The Ecology of Tijuana Estuary, California: An Estuarine Profile

More documents

Recommendations

Info

d High cordgrass mortalrty in 1984 (Figure 65) suggested that watered plants, I e, those that did not experience gradual decrease In soil morsture, should be highly susceptible to drought Thus. winter- and summer-watered plants should have hlgher mortality after the irrrgation ended than plants In unwatered control plots All treated plots expertenced cordgrass mortalrty In the last 5 weeks of the expernment, when soils drred out between waterings However, one control plot increased In denstty While evrdence is scanty, there is a! least a suggestran that infrequently wetted areas wrthstand drought better, and differentral rooting depths might explarn differential survlval Studres of below-ground plant growth at different intertrdal elevatrons are needed to explarn the high creek-edge rnortalrty seen during the 1984 drought The importance of seedlrng recrurtmerit was not addressed in these year-long experiments Most of the dynamrcs of cordgrass have resulted from changes in vegetative growth Although we expected to see some seedlings appear In plots watered all year, such lnvastons were ~nsignificant, perhaps because of the srnall srze of the quadrats and short duration of the experrrnent The hypotheses that grew out of the monitoring program withstood experimental tasting, and we provide 8 conceptual model of the control of cordgrass growth as fallows Cordgrass ts comtnonly under stress due to hypersaline soils Freshwater influxos to the marsh stimulate increased growth If the influx occurs in winter, plants are able to respond by increasing their height If the tnflux occurs in summer, during the peak of the growing season, plants respond by increasing vegetative reproductron From the standpoint of an rndrvrdual plant, it is a matter of carbon allocation the later that fresh water ts applied, tho less likely the plants can respond by Increasing tn height increased productron late In the season wtl! be channeled primarily to new shoots 5.4.2 Nutrient Addition Experiments From the flrst year on, the annual censuslng of cordgrass documented considerable spatial variabll~ty from quadrat to quadrat and transect to transect While strong year-to-year differences have been explained, local var~atioris have only recently been investigated It is now clear that nutr~ents and insects add to both spatral and temporal changes As discussed 117 Chapter 4 Covrfi (1984) found that sol! nrtrogen was important to cordgrass growth His experimental manipulations showed that urea Increased cordgrass growth in pure stands (although in different amounts for the two sets of plots), but not rn stands mrxed with p~ckleweed The rnfluence of urea on cordgrass thus depended in part on the presence of its most frequent co-occurnng species, with ptckleweed the better competitor for urea Nutrient-additron expertments also suggested that rnsect grazing has signrficant impact on cordgrass growth and densrtres Covin's ureaadditron plot at TJE-28 produced cordgrass with higher tissue nitrogen content than at TJE-37, and a late-season dieback occurred on those plants Patches of cordgrass d~ed along that same transect after the 1980 flood Because prckteweed was lacktng, we know that compet~lion was not the cause If nrtrogen inputs are commonly high at TJE-28, nrtrogen uptake should be h~gh, which should increase the probabilrty of insect attack We have yet to rdentlfy patterns of nrtrogen influx to different transects or quadrats, and we need to evaluate directly the retattonship between rnsect grazing and nutilent additions to help explain spatial heterogenerty In the salt marsh vegetation Research w~th other wetland (Onuf et a!. 19773 and grassland (McNeil and Southwood 1978) vegetai~on has shown that insects are attracted to plants w~th high nrtrogen concentrations and that herbivory is greater on leaves with augmented nltrogen Clearly, these secondary effects of added nitrogen can have lmportanl effects In nature
CHAPTER 6 MANAGEMENT CONSIDERATIONS Tijuana Estuary has two management programs; types of projects have shifted as the estuary it serves as an endangered species refuge and a experienced new and different environmental sanctuary for research and education. The assaults northern part of the estuary (428 ha; 1,056 acres) is the Tijuana Slough National Wildlife Refuge, With different management problems have come which is managed by the U.S. Fish and Wildlife new opportunities for research support. In 1976, Service. The speciflc goal is to protect three research funding was provided by Sea Grant to test endangered species, the light-footed clapper rail, paradigms of wetland plant productivity and export the California least tern, and salt marsh bird's beak. that were developed in Georgia and to determine An area including the refuge, Border Field State how disturbance affected wetland productivity. Park (160 ha), and adjacent lands (a total of 1 ,I 25 Associated studies of endangered species habitat ha) was designated as a National Estuarine were supported by the U.S. Navy and U.S. Fish and Sanctuary in 1982. It joins 14 other estuaries Wildlife Service. The finding that disturbance within the United States that are set aside for dramatically alters marsh productivity then led Sea research, education, and interpretation. A Grant to support development of wetland management plan for the sanctuary (Dobbin restoration techniques and, later, studies of how Associates 1985) was recently developed and altered hydrology (amount and timing of freshwater adopted by the Tijuana National Estuarine influx) affects estuarine functioning. The frequent Sanctuary Management Authority and associated sewage spills of the 1980's and the threat of agencces. The slated goals are resource continuous wastewater discharge from Tijuana, protection, research, interpretation, land Mexico, led to the analysis of streamflows, acquisition, and facility development estuarine salinities, and bioloaical impacts of year-round discharges (~nvironhental Protection 6.1 RESEARCH NEEDS AND OPPORTUNITIES Agency support through Section 205(j) of the In order to accomplish the matn purposes of the ciean Water Act) The deslgnatton Ti~uana refuge and sanctuary, the nat~ve biota of Tijuana Estuary as a National Estuarine Sanctuary allowed Estuary must be A brief history of funding of specific management-related research research actrvftles and a discussion of the most projects through the Sanctuary programs ~ivis~on ~mportant management problems wtll show how this Of the Nat'onal Oceanic and AtmOspher'c estuary contributes to the overall understanding of Admintstration Several problems+ regional wetlands including wastewater effects on channel algae and Since the 19703, there has been a continuing research interest in Tijuana Estuary, with emphasis on the salt marsh vegetation The research projects have directly followed the challenges posed by environmental changes and ecosystem responses. Studies have progressed from descriptions of species occurrences and measurements of wetland processes to long-term comparisons of the effects of disturbances There has been a growing emphasis on the experimental determination of cause-effect relationships. The cordgrass, dune revegetation and exotic species management, and recovery of plant populations from the 1984 drought, are now being addressed. Tijuana Estuary, as a system subject to multiple disturbances, provides a rich laboratory for science. It is unusual In that a vegetationmonitoring program has been in place since 1979 and several drstinct disturbance events were documented by that program. In many cases, however, the changes went unquantified (e.g., effects on benth~c invertebrates and fishes),
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 and 12:
ACKNOWLEDGMENTS The California Sea
Page 13 and 14:
Figure 1. Lacatlcrn of 71juana Estu
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: An experiment was designed to deter
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
show all

The Ecology of Tijuana Estuary, California: An Estuarine Profile

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?