LOCATION ILACHETOMEL PW+ FM PBEstablished Series
TAXONOMIC CLASS: Euic, isohyperthermic Typic Sulfihemists
TYPICAL PEDON: Ilachetomel peat in a level area of Volcanic Mangrove Tidal Forest plant communities at an elevation of 0.5 meters (1.6 feet.) (Colors are for moist soil unless otherwise noted. All textures are apparent field textures. When described on December 16, 1979, water table due to semi-diurnal tides was at 10 centimeters (4 inches) above the soil surface. )
Oi1--0 to 20 centimeters (0 to 8 inches); black (10YR 2/1) peat, about 70 percent fiber rubbed; weak fine and medium subangular blocky structure; many very fine and fine roots and few medium roots; common very fine interstitial pores; moderate odor of sulfur; moderately acid (pH 6.0 in calcium chloride); clear smooth boundary.
Oi2--20 to 41 centimeters (8 to 16 inches); very dark grayish brown (10YR 3/2) peat, about 70 percent fiber rubbed; weak fine and medium subangular block structure; many very fine and fine roots and few medium roots; common very fine interstitial pores; slight odor of sulfur; common medium and coarse decomposing roots; moderately acid (pH 6.0 in calcium chloride); gradual smooth boundary. (combined thickness of the Oi1 and Oi2 horizons is 10 to 100 centimeters)
Oi3--41 to 81 centimeters (16 to 32 inches); very dark grayish brown (10YR 3/2) peat; about 55 percent fiber rubbed; weak fine and medium subangular blocky structure; many very fine and fine roots and few medium and common coarse roots; common very fine interstitial pores; slight odor of sulfur; common medium and coarse decomposing roots; moderately acid (pH 5.6 in calcium chloride); gradual smooth boundary.
Oi4--81 to 150 centimeters (32 to 59 inches); very dark grayish brown (10YR 3/2) mucky peat, about 42 percent fiber rubbed; weak medium and coarse subangular blocky structure; many very fine and fine roots and few medium and common coarse roots; common very fine interstitial pores; moderately acid (pH 5.8 in calcium chloride). (combined thickness of the Oi3 and Oi4 horizons is 50 to 140 centimeters)
TYPE LOCATION: Aimeliik Municipality, Babeldaob Island, Republic of Palau; about 27 meters (88 feet) W. of first land fall up channel through mangroves leading to the Dabador area in Aimeliik, then about 5 meters (16 feet) N. into mangroves; WGS 84 UTM 445780 meters E, 818773 meters N, zone 53; Lat 7 24' 25.11." N and Long 134 30' 31.22" E
RANGE IN CHARACTERISTICS:
Soil moisture:
Soil moisture regime subclass: oxyaquic
Soil moisture regime class: aquic
Seasonal pattern: Precipitation falls mostly even during the year with the exception of February to April being the driest months averaging 179 to 229 millimeters (7 to 9 inches) per month. The soils are flooded semi-diurnally with ocean salt water during periods of high tide; 30 centimeters above (12 inches) to 30 centimeters (12 inches) below the surface.
Depth to diagnostic feature: 0 inches (0 centimeters) to sulfidic materials
0 inches (0 centimeters) to aquic conditions
0 inches (0 centimeters) to fibric soil materials
Seasonal high water table: All months of the year
Depth to top: 0 to 30 centimeters (0 to 12 inches)
Oi horizon(s):
Hue: 2 or 3 moist
Value: 2 or 3 moist
Chroma: 1 or 2 moist
Texture: peat
Rubbed fiber content: 40 to 85 percent
Clay content: 0 to 15 percent
Sand content: 70 to 100 percent
Silt content: 0 to 25 percent
Fragment size and content: Rock fragments are mixed; 0 to 5 percent total rock fragments; 0 to 5 percent gravel.
Electrical conductivity: 5 to 30 mmhos/cm
Sodium adsorption ratio: 0 to 5
Reaction: pH 3.2 to 5.0
Cation exchange capacity: 75.0 to 110.0 meq/100grams
Effective cation exchange capacity: 100 to 115 meq/100grams
Organic matter content: 70.0 to 90.0 percent
COMPETING SERIES: There are no other series in this family at this time.
