Bottom Of Lagoon Research Articles

Fish stock assessment of the northern New Caledonian lagoons:2 – Stocks of lagoon bottom and reef-associated fishes

Fish stocks found on lagoon bottoms and near reefs are characterized by a high diversity and heterogeneous habitat which make stock estimation difficult. In particular, it is necessary to combine several methods in order to evaluate the major components of these stocks. The present study aimed at estimating reef fish stocks in the Northern Province of New Caledonia, a region where they represent a major target for the local fishermen. These estimates were based on experimental fishing with handlines and bottom longlines. Handlines were used to assess the stocks near reefs, and longlines for those in areas away from reefs and on lagoon soft bottoms. Handline stations (363) were sampled in three different regions (west, north and east lagoons) and three biotopes (nearshore, middle lagoon and barrier reef). A total of 104 species were caught, the major families being Lethrinidae, Lutjanidae and Serranidae. Species composition and catch per unit of effort (CPUE) varied among regions and biotopes. In particular, the north zone showed characteristics of an unexploited area with very high yields. An increase in CPUE and fish size from the coast towards the barrier reef and with increasing depth was observed in all regions. Correlations between CPUE from handlines and the numerical density and biomass estimates from underwater visual censuses (UVC) performed on nearby reefs were significant. A total of 206 longline stations were sampled in the west and east regions. A total of 80 species were caught, the major families being the same as those caught in stations with handlines with the addition of Carangidae. The CPUE of longlines was significantly correlated with numerical density and biomass estimates made by UVC along the longlines. Stock estimates based on the correlations between CPUE from handlines or longlines and UVC estimates indicate that 90 % of the lagoon stock were found on soft bottoms and near reefs. Reefs, despite biomasses that were five times larger than soft-bottom and near-reef areas, made only a small contribution to total stock. The ratio between density and CPUE was highest for the lowest densities, thus indicating that fishing efficiency increased with density. Comparison of handline catch performed around reefs and UVC data from nearby reefs suggests that there were strong relationships between the fish assemblages of these two biotopes.

The diet and digestive energetics of an Australian short-necked turtle, Emydura macquarii

We described the diet of Emydura macquarii, an omnivorous turtle from south-eastern Australia, compared its digestive performance on diets of fish or plants at two temperatures, and related how both diet and temperature affect its food selection in nature. Filamentous algae constituted 61% of the stomach content of E. macquarii. The turtles rarely fed on motile prey, but selected carrion from the lagoon bottom and terrestrial insects (Diptera, Hymenoptera and Coleoptera) trapped on the surface of the water. Digestive efficiency of E. macquarii was affected little by body temperature, in contrast to consumption rates and rates of passage which were strongly influenced by both temperature and diet. In combination, these responses resulted in a slower rate of digestion at 20°C than at 30°C. Digestive efficiency of E. macquarii on a herbivorous diet at 30°C (49%) was about half that of turtles on a carnivorous diet (91%), but they had longer transit times (118 h on the plant diet versus 70 h). Lower consumption rates and longer mean retention times in turtles fed plants compared those fed fish relate to slower digestive processing of the plant. Rapid processing and higher consumption rates of fish by E. macquarii resulted in higher energy gains compared to turtles consuming plants (almost 100 times more energy at 30°C). The laboratory results suggest that fish carrion and aquatic and terrestrial invertebrates are probably essential dietary items of E. macquarii in the wild, because its metabolic requirements cannot be met from aquatic macrophytes alone.

Predation by diving ducks on the biofouling messel Musculista senhousia in a eutrophic estuarine lagoon

The effect of predation by diving ducks (Aythya fuhgula, Aythya fenna, and Aythya marila) on filter-feeding bivalves was evaluated in eutrophic estuanne lagoons, Lakes Nakaumi and Shinji, in Japan. Bivalves take up nutrients in the form of phytoplankton and detritus. Winter-migrating diving ducks feed on these bivalves during the cold season. In Lake Nakaumi, diving ducks chiefly consumed the biofouling mussel Musculista senhousia. The biomass of M. senhousia decreased markedly at most sampling points during duck wintering, averaging 1126 g m-' (wet weight) at 4 2 sampling points in November 1996 and 24 g m-' in March 1997 The amount of nitrogen in M. senhousia eaten by ducks during winter was estimated at 52 t and phosphorus at 3.8 t . In the absence of ducks, M. senhous~a death in summer would add equivalent nitrogen and phosphorus loads to the lagoon. The decomposition of M. senhousia in summer when water mixing is weak would also accelerate oxygen depletion at the lagoon bottom. Mussel predation by wintering ducks would therefore decrease unfavorable effects of biofouling mussel decomposition in summer when nuisance phytoplankton blooms and anoxia occur easily.

