Urban Development and Ecology of the City of Ensenada, B.C. (61) 77-24-66

Gobierno de Baja California

Early last century, american boats and later on whale hunting boats visited the area. Sea otter was also hunted and extirpated from the area before 1850.

The tree main processes that cause variability of the different properties at the San quintín Bay mouth are upwelling events and the cycles of the tides and solar radiation.

Tributaries and Flow

Arroyo Agua Chiquita (27 km long) is found at the slope of Mesa Agua Chiquita. It is fed by two tributaries Agua Amarga and Las Animas, it extends to the southwest and empties into Bahía de San Quintín. Arroyo San Simón (95 km long) is on the south part of the valley, it arises from the runoff of Santa Eulalia and El Rosario and empties, forming a wide delta, into Bahía de San Quintín.

In the region, runoff coefficient ranges 0-5% of the precipited volume and related to the medium to low permeability of the terrain. Due to the topography and type of rocks, runoff is semiparallel dendrites-like and runs toward the Pacific coast.

Average extraction flow ranges from 2 to 20 l/sec and water quality is tolerable (525-144 mg/l of dissolved solids) to salty (1400 mg/l). Underground flow direction tends to be southwest.

There is a temporal lagoon south of Lazaro Cardenas, that is formed by intermittent runoff from the sierras. Superficial water have no use in the area. Runoff collected during rainy season is used to water cattle, whereas underground water is allocated to agriculture and domestic use.

A 1995 study on heavy metals in superficial sediments at Bahía Falsa found two principal sources: from the ocean and from the continent. The first one transports heavy metals (especially Cadmium and Zinc) through upwelling; the second source supply mainly Copper and Iron and it consists of detritus eroded from granitic rocks and volcanic rock from San Quintín area, which is rich in Aluminum, Iron, Manganese, Chrome, and Nichel.

Mercury concentration levels detected in California mussels were 3-12 times below the limits established in several countries (0.5mg/g wet weight) for human consumption.

Studies on presence and accumulation of DDT and its metabolites in cultivated oysters have shown that the higher bioaccumulation (46.812 ug/gr) is found in older individuals, in concentrations below the tolerance limit for human compsumption (5 ug/kg).

A DDT study done during February, April, June and August of 1893 used pismo clam as bioindicator and found higher levels of DDT at Playa San Ramón, but three orders of magnitud below the tolerance limit for human. The potential contribution of organochlorines used in the agriculture of Valle de San Quintin to the wetland has not been evaluated. Such contaminants can be transported to the bay via wind or water runoff during rainy years.

A 1991 study showed low concentration levels of DDT residues in western gull eggs, collected at San Martin Island (5 km apart of Valle de San Quintín) and a recovery or increase in the egg-shell thickness. The same study found pp’-DDE, op’-DDT, the a BHC, the HCB and BPCs in the red sea urchin Strongylocentrotus purpuratus (a prey of the western gull). The pp’-DDE was the most abundant component of the DDT complex but in low concentrations that do not represent a risk to the reproduction of this gull.

According to SARH 1979, water quality in terms of coliforms bacteria have been always below the limits established by the FDA and comply with the Mexican government and the requirements set by the Programa Mexicano de Sanidad de Moluscos Bivalvos (PMSMB), to exporting cultivated mollusks.

A 1988 study on the water quality of the site reported that only five out of 20 sampling stations exceeded the value of 70 NMP/100 ml.

The number of aerobic bacteria were low and no stations exceeded the limit of 500,000 colonies.

Usinf the most likely number method, another study carried out in Bahía Falsa documented low values of fecal coliforms at all eight sampling stations, but in winter 1992-93 when mean values were higher than usual (264 TC ml^-1 y 29 FC 100 ml^-1). Because of high pluvial precipitation (in January 1993 was 376 mm) that caused a larger runoff to the bay, salinity decreased and coliform bacteria concentration increased up to 2,400 TC 100ml^-1 and 140 FC 100 ml^-1

Primary production is dominated by phytoplankton (~60%) and seagrass (~30%). Primary productivity (chlorophill a) decreases from the mouth to the interior of the lagoon. The tidal effect accounted for the observed diurnal variation of chlorophill a

Nutrient concentration (phosphate and silicates) usually augments from the mouth to the interior of the lagoon, and are higher inside the lagoon than in the adyacent open ocean. Maximum values are 4 mM for phosphates and more than 38 mM for silicates. Nutrient concentration in the mouth are higher during summer than in winter, due to upwelling effect.

