History, landforms, and vegetation of the estuary's tidal marshes

Full text

SAN
FRANCISCO BAY:
THE URBANIZED ESTUARY
Investigations into the Natural History of San Francisco Bay and Delta
With Reference to the Influence of Man

SAN FRANCISCO BAY AND ENVIRONS
Courtesy of the National Aeronautics and Space Administration

FIFTY-EIGHTH ANNUAL MEETING
of the
PACIFIC DIVISION/AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE
held at
SAN FRANCISCO STATE UNIVERSITY, SAN FRANCISCO, CALIFORNIA
June 12-16, 1977
SAN FRANCISCO BAY: THE URBANIZED ESTUARY
Investigations into the Natural History of San Francisco Bay and Delta
With Reference to the Influence of Man
Editor
T. John Conomos
U. S. Geological Survey
Executive Editor
Alan E. Leviton
Pacific Division, AAAS and
California Academy of Sciences
Assistant Editor
Margaret Berson
California Academy of Sciences
San Francisco,
California
1979

ISBN 0-934394-01-6
This volume has been typeset in
Press Roman
type on an IBM Mag Card Composer
in the Department of Herpetology, California Academy of Sciences.
Copyright © 1979 by the Pacific Division of the
American Association for the Advancement of Science
c/o California Academy of Sciences
Golden Gate Park
San Francisco, California 94118
Manufactured in the United States of America by the Allen Press, Lawrence, Kansas 66044

title History, Landforms, and Vegetation of the Estuary’s Tidal Marshes
creator B. F. Atwater, S. G. Conard, J. N. Dowden, C. W. Hedel, R. L. MacDonald, W. Savage
Subject benthic, ecology, geology/soils, ocean waves, vegetation, plants
Description History, Events Before the California Gold Rush, Events Since the California Gold Rush, Landforms,
Plains Near High-Tide Levels, Sloping Surfaces Bordering Mudflats, Waterways, Vegetation,
Distribution of Species, Productivity, Acknowledgements, Literature Cited
Coverage San Francisco Bay, Sacramento-San Joaquin Estuary
Temporal 1850-1980
Source Fifty-eighth Annual Meting of the Pacific Division of the American Association for the Advancement
of Science, San Francisco State University, San Francisco, California, June 12-16, 1977
Date 1977-06-12
IsPartOf SAN FRANCISCO BAY: THE URBANIZED ESTUARY Investigations into the Natural History of San
Francisco Bay and Delta With Reference to the Influence of Man (347-386)
Publisher Pacific Division of the American Association for the Advancement of Science c/o California
Academy of Sciences Golden Gate Park San Francisco, California 94118
Issued 1979
Type text
Format 8-1/2" x 11" bound document
Identifier ISBN 0-934394-01-6
Language English
Rghts Copyrighted, Pacific Division of the American Association for the Advancement of Science
Abstract
Around 8,000 to 10,000 years ago, sharply rising sea levels nursed a newborn San Francisco Bay
estuary whose tidal marshes probably covered less area than open water. Thereafter the rate of
submergence decreased about 10-fold, and by 6,000 years ago sediment began to maintain marshes that
later spread across marginal parts San Francisco Bay. By thus counteracting or overtaking submergence,
sedimentation created marshes that, as of 1850, covered about 2200 km2, nearly twice as much area as
the bays. People have leveed or filled all but approximately 85 km2 of these marshes during the past 125
years. Concurrently, human activities have caused the delivery of enormous quantities of sediment to the
bays and the slackening of tidal currents in sloughs, thereby contributing to the creation of nearly 75 km2 of
marsh, about half of which remains pristine. Plains situated near high-tide levels are the most extensive
landforms of both historic and modern marshes. Tides rather than upland tributaries created most sloughs
around the bays, but riverine floods erected natural levees that confined tidal water in the Delta. Tidal
marshes around San Francisco Bay typically contain13 or 14 species of vascular plants characteristic of
salt marshes and are dominated by common pickleweed (Salicornia pacifica) and California cordgrass
(Spartinafoliosa). In the Delta, tidal marshes support about 40 species characteristic of fresh-water
marshes and are dominated by tules and bulrushes (Scirpus spp.), cat-tails (Typha spp.), and common
reed (Phragraites communis). These contrasting communities overlap around San Pablo Bay, Carquinez
Strait, and Suisun Bay. Damage to tules and bulrushes during the drought of 1976-1977 confirms that
intolerance of salt causes these plants to disappear toward San Francisco Bay. The disappearance of
California cordgrass and common pickleweed toward the Delta, alternatively, may result from unsuccessful
competition against tules, bulrushes, and other species. If export equals one quarter of net above-ground
productivity, then vascular plants of the tidal marshes collectively contribute about 10 billion grams of
carbon per year to other parts of the estuary.
© 2005 Envirospectives, Inc.

HISTORY, LANDFORMS, AND VEGETATION
OF THE ESTUARY’S TIDAL MARSHES
BRIAN F. ATWATER
U. S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025
SUSAN G. CONARD
Botany Department, University of California, Davis, CA 95616
JAMES N. DOWDEN
California State Lands Commission, 1807 13th Street, Sacramento, CA 95814*
CHARLES W. HEDEL
U. S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025
RODERICK L. MACDONALD
Botany Department, University of California, Davis, CA 95616
WAYNE SAVAGE
Biology Department, San Jose State University, San Jose, CA 95192
Around 8,000 to 10,000 years ago, sharply rising sea levels nursed a newborn
San Francisco Bay estuary whose tidal marshes probably covered less area than
open water. Thereafter the rate of submergence decreased about 10-fold, and by
6,000 years ago sediment began to maintain marshes that later spread across
marginal parts of San Francisco Bay. By thus counteracting or overtaking sub-
mergence, sedimentation created marshes that, as of 1850, covered about 2200
km
2
, nearly twice as much area as the bays. People have leveed or filled all but
approximately 85 km
2
of these marshes during the past 125 years. Concurrent-
ly, human activities have caused the delivery of enormous quantities of sediment
to the bays and the slackening of tidal currents in sloughs, thereby contributing
to the creation of nearly 75 km
2
of marsh, about half of which remains pristine.
Plains situated near high-tide levels are the most extensive landforms of both his-
toric and modern marshes. Tides rather than upland tributaries created most
sloughs around the bays, but riverine floods erected natural levees that confined
tidal water in the Delta. Tidal marshes around San Francisco Bay typically con-
tain 13 or 14 species of vascular plants characteristic of salt marshes and are
dominated by common pickleweed
(Salicornia pacifica)
and California cordgrass
(Spartinafoliosa).
In the Delta, tidal marshes support about 40 species characteris-
tic of fresh-water marshes and are dominated by tules and bulrushes
(Scirpus
spp.), cat-tails
(Typha
spp.), and common reed
(Phragraites communis).
These
contrasting communities overlap around San Pablo Bay, Carquinez Strait, and
Suisun Bay. Damage to tules and bulrushes during the drought of 1976-1977
confirms that intolerance of salt causes these plants to disappear toward San
Francisco Bay. The disappearance of California cordgrass and common pickle-
weed toward the Delta, alternatively, may result from unsuccessful competition
against tnles, bulrushes, and other species. If export equals one quarter of net
above-ground productivity, then vascular plants of the tidal marshes collectively
contribute about 10 billion grams of carbon per year to other parts of the estuary.
* The views expressed herein are not necessarily those of the California State Lands Commission (CSLC) or
of other bureaus of the State.
Copyright ©1979, Pacific Division, AAAS.
347

SAN FRANCISCO BAY
Though initially regarded as wastelands, tidal marshes of the San Francisco Bay estuary have
gained considerable human significance during the past 125 years. The monetary value of these
marshes derives chiefly from their historical conversion to farmlands, salt ponds, and sites for com-
merce, industry, recreation, and residence. Areas of former marshland in the Sacramento-San
Joaquin Delta, for example, currently yield about $300 million in crops, including one quarter of
America’s domestic asparagus (Delta Advisory Planning Commission 1976:77, 80). From im-
pounded marshes around San Francisco and San Pablo bays, the Leslie Salt Company annually
harvests approximately 400,000 metric tons of crude salt worth $7 million (M. Armstrong pers.
comm.). Other leveed areas of former tidal mar.,;h attract hunters, particularly north of Suisun Bay,
where the annual duck kill equals about 10% of California’s total (Jones and Stokes Associates
Inc., and EDAW, Inc. 1975:46).
Few people deliberately maintained tidal marshes in their pristine condition until the 1960’s,
when concern about human encroachment on the bays led to the creation of the San Francisco
Bay Conservation and Development Commission (BCDC) (Gilliam 1969). Since 1969, this regula-
tory agency has mandated the preservation of most remaining tidal marshes around San Francisco,
San Pablo, and Suisun bays. According to the Commission’s findings, tidal marshes warrant such
protection because, directly or indirectly, they nourish and shelter many estuarine animals (BCDC
1969:11). Some people also value pristine tidal marshes as sties for outdoor education or re-
creation. In response to this interest, local governments have established parks that preserve tidal
marshes for students, bird-watchers, and strollers.
This chapter reflects the current concern for pristine tidal marshes by providing an overview
of their history, landforms, and vegetation. Drawn partly from unpublished observations by the
authors, the overview also depends on information from published sources, particularly topo-
graphic surveys by the U. S. Coast and Geodetic Survey (USC&GS); geologic investigations by
Gilbert (1917), Pestrong (1963, 1972), and Atwater et al. (1977); and botanical studies by Cooper
(1926), Marshall (1948), Hinde (1954), Mason (1957), Cameron (1972), Mahall and Park (1976a,
b, c) and Conard et al. (1977). Much additional information remains to be gathered and assimi-
lated, so we expect that others will improve many of the ideas put forth in this synthesis.
HISTORY
The discovery of gold at Sutter’s mill in 1848 initiated human activities that have worked
vast changes in tidal marshes of the San Francisco Bay estuary. Before the Gold Rush, people in-
terfered with few of the natural processes that create, maintain, or destroy tidal marshes. Since the
Gold Rush, however, people have leveed or filled most preexisting marshes, accidentally promoted
the erosion of others, and created some new marshes by both accident and design.
Events Before the California Gold Rush
Rates of submergence (rise in sea level relative to the land) and sedimentation largely con-
trolled the areal extent of tidal marshes in the San Francisco Bay estuary between the inception of
the estuary and the arrival of the Forty-Niner:g about 10,000 years later. Known tidal-marsh de-
posits older than 8,000 years form lenses no more than a few meters thick and underlie sediments
that accumulated in open-water bay environments. This distribution implies that 8,000 to 10,000
years ago a discontinuous fringe of tidal marsh retreated from a rising, spreading bay, presumably
because sediments accumulated in tidal marshes less rapidly than the level of the Bay climbed.
By about 6,000 years ago, the rate of submergence had slowed by nearly lO-fold to its subse-
quent average of 1-2 m per millenium (Atwater 1979, Fig. 5), thereby allowing sedimentation to
348

