Hydrological Changes and Estuarine Dynamics

101 Pages·2013·3.51 MB·English

by  Paul A. Montagna, Terence A. Palmer, Jennifer Beseres Pollack (auth.)

SpringerBriefs in Environmental Science
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Paul A. Montagna · Terence A. Palmer
Jennifer Beseres Pollack
Hydrological Changes
and Estuarine Dynamics
1 3
Paul A. Montagna Jennifer Beseres Pollack
Harte Research Institute Life Sciences Department
Texas A&M University-Corpus Christi Texas A&M University-Corpus Christi
Corpus Christi Corpus Christi
TX, USA TX, USA
Terence A. Palmer
Harte Research Institute
Texas A&M University-Corpus Christi
Corpus Christi
TX, USA
ISSN 2191-5547 ISSN 2191-5555 (electronic)
ISBN 978-1-4614-5832-6 ISBN 978-1-4614-5833-3 (eBook)
DOI 10.1007/978-1-4614-5833-3
Springer New York Heidelberg Dordrecht London
Library of Congress Control Number: 2012950862
© The Author(s) 2013
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Abstract
Nothing is more fundamental to an estuary than the mixing of fresh and salt water,
but there has been explosive growth in water diversions for human needs since the
middle of the twentieth century. Today more than 60 % of all runoff on Earth is
captured, thus water development projects where dams and diversions have been
built have altered the environmental flow landscapes. In fact, there is currently
more water in reservoirs than natural lakes and rivers.
Estuaries are the most productive environments on Earth, and this is in part due
to freshwater inflow from rivers to the coast. The freshwater dilutes marine water
and transports nutrients and sediments to the coast. Estuaries are characterized
by salinity and nutrient gradients, which are important in regulating nearly
all e cological and biological processes in estuaries. Sediment is important for
b uilding habitats and balancing erosive forces. However, hydrological patterns are
being altered as flow is diverted for human use, and this is reducing flows to the
coast in all parts of the developed world. A review of available research shows
that this reduction of freshwater flow leads to increased salinities, but in contrast
reduced nutrient and sediment loading; and that these alterations are having
p rofound effects on coastal resources, particularly for estuarine dependent species.
However, there are still many research gaps, and in particular estuaries r epresent
a continuum, so it is very difficult to identify freshwater needs to maintain
e cosystem services.
While many countries have water quality programs, few have policies or
r egulations that protect water quantity alterations. So, while pollution has gener-
ally decreased since the first environmental laws of the 1970s, habitats have been
degraded in part because of alterations in hydrological regimes. Where there are
laws or rules to protect riverine or estuarine habitats, it is very difficult to identify
how much instream flow is needed for a river to function like a river, or how much
inflow is needed to maintain the characteristics of the estuary that make up the
estuarine signature unique to each estuary. Inflow needs studies generally follow a
sequence of steps. The first step is to define the natural and historical flow regimes
and how the rivers have contributed to salinity zonation in the estuaries. The
s econd step is to define the marine biological resources to be protected, and
the water quality conditions those resources require to thrive. The third step
is to determine the flow regimes needed to maintain the desired water quality
v
vi Abstract
conditions. Using this approach it is possible to identify flow regimes that are
required to sustain ecosystem services in estuarine environments.
Managing both water supplies for people and environmental flows to sustain
coastal resources is very difficult. Can we have stable, secure, and sufficient water
resources for people and still protect estuarine health? To answer this question,
many regions are using adaptive management programs to manage freshwater
resources. These programs set goals to protect ecosystem resources, identify indi-
cators, and monitor the indicators over time to ensure that the goals are appro-
priate and resources are protected. Case studies demonstrate that monitoring and
research can determine the ecological and socio-economical impacts of altered
freshwater inflows so that stakeholders and managers can make well-informed
decisions to manage freshwater inflows to local coasts wisely.
Acknowledgments
When you drink the water, remember the spring—Chinese Proverb
Then said he unto me, These waters issue out toward the east country, and go
down into the desert, and go into the sea: which being brought forth into the sea,
the waters shall be healed—Ezekiel 47:8
This book is based on work that was partially supported by a number of organi-
zations and funding agencies including: the Harte Research Institute for Gulf of
Mexico Studies at Texas A&M University-Corpus Christi; the Korea Maritime
Institute; the National Oceanic and Atmospheric Administration, CAMEO
award NA09NMF4720179; Environmental Protection Agency, grant agreement
MX954526; and the Texas Water Development Board, which has provided grant
support continuously since 1986 for freshwater inflow studies that led to sampling
and analyses that form the basis of many of the approaches described here.
This book is inspired by collaborations with many individuals, but three in
p articular bear mentioning here. In 1986, Gary Powell (then director of the Bay
and Estuary Program, Texas Water Development Board, Austin, TX, USA) asked
a seemingly simple question: how much water has to flow into San Antonio Bay to
maintain productivity? At the time, it appeared to be a simple question that would
be easy to answer within two or three years by measuring processes along salin-
ity gradients and comparing them to changes in flow rates over time. So, there
c ommenced a long period where the focus was on measuring various ecosystem
components and discovering that the correlations with inflow were none-existent
or so noisy as to be useless. Looking back, it was a rather naïve assumption, and
