Diatom nutrient requirements change with lake nutrient limitation and enrichment in New Zealand dune lakes

ABSTRACT Nutrients are important determinants of diatom growth in lakes, and diatoms are considered reliable indicators of changing lake nutrient concentrations and eutrophication. However, diatom ecologies are not static, nor are they linked to single environmental variables, leading to imprecise diatom nutrient inferences. Anthropogenic nutrient enrichment is the principal issue facing New Zealand’s lakes. Thus, knowledge of diatom responses to nutrients in New Zealand lakes will be important for understanding contemporary and past changes in nutrient availability. Using a nutrient amendment experiment and diatom communities from dune lakes, here we show that the response of specific diatom species is not universal among lakes and is partly determined by lake nutrient concentrations and limitation status. The response of focal diatom species to nutrient additions differed from previously reported nutrient requirements, and did not align with published, assigned trophic statuses. This study highlights that the response of diatoms to nutrient enrichment is context-dependent, and that intraspecific generalisations of diatom ecologies between geographic locations or through time should be made with caution. To apply diatoms to making nutrient inferences, more work focusing on how physiochemical and biological factors influence diatom nutrient requirements is required.