ATWATER ET AL: TIDAL MARSHES
counterbalance submergence in some parts of the estuary. In the western Delta, peat as thick as 20
m indicates that vertical accretion in marshes has kept pace with submergence during the past
4,000-6,000 years (Weir 1950; Schlemon and Begg 1973). A balance between sedimentation and
submergence likewise accounts for thick accumulations of tidal-marsh deposits in Massachusetts
(Mudge 1858; Davis 1910; Redfield 1972).
The establishment of extensive tidal marshes around southern San Francisco Bay appears to
have occurred later than in the Delta, probably close to 4,000 years after the rate of submergence
reached 1-2 m per millenium (Atwater et al. 1977). This delay is evidenced by deposits of tidal-flat
mud that typically underlie peaty tidal-marsh sediments at elevations close to modern mean tide
level (MTL) (Table 1). The boundary between tidal-fiat and tidal-marsh sediment records the
colonization of mudflats by marsh plants, so it marks the inception of a marsh (Shaler 1886:
364-365). The date at which MTL equalled the elevation of this boundary approximates the
minimal ages of the marsh because California cordgrass
(Spartina foliosa),
the pioneer vascular
plant of San Francisco Bay’s mudflats, colonizes surfaces near MTL (Pestrong 1972; Hinde 1954).
Approximately equating MTL with mean sea level, estimating former mean sea levels from radio-
carbon-dated marsh deposits elsewhere in southern San Francisco Bay (Atwater 1979, Fig. 5), and
correcting elevations for local subsidence due to withdrawal of groundwater (Poland 1971), we
infer that marshes such as Palo Alto Baylands originated within the past 2,000 years. The 4,000-yr
lag between the inception of a slow rate of submergence and the creation of such marshes prob-
ably represents the time required for sedimentation to make up for the effects of earlier, more
rapid submergence.
TABLE 1. DATUMS FOR TIDE LEVELS AND HEIGHTS.
a
Datum
Abbreviation Definition
Mean higher high water
MHHW
Mean high water
MHW
Mean tide level
MTL
Mean low water
MLW
Mean lower low water
MLLW
Mean sea level
National Geodetic
Vertical Datum
of 1929
MSL
NGVD
Average height of the higher of the daily high tides
Average height of all high tides
Plane halfway between mean high water and mean
low water, also called half-tide level
Average height of all low tides
Average height of the lower of the daily low tides.
Adopted as plane of reference for hydrographic
surveys and nautical charts of the west coast of
the United States
Average height of the water surface for all stages of
the tide, determined from hourly readings
The standard datum for heights across the nation.
Formerly called the "U.S. Coast and Geodetic
Survey sea-level datum of 1929," and originally
determined from mean sea levels at 26 tide sta-
tions in the United States and Canada. General-
ly differs from local mean sea level (Fig. 1), so
it is best regarded as an arbitrary datum that
happens to be close to mean sea level.
a Tidal datums are ideally determined from 19 years of measurement, but shorter series of observations
may be compared with a long-term record to determine mean values.
349

SAN FRANCISCO BAY
350

ATWATER ET AL: TIDAL MARSHES
351

SAN FRANCISCO BAY
¯ Tidal marsh at whlchvosculor plants
have
been iO~rntified
¯ Tidal marshintention(~lly created o~
restored ~nC~ 197:5
ISLAND
POINT
Son Peblo 8oy
CHINA
CAMP
8NOOGRASS
SLOUGH
~¢ocromenfo-
~
Son dooquin De~to ~
DUMBARTON POINT
Fig. 2. San Francisco Bay estuary and the Sacramento-San Joaquin River Delta. Locations of
newly created marshes follow Kingsley and Boerger (1976), Knutson et al. (1976), and Harvey
et al. (1977:85). Thin lines approximate shorelines or margins of tidal marsh ca. 1860 as shown on
compilations by Gilbert (1917: 76) and Nichols and Wright (1971).
Events since the California Gold Rush
Early surveys by Ringgold (1852) and the USC&GS portray the San Francisco Bay estuary
as it appeared during the California Gold Rush. Collectively, the tidal marshes and open-water bays
covered about 3400 km
2
, an area slightly larger than Rhode Island. The area of tidal marsh was
nearly double the area of the bays, with the Delta marshes making up about 1400 km
2
and the
marshes bordering San Francisco, San Pablo, and Suisun bays accounting for another 800 km
~
(Gilbert 1917:78).
Approximately 95% of the estuary’s tidal marshes have been leveed or ffdled since the Gold
Rush (Figs. 1, 3). The typical age of levees varies with location and appears to depend on the
352

ATWATER ET
AL: TIDAL MARSHES
CONDITION
OF MARSH
M~tly p~istine since
dote of creotio~
Mostly leveed or
filled by people
during the indicated
period of time
APPROXIMATE
DATE OF CREATION
OF MARSH
Fig. 3. Generalized and approximate historic changes in aerial distribution of tidal marshes.
The map scale requires that patterned areas exceed about 0.5 km in width and about 0.5 km
2
in area. Dates for levees and fill follow Van Royen and Siegel (1959) for San Francisco Bay.
Around San Pablo and Suisun Bays, dates are estimated by inspection of archival maps of the
USC&GS (scale generally 1:10,000) and the USGS (scale 1:31,680; Suisun Bay only); Van Royen
and Siegel incompletely discriminate for these bays between marshes enclosed by levees and
marshes subject to natural inundation by tides. Changes in the Delta follow Matthew et al. (1931,
pl. 34). Areas of modern tidal marsh are compiled from topographic maps of all areas by the USGS
(1968 and 1973 editions, scale 1:24,000), from a landuse map of San Francisco, San Pablo, and
Suisun bays by the BCDC (1969; approximate scale 1:250,000), and from maps by the California
Department of Fish and Game (CDF&G) showing dominant vascular plants north of Suisun Bay as
of 1973 (H. A. George, unpublished map). Some modern marshes have undoubtedly been omitted
or misrepresented.
suitability of marshland for agriculture. Fresh-water marshes characterized the pristine Delta, and
most of these were leveed for farming before 1920. Marshes nearer the Golden Gate, on the other
353

SAN FRANCISCO BAY
o ]
SECONDS
2
I
20 METERS
LOCAL DATUM
(1896-1898)
4~-
LOCAL DATUM
(1852-1857)
_~NORTH AMERICAN 1927 DATUM
(1931-present)
~
.U. S, STANDARD DATUM
(1902-1930)
Fig. 4. Horizontal datums for maps of southern San Francisco Bay. The circled crosses locate
intersecting lines of the geographic projection for latitude and longitude. For example, the inter-
section of a latitude and longitude according to the local datum of 1896-1898 is located 176 m N
and 117 m E of the intersection of the same latitude and longitude according to the North Ameri-
can 1927 Datum. Such relationships provide precise geodetic means for comparing features shown
on archival and modern maps (Fig. 5). The local datums are reconciled to each other and to the
nationwide datums by comparing the published positions, as referenced to the various horizontal
datums, of persistent triangulation stations. These positions appear in: (1) annual reports of the
superintendent of the USC&GS, 1851-1868, 1904, and 1910; (2) "Old Registers" maintained by
the Early Drawing Division, U. S. Coast Survey, 1850-1927; and (3) a special publication on tri-
angulation in California (Mitchell 1936). Early geodesists in California, led by George Davidson,
established local datums astronomically and projected them according to a mathematical model of
the shape of the earth called the Bessel Spheroid of 1841. These datums yielded to others as a re-
sult of several advances in geodesy: (1) a more accurate determination of longitude in the 1870’s;
(2) the application of the Clarke Spheroid of 1866; (3)the completion of the transcontinental tri-
angulation network in the late 1880’s, which led to the adoption of the U. S. Standard Datum in
1902; and (4) readjustment of the network during the early 1920’s, which resulted in the North
American 1927 Datum (Shalowitz 1964:112-114, 141-158).
hand, contained more salt in their soils and sloughs. This salt presumably limited the agricultural
value of the marshland and therefore delayed the construction of levees until other human uses
were found. For example, whereas agricultural levees in 1900 enclosed about half of the historic
marshes of the Delta and Suisun Bay, less than one fifth of the Bay’s marshes had been leveed by
that time, and these mostly for production of salt. Tidal marshes around the Bay remained largely
pristine until later in the 20th century when, coincident with a rapid increase in the population of
suburban areas, most of the marshes were converted to salt-evaporation ponds or to sites for resi-
dential and industrial structures, transportation facilities, and garbage dumps.
Changes in mapped shorelines (Figs. 3,5,6) indicate that approximately 75 km
2
of new tidal
3:54

