ECOLOGY OF SMALL MARSHES USING
THREE DIFFERENT WATER SOURCES
by
Richard A. Grosz
A Thesis
Presented to
The Faculty of Humboldt State University
In Partial Fulfillment
Of the Requirements for the Degree
Master of Science
May, 1992 ECOLOGY OF SMALL MARSHES USING
THREE DIFFERENT WATER SOURCES
by
Richard A. Grosz
Approved by the Master's Thesis Committee
Stanley W. Harris. Chairman
David W Kitchen
William R. Sise
Director, Natural Resources Graduate Program Date
92/W-253/06/15 Natural Resources Graduate Program Number
Approved by the Dean of Graduate Studies
Susan H. Bicknell ABSTRACT
Waterbird use and aquatic vegetation were studied during seven seasons and in five units representing three water types at Arcata Marsh and Wildlife Sanctuary (AMWS), 1 July 1990-30 June 1991. Dominant vegetation types were cover-mapped and sampled for species composition, biomass, and stem density. The PH, salinity, turbidity, and water depth measurements also were taken at appropriate vegetation plots. The five study units represented, a saline basin (Klopp Lake) filled with water from Humboldt Bay, a freshwater unit (Butcher Slough Log Pond, BSLP) filled with well water; and three freshwater units filled with treated domestic wastewater effluent.
The PH was greatest in the units in late spring except BSLP where it was highest in late fall. Salinity was greatest in Klopp Lake in mid fall. All four freshwater units had salinities of less than one ppt. The BSLP was significantly less (p<0.05) turbid than the wastewater units from late fall through summer.
Dominant vegetation types included marsh pennywort (Hydrocotyle ranunculoides), lesser duckweed (Lemna minor), broad-leaved cattail
(Typha latifolia), hard-stemmed bulrush (Scirpus acutus), and sago pondweed (Potamogeton pectinatus). Marsh pennywort and lesser duckweed also commonly occurred as understory species in the emergent cover types. Mean stem densities of broad-leaved cattail and hard-stemmed bulrush were greatest in summer and were greater in the wastewater units
(p<0.05) than in BSLP. Biomass of sago pondweed was greatest in all freshwater units during mid fall. BSLP maintained submergent beds later into the fall than the wastewater units. The wastewater units developed
iii iv heavy mats of lesser duckweed over most of their surfaces in the fall.
Coverage of marsh pennywort mats peaked in early fall in Gearheart Marsh and BSLP and in summer in Allen and Hauser Marshes.
Ninety-four species of birds were recorded. There was an annual total of 768,586 bird use-days on the five units. Almost 1/3 of the annual bird use-days occurred during late fall. Shorebirds (58.1 percent) and waterfowl, coots and rails (35.2 percent) accounted for
93.3 percent of annual bird use-days. Lowest bird use occurred in summer.
Bird densities were greatest on Klopp Lake for diving ducks, large and small shorebirds, gulls, and terns. Based on relative area use, great blue herons (Ardea herodias) and ospreys (Pandion haliaetus) used Klopp Lake at greater than expected rates.
BSLP and Allen, Gearheart, and Hauser units had similar patterns of annual bird use. Densities were greatest on these units for herons, egrets, puddle ducks, coots, rails and raptors. Annually, fish-eating divers, represented mostly by some resident pied-billed grebes
(Podilymbus podiceps) used BSLP more than either Klopp Lake or the wastewater units. Black-crowned night-herons (Nycticorax nycticorax) used BSLP at more than twice expected rates but other herons used BSLP at less than expected rates. Cinnamon teal (Anas cyanoptera) and mallards (A. platyrhynchos) were most common on BSLP. The wastewater units were used at or more than 1.5 times than expected rates by herons, all puddle ducks, dowitchers (Limnodromus spp.), and Bonaparte's gulls
(Larus philadelphia). The lesser scaup (Avthya affinis) was the only diving duck present on the wastewater units at expected or greater than V expected rates. American coots (Fulica americana) and rails used all four freshwater units at least 1.5 times more than expected.
Continued annual marsh pennywort removal is strongly recommended, and guidelines should be established to stop encroachment of emergent vegetation into open water and submergent beds. If possible, a freshwater source should be routed into Klopp Lake to reduce high salinities and to allow for possible introduction of additional aquatic vegetation into the water column. An alternative to freshwater would be to introduce eelgrass (Zostera marina) into Klopp Lake. ACKNOWLEDGEMENTS
Although credit is given to one person ultimately, a successfully completed masters thesis can only be accomplished with the support from family, friends, and professors.
It is in this light that I would like to thank my mother and father, Donna and Terry Grosz, for always having faith in my abilities and for supporting me in my decisions. For showing me how to set goals, and more importantly how to achieve them. For teaching me how to look
"down the road" and to be responsible for my actions. Lastly, in raising me with a hard work ethic realizing that nothing of value in life comes easy.
I would like to thank Dr. Stan Harris ("Doc") for accepting me into the Humboldt Graduate Program. In giving me guidance throughout my graduate career and when need be, the extra time not only when dealing with my thesis but also in the classroom. Special thanks to Doc's wife
Lorie for always offering their house to me and my wife Carrie, especially on holidays, but also on those "moments" notice occasions.
Thank you Dr. Kitchen and Dr. Sise for your guidance in statistics as well as helping me with unforseen problems in my thesis.
Carrie, how can I begin to thank you for the endless hours of typing, editing, putting up with the odd hours and late nights. In making sure that I had a warm meal after long hours of working on my thesis. For not letting me quit when times got tough and for providing me support and when time called for it, a push! Not only in being my wife, but also my best friend. Carrie thank you and I love you.
vi TABLE OF CONTENTS Page ABSTRACT � iii
ACKNOWLEDGEMENTS � vi
LIST OF TABLES � x.
LIST OF FIGURES � xi
INTRODUCTION � 1
STUDY AREA � 4
METHODS � 8
Physical and Chemical Sampling � 8
Vegetation Sampling � 9
Wildlife Counts � 10
Statistical Methods � 12
RESULTS � 14
Physical and Chemical Parameters � 14
Vegetation � 18
Bird Use � 33
DISCUSSION � 64
Vegetative Considerations � 64
Waterbird Considerations � 69
MANAGEMENT IMPLICATIONS � 87
CONCLUSION �
LITERATURE CITED � 93
APPENDIXES � 98
A� Mean Number and Standard Deviation of Birds Recorded per Survey on the Marsh Units of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n=number of surveys) � 98
vii viii
TABLE OF CONTENTS (Continued) � Page
B Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Marsh Units During the Early Fall Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 21 August � 1990 108
C� Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Early Fall Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 21 August � 1990 109
D Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Marsh Units During the Mid Fall Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 22 August 1990 - 12 October � 1990 110
E Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Mid Fall Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 22 August 1990 - 12 October � 1990 111
F� Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Marsh Units During the Late Fall Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 13 October 1990 - 3 December 1990 112
G Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Late Fall Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 13 October 1990 - 3 � December 1990 113
H Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Marsh Units During the Winter Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 4 December 1990 - 24 January � 1991 114
Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Winter Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 4 December 1990 - 24 January � 1991 115 ix
TABLE OF CONTENTS (Continued)� Page
J Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Marsh Units During the Early Spring Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 25 January 1991 - 17 March 1991 �116
K Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Early Spring Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 25 January 1991 - 17 March 1991 �117
L Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Marsh Units During the Late Spring Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 18 March 1991 - 8 May 1991 . . . �118
M� Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Late Spring Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 18 March 1991 - 8 May 1991 119
N Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Marsh Units During the Summer Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 9 May 1991 - 30 June 1991 . . . . 120
O Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh units During the Summer Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 9 May 1991 - 30 June 1991. . . . � 121 ����������
LIST OF TABLES Table� Page
1�Average Depth of Secchi Disc Disappearance (cm) in Dominant Free-Floating and Submergent Cover Types at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n = number of samples) �15
2�Salinity (Klopp Lake only) and pH of Five Marsh Units, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 �16
3�Seasonal Average Water Depths (cm) and Standard Deviation under Dominant Cover Types at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. (n = 5 samples/marsh/season).� 19
4� Percentage Cover of Dominant Cover Types, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, Calculated from Aerial Photographs, 1990 - 1991 � 20
5� Percentage Species Composition within Dominant Cover Types at Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 and 30 June 1991, as Measured by Point-frame Scores (N=number of points scored) . . . � 21
6� Mean Number and Standard Deviation of Stems per 30.5 cm x 30.5 cm Plot for Emergent Vegetation, of Oven-dried Biomass (gm) per 35.5 cm x 25.5 cm Plot for Free Floating and Mat Vegetation, and of Mean Rake Readings for Submergent Vegetation at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 and 30 June 1991 � 22
7� Statistical Comparisons of Vegetation Types between Marshes within Seasons. Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 . � 26
8� Number and Percentage of Bird Use-Days (BUD) of Important Species and Percentage of Yearly Bird Use-Days, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, � 1 July 1990 - 30 June 1991 35
9� Comparison of Total Annual Bird Use-Days Per Five Hectares at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California. 1984-1986, 1990-1991. .� 40
10� Total Annual Bird Use-Days (BUD) and Relative Area Use Indices of Important Birds According to Water Sources of Marsh Units at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 . � 43 �����������
LIST OF FIGURES Figures� Page
1� Location of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California � 5
2� The Water Flow Patterns (arrows) and Water Sources of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 6
3� Approximate Location of Bird Survey Points and Area Surveyed From Each Survey Point at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 11
4� Seasonal Mean Water Depth for Allen, Gearheart, and Hauser Marshes, Arcata Marsh and Wildlife Sanctuary, Humboldt � County, California 1 July 1990 - 30 June 1991 17
5� Mean Rake Reading and one Standard Deviation of Widgeon Grass in Klopp Lake, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 23
6� Mean Stem Density (stems per 30.5 cm x 30.5 cm plot) and One Standard Deviation of Broad-leaved Cattail for the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 25
7� Mean Stem Density (stems per 30.5 cm x 30.5 cm plot) and One Standard Deviation of Hard-stemmed Bulrush for the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 28
8� Mean Dry Weight (grams per 35.5 cm x 25.5 cm plot) and One Standard Deviation of Marsh Pennywort for the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 30
9� Mean Dry Weight (grams per 35.5 cm x 25.5 cm plot) and One Standard Deviation of Lesser Duckweed for the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 32
10� Mean Rake Reading and One Standard Deviation of Sago Pondweed for the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. . � 37
11� Total Seasonal Bird Use-Days (BUD) (A) and BUD per 5 Ha (B) by Bird Groups at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 38
xi xii 12� Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Fish-Eating Divers, Arcata Marsh and Wildlife Sanctuary, Humboldt County, � California, 1 July 1990 - 30 June 1991 41
13� Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Herons and Egrets, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 45
14� Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Puddle Ducks, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 47
15� Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Diving Ducks, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 50
16� Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Coots and Rails, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 53
17� Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Large Shorebirds, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 55
18� Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Small Shorebirds, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 58
19� Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Gulls and Terns, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 59
20� Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Raptors, Arcata Marsh and Wi ldlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 � 62 INTRODUCTION
Wetlands lona have been considered wastelands suited for "reclamation projects," such as drainage for agriculture or filling for
industrial and residential development (Tiner 1984). An estimated 54
percent of the original wetlands once present in the lower 48 states has been lost (Frayer et. al 1984). California has lost more than 90% of
it's original wetland resources (Tiner 1984). In California,
Onuf et. al (1978) estimated that 50 percent of the coastal marshes, mud
flats, bays, lagoons, sloughs, and estuaries exclusive of San Francisco
Bay had been destroyed by dredging and filling.
Man's concern for the value of wetlands has changed dramatically during the past three decades as the inherent worth of wetlands has become better recognized (McCormick 1978). In addition to providing year-around habitats for resident birds, wetlands are especially important as breeding grounds, wintering areas, and feeding grounds for migratory waterfowl and numerous other birds (Tiner 1984). Recently wetlands also have been shown to be useful in wastewater treatment
(Office of Technology Assessment 1984, Tiner 1984).
Creation of artificial ponds for waterfowl can partially offset loss and degradation of natural wetlands (Uhler 1964). Lokemoen (1973) and Evrard (1975) suggested that man-made stock ponds and dug ponds can serve as valuable wildlife habitat. However, relatively little research has been conducted to determine the importance of man-made ponds for waterfowl (Belanger and Couture 1988).
Humboldt Bay is the largest estuary and wetlands complex in
California north of San Francisco (ESA/MADRONE Environmental Consultants
1 2
1982) but industrialization, development, and drainage for agriculture have removed 90 percent of the nearly 7,000 acres of salt marsh originally present (Glatzel 1982, Springer 1982). A few mitigation
projects have resulted in restoration of some wetlands near Humboldt Bay
(ESA/MADRONE Environmental Consultants 1982).
Use of marshes for wastewater treatment shows promise (Kadlec
1978). The Arcata Marsh and Wildlife Sanctuary (AMWS) was one of the
first man-made marsh systems built to receive and process domestic
secondary sewage effluent as a primary water source. If the AMWS can provide tertiary treatment of domestic sewage while simultaneously providing wildlife habitat and recreational areas for public use, other communities faced with sewage problems and a lack of recreational areas also may use treated sewage effluent to provide wildlife habitat.
