The Ecology of Tijuana Estuary, California: An Estuarine Profile

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WET SEASON: Plants take up nutrients; animals consume POC. Sediments eposited in channels. DRY SEASON: No input from the watershed; organisms filter food from water; salts accumulate in T d a l soils. FLOOD EVENT: Biological filters may break down; physical phenomena predominate. Ocean Figure 59. Conceptual model of filtering functions during nonflood years and during catastrophic flooding; white arrows indicate fresh water; black arrows indicate sea water (from Zedler and Onuf 1984, with permission from Academic Press).
CHAPTER 5 THE ROLE OF DISTURBANCES IN MODIFYING SALT MARSH COMMUNITY STRUCTURE AND FUNCTION Recent changes In specles d~strrbutions and growth rates have been documented In detail for the salt marsh of Tijuana Estuary A general understanding of what controls rnvasron and exlinctron of species at the ecosystem scale has developed, as well as abrlrty to predrct expanstons and declrnes at the population scale Catastrophrc events, though destructive in many ways, have proved to be scrent~frcally valuable Thelr effects have been documented through an exterls~ve monltor~ng program that began as a survey of cordgrass habrtats in 1979 and has continued to date This chapter provides extensive ev~dence of the estuafy's temporal variabil~ty and lndrcates why no slnglc descrrption of productivcty or bromass can fully characterize the salt rnarsh ecosystnm cordgrass, and the monitoring program has helped to elucidate these and other distributional patterns. Mcasurements taken at the monitoring statlons are as follows Elevatrons are periodically measured relatrve to Army Corps of Engineers benchmarks Each Aprll, soil salinity IS measured In samples near all statrons In the iower marsh, ~nterst~tial soil water IS collected by expressing so11 water (from 0 to 10 crn depth) through frlter paper onto a salinity refractometer In the upper marsh, the dr~er soil samples (0-10 crn depth) are collected and taken to the laboratory, where unrform so11 pastes are made and measured wrth a conductrvtty meter (Rrchards 1954) In September, soil salinrty sampling is repeated and veqetation IS measured Cordqrass IS assessed bv 0 25-m7 ctrcula; quadrats (or 25"a of that area if densities are too 5.1 MONITORING PROGRAM m&asurlng helghts of stems wih~n The lower salt rnarsh has been sampled high for complete measurements) Flowering stems consistently at apgrOxlmately 100 stations along are noted, live and dead stems are counted The eight transects (Frgure 601 The exact number of percent cover of each of the other species present stat~ons has varied sirgb)tly wrth our abrlrtv to 1s estrrnated w,thin cover classes (i I",. lo0-5%,, relocaie station markers and the expansion of the 6",-25",,, 26"~~-50~,,, 51 ?,-75"0. 76uu-1 OOL",) distributiorl of corclarass The transects were set up to characterize fhe cordgrass cornmunrty, thus 5.2 PHYSICAL CHANGES FOLLOWING they extended from upper drstributionai limits ECOSYSTEM-WIDE DISTURBANCES toward channeis In ail cases. trarisects were 5.2.1 Soif Salinity Changes named tor the nearest Army Corps of Erlg~neers beilchmark (e g . TJE-31) In 1984, the monitoring program was expanded to rnclude upper marsh habltals An additional 115 stattons were set up lo extend from the upper dfstrrbutlonal llmlt of cordgrass inland. After surveying their elevations, we found that many of the sampling StatlOnS set up to characterrre upper rrlarsh dtstrtbution were within the :ange oi eievatlcrns included rn the lower marsh transects (Table 241 They are actually cordgrass and noncordgrass transects This emphasrzes that the distrrbutlon of cordgrass IS not entrrely predtctahie from eievation Other factors, rnclud~ng competrt~an by succulent species, ltrnrt the occurrence of Interstitial soil salinrties, which have been measured annually In April and September, Indicate that the lower marsh is usually hypersaline (I e, more saline than sea water, Figure 61) The followrng data stand out a Reductrons in soil salintty (to 15 ppt) occurred in April 1980, after the "100-year" flood Because !he f!ood:ng occ3rrcd pr:msrtiy tc Jaituarp and February, the April measurement may not represent mrnimum sot! salrniiy Evaporatron was no doubt hrgh throughout the spring (Sectton 2 21, arrd t~dal waters influenced the marsh throughout f 980, thus the perrod of brackish so~ls was shortlived
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June 1986 I THE ECOLOGY OF TIJUANA
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The findings in this report are not
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CONVERSION TABLE Metric to U.S. Cus
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Page 4.5 Energy Flow ..............