ATWATER ET AL: TIDAL MARSHES
marsh have appeared around San Francisco, San Pablo, and Suisun bays since the Gold Rush. It
seems likely that humans accidentally created much of this marshland by supplying sediment to
the bays and by building levees and jetties that promoted deposition.
The widespread and rapid expansion of marshland during the late 19th century (Fig. 6)
probably resulted in large measure from contemporaneous hydraulic mining in the Sierra Nevada.
Between 1853 and 1884, gold miners washed prodigious quantities of sediment into Sierran
streams. Further downstream, this debris caused damage to farmlands and waterways and thereby
led to court injunctions that effectively halted hydraulic mining (Gilbert 1917:11; Briscoe 1979).
Much debris travelled even further and entered the San Francisco Bay estuary, as evidenced by the
wave of river-bottom sediment, presumably sand and gravel, that crested near the northern end of
the Delta between 1890 and 1900 (Fig. 1, "minimum low water"). Clay and f’me silt from the
hydraulic mines should have reached the estuary sooner because they move in suspension, and
deposition of this free sediment apparently caused both shoaling of subtidal areas in San Pablo and
Suisun bays and rapid horizontal expansion of marshlands into mudflats of northern Suisun Bay,
western San Pablo Bay, and southern San Francisco Bay during the late 19th century (Gilbert
1917: 36, 86-88; Figs. 1, 6). The delivery of mining debris to the margins of southern San Francis-
co Bay may be doubted because few subtidal areas of this bay shoaled greatly during the late 19th
century (Fig. 6; Krone 1979) and because Ferdinand Westdahl, the topographer who mapped
much of the expanded marshland, designated commercial oyster shells and Oakland’s growing port
as the causes of tidal-marsh accretion (Westdahl 1897). Nevertheless, large quantities of silt- and
clay-size mining debris certainly reached San Pablo Bay; some of this sediment undoubtedly
entered the layer of low-salinity water that, according to McCulloch et al. (1970) and Carlson and
McCulloch (1974), spreads across southern San Francisco Bay during periods of high discharge
from the Sacramento River; and, once delivered to southern San Francisco Bay, mining debris
might have preferentially accumulated on marginal tidal fiats as clay and silt appear to be doing
today (Conomos and Peterson 1977).
Tidal marshes have probably received additional sediment from farmlands (Gilbert 1917: 36),
urbanized uplands (Knott 19’/3), and dredged channels and harbors. Moreover, many future
marshes may rest entirely on dredged material if, as currently planned, public agencies mitigate the
disposal of dredged material by intentionally creating tidal marshes on spoils. Beginning with the
experiments of H. T. Harvey during the 1960’s, both independent parties and members of the U.S.
Army Corps of Engineers have demonstrated that people can establish such marshes by planting
seeds, seedlings, and cuttings of Califomia cordgrass in previously barren areas (Knutson et al.
1976; Kingsley and Boerger 1976; Fig. 2).
Levees and jetties have also contributed to the creation of marshiands, particularly during
the 20th century. Construction of levees around tidal marshes almost invariably preceded and pro-
bably caused the historic appearance of new marshes along the banks of sloughs that formerly
served the marshes (K. Dedrick pers. comm.). Presumably, sediment accumulated because the
levees prevented exchange of water with the former tidal marshes and thereby slackened currents
in the sloughs (Gilbert 1917:102-103). Levees may have also promoted expansion of marshland in-
to the bays by reducing the area in which sediment could accumulate. According to Robert Nadey
(pers. comm.), this effect may account for part of the spectacular growth of marshes into western
San Pablo Bay during the period of hydraulic mining. Extension of a jetty south of Mare Island
during the 20th century coincides with shoaling of nearby tidal fiats (Smith 1965) and expansion
of nearby marshland. The jetty probably caused these changes because, during the late 19th cen-
tury, the marsh eroded rather than advanced, even though other parts of San Pablo Bay were trap-
ping large quantities of hydraulic-mining debris (Figs. 6, 7).
Many changes in mapped shorelines indicate erosion rather than deposition at the bayward
355

SAN FRANCISCO BAY
356

ATWATER ET AL: TIDAL MARSHES
margins of tidal marshes (Fig. 6). As inferred by Gilbert (1917:21-22), such retreat may result in
part from a rise in sea level relative to the land. Other contributing factors include burrowing by an
introduced isopod (Carton 1979).
Available inventories of the areal size of tidal marshes ~t a given date employ different means
of distinguishing "tidal" from "leveed" and rarely discriminate between marshes formed before
and after 1850. These problems, together with the infrequency of such inventories, currently pre-
clude a detailed summary of historic changes in tidal-marsh areas. Even the generalized graphs and
maps (Figs. 1, 3) imply unwarranted precision, as the reader can determine by consulting the cited
sources. Despite such deficiencies, our estimates justify several conclusions about the effects of
levees and fill on the San Francisco Bay estuary: (1) The present area of tidal marsh within the
entire estuary is about 125 km
~
, one third of which has originated since 1850. Both Van Royen
and Siegel (1959) and Nichols and Wright (1971) offer a much higher figure for the total area of
marshland because their tallies include many non-tidal leveed marshes. (2) Even excluding the Del-
ta, leveed or filled tidal marshes cover far more area than the 140 km
~
of open-water baylands that
have been leveed, filled, or converted to tidal marsh since the Gold Rush (Nichols and Wright
1971). Thus, tidal marshes rather than open-water bays have provided most of the leveed and filled
areas of the San Francisco Bay estuary.
LANDFORMS
Natural topographic features of the tidal marshes of the San Francisco Bay estuary include
broad, nearly fiat surfaces; narrower surfaces that descend into tidal flats, some precipitously;
beach ridges and related berms; tidal sloughs; riverine channels and their natural levees; shallow
ponds and pans; and islands of pre-existing bedrock and sand dunes. The following discussion em-
phasizes the principal kinds of marshlands and waterways.
Plains near High-Tide Levels
Around the turn of the century, the "typical tidal marsh" of the San Francisco Bay estuary
Fig. 5. Historic changes in tidal marshes near Dumbarton Point, southern San Francisco Bay.
The archival maps copy lines and names from l:10,000-scale plane-table sheets of the USC&GS:
T-634, surveyed in 1857 by David Kerr; T-2258, surveyed in 1896 by Fremont Morse and Ferdi-
nand Westdahl (low-water line from contemporary hydrographic surveys H-2304 and H-2413);
and T-4626, surveyed in 1931 by H. G. Conerly (low-water line from contemporaneous hydro-
graphic survey H-5135). The modern map is traced from a 1:24,000-scale photogrammetric map
(Newark 7.5-min quadrangle). Additional symbols show old shorelines and inferred areas of ero-
sion and deposition. Registration of archival maps to the North American 1927 Datura (Fig. 4)
controls the comparisons of charted shorelines. Though subject to uncertainties related to method
and season of surveying, shorelines approximate the bayward limit of vegetation (Gilbert 1917:86;
Shalowitz 1964: 177). The density and distribution of sloughs reflects methods of mapping and
changes related to human structures. Morse and Westdahl apparently traced Kerr’s lines for most
of the mid-19th century sloughs (R. Nadey pets. comm.); according to Westdahl’s (1896) descrip-
tion of a nearby survey "on the salt marshes only the sloughs used for navigation, the shore-line,
the area between the old and new bayshore, and improvements, such as dykes, houses, and salt-
works, have been surveyed." Conerly apparently neglected all but the largest sloughs. Differences
between modern sloughs and those mapped by Kerr imply that the railroad and salt ponds have
disrupted the original pattern of drainage.
357

SAN FRANCISCO BAY
Approximate
periods
of
A. LATE NINETEENTH CENTURY
Apperen~
qreoter than
- - _
i m in’rot~he:nge
~’~
+ Shallower water i~
-
[] I-minute
quadrangle
marsh shorelines
~
Advance > I
m/yr
¯ LATEST NINETEENTH AND EARLY TWENTIETH
CENTURIES
Fig. 6. Historic changes in tidal-marsh shorelines and subtidal bathymetry (A) during the late
19th century and (B) during the latest 19th century and early 20th centuries.
SHORELINES. Changes in shoreline area measured by comparing archival topographic maps
that were prepared by the USC&GS. Comparisons make use of 1:24,000-scale photographic reduc-
tions of the CSLC. Most maps are registered to o:ne another by matching persistent features such as
hills, rocky shorelines, intricately meandering sloughs, railroad tracks, and occasional triangulation
stations. Precise geodetic registration (Figs. 4, 5) is limited to the southern and eastern shores of
San Francisco Bay. Elsewhere the uncertainties in registration, together with errors in surveying,
possible distortion of original map paper, and possible differences in notation for tidal-marsh
shorelines (Gilbert 1917: 86), prevent resolution of changes that average less than 1 m"yr
-1
over 20-
to 40-yr intervals.
BATHYMETRY. Changes in bathymetry for subtidal areas excluding sloughs are adapted from
Smith’s (1965) comparison of archival hydrographic maps. Smith compared average depths within
1/8-min quadrangles and reported the sum of changes for 1-min quadrangles. The distribution of
areas showing large changes in bathymetry must: be interpreted with reference to index maps be-
cause the magnitude of change depends partly on the length of the period of record. Dates on in-
dex maps omit numerals for century and millennium.
resembled "a plain traversed by a branching system of sloughs" (Gilbert 1917:75). Excluding
sloughs, the relief on such "plains" must have been slight because topographers such as Ferdinand
Westdahl (1897) used "the level of the salt-marsh in its natural state" as a datum plane for upland
elevations.
Nearly flat surfaces appear to remain the most extensive landforms of the tidal marshes of the
San Francisco Bay estuary (Fig. 7; Bodnar et ~. 1975: Figs. 32, 33; Hinde 1954). These plains
characterize marshland formed both before and after 1850, and they cross historic shorelines
without appreciable change in level or relief (China Camp and Mare Island marshes, Fig. 7).
358