Heavy Metal Pollution in Central Venice Lagoon Bottom Sediments: Evaluation of the Metal Bioavailability by Geochemical Speciation Procedure

Bottom sediments of the central area of the Venice Lagoon (Italy) and some lagoon canals, chosen as an anaerobic reference environment, were analyzed by a sequential extraction procedure for Cr, Cu, Ni, Pb, Zn, Mn, and Fe. Bio-Available Phases (BAPs) and Non-Bio-Available Phases (NBAPs) have been determined in the Malamocco-Marghera Canal, to define the significant level of heavy metal contamination of the sediment. Relationships among metal distributions with Fe/Mn oxides/hydroxides and sulfides were determined in both environments, using statistical methods. The central lagoon area shows low pollution and a balanced influence of all the sediment components in the metal complexing processes, mostly due to the manganese and iron matrices. The inner canals are very polluted with heavy metals strongly bonded to H2S that form highly insoluble compounds, as demostrated through the correlation analysis. The authors suggest different procedures for lagoon restoration due to the different sediment behaviours, i.e., to avoid sediment turbation by dredging or by artificial bottom aeration which could result in an accelerated formation of more soluble oxygenated metal compounds making the toxic metals readily available to the aquatic environment. The sedimentological study of the central lagoon given here evidenced the correlation between grain size and mineralogical composition and heavy metal concentrations in bottom sediments. While Fe, Mn, Zn and Cu show a good correlation with the percentages of mud (grain size < 62 micron) Cr, Cd, Pb and Ni are quite independent from the grain size of the sediment.

Metal pollution loading, Manzalah lagoon, Nile delta, Egypt: Implications for aquaculture

High cultural enrichment factors are found for Hg (13×), Pb (22.1×), and other potentially toxic metals (e.g., Sn, Zn, Cu, Ag) in the upper 20 cm of sediment cores from the southeastern Ginka subbasin of Manzalah lagoon, Nile delta, Egypt. Cores from other areas of the lagoon show little metal loading. Metal loading followed the closure of the Aswan High Dam, the availability of abundant cheap electricity, and the development of major power-based industries. Industrial wastes containing potentially toxic metals are dumped into the Nile delta drain system. The load carried by Bahr El-Baqar drain discharges into the Ginka subbasin, which acts as a sink and results in metal loading of the sediment deposited there. Further development of aquaculture in this subbasin, of food-stuff agriculture on recently reclaimed lagoon bottom, or where irrigation waters come from Bahr El-Baqar drain or its discharge should be halted or strictly limited until potentially toxic metals in the drain waters and sediment are removed and polluted input drastically reduced. This environmental assessment of heavy metals in aquaculture or agriculture development should extend to other waterbodies in the northern Nile delta, particularly Idku lagoon and lake Mariut, where industrial metal-bearing wastes discharge into the waterbodies.

Investigations of the Benthos of Mangrove Coastal Lagoons in Southern Cuba

AbstractBenthic studies were undertaken in two mangrove‐lagoons on the south coast of Cuba. Both lagoons are approximately 30–50 cm deep and the tidal range is 15–20 cm. There is little influx of fresh water, and the lagoons are normally euhaline. Most of the lagoon bottom is not colonized by plants, although filamentous algae (Cladophora and Enteromorpha spp.) and Thalassia testudium grow in a few places. Meiobenthic organisms account for 92% of the invertebrates in the benthic zone of the lagoon. The five most common taxa (Nematoda, Copepoda, Tanaidacea, Oligochaeta, Polychaeta) account for 88–94% of the total number of individuals in Tolete Lagoon and in Basto Lagoon the five most common taxa (Nematoda, Copepoda, Ostracoda, Amphipoda, Polychaeta) account for 97–98%. Biomasses were 26.6 g/m2 in Tolete and 20.2 g/m2 in Basto Lagoon. The dominant taxon on the roots of Rhizophora mangle is Crustacea (Balanus eburneus, B. recurvus and Corophium insidiosum), accounting for over 60% of the total number of individuals. They are followed by molluscs (Crassostrea rhizophora) and the polychaetes (serpulids).