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Number Page The channel fish cornrn
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ACKNOWLEDGMENTS The California Sea
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Figure 1. Lacatlcrn of 71juana Estu
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Figure 3. Map6 of Tijuana Estuary s
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FI(I(uPc$ 4. Wei&rahOt@ patt@rns of
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also limitrng Hot, dry desert winds
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2.3 LAND USE HlSPQWV Through exami!
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The nearby bridge remained, and ext
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flushing until mid-December 1984. E
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with seawater. Even in years with s
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flats ~n winter but not in midsumme
Page 31 and 32:
Each "island" of higher topography
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The vegetation and soils of the upp
Page 35 and 36: populations (Massey 1979) The brrds
Page 37 and 38: c~n~entrations of insects, especial
Page 39 and 40: Frgufe 29. The Ifght-footed clapper
Page 41 and 42: Figure 30. During winter (above) th
Page 43 and 44: anlmal footprints, In the hardpan f
Page 45 and 46: Tijuana Estuary salt marsh Such exp
Page 47 and 48: Frgura 36 The etraracrel an& tidal
Page 49 and 50: ^_ _I __"___I _-a_. -- fable 7. Inv
Page 51 and 52: Pre- 1980 (excluding Hosrner Rehse
Page 53 and 54: Table 8. Average density (number/m2
Page 55 and 56: changes in envlronment has not been
Page 57 and 58: was dominated by goby species, Cali
Page 59 and 60: compared the ,chthyoplankton commun
Page 61 and 62: Figure 43, Birds of the intertidal
Page 63 and 64: -" and that the community was compo
Page 65 and 66: Willet (1 73) i - Water Depth (cm)
Page 67 and 68: Table 14. Early information on dune
Page 69 and 70: Figure 48. Birds that nest on the s
Page 71 and 72: CHAPTER 4 ECOSYSTEM FldNCTlONlNG St
Page 73 and 74: were no? irght-saturated untri expo
Page 75 and 76: Table 17. Conceptual model of chann
Page 77 and 78: Table 19. Net aboveground productiv
Page 79 and 80: _I___ I__-~--- 4.4.1 Nitragen Fluxe
Page 81 and 82: i i t 1 1 I Table 22. Standing crop
Page 83 and 84: calculated from chlorophyll a measu
Page 85: Dissolved Organic Biomass Carbon De
Page 89 and 90: Table 25. Changes in elevation in t
Page 91 and 92: Table 26. Change in pickleweed cano
Page 93 and 94: Table 27. Occurrence (in circular 0
Page 95 and 96: perennials can survive long periods
Page 97 and 98: An experiment was designed to deter
Page 99 and 100: CHAPTER 6 MANAGEMENT CONSIDERATIONS
Page 101 and 102: Closely associated with the researc
Page 103 and 104: c. Dredging at Tijuana Estuary will
Page 105 and 106: Table 30. Predicted impacts of redu
Page 107 and 108: footed clapper rails; the picklewee
Page 109 and 110: overwashas, and slabiiizatran rs rl
Page 112 and 113: REFERENCES Allen, L.G. 1980. Struct
Page 114 and 115: Minsky, D. 1984. California least t
Page 116: 30272 -101 REPORT WUMENTATION 1. RE
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The Ecology of Tijuana Estuary, California: An Estuarine Profile

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