Distributions of diatoms in surface sediments from the Chanthaburi coast, Gulf of Thailand, and correlations with environmental factors

Abstract

This paper presents an analysis of diatoms collected from surface sediments in the Chanthaburi and Welu estuaries on the northern coast of the Gulf of Thailand. In total, 144 species are identified, representing 41 genera. Diatom abundance ranges from 645 to 24,979 valves/g, with an average of 7,215 valves/g. Diatoms primarily consist of common coastal species, warm water species and a few freshwater species. Additionally, Surirella tenera is identified as a unique freshwater species of the Welu River. Using cluster and redundancy analysis, we identified four diatom assemblages representing different environmental conditions. Diatom assemblages I and II are related to freshwater inputs from the Chanthaburi and Welu rivers. Assemblage III is closely related to nutrient concentrations and assemblage IV is representative of offshore waters from the Gulf of Thailand. The environmental factors controlling the distribution of diatoms are temperature, salinity, water depth and turbidity. The interior of the Welu Estuary was characterized by a brackish water environment strongly influenced by freshwater inputs to the south branch of the estuary and invasion of seawater into the north branch of the estuary. The Chanthaburi Estuary is a brackish water environment dominated by a single diatom assemblage. The main causes of differences in the distribution of diatoms between the Chanthaburi and Welu estuaries are runoff, estuary size, river width and nutrient concentrations.