Stratification in a small lagoon in the Great Barrier Reef

Temperatures were measured in a small lagoon in the windward reef flat of Davies Reef in the central Great Barrier Reef and examined on three time scales to gain three perspectives on thermal stratification and the trapping of bottom water. Profiling for stratification and dye revealed layering where bottom water was trapped and released by the successive capping and uncapping of the lagoon by a diurnal thermocline. A 1-month monitoring array revealed a solar synchronization, with the temperature of reef-flat water exceeding temperatures of lagoon water by up to 1 5�C within 1 h of midday, and lagoon stratification lagging this by 1 h. There was also a lunar synchronization with mixing proceeding during nocturnal rising tides. Lagoon surface and bottom temperatures were also monitored for 11 months. The amplitude of the diurnal stratification showed no coherence either with the amplitude of the tide (marked spring-neap tides) or with scalar wind stress. The low frequency amplitude of the diurnal oscillation was coherent with the longshore wind vector at periods near 3 6 days and in a band approximately from 10 to 40 days. Daily stratification increased when winds were poleward and decreased when winds were equatonvard. Events of flushing were separated on average by 9 h, but the most frequently observed separation was 5 h and only 10% of separations exceeded 18 h during the 11 months.

ON THE LANDSCAPE OF “SHIMABATA” (ISLAND-LIKE UPLAND FIELDS) IN THE KUJUKURI COASTAL PLAIN—WITH SPECIAL REFERENCE TO THE RECLAIMED LAND OF CHINKAI LAGOON—

The Kujukuri Coastal Plain located in Chiba Prefecture is a narrow elevated coastal plain stretching approximately 60 kilometers in length and 7_??_9 kilometers in width. Topography of this plain consists of sandy beach ridges (or sand banks) running in parallel to the coastline and marshy lowlands lying between these parallel ridges. Until recent it was said that, largely in conformity with these topographical features, the sandy beach ridges were used for settlements, upland fields, etc., while the marshy lowlands were used for paddy cultivation, creating such a characteristic land use of this coastal plain. On the basis of 1 : 10, 000_??_1: 3, 000 large-scale maps, the present author carried out an investigation into the land use of this plain, and came to the conclusion that this view hitherto held as general knowledge was erroneous. In other words, the view that the sandy beach ridges are used by upland fields or that there are no paddy fields there is a fallacy. As a matter of fact, most of the sandy beach ridges include many island-like upland fields or “shimabata”, therefore even here, there are many paddy fields. Stating it in other terms, numerous paddy fields are found not only in the marshy lowlands but also in the sandy beach ridges. As clearly presented by the author's survey on the distribution of “shimabata” in Japan (see Geographical Review of Japan, Vol. 41, No. 4, 1968), the Kujukuri Coastal Plain is an area noted for the distribution of “shimabata” landscape. The main purpose of the present paper is to clarify the reasons for the large-scale development of this type of land-scape. Lagoons in the marshy lowlands and a few irrigation reservoirs built in dissected valleys of the diluvial uplands bordering the western boundary of the plain have long been used for paddy cultivation. However, paddy fields that could be irrigated by these sources amount to only a small proportion of the total paddy fields in the marshy lowlands, and so the majority were rainfed ones. Even if the sandy beach ridges were only slightly higher than the marshy lowlands by 50 centimeters or so, it was impossible to make any paddy fields unless the elevation of the ground surface was lowered. In order to expand paddy fields into the sandy beach ridges, the farmers dug the lower parts of the ridges. Cultivation was practiced on piled up spots, while in the dug places, paddy fields were realized. The result was the island-like upland field landscape where upland fields and paddy fields are found alternately. Groundwater table is generally high in the Kujukuri Coastal Plain, and so if rain falls at suitable intervals, rice can be grown well in rainfed paddy fields. The reclaimed land of Chinkai Lagoon is located in the northern part of the Kujukuri Coastal Plain. This reclaimed land was created in the early years of the Tokugawa Period. This is an area always suffering from shortage of irrigation water. There is a wide distribu-tion of “shimabata” on this reclaimed lands, too. Blank parts enclosed by dotted lines in Fig. 2 indicate places where “shimabata” are found. The distribution pattern corresponds to the shallow lagoon bottoms that were reclaimed. Two sample areas were taken from the distribution areas of “shimabata” in Figs. 3 and 4. The black parts are “shimabata”, while blank parts show paddy fields. A complicated pattern shown in Fig. 3 is surprising. Difference in elevation between “shimabata” and paddy fields is, in general, 30 to 40 centi-meters. Slightly higher lands (about 50 cm) in this reclaimed land, the ground water table is relatively low. In order to have it closer to the groundwater table, earth should have been dug to make paddy fields. The result is the landscape of “shimabata”.Figure. 4 shows the narrow “shimabata” made alternately with narrow paddy fields.

