree
Master of Science

Moheb A. Ghali, Dean of the Graduate School

ADVISORY COMMITTEE

Chair, Dr. John M. Rybczyk

Dr. Andrew G. Bunn

Dr. Douglas A. Bulthuis
MASTER’S THESIS

In presenting this thesis in partial fulfillment of the requirements for a master’s degree at
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Kara Kuhlman

November 3, 2011
SEA LEVEL RISE AND SEDIMENT ELEVATION DYNAMICS
IN A HYDROLOGICALLY ALTERED
PUGET SOUND ESTUARY

A Thesis
Presented to
The Faculty of
Western Washington University

In Partial Fulfillment
Of the Requirements for the Degree
Master of Science

By
Kara D. Kuhlman
November 2011
iv

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 yrˉ¹, values ranged from -0.80
cm yrˉ¹ to 0.22 cm yrˉ¹. Accounting for surface elevation change, eustatic SLR (0.33 cm
yrˉ¹), and regional geologic uplift (0.09 cm yrˉ¹), I calculated a mean surface elevation deficit
of -0.46 ± 0.27 cm yrˉ¹. 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,
v

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.
vi

ACKNOWLEDGEMENTS
I would like to thank the following people and institutions whose generous support made this
project possible: my graduate advisor Dr. John Rybczyk for his thoughtful guidance and
unwavering support; my graduate research committee, Dr. Douglas Bulthuis and Dr. Andrew
Bunn, for their advice and encouragement; Sacha Maxwell, Richard Gwozdz, and Peter
Kairis for the invaluable contributions of their graduate research; Michael Hannam for
facilitating the elevation survey; staff at Huxley College of the Environment, Shannon Point
Marine Center, and the Padilla Bay National Estuarine Research Reserve who made
numerous and varied contributions. I would like to extend a special thanks to those who
participated in my field research: Kevin Hager, Kyle Hager, Tristan Currin, and Monte
Richardson.
vii

TABLE OF CONTENTS Page
ABSTRACT……………………………………………………………………………... iv
ACKNOWLEDGEMENTS……………………………………………………………... vi
LIST OF FIGURES AND TABLES…………………………………………………….. xi
1 INTRODUCTION………………………………………………………………. 1
1.1 Estuaries and seagrasses…………………………………………………. 1
1.1.1 Economic and ecological valuation of estuaries and seagrasses… 1
1.1.2 Anthropogenic impacts on estuaries and seagrasses…………….. 2
1.2 Estuarine surface elevation dynamics…………………………………… 6
1.2.1 Accretion, deterioration, and dynamic equilibrium……………... 6
1.2.2 Patterns in estuarine surface elevation change…………………... 8
1.3 Study area………………………………………………………………... 9
1.3.1 Puget Sound……………………………………………………… 9
1.3.2 Padilla Bay………………………………………………………. 9
1.3.3 Project history.....................................................………………... 13
1.4 Project scope and objectives…………………………………………….. 14
2 ESTUARINE SURFACE ELEVATION DYNAMICS………………………… 17
2.1 Introduction……………………………………………………………… 17
2.1.1 Estuarine surface elevation change……………………………… 17
2.1.2 Objectives………………………………………………………... 17
2.2 Methods………………………………………………………………….. 18
2.2.1 Elevation change………………………………………………… 18
viii

2.2.2 Sediment elevation table QA/QC………………………………... 22
2.2.3 Elevation…………………………………………………………. 22
2.2.4 Biomass………………………………………………………….. 23
2.2.5 Data analysis…………………………………………………….. 24
2.2.5.1 Rate of surface elevation change………………………… 24
2.2.5.2 Surface elevation deficit…………………………………. 24
2.2.5.3 Seasonal variance in surface elevation change………….. 25
2.2.5.4 Physical and biological variance in surface elevation
change…………………………………………………… 26
2.2.5.5 Statistical analysis……………………………………….. 26
2.3 Results…………………………………………………………………… 26
2.3.1 Rate of surface elevation change and surface elevation deficit….. 26
2.3.2 Seasonal variance in surface elevation change…………………. 30
2.3.3 Elevation…………………………………………………………. 32
2.3.4 Biomass………………………………………………………….. 33
2.3.5 Physical and biological variance in surface elevation change…... 35
2.4 Discussion……………………………………………………………….. 37
2.4.1 Surface elevation deficit and deteriorative processes…………… 37
2.4.2 Previous accretion studies……………………………………….. 38
2.4.3 Long-term surface elevation projections………………………… 39
2.4.4 Factors affecting elevation gain at site 8..……………………….. 39
2.4.5 Seasonal variance in surface elevation change………………….. 40
ix

2.4.6 Physical and biological variance in surface elevation change…... 42
3 SEDIMENT CHARACTERISTICS…………………………………………….. 45
3.1 Introduction……………………………………………………………… 45
3.1.1 Sediment characteristics in Padilla Bay…………………………. 45
3.1.2 Objectives………………………………………………………... 45
3.2 Methods………………………………………………………………….. 46
3.2.1 Sediment core collection………………………………………… 46
3.2.2 Sediment core processing………………………………………... 46
3.2.3 Data analysis…………………………………………………….. 48
3.3 Results…………………………………………………………………… 48
3.3.1 Sediment characteristics at each site…………………………….. 48
3.3.2 Bay-wide vertical profile of sediment characteristics…………… 50
3.4 Discussion……………………………………………………………….. 53
4 SCOUR CORRECTION……………………………………………………........ 54
4.1 Introduction……………………………………………………………… 54
4.1.1 What is scour?..………………………………………………...... 54
4.1.2 Observations of scour………………………………………......... 54
4.1.3 Objectives………………………………………………………... 56
4.2 Methods………………………………………………………………….. 56
4.3 Results…………………………………………………………………… 60
4.4 Discussion……………………………………………………………….. 62
5 CONCLUSIONS………………………………………………………………. 64