In ecology, base-richness is the level of chemical bases in water or soil, such as calcium or magnesium ions.  Many organisms<nowiki/> prefer base-rich environments. Chemical bases are alkalis, hence base-rich environments are either neutral or alkaline.  Because acid-rich environments have few bases, they are dominated by environmental acids (usually organic acids).  However, the relationship between base-richness and acidity is not a rigid one &ndash; changes in the levels of acids (such as dissolved carbon dioxide) may significantly change acidity without affecting base-richness.  
Base-rich terrestrial environments are characteristic of areas where underlying rocks (below soil) are limestone. Seawater is also base-rich, so maritime and marine environments are themselves base-rich.
Base-poor environments are characteristic of areas where underlying rocks (below soil) are sandstone or granite, or where the water is derived directly from rainfall (ombrotrophic).