Shallow-Water Geology and Environments of Alacran Reef Complex, Campeche Bank, Mexico

Alacran is an oval, shallow-water platform approximately 100 square miles in extent which rises above the general surface of the continental shelf 70 miles off the Yucatan Peninsula of Mexico. The reef complex includes the long, arcuate reef which forms the windward side of the platform, a deeper and less sharply defined belt of reef growth outlining the leeward margin, and a multitude of reefs of various shapes and sizes in the enclosed lagoon. Contemporary sedimentation at Alacran is resulting in three major types of accumulations: loose sediment, rigid frames, and non-rigid frames. The loose sediment, primarily skeletal debris in the form of silt, sand, and gravel, covers inter-reef parts of the lagoon bottom. The rigid frames are built by a succession of organic overgrowths during which new colonies spread over the in situ skeletons of their predecessors. Non-rigid frames are being built on the protected side of some rigid frames where branching colonies of coral or algae are so abundant on the loose sediment surface that the individual colonies nearly touch each other, or even intermesh, although they are not cemented to one another. In terms of their roles as geologic agents, the organisms of the area can be categorized as frame builders, cementing agents, sediment contributors, frame destroyers, inhibitors of reef growth, and sediment movers. Many non-fossilizable members of the fauna and flora have considerable influence on sediment character and on rate and place of sedimentation. Lateral changes in benthonic organisms and bottom character are prominent on and around the Alacran reefs. Reef surfaces are divisible into two and sometimes three zones based on distribution of species which build rigid frames. Two other zones are based on distribution of species which build non-rigid frames. Other zones, such as one recognizing prominence of sediment-binding plants, are differentiated in lagoonal areas between reefs. All the Alacran reefs appear to be thriving, or at least holding their own in relation to the destructive forces of wave action and burrowing organisms. The outward expansion of the reefs into deeper water seems to depend primarily on some of the massive corals which attain great size but do not require a hard substrate. Such species create the foundation of reef rock on which other frame builders can establish and to which they subsequently contribute. Several environmental factors influence the morphology of individual coral colonies. Change in colony form correlated with increase in water depth is well shown by one species of branching coral, and several other species illustrate the influence of wave action, sedimentation rate, and the presence of intruding organisms on colony morphology. The reefs which are exposed to the strongest wave action differ in several respects from those in more protected areas. Some of the major frame-building coral species on less protected reefs are absent or uncommon on most lagoonal reefs. Encrusting calcareous algae contribute to windward reef frames but are inconspicuous in lagoonal reefs. Study of reef surfaces suggests that cross sections of lagoonal reefs would show less tightly knit reef frames with larger pockets of loose sediment than would be the case in windward reefs.

On the Test Dikes for Hachiro-Gata Impoldering project

Hachiro-Gata Impoldering Project is one of the greatest impoldering works which have been performed in Japan. The major part of the lagoon bottom is covered with deep and very soft clay deposits and some parts of the polder dikes are compelled to be built on these bad subsoils. Two types of test dikes, that is replacement type and sand-bed type, were built to examine the calculated results of dike design before the construction of dikes. The authors intend to present the characteristics of Hachiro-Gata Clay and some investigations observed during the construction of test dikes, including dike failure test performed on them.

