Comparative Phosphorus Sorption by Marine Sediments and Agricultural Soils in a Tropical Environment

Abstract

The influence of soil phosphorus (P) sources on P sorption characteristics of marine sediments was investigated for Pearl Harbor and off shore Molokai in Hawaii. Estuary sediments were sampled in seven locations; these represented different soils and on-shore activities. The soil samples included nine major soils that contributed sediment to the Harbor and coastal sediments near the island of Molokai. Sediment and soil samples were equilibrated for 6 days in 0.01 M CaCl₂ solution and synthetic seawater containing differing amounts of P. Phosphorus sorption curves were constructed. The equilibrated solution P, with no P added, ranged from 0.01 to 0.2 mg L⁻¹; P sorption by sediments at standard solution concentration 0.2 mg L⁻¹, ranged from 0 to 230 mg kg⁻¹. Sediment P sorption corresponded closely with soil sorption characteristics. Soils contributing sediments to the west reach of Pearl Harbor are highly weathered Oxisols with high standard P sorption values while those in the southeast of the Harbor were Vertisols and Mollisols which sorb little P. The influence of source materials on sediment P sorption was also observed for off-shore sediments near Molokai. Sediments serve as both source and sink for P in Pearl Harbor and in this role can be a stabilizing influence on P concentration in the water column. Phosphorus sorption curves in conjunction with water quality data can help to understand P dynamics between sediments and the water column and help evaluate concerns about P loading to a water body. For Pearl Harbor, solution P in equilibrium with sediments from the Lochs was 0.021 mg L⁻¹; a value unlikely to produce an algal bloom. (Measured total P in the water columns (mean) was 0.060.)

Keywords:

• Key Words Sediment
• Phosphorus sorption
• Marine water quality
• Estuary
• Tropical environment

Notes

*Wahiawa soil contains (∼2%) Manganese.

*Determined in 1971–1972.