ATWATER ET AL: ~[IDAL MARSHES
Within uncertainties of measurement
1
, most of the broad surfaces (Fig. 7) are probably situ-
ated within a few decimeters of MHHW. This coincidence implies a widespread tendency of tidal-
marsh surfaces to approach high-tide levels. Presumably, such heights equilibrate deposition, ero-
sion, and subsidence (Pestrong 1972).
Differences in elevation between some tidal-marsh plains, however, exceed probable errors in
measurement. The fiat surface of the marsh at Richardson Bay appears to be situated about 0.2 m
below MHHW (Fig. 7), and broad parts of several tidal marshes also occupy elevations below MHHW
along the western shore of southern San Francisco Bay northwest of Palo Alto Baylands (K. De-
drick, pers. comm.). Typical elevations near Point Pinole, on the other hand, approximately equal
MHHW according to third-order leveling (Bodnar et al. 1975: Figs 32, 33), and less precise measure-
ments at the nearby China Camp marsh (Fig. 7) suggest similar elevations. Furthermore, marshland
near Mare Island appears to rise 0.2-0.5 m above MHHW (Fig. 7). Both here and at Palo Alto Bay-
lands, however, probable but unmeasured subsidence of the bench mark at the origin of the transect
(Table 2, footnotes 3, 5) may erroneously heighten the measured elevations.
These geographic variations in the elevation of marshlands with respect to tidal datums imply
that local conditions influence topography. The entrapment of suspended sediment in San Pablo
and Suisun bays (Conomos and Peterson 1977), for example, may partly explain why post-1850
marshes at Richardson Bay have reached lower levels than contemporaneous marshes at China
Camp. Anomalously high elevations near Mare Island may reflect not only such entrapment but also
southerly high winds, which potentially pile water above normal high-tide levels, and the nearby
jetty, which has promoted intertidal deposition (see above discussion of levees and jetties). Finally,
subsidence due to withdrawal of groundwater (Poland 1971) dropped the tidal marsh at Palo Alto
Baylands to a lower level between 1954 and 1965, as evidenced by the spread of cordgrass into areas
whose former elevation may have excluded this plant (Harvey 1966). Most of this marsh is neverthe-
less situated at or near MHHW (Fig. 7), so it seems likely that sedimentation has, on the average,
largely maintained the level of the marsh against subsidence, which amounts to nearly 1 m since
1931 (Table 2, footnote 3).
Uncertainties and geographic variation in the elevations of modern tidal-marsh plains com-
pound the problems of defining, relative to tidal datums, the "level of salt-marsh in its natural state"
as of the 19th century. One possible solution presumes similarity between the elevations of modern
and historic marshes and therefore must allow for differences between localities. Additional compli-
cations arise if marshlands have reached unnaturally high levels because of human activities such as
hydraulic gold-mining, disposal of dredge spoils, and construction of levees and jetties. A remark by
Gilbert (1917:77) indirectly supports this hypothesis by equating areas vegetated by tules
(Scirpus
spp.) and California cordgrass with the "broader parts" of marshes. Currently, these plants mostly
grow along narrow surfaces that descend into mudflats or sloughs (Fig. 7), so it seems possible that
the few remaining pristine marshlands have risen to extraordinary heights during this century, per-
haps by trapping hydraulic-mining debris and dredge spoils. Alternatively, Gilbert erred, perhaps by
attributing to all marshlands the characteristics of those that spread across mudflats during the late
19th century (Figs. 5, 6) and initially supported California cordgrass and rules rather than common
1 With respect to tide levels, the elevations of modern surfaces reported in Fig. 7 may err by 0.1 m or more
because of undetermined changes in the published elevations of bench marks and tidal datum planes (Table 2), ex-
trapolation or interpolation of datums from distant tide stations, and imprecise methods of leveling. The leveling
generally fails to meet several of the National Ocean Survey’s (NOS) standards for third-order work (NOS 1974):
(1) maximum length of sights-some sights exceed the 90-m standard by 10-30 m; (2) difference in length of for-
ward and backward sights-the 10-m standard is met for turning points, but most elevations along transects repre-
sent unbalanced forward and backward sights between turning points; and (3) minimum error in closure-complete
closure was not attempted at marshes shown in Fig. 7, and partial closure at China Camp and Palo Alto Baylands
indicate cumulative errors of about 5 cm, roughly three times as large as the standard.
359

SAN FRANCISCO BAY
360

ATWATER
ET AL: TIDAL
MARSHES
TABLE 2. REFERENCE STATIONS FOR ELEVATIONS AND TIDAL DATUMS SHOWN IN FIG. 7
MARSH
BENCH MARK
a
Designation Elevation Year of
(m) leveling
Palo Alto Tidal 1.09
c
1965
Baylands
No. 1
Richardson
R481
2.60
d
1955
Bay
China Camp
D552
12.56
d
1956
Mare Island
N466
1.21
e
1956
Southampton
C467
4.94
d
1951
Bay
TIDAL DATUMS
Location of gauge Elevations at gauge (m)
b
Distance
Place name from marsh
MLLW
MTL
MHHW
(km)
Palo Alto
1
-1.3
0.2
1.4
Yacht Harbor
San Francisco
10
-0.8
0.1
0.9
(Presidio)
Pinole Point
11
-0.9
0.2
1.0
11
-0.8
0.2
1.0
-0.8
0.2
1.0
Hercules
Crockett
4
a From "Vertical Control Data" compiled by the National Geodetic Survey. Datum is NGVD.
b Compiled by the National Ocean Survey (1977a, 1977b) and referenced to leveling completed in 1956 or, for
Palo Alto, 1967. Datum is NGVD. See Table 1 for definition of reference planes.
c Repeated leveling by the U. S. Coast and Geodetic Survey indicates that the elevation of Tidal No. 1 de-
creased 0.76 m between 1931 and 1965, chiefly because of regional subsidence accompanying ground-water with-
drawal (Poland: 1971). Hinde (1954: 217) apparently used the initial elevation of the benchmark, and his mea-
sured elevations may therefore be too high by 0.5 m, the change in elevation of Tidal No. 1 between 1931 and
1955. Changes in elevation since the 1965 leveling are ignored here because they are probably 0.2 m or less; arti-
ficial recharge of ground water halted subsidence near Palo Alto by 1971 (Poland: 1971).
d
Leveled only once by the U. S. Coast and Geodetic Survey. Changes in elevation since year of leveling pre-
sumably do not exceed 0.05 m because monument rests on bedrock (D552, C467) or on a concrete pier support-
ing a 10-lane bridge (R481).
e According to repeated leveling by the U. S. Coast and Geodetic Survey, bench mark N466 subsided 0.04 m
between 1951 and 1956. No correction for unmeasured, subsequent movement is attempted here, but at least 0.10
additional subsidence seems likely because the road embankment beneath the monument overlies compressible
estuadne sediments and because f’fll has been added to the embankment or adjacent road since 1956.
Fig. 7. Generalized landforms, vegetation, and subsurface sediments of some salt- and brack-
ish-water tidal marshes. (Vertical exaggeration 50X). Dots on profiles denote places where elevation
was surveyed in 1975 or 1976. Elevations were transferred with a rod and tripod-mounted level
from the nearest geodetic or tidal bench mark (Table 2). No correction is made for probable but
unmeasured subsidence of bench marks near Palo Alto Baylands and Mare Island. Methods of
surveying meet only some of the standards for third-order leveling (see footnote 1 in text). Tidal
datums are extrapolated from the nearest long-term tide gauge for which the relationship between
MLLW and NGVD has been determined (Table 2). Collectively, these procedures may cause mea-
sured elevations to err by 0.1 m or more with respect to tidal datums. Elevations away from dots are
estimated by extrapolation, chiefly with reference to vegetation. Small channels are generally
omitted. The water surface is at MTL. Gray bands approximate the horizontal position of the
bayward limit of vascular plants at the indicated date, as interpreted from archival maps (Figs. 5, 6).
The distribution of vascular plants on the surface shows approximate conditions in 1975 (Fig. 10).
Appendix A lists native species at all localities except Mare Island. Fossil rhizomes (below-ground
stems) and roots are tentatively identified by macroscopic examination of core samples. Most of the
tidal-flat mud lacks roots or rhizomes in growth position. The Mare Island diagrams join at center.
361