DISPERSION IN SEISMIC SURFACE WAVES

A non‐mathematical summary is presented of the published theories and observations on dispersion, i.e., variation of velocity with frequency, in surface waves from earthquakes and in waterborne waves from shallow‐water explosions. Two further instances are cited in which dispersion theory has been used in analyzing seismic data. In the seismic refraction survey of Bikini Atoll, information on the first 400 feet of sediments below the lagoon bottom could not be obtained from ground wave first arrival times because shot‐detector distances were too great. Dispersion in the water waves, however, gave data on speed variations in the bottom sediments which made possible inferences on the recent geological history of the atoll. Recent systematic observations on ground roll from explosions in shot holes have shown dispersion in the surface waves which is similar in many ways to that observed in Rayleigh waves from distant earthquakes. Classical wave theory attributes Rayleigh wave dispersion to the modification of the waves by a surface layer. In the case of earthquakes, this layer is the earth’s crust. In the case of waves from shot‐holes, it is the low‐speed weathered zone. A comparison of observed ground roll dispersion with theory shows qualitative agreement, but it brings out discrepancies attributable to the fact that neither the theory for liquids nor for conventional solids applies exactly to unconsolidated near‐surface rocks. Additional experimental and theoretical study of this type of surface wave dispersion may provide useful information on the properties of the surface zone and add to our knowledge of the mechanism by which ground roll is generated in seismic shooting.

SUBMARINE GEOLOGY OF BIKINI LAGOON AS INDICATED BY DISPERSION OF WATER-BORNE EXPLOSION WAVES1

The normal-mode theory of Pekeris has been applied to the water-wave dispersion recorded from the under-water explosions set off in the 1946 seismic-refraction shooting in Bikini lagoon. The aim was to ascertain from the dispersion data the velocity of sound in the sediments down to several hundred feet below the lagoon bottom and thereby gain information about the recent sedimentary history of the lagoon. Because of the lack of short shots this information could not be obtained from the refraction results. The principal merit of the dispersion method here is that the long refraction shots supplied some information about the superficial layers. Information on the first 100 feet or so of sediments below the lagoon bottom was sought from the “high-frequency” dispersion of water waves 50 cps and higher. The data from shots along the edge of the lagoon within 1-2 miles of the reefs and islands appear to be compatible both with normal-mode predictions for a liquid bottom and with refraction indications. From these data it is concluded that the speed within 20 feet of the water bottom averages 1.05 times that in water, with a rapid increase (probably from compaction) to a speed 1.3 times that in water at a depth of about 40 feet. Shots fired somewhat farther from the edge of the lagoon give dispersion curves indicating bottom speeds (on the basis of the Pekeris theory for liquid bottoms) much higher than the refraction data allow. Shots fired in the more central portion of the lagoon give dispersion patterns to which the Pekeris theory does not appear to apply. The author attributes the discrepancy to a lateral variation in sedimentary composition between the edge and center of the lagoon, possibly a downward continuation of the surface change from sand to Halimeda debris observed by Emery on going toward the lagoon9s center. The Airy waves (high-amplitude, low-frequency waves at minimum group velocity) give information on the bottom structure to about 400 feet. In virtually all parts of the lagoon their group velocity and frequency are as predicted by the Pekeris theory for a bottom velocity of 6500 ft/sec. This agrees with the first branch of the refraction travel-time curves, which were drawn from very limited data. That the Airy waves fit the theory for shots fired near the center of the lagoon while the higher-frequency waves do not suggests that the lateral change in sediment type within the uppermost layer disappears within a depth of about 100 feet. The change comes at a depth which can only be estimated roughly as 300 feet below sea level and was detected only in the central portion of the atoll.