The AMWS consists of three man-made units used to treat sewage effluent, a freshwater unit unrelated to sewage treatment, and a unit filled with salt water from Humboldt Bay. Spitler (1985) and Higley
(1989) both studied vegetation responses and waterbird and raptor use at the AMWS prior to the introduction of treated effluent into three of the marsh units. I studied the waterbird and raptor use and vegetation
responses at the AMWS from 1 July 1990 to 30 June 1991, three years after wastewater had been introduced into three units.
The goals of this study were: (1) to determine and compare bird use and vegetation responses in units flooded with fresh water, sewage effluent, and brackish bay water; (2) to compare waterbird use and vegetation responses before and after the introduction of secondary 3 sewage effluent; (3) to relate these data to water depth, salinity, and pH; and (4) to evaluate current management practices. STUDY AREA
The study was conducted at the Arcata Marsh and Wildlife
Sanctuary (Spitler 1985, Higley 1989) Arcata, Humboldt County,
California (Figure 1). The study units were: (1) Klopp Lake, an 11.9 ha
open, shallow basin, that receives back flow water from Humboldt Bay at high tide resulting in salinities nearly equal to Humboldt Bay; (2)
Butcher Slough Log Pond (BSLP), a restored 3.6 ha log pond, that receives fresh water from nearby wells; and (3) Allen (5.9 ha),
Gearheart (3.7 ha), and Hauser (5.3 ha) units, all of which receive treated, chlorinated, dechlorinated secondary effluent from Arcata's
Waste Treatment Facility (Figure 2). These five units provided a site where comparative studies could be made of vegetation and waterbird responses to the three water types. In addition to the main water sources (Figure 2), all five units received whatever rain fell directly
into them during the wet season. Klopp Lake, Allen, and Hauser units also received relatively minor amounts of runoff from the sealed "Mt.
Trashmore" landfill site, but Gearheart and BSLP had virtually no external watershed.
Originally, much of the study site consisted of upper elevation
Humboldt Bay mudflats and salt marsh. Early settlers developed the
Humboldt Bay shoreline and salt marshes for industrial, commercial, and agricultural purposes (TerraScan 1979). The salt marshes of the Arcata
Bottoms lying west of AMWS had been reclaimed and were used primarily for pasture by 1903 (Shapiro and Assoc. Inc. 1980).
The reclamation, economic, and development history of the specific study sites were outlined by TerraScan (1979), Gearheart et al.
4 5
Figure 11Location of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California 6
Figure 2� The Water Flow Patterns (arrows) and Water Sources of the Arcata Harsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 7
(1982), Spitler (1985) and Higley (1989). At the time of my study,
Klopp Lake consisted mostly of a shallow, open, saline, basin without substantial hydrophytes and the remaining four units supported luxuriant growths of various mixtures of emergents, floating mats, and submergent hydrophytes. All five units contained three to seven islands each. The islands in Klopp Lake were nearly bare, but all the rest supported dense mixtures of willows (Salix sp.), blackberries (Rubus sp.), grasses, and herbaceous plants. METHODS
This study extended from 1 July 1990 to 30 June 1991. The year was subdivided into seven biological seasons, each 52-53 days long for data collection and analysis as follows (Spitler 1985, Higley 1989,
Nelson 1989, Harris 1991):
1) Early Spring (25 January-17 March) 2) Late Spring (18 March-8 May) 3) Summer (9 May-30 June) 4) Early Fall (1 July-21 August) 5) Mid Fall (22 August-12 October) 6) Late Fall (13 October-3 December) 7) Winter (4 December-24 January).
Physical and Chemical Sampling
Water pH and salinity were measured at incoming water gates for each waterbody during vegetation sampling. A wide-pH-range Hach kit
(Hach Chemical Company, PO Box 389, Loveland CO 80537) was used to measure pH and a salinometer (Yellow Springs Instrument Company Inc.,
Box 279, Yellow Springs OH 45387) was used to measure salinity. City personnel made pH readings for the wastewater units during four of the seven seasons but none for BSLP or Klopp Lake. Water clarity was measured with a secchi disk at submergent plant bed and open water plots. Water depth was measured to the nearest centimeter at the vegetation sample plots using a incremented wooden dowel. Water level fluctuation readings were made by city personnel for the wastewater units.
8 Vegetation Sampling
Aquatic vegetation present in each unit was sampled at the approximate midpoint of each season. Only plants growing in the water or shoreline vegetation dependent on saturated soils were included.
Cover maps were drawn from low altitude aerial photographs taken near the midpoint of each season (Appendix A-0). Dominant vegetation was identified from the cover maps and a random sample of five plots was taken in each dominant cover type using a transparent grid overlay of each unit. Sample plots were selected using a table of random numbers
(Zar 1974). "Dominant vegetation" was defined in two ways: first, as stands covering more than five percent of the surface area of a waterbody as measured by a planimeter; second, vegetation covering less than five percent of the surface area of a waterbody but that was detectable from low altitude aerial photographs, and that grew in stands dense enough to provide aerial coverage within the stands greater than
90 percent. A 10-foot flat-bottomed aluminum boat was used for transportation during sampling. Five plots were sampled in each water body in each dominant vegetation type each season. Emergent vegetation plots were sampled only in alternate seasons for a total of four times.
At the selected plot locations, the following procedures were used: submergent vegetation was sampled by throwing a steel-toothed rake in the four cardinal compass points from the center of the plot. The relative amount of vegetation recovered was scored using the method of
Jessen and Lound (1962). Submergent vegetation plots were sampled only once annually. Stem density counts of persistent emergents were taken 10
in plots 30.5 cm X 30.5 cm in size. Mat and free-floating vegetation
was collected with a screened sampling frame 35.5 cm X 25.5 cm in size.
Plugs of mat vegetation were cut with a machete and marked one day
before removal. The collected samples were oven-dried (105°C) for
approximately 48 hours before weighing. A measure of plant species
composition was made using a one-meter point frame with points at
decimeter intervals. Plants touching the end of each point were
recorded. Species composition data were taken in the four cardinal
compass positions from the center of each plot.
Wildlife Counts
Birds were counted by direct observation (Davis and Winstead
1980) using a 20-45X spotting scope and 8 X 56 binoculars at 1-5 day
intervals for an average of 2.7 surveys per week. A total of 141 bird
surveys was conducted. Counts were conducted in daylight during high
tides on the adjacent Humboldt Bay since Higley (1989) showed that most waterbirds exhibited no significant difference in use rates of the units
between high and low tides or occurred in significantly greater numbers
during high tides. High tide was defined as the highest diurnal tide
which covered 100 percent of the adjacent mud flats in Humboldt Bay.
Counts were made from the fixed stations used by Higley (1989), and
additional stations were established as necessary to allow visibility
behind vegetation that was not present when Higley (1989) conducted his
study (Figure 3). Counts required one to three hours to complete. Each
census was begun approximately 20 minutes before the scheduled time of
high tide (Elliot Sales Corporation 1990, 1991). Shorebirds loafing on 11
Figure 3� Approximate Location of Bird Survey Points and Areas Surveyed at the Arcata Harsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. 12 the islands in Klopp Lake were estimated by counting part of the flock and extrapolating to the total flock (Gerstenberg 1972, Spitler 1985,
Higley 1989).
Bird data were recorded in the field on data sheets or using a tape recorder. Data were later transcribed to data sheets and entered into a computer. Peterson (1990) was used to aid field identification.
Scientific and common names follow American Ornithological Union (1983) and supplements. Ducklings were identified to species by noting the female they responded to when disturbed. Long-billed (Limnodromus scolopaceus) and short-billed (L.griseus) dowitchers were recorded as dowitcher spp. Bird data were grouped for analysis as follows
(Higley 1989):
1) Fish-Eating Divers (Gaviidae, Podicipedidae, Pelecanidae, Phalacrocoracidae) 2) Herons and Egrets (Ardeidae) 3) Puddle Ducks (Cygnini, Anserini, Anatini, Cairini) 4) Diving Ducks (Mergini, Aythyini, Oxyurini) 5) Coots and Rails (Rallidae) 6) Large Shorebirds (Avocets, Stilts, Plovers, Godwits, Curlews, Willets, Yellowlegs, Dowitchers, Turnstones, Snipe, Red Knots) 7) Small Shorebirds (Dunlins, Western, Least and Spotted Sandpipers, Sanderlings, Phalaropes) 8) Gulls and Terns (Larinae, Sterninae) 9) Raptors (Accipitridae, Falconidae, Cathartidae, Strigidae, Tytonidae).
Statistical Methods
Paired T-tests were used to test for differences in stem densities of hard-stemmed bulrush and when a waterbird species occurred in only two units during a season. ANOVA's were used to test for differences in vegetation biomass, stem density, and rake readings between waterbodies in the same season or within waterbodies during 13 different seasons and to test for differences in waterbird abundances within seasons.� P value of <0.05 were used to indicate significance.
In order to make a direct comparison between the various units, bird use data were converted to bird use-days per five ha for each unit.
Comparisons of bird numbers and species composition recorded in this study with that recorded by Higley (1989) before wastewater effluent entered the units were made using unpaired T-tests (Zar 1974).
Important bird species were defined as species of birds which accounted for more than 15 percent of the bird use-days of a bird group and that were generally present in all seasons. Area use indices of important bird species were calculated by dividing each individual unit's percent total birds by that unit's percent of total surface area times 100. An index of 100 indicates the area was used at the same expected rate as it's percentage of total available habitat. Indices of less than 100 indicate use by birds at rates less than expected based on surface area and indices of more than 100 indicate use at greater than expected rates. Surface area is defined as the area within the perimeter of a unit including islands. RESULTS
Physical and Chemical Parameters
Klopp Lake was most turbid in winter and least turbid in mid fall as measured by secchi disc readings (Table 1).
Seasonal mean secchi disc readings in the freshwater submergent beds ranged from 3.4 to 148.0 cm for all units (Table 1). BSLP was significantly less (p<0.05) turbid than the wastewater units from late fall through summer (Table 1). Allen Marsh was significantly less turbid (p<0.05) under submergent beds than Gearheart and Hauser units during summer (Table 1). The water under submergent beds in BSLP was significantly less turbid (p<0.05) than in Gearheart Marsh in early fall and Hauser Marsh in mid fall (Table 1).
Lesser duckweed occurred in large quantities in the wastewater units in early and mid fall. The secchi disc disappeared almost at once under their mats (Table 1). Water turbidity was similar under lesser duckweed for all wastewater units in mid fall (Table 1).
Salinity was less than one ppt on the freshwater units for all seasons. Salinity on Klopp Lake ranged from 21.0 to 27.0 ppt in my study and was highest in mid fall. During the same year, city personnel recorded a range of 21.5 to 29.8 ppt at Klopp Lake (Table 2).
BSLP had the highest pH of the freshwater units for all seasons except late fall (Table 2).
In general, Allen and Gearheart units remained fairly stable throughout the year. Hauser Marsh was allowed to decline in depth by
20 cm seasonally and exhibited the most fluctuation annually (Figure 4)
14 TABLE 1 Average Depth of Secchi Disc Disappearance (cm) in Dominant Free-Floating and Submergent Cover Types at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n = number of samples). Table 2 Salinity (Klopp Lake Only) and pH of Five Marsh Units, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. Figure 41Seasonal Mean Water Depth for Allen, Gearheart and Hauser Marshes, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. EF = Early Fall ( 1 July 21 August), MF = Mid Fall (22 August -12 October), LF = Late Fall (13 October - 3 December), WI = Winter (4 December - 24 January), ES = Early Spring (25 January -17 March), LS = Late Spring (18 March - 8 May ), SU = Summer (9 May - 30 June) (Data from Arcata Waste Treatment Facility). 18
Water depth measurements taken at vegetation sample plots varied greatly between seasons and units (Table 3). This great variance was due largely to the small number of samples (n=5) taken each season in each unit and probably does not accurately reflect the true mean depths for each of the unit.
Vegetation
Klopp Lake, the deepest and most saline unit, had a very different ecology than the other units. It held few hydrophytes and consisted mostly of open water with some early fall development of filamentous algae (Table 4).
Annually, algae and widgeon grass (Ruppia maritima) were the only two plants detected using the point frame and were counted at 4.4 and 3.5 percent of points respectively (Table 5). During my study widgeon grass in Klopp Lake was clumped loosely in thin stands. In
Klopp Lake rake samples of widgeon grass occurred most commonly during early and mid fall (Table 6, Figure 5). The four freshwater units all supported similar vegetation types regardless of their water source or their position in the water treatment flow regime (Tables 4, 5). In the four units, the following major cover plants were identified: broad-leaved cattail (Typha latifolia), hard-stemmed bulrush (Scirpus acutus), alkali bulrush (S. paludosus), marsh pennywort (Hydrocotyle ranunculoides), lesser duckweed
(Lemna minor) and pondweeds, (Potamogeton pectinatus and P. crispus).
