Phosphatase and microbial activity with biochemical indicators in semi-permafrost active layer sediments over the past 10,000 years

Core samples of boreal terrestrial sediments from depths of 0–300 cm at Rikubetsu, Hokkaido, Japan were analyzed for alkaline and acid phosphatase enzymatic activities. Enzymatic activities of alkaline phosphatase (ALP) and acid phosphatase (ACP) were greatest at the surface and decreased with depth; ALP and ACP activities were 25.5 and 22.0 nmol min⁻¹ g⁻¹, respectively, within the top 5 cm. These biological indicators were compared with measurements of microbial cell density and chemical indicators, including total organic C (TOC) and total hydrolyzed amino acids (THAA). The product–moment correlation coefficients (r) for ALP and ACP versus microbial cell density were 0.949 and 0.810, respectively. The coefficients for THAA and TOC versus ALP were 0.997 and 0.995, respectively. Vertical distributions of enzymatic activity are highly consistent with the observed microbial biomass profile and diagenetic organic matter in the sediment. However, the vertical profile of PO₄ concentration shows a negative correlation coefficient for ALP and ACP of −0.937 and −0.855, respectively. Consequently, ALP and ACP were shown to be useful biomarkers of microbial activities in the terrestrial sediment over the past 10 ka at Rikubetsu, Hokkaido, Japan.