Phosphorus Sorption Characteristics of Acid Sulfate Soils of Thailand.

The study of P-sorption by soils has practical interest but little is known on the P-sorption characteristics of acid sulfate soils of Thailand, particularly under reduced soil conditions. The effects of pH, redox potential, and various forms of Fe, Al, and Mn on P-sorption of the actual acid sulfate soils (Sulfic Tropaquept) and the para-acid sulfate soil (Typic Tropaquept) were studied in laboratory microcosms. Soil suspensions with a soil to 0.01 M CaCl\sb2 solution ratio of 1:7 were incubated under various pH and redox potential conditions. After the incubation period, the soil suspensions were equilibrated with KH\sb2PO\sb4 ranging from 0 to 500 mg P kg\sp{-1} soil. Some sets of soil suspensions were extracted by 1 N NH\sb4OAc (pH 4.0) and sodium-citrate dithionite solution (20%), intended to remove Fe, Al, and probably Mn in the forms of exchangeable and free oxides, before P addition. Three sorption equations were used to describe the P-sorption data. The classical Langmuir equation provided the best fit of the P-sorption data. More native insoluble P was released under reduced than oxidized conditions. Para-acid sulfate soil released more native insoluble P than did actual acid sulfate soils under both conditions. Para-acid sulfate soil also sorbed less added P than did actual acid sulfate soils. The P-sorption of both actual and para-acid sulfate soils was significantly affected by pH, redox potential, the extracted treatment before P addition, and their interactions. The P-sorption increased significantly with increasing pH and decreasing redox potential. Treating soils with NH\sb4OAc and sodium-citrate dithionite solutions reduced P-sorption, and decreased the differences in P-sorption due to the effects of pH and redox potential. The treatments did not remove the difference in P-sorption between the actual and para-acid sulfate soils. Closely significant correlation between P-sorption parameters and iron-oxides indicated the primary role of iron-oxides in P-sorption of the acid sulfate soils of Thailand. Aluminum-oxides seemed to play a secondary role in P-sorption of these soils. Manganese also showed a significant effect on P-sorption

Sulfur Chemistry of Louisiana Tidal Marsh Soils.

The amounts and profile distribution of various sulfur forms in Louisiana coastal marshes were investigated to understand sulfur cycling as related to the origin and type of tidal wetland marshes. Sampling was conducted quarterly from a Panicum hemitomon freshwater marsh, a Spartina patens brackish marsh, and a Spartina alterniflora salt marsh in Barataria Basin, Louisiana. Soil samples were fractionated into acid-volatile sulfides (AVS), elemental sulfur, HCl-soluble sulfur, pyrite sulfur, ester-sulfate sulfur, carbon-bonded sulfur, and total sulfur. Seasonal changes showed a greater effect on the distribution of S fractions in brackish and salt marsh than in the freshwater marsh. Season appeared to have a pronounced effect on the distribution of acid-volatile sulfides, elemental sulfur, and pyrite sulfur. The profile distribution of acid-volatile sulfides and elemental sulfur in all marshes was similar. These sulfur forms showed the greatest abundance in the oxidized zone ($\u3c$20 cm) during spring, summer, and fall. Marsh soil oxidation processes occurring during the plant growing season and a falling water level over the marsh surface resulted in a low pyrite sulfur concentration in the surface. The maximum concentration of pyrite sulfur was observed below 20 cm in all marsh types and its concentration was relatively high during winter. The presence of HCl-soluble sulfur was contributed largely from pore water sulfate, which was greater in salt marsh than in brackish and freshwater marshes, respectively. Organic sulfur, in the forms of ester-sulfate sulfur and carbon-bonded sulfur, was the major contributor to the total sulfur pool in all marsh types. Carbon-bonded sulfur was generally 2 to 3 times more abundant than ester-sulfate sulfur with less seasonal variation. Sulfur concentration (volume basis) and sulfur accumulation rates increased from freshwater marsh to salt marsh. Reduced sulfur species removed by marsh accretion or sedimentation process are likely significant in marsh energy flow. Plant activity, tidal fluctuation, and distance along a salinity gradient from the Louisiana coast seemed to have a strong influence on the distribution of sulfur