Between 8.0 and 17.3 percent of the surface area of the units was occupied by islands and these values did not change seasonally within TABLE 3 Seasonal Average Water Depths (cm) and Standard Deviation under Dominant Cover Types at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. (n=5 samples/marsh/season). 20 TABLE 4 Percentage Cover of Dominant Cover Types, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, Calculated from Aerial Photographs 1990-1991. Table 5 Percentage Species Composition within Dominant Cover Types at Arcata Marsh and Wildlife Sanctuary, Humboldt County, California 1 July 1990 - 30 June 1991 as Measured by Point-frame Scores (N=number of points scored). TABLE 6 Mean Number and Standard Deviation of Stems per 30.5 cm x 30.5 cm Plot for Emergent Vegetation, of Oven- dried Biomass (gin) per 35.5 cm x 25.5 cm Plot for Free Floating and Mat Vegetation, and of Mean Rake Readings for Submergent Vegetation at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. Figure 51Mean Rake Reading and one Standard Deviation of Widgeon Grass in Klopp Lake, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California 1 July 1990 - 30 June 1991. EF = Early Fall ( 1 July 21 August), MF = Mid Fall (22 August -12 October), LF = Late Fall (13 October - 3 December), WI = Winter (4 December - 24 January), ES = Early Spring (25 January -17 March), LS = Late Spring (18 March - 8 May ), SU = Summer (9 May - 30 June) (n=5 samples/season). 24
any waterbody (Table 4). Open water covered 30.1 to 66.1 percent of the
units between winter and summer, but this was mostly occupied by mat and
submergent cover types by fall (Table 4).
Cattail
Cattail stands occupied narrow shoreline borders or created
floating islands or island borders in all freshwater units. The
percentage cover of cattails varied from 30.4 percent in winter at BSLP
to 4.1 percent in early spring at Hauser Marsh (Table 4). Within any
one unit, these stands tended to be static with some increase in
coverage during the growing season (Table 4). Seasonal mean water
depths under cattail stands varied with each unit and ranged from 5.4 cm
in late fall in Gearheart Marsh to 77.9 cm during early fall in BSLP
(Table 3).
Mean stem densities of cattails ranged from 5.8 to 10.8 stems per frame (Table 6, Figure 6). There was no significant difference
(p>0.05) in mean cattail stem densities between the units during early fall and summer but BSLP had significantly smaller mean stem densities than the wastewater units in late fall and early spring (Tables 6, 7,
Figure 6).
Species composition data within cattail stands as measured by the point frame technique revealed an understory of marsh pennywort in all four units (36.0 to 55.3 percent of point scores) and water celery
(Oenanthe saementosa) (14.0 to 19.3 percent of point scores) in three of
the four units (Table 5). Water celery was not encountered in the point
samples at BSLP but incidental observations revealed it to be present
there as well. 25
Figure 61Mean Stem Density (stems per 30.5 cm x 30.5 cm plot) and one Standard Deviation of Broad-leaved Cattail for the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. EF = Early Fall ( 1 July 21 August), MF = Mid Fall (22 August -12 October), LF = Late Fall (13 October - 3 December), WI = Winter (4 December - 24 January), ES = Early Spring (25 January -17 March), LS = Late Spring (18 March - 8 May ), SU = Summer (9 May - 30 June) (n=5 samples/marsh/alternating season). Table 7 Statistical Comparisons of Vegetation Types Between Marshes within Seasons. Arcata Marsh and Wildlife Sanctuary, Humboldt County, California 1 July 1990 - 30 June 1991. 1| 27
Hard-stemmed Bulrush
Substantial beds of hard-stemmed bulrush occurred only in the north end of BSLP (7.9 to 13.6 percent of coverage) and in Hauser Marsh
(6.8 to 12.9 percent of coverage) (Table 4). Seasonal mean water depth
in measured hard-stemmed bulrush stands ranged from 17.4 to 92.3 cm
(Table 4). Hauser Marsh exhibited a greater stem density (p<0.05) than BSLP for each season (Tables 6, 7, Figure 7).
Like cattail, hard-stemmed bulrush stands also supported
substantial understories of marsh pennywort (Table 5).
Alkali Bulrush
Hauser Marsh supported a small strip of alkali bulrush (1.3 percent of surface coverage (Table 4). This occurred on an under water ridge and represented a remnant of a pre-impoundment stand. Alkali bulrush occurred in water 0.6 to 6.0 cm deep with mean stem densities of
14.2 to 16.6 per frame (Tables 3, 6). Alkali bulrush also supported an under story of marsh pennywort with lesser amounts of water celery
(Table 5).
Marsh Pennywort
All four freshwater units supported mats of marsh pennywort
(Table 4). These occurred mostly as floating mats anchored to the shore; these mats spread into deep water in bands up to seven meters wide. Nearly all shoreline and island edges supported some bands of marsh pennywort which filled quiet corners of many units by mid fall (Table 4). City personnel mechanically removed marsh pennywort from 28
Figure 71Mean Stem Density (stems per 30.5 cm x 30.5 cm plot) and one Standard Deviation of Hard-stemmed Bulrush for the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. EF = Early Fall ( 1 July 21 August), MF = Mid Fall (22 August -12 October), LF = Late Fall (13 October - 3 December), WI = Winter (4 December - 24 January), ES = Early Spring (25 January -17 March), LS = Late Spring (18 March - 8 May ), SU = Summer (9 May - 30 June) (n=5 samples/marsh/alternating season). 29
Allen, Gearheart, and BSLP in late winter and early spring resulting in
sharp declines in percentage cover (Table 4).
The mats of marsh pennywort reached peak coverage in summer and early fall (Table 4). Within the stands, the dry weight biomass per sample was lowest during winter for all freshwater units (Table 6,
Figure 8). In Hauser, Gearheart, and BSLP, biomass of pennywort mats increased in early spring after their winter lows but then decreased again in late spring (Table 6, Figure 8). Peak dry weight biomass was greatest in mid fall for Hauser Marsh, in late fall for Allen Marsh and
BSLP, and in summer for Gearheart Marsh (Table 6, Figure 8). All units were significantly different (p<0.05) from each other in dry weight biomass in late fall but were not significantly different from each other in dry weight biomass in early fall (p>0.05) (Tables 6, 7,
Figure 8). Gearheart and Hauser units held significantly more (p<0.05) dry weight biomass of marsh pennywort than Allen Marsh and BSLP in mid fall (Tables 6, 7, Figure 8), BSLP and Hauser Marsh held significantly more (p<0.05) than Allen and Gearheart units did during winter (Tables
6, 7, Figure 8), and Gearheart Marsh held significantly less (p<0.05) than Hauser Marsh and the BSLP in early spring (Tables 6, 7, Figure 8).
No samples were taken from Allen Marsh in early spring because the city had removed 95+ percent of its marsh pennywort mats. Allen and Hauser units held significantly smaller (p<0.05) dried weight biomass of marsh pennywort than Gearheart Marsh and BSLP during late spring (Tables 6, 7,
Figure 8) and Gearheart and Hauser units held significantly more
(p<0.05) than Allen Marsh or BSLP during the summer (Tables 6, 7,
Figure 8). 30
Figure 81Mean Dry Weight (grams per 35.5 cm x 25.5 cm plot) and one Standard Deviation of Marsh Pennywort for the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. EF = Early Fall ( 1 July 21 August), MF = Mid Fall (22 August -12 October), LF = Late Fall (13 October 3 December), WI = Winter (4 December - 24 January), ES = Early Spring (25 January -17 March), LS = Late Spring (18 March - 8 May ), SU = Summer (9 May - 30 June) (n=5 samples/marsh/season). 31
The average water depths under marsh pennywort mats ranged from
25.2 to 163.6 cm (Table 3).
Water celery grew as a co-dominant in many marsh pennywort mats
(Table 5).
Duckweed
Duckweed coverage was seasonal and was largely confined as a dominant to the three wastewater units (Table 4). It reached peak coverage in early and mid fall when it covered nearly all open areas that otherwise were occupied by submergent beds (Tables 4, 5). In many locations it also formed mats on top of pondweed beds and suppressed them greatly by shading. It also occurred as an understory plant in most emergent cover types (Table 5). The seasonal mean water depth under locations dominated by duckweed ranged from 33.2 to 50.7 cm
(Table 3). Duckweed occurred over significantly deeper (p>0.05) water in Allen Marsh than in Gearheart and Hauser units in mid fall
(Table 3). Lesser duckweed was found in measurable quantities in Hauser
Marsh only in early fall but no significant differences (p>0.05) were detected in dry weight biomass between the wastewater units in mid fall
(Tables 6, 7, Figure 9).
Pondweeds
The open water areas of the four freshwater units supported seasonal crops of pondweeds, mostly sago pondweed, but Hauser Marsh also supported some curly-leaf pondweed (Tables 4, 5). Pondweed was present in the three fall seasons as a dominant plant and, together with duckweed, occupied most of the open areas during fall (Table 4). 32
Figure 91Mean Dry Weight (grams per 35.5 cm x 25.5 cm plot) and one Standard Deviation of Lesser Duckweed for the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. EF = Early Fall ( 1 July 21 August), MF = Mid Fall (22 August -12 October), LF = Late Fall (13 October 3 December), WI = Winter (4 December - 24 January), ES = Early Spring (25 January -17 March), LS = Late Spring (18 March - 8 May ), SU = Summer (9 May -30 June) (n=5 samples/marsh/season). 33
Pondweed and duckweed were heavily utilized by waterfowl in fall resulting in its virtual absence from late fall until mid summer the
following year. Average water depths of sampled pondweed beds ranged
from 30.0 to 139.8 cm (Table 4).
There was no significant difference (p>0.05) in rake samples of pondweed densities between the four units from mid fall through summer (Tables 6, 7, Figure 10), but BSLP had significantly greater (p<0.05) rake scores than Allen, Gearheart, and Hauser units in late spring, and than Allen Marsh during early fall (Tables 6, 7, Figure 10).
Bird Use
Species Composition
Ninety-four species of birds were recorded during this study
(Appendix A). Klopp Lake had the highest total number of species (68),
Allen, Gearheart, and Hauser units held 44, 42, and 49 species respectively and BSLP held 41. The four freshwater units attracted a
similar species complex of birds irrespective of water source
(Appendix A).
Seasonal Patterns of Use
Nearly 31 percent of the annual bird use-days were recorded during late fall, and only 2.2 percent of annual bird use-days occurred
in summer (Table 8, Figure 11).
On an annual basis, the most numerous groups were large shorebirds (41.7 percent annual bird-use days), waterfowl, coots, and rails (35.2 percent annual bird-use days) and small shorebirds
(16.4 percent annual bird-use days, Table 8, Figure 11). TABLE 81Number and Percentage of Bird Use-Days (BUD) of Important Species and Percentage of Yearly Bird Use-Days, Arcata Marsh and Wildlife Sanctuary. Humboldt County. California, 1 July 1990 - 30 June 1991. TABLE 81Number and Percentage of Bird Use-Days (BUD) of Important Species and Percentage of Yearly Bird Use-Days, Arcata Marsh and Wildlife Sanctuary. Humboldt County. California. 1 July 1990 - 30 June 1991. (Continued). TABLE 81Number and Percentage of Bird Use-Days (BUD) of Important Species and Percentage of Yearly Bird Use-Days, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. (Continued). 37
Figure 101Mean Rake Reading and one Standard Deviation of Sago Pondweed for the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. EF = Early Fall ( 1 July 21 August), MF = Mid Fall (22 August -12 October), LF = Late Fall (13 October - 3 December), WI = Winter (4 December - 24 January), ES = Early Spring (25 January -17 March), LS = Late Spring (18 March - 8 May ), SU = Summer (9 May - 30 June) (n=5 samples/marsh/season). 38
Figure 11 Total Seasonal Bird Use-Days (BUD) (A) and BUD per 5 Ha (B) by Bird Groups at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. E.Fall = Early Fall (1 July - 21 August), M.Fall = Mid Fall (22 August - 12 October), L.Fall = Late Fall (13 October - 3 December), Winter = (4 December - 24 January) E. Spring = Early Spring (25 January - 17 March), L.Spring = Late Spring (18 March - 8 May), Summer = (9 May - 30 June). 39
Klopp Lake with its shorebird use, supported more bird use-
days per five ha than any other unit and BSLP supported the fewest birds
per five ha (Table 9). Among the wastewater units Hauser Marsh was used
at greater densities than Allen and Gearheart units (Table 9).
Fish-eating Divers. Fish-eating divers peaked in abundance in
mid fall and late fall when 33.0 and 25.8 percent of annual fish-eating
diver use-days were recorded respectively (Table 8, Figure 12). Fish-
eating divers reached a seasonal low in summer (2.5 percent) (Table 8,
Figure 12). On a per five ha basis, BSLP and Klopp Lake supported the
largest population of fish-eating divers and the wastewater units each had densities between one-fourth to one-third of the densities on BSLP
or Klopp Lake (Table 9). Peak numbers of fish-eating divers per five ha
occurred on Klopp Lake and Allen Marsh in mid fall, BSLP in early fall,
Hauser Marsh in late fall, and Gearheart Marsh in winter (Figure 12).
The use of Klopp Lake and BSLP was significantly greater (p<0.05) by
fish-eating divers on a per five ha basis during mid fall and summer than in the wastewater units. In early fall the use per five ha of BSLP was significantly greater (p<0.05) than any other unit and Hauser Marsh held significantly more (p<0.05) fish-eating divers per five ha during
late fall than all other units.
Pied-billed grebes and double-crested cormorants (Phalacrocorax
auritus) together accounted for 75.2 percent of fish-eating diver use-
days during mid fall and 86.2 percent of fish-eating diver use-days
annually (Table 8).
