Expanding Perspectives of Element Cycling from 1970 to 2020: The Influence of Stumm and Morgan

There has been significant advancement in understanding of element cycles over the past 50 years, and the contributions of the three editions of Aquatic Chemistry by Stumm and Morgan on the critical role of reactions in the aqueous phase on the global cycles of elements have been substantial. The primary focus of investigation of biogeochemical element cycles has been on the "grand nutrients" carbon, nitrogen, phosphorus, and sulfur. The basic chemistry and chemical systems perspective of Aquatic Chemistry helped elucidate the cycles of these elements. Most of the element cycling research beyond the grand nutrients has occurred in the past 20 years and has focused on commodity metals in widespread use, that is, the "technological nutrients". Focus in Aquatic Chemistry on metal chemistry has contributed to understanding of metal cycles. Development of integrated anthropogenic-biogeochemical cycles of metals, led by Graedel and collaborators, has revealed that anthropogenic mobilization of metals dominates the cycles. Integrated "anthrobiogeochemical" element cycles provide for more detailed understanding of sources and their cascading impacts, and enable identification of priorities for source control and/or element recovery. The fundamentals of water chemistry and their application in engineered and natural systems, as presented so effectively in Aquatic Chemistry, have contributed to advancement of anthrobiogeochemical cycle development and analysis and, directly or indirectly, to the scholars who will continue to evolve the understanding and use of element cycles in the years ahead.