Understanding transport and mixing processes to mitigate detrimental effects of algal blooms in a

119 Pages·2014·4.2 MB·English

Understanding transport and mixing
processes to mitigate detrimental effects of
algal blooms in a large shallow estuary

Cristina Perbelini Silva

B.Eng. (Hons.) (Agricultural Engineering)
Centro de Ciências Agrarias,
Universidade Federal de São Carlos, São Carlos - SP, Brazil

This thesis is presented for the degree of
Doctor of Philosophy of
The University of Western Australia

Centre for Water Research
May 2014
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Abstract

High biomass algal blooms tend to occur when transport and mixing time scales
exceed phytoplankton growth time scale, resulting in many detrimental effects to the
ecosystem and possibly to humans. In order to implement appropriate management
strategies to overcome the nuisance of such blooms, it is essential to study the
hydrodynamic mechanisms influencing horizontal transport and mixing rates that in
turn determine locations conducive to excessive phytoplankton growth.
An integrated approach consisting of a theoretical method, a field experiment,
historical data and three-dimensional hydrodynamic and ecological modeling was used
to understand the physical processes affecting high biomass blooms of the diatom
Aulacoseira sp. in the shallow upper Río de la Plata estuary (Argentina-Uruguay). Two
high biomass blooms events impacted the drinking water treatment plants of the city of
Buenos Aires (Argentina) causing a disruption to normal operation of the plants and
risked the drinking water supply to more than 10 million people.
Firstly, it was shown that the shallow nature of the estuary tends to direct the
flow towards the deeper shipping channels, creating stagnation zones near the
Argentinean boundary. Energy levels available for mixing were higher near the
Uruguayan boundary and center of the estuary than in the stagnant region along the
Argentinean margin. High discharge regimes were shown to also intensify mixing, as
opposed to periods of low inflow rates.
Secondly, it was demonstrated that these stagnation zones, combined with the
transport of algae cells from contributing inflows, and low concentrations of suspended
solids in the water column were the main drivers for the occurrence of two high biomass
bloom events.
Finally, three mitigation strategies were explored to decrease the effects of high
biomass algae blooms on the drinking water intakes. An automated real-time and
forecast management system was successfully implemented in the Río de la Plata
estuary to monitor and predict the occurrence of Aulacoseira sp. near the drinking water
intakes. Two engineering solutions were proposed and the results demonstrated that
extending the drinking water intakes further offshore or placing groynes near the
drinking water intakes would decrease the concentration of Aulacoseira sp. by up to 50
% and 40 % respectively.

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Table of Contents

ABSTRACT .................................................................................................................................... III
ACKNOWLEDGEMENTS ............................................................................................................. IX
PREFACE ......................................................................................................................................... XI
CHAPTER 1. INTRODUCTION ................................................................................................... 1
1.1 MOTIVATION .............................................................................................................................................. 1
1.2 OVERVIEW .................................................................................................................................................. 2
CHAPTER 2. HORIZONTAL TRANSPORT, MIXING AND RETENTION IN A LARGE,
SHALLOW ESTUARY: RÍO DE LA PLATA ............................................................................... 5
2.1 ABSTRACT ................................................................................................................................................... 5
2.2 INTRODUCTION .......................................................................................................................................... 5
2.3 THE INFLUENCE ON THE FLOW OF A SLOPING BOTTOM IN A SHALLOW DOMAIN ............................ 9
2.4 METHODS ................................................................................................................................................. 13

2.4.1 Study site .................................................................................................................................................... 13

2.4.2 Field data .................................................................................................................................................... 14

2.4.3 Hydrodynamic model ............................................................................................................................ 16

2.4.4 Model set up .............................................................................................................................................. 16

2.4.5 Horizontal dispersion analyses ........................................................................................................ 18
2.5 RESULTS ................................................................................................................................................... 19

2.5.1 Model validation ..................................................................................................................................... 19

2.5.2 Transport and dispersion ................................................................................................................... 25
2.6 DISCUSSION AND CONCLUSIONS ........................................................................................................... 32
CHAPTER 3. PHYSICAL AND BIOLOGICAL CONTROLS OF ALGAL BLOOMS IN THE
RÍO DE LA PLATA ....................................................................................................................... 37
3.1 ABSTRACT ................................................................................................................................................ 37
3.2 INTRODUCTION ....................................................................................................................................... 37

3.2.1 The Río de la Plata system .................................................................................................................. 39
3.3 METHODS ................................................................................................................................................. 41

3.3.1 Study site description ............................................................................................................................ 41

3.3.2 Model description ................................................................................................................................... 42

3.3.3 Model configuration .............................................................................................................................. 43

3.3.4 Model bathymetry .................................................................................................................................. 44

3.3.5 Meteorological forcing ......................................................................................................................... 46

3.3.6 Inflows and open boundary conditions ........................................................................................ 46
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3.3.7 Initial conditions ..................................................................................................................................... 51

3.3.8 Validation data ........................................................................................................................................ 51
3.4 MODEL RESULTS..................................................................................................................................... 51

3.4.1 ELCOM validation ................................................................................................................................... 51

3.4.2 Mild biomass bloom (2006-2007) ................................................................................................... 53

3.4.3 High biomass bloom (2007-2008) .................................................................................................. 55

3.4.4 No bloom (2009-2010) ......................................................................................................................... 58

3.4.5 Sensitivity Analysis ................................................................................................................................. 62

3.4.6 Horizontal variation .............................................................................................................................. 63
3.5 DISCUSSION ............................................................................................................................................. 65
CHAPTER 4. MITIGATING THE EFFECTS OF HIGH BIOMASS ALGAL BLOOMS AT
THE DRINKING WATER INTAKES OF THE CITY OF BUENOS AIRES, ARGENTINA 73
4.1 ABSTRACT ................................................................................................................................................ 73
4.2 INTRODUCTION ....................................................................................................................................... 73