it actually took nearly 20 years to figure out how to reframe the question in a way
that it could actually be answered. My friend and colleague, David Maidment
(Professor, Civil Engineering, University of Texas at Austin) provided a key
insight. We were at a freshwater inflow workshop in 2005 discussing how diffi-
cult it was to connect inflow with biological responses when he suggested that we
might simply use the water quality paradigm developed by the US Environmental
Protection Agency and the Texas Commission on Environmental Quality in anal-
ogy to water quantity. This key insight provided a new path of inquiry whereupon
the focus changed to characterizing environmental conditions and the response
vii
viii Acknowledgments
of ecological health to those conditions. Over the decades, key insights into
the “Rube Goldberg” nature of water systems and physical processes were pro-
vided by George Ward (Senior Research Scientist, Center for Research in Water
Resources, University of Texas at Austin). But more importantly, being an engi-
neer, George continually challenged the idea that an ecosystem could be “healthy.”
With his rapier wit and dry sense of humor, George provided the last piece of the
puzzle by forcing us to continually refine, rescope, and rejustify every conclusion
we made about the health of the bay or estuary.
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Problem and Need . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Conceptual Model of Estuary Ecosystems . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Estuaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Human Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3 Hydrology and the Water Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4 Tides and Residence Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.5 Estuarine Condition and Water Column Effects . . . . . . . . . . . . . . . . . 13
2.5.1 Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.5.2 Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.5.3 Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.5.4 Biological Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3 Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1 Texas, USA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1.1 Physical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1.2 History of Freshwater Management . . . . . . . . . . . . . . . . . . . . 29
3.1.3 Recent Texas Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.2 Florida, USA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2.1 Water Management District Profiles . . . . . . . . . . . . . . . . . . . 40
3.2.2 Florida Water Resource Policy . . . . . . . . . . . . . . . . . . . . . . . . 41
3.2.3 District Management Approaches . . . . . . . . . . . . . . . . . . . . . 42
3.2.4 Southwest Florida Mollusks . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.2.5 St. John’s River Macroinvertebrates . . . . . . . . . . . . . . . . . . . . 45
3.3 Tri-State Water Sharing Issues Within the
Apalachicola-Chattahoochee-Flint Basin . . . . . . . . . . . . . . . . . . . . . . 50
3.4 California, USA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.4.1 Regional Water Quality Control Board Profiles . . . . . . . . . . . 56
3.4.2 San Francisco Bay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.5 Gulf of California, Mexico . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.6 Guadiana River Estuary, Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
ix
x Contents
3.7 Australia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.7.1 The Murray–Darling River Basin . . . . . . . . . . . . . . . . . . . . . . 71
3.7.2 History of Murray–Darling Management. . . . . . . . . . . . . . . . 72
3.8 South Africa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.9 Mthatha Estuary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4 Summary: Water Supply, People, and the Future . . . . . . . . . . . . . . . . . 79
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Chapter 1
Introduction
Water development projects are constructed worldwide for many purposes, but most
commonly for water supply, flood control, and energy production. Projects always
alter hydrology, which means that environmental flow regimes are also altered.
There are three types of environmental flow: instream, inflow, and outflow.
Instream flows occur within rivers and streams, and much has been written about
the environmental consequences of altered instream flows (Postel and Richter
2003). Inflows occur when rivers flow into the coastal zone, which dilutes marine
water and creates brackish estuary habitat. Outflows occur when rivers or estuaries
flow out onto continental shelves or nearshore coastal ocean zones.
The purpose of this book is to describe what is currently known about the eco-
logical effects of altered hydrological cycles on coastal and marine areas. It is
important to define potential impacts of developments and plan for adaptation or
mitigation in the coastal zone.
1.1 P roblem and Need
Demand for freshwater by human populations is large and continues to grow.
Half of the world’s major cities are within 50 km of the coast, and coastal popula-
tions are 2.6 times more dense than those further inland (Crossland et al. 2005).
Because of this, water scarcity and limited or reduced access to water are major
challenges facing society and limiting economic development in many countries
(MEA 2005). As humans further develop technologies for diverting and captur-
ing freshwater from rivers and streams, greater reductions in freshwater deliv-
ery to the coastal zone will occur. The amount of water impounded behind dams
globally has quadrupled since 1960 and three to six times as much water is held
in reservoirs as in natural rivers (Fig. 1.1; MEA 2005). One of the most severe
anthropogenic impacts on coastal areas in the near future will likely be through
continued interference with hydrology and water flows to the coast (Pringle et al.
P. A. Montagna et al., Hydrological Changes and Estuarine Dynamics, 1
SpringerBriefs in Environmental Science, DOI: 10.1007/978-1-4614-5833-3_1,
© The Author(s) 2013