5:15 PM - 6:30 PM
[MIS11-P05] Mobilization and accumulation of phosphorus within the soil in a forested watershed
Keywords:Yato , ecosystem , phosphate, living things
[Introduction]
Forested watersheds in Japan include a terrain called "Yato", which consists of slopes and a relatively wide valley. The valley has humid conditions and usually provides habitats for many biological species including amphibian, fishes, fireflies (Lampyridae) and shellfish. Despite of a number of biological studies for these species, little knowledge is available for biogeochemical ground to survive these living things in this ecosystem. Thus, the present study aims to clarify the nutritional mechanisms to support these living organisms, with a special focus on the biogeochemical behavior of phosphorus in a “Yato” wetlands.
[Methods and Materials]
In a forested watershed located in Ome City, Tokyo, covering the slope and downstream wetlands, soil pore water and soil were collected in different depths. Fe2+ concentration and PO43- concentration were measured for soil pore water. In addition, phosphorus (P-HCl, P-inorg, P-org) concentration, iron concentration (P-HCl), ignition loss and water content were measured for soils. Total phosphorus (P-HCl), inorganic phosphorus (P-inorg) and organic phosphorus (P-org) concentration were measured for the phosphorus extracted with HCl after ignition in a muffle furnace, the phosphorus extracted with HCl from air-dried soil, and the difference in concentration between the above mentioned two (P-HCl - P-inorg), respectively. Fe-HCl was analyzed for the Fe treated in the same manner as P-HCl.
[Results and Discussion]
Elevated concentrations of Fe2+ were detected in pore waters within the soil throughout the slopes to the wetlands, indicating that iron reduction could prevail even in considerably steep slopes in the watershed. Inversely, PO43- concentration remained as low as approx. 0.1 μmol/L at most sites, but was around 1.0 µmol / L at the boundary between the slope and the wetland. It appears that the behavior of PO43- was not necessarily paralleled with iron reduction.
Nevertheless, a systematic variation in P-HCl was found along the slope: P-HCl was low in the upper part of the slope, but increased slightly in the lower part, and reached the highest concentration in the wetland. It is likely that P-HCl fraction would be mobilized partially and move from the upper part to the lower part of the slope and finally accumulated in the wetland. In the wetland sites, Fe-HCl was also highest, where a large amount of deposit of iron (hydro) oxide was invariably observed. The accumulation of P-HCl fraction in wetland sites would be associated with this iron (hydro) oxide deposition, which could contribute as a source of phosphate to support living things in this ecosystem.
This study is the first to show the movement and behavior of phosphorus from the slope to the wetland in “Yato”.
Forested watersheds in Japan include a terrain called "Yato", which consists of slopes and a relatively wide valley. The valley has humid conditions and usually provides habitats for many biological species including amphibian, fishes, fireflies (Lampyridae) and shellfish. Despite of a number of biological studies for these species, little knowledge is available for biogeochemical ground to survive these living things in this ecosystem. Thus, the present study aims to clarify the nutritional mechanisms to support these living organisms, with a special focus on the biogeochemical behavior of phosphorus in a “Yato” wetlands.
[Methods and Materials]
In a forested watershed located in Ome City, Tokyo, covering the slope and downstream wetlands, soil pore water and soil were collected in different depths. Fe2+ concentration and PO43- concentration were measured for soil pore water. In addition, phosphorus (P-HCl, P-inorg, P-org) concentration, iron concentration (P-HCl), ignition loss and water content were measured for soils. Total phosphorus (P-HCl), inorganic phosphorus (P-inorg) and organic phosphorus (P-org) concentration were measured for the phosphorus extracted with HCl after ignition in a muffle furnace, the phosphorus extracted with HCl from air-dried soil, and the difference in concentration between the above mentioned two (P-HCl - P-inorg), respectively. Fe-HCl was analyzed for the Fe treated in the same manner as P-HCl.
[Results and Discussion]
Elevated concentrations of Fe2+ were detected in pore waters within the soil throughout the slopes to the wetlands, indicating that iron reduction could prevail even in considerably steep slopes in the watershed. Inversely, PO43- concentration remained as low as approx. 0.1 μmol/L at most sites, but was around 1.0 µmol / L at the boundary between the slope and the wetland. It appears that the behavior of PO43- was not necessarily paralleled with iron reduction.
Nevertheless, a systematic variation in P-HCl was found along the slope: P-HCl was low in the upper part of the slope, but increased slightly in the lower part, and reached the highest concentration in the wetland. It is likely that P-HCl fraction would be mobilized partially and move from the upper part to the lower part of the slope and finally accumulated in the wetland. In the wetland sites, Fe-HCl was also highest, where a large amount of deposit of iron (hydro) oxide was invariably observed. The accumulation of P-HCl fraction in wetland sites would be associated with this iron (hydro) oxide deposition, which could contribute as a source of phosphate to support living things in this ecosystem.
This study is the first to show the movement and behavior of phosphorus from the slope to the wetland in “Yato”.