GEOGRAPHIC SETTING: Ilachetomel soils are in the intertidal zone of mangrove swamps, salt marshes, and tidal marshes adjacent to volcanic islands. Slope is 0 to 2 percent. These soils formed in organic deposits derived predominantly from decomposing mangrove roots and litter. Elevation is -1 to 4 meters (3.3 to 13.1 feet.) The soils are flooded semi-diurnally with ocean salt water during periods of high tide; 30 centimeters above (12 inches) to 30 centimeters (12 inches) below the surface. Areas closer to the lagoon are submerged longer than areas closer to land. The climate is tropical and moist. Because of the strong marine influence, the diurnal and annual range of temperature is limited. Rainfall averages about 3685 millimeters (145 inches) per year and ranges from approximately 2900 to 4400 mm (114 to 173 in.) The seasonal wet (May to November) and dry seasons (December to April) with the driest months (February, March, and April) averaging 178 to 229 milliliters (7 to 9 inches) per month. Rainfall is derived from convective uplift, which results in short duration rainstorms of high intensity. Rainfall is irregularly distributed geographically. These soils lie within the latitudinal zone that receives more solar radiation than it re-radiates back to space. This imbalance maintains the atmospheric temperatures in a quasi-steady state. The mean daily temperature throughout the year averages 27 C (81 F) with a mean diurnal range of about 4 C (7 F.) Relative humidity averages about 90 percent at night and 75 to 80 percent during the day.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Chia, Dechel, Mesei, Ngersuul, and Naniak series. The Chia soils are organic to 75 centimeters (30 inches) and over coralline sand. Dechel soils are very poorly drained and are stratified. Ilachetomel soils are organic and Naniak soils are mineral both with sulfidic materials, flooded semi-diurnally with seawater, and support mangrove vegetation. Mesei soils are organic soils overlying clayey alluvium. Ngersuul is a better-drained version of the Dechel series and lacks stratification.
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Very poorly drained. Negligible runoff, very high-saturated hydraulic conductivity. The soils are flooded very frequently for extremely brief periods, semi-diurnally, by high tides that fluctuate between about 30 centimeters (12 inches) above and 30 centimeters (12 inches) below the soil surface. These soils are ponded frequently for very long periods all months of the year.
USE AND VEGETATION: These soils are in Volcanic Mangrove Forest plant communities and are used for sediment catchment and some timber harvest for local use. The mangroves trap about 30% of sediments in Palau and other volcanic islands from entering their coral reefs; it is an important buffer protecting the reefs from excessive sedimentation or eutrophication. Eutrophication will lead to coral reef degradation and stimulate algae growth on corals. These algae communities vigorously strip excess nutrients from the water as they grow much faster than the corals. As the algae blooms get much larger, they trap more sediment in the reefs and ultimately causing coral bleaching. As the old algae decay, they consume the oxygen in the water; the low oxygen then will kill off fish, crabs, shrimp, and the living reef devastating tourism and fishing in these local island economies.
Mangrove forests are located adjacent to the sea and are affected by the semi-diurnal tidal cycle. The remaining areas of mangrove forest are located inland behind coastal strands, which were probably once open to the sea. Mangrove forests are generally closed-canopied with only a single to few mangrove species .The native vegetation is Rhizophora mucronata, R. apiculata, Sonneratia alba, Lumnitzera littorea, Bruguiera gymhorhize, Bruguiera sp., and Xylacarpus granatum. The moderate tree sizes and density of trees within the mangrove forest ecological type result in stands containing a relatively high biomass. The species are adapted to reproducing and surviving on the deep soils inundated with brackish seawater. Although the bottomland soils contain large quantities of organic material, the woody biomass above and below ground serves as an important reservoir of nutrients. The mangrove plant communities are efficient in cycling plant nutrients.
DISTRIBUTION AND EXTENT: MLRA 193 Volcanic Islands of Western Micronesia; Republic of Palau; Yap Islands, Federated States of Micronesia. This series is of moderate extent; about 11,000 acres in the Republic of Palau; about 3,500 acres Yap State, Federated States of Micronesia.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Babeldaob Island, Republic of Palau 1981. Local pronunciation of the word Ilachetomel is "E-lat-tum."
REMARKS: Reactions of all horizons decreased by 0.6 to 2.0 pH values after exposure to air for a period of 1 week. The color of the exposed material in each horizon changed to black (N 2/0). Pyrophosphate test color is white (10YR 8/1) for all horizons. These soils are susceptible to subsidence, adverse effects from high salt levels, and have poor engineering properties.
Diagnostic horizons and features recognized in this pedon are:
Aquic conditions - Surface to 150 centimeters (59 inches)
Fibric soil materials - Surface to 200 centimeters (79 inches)
Sulfidic material Surface to 200 centimeters (79 inches)
ADDITIONAL DATA: University of Hawaii at Manoa - College of Tropical Agriculture and Human Resources # 06-4565 to 06-4566 were used to define mineralogy, and Military Geology of Palau Islands, 1956, and Yap Islands, 1960, are used to define the series.
Taxonomic Version: Keys to Soil Taxonomy, 10th edition 2006.