Fluvial diatom database for forensic drowning investigation in Himachal Pradesh, India: a baseline study of rivers in Kangra district

Diatoms are single-celled algae with hard shells made of silica. They live in almost every freshwater body, and each river has its own mix of species. In a suspected drowning, the diatoms found inside a body can be compared with those in the suspected water. This gives supportive evidence about where the drowning took place. Reference data on diatoms for the rivers of Himachal Pradesh are still scarce. This study recorded the diatoms of 16 rivers and streams in Kangra district, nine in the hilly area and seven in the plain area. Water was collected from one upstream and one downstream point on each river in January and February. The samples were digested with nitric acid, mounted in Naphrax and examined under a light microscope with a 100× oil-immersion objective. About 26 genera were recorded. Navicula was found in 31 of the 32 samples, and Asterionella, Diatoma, Nitzschia and Cyclotella were also widespread. Water temperature ranged from 6.8 to 24.6 °C. Many taxa were shared between rivers, but the combination of taxa differed from river to river and from site to site. The study gives a first baseline for Kangra district and shows what a regional diatom reference database should contain. Sampling in other seasons and larger counts per sample are needed before the data can be used routinely in casework.