Changes in sedimentation rates and phosphorus accumulation in shallow Japanese lakes during 30 years

Sediment-water exchange of phosphorus strongly influences lake biogeochemical processes and ecosystems, especially in shallow lakes ( e.g., WETZEL 2001 ). In Lake Sebygaard, a shallow Danish lake, the net release of total phosphorus (TP) was calculated by comparisons of the vertical pro files of TP in sediments of different cores taken in different years, and influence of interna) phosphorus loads on lake water could last for more than 30 years, despite reduction of externa) loads (S0NDERGAARD et al. 1999). Phosphorus is deposited with sedimentation of particulate matter (FUKUSHIMA et al. 1987); thus, calculation of sedimentation rates and investigation of changes in vertical profiles of TP contents in sediments during severa) decades are important for determining the phosphorus balance in a lake. In this study, we analyzed the changes in sedimentation rates and TP contents in sediment over the 1ast 30 years in Lakes Kasumigaura and Suwa, shallow eutrophic 1akes in Japan. Based on these analyses, we compared TP accumulation rates estimated by: ( 1) net 1oads; (2) difference in vertical profiles ofTP content; and (3) mass sedimentation rates multiplied by TP contents.