Tohru Yabe

Spatial variation of phosphorus fractions in bottom sediments and the potential contributions to eutrophication in shallow lakes

Spatial variation of phosphorus fractions in bottom sediment, pore water and overlying water in three shallow eutrophic lakes, Nishiura, Kitaura and Sotonasakaura, Japan, and the contributions of the fractional P to mobilization of phosphorus from sediment were examined in this study. The vertical distributions of dissolved inorganic phosphorus (DIP) concentrations in overlying and pore water differed with lake and sampling site. In particular, DIP was high in pore water in the surface layer of the sediment for the middle to downlake areas of Lake Kitaura. DIP release flux calculated from a gradient of the concentrations at the sediment–water interface was high compared with other sites. The distribution of fractional P content in sediments was highly variable. The citrate–dithionite–bicarbonate–non-reactive phosphorus (CDB–NRP) fraction, in particular, differed greatly among the three lakes. According to correlation in the ratios between CDB–NRP and loss on ignition, sediments of these lakes were classified in three clusters. The CDB–NRP fraction was suggested to play a role in DIP release from sediment. The possibility of nitrate concentration playing a role in the control of DIP release was considered.

ENZYMATIC EVALUATION OF DECOMPOSITION IN MOSAIC LANDSCAPES OF A TIDAL FLAT ECOSYSTEM

Organic matter decomposition is an important ecological function in tidal flat ecosystems, and extracellular hydrolytic enzyme activities can be used as indices of this process. In this study, the spatial and temporal variations of enzyme activities were determined to establish easily measured variables that could be used to assess wetland functions. Seven sampling sites belonging to the hydrogeomorphic subclasses estuary, foreshore, and lagoon were selected in the intertidal zone of the Obitsu River Delta and the Banzu Tidal Flat in Tokyo Bay, Japan. Ten field surveys were conducted between June 2001 and April 2003. In each survey triplicate sediment samples were collected from each sampling site. For each sample, fluoresceindiacetate hydrolysis (FDH), β-glucosidase (GLU), and β-acetylglucosaminidase (AGA) activities were measured. Among the 210 samples, the means and standard deviations were 0.018 ± 0.011 unit g−1 h−1 for FDH, 0.074 ± 0.043 mmol kg−1 h−1 for GLU, and 0.043 ± 0.041 mmol kg−1 h−1 for AGA. According to analysis of variance, sampling time, site location, and their interaction significantly influenced FDH activity. Both the sampling time and sampling location affected GLU and AGA activities, although no significant interaction was found. GLU and AGA activities were higher in the estuary sites than in the foreshore sites and the lagoon site. GLU and AGA activities differed among the estuary sites, although there were no significant differences in GLU and AGA activities among the foreshore beach sites. We recorded significant temporal changes of GLU and AGA activities, and seasonal changes differed across the three years of the study.

Abstracts from the Japanese Journal of Limnology

The Japanese Journal of Limnology is another official publication of the Japanese Society of Limnology. The original papers in the journal were peer-reviewed by a few authorized referees, and appeared in Japanese with English abstracts.