Pied-billed grebes were significantly more abundant (p<0.05) on
BSLP than on all other units from late spring through mid fall. Klopp 40
TABLE 91Comparison of Total Annual Bird Use-Days Per Five Hectares at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California. 1984-1986, 1990-1991 41
Figure 12 Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Fish-Eating Divers, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. E.Fall = Early Fall (1 July - 21 August), M.Fall = Mid Fall (22 August - 12 October), L. Fall - Late Fall (13 October - 3 December), Winter = (4 December - 24 January) E.Spring = Early Spring (25 January - 17 March), L.Spring = Late Spring (18 March - 8 May), Summer = (9 May - 30 June). 42
Lake and Hauser Marsh held significantly more (p<0.05) pied-billed
grebes than Allen, Gearheart, and BSLP during the late fall and Hauser
Marsh had significantly more (p<0.05) pied-billed grebes than BSLP in
winter. Allen and Gearheart units had significantly fewer pied-billed
grebe use-days than Hauser Marsh and BSLP in early spring. Annually, on
a surface area basis, pied-billed grebes used BSLP at about three times
the expected rate (Table 10). They used the wastewater units at about
the expected rates and Klopp Lake was used about half as much as would
be expected (Table 10). Klopp Lake had significantly more double-
crested cormorant use-days (p<0.05) in all seasons than the other units.
On an area basis, double-crested cormorants were found at about twice
the expected rate on Klopp Lake (Table 10).
Herons and Egrets. Herons and egrets peaked in abundance in mid
and late fall (Table 8, Figure 13). Heron use was greatest in Allen
Marsh on an annual basis and in Hauser Marsh in early and mid fall
(Figure 13). Peak heron and egret use-days per five ha occurred on BSLP
and Hauser Marsh in mid fall and on Klopp Lake, Allen, and Gearheart
units in late fall (Figure 13). Allen Marsh had significantly greater
(p<0.05) use by herons per five ha than all other units from late fall
through late spring. In summer, herons used Allen Marsh significantly
more (p<0.05) than Gearheart Marsh. Hauser Marsh was used significantly
more (p<0.05) by herons in early fall than any other marsh unit. Allen
and Hauser units were used significantly less (p<0.05) by all herons and
egrets than Gearheart Marsh, Klopp Lake, and BSLP in early and mid fall.
Snowy egrets (Egretta thula) and black-crowned night-herons
(Nycticorax nycticorax) accounted for 61.8 and 28.3 percent 43 TABLE 10 Total Annual Bird Use-Days (BUD) and Relative Area Use Indices of Important birds According to Water Sources of Marsh Units at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. 44 TABLE 10 Total Annual Bird Use-Days (BUD) and Relative Area Use Indices of Important birds According to Water Sources of Marsh Units at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (Continued). 45
Figure 13 Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Herons and Egrets, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. E.Fall = Early Fall (1 July - 21 August), M.Fall = Mid Fall (22 August - 12 October), L. Fall = Late Fall (13 October - 3 December), Winter = (4 December - 24 January) E.Spring = Early Spring (25 January - 17 March), L.Spring = Late Spring (18 March - 8 May), Summer = (9 May 30 June). 46
respectively of all annual heron and egret use-days (Table 8,
Figure 13). There were no significant differences in use of the various
units by snowy egrets in summer and winter (p>0.05) but Allen Marsh was
used significantly more (p<0.05) by snowy egrets than Gearheart, Hauser,
and Klopp Lake during early and late spring. Annually, snowy egrets
were found only about one-half as often as expected on Klopp Lake and at
about 1.5 times more than expected on the freshwater units (Table 10).
Black-crowned night-herons were not recorded on Klopp Lake
(Table 8). Black-crowned night-herons used Allen Marsh significantly
more (p<0.05) than any other marsh from late fall through summer.
Hauser Marsh was used significantly more (p<0.05) by black-crowned
night-herons in early fall, and BSLP was used significantly more
(p<0.05) by black-crowned night-herons than any other marsh during mid
fall. Annually, black-crowned night-herons used freshwater units at 1.5
to 2.5 times the expected rates based on surface area alone (Table 10).
Puddle Ducks. Puddle ducks accounted for 25.0 percent of all bird use-days at the AMWS (Table 8). About 70 percent of all puddle
duck use occurred in late fall and winter (Table 8, Figure 14). Only
17.2 percent of all puddle duck use-days were recorded between
25 January and 21 August (Table 8). On a density basis, Hauser and
Gearheart units exhibited the greatest bird-use days per five ha. Klopp
Lake was almost unused by puddle ducks (Table 9, Figure 14). Peak
puddle duck use-days per five ha occurred on Klopp Lake, Gearheart, and
Hauser units in late fall and on BSLP and Allen Marsh in winter
(Figure 14). Hauser Marsh had significantly more (p<0.05) puddle duck
use days per five ha in late fall and spring than any other unit. The 47
Figure 14 Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Puddle Ducks, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 30 June 1991. E.Fall = Early Fall (1 July - 21 August), M.Fall - Mid Fall (22 August - 12 October), L.Fall = Late Fall (13 October - 3 December), Winter = (4 December - 24 January) E.Spring = Early Spring (25 January - 17 March), L.Spring = Late Spring (18 March - 8 May), Summer = (9 May - 30 June). 48 wastewater units supported significantly more (p<0.05) puddle ducks per five ha in mid fall and winter than either Klopp Lake or BSLP. One or more of these units had significantly greater (p<0.05) numbers of puddle ducks than Klopp Lake or BSLP in all other seasons.
American green-winged teal (Anas crecca carolinensis) accounted for 56.5 percent of annual puddle ducks present at the marsh complex
(Table 8). Nearly 83 percent of all green-winged teal use days occurred between 13 October and 24 January (Table 8, Figure 14). Hauser Marsh was used significantly more (p<0.05) by green-winged teal than any other marsh in early, mid and late fall, and during late spring. No significant differences (p>0.05) in use by green-winged teal were found between Allen, Gearheart, and Hauser units in early spring and winter, but all three units were used significantly more (p<0.05) by green- winged teal than Klopp Lake and BSLP. Annually, based on relative surface area of the units, green-winged teal used the wastewater units at nearly twice the expected rate and used BSLP at only about half the expected rate (Table 10). Klopp Lake was almost unused by green-winged teal (Table 10, Figure 14).
American wigeon (A. americana) were important only in late fall when they constituted 17.5 percent of puddle duck use-days (Table 8).
Cinnamon teal (A. cyanoptera) and mallards (A. platyrhynchos) occurred year-around on the study area and together accounted for 27.8 percent of annual puddle duck use-days (Table 8).
* Mallards used Hauser Marsh significantly more (p<0.05) in summer and early fall than all other units. Gearheart Marsh was used by mallards significantly more (p<0.05) than all other units during late 49 spring and was used significantly more (p<0.05) than Klopp Lake or BSLP in mid fall. Allen Marsh was used significantly more (p<0.05) than all other units by mallards during winter. Allen Marsh was used by mallards significantly more (p<0.05) than Gearheart and Hauser units in late fall and more than Klopp Lake and Hauser Marsh in early spring. Annually, mallards used the freshwater units at about 1.5 times the expected rate based on their surface area, and Klopp Lake was almost unused
(Table 10).
Diving Ducks. Diving ducks constituted 5.0 percent of annual bird use-days but were nearly absent in early and mid fall (Table 8, Figure 15). Diving duck numbers peaked in winter (40.6 percent of annual diving duck use-days; Table 8, Figure 15). Klopp Lake exceeded all other units combined in diving duck use-days per five ha during all seasons (Table 9, Figure 15). Diving ducks used Allen Marsh at only about one-third to one-half the rate of the other freshwater units and only about one-tenth the rate of Klopp Lake (Table 9). Klopp Lake had significantly greater (p<0.05) use by diving ducks per five ha from late fall through late spring than all other marsh units and had signifi cantly greater (p<0.05) use in summer than Allen and Hauser units.
Among diving ducks, lesser scaup (Aythya affinis) were the most common in late fall, ruddy ducks (Oxyura jamaicensis jamaicensis) most common in winter and early spring, and greater scaup (Aythya marila mariloides) most common in late spring and summer (Table 8, Figure 15). Buffleheads
(Bucephala albeola) were abundant from late fall through late spring
(Table 8, Figure 15). Ruddy ducks and greater scaup together accounted for 49.8 percent of the annual diving duck use-days (Table 8). 50
Figure 15 Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Diving Ducks, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 30 June 1991. E.Fall g. Early Fall (1 July - 21 August), M.Fall Mid Fall (22 August - 12 October), L.Fall - Late Fall (13 October - 3 December), Winter = (4 December - 24 January) E.Spring Early Spring (25 January - 17 March), L.Spring Late Spring (18 March - 8 May), Summer (9 May - 30 June). 51
Klopp Lake was used significantly more (p<0.05) by lesser scaup
in late fall and winter than all other units, but there was no
significant difference (p<0.05) in lesser scaup use between Gearheart
Marsh and Klopp Lake in late spring. Annually, lesser scaup occurred on
Klopp Lake at 2.5 times the expected rates, only one-third the expected
rates in BSLP, and lesser scaup occurred on the wastewater units at about the expected rates based on surface area alone (Table 10).
Ruddy duck numbers were least during summer and early and mid
fall (Table 8). Klopp Lake was used significantly more (p<0.05) by
ruddy ducks from winter through summer when compared to all other units.
Gearheart Marsh and Klopp Lake were used significantly more (p<0.05) by
ruddy ducks in late fall compared to the other units. Annually, ruddy ducks used Klopp Lake at about 1.5 times the expected rates and the
freshwater units about one-half the expected values based on surface area (Table 10).
Greater scaup were absent in early fall and nearly so in mid
fall (Table 8, Figure 15). Klopp Lake was used significantly more
(p<0.05) by greater scaup than all other units in late fall, winter, and
late spring but no significant difference (p>0.05) in greater scaup use was detected between Allen Marsh and Klopp Lake in mid fall. Annually,
greater scaup used Klopp Lake at 2.5 times the expected rate and were
nearly absent on the freshwater units (Table 10).
Buffleheads were absent or nearly so from early May through mid
October (Table 8, Figure 15). Klopp Lake was used significantly more (p<0.05) by buffleheads than all other units from late fall through late
spring. Annually buffleheads used Klopp Lake at nearly twice the 52 expected rates and the freshwater units at one-third to two-thirds of the expected rates based on surface area (Table 10).
Coots and Rails. Coots and rails comprised 5.1 percent of the annual bird use-days (Table 8). Coots and rail numbers peaked in late fall and fell to a seasonal low in summer (Table 8, Figure 16). The use by coots and rails (mostly coots) was relatively uniform per five ha for all four freshwater units. Klopp Lake was used at a rate less than 10 percent of the other units on a per five ha basis (Table 9). No significant differences (p<0.05) were detected in coots and rails between the freshwater units in late fall, winter, and summer. BSLP had significantly greater (p<0.05) use by coots and rails per five ha in early fall than the wastewater units. Allen Marsh and BSLP held significantly more (p<0.05) coots and rails per five ha than the other units during mid fall.
American coots (Fulica americana) comprised 98.3 percent of annual coot and rail use-days (Table 8). American coots were conspicuous throughout the year but were most common in late fall
(48.8 percent of the annual coot use-days; Table 8, Figure 16).
Virginia rails (Rallus limicola) and soras (Porzana carolina) usually were detected in mid and late fall and the data, based largely on calls, probably underestimated their true numbers (Table 8, Figure 16).
No significant differences (p>0.05) were detected in coot use between the units in summer. Klopp Lake was used significantly less
(p<0.05) by coots in late fall and winter when compared to the freshwater units and BSLP was used significantly more than (p<0.05) the other units in early fall. Allen Marsh and BSLP were used significantly 53
Figure 16 Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Coots and Rails, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. E.Fall = Early Fall (1 July - 21 August), M.Fall = Mid Fall (22 August - 12 October), L.Fall = Late Fall (13 October - 3 December), Winter = (4 December - 24 January) E.Spring = Early Spring (25 January - 17 March), L.Spring = Late Spring (18 March - 8 May), Summer = (9 May 30 June). 54 more than the other units (p<0.05) by American coots in mid fall. Klopp
Lake was used significantly less (p<0.05) than Gearheart and Hauser units in late spring, and Allen and Gearheart units were used significantly more than (p<0.05) Hauser Marsh and Klopp Lake by coots in early spring. Annually, coots used the freshwater units at 1.5 to two times the expected rate (Table 10).
Large Shorebirds. Large shorebirds accounted for 41.7 percent of all annual bird use-days (Table 8). Large shorebird use was greatest from mid fall into early spring with a peak in late fall (Table 8,
Figure 17). Mid fall and winter accounted for 22.6 and 19.3 percent of annual large shorebird use-days respectively (Table 8). The seasonal low for large shorebird numbers occurred in summer (0.4 percent of annual use-days) (Table 8, Figure 17). Klopp Lake had the greatest large shorebird use-days per five ha of all study units (Table 9). Annually,
Klopp Lake had three times as many large shorebird use-days per five ha as all other units combined (Table 9). For the individual units, peak numbers of large shorebirds per five ha occurred in mid fall on Hauser
Marsh, in late fall on Klopp Lake, and in winter on BSLP, Allen, and
Gearheart units (Figure 17). The numbers on Klopp Lake were significantly greater (p<0.05) per five ha in early and mid fall and early spring than on the freshwater units, and were greater on Klopp
Lake (p<0.05) than on Gearheart and Hauser units in late fall and winter, and than on BSLP in late spring.