SAN FRANCISCO BAY
pickleweed
(Salicornia pacifica)
and salt grass
(Distichlis spicata)
(see description by Westdahl
1896).
Sloping Surfaces Bordering Mudflats
Marshes unquestionably vary in the slope of surfaces that descend into tidal mudflats. Near
China Camp and at Southampton Bay, marshland dips gently into adjacent mudflats (Fig. 7). At
Palo Alto Baylands and Richardson Bay, on the other hand, most of the bayward edge of the
marsh drops precipitously.
Gently sloping margins imply net deposition and precipitous margins imply net erosion.
Several lines of evidence support these inferences: (1) gently sloping margins correspond with
shorelines that typically migrated toward the Bay during the late 19th and early 20th centuries,
and precipitous margins characterize shorelines that generally retreated during this period of time
(Fig. 6); and (2) precipitous slopes locally correlate with ongoing erosion, as indicated around
parts of southern San Francisco Bay by blocks of tidal-marsh mud that slump from vertical or
overhanging scarps onto the adjacent mudflat.
Low beach ridges historically bordered some tidal marshes of the San Francisco Bay estu-
ary (Gilbert 1917:86), and a few ridges rernain today. Beach ridges apparently impounded
marshlands near San Lorenzo and thereby created natural salt ponds (Fig. 8). By analogy with
sandy barriers that fringe marshes of Delaware Bay (Kraft et al. 1976:98-104), these ridges may
have contained sand that had been derived from eroding headlands, particularly the ancient dune
sands near Oakland (Atwater et al. 1977). Other beach ridges of the San Francisco Bay estuary
are made of shell (Westdahl 1897). A possibly related feature of unknown origin is the broad
berm of mud that currently appears to rise above MHHW at the bayward margin of a marsh near
Mare Island (Fig. 7). A similar berm probably fi~rced sloughs near this locality to drain away from
San Pablo Bay in 1856 (Fig. 8).
Waterways
Patterns of tidal-marsh drainage around San Francisco, San Pablo, and Suisun bays depend
partly on the age of surrounding marshland. Whereas prominent meanders characterize the sloughs
of marshes created before 1850, the sloughs of younger marshes follow relatively straight paths
that trend nearly perpendicular to the bayward edge of the marsh. Such direct paths cross modem
marshlands (Fig. 7, China Camp) as well as their 19th-century ancestors (Fig. 5; Westdahl 1897)
and therefore appear to have gained little sinuousity since formation. The contrast between
straight and meandering sloughs may reflect differences in the rate of formation of marshland if, as
seems likely from enormous changes in historic shorelines (Fig. 6), marshes drained by straight
channels initially spread and rose at an extraordinarily rapid pace during the late 19th century.
Tidal water rather than the discharge of upland creeks controls the dimensions of most
sloughs around the bays. Pestrong (1965:32-33) and Gilbert (1917:102-103) implicitly advocated
such control, Pestrong by adopting Chapman’s (1960:30) conclusion that sloughs grow because of
the flow of tidal water to and from an upward-building marsh, and Gilbert by proposing that reduc-
tion of this flow, owing to impoundment of marshland behind levees, caused shoaling of a slough
near Mare Island. Moreover, although the widths of waterways commonly increase with discharge
(Myrick and Leopold 1963), the widths of historic tidal sloughs north of San Pablo Bay greatly ta-
pered toward upland creeks (Nichols and Wright 1971), so it seems likely that the widths of these
sloughs depended mainly on the areas of their tidal-marsh drainage basins. Such drainage basins
must also account for the considerable widths of sloughs near Guadalupe Slough and Mare Island
(Fig. 8) that drained no major upland creeks.
Riverine floods, on the other hand, probably restricted the reach of tides in the northern
362

ATWATER ET AL: TIDAL MARSHES
Delta by creating natural levees along the channels of rivers and distributaries. Near Babel Slough,
the Sacramento River built natural levees about 1 km wide and up to 5 m high (Fig. 9). Such
levees diminished in height toward Suisun Bay but extended as far downstream as the confluence
of the Sacramento and San Joaquin Rivers (Thompson 1958:26; Ringgold 1852). At autumnal low
stages of the rivers, high tides probably could not surmount many of the levees in the northern
Delta, so perhaps only rivefine floods inundated low-lying marshes that were enclosed by naturally
leveed channels. Thus, some areas designated as historical tidal marsh in Figs. 1-3 may have actu-
ally been isolated from autumnal tides.
Natural levees in the southern Delta generally reached much lower elevations, as evidenced
by archival records (Thompson 1958: 37), by tidal sloughs that transect levees of the San Joaquin
River (Fig. 9), and by peaty soils along the San Joaquin River that contrast with the bands of inor-
ganic soil bordering waterways of the northern Delta (Coshy 1941). Consequently, it seems pro-
bable that the southern part of the pristine Delta was flooded and drained more nearly like tidal
marshes of the bays than like the naturally leveed marshes near the Sacramento River.
VEGETATION
Vascular plants
~
visually dominate the vegetation of tidal marshes and distinguish the mar-
shes from mudflats. Our discussion of these plants considers their distribution with respect to geo-
graphic location, elevation, and other environmental variables. In addition, we attempt to estimate
the quantity of organic material that vascular plants of tidal marshes export to the rest of the
estuary. Distribution of Species
Geographic and vertical trends.
About 125 species of vascular plants have been reported
from tidal marshes of the San Francisco Bay estuary. Most of these species are native to California
(Appendix A), but some have been introduced from other parts of the world (Table 3).
Diversity generally increases from San Francisco Bay to the Delta. Whereas individual
marshes around San Francisco Bay typically contain 13 or 14 species of native plants, specific
sites in the Delta contain about 40 species. Composite regional lists imply even greater differences
in diversity: only 15 native species reportedly live in tidal marshes around San Francisco Bay,
but about 30 reportedly live around San Pablo Bay and Carquinez Strait, 40 around Suisun Bay,
and 80 in the Delta.
San Francisco Bay and the Delta differ in kinds as well as numbers of tidal-marsh plants.
Inhabitants of San Francisco Bay’s marshes belong to the group of plants that characterize
California salt marshes (Macdonald 1977). Few species from San Francisco Bay, however, have
also been reported from tidal marshes of the Delta. Rather, the Delta’s marshes are dominated by
other plants that typically inhabit low-altitude fresh-water marshes in California (Mason 1957).
Common picldeweed
(Salicornia pacifica)
and California cordgrass
(Spartina foliosa)
domi-
nate the tidal-marsh vegetation around San Francisco Bay. Common pickleweed generally mono-
polizes tidal-marsh plains at elevations near and above MHHW (Hinde 1954:218). Excepting salt-
marsh dodder
(Cuscuta salina,
a parasite on common pickleweed), additional species on tidal-
marsh plains typically grow in scattered patches next to sloughs, natural uplands, and man-made
levees. These plants include salt grass
(Distichlis spicata),
marsh Grindelia (Grindelia humilis),
halberd-leaved saltbush
(Atriplex patula
ssp.
hastata),
alkali heath
(Frankenia grandifolia), and
2 Vascular plants (Phylum
Tracheophyta)
contain veinlike channels that convey metabolic materials
between roots, stems, and leaves. Other kinds of tidal-marsh plants, such as diatoms, are not described in this
chapter.
363

SAN FRANCISCO BAY
Fig. 8. Marshes of San Francisco and San Pablo bays as mapped before significant human
disturbance. Locations on Fig. 2.
SOURCES OF INFORMATION. Channels and ponds are traced from unpublished 1:62,500-
scale compilations, by D. R. Nichols and N. A. Wright, of l:10,000-scale topographic maps pre-
pared shortly after the California Gold Rush by A. F. Rodgers and David Kerr of the U. S. Coast
Survey. Topographic contours, shown near Palo Alto Baylands only, are generalized from a mo-
dern 1:24,000-scale topographic map.
INTERPRETATIONS. Sloughs near Palo Alto Baylands, surveyed in 1857, show relation of
tidal-marsh channels to active and abandoned mouths of an ephemeral fresh-water stream, San
Francisquito Creek. The active mouth of this stream joins an average-size slough. The abandoned
mouth lacks a comparable connection with San Francisco Bay, and a finger of marsh occupies a
vestige of the old stream channel. Natural levees of both the active and abandoned courses of San
Francisquito Creek, built by the stream when it overtopped its banks (Westdahl 1897; Gerow and
Force 1968:24-27), cause the topographic con.tours to point downstream, as on a ridge, rather
than upstream, as in a valley.
Guadalupe Slough followed a shortcut to San Francisco Bay when Rodgers and Kerr surveyed
its course in 1857. At some earlier time, marshland presumably intervened between the starred
meander and the bay (K. Lajoie pers. comm.). Erosion along the edge of the Bay probably re-
moved this marsh. Similar erosion took place in this area during the late 19th century despite the
predominance of deposition along most other shorelines (Fig. 6).
Ridges at the bayward margins of marshland may have caused water to collect in large ponds
near San Lorenzo and to drain away from San Pablo Bay near Mare Island. Ponds near San Loren-
zo appear on maps as old as F. W. Beechey’s chart of San Francisco Bay, surveyed in 1827-1828
(Harlow 1850:64). When Kerr mapped them in detail 30 years later, he labelled the largest, "crys-
tal salt pond." Predictably, commercial production of salt from San Francisco Bay began in this
area (Ver Planck 1958:107). The berm along the bayward edge of a modern marsh near Mare Is-
land (see Fig. 7) probably resembles the landform that caused the sloughs to drain northward
when A. F. Rodgers surveyed them in 1856. A possible ancestor of the discontinuous trough at
the southern edge of the modem marsh supplied Rodgers with a name, "Long Pond", for the tri-
angulation station at left.
364

ATWATER ET AL" TIDAL MARSHES
SAN
FRANCISCO
PALO
ALTO BAYLANDS
GUADALUPE SLOUGH
MARE ISLAND
Tidal channels
Pond
Ephemeral stream
Topographic contour
Elevations in meters above
NGVD
Land above reach of autumnal high tides
SAN LORENZO
0
I
2
3
Km
365

SAN FRANCISCO
BAY
Fig. 9. Marshes of the Sacramento-San Joaquin Delta as mapped before significant human
disturbance. Locations on Fig. 2.
SOURCES OF INFORMATION. The USC&GS prepared no detailed maps of pristine marshes
in the Delta until 1930-1940. Most channels and topographic contours on these diagrams are based
on 1:31,680-scale plane-table sheets surveyed in 1906-1908 by the USGS. Some marshes had been
leveed (Fig. 3) and some channels modified before these maps were made. Allowing for errors in
map-making, the courses of river channels match the meanders shown on a 1:250,000-scale map
by Ringgold (1852). The approximate courses of tributaries to Disappointment Slough are sketch-
ed from Cosby’s (1941) l:63,360-scale base map and, where highlighted by tonal differences be-
tween soils, from modern aerial photographs. Additional waterways probably existed before con-
struction of dikes, but tall, dense stands of tules
(Scirpus
spp.) and other plants undoubtedly
prohibited detailed mapping by plane-table methods. Elevations of natural levees along the Sacra-
mento and San Joaquin rivers are consistent with verbal descriptions assembled by Thompson
(1958: 36-37).
INTERPRETATIONS. The Sacramento River created most of the landforms near Babel Slough.
The complex lobes of high ground, the largest of which enclosed Babel Slough, were built by sedi-
ment-laden flood waters that surged over or through the broad natural levees that flank the Sacra-
mento River. In the bird-foot delta of the Mis.,dssippi River, such lobes are called crevasse or over-
bank splays (Coleman and Gagliano 1964). Paired fingers at the distal ends of the lobes represent
the narrow levees of distributaries. Floods converted the Yolo Basin into a lake or river (Gilbert
1917:14-15) that accommodated so much more water than its parent that, on occasion, the dis-
charge from the Yolo Basin transected and hydraulically dammed the Sacramento River near Rio
Vista (Thompson 1958:448,453). The 1.5-m contour locates the approximate northern limit of
tidal water in the historic Yolo Basin during times of low Sacramento River discharge. During such
low river stages, tides in Yolo Basin probably communicated with the rest of the estuary via the
basin’s outlet near Rio Vista. The top edge of the map approximates the northern boundary of
tidal marsh as mapped in 1906-1908 and as generalized in Figs. 2, 3. Additional marshes covered
higher parts of the Yolo Basin according to the USGS plane-table sheets.
Disappointment Slough and its tributaries more nearly resemble the typical drainages of tidal
marshes bordering the bays. Lacking a river at its head, Disappointment Slough was probably cre-
ated and maintained by tidal water that flowed in and out of nearby marshes. Low levees appar-
ently forced some adjoining marshes to drain away from the San Joaquin River but, unlike the
high borders of the Sacramento River near Babel Slough, these levees allowed tidal water to tra-
verse the banks of the river in such channels as Disappointment Slough and Twenty-one-mile
Slough.
366

