Watershed ‘chemical cocktails’: forming novel elemental combinations in Anthropocene fresh waters
Kaushal, S.S., Gold, A.J., Bernal, S., Johnson, T.A.N., Addy, K., Burgin, A., Burns, D.A., Coble, A.A., Hood, E., Lu, Y.H., Mayer, P., Minor, E.C., Schroth, A.W., Vidon, P., Wilson, H., Xenopoulos, M.A., Doody, T., Galella, J.G., Goodling, P., Haviland, K., Haq, S., Wessel, B., Wood, K.L., Jaworski, N., Belt, K.T. (2018). Watershed ‘chemical cocktails’: forming novel elemental combinations in Anthropocene fresh waters. Biogeochemistry, [online] 141(3), 281-305. http://dx.doi.org/10.1007/s10533-018-0502-6
Plain language summary
Usually water quality management strategies are considering one chemical at a time. Human modification of the landscape changes the ways in which multiple chemicals are transported from land to water and then through streams. Better management strategies might be developed if multiple chemicals are considered at the same time and by understanding that some groups of chemicals move in the same way and can be managed together. Classifications of the ways that chemicals are transported are proposed. These included chemicals that are removed when the landscape acts as a sieve, chemicals that are filtered by different parts of the landscape, those that stick to and are released from soil, and those that are impacted by both chemical and biological reactions.
In the Anthropocene, watershed chemical transport is increasingly dominated by novel combinations of elements, which are hydrologically linked together as ‘chemical cocktails.’ Chemical cocktails are novel because human activities greatly enhance elemental concentrations and their probability for biogeochemical interactions and shared transport along hydrologic flowpaths. A new chemical cocktail approach advances our ability to: trace contaminant mixtures in watersheds, develop chemical proxies with high-resolution sensor data, and manage multiple water quality problems. We explore the following questions: (1) Can we classify elemental transport in watersheds as chemical cocktails using a new approach? (2) What is the role of climate and land use in enhancing the formation and transport of chemical cocktails in watersheds? To address these questions, we first analyze trends in concentrations of carbon, nutrients, metals, and salts in fresh waters over 100 years. Next, we explore how climate and land use enhance the probability of formation of chemical cocktails of carbon, nutrients, metals, and salts. Ultimately, we classify transport of chemical cocktails based on solubility, mobility, reactivity, and dominant phases: (1) sieved chemical cocktails (e.g., particulate forms of nutrients, metals and organic matter); (2) filtered chemical cocktails (e.g., dissolved organic matter and associated metal complexes); (3) chromatographic chemical cocktails (e.g., ions eluted from soil exchange sites); and (4) reactive chemical cocktails (e.g., limiting nutrients and redox sensitive elements). Typically, contaminants are regulated and managed one element at a time, even though combinations of elements interact to influence many water quality problems such as toxicity to life, eutrophication, infrastructure corrosion, and water treatment. A chemical cocktail approach significantly expands evaluations of water quality signatures and impacts beyond single elements to mixtures. High-frequency sensor data (pH, specific conductance, turbidity, etc.) can serve as proxies for chemical cocktails and improve real-time analyses of water quality violations, identify regulatory needs, and track water quality recovery following storms and extreme climate events. Ultimately, a watershed chemical cocktail approach is necessary for effectively co-managing groups of contaminants and provides a more holistic approach for studying, monitoring, and managing water quality in the Anthropocene.