Marbled godwits (Limosa fedoa) were the single most numerous species and accounted for 52.6 percent of annual large shorebird use- days and 21.9 percent of all bird use-days on an annual basis (Table 8). 55
Figure 17 Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Large Shorebirds, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. E.Fall - Early Fall (1 July - 21 August), M.Fall = Mid Fall (22 August - 12 October), L.Fall = Late Fall (13 October - 3 December), Winter = (4 December - 24 January) E.Spring = Early Spring (25 January - 17 March), L.Spring = Late Spring (18 March - 8 May), Summer = (9 May 30 June). 56
Marbled godwit numbers peaked in mid and late fall (Table 8, Figure 17).
Marbled godwits were found only in Klopp Lake except in early fall.
American avocets (Recurvirostra americana), the second most
abundant large shorebird (Table 8), reached peak numbers in late fall
(19.6 percent of late fall large shorebird use-days) (Table 8,
Figure 17). Avocet numbers were lowest in summer and early spring
(Table 8). American avocets were recorded only on Klopp Lake(Table 8).
Dowitcher spp., the third most abundant large shorebirds,
reached peak numbers in late fall and lowest numbers in summer (Table 8,
Figure 17). Unlike other large shorebirds, dowitchers were found in all units except BSLP (Table 8). No significant differences (p>0.05) in dowitcher use were detected between Klopp Lake and Hauser Marsh in early
fall, between Allen Marsh and Klopp Lake in summer, or between Klopp
Lake, Allen, Hauser, and Gearheart in late fall. Hauser Marsh was used
significantly more (p<0.05) by dowitchers in mid fall and late spring than Klopp Lake and Gearheart Marsh in early spring. Allen Marsh was used significantly more (p<0.05) by dowitchers in winter than all other units. Based on unit surface areas, dowitchers were found at greater than expected rates on the wastewater units and smaller than expected on
Klopp Lake and BSLP (Table 10). Other large shorebirds frequently encountered in large numbers
included willets (Catoptrophorus semipalmatus) and black-bellied plovers
(Pluvialis squatarola). These two species accounted for 10.8 percent of
total annual large shorebird use-days (Table 8). Willets and black- bellied plovers were found only on Klopp lake (Table 8). 57
Small Shorebirds. Small shorebirds accounted for 16.4 percent of annual bird use-days (Table 8). Peak numbers of small shorebirds occurred in late fall and late spring (Table 8, Figure 18). Small shorebirds were nearly absent in summer (1.6 percent of total annual small shorebird use-days) (Table 8). Highest small shorebird use per five ha was on Klopp Lake (Table 9, Figure 18).
Dunlins (Calidris alpina) and western sandpipers (C. mauri) were the most abundant small shorebirds (Table 8, Figure 18). Dunlins were recorded only on Klopp Lake (Table 8). Western sandpipers occurred only in Hauser Marsh and Klopp Lake, and used Klopp Lake significantly more
(p<0.05) than Hauser Marsh in all seasons. Dunlins were most abundant in late fall, winter, and late spring (Table 8, Figure 18), and western sandpipers were most abundant in early and mid fall and early spring
(Table 8, Figure 18). Annually, western sandpipers were found on Klopp
Lake at 2.5 times the expected rate (Table 10).
Gulls and Terns. Except for late spring, gulls and terns used the study area at even rates (Table 8, Figure 19) with a seasonal peak in winter and early spring associated with an influx of mew gulls (Larus canus) and a summer peak occurred when substantial numbers of
Bonaparte's gulls (L. philadelphia) were present (Table 8, Figure 19).
Nearly all gull and tern use per five ha occurred on Klopp Lake
(Table 9, Figure 19), and Klopp Lake was used on a per five ha basis significantly more (p<0.05) than all other units for all seasons.
On an annual basis ring-billed gulls (L. delawarensis) were most abundant (Table 8). They were abundant in summer, when together with
Bonaparte's gulls, the two species accounted for 91.1 percent of summer 58
Figure 18 Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Small Shorebirds, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. E.Fall = Early Fall (1 July - 21 August), M.Fall = Mid Fall (22 August - 12 October), L.Fall = Late Fall (13 October - 3 December), Winter = (4 December - 24 January) E.Spring = Early Spring (25 January - 17 March), L.Spring = Late Spring (18 March - 8 May), Summer = (9 May 30 June). 59
Figure 19 Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Gulls and Terns, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991. E.Fall = Early Fall (1 July - 21 August), M.Fall = Mid Fall (22 August - 12 October), L.Fall = Late Fall (13 October - 3 December), Winter = (4 December - 24 January) E.Spring = Early Spring (25 January - 17 March), L.Spring = Late Spring (18 March - 8 May), Summer = (9 May 30 June). 60
gull and tern use (Table 8). California gulls (L. californicus), present in small numbers throughout the year, reached their peak in mid
fall (19.7 percent of mid fall gull and tern use-days; Table 8,
Figure 19).
Ring-billed gulls occurred mostly on Klopp Lake throughout the year and were significantly more common (p<0.05) there in all seasons compared to the other units. On an surface area basis, ring-billed gulls used Klopp Lake at 2.5 times the expected rate, the wastewater units at about the expected rate, while BSLP was nearly unused
(Table 10).
Mew gulls used only Klopp Lake, mostly during winter and early spring (Table 8).
California gulls, present in small numbers throughout the year, reached a peak in mid fall (19.7 percent of mid fall gull and tern use- days) (Table 8, Figure 19). California gulls were present in low numbers on Klopp Lake during most seasons (Table 8, Figure 19) but were nearly absent in late spring. Klopp Lake was used by California gulls significantly more than Hauser Marsh in early and mid fall and more than
Allen Marsh in late fall (p<0.05). California gulls were found at rates
2.5 times more than expected on Klopp Lake and about half the expected rate on the wastewater units (Table 10).
Bonaparte's gulls used Klopp Lake significantly more (p<0.05) than all other units from early fall through early spring. Bonaparte's gulls were absent in late spring (Table 8). Bonaparte's gulls used
Allen and Gearheart units significantly more (p<0.05) than Klopp Lake in 61 summer. Annually, Bonaparte's gulls used the wastewater units and Klopp
Lake at approximately expected rates based on surface area (Table 10).
Raptors. Raptors comprised only 0.1 percent of the annual bird use-days at AMWS (Table 8). Raptor use of the area was relatively uniform throughout the year (Table 8, Figure 20). Turkey vultures
(Cathartes aura) and northern harriers (Circus cvaneus) were the most abundant raptors on an annual basis (Table 8, Figure 20). Ospreys
(Pandion haliaetus) occurred from early spring through early fall
(Table 8, Figure 20), with a peak in summer with (37.8 percent of the summer raptor use-days) (Table 8, Figure 20). Northern harriers were the most abundant raptors from late fall through late spring when they comprised 48.3 percent of all raptor use-days (Table 8, Figure 20).
Turkey vultures were most abundant from summer through mid fall when they accounted for 63.0 percent of all raptor use-days (Table 8,
Figure 20). Raptors hunted over the freshwater units approximately equally but they hunted over Klopp Lake at only about one-third to one- half the rate of use for the freshwater units (Table 9). Peak raptor use-days per five ha occurred on BSLP and Allen Marsh in winter,
Gearheart and Hauser units in late fall, and Klopp Lake during summer (Figure 20). No significant difference (p<0.05) was detected in raptor use-days per five ha for any marsh from mid fall through early spring.
Hauser Marsh had significantly greater (p<0.05) use by raptors per five ha compared to all other units in early fall and greater use than Allen
Marsh, Klopp Lake, and BSLP in the late spring. 62
Figure 20 Number of Bird Use-Days (BUD) by Species (A) and Number of BUD per 5 Ha by Marsh Unit (B) for Raptors, Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 30 June 1991. E.Fall = Early Fall (1 July - 21 August), M. Fall = Mid Fall (22 August - 12 October), L. Fall = Late Fall (13 October - 3 December), Winter = (4 December - 24 January) E.Spring = Early Spring (25 January - 17 March), L.Spring Late Spring (18 March - 8 May), Summer - (9 May - 30 June). 63
No significant difference (p>0.05) in turkey vulture use-days was detected between any units, but they tended to hunt over the freshwater units more than expected on an surface area basis (Table 10).
Northern harriers used Gearheart Marsh significantly more
(p<0.05) in winter than Klopp Lake and BSLP, and Klopp Lake and BSLP were used significantly less (p<0.05) by northern harriers in late fall than Allen, Gearheart, and Hauser units. On an area basis, northern harriers used the wastewater units more than expected and they used BSLP and Klopp Lake less than expected (Table 10).
Ospreys were absent from mid fall through winter (Table 8).
Klopp Lake was used significantly more (p<0.05) by ospreys than Allen
Marsh in late spring and more than Allen and Hauser units in summer. No significant difference (p>0.05) in osprey use was found between
Gearheart Marsh, BSLP, and Klopp Lake in early fall and between
Gearheart Marsh and Klopp Lake in early spring. Annually, ospreys used
Klopp Lake at twice the expected rate and the freshwater units at about one-third expected rates (Table 10). DISCUSSION
Vegetative Considerations
A major objective of this study was to compare the ecology of three wastewater units (Allen, Gearheart, and Hauser units) with a non- wastewater freshwater unit (BSLP) and a brackish lake (Klopp Lake) as a means of evaluating the use of wastewater for marsh creation.
Two previous studies had been conducted at AMWS. Spitler (1985) reported on the early vegetative responses to initial flooding of
Gearheart and Hauser units with well and brackish creek water before the introduction of wastewater. At the time of Spitler's studies, Allen
Marsh was essentially dry and Klopp Lake was newly flooded with a combination of bay and freshwater. Higley (1989) continued Spitler's
(1985) studies of Klopp, Allen, Gearheart, and Hauser units in 1984-1986 at a time when wastewater had not yet been introduced into the system.
Neither Spitler (1985) nor Higley (1989) studied BSLP. During both of these previous studies, a connection between Hauser Marsh and Klopp Lake allowed a freshwater flow into Klopp Lake reducing its salinity by an unknown level. The connection was removed in 1985/86 before the introduction of wastewater and, since that time, Klopp Lake has received only rainwater and back flow water from Humboldt Bay during high tide.
Klopp Lake
Klopp Lake was very different from the three freshwater units.
This saline (Table 2) basin was connected to Humboldt Bay and consisted of an open basin about two meters deep without substantial hydrophyte cover (Tables 4, 5). Sparse, scattered stands of widgeon grass grew in
64 65
Klopp Lake with peak growths in mid fall (Figure 5). Diving ducks were observed consuming widgeon grass in early, mid, and late fall. I suspect the poor growths of widgeon grass resulted from excessive salinities, turbidity, and water depth (Kadlec and Wentz 1974, Tables 1,
2). Setchell (1924) and Bourn (1935) reported the optimum salinity range for widgeon grass to be smaller than 18 ppt. Generally, the salinities measured in Klopp Lake equalled or exceeded this level
(Table 2). I do not believe the algal blooms noted during this study would have reduced light availability sufficiently to cause reduced widgeon grass growth. The mean secchi disc readings were at 1.4 meters in early, mid, and late fall, but Klopp Lake was only about two meters deep and the algae only covered 12.7 percent of the surface of Klopp
Lake during early fall. Much of the bottom of Klopp Lake consists of bay clay which also may have prevented the widgeon grass from flourishing. During the time when Klopp Lake had a freshwater inflow from Hauser Marsh, widgeon grass was slowly developing into fairly luxuriant beds over part of the basin (Higley 1989, S. Harris Dept. of
Wildlife, Humboldt State Univ. Arcata, CA. pers. comm). With the closure of the freshwater connection, Klopp Lake has become uniformly more saline and widgeon grass growth has declined.
Freshwater Units
The four freshwater units all had similar physical, chemical, and vegetative characteristics regardless of water source (Tables 1-7).
The BSLP was first flooded in the early 1980's and the water level has been maintained ever since with well and rain water. It has never contained wastewater. Wastewater began to flow through the other 66 units (Allen, Gearheart, and Hauser) in July and August 1986 (Higley
1989).
The creation or rehabilitation of units improves wildlife habitat, aids in abatement of shore erosion, and can be important in biological treatment of wastewater (Garbisch and Coleman, 1978).
Wastewater is rich in phosphorus and nitrogen and soon produces large numbers of snails, midge larvae, and other aquatic invertebrates that are important as food for waterfowl and shorebirds (Uhler 1964).
Additionally, nutrient-rich wastewater produces vegetation at accelerated rates compared to other water types.
Higley (1989) expressed concern that vegetation might encroach into the open areas of the wastewater units and eventually fill the available water column. He reported a 20 percent increase in vegetative cover in Gearheart Marsh between 1984 and 1986. To date, the increase in coverage of vegetation noted by Higley (1989) has continued in all four freshwater units, but especially in the wastewater units. The coverage of broad-leaved cattails and marsh pennywort in the wastewater units has increased since 1985-86 (Higley 1989, Table 4). This supports the hypothesis that broad-leaved cattail and marsh pennywort will continue to encroach into the units unless they are removed periodically.
