We collected 68 fresh, brackish, and seawater samples from various sites around the estuaries of 2 rivers at high and low tides. Seawater flowed approximately 2.4 (salinity, 2.2% at the site) and 1.2 km (1.8%) upstream of the estuaries, but the surface comprised essentially fresh water up to the mouth. Sites contained 69 to 22,200 diatoms/50 mL of water, and the numbers varied by depth and at sites separated by only approximately 1.2 km. Diatoms ranged from 2.8 to 429 μm (mean range, 16.1-59.2 μm) in size. Large pennate diatoms populated fresh water areas, and most sedimented before reaching the sea. Numbers of pennate diatoms of less than 20 μm were decreased in areas of seawater. Numbers of centric diatoms tended to increase nearer the sea, and seawater contained large centric diatoms. Brackish water containing large volumes of seawater was easily discriminated by assemblages of marine diatoms, unlike that containing a little seawater, because marine diatoms could be found in fresh water around estuaries. Tides and the nature of the river often altered diatomaceous assemblages at the same estuarial sites. Caution is recommended for forensic interpretation of aqueous media to deduce drowning sites.
From the *Division of Legal Medicine, Department of Social Medicine, Faculty of Medicine and †Department of Biochemistry and Applied Biosciences, Faculty of Agriculture, University of Miyazaki, Miyazaki, Japan.
Manuscript received December 19, 2007; accepted March 20, 2008.
This study was supported by a Grant-in-Aid for Scientific Research (C) (no. 18590640) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
Presented in part at the 89th and 90th congresses of the Japanese Society of Legal Medicine (Kagawa 2005; Fukuoka 2006).
The authors report no conflicts of interest.
Reprints: Eiji Kakizaki, PhD, Division of Legal Medicine, Department of Social Medicine, Faculty of Medicine, University of Miyazaki, 5200 Kihara, Kiyotake-cho, Miyazaki 889-1692, Japan. E-mail: firstname.lastname@example.org.