Oxigen (DO)

During Fall, Winter and early Spring, Do levels remain the same or higher than those saturation levels (5.25 ml/ - 8.00 ml/l), during late Spring and during summer values of 3.0 ml/lt of DO have been detected, which is 60 % of saturation level. In Bahía Falsa DO range is between 4.5 ml/l and 8 ml/l; in Bahía de San Quintín, DO ranges between 3ml/l and 8ml/l.

Eelgrass beds and its detritus cover most of the botton of the bay and form reduction zones, where DO is lower (1.79 ml/l in the bottom during fall-winter). However, eelgrass and saltmarsh vegetation in the bay contribute importantly to the fertility of the bay, by means of direct photosynthetic production and as traps for nutrients and microbial enriched detritus. Thus, fertility in this wetland is a matter of both: suspended and sedimented particles (plankton and detritus).

Salinity diurnal variation is caused by tidal cycles, whereas temperature diurnal variation is dur to tidal cycles and solar radiation. Temperature and salinity augment from the mouth to the head of the lagoon, however its relationship is also affected by irregular topography causing heterogenous warming and evaporation inside the lagoon, litoral currents outside of the lagoon, oceanographic conditions (for instance upwelling) in the zone adjacent to the mouth, and turbulence. Water density in the head is lower than in the mouth and is controlled mostly by temperature.

No tributaries reach the wetland from their origins except during or after heavy rains. Both winter storms (from December to April) and tropical storms (from August to September) can unload in one day as much water as in one year. Therefore, in some events the site can receive considerable amounts of water that provoke sudden changes in salinity and load of suspended particles in the water column with its associated effects (water transparency, pH changes, temperature, nutrients, etc.).

Soils of the western coastal plain, from Colonet to Campo Viejo, are limited to intensive agriculture due to chemical phases of salinity and soda.

According to the soil chart published in Atlas Nacional del Medio Físico, in Bahía San Quintín there are three types of soil: Solonchak unit (Z) (Subunits: Gleyco (Zg), Molico (Zm), Ortico (Zo) Takyrico (Zt). The Solonchank present a high salt content in some parts or all of the soil. Its typical vegetation is grasslands or halophytas and it is less susceptible to erosion.

Andosol unit (T) Subunits: Humico (Th), Molico (Tm}, Ortico(To), Vitrico (Tv). The Andosol is formed by volcanic ashes. It has a black color surface and it is very susceptible to erosion.

Xerosol unit (X) Subunits: Calcico (Xk), Gypsico (Mg), Haplico (Xh) Luvico. The xerosol has a light color surface and is poor in organic matter. Its vegetation is usually grasslands and shrubs. Its susceptibility to erosion is low.

Subunits include: Calcico (Xk), Gypsico (Mg), Haplico (Xh) Luvico.

Habitat

The dominantly shallow, mud flat character of Bahía San Quintín provides for its dominant vegetation characteristics wich are of two kinds: a marine flora consisting of extensive beds of eelgrass Zostera marina covering many acres of mud flats only slightly submerged at low tide and a salt marsh flora of extensive development along nearly half of the low-lying margins of the bay subject to tidal flooding. Those two vegetations are contiguos, but usually separated by broader or narrower bands of barred, sandy or muddy flats exposed at low water.

Eelgrass forms broad, dense stands occupying that greater part of the muddy bottom of the bay. The best developed beds occur in the middle parts of the bay on flats. The deeper channels in the bay with depth more than four feet at low water are uniformly free of eelgrass, all other depths are less than four feet at low water, and a large part of the shallows on the shoreward sides of the eelgrass beds are exposed or nearly so at lowest low water springs Generally the channels have depths of 18 to 24 feet, with one record of 38 feet. The upper east arm of the bay seems to support only scatered patches of eelgrass The algal vegetation of the bay is incospicuos and except for a very few epiphytes on the eelgrass macroscopic benthic algae are largely confined to the rocky shore along the central peninsula between the two arms of the bay. Nevertheless several species occur in moderated abundance.

The lower flats have numerous small meandering tidal channels running through the marsh and the muddy bottoms of these at low waters shows frequent colonies of blue-green algae

Algal mats were commonly found in the marginal marsh areas lying on silt-clay in the intertidal zone.

