The Ecology of Tijuana Estuary, California: An Estuarine Profile

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CHAPTER 1 ONTROBkBCTiON - AN OVERVlEW The story of Tijuana Estuary is complex. Ecologically, it has been influenced by its highly variable environment. Historically, it has shifted from a natural to a highly modified system. Politically, its fate has been hotly debated and competing interests continue to influence its management. This is the first attempt to synthesize and interpret a rapidly growing data base on the estuary's diverse biota - its vegetation, algae, birds, fishes, and invertebrates. Because so many changes have occurred in response to recent catastrophic events, we describe how each aspect of the estuary appeared before 1980 and how it has responded to several perturbations. The experimental tests of these cause-effect relationships have not been completed, and there is little reason to expect that environmental conditions have stabilized or that new types of disturbances won't occur. Thus, this profile should be viewed as a stage in the process of understanding Tijuana Estuary. Like the estuary itself, our knowledge is continuously evolving. 1.1 THE lMTERNATlONAL SETTING Tijuana Estuary is entirely within San Diego County, California, although three-fourths of its watershed is in Mexico (Figure 1). The Tijuana River originates in the mountains of Baja California. Water from the United States portion of its watershed flows down Cottonwood Creek and joins the Tijuana River in Mexico. The river then crosses the border just north of the city of Tijuana, Baja California. On old maps, Tijuana Estuary IS called Oneonta Lagoon or Siough The T~tudna River, which feeds it, has been variously called Rio Tecate, Rio Tlajuana, Tla Juana River, and Tiajuana River In 1968, the U S Board on Geograph~c Names approved the name Tijuana River fD Orth, Executive Secretary, U S Board on Geographic Names, letter). Somewhat later, the name Tijuana began to replace Oneonta, but not everyone recognizes the term "Tijuana Estuary." A number of scientists still doubt that it qualifies as an estuary. Yet, this southwesternmost estuary of the continental United States is not only a "coastal water body that is substantially diluted by fresh water" (Pritchard 19671, but one of national and international significance. As discussed throughout this profile, the estuary IS very much a function of ~ts watershed The land uses and management practices on both sides of the border greatly influence the quantity and quality of water entering Tijuana Estuary Thus, it IS ~mportant to characterize the regional env~ronmental conditions that have shaped and cont~nue to shape this international estuary (Chapter 2 and Chapter 3, respectively) 1.2 ESTUARY TYPE CLASSlFlCATlON Pritchard (1967) developed an estuar~ne classification scheme based on geologic origin and phystography In this frame of reference, Tijuana Estuary is very much l~ke most of the world's estuaries, because it is a flooded rlver valley, also known as a coastal plaln estuary As sea level rose during the last postglacial per~od, marine waters submerged the Tijuana River valley Sed~ments that were brought downstream from the watershed spread out between the coastal mountains to create a small but well-defrned coastal plain (Figure 2) The action of wind and waves gradually bu~lt up a sandbar and dune system parallel to the coast, and formed a semienclosed body of water The area where marlne waters are interm~ttently mlxed with fresh water from Tijuana River is a small estuary immediately adjacent ta the coast In other respects, Tijuana Estuary is very d~fferent from most of the world's estuaries ft does not fit well within the salinity character~zalion
Figure 1. Lacatlcrn of 71juana Estuary and map of watershed. Stations are indicated where rainfall and precipitation were mea$ur@;.d (frsm lBWC 1983). sch~mes that I-lavt? bean developed to describe Because most of the estuary has shallow-water astuarlr~e ensbaylrrentv {fJavi$ 1978) Estuarres habrtal, the wetland classifrcatlon of Cowardrn et at can bc divrdcd tntu sail-wedge (rtver-dominated),, (1979) IS also applrcable The intertidal portion of g3arlially mcxsd (saltnily gradrent downstrearmi or the system fits wrthin the California Province verttcaily humogeclersus (brackish water estuarrne system, tnterttdal subsystem, emergent throughout) types They can also be distingurshed wetland class, persistent subclass, domrnated by by thetr simirr~rty profiles as either posittve (fresh common pickleweed (Saitcornla v~rgrn~ca) and water floating aver saline water) or negative {warm Pacrfic cordgrass (Sparllna follosal saicne water floating over cool tresh water) As we describe sn Chapter 3, Tijuana Estuary is Tijuana Estuary 1s a highly variable system that sornet~mes rrver dominated, sometimes parUially may best be terrnea an 'rntermitrent estuary ' mixed, and usually veri~cally hOmogeneOus. During the winter wet season. rts waters are diluted although wtth marine, rather than brackish. water by rarnfatl and streamfiow, dur~ng the rest of the its vertical salrnrly pt-afrie can become ~osrtrve or year rt ts an extension of the ocean As streamflow negatuve, dependtng on weather and tidal flushing and wetland sail salrnrties suggest (Chapter 3), tt c~ndrtions may be one of the nation's most variable estuaries 2
Page 1 and 2: June 1986 I THE ECOLOGY OF TIJUANA
Page 3 and 4: The findings in this report are not
Page 5 and 6: CONVERSION TABLE Metric to U.S. Cus
Page 7 and 8: Page 4.5 Energy Flow ..............
Page 9 and 10: Number Page The channel fish cornrn
Page 11: ACKNOWLEDGMENTS The California Sea
Page 15 and 16: Figure 3. Map6 of Tijuana Estuary s
Page 17 and 18: FI(I(uPc$ 4. Wei&rahOt@ patt@rns of
Page 19 and 20: also limitrng Hot, dry desert winds
Page 21 and 22: 2.3 LAND USE HlSPQWV Through exami!
Page 23 and 24: The nearby bridge remained, and ext
Page 25 and 26: flushing until mid-December 1984. E
Page 27 and 28: with seawater. Even in years with s
Page 29 and 30: flats ~n winter but not in midsumme
Page 31 and 32: Each "island" of higher topography
Page 33 and 34: 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 and 86:
Dissolved Organic Biomass Carbon De
Page 87 and 88:
CHAPTER 5 THE ROLE OF DISTURBANCES
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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