The wastewater units and the BSLP all had peak growths of broad- leaved cattail in summer. Allen, Gearheart, and Hauser units consistently had greater mean stem densities of cattail than BSLP. The generally deep water in BSLP and the extra nutrients in the wastewater 67 units may have contributed to the slight differences in stem densities counts between the two water types (Weller 1975).
Hard-stemmed bulrush grew only in Hauser Marsh and BSLP. Hard- stemmed bulrush had been planted into Hauser Marsh in 1985 to aid in wastewater treatment (D. Hull City of Arcata, Dept. of Public Works,
Arcata CA. pers. comm) and the stand in BSLP was a remnant left from pre-impoundment times. The generally greater stem densities of hard- stemmed bulrush in Hauser Marsh compared to BSLP probably were related to the shallower water depths in Hauser Marsh. In 1985-86, hard-stemmed bulrush in Hauser Marsh consisted of a thin band located in the central portion of the unit and several randomly spaced clumps in the southern one-fourth of the unit, which together only covered 2.3 percent of the marsh (Higley 1989). By the time this study was completed, the coverage of hard-stemmed bulrush had increased by four to five times that reported by Higley (1989), had grown to a thick belt approximately three meters wide in the central portion of the marsh and had nearly covered the entire southern portion of the marsh (Table 4, Appendix B).
Additionally, hard-stemmed bulrush has pioneered into shallow portions of Hauser Marsh where it had not been planted in 1985-86.
Measurements of marsh pennywort biomass varied between seasons and units (Table 6, Figure 8). Some of the variability may have resulted from imprecise sampling methods. Marsh pennywort was cut loose from the mats with a machete, and it was often difficult to obtain an exact 35.5 cm x 25.5 cm sample. This was compounded on windy days since sampling was done from an unstable boat. Marsh pennywort mats grew along the shallows of all freshwater units and as understories to 68 emergents. By fall they had covered substantial areas. City workers physically removed these mats from Allen and Gearheart units in February
1991 causing a temporary, seasonal, decline in coverage (Table 4). In
1991, the city did not remove these mats from Hauser Marsh and mats there continued to spread throughout the study period.
During the present study, open water decreased to less than 1.0 percent aerial coverage by mid fall as it became filled with pondweeds and duckweed seasonally (Table 4). By early spring most of the duckweed and pondweed had been removed by foraging waterfowl and marsh pennywort mats had been removed by the city workers, increasing open water coverage to 51 to 66 percent by early spring in the three wastewater units (Table 4). In spite of this, open water coverage in Allen,
Gearheart, and Hauser units had decreased between the time of Higley's
(1989) study and the present time, mainly as a result of increases in emergent and marsh pennywort stands.
From a waterbird food standpoint, the submergent plants in the open water, the duckweed, and invertebrates associated with these plus the marsh pennywort mats all seem to be important. Sago pondweed has been considered the single most important waterfowl food plant in North
America (Yeo 1965, Krull 1970, Anderson and Jessop 1976). It therefore, would be desirable to manage the units in such a way as to produce the highest quantities of sago pondweed possible. All four freshwater units had peak sago pondweed rake scores in mid fall (Table 6, Figure 10) and sago pondweed coverage peaked in early fall in the wastewater units and in late fall at BSLP (Table 4). This time difference in coverage may have been due to differences in water depth (Robel, 1961), nutrient 69
availability or turbidity (Robel 1961, Office of Technology Assessment
1984), competition with duckweed, or a combination of factors.
Duckweeds are reported to harbor more invertebrate organisms per
100 g of vegetation than most other aquatic plants (Krull 1970), and
both the duckweed and its associated invertebrates provide vital food
for waterbirds. Lesser duckweed appeared in significant quantities
during early and mid fall in Hauser and Gearheart and to a lesser extent
in Allen Marsh (Table 4). Lesser duckweed increased exponentially after
sago pondweed broke the water's surface to pollinate (S. Harris Dept. of
Wildlife, Humboldt State Univ. Arcata, CA. pers. comm). The floating
duckweed lodged on the emerging pondweed foliage rather than drifting to
shore. This allowed duckweed to cover nearly the entire surface of the
open water area within 2-3 weeks and resulted in shading the pondweeds
and beginning the process of senescence for pondweed beds. In areas
without duckweed such as BSLP, the peak pondweed growth occurred
somewhat later.
Waterbird Considerations
The AMWS provides habitat for a substantial number of waterbirds
annually.� Species richness at Klopp Lake resulted from the use of
islands as a high tide roost by shorebirds, gulls, and terns.
Additionally, the deep, open water of Klopp Lake attracted loons,
grebes, and diving ducks not found elsewhere. Higley (1989) pointed out
that the density of use at AMWS matched or exceeded the use of other local waterbird areas. Funderburk (1979) recorded an average annual
total of 3,091,305 waterbird use-days on Lake Earl, Del Norte County, 70
California in 1974-1976. Nelson (1989) recorded 3,968,218 use-days and
91 species in 1987-1988 on South Humboldt Bay. Both Lake Earl and South
Humboldt Bay are many times larger in size than AMWS. Tousley (1982)
recorded 224,360 waterbird use-days and 63 species in 1979-1980 at the
Arcata Oxidation Pond. At AMWS, Spitler (1985) recorded 75 waterbird
species during the first year of flooding in 1980-1981, and Higley
(1989) recorded 1,434,633 use-days in 1984-1985 and 1,429,837 use-days
in 1985-1986 and 98 species in both years. Neither Spitler (1985) nor
Higley (1989) included BSLP in their data and for most of their studies,
Allen Marsh was unflooded. Including BSLP and a fully operational Allen
Marsh, I recorded substantially fewer (768,586) total bird use-days than
Higley (1989), but nearly as many species (94). Most of this difference resulted from my lower totals for shorebird use-days on Klopp Lake
islands than reported by Higley (1989). Although these differences between my numbers and those reported by Higley (1989) may have represented true changes in populations using the area or variations in the time shorebirds used the roost, I believe the differences were largely due to variations in estimating the size of large flocks of shorebirds.
Estimating large concentrations of shorebirds on the roosting islands was extremely difficult. Higley (1989) pointed out that each
shorebird species presented a different set of variables in estimating population size. Marbled godwits, the largest species, roosted in densely packed flocks that acted as a visual wall obscuring smaller species. American avocets were conspicuous and easily counted except when they occurred in large moving concentrations. Willets often 71 roosted at the perimeter of other flocks where they were relatively easy to count. Black-bellied plovers roosted in the center of godwit flocks and were very difficult to see. Small shorebirds, such as dunlins and western sandpipers, often roosted among the larger birds where they became impossible to see. In view of these difficulties, I believe it is likely that I either underestimated or Higley (1989) overestimated true numbers present in these shorebird flocks.
Both Higley (1989) and I converted our data to bird use-days per five ha to allow a direct comparison of the marsh units of variable size
(Table 9).
Klopp Lake
Use by waterbirds at Klopp Lake was determined by the nature of the habitat, depth, salinity, food supplies, and the availability of habitats elsewhere. Based on relative area use indices, Klopp Lake was
"preferred" by double-crested cormorants, "other fish-eating divers"
(mostly loons and brown pelicans Pelicanus occidentalis), diving ducks, shorebirds, gulls and terns, and osprey (Table 10).
Shorebirds. Klopp Lake supported 61.1 percent of all bird use- days recorded in this study (Table 8). Spitler (1985) and Higley (1989) reported similar use on Klopp Lake. Shorebirds accounted for 85.6 percent of the use of Klopp Lake. Nearly all of this use was by roosting shorebirds during high tides. The shorebirds roosted on the three low, bare islands that had been especially designed as shorebird islands (S. Harris Dept. of Wildlife, Humboldt State Univ. Arcata, C pers.comm). On an equal area basis, I recorded only about half as many 72 large shorebirds and only about 1/5 as many small shorebirds as Higley
(1989) (Table 9). The differences may have been related to difficulties in estimating numbers, but the differences in small shorebird numbers probably cannot be explained totally on that basis. Dowitchers were the only important large shorebird to use Klopp Lake at less than expected rates based on acreage (Table 10).
Large shorebirds were numerous from mid fall through early spring and were least abundant in summer (Table 8, Figure 17). Higley
(1989) reported a similar seasonal pattern. Gerstenberg (1972) reported that marbled godwits arrived in early fall, declined in mid fall, and increased in late fall to remain stable through winter. Higley (1989) reported that marbled godwits declined in late fall presumably related to changing use of high tide roosts. During this study, peak numbers of marbled godwits arrived in late fall (Table 8, Figure 17) and I did not detect a decline in numbers in late fall and winter as reported by
Gerstenberg (1972) and Higley (1989).
Evans (1988) and Higley (1989) reported peak American avocet numbers in late January. Higley (1989) reported 725 individuals and
Evans (1988) reported 736 individuals on 17 January 1985 and 22 January
1985 respectively. Additionally, Higley (1989) reported 800 individuals on 6 January 1986. My peak count of avocets was 724 individuals, on 3
November 1990 (Figure 17, Appendix A). American avocet numbers were highly variable between surveys as this small, local population shifted between the Klopp Lake Islands, the salt marsh at the mouth of Jacoby creek approximately one mile away, and the Arcata Oxidation Pond. All avocets were seen on the bare islands in Klopp Lake at high tide. 73
Numbers of black-bellied plovers peaked in mid fall and early
spring in 1984-85 and 1985-86 (Higley 1989) and in this study.
I detected black-bellied plover on 75.2 percent of my surveys. They were found only on the Klopp Lake islands by Higley (1989) and myself.
I found peak willet numbers in late fall (Table 8, Figure 17)
but Higley (1989) reported willet peaks in winter. Willets were detected on 76.6 percent of my surveys.
Gerstenberg (1972) reported peak numbers of western sandpipers at Humboldt Bay during the early and late spring and Higley (1989)
reported peaks in late spring. I found a high peak in early and mid
fall and a smaller peak in early and late spring (Table 8, Figure 18).
Both Gerstenberg (1972) and Higley (1989) reported dunlins arriving in Humboldt Bay in mid fall and migrating north in late spring.
I found the same pattern.
Diving Ducks. Diving ducks were second in importance on Klopp
Lake (6.6 percent of total Klopp Lake use, (Table 9). These were dominated by greater scaup, ruddy ducks, lesser scaup, and buffleheads
(Table 8).
In the Humboldt Bay region, diving ducks generally arrived in late fall and departed in early spring (Higley 1989, Nelson 1989, this study, (Table 8, Figure 15). For Humboldt Bay generally, Monroe et al.
(1973) and Nelson (1989) reported surf scoters (Melanitta perspicillata), greater scaup, and buffleheads as the most abundant diving ducks in winter. For the AMWS as a whole, Spitler (1985), Higley
(1989) and I found the ruddy duck to be the most common diver, except 74 that in 1985-86, lesser scaup exceeded ruddy ducks in total annual bird use-days (Higley 1989).
Diving ducks used Klopp Lake significantly more (p<0.05) than the other units. On an equal area basis, I recorded diving ducks at a rate remarkably similar to that seen in 1984-85 by Higley (1989)
(Table 9), but at only about one-half the rate reported by Higley (1989) in 1985-86. The doubling of use in 1985-86 reported by Higley (1989) was almost all due to the presence of a flock of 300 to 400 lesser scaup present on Klopp Lake for much of November and December 1985. These birds apparently responded to an excellent growth of widgeon grass that had developed in the lake that year as a result of the brackish conditions created by the freshwater inflow from Hauser Marsh (Higley
1989, S. Harris Dept. of Wildlife, Humboldt State Univ., Arcata, CA. pers. comm). Since the freshwater flow in Klopp Lake was cut off, widgeon grass growth and pochard use have both declined.
Higley (1989) also recorded a 10-fold increase in coot numbers on Klopp Lake during the same period compared to relatively low use in
1984-85 and during this study (Table 9). These coots probably also responded to the widgeon grass present during the 1985 growing season.
Gulls and Terns. Gulls and terns accounted for 5.9 percent of the annual Klopp Lake bird use-days (Table 8). Klopp Lake accounted for
96 percent of all gull and tern use-days recorded during this study.
Ring-billed gulls accounted for 61.9 percent of all the Klopp Lake gull and tern use (Table 8). Both Spitler (1985) and Higley (1989) reported similar results. Tousley (1982) reported California gulls and
Bonaparte's gulls as the most abundant gulls on the Arcata Oxidation 75
Pond. During my study, California and Bonaparte's gulls contributed to seasonal peaks in gull numbers (Table 8, Figure 19). Mew gulls were present on 26.2 percent of my surveys and were the second most numerous gull recorded (Table 8, Figure 19). They occurred mostly during winter and early spring (Table 8), a pattern also reported by Spitler (1985) and Higley (1989).
Western gulls (Larus occidentalis) were reported by Higley
(1989) and Nelson (1989) as one of the three most common gulls at AMWS and the most abundant gull on South Humboldt Bay respectively. During this study, western gulls were present year-around on Klopp Lake and
Gearheart Marsh but were not abundant enough to be considered an important species. This may have been due partly to misidentification in recording western gulls as California gulls.