A 1960-61 study reports 36 species of algae (Rhodophyta 23 species, Clorophyta 9 species, Phaeophyta 4 species and one blue-green algae).

A 1982 study lists 10 genus and eleven species of algae (Rhodophyta 4 species, Clorophyta 5 species, Phaeophyta 1 specie), and reports for the first time Enteromorpha clathrata, Giffordia sandriana and Cryptopleura spatulata, which raises the total number to 30 genera, 39 species and one variety.

A 1960 study on seeweeds reported 86 species of algae for the open coast of Bahía San Quintín Frequent colonies of Entophysalis deusta, E. conferta, Microcoleus chthonoplastes and Calothrix crustacea (blue-green algae) were also found

Over 95% of the marine vegetation consist of the Eelgrass Zostera marina.

Two studies in 1982 on epiphytic diatom flora living upon Zostera marina from July to December, report a total of 235 taxa in both species and varieties, (genera, species and varieties) The most abundant species were Navicula parva, Cocconeis scutellum, Cocconeis seutellum var. parva, Cocconeis dirupta y Nitzschia frustulum var. perminuta, the specie with the wider niche breadth was Cocconeis placentula var. euglypta.

The areas of tidal salt marsh are most extensive along the northern end and eastern margins of the east arm of the bay. This area consist largely of very low sand hills and flats with almost no rocky outcrops, on the other hand the central and western parts of the bay has border rough lava flows from four extinct volcanos, and salt marshes occur only in four relatively small, flat shore areas between these prominences, as in one sector in the northwestern part of the west arm. Marshes predominate the southeast and south shore of the bay proper. Lowest parts of the marshes in almost all areas consist of a band of Spartina foliosa, above the Spartina belt the dominant marsh cover consist of Salicornia virginica alone or mixtures. In a past time the western arm of the bay was flooded first and, thus, the marshes in the margins of this arm are probable greater age than those that developed along shores of the inner arm of Bahia San Quintín.

In a 1962 study Salicornia virginica was the dominant marsh vegetation (this plant covers an area approximately 2 1/2 square mile around the uppermost lobe of the east arm of the east arm of the bay alone). It can be found alone or mixtures with Batis maritima and Suaeda californica, other plants that occurs in this area are Frankenia grandiflora, Limonium californicum var mexicanum and Monanthochloe littoralis

A 1979 study found that the marsh flora were composed of only 17 phanerogams species. The lower littoral zone contains 9 species and was dominated by Spartina (90.8% & 47.0%), Salicornia virginica (34.4% &. 33.1%), and Batis (27.0% & 6.4%). The middle littoral zone contains 12 species. Salicornia virginica (86.7% & 22.7%) dominates. The upper littoral zone contains 14 species with Monanthochloe (75.1 & 45.7%) dominant and Salicornia subterminalis (46.5% & 2.7%). The transition zone is dominated by Salicornia subterminalis (38.7% & 20.5%) and Monanthochloe (42.7% & 22.0%)

A 1992 phytosociological study characterized the marshes and mangroves of Baja California by zones: The lowmarsh is occupied by two asociations dominated by perennials, Spartina foliosa and Salicornia pacifica. Middle marsh was caracterized by two asociations Salicornia pacifica and Frankenia grandifolia, highmarsh was composed by a new community frequent in disturbed habitats, the major cover were made by Mesembryanthemum crystallinum and M. nodiflorum and two asociations Jaumea carnosa and Distichlis spicata in soils with sandy texture and Monanthochloe littoralis-Salicornia subterminalis in soil with clay texture. All the asociation were present 81-100% of sampling events. Another 1994 study include one more asociation: Salicornia bigelovii.

The saliconia marsh grades rather abruptly in most areas into the arid scrub vegetation of higher ground. This narrow transition zone is occupied for the most part by three species of marsh plants not characteristic of those areas that are regularly flooded, but subject to inundation only at highest tides of winter and summer high water springs: Salicornia subterminalis, Distichlis spicata and Frankenia palmeri dawson.

The most common ecotones between marshlands and upland vegetation occur on a variable slopes in a stabilized sandy loam hills, few marshes are backed by abrupt lava flows or sand dunes. Recently disturbed dunes have spread directly into marshlands as a result of strong northwest winds. Most of the transition zones occur on relatively steep slopes, and vegetation changes are abrupt.

