Volume 4 covers Kimberley, Northern Territory (NT), Queensland, and Christmas Island. It contains a comprehensive description of ca. 520 diatom taxa from 112 genera, accompanied by information on their geographical distribution and environmental parameters. Key genera include Eunotia (46 taxa), Pinnularia (45), Nitzschia (30), Gomphonema (26), and Navicula (18). This work is a crucial resource for understanding the biodiversity and ecological roles of diatoms in tropical Australia's unique habitats.
In his preface, Peter A. Siver adds that "The work contains analysis of diatoms from 397 sites, including lakes, pools, hot springs. streams and rivers, spread over approximately 46% of the continent, and including rainforest, monsoon and savannah climates. Although there is a large range in pH, the vast majority of sites represent neutral alkaline waters. Dr. John further presents the geologic, biologic and social histories of each region explored, providing insights to the past and current environmental impacts on these aquatic communities."