ATWATER ET AL: TIDAL MARSHES
BABEL SLOUGH
:,
DISAPPOINTMENT SLOUGH
o
~
2
3 Km
38002
’
30"-
Topographic contour.
~
Channels, chiefly tidal during late
.... :~.0 ....
Elevolions in meters
...~////-"~-.~
summer and autumn. Arrow
above NGVD.
gives direction of flow toward
Suisun Bay.
~
Land above reach of most
autumnal high tides
Ephemeral distributary
367

SAN FRANCISCO BAY
TABLE
3. COMMON INTRODUCTIONS IN TIDAL MARSHES
OF THE SAN FRANCISCO BAY ESTUARY.
a
FAMILY
(Monocotyledons)
GRAMINEAE
Grass family
(Dicotyledons)
CAROPHYLLACEAE
Chickweed family
CHENOPODIACEAE
Goosefoot family
COMPOSITAE
Sunflower family
CRUCIFERAE
Mustard family
DIPSACACEAE
Teasel family
LABIATAE
Mint family
LEGUMINOSEA
Pea family
PLANTAGINACEAE
Plantain family
POLYGONACEAE
Buckwheat family
PONTEDERIACEAE
Pickerel-weed family
SOLANACEAE
Nightshade family
UMBELLIFERAE
Carrot family
VERBENACEAE
Vervain family
Linnean name SPECIES Common name
Bromus diandrus
Roth var.
gussonei
(Pad.)
Coss & Durieu
B. mollis L.
Cortaderia selloana
(Schult.) Asch. & Graebn.
Festuca elatior L.
Hordeum leporinum
Link.
Polypogon monspeliensis
Buckl.
Spartina patens
(L.) Greene
Spergularia media
(L.) Presl.
Atriplex semibaccata
R. Br.
Chenopodium album L.
Cirsium vulgare
(Savi) Ten.
Cotula australis
(Sieber) Hook.
C. coronopifolia L.
Lepidium lat~folium L.
Dipsacus fullonum L.
Mentha piperita L.
Melilotus albus
Desr.
Plantago major L.
Rumex crispus L.
Eichhornia crassipes
(Mart.) Solms.
Solanum dulcamara L.
S. nodifolium
Jacq.
Apium graveolens L.
Conium maculatum L.
Foeniculum vulgare Mill.
Lippia nodillora
Michx. var.
rosea
(D. Don) Munz
Gussone’s dpgut grass
Soft chess
Pampas grass
Meadow fescue
Hare barley
Rabbit’s-foot grass
Salt hay
Sand-spurrey
Australian saltbush
Lamb’s quarters
Common thistle
Australian Cotula
Brass buttons
Broad-leaved pepper-grass
Fuiler’s teasel
Peppermint
White sweet clover
Common plantain
Cudy dock
Water hyacinth
Climbing nightshade
Small-flowered nightshade
Celery
Poison-hemlock
Sweet fennel
Garden Lippia
a The list draws from the same sources as Appendix A. In addition, it includes R. E. Mall’s report of salt hay
at Southampton Bay (Munz 1968:195), a find which we have not duplicated either at Southampton Bay or
anywhere else in the estuary. Among grasses other than salt hay, all commonly inhabit the landward fringes of
tidal marshes around San Pablo and Suisun Bays except for pampas grass, which grows mainly in the Delta. The
principal species among dicotyledons include Australian saltbush (all bays), curly dock (San Pablo and Suisun
bays in 1975 but not, with a few exceptions, in 1977), brass buttons (wet places near high-tide levels around
Suisun Bay), and garden Lippia (the Delta).
fleshy Jaumea
(Jaumea carnosa).
California cordgrass fringes tidal-marsh plains where they descend
into mudflats. Near MTL it forms pure stands, but midway between MTL and MHHW it interming-
les with red pickleweed
(Salicornia rubra),
and at higher elevations it yields to common pickle-
weed. Subsidence due to ground-water withdrawal probably accounts for the anomalous presence
of Califomia cordgrass on the tidal-marsh plain at Palo Alto Baytands (Fig. 7; Harvey 1966).
Common tule
(Scirpus acutus), Olney’s bulrush
(Scirpus olneyi),
cat-tails
(Typha spp.), com-
mon reed
(Phragmites communis)
and arroyo willow (Salix lasiolepis)
dominate islands of pristine
368

ATWATER ET AL: TIDAL MARSHES
marsh in the Delta. Typical associates of these plants include swamp knotweed
(Polygonum
coccineum),
broadfruited bur-reed
(Sparganium eurycarpum)
and Pacific
silverweed (Potentilla
egedei) (Scirpus-Phragrnites-Typha
association, Table 4). Another associated species is marsh
bindweed
(Calystegia sepium),
a morning glory that twines around tules and reeds. Below MTL
these plants yield to monotonous stands of tules
(Scirpus acutus and Scirpus californicus)
and, in
areas of quiet water, to floating aquatic species
(Ludwigia
association, Table 4).
Tidal-marsh plants of San Pablo Bay, Carquinez Strait, and Suisun Bay provide an intricate,
mutable transition between salt marshes of San Francisco Bay and freshwater marshes of the Delta
(Table 4, Appendix A; Figs. 7, 10). Details of this transition include: (1) Species from opposite
ends of the spectrum overlap to varying degrees in the middle. Most salt-marsh plants of San Fran-
cisco Bay live around San Pablo Bay and Carquinez Strait
(Spartina and Salicornia pacifica
associa-
tions, Table 4) and also around Suisun Bay (Appendix A). Salt grass and marsh Grindelia even
grow in the western Delta. Neither California cordgrass nor red pickleweed, however, appear to
grow east of Carquinez Strait. Cosmopolitan species of the Delta include rules and bulrushes
(Scirpus acutus, S. californicus, S. olneyi),
cat-tails, and common reed. All of these plants range as
far west as the large sloughs north of San Pablo Bay. East of San Pablo Bay they generally supplant
California cordgrass (Fig. 10;
Scirpus californicus
association, Table 4). (2) Some common plants
of San Pablo and Suisun bays are scarce or absent in tidal marshes of the Bay and Delta. These spe-
cies include alkali bulrush
(Scirpus robustus),
sea milkwort
(Glaux marit#na),.and
soft bird’s beak
(Cordylanthus mollis).
(3) The vertical range and relative abundance of many species vary with
geographic location. Common pickleweed, for instance, shortens its vertical range and reduces its
ubiquity and abundance from west to east (Fig. 10). (4) Plant communities change not only from
the Pacific Ocean to the Sacramento and San Joaquin rivers but also from mouths to heads of
sloughs that drain major upland creeks north of San Pablo and Suisun bays. (5) The vertical and
geographic ranges of some species, most conspicuously the tules and bulrushes, can change signi-
ficantly within one or two years (Figs. 10, 11).
Reasons for trends. Environmental variables that may influence the distribution of vascular
plants in tidal marshes include the reproductive methods of the plants, the frequency and duration
of tidal flooding, and characteristics of the soil such as particle size, salinity, aeration, moisture,
and nutrients (Chapman 1960). Competition between species may also restrict the ranges of some
plants. Available evidence from the San Francisco Bay estuary used to test several of these possi-
bilities implies that soil salinity, tidal inundation, and interspeciflc competition largely control the
distribution of local species.
High soil salinity related to saline tidal water causes many plants to disappear toward San
Francisco Bay. Too much salt inhibits growth, as evidenced in the case of bulrushes and tules west
of the Delta by the decrease in their size and abundance during the drought of 1976-1977 (Figs.
10, 11). The damage or demise of these plants mostly reflects the increased salinity of tidal water
rather than the decreased local rainfall because daily high tides inundate the softs of most bulrush-
es and tules. Excessive salt likewise appears to discourage the growth of bulrushes, cattails, and
rushes
(Juncus
spp.) in leveed marshes north of Suisun Bay (Mall 1969:36). Consistent with its
reduced seed production in tidal marshes during 1976 and 1977, alkali bulrush produces few seeds
in these leveed marshes if vemal soils contain more than 24 % o salt (Mall 1969:38).
The salinity of soils may also contribute to the vertical zonation of vascular plants if, as
reported from north of San Pablo Bay, salinity during the growing season increases with elevation
(Fig. 12)o According to field and greenhouse studies by Mahall and Park (1976b), salt rather than
aeration or nutrients probably favors pickleweed over cordgrass at high elevations near Black John
Slough and Mare Island. Similar considerations may account for the scarcity of tules and bulrushes
above high-tide levels around San Pablo Bay, Carquinez Strait, and Suisun Bay.
369