Higley (1989) reported a 50+ percent decrease in gull and tern use on Klopp Lake between 1984-85 and 1985-86. In 1985-86, Higley
(1989) recorded 11,549 gull and tern use-days per 5 ha and I recorded
11,727 gull and tern use-days (Table 9). Higley (1989) attributed the decline in gull use at Klopp Lake to an increased use of newly created dikes at the nearby Arcata Oxidation Pond, and during this study, I also observed hundreds of gulls swimming on the oxidation pond or loafing on the pond's dikes.
Fish-eating Divers. More than half of the fish-eating divers recorded on Klopp Lake were double-crested cormorants (54.4 percent) (Table 8, Figure 12). Spitler (1985) recorded double-crested cormorants on only 14 percent of her surveys in 1980-81. At the time of Spitler's
(1985) study, Klopp Lake was not yet complete and consisted of a newly 76 flooded, barren basin of shallow water. Higley (1989) found double- crested cormorants on 46 percent of his surveys in 1985-86. By then,
Klopp Lake had matured somewhat as an ecosystem, but a substantial freshwater flow entered the lake from Hauser Marsh. I found double- crested cormorants on 73.8 percent of my surveys, mostly on Klopp Lake where they fished in the saline basin and rested on the bare islands.
The nearby Humboldt Bay supported a large nesting and year-around foraging population of this species (Ayers 1975). During my study, the freshwater inflow into Klopp Lake had been cut off and the basin was essentially an isolated arm of bay water with high salinities
(Table 2). Other fish-eating divers on Klopp Lake consisted mostly of brown pelicans in mid fall and pied-billed grebes. These were probably attracted to Klopp Lake's fish population.
Raptors. Eighty-one percent of all the osprey bird use-days were recorded at Klopp Lake, mostly in summer and early fall (Tables 8,
Figure 20), where they foraged for fish.
BSLP
BSLP was the only freshwater unit studied that did not receive nutrient-rich wastewater. It also had a generally deeper basin and was smaller and less turbid than the three wastewater units. It had a steep artificial shoreline around all four sides, was heavily vegetated with mats of shoreline emergents and marsh pennywort. Banks were occupied by willows giving the marsh a generally more "closed in" appearance than the three wastewater units. 77
The open areas of the pond were occupied by sago pondweed beds in fall. City personnel accomplished partial removal of marsh pennywort mats in February 1991 leaving substantial areas still covered with mats
(Table 4). Of all freshwater units, BSLP developed more filamentous algae, often associated with sago pondweed beds, hard-stemmed bulrush, and marsh pennywort mats (Table 5). BSLP was the only freshwater pond not to develop dominant stands of lesser duckweed, though this species was associated somewhat as an understory in emergent and marsh pennywort cover stands (Table 5).
These slightly unique physical and vegetative features may have created an environment that attracted a waterbird complex very similar to that in the wastewater units yet one that differed in subtle ways.
BSLP was totally or essentially unused by all shorebirds with common snipe (Gallinaqo gallinago) as a rare exception. It was also nearly unused by gulls, terns, fish-eating divers (except pied-billed grebes), great blue herons, wigeon, and scaup (Table 8).
Species that seemed especially prevalent on BSLP included pied- billed grebes, black-crowned night-herons, mallards, cinnamon teal, gadwalls (Anas strepera), ring-necked ducks (Aythya collaris) and
American coots (Tables 8, Appendix A). These species all had relative area use indices that far exceeded the expected rates of use based on the size of BSLP alone (Table 10).
Two pairs of pied-billed grebes were residents on BSLP and successfully nested there in the sago and algae beds. The black-crowned night-herons were attracted to the cattail and willow cover on the islands as a daytime roost. The mallards, cinnamon teal, and 78
substantial numbers of green-winged teal fed in the sago beds and
pennywort mats and the teal, especially, used the pennywort mats as a
sheltered, loafing site in winter. The gadwalls and ring-necked ducks
seemed to be attracted to the pond for food. One to three pairs of
resident coots nested successfully in the BSLP and they were joined in
winter by an influx of additional birds. BSLP is farther removed from
human disturbance than any of the other units and this may have
accounted for some of these use patterns. Since neither Spitler (1985)
nor Higley (1989) studied BSLP, no historic comparisons are possible.
Wastewater Units
Generally, the wastewater units were used by all herons, all puddle ducks, coots and rails, dowitchers, and some raptors at rates
which exceeded their relative surface area (Table 10).
Fish-eating Divers. Only pied-billed grebes occurred on the wastewater units to any extent. They were found throughout the year but
their use peaked in late fall (Table 8, Figure 12). Higley (1989) found
pied-billed grebes on 76.0 percent of his surveys, but at the open,
nearby Oxidation Pond, Tousley (1982) found pied-billed grebes on only
1.9 percent of her surveys. In this study pied-billed grebes were
consistently present at BSLP (not included in Higley's 1989 study) and
on Hauser Marsh. I found this species on 96.5 percent of my surveys.
Clearly, the Arcata Oxidation Pond was not as suitable for pied-billed
grebes (Tousley 1982) as the AMWS units. This could be related to differences in emergent cover for nesting and to differences in food
supplies. 79
The distribution of fish-eating divers use within the three wastewater units was remarkably uniform on an area basis (Table 9).
Higley (1989) found many fewer fish-eating divers on Allen Marsh and many more on Gearheart Marsh than I did (Table 9). Allen Marsh was dry or had low water levels for much of Higley's (1989) study. Perhaps the introduction of wastewater has reduced the availability of fishes in
Gearheart Marsh since Higley's (1989) study. Generally, the wastewater units were used at rates only about one-third that of the other two water types when considered on an area basis (Table 10). Clearly, wastewater units were not as attractive to fish-eating divers as the other types of units.
Herons and Egrets. The wastewater units were used by all local herons and egrets at rates that equalled or exceeded expected rates based on surface area (Table 10).
Higley (1989) reported snowy egrets and great egrets
(Casmerodius albus) as the most abundant herons at AMWS. Nelson (1989) found mostly great egrets on South Humboldt Bay. In this study, snowy egrets, the most abundant heron, were recorded on 93.6 percent of all surveys (Table 8, Figure 13). Black-crowned night-herons, the second most abundant heron, were seen on 97.2 percent of surveys (Table 8,
Figure 13). Great egrets occurred on 66.0 percent of my surveys and were the third most common heron (Table 8, Figure 13). Spitler (1985) reported snowy egrets and great egrets on 64 percent and 87 percent of her surveys, respectively, and Higley (1989) reported snowy egrets and great egrets on 87 percent and 80 percent of his surveys, respectively.
Tousley (1982) reported snowy egrets on five percent and great egrets on 80
14 percent of her surveys at the deep, open Oxidation Pond. Clearly, snowy egrets have increased their use of these habitats. Snowy egrets were detected most often on Allen and Hauser units where they roosted on islands and in flooded willows and where they fed on marsh pennywort mats. The greater frequency of black-crowned night-herons in my data compared to earlier work was related to the use of a tree clump in Allen
Marsh and of islands in BSLP by roosting birds. None of the previous workers included the BSLP in their data sets. Comparing the three wastewater units with Higley's (1989) pre-wastewater data, heron use on both Hauser and Allen units increased greatly (Table 9). Heron use increased nearly 10-fold from Higley's (1989) study on Allen Marsh, but
Allen Marsh was dry for part of Higley's study. Use by herons has increased 4-10 times in Hauser Marsh compared to Higley's (1989) data
(Table 9). Higley (1989) had high use in 1985-86 in Gearheart Marsh because of a partial drawdown that attracted large numbers of herons and egrets for several weeks. Hauser Marsh is generally the shallowest of all waterbodies at AMWS. Herons and egrets waded and foraged throughout
Hauser Marsh and they rested on mud islands and among persistent emergents. In Allen Marsh, the high use by herons and egrets (Table 9) resulted from black-crowned night-herons and snowy egrets roosting on the islands and snowy egrets foraging on the marsh pennywort mats.
Puddle Ducks. The wastewater units have proven to be very attractive to puddle ducks of several species. Generally, the use of the three units by puddle ducks has equalled or exceeded that reported by Higley (1989) before the introduction of wastewater (Table 9). Allen
Marsh was used at only about one-half the rate as the other two units 81 during this study (Table 9). Hauser and Gearheart units were used at twice the rate as the BSLP and many times the rate of Klopp Lake (Tables
8, 9). Puddle duck use peaked during late fall with a slight decline in winter (Table 8, Figure 14). Higley (1989) reported peak puddle duck numbers in winter. All AMWS studies to date, including this one, have reported low puddle duck numbers in summer and early fall (Table 8,
Figure 14).
Nelson (1989) reported that American wigeon were the most abundant puddle duck on South Humboldt Bay and green-winged teal and northern pintails (Anas acuta) ranked second and third, respectively.
Monroe et. al (1973) found American wigeon most abundant and northern pintails second for Humboldt Bay generally. At the Arcata Oxidation
Pond, Tousley (1982) recorded northern shovelers (A. clypeata),
mallards, American wigeon and northern pintail as the first, second, third, and fourth most abundant puddle ducks, respectively. Spitler
(1985) found mallards, northern shovelers, cinnamon teal, and northern pintails as the most abundant puddle ducks in rank order during the first year of flooding at AMWS. Higley (1989) reported that green winaed teal accounted for 38 percent of annual puddle duck use-days while mallards and cinnamon teal accounted for 36 and 15 percent respectively. My results were similar to Higley's (1989). Green-winged teal were the most abundant puddle duck followed by mallards and cinnamon teal (Table 8, Figure 14). Green-winged teal were seen on 83.7 percent of my surveys and accounted for 56.5 percent of annual puddle duck use-days while mallards and cinnamon teal were seen on 98.6 and 82
100.0 percent of my surveys and accounted for 16.9 and 10.8 percent, respectively (Table 8).
Mallards and green-winged teal were found on the wastewater units in significantly greater (p<0.05) numbers for all seasons compared to the BSLP and Klopp Lake. Green-winged teal used Hauser Marsh significantly more (p<0.05) than the other units from early fall through late fall and again in late spring. Mallard use was concentrated significantly (p>0.05) on the wastewater units.
Cinnamon teal used Hauser Marsh significantly more (p<0.05) than the other units from late spring through early fall (Table 8,
Figure 14), and they used the BSLP significantly more (p<0.05) from late fall through early spring where they fed and rested among the marsh pennywort mats.
American wigeon arrived in large numbers at AMWS in late fall
(17.5 percent of seasonal puddle duck use-days) which coincided with peak pondweed and duckweed growth and were seen consuming duckweed and submergent vegetation until it disappeared in November when 91.9 percent of wigeon left the wastewater units (Table 8).
Mostly the puddle ducks foraged in the units and rested on the islands (all species) and marsh pennywort mats (teal). Puddle ducks were most common during late fall and winter and were found mostly in the wastewater units where they ate pondweeds and lesser duckweed.
Puddle ducks made a gradual transition from Gearheart to Hauser Marsh as pondweeds and lesser duckweed became depleted in Gearheart Marsh.
Gearheart and Hauser units accounted for 64.0 percent of annual puddle duck use per five ha in AMWS and more than 50 percent of the puddle duck 83 use in AMWS in late fall and winter (Table 9, Figure 14). Allen Marsh and BSLP were used at rates lower than Gearheart and Hauser units, and puddle ducks did not use Klopp Lake to any significant degree (Table 9).
Diving Ducks. The wastewater units attracted some ruddy ducks and buffleheads, but few other diving ducks (Table 8). As the units have matured, the use by diving ducks generally has declined (Table 9).
I found only one-fourth to one-half as many divers on Gearheart Marsh and generally fewer on Hauser Marsh than Higley's (1989) pre-wastewater data (Table 9).
Coots and Rails. The wastewater units provide ample habitat for coots and rails (Table 8). Monroe et al. (1973) reported American coots as most abundant in winter and that they generally used fresh water units surrounding Humboldt Bay. In this study, peak numbers of coots and rails occurred in late fall. This consisted mostly of coots
(99.1 percent of seasonal coot and rail use-days and 98.3 percent of annual coot and rail use-days, Table 8, Figure 16). Higley (1989) also reported peak numbers of American coots in late fall and winter and only a few birds each summer. Although I had few coots in summer, they were detected on 97.2 percent of my surveys and used the freshwater units significantly more (p<0.05) than they used Klopp Lake (Table 8,
Figure 16)
Virginia rails and soras usually were detected only by calls, rarely by sight, and I almost certainly underestimated their true numbers. 84
The three wastewater units attracted coots and rails at only slightly lower rates per five ha than BSLP and at 10-12 times the rate of Klopp Lake (Table 9). Within the three wastewater units, the use of
Gearheart had declined by about 20 percent compared to the pre- wastewater period (Table 9). Allen Marsh had more use than during
Higley's (1989) study, but Allen was mostly unflooded in 1984-1986.
Hauser Marsh had twice the use by coots in 1984-85 as in this study but only one-fourth the number in 1985-86, an unexplained difference.
Shorebirds. In this study, 76.7 percent of all dowitchers recorded were on the three wastewater units (Table 8). They were the only shorebirds recorded in important numbers except at Klopp Lake.