Distribution of organic and reduced sulfur forms in marsh soils of coastal Louisiana

Soil samples from a Louisiana Barataria Basin brackish marshes were fractionated into acid-volatile sulfides (AVS), HCl-soluble sulfur, elemental sulfur, pyrite sulfur, ester-sulfate sulfur, and carbon-bonded sulfur. Inorganic sulfur composed 13% of total sulfur in brackish marsh soil with HCl-soluble sulfur representing 63–92% of the inorganic sulfur fraction. AVS represented less than 1% of the total sulfur pool. Pyrite sulfur and elemental sulfur together accounted for 8–33% of the inorganic sulfur pool. Organic sulfur, in the forms of ester-sulfate sulfur and carbon-bonded sulfur, was the most dominant pool representing the majority of total sulfur in brackish marsh. Results were compared to values reported for fresh and salt marshes. Reported inorganic sulfur fractions were greater in adjacent marshes, constituting 24% of total sulfur in salt marsh, and 22% in freshwater marshes. Along a salinity gradient, HCl-soluble sulfur represented 78–86% of the inorganic sulfur fraction in fresh, brackish, and salt marsh. Organic sulfur in the forms of ester-sulfate sulfur and carbon-bonded sulfur was the major constituent (76–87%) of total sulfur in all marshes. Reduced sulfur species, except elemental sulfur, increased seaward along the salinity gradient. Accumulation of reduced sulfur forms through sedimentation processes was significant in marsh energy flow in fresh, brackish and salt marshes

Spatiotemporal Distribution Characteristics of Soil Organic Carbon in Newborn Coastal Wetlands of the Yellow River Delta Estuary

The distribution and seasonal variation of soil organic carbon (SOC) in newborn coastal wetland of the Yellow River Delta (YRD) estuary at eastern China were studied based on monitoring data in 2009 at two transects from the bank of the Yellow River to the seaside. The results showed that SOC contents of 0-60cm soil layer in transects ranged from 0.46 to 10.15gkg(-1) and average values of soil profiles ranged from 2.15 to 5.00gkg(-1). The SOC contents tended to increase from the river flood land to the salt beach, which could be accounted for the organic matters including large algae, the bodies and excretion of marine animals due to the feedback of tides. The significant difference of SOC contents at different vegetation communities was observed, while the difference of SOC in soil profiles was not obvious. The SOC contents in 0-30cm soil layers decreased with plant growth period, while in 40-60cm soil layers were relatively stable. The mean soil organic carbon density was 3.05kgCm(-2) in study region, which was much lower than that reported in other ecosystems, and its spatiotemporal variations were consistent with that of SOC content. Further analysis revealed that SOC was positively correlated with total nitrogen and clay contents. Our findings indicated that the newborn coastal wetland in the YRD should be a potential sink of SOC.The distribution and seasonal variation of soil organic carbon (SOC) in newborn coastal wetland of the Yellow River Delta (YRD) estuary at eastern China were studied based on monitoring data in 2009 at two transects from the bank of the Yellow River to the seaside. The results showed that SOC contents of 0-60cm soil layer in transects ranged from 0.46 to 10.15gkg(-1) and average values of soil profiles ranged from 2.15 to 5.00gkg(-1). The SOC contents tended to increase from the river flood land to the salt beach, which could be accounted for the organic matters including large algae, the bodies and excretion of marine animals due to the feedback of tides. The significant difference of SOC contents at different vegetation communities was observed, while the difference of SOC in soil profiles was not obvious. The SOC contents in 0-30cm soil layers decreased with plant growth period, while in 40-60cm soil layers were relatively stable. The mean soil organic carbon density was 3.05kgCm(-2) in study region, which was much lower than that reported in other ecosystems, and its spatiotemporal variations were consistent with that of SOC content. Further analysis revealed that SOC was positively correlated with total nitrogen and clay contents. Our findings indicated that the newborn coastal wetland in the YRD should be a potential sink of SOC