SAN FRANCISCO BAY
50:
e
TYPICAL ABUNDANCE
UBIQUITY OF
WHERE PRESENT
OCCURRENCE
o
Locally present
~
~i~iiiiiiii
u~~
Typically present
20 -Ju~
(~
Z<C
A
\
1o
0
0
20
40
60
80
100 km
1.0-
’ ’ ;’
1.0
0
rv
I0
0
-1.0
0
- i~L,T~ ~-~
-1.0
~
""
~
:s
"
CC SS
SMS
San Pablo
Carquinez
Suisun
I
Sacramento-
Golden
S,F.
I
~
IE
W Gate I
Bay
Bay
Strait
Bay
San Joaquin Delta
- 1.0
-0
-1.0
CLIMATE AT
NEARBY
LOCALITIES
APPROXIMATE
SALINITY OF
APPLIED WATER,
1969-1975
Distich/is spicata
salt grass
Salicornia pacifica
common pickleweed
Sci~pus Spp,
a - S.
} rules
acutus
c - c ~alifornicus
r
-
S. robustus
alkali bulrush
S~artina foliosa
California co~dgross
LOCATION
370

ATWATER ET AL: TIDAL MARSHES
The frequency and duration of tidal flooding commonly correlate with vertical ranges of
vascular plants in tidal marshes (Johnson and York 1915; Purer 1942; Hinde 1954). For the San
Francisco Bay estuary, this correlation implies causation according to two lines of evidence: (1)
the scarcity of cordgrass, tules, and bulrushes above MHHW (Fig. 10) may indirectly result from
tidal inundation, if, as seems likely, the vertical increase in salinity reflects more prolonged desic-
cation at higher elevations; and (2) tidal water may prevent pickleweed from growing at low
elevations by dislocating, suffocating, or leaching seeds and seedlings (Chapman 1960:45-49;
Mahall and Park 1976c).
Though the disappearance of species toward the Golden Gate reflects the physiological
hardships of saline water, the disappearance of species toward the Delta may represent a socio-
logical consequence of fresh water. According to greenhouse experiments, the principal vascular
plants of San Francisco Bay’s tidal marshes grow better in fresh water than in saline water (Bar-
bour and Davis 1970; Barbour 1970; Phleger 1971). The paradoxical disappearance of these
species toward the Delta therefore implies either that saline soils uniquely contain vital nutrients
or that other species competitively exclude salt-marsh plants from brackish- and fresh-water areas.
The vertical ranges of coexisting, potential competitors (Fig. 10) suggest a role for competition.
California cordgrass, for instance, seems to yield to alkali bulrush at elevations greater than 0.5 m
at Schultz Slough, but below 0.5 m the abundance of California cordgrass remains the same as at
more saline marshes such as China Camp. Similarly, bulrushes and rules appear to eliminate
Fig. 10. Regional and vertical distribution of the principal vascular plants in six tidal marshes
of the northern San Francisco Bay estuary. SYMBOLS FOR UBIQUITY
AND
ABUNDANCE OF
PLANTS (top). Solid lines and black shading indicate widespread occurrence at or near a given
elevation; dashed lines and stippled shading show relatively sparse occurrence. The width of each
figure represents abundance and ranges from 1-10% (one line-width) to 100% (broadest part of
figure). Abundance approximates the area, relative to other vascular plants, covered by the pro-
jected canopy of the live individuals of a given species within a 3-m
2
circle centered at a point of
measured elevation. Symbols depict conditions as of autumn 1975, and principal changes observed
in autumn 1977.
DISTRIBUTION
OF
PLANTS
’WITH RESPECT TO APPROXIMATE TIDE
LEVELS, BAY-WATER SALINITY, AND CLIMATE (main figure). All localities are projected to
the nearest point along a longitudinal profile of the estuary. This procedure generalizes the com-
parison of vegetation with longitudinal trends in environmental variables; for example, the water
serving the marsh near Schultz Slough can contain less salt (Matthew et al. 1931:340-364) and rise
to slightly higher levels (see MHHW for Lakeville, identified elsewhere in this caption) than water
at the nearest point along the longitudinal profile in southeastern San Pablo Bay. Vertical ranges of
plants were measured along or near leveled transects (Fig. 7; Atwater and Hedel 1976). With
respect to tidal datums these ranges may err by 0.1 m or more (see text). Horizontal rows of dots
show the highest elevation of pristine tidal marsh near transects at Richardson Bay and Sand
Mound Slough; plants above this level are rooted in artificial levees. Marshes are abbreviated as
follows: RB, Richardson Bay; CC, China Camp; SS, Scliultz Slough; SB, Southampton Bay; HS,
Hill Slough, SMS, Sand Mound Slough (see Fig. 2 for locations). Open circles along lines for tidal
datums represent gauges for which differences between various planes of reference have been
determined by the NOS (1977a, 1977b; Table 1). Locations of tide gauges are, from west to
east: Presidio (San Francisco); Pinole Point and, for the higher MHHW, on the bottom graph,
Lakeville (3 km SE of SS); Crockett (4 km W of SB); entrance of Suisun Slough (about 13 km SW
of HS); Port Chicago (between Martinez and Shore Acres), Pittsburg (3 km W of SMS); and Old
River at Orwood (10 km SE of SMS). Surface-water salinities follow Conomos and Peterson
(1977). Climatic data (U. S. Department of Commerce 1964) refer to the following localities, list-
ed from west to east: downtown San Francisco; San Rafael (between RB and CC); Hamilton Air
Force Base (2 km N of CC); Petaluma (3 km NW of SS); Crockett; Port Chicago; Fairfield (3 km W
of HS); and Antioch (15 km W of SMS).
371

SAN FRANCISCO BAY
372

ATWATER ET AL: TIDAL MARSHES
CALENDAR YEAR
1974
1975
1976
1977
Og 10’
>’E
0 Ja A JI O Ja A JI O Ja A JI 0
~m 20
<
]k
S. olneyi
/~
S, robustus
~
S. cafifornicus
- 20
-10
,4O
’2O
0 I
1975
1976 1977
GROWING SEASON
Fig. 11. Decrease in size and abundance of
Scirpus spp. (bulrushes and tules) bordering Car-
quinez Strait during the drought of 1976-1977. The plots are located near the leveled transect at
Southampton Bay (Fig. 7) at approximate elevations of 0.9 m, 0.4 m, and -0.5 m. Conditions in
1975 are estimated by comparing (qualitatively) living culms (above-ground stems) in plots along
the transect in October 1975, with dead culms in September 1976. Measurements and counts of
dead culms attempt to exclude those that grew before 1975, but similarities among dead culms of
differing vintage result in large uncertainties, particularly for
S. californicus.
Conditions in 1976
and 1977 were determined from measurements and counts of living plants within the plots, ex-
cepting heights for 1977, which had to be scaled elsewhere because of the scarcity and absence of
Scirpus
within the plots. Vertical bars approximate the range of observed or estimated values. The
top graph shows monthly averages of salinity of near-surface water at the eastern end of Carquinez
Strait (USBR station D-6). The shaded area spans 1 SD (approximately 70%) of the monthly ave-
rages from October 1974 to September 1977. Data show that Carquinez Strait contained unusual-
ly saline water during the winter and spring of 1976 and 1977.
common pickleweed from the lower part of its salt-water range, as confirmed by the reciprocal
spread of common pickleweed into low-lying areas denuded of tall tules and bulrushes during the
drought of 1976-1977 (Fig. 10).
Productivity
According to classic investigations in the southeastern United States, the vascular plants of
extensive tidal marshes supply most of the organic material on which local estuarine animals
depend (Teal 1962; Day et al. 1973). Recent studies in Georgia and Holland, however, point to
373

SAN FRANCISCO BAY
estuarine algae and riverine or marine debris as principal sources of estuarine food (Haines 1976,
1977; Wolff 1976). Given current controversy about these studies and shortcomings of related
information about the San Francisco Bay estuary, we can hardly guess what percentage of food in
this estuary originates in the vascular plants of its tidal marshes. In the following discussion we
merely assemble information about the production of food in tidal marshes, estimate how much of
this food enters other parts of the estuary, and offer a tentative comparison with the production
of food by floating algae.
Conventional
methods equate export by tidal-marsh plants with a calculated or arbitrary
percentage of their net productivity. Net productivity refers to the quantity of organic matter that
living plants store in excess of what they respire (Odum 1971:43). Bacteria, insects, and other or-
ganisms may consume some of this organic matter in the marsh, and high tides may move another
fraction toward upland areas; hence, only a fraction of net productivity in a marsh can reach other
parts of the estuary. The simplest measure of net productivity is the seasonal peak in the weight of
live, above-ground, annual tissues (peak standing crop). Peak standing crop underestimates net pro-
ductivity, however, because living tissue disappears during the growing season (Hardisky and Rei-
mold 1977; Reimold and Linthurst 1977:87; Kirby and Gosselink 1976).
Local measurements of standing crop (reported herein as grams of dry plant material per
SW
PP-CC
8OO
600
400
200
0
20
191o
AUTUMNAL
WEIGHT OF
LIVE, ABOVE-
GROUND TISSUES,
1972
Salicornia .....
Spartina -- --
AERATION OF SOIL
AT END OF GROWING
SEASON,
1973
(rate of diffusion,
ng
0
2
cm-2,min
-1)
0.4
0.2
0
P4 P3 P2
P1
SALINITY OF WATER
IN SOIL DURING
GROWING SEASON,
1972 (%*)
DOMINANT VASCULAR PLANT
0
Salicornia
pacifica
y Spartina
foliosa
RELATIVE HEIGHT
OF GROUND (rn)
DISTANCE (m)
STATION
Fig. 12. Autumnal weight (dry) of above-ground tissues of
Spartina foliosa
and
Salicornia
pacifica
and environmental variables of a profile near Black John Slough. Aeration of soil (upper
30 cm) at end of 1973 growing season and salinity of water in soil (upper 35 cm) in 1972 are data
of Mahall 1974 and Mahall and Park 1976a, c. These data are compared with normal ocean salini-
ties (SW) and the range of salinity of Bay water between Pinole Point (PP) and China Camp (CC)
during 1969-75 (station 14 of Conomos and Peterson 1977). Topographic profile is referenced to
estimated MHW datum. Vertical bars represent I SD of the measurements at each station; the
diameter of dots on lower two graphs exceeds the length of bars.
374