SUBSURFACE CONSTITUTION OF BIKINI ATOLL AS INDICATED BY A SEISMIC-REFRACTION SURVEY*

As a part of the fundamental scientific investigation carried out in connection with the atomic bomb tests of 1946, a seismic refraction survey was made by Joint Task Force One to obtain information on the subsurface structure of Bikini Atoll. Naval depth charges were fired on the lagoon bottom along four lines extending across the atoll and the resulting seismic waves were picked up by water-coupled microphones near shore. A total of 126 charges were exploded in the survey. The time-distance curves indicate the existence of three zones with different sound velocity beneath the lagoon floor. For the uppermost layer, averaging about 2500 feet thick, the speed is 7000 ft/sec. Below this is a layer ranging from approximately 5000 to 10,000 feet in thickness with a seismic velocity of 11,000 ft/sec. Underlying the latter is a zone of undetermined thickness having a speed of 17,000 ft/sec. The recent boring, 2556 feet deep, on Bikini Island appears to confirm the conclusion reached from the seismic data alone that the uppermost zone consists of diverse calcareous materials such as are encountered on the sea floor within and around atolls at shallow depths,— i.e., a few hundred feet at the most. Results of a vertical velocity survey to 1800 feet in the same hole show a continuous transition from a velocity of 7000–11,000 ft/sec. It appears probable, therefore, that no essentially different rock materials enter into the composition of the atoll down to the top of the 17,000 ft/sec zone, and that the change in velocity is due mainly to progressive compaction and cementation of the calcareous sediments. In this case the 11,000 ft/sec layer indicated by the refraction data might consist of such sediments in a state of maximum cementation or of finer calcareous material, deposited in deeper water, that might have undergone greater compaction than the overlying coarser sediments. Parts of it, or even most of it, may be dolomitized; it might possibly consist mainly of pyroclastic sediments, although this seems less likely. Only a boring can provide a positive identification. The zone with a velocity of 17,000 ft/sec appears to represent the igneous basement. Its surface has considerable relief, the highest portion being near the center of the atoll about 7000 feet below sea level. From this summit a sharp nose plunges southeastward to the atoll9s edge, the greatest observed depth being about 13,000 feet. The seismic data suggest several possible histories of Bikini Atoll, but all require relative subsidence in the thousands of feet. If the material down to the 17,000 ft/sec zone is calcareous sand, the seismic evidence calls for a minimum of 7000 feet of subsidence. If a terrace on the surface of this zone at 13,000 feet is attributed to subaerial erosion, a minimum of 13,000 feet of subsidence is then required. If, on the other hand, the intermediate zone is identified as volcanic or pelagic material, it is still necessary to assume that there was at least 2000 feet of subsidence. Thus, for Bikini at least, the seismic results tend to favor the conception, first advanced in its simplest form by Darwin, that atolls are formed by long-continued subsidence of initial noncalcareous islands or shallow banks.

The Breeding Birds of Central Lower California

By wagon road and burro trail it is an even one hundred miles from Santa Rosalia, on the Gulf of California, to the tide line of the Pacific at San Ignacio Lagoon. The intervening country is essentially a desert. The summit, which is two thousand feet high in the passes and nearly three times that altitude in the mountains, lies within ten or twelve miles of the Gulf. The two watersheds are thus of unequal length. They are also of quite distinct configuration. On the eastern side the descent to sea-level is abrupt and precipitous, checked by two rather extensive valleys. The long western slope, on the other hand, is broken by valleys, cations, and pretentious hills. It is marked with the weird formations which are characteristic of arid North America and which are here exaggerated. Angles and profiles of silhouetted hills and table-tops are unusually harsh and forbidding. There is not even the softening effect of grandeur. Over the major portion of the entire region lava has flowed and mesa, valley and mountains are covered with dull brown rocks. This lava sheet, though of varying thickness, normally does not exceed three feet in depth. In overlaying the ancient sandstone it parallels the slopes of the hills and the sides of the cations, while on the mesas, and sometimes in the valleys too, it is as level as they and often stretches away as far as the eye can see. The lava covering, in the process of cooling, has broken into fragments that rarely exceed a cubic yard in size. The edges are sharp and the lines of cleavage easily traceable. Indeed, so slightly has the deposit weathered, it seems as though but yesterday it solidified and cracked. The lava surface is not present everywhere, but it does cover four-fifths of the area we examined. Where it is absent it presumably either has been removed bty water or covered with ashes or sand. An exception is the western margin of the cross section where the ocean and lagoon bottoms have changed position in recent geological times. These are either smooth and salt-crusted or else they have been worked into sand dunes. There are several systems of dry river beds which have an important influence on the biology of this region. Even though the country be arid, beyond anything known in the United States there still is enough rainfall to provide some moisture. This water, as well as a part of that from the cloud-bursts that come once in a decade, finds its way to the sea by means of a subterranean flow. The conspicuously marked stream courses and the accompanying level valley floods are outstanding features of the landscape. The alluvial deposits are usually river sand, but they also include extensive beds of cobble stones or of relatively fertile silt. Occasionally the subterranean flow encounters bed rock formations which force the water to the surface. On the Gulf side, three miles west of Santa Agueda, there is an oasis which supplies water for Santa Rosalia and its suburbs as well as for numerous truck gardens. On the Pacific watershed, where the drainage lines are longer, we found natural surface water at San Joaquin, the Alamo, and in Jose Maria Cation. Outstandingly the most extensive of the oases is San Ignacio, where a town of a thousand people is supported. The settlement contains truck gardens and orchards in addition to a jungle of date and fan palms.