Another study in 1979 report the transitional flora was represented by 33 species from 28 genera and 19 families. Of these species, 12 are characteristically found in salt marsh, and 21 are normallly associated with desert and coastal uplands. The dominant species in the upland parts on the transition zone are Frankenia palmeri ( 31.7% & 19.0%), Atriplex julacea (8.8% & 2.0%), Lycium brevipes (6.2% & 2.7%).

Coastal sage scrub intermingles with chaparral on dry, gravelly, rocky, south facing slopes and becomes dominant at low elevations, this community have more open appearance, more barrel and hedgehog cacti and many shorter-lived species , the shrubs are less evergreen, rigid, and woody, with thinner, softer leaves. Many of the species are partially deciduos, dying back during drought periods. Coastal sage scrub can be found along the immediate northwest coast of the peninsula from Tijuana to El Rosario.

A 1979 study reports a 13 upland species with frequencies less than 2%, the highest were Lichens (6.9%), Mesembryanthemum nodiflorum (2.6%) and Euphorbia misera (0.7%).

In a 1991 survey founded 20 diferents species in three kinds of habitats, cinder cones, lava fields and canyons. .

Riparian systems on the pacific slopes at lower elevations are streams semi-perennial, supporting agriculture in the lower valleys and flood plains. None reach the sea from their origins except during or after heavy rains. Each riparian element exhibits individual characteristics, certain species are common to all where the ecosystem has remained relatively pristine.

The principal agricultural products are: tomato, strawberry, flowers, potato, green onion, peppers, zuchinni, lettuce, cabbage, cucumber, squash, and alfalfa, barley, oat, wheat, rye grass etc.

Bahía San Quintín shelters important breeding

populations of several species or subspecies of birds that are threatened or endangered: The Light-footed clapper rail + # population in Bahía San Quintin (500 pairs) is larger than the total population of this subspecies in all of California. The endangered California least tern + # breeds on five nesting colonies. In 1991, more than 100 pairs nested in three of these colonies (67 in Punta Azufre, 30 in Laguna Figueroa, and 9 in Marisma La Salina). Belding´s Savannah Sparrow + # is a common resident breeding bird in the area.

A 1991 survey documented 334 breeding snowy plovers + # using the site (236 in Laguna Figueroa and 98 in Bahía San Quintín). San Quintin Bay is the only place where there has been recent detection of the black rail on the Pacific Coast of Baja California (2-3 individuals in 1991 in Bahía San Quintín, and one specimen taken at Bocana de Santo Domingo in 1925).

The volcanic field west of San Quintín, at the base of the wetland seems to have the highest density of Polioptila californica atwoodi (a nova subspecies of California gnatcatcher + #, which ranges along the coastal plain, from near the northern international border to Arroyo El Rosario).

It is the wintering site for 30-50% of the total population Black brant that winter in Mexico. In 1992 a ground survey documented 31,925 migratory shorebirds for this wetland. Of these, 85.5% were in Bahía San Quintín, 3.6% in nearby salt ponds, and 10.9% at Laguna Figueroa. Western sandpiper in Laguna Figueroa and dunlins in Bahía San Quintín were the most abundant species. It is one of the most important places along the migratory route of the Pacific Flyway for waterfowl, shorebirds, and song birds. It is the wintering area for raptors such as: peregrine falcon + #, burrowing owl + #, and short-eared owl + #, the first of which is endangered and the others are threatened.

Other endemic subspecies to the Mediterranean region of Alta and Baja California that occur in the transition zone and upland desert scrub of the site are, Callipepla californica californica, Eremophila alpestris actia, Aimophila ruficeps lambi, Melospiza melodia cooperi, Pipilo fuscus senicula, Lanius ludovicianus grinnelli, Agelaius tricolor, Geothlypis trichas, Toxostoma cinererum, Campylorhynchus brunneicapillus bryanti, Thryomanes bewickii chorianturus, and Chamaea fasciata canicauda.

Laguna Figueroa is the only nesting site for the Caspian tern (10 pairs) in the state of Baja California. The only two nesting colonies of Forster's Tern in the Mexican Pacific are found in the site (15 pairs in Laguna Figueroa and 15 in La Pinta Pond during 1990). Laguna Figueroa was the only location with the declining mountain plover (148 individuals).