No attempt was made to differentiate between long and short billed dowitchers in this study although both species are known to occur in the region and also at the AMWS (Gerstenberg 1972, Higley 1989,
Harris 1991). Gerstenberg (1972), Spitler (1985) and Higley (1989) all reported peak dowitcher numbers during spring and fall migration. I found more dowitchers during fall (Table 8).
Comparing the units, Gearheart Marsh was little used by shorebirds in this study and during the previous study reported by
Higley (1989, Table 9). I found more use by dowitchers in Allen and
Hauser units than did Higley (1989, Table 9). The only important use of the wastewater units by small shorebirds was reported for 1985-86 by
Higley (1989) in Hauser Marsh (Table 9). I found only incidental use by small shorebirds on any of the freshwater units. The water levels in two of three units were stable during this study period (Figure 4) and few suitable shallows were created that might attract small shorebirds 85 even in Hauser Marsh where some fluctuations in water levels were recorded (Figure 4). The dowitchers stood belly deep in the only area shallow enough to provide habitat for shorebirds. In 1985-86, water levels in Hauser Marsh were more uneven and mud islands appeared from time to time. Since the introduction of wastewater, vegetation has colonized and overgrown all the shallow areas which might have been attractive to small shorebirds, leading to the virtual elimination of these species in these units. The only small shorebirds recorded in any numbers in the wastewater units were spring migrant red-necked phalaropes (Phalaropus lobatus) (Appendix A).
Gulls and Terns. Aside from an occasional ring-billed gull, the only substantial number of gulls on the wastewater units in this study was an influx of Bonaparte's gulls in summer in Allen Marsh (Table 8).
These birds represented late spring migrants. Higley (1989) did not record any significant use of these units by gulls and terns before the introduction of wastewater.
Raptors. Except for the ospreys at Klopp Lake, most raptors recorded were not really associated with the wetlands except that they occasionally hunted along the shore or passed over them enroute to another area. During both Higley's (1989) and this study, some raptors were found all year.
Northern harriers were the most abundant raptor during Higley's
(1989) and the present study. In both studies, peak numbers of northern harriers were recorded in winter but they were not associated with any 86 water type. Turkey vulture numbers were not significantly associated with any water type.
The use by raptors of the four freshwater units was very uniform on an surface area basis (Table 9). There seems to have been a small increase in raptor numbers at Gearheart and Hauser units since Higley's
(1989) study (Table 9). MANAGEMENT IMPLICATIONS
Sago pondweed is probably the single most important natural waterfowl food plant on the continent (S. Harris Dept. of Wildlife,
Humboldt State Univ. Arcata, CA pers. comm). Sago pondweed beds harbor many macro-invertebrates used by waterfowl (Collias and Collias 1963,
Krull 1970). Additionally, sago may form a significant portion of foods consumed in fall pre-migratory populations, pre-molting birds, molting ducks, and older ducklings (Keith and Stanislawski 1960, Chura 1961,
Bartonek and Hickey 1969, Bergman 1973, Hay 1974).
Spitler (1985) predicted that Gearheart Marsh would continue to develop as an area of major importance to dabbling ducks and American coots as submergent plants became established. Higley (1989) noted high use of Hauser and Gearheart units by waterfowl and coots as sago pondweed became available. During this study, puddle ducks were the most abundant group of waterbirds on Allen, Gearheart, and Hauser units and American coots ranked second or third in abundance on the wastewater units (Table 8). This high use of the wastewater units by waterfowl and coots will continue only if suitable food continues to be available.
There is increasing evidence that crops of sago pondweed in the wastewater units are declining as predicted by Higley (1989).
Several possible mechanisms may be responsible. Sago pondweed was reduced dramatically in late fall by waterfowl and coot consumption.
Anderson and Jessop (1976) reported that heavy use of a stand of sago pondweed over several consecutive seasons might result in decreased plant production. Mallards have been reported to consume sago pondweed tubers (Chura 1961).
87 88
Another possible mechanism in the reduction of pondweed beds that concerned Spitler (1985) and Higley (1989) was the encroachment of marsh pennywort and broad-leaved cattail in the wastewater units at the expense of open water and submergents. A comparison of my cover maps
(Appendix B-0) with those produced by Higley (1989) reveals an increased growth of pennywort in all units, a rapid increase of hard-stemmed bulrush in Hauser Marsh, and seasonal fluctuations in cattail coverage.
City personnel physically remove marsh pennywort each winter in Allen,
Gearheart, and Hauser units. This practice should continue. Because pennywort was heavily used by green-winged teal, northern shovelers, cinnamon teal, and American wigeon late in the fall and winter, the removal operations should be timed to allow for waterfowl use of these mats, and removal should occur after most waterfowl have migrated away in early spring. Besides the waterfowl, pennywort was used heavily as a foraging area by snowy egrets, especially in Allen Marsh.
BSLP had beds of pondweed comparable to the wastewater units.
Marsh pennywort mats covered large quantities of open water during peak pondweed production (early fall through late fall) at BSLP and may hinder sago pondweed growth by shading out the submergents. Removal of pennywort mats would be desirable after waterfowl have migrated.
Spitler (1985) and Higley (1989) expressed concern that lesser duckweed might cover the water column and shade out pondweeds. During this study, pondweed stands in BSLP where no duckweed mats developed matured later and lasted longer than in the wastewater units. Although duckweed is an important food in its own right and harbors invertebrate foods (McAttee 1939, Hillman and Culley 1978), duckweed does not produce 89
seeds or tubers and is produced at the surface, not throughout the
entire water column. For this reason, it may not be as desirable as
food for waterfowl as sago pondweed. It has been suggested (Teeter
1965, Sculthrope 1967) that control of lesser duckweed might be achieved by manipulating salinities. Sago pondweed can withstand salinities up to
9 ppt while lesser duckweed can only tolerate up to 3 ppt (Teeter 1965,
Sculthrope 1967). A slight introduction of bay water into the system would create salinity levels suitable for sago pondweed or widgeon grass while eliminating duckweed and possibly marsh pennywort.
Water levels should be closely monitored, especially in the wastewater units where large amounts of organic detritus and particles
settle to the bottom. As the marsh fills with sediments, broad-leaved cattails and hard-stemmed bulrush will encroach farther into the open
areas and further reduce pondweed production. Exposure of the bottom might allow seeds to germinate and new stands of broad-leaved cattails
and hard-stemmed bulrush may root and increase their aerial cover.
While interspersed islands of cattails are important to marsh wildlife
(Weller, 1975), continuous unbroken stands provide little or no wildlife value (Weller and Spatcher 1965, Nelson and Dietz 1966). Hard-stemmed
bulrush has increased dramatically in Hauser Marsh since Higley's (1989)
study. Physical removal or digging deep ditches around present cattail
and hard-stemmed stands would help prevent their further encroachment
into the open water areas.
Delaying any drawdown in the BSLP or wastewater units until fall would provide stable water levels for aquatic vegetation growth for the
summer and would inhibit cattail seed germination (Green et al. 1964). 90
If cattails, duckweed, hard-stemmed bulrush, or marsh pennywort increase to a point where they shade out submergent vegetation, it may be necessary to take a unit out of production long enough to drain it and effect a vegetation control program to restore it to a more balanced condition (Spitler 1985). These manipulations will likely be necessary periodically. City officials should begin planning for this and should provide additional units that can provide wastewater treatment and habitat on a rotating schedule while other units are being rehabilitated.
Klopp Lake did not support large quantities of hydrophytes during this study. This was probably caused by excessive salinities, water depth, and turbidity. Water levels could be decreased and maintained at a level that promotes widgeon grass growth. It would likely be necessary to introduce freshwater into the system to reduce the salinity to a more optimum range for widgeon grass. If the introduction of freshwater into Klopp Lake is not feasible, consideration should be given to making experimental plantings of eel grass (Zostera marina) in this stable saline basin as a means of increasing ecosystem productivity. Additional manual plantings of alkali bulrush or cord grass (Spartina densiflora) along the shoreline perimeter of Klopp Lake are also recommended to increase shoreline protection.
The islands in Klopp Lake should be maintained as bare clay islands to continue to provide loafing areas for shorebirds. This will mean eliminating grasses and other vegetation that invades them from time to time. I recommend developing a formal plan to accomplish this 91 goal. The islands should be maintained at their original size or enlarged, especially during the spring and fall migrations of shorebirds. The size of the islands can be manipulated by altering the water levels in Klopp Lake.
Some of the islands in BSLP and the wastewater units are overgrown with dense stands of blackberries and willows and are rarely used by waterbirds. Islands with grasses and other herbaceous plants were used heavily by herons, egrets, waterfowl, coots, and rails. It is recommended that shrub control on the islands be an integrated part of any future management plan. Except for the large trees on the Allen
Marsh islands used as roosts by herons and egrets, it would be useful to clear brush away from the other islands.
Domestic waterfowl frequently were seen at the AMWS during this study. One brood of domestic X wild strain mallards was observed on
Gearheart and Allen units. Any domestic waterfowl found on these units should be removed immediately to preserve the wild stock, reduce competition for food, and prevent introducing diseases into the wild stock.
Feral cats and dogs were seen frequently on the AMWS during this study. Since these feral cats and dogs harass and kill waterfowl, coots, and shorebirds, these animals should be removed immediately from the area by any means necessary. CONCLUSIONS
AMWS provides suitable habitat where many local and migratory waterbirds roost, forage, breed or loaf. AMWS consists of five man-made units using three water sources. The freshwater and wastewater units had generally similar vegetative structure and waterbird use, but the brackish unit had very different vegetative and avian use.
On balance, the wastewater units provided an efficient means of natural filtration for domestic sewage while providing important food and loafing sites for puddle ducks, coots, rails, herons and egrets.
BSLP, a more secluded freshwater basin, provided coots and rails, pied-billed grebes, black-crowned night-herons, cinnamon teal, and mallards with loafing sites on the marsh pennywort mats and within emergent vegetation.
Klopp Lake, an open, shallow, brackish basin with few hydrophytes provided loafing sites for shorebirds, gulls, and terns and a large open water area for fish-eating divers and diving ducks.
Together, all five marsh units provided aesthetically pleasing areas for bird watchers, joggers and tourists while simultaneously supplementing diminishing wetlands.
92 LITERATURE CITED
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Zar, J.H. 1974. Biostatistical Analysis. Prentice-Hall, Inc., Englewood Cliffs, N.J. 620 pp. Appendix A Mean Number and Standard Deviation of Birds Recorded per Survey on the Marsh Units of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n=number of surveys). Appendix A Mean Number and Standard Deviation of Birds Recorded per Survey on the Marsh Units of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n=number of surveys). (Continued). Appendix A Mean Number and Standard Deviation of Birds Recorded per Survey on the Marsh Units of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n=number of surveys). (Continued). Appendix A Mean Number and Standard Deviation of Birds Recorded per Survey on the Marsh Units of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n=number of surveys). (Continued). Appendix A Mean Number and Standard Deviation of Birds Recorded per Survey on the Marsh Units of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n=number of surveys). (Continued). Appendix A Mean Number and Standard Deviation of Birds Recorded per Survey on the Marsh Units of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n-number of surveys). (Continued). Appendix A Mean Number and Standard Deviation of Birds Recorded per Survey on the Marsh Units of the Arcata Marsh and
Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n =number of surveys). (Continued). Appendix A Mean Number and Standard Deviation of Birds Recorded per Survey on the Marsh Units of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n=number of surveys). (Continued). Appendix A Mean Number and Standard Deviation of Birds Recorded per Survey on the Marsh Units of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n=number of surveys). (Continued). Appendix A Mean Number and Standard Deviation of Birds Recorded per Survey on the Marsh Units of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 30 June 1991 (n=number of surveys). (Continued). 108
Appendix B Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Marsh Units During the Early Fall Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 21 August 1990. 109
Appendix C Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Early Fall Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1 July 1990 - 21 August 1990. K]
Appendix D Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Marsh Units During the Hid Fall Season at the Arcata Harsh and Wildlife Sanctuary, Humboldt County, California, 22 August 1990 - 12 October 1990. 11
Appendix E Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Mid Fall Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 22 August 1990 - 12 October 1990. PEN
Appendix F Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Marsh Units During the Late Fall Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 13 October 1990 - 3 December 1990. 113
Appendix G Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Late Fall Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 13 October 1990 - 3 December 1990. •ppendix H Dominant Vegetation Cover of the Allen, Gearheart, and Hause Marsh Units During the Winter Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 4 Decembe 1990 - 24 January 1991. Appendix 115
Appendix I Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Winter Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 4 December 1990 - 24 January 1991. 116
Appendix J Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Marsh Units During the Early Spring Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 25 January 1991 - 17 March 1991. 117
Appendix K Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Early Spring Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 25 January 1991 - 17 March 1991. 118
Appendix L Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Harsh Units During the Late Spring Season at the Arcata Harsh and Wildlife Sanctuary, Humboldt County, California, 18 March 1991 - 8 May 1991. 119
Appendix M Dominant Vegetation Cover of the Klopp Lake and Butcher Slough Log Pond Marsh Units During the Late Spring Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 18 March 1991 - 8 May 1991. 120
^Appendix N Dominant Vegetation Cover of the Allen, Gearheart, and Hauser Harsh Units During the Summer Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 9 May 1991 - June 1991. 121
Appendix 0 Dominant Vegetation Cover of the Klopp Lake and Butcher Slouch Log Pond Marsh units During the Summer Season at the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 9 May 1991 - 30 June 1991.