4.2.1 Río de la Plata........................................................................................................................................... 75

4.2.2 Buenos Aires drinking water system .............................................................................................. 77
4.3 METHODOLOGY ....................................................................................................................................... 77

4.3.1 Numerical models ................................................................................................................................... 77
4.3.2 Aquatic Real-time Management System (ARMS) and Real-time Management

System Online (RMSO) ..................................................................................................................................... 78

4.3.3 ELCOM-CAEDYM configuration ....................................................................................................... 82
4.4 MITIGATION OPTIONS ............................................................................................................................ 85

4.4.1 Real-time and forecast management system ............................................................................. 85

4.4.3 Modifying flushing time ....................................................................................................................... 90
4.5 DISCUSSION ............................................................................................................................................. 93
CHAPTER 5. CONCLUSIONS .................................................................................................... 95
5.1 SUMMARY ................................................................................................................................................. 95
5.2 RECOMMENDATION FOR FUTURE WORK ............................................................................................ 96
REFERENCES ................................................................................................................................ 99

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To my mum Dirce and my dad Aecio,
for everything you have taught me.
To my brother Alex and my nephew Gabriel.
To my Royden.

Para minha Mãe e meu Pai
Meu irmão Alex e meu sobrinho Gabriel.
Mesmo longe,
nunca deixo de pensar
em vocês.

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Acknowledgements

I would like to thank my coordinating supervisor, Professor Jörg Imberger, for
believing in me since the beginning even though I barely spoke any English. Jörg and
his wife Barbara were patrons of the restaurant I used to work at as a waitress and after
a few discussions and a review of my CV he invited me to join his team. Now, here I
am finishing my PhD and this work would not be possible without Jörg’s
encouragement, inspiration, enthusiasm, guidance and support. Jörg has the talent to
explain complicated concepts in the most simplified way, through using day-to-day
examples, which was crucial for my understanding of fluid mechanics.
I also would like to extend my many thanks to my co-supervisor, Associate
Professor Clelia L. Marti, for her dedication, patience and guidance throughout the
course of my PhD. Clelia’s role was essential for the completion of this work and she
has been an amazing supervisor since the beginning. Thank you for giving me a minute
every time I knocked on your door (and these were MANY).
The support of the CWR Field Operations group, Greg Attwater, Roger Head
and Carol Lam was essential for the execution of the fieldwork in Argentina. I am also
very grateful for the contribution provided by Lee Goodyear from CWR, and
Christopher Dallimore from Hydronumerics. The help received from Angus Stewart is
also acknowledged. I would also like to thank Dr. Gabriel Raggio and Dr. Fabian Lopez
for providing support regarding logistics and data collection in Argentina.
Data for this study was provided by a number of institutions: Aguas y
Saneamientos Argentinos (AySA), Servicio de Hidrografia Naval - Argentina (SHN),
Servicio Meteorológico Nacional - Argentina (SMN), Subsecretaria de Puertos y Vias
Navegables - Argentina (SPVN), and Compañía Administradora del Mercado Mayorista
Eléctrico Sociedad Anónima (CAMMESA). A special thank you to Maria de la Plaz
from AySA, Enrique D’Onofrio from SHN and Arnoldo Valle Levinson for providing
bathymetric data. During the course of this work I was a recipient of the Scholarship for
International Research Fees from the University of Western Australia, the University
Postgraduate Award and a CWR ad-hoc scholarship. I also would like to acknowledge
the financial support from Jörg and Barbara Imberger received at some stage of my
PhD.
My experience at CWR would not had been as much fun if it wasn’t for all my
fellow students, CWR staff members and CWR visitors. I have met many special people
that contributed to what I have become, personally and professionally. A huge and
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special thank you to my closest and dearest friend Leticia Vilhena, who was always
there for me, I know I can trust you and count on you at any time, and I am grateful for
your sincere friendship, support, and for the fun times. I also would like to thank you
for your suggestions to improve Chapter 3 of this thesis.
I am extremely grateful to Sandy Ng for all the MATLAB tricks she has taught
me, to Ryan Alexander for his contribution during the fieldwork in Argentina and for
his insights about ecology, and to Daniel Machado for the very helpful discussions.
Thank you to Andrea Papparini and Mathew Hipsey for guidance during the time I was
working at CWR. Dear Zhenlin Zang, I am very grateful for the many times you have
helped me, including during an Easter Sunday, you were my dearest officemate and I
will not forget the support you have given me.
Thank you to all the personal friends I made at UWA, for making me laugh and
making my social life more interesting - Ria Kristiana, Loretta Scolaro, Ingrid Jaffari,
Mark Andrich, Andrea Curatolo, Roberta Fornarelli, Cibele Gaido, and Blake Kylen.
Thank you also to the CWR bench crew, Askale Abebe and Jacqui Da-Gama, for their
friendship and support. Thank you to the nerdy volleyball team that I am part of, with
you guys I was able to win the first sports medal in my life – Go Shear Force! Also
thanks to all the good friends I made in Perth, for their encouragement and support.
Most importantly, thanks to my parents, Dirce and Aécio, for their love,
dedication and encouragement. They worked extremely hard so I could receive the
education they always dreamed of. Thank you to my brother, Alex and my aunties Sirlei
and Tania, for looking after my parents while I was not there. Finally, to my wonderful
partner Royden Monteiro, for his love, patience, understanding, personal and financial
support, and companionship since the beginning.

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