The other two studies sampled fishes from Bahia de San Quintín and the adjacent open coast. One from April 1992 to September 1995 and another during 1994 and March, August and September 1995. The first one recorded 64 species in Bahía de San Quintín and 67 species in the adjacent open coast. The other study reported a total of 90 species, nine of wich were elasmobranchs. 69 species were collected from Bahía de San Quintín and 71 species on the coast. The most abundant species founded in both studies were for Bahía de San Quintín Bay pipefish Syngnathus leptorhynchus (23.7%) , Shiner perch Cymatogaster aggregata (14.5%) and Topsmelt Atherinops affinis (10%). In the adjacent open coast were the white croacker Genyonemus lineatus (20.1%) and Northern anchovy Engraulix mordax (12.6%). In Bahía de San Quintín the endemic species, the clinid Paraclinus walkeri was collected. The gear used in boths studies included beamtrawl, otter trawl, beach seine, gillnet, hook and line.

In a 1995 study reports first freshwater record of Pacific lamprey (Lampetra tridentata) in a lagoon near to the mouth of Río Santo Domingo.

Also reports 34 species in 31 genus of mollusca. The most abundant were Acteocina carinata, Tellina buttoni (=T. modesta) and Tellina buttoni, another common mollusk were Modiolus sp. and Solen rosaceus.

A quantitative study of benthic polychaetous presented a 48 species, six of them (Prionospio mamgreni, Exogone verugera, Cossura candida, Capitia ambiseta, Scoloplos acmeceps and Fabricia limnicola) where dominant species at the bay. One new specie Megalomma pigmentum was found widely distributed in the bay.

Marine isopod fauna were constitute by 15 species, four of them (Dynamenopsis dianae, Cirolana diminuta, Excorollana kathyae and Gnathia steveni) were new species.

A 56 species of amphipods were reported, the most abundant were Ampelisca compressa, Ericthonius brasiliensis , Rudilemboides stenopropodus, Acuminodeutopus heteruropus and Hyale nigra (=frequens).

A new specie of trematoda (Parahemiurus noblei) was described from of stomach of the Pacific sardine.

During a 1992-1994 study report a 19 species of amphipods in Zostera marina Gammaridea were the predominat family.

Two studies in 1981-1982. One report eight species from five families of polychaetes previously not reported they were Phylo felix, Aricidea suecica, Prionospio heterobranchia, sub. newportensis, Prionospio cirrifera, Pseudopolydora kempi, Magelona pitelkai, Notostamus (Clistomastus) tenuis and Mediomastus californiensis. Other study reports a 39 species in 21 families of polychaetes, five species were the dominants Exogone occidentalis, Pseudopolydora kempi, Scoloplos acmeceps, Prionospio heterobranchia and Neanthes arenaceodentata).

A 1987 study report a new record of the oligochate Tectidrilus diversus. In 1992 study shows a total of 677 polychaetes (17 families, 28 genera and 32 species) were recognized. Sixteen species and four genera were recorded for the first time in the area. The most abundant species were Scoletoma tetraura (100 organisms), Brada villosa(75), Cossura candida (73), Neanthes acuminata(72), Pionosyllis sp.(70), Notostamus sp.(49), Exogone lourei (34), Prionospio heterobranchia (34), Chaetozone sp.(28), and Exogone dispar (15).Díaz-Castañeda and Rodriguez-Villanueva 1998.

Forty-seven endemic species and subspecies have been described in the Mediterranean region of Baja California, (1 amphibian, 13 reptiles, and 33 mammals) although the majority occur on islands or occupy a large area within a continuous distribution. One species and six subspecies range only on the southern coastal plain—that is, between Arroyo San Telmo and Arroyo El Rosario: San Quintin kangaroo rat (Dipodomys gravipes) Baja California rattlesnake (Crotalus enyo furvus), Chaetodipus arenarius helleri , kangaroo rat (Dipodomys merriami quintinensis), long-tailed harvest mouse (Reithrodontomys megalotis peninsulae), Meadow mouse (Microtus californicus aequivocus), and Wood rat (Neotoma lepida egressa). The Baja California legless lizard Aniella geronomensis , Microtus californicus aequivocus, and Dipodomys gravipes have all become nearly globally extinct.

The combined effects of water table lowering and salt intrusion have led to the abandonment and/or replacement of a large fraction of the well in the region. In 1994, 763 wells were inventoried in the San Quintín and parts of San Simon watersheds of these, 327 were active an 436 inactive or destroyed.