ATWATER ET AL: TIDAL MARSHES
square meter, g’m
"2)
suggest that vascular plants of the San Francisco Bay estuary produce at least
as much organic material as their counterparts in the eastern United States (Fig. 13). Peak standing
crops of California cordgrass
(Spartinafoliosa)
range from 300 to 1700 g-m
"2
, comparable with its
eastern relative, smooth cordgrass
(Spartina alterniflora).
Common pickleweed
(Salicornia pacifica)
creates standing crops of 500-1200 g-m
"x
, likewise similar to the salt hay
(Spartina patens),
salt
grass
(Distichlis spicata),
and short variety of smooth cordgrass which commonly inhabit high parts
of Atlantic-coast marshes. The largest reported above-ground standing crop in North American ti-
dal marshes may belong to rules in the Sacramento-San Joaquin Delta which, at low elevations
along sloughs, grow 3-4 m tall and weigh about 2500 g-m
"z
.
Adjusted for slight loss during the growing season and extrapolated to other species and
localities, the standing crops of plants from a variety of marshes (Fig. 13) imply that net above-
SPECIES
alterniflora
Spart,’na
foliosa .....
Salicomiapacifica ......
Distichlis
spicata
.......
Typha
spp
........
Phragmites
communis ......
Mixed
Phragmites,
__
Tyl~ha,
Scirpus
spp.
Scirpus
sp. cf.
S. californicus .....
Scirpus lacustris
(cultivated)
.....
SEASONAL PEAK IN WEIGHT OF
LIVE ABOVE-GROUND TISSUES
(g,m
-2)
1000 2000
.J. j
~ } tall variety
~
~,
mixed short and
~
~"
tall varieties
,
~"
N= 15
~
N= 16
~
N=8
N=15
~
N =
24
~
’N=8
"N=5
1000
2000,
300O
LOCATION & REFERENCE
Louisiana
K&G
Delaware
D
Louisiana
K&G
Delaware
D
Tota¥ Ck. C
Black John
SI. M (P1,P2)
Mare
Is. M (MI)
Tola¥ Ck. C
Mare
Is. M (M4-M6)
Black John
SI. M (P4)
Delaware
D
Virginia
K
New Jersey
K
Delaware
D
t
Sand
Mound A
t Slough
Germany
K
3000
Fig. 13. Comparison of peak above-ground standing crops (dry weight) for some tidal-marsh
plants. Weights refer to annual tissues that were harvested from multiple plots near the end of the
growing season. Error bar shows 1 SD and N denotes the number of plots. Abbreviations for
references: A-Brian Atwater unpublished data. Harvests were made in October 1977. Plots, 0.50
m: for mixed vegetation and 0.12 m
=
for
Scirpus,
are located on a remnant of pristine marsh near
the transect of Atwater and Hedel (1976, pl. 8). Elevations relative to NGVD are 0.6+0.2 m for
mixed plots and -0.4+0.2 m for
Scirpus.
Brown leaves attached to green Phragmites are included
with live standing crop. Samples were oven-dried to constant weight at 100
°
C. Infertile flowers
prevented definite identification of Scirpus
sp. C-Cameron (1972:61, 64, 66; pers. comm.). Graph
shows harvests of July 1969. Peak standing crops at Tolay Creek in autumn 1968 were 1400
g’m
-~
(dry weight) for
Spartina
and 1050 g’m
-2
for
Salicornia.
D-Compilation by Daiber et
al. (1976:76, 78, 82). K-Compilation by Keefe (1972). K & G-Kirby and Gosse[ink (197.6).
M-Mahall and Park (1976a): Harvests made in 1972. Weights for
Salicornia
exclude living stems
from previous years. Symbols in parentheses denote stations. Mahall’s Mare Island marsh is located
a few kilometers west of the locality plotted on Fig. 2.
375

SAN FRANCISCO BAY
ground productivity by the vascular plants of our estuary’s tidal marshes averages between 500
and 1500 g-m
"2-yr"1
. Selecting 800 g’m
"2"yr"I
as a typical value and multiplying by the present
area of tidal marsh yields an estimated net above-ground productivity of 10
x
l g.yr
"1.
Tides and
rain flush approximately half of such organic: material from cordgrass marshes (Teal 1962; Day
et al. 1973; Cameron 1972:60), but the average fraction that enters the waterways and bays of
the San Francisco Bay estuary is probably smaller because of the proximity of most tidal-marsh
surfaces to high-tide levels (Fig. 7), which reduces the frequency of tidal flushing relative to the
lower areas dominated by California cordgrass. If one fourth of net above-ground productivity
enters other parts of the estuary, then annual export equals 2.5 x 101 o g (dry weight), which in
turn equals 101° gC because carbon constitutes about 40% of the dry organic matter (Keefe
1972). We therefore estimate that the vascular plants of tidal marshes annually contribute 10 bil-
lion grams of carbon to the rest of the San Francisco Bay estuary.
Several perspectives aid in conceptualizing l 0 billion grams of carbon. (1) Net productivity
of floating algae in the bays, chiefly diatoms and flagellates, averaged about 200 gC’m
"2-yr"1
in
1976-77 (Peterson 1979), all of which is available to other aquatic organisms. The bays currently
cover approximately 100 km
~
(Conomos and Peterson 1977), so these algae produced 2 x 1011
g of carbon, roughly 20 times our estimate of export by vascular plants of tidal marshes. (2)
Historic destruction of tidal marshes (Figs. 1, 3) has probably caused a 10- to 20-fold reduction
in their export of organic material. (3) At 101 o gC, export from vascular plants of tidal marshes
translates into roughly 5 lbs. of carbon per year for each of the 5 million human inhabitants who
surround the San Francisco Bay estuary.
ACKNOWLEDGMENTS
Persons who contributed opinions, information, or logistical assistance not otherwise ac-
knowledged include Joel Bergquist, Frances DeMarco, Harry George, H. T. Harvey, E. J. Helley,
R. F. Holland, Zondra Kilpatrick, H. L. Mason, F. H. Nichols, David Plummer, and G. J. West. Our
principal illustrators are Yosh Inouye (Fig. 10-13), Barbara Lee (Fig. 5), Hylton Mayne (Fig. 6),
and Steven Talco (Figs. 1, 2, 3, 7). The text incorporates suggestions from reviews by John Bris-
coe, K. G. Dedrick, R. T. Huffman, J. C. Kraft, Robert Nadey, and G. F. Somers. Authors divide
and share responsibilities as follows: Atwater--text, tables, and Figs. 1, 2, 3, 6-13; Conard-Ap-
pendix A, Tables 4-5 and related text; Dowden-Figs. 4, 5; Hedel-Figs. 2, 3, 7, 10; Macdonald-
Appendix A, Tables 4-5; and Savage-Append:~x A, Table 4. John Coburn (USBR) supplied the
salinity data shown in Fig. 13.
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376

ATWATER
ET AL: TIDAL MARSHES
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ATWATER ET AL: TIDAL MARSHES
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38O

ATWATER ET AL: TIDAL MARSHES
APPENDIX A
COMMON VASCULAR PLANTS IN TIDAL MARSHES
OF THE SAN FRANCISCO BAY ESTUARY.
The list excludes introduced species denoted by Munz and Keck (1959). Asterisk designates
rare or endangered plant according to Powell (1964). Scientific names follow Munz (1968) and
Munz and Keck (1959) excepting nomenclature for
Athyrium, Cornus
and
Salicornia,
which
follows Mason (1957). Many of the common names are taken from Abrams (1923-1960), and
parenthetical descriptions of principal taxonomic groups are abridged from Mason (1957). Abbre-
viated headings refer to localities (Fig. 2): Palo Alto Baylands; RB, Richardson Bay; CC, China
Camp; SS, Schultz Slough; NA, Napa marshes; SB, Southampton Bay; MZ, Martinez, SA, Shore
Acres; HS, Hill Slough; SN, marshes N of Suisun Bay; BI, Browns Island; SMS, Sand Mound
Slough; SGS, Snodgrass Slough; DL, marshes and sloughs in the Delta.
Sources of information:
PA-Cooper (1926), Hinde (1954), and observations by Atwater in 1976.
RB, CC, SS, SB, SA, HS-Collections by Savage in 1975 (SA), 1976 (RB, CC, SS, SB), and 1977
(HS), and supplemental observations by Conard and Macdonald in 1976 (SS, SB)and by Atwater
in 1975 (CC) and 1977 (SB).
NA-Kingsley et al. (1977, Appendix A), lower-marsh and higher-marsh communities.
MZ-Observations by H. L. Mason in 1974.
SN, DL-Observations by H. L. Mason ca. 1970, supplemented with reference to earlier collec-
tions. Listed species belong to the following communities of Mason (undated, pp. 57-59, 71-75):
palustrine,
Salicornia, and Distichlis
(SN); and neuston, buoyan, palustrine, and willow-fern (DL).
BI, SMS, SGS-Reconnaissance by Conard and Macdonald in 1976.
[N. B.: During 1978 and 1979 Atwater collected 40 species at SMS and 38 at SGS, many more
than listed here, and also observed widespread
Salicornia pacifica, Jaumea carnosa,
and
Triglochin
maritima
in pristine marshland at BI. Mason’s
Eupatorium occidentale
is probably
Pluchea pur-
purascens
(Sw.) DC. (marsh-fleabane).]
381

SAN FRANCISCO BAY
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