Pre-Mining Pattern of Soils on Nauru, Central Pacific

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Pre-Mining Pattern of Soils on Nauru, Central Pacifific

The environment of Nauru, a raised atoll located in the central Pacific Ocean (0° 32′ S, 166° 56′ W), was

devastated by mining of phosphate “rock” during the twentieth century. Some 100 million tonnes of

phosphate material has been removed, leaving more than 80% of the island as a dolomite

pinnacle–dominated karrenfeld. Based on fieldwork examining sites unmined at that time, laboratory

studies on undisturbed profiles, aerial photographs, and old mining maps, a picture of what the soil

pattern on Nauru was before mining has been developed. Four major soil associations were identified: the

coastal fringe carbonate dominated soils set on a recent fringing reef; deep and relatively deep

phosphate-dominated soils free of substantial influence from the underlying dolomite pinnacles occurring

on the NE, NW, SE, and SW sectors of the uplifted section of the island (known locally as “Topside”); a

complex set of soils found on Topside and on the scarp where the pinnacle influence is important but

containing some deep soils where phosphate material accumulated between the pinnacles; and a

complex set of soils in low-lying areas around the old lagoon at Buada. Distribution of soils is discussed

and physical, chemical, and mineralogical properties of the soils are presented. Soils were basically AC

profiles, with coarse textures, free drainage, and limited moistureretention capacities. Organic matter

accumulated to various depths from about 5 to 50 cm. Soil pH was generally above 6, cation exchange

capacities were closely aligned to organic matter contents, but trace element deficiencies would have

been common. Cadmium concentrations were relatively high in Nauru soils. The soils are likely to have

been of limited fertility, with moisture being a major limitation in many years. Classification of the soils

indicated a dominance of Ustropepts and Ustolls, with smaller areas of Ustipsamments and Ustorthents,

and very small areas of soils showing aquic features. The postmining situation is also discussed; only

very limited areas of three of the original soil associations remain (the relatively deep profiles free of

pinnacle influence have completely disappeared). Limitations to rehabilitation are also briefly reviewed.