1. American Public Health Association (1992), Standard methods for the examination of water and wastewater, 18th edn. Methods 4500 NH3 H
2. Bishop RA (1981) Iowa’s wetlands. Proceedings of the Iowa Academy of. Science 88:11–16
3. Bishop RA, Joens AJ, Zohrer J (1998) Iowa’s wetlands, present and future with a focus on prairie potholes. Journal of the Iowa Academy of Science 88:11–16
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5. Bishop RA, van der Valk AG (1982) Wetlands. In: Cooper TC (ed) Iowa’s Natural Heritage. Iowa Natural Heritage Foundation and Iowa Academy of Science, Des Moines, IA, USA, pp 208–229