Collaborative Research: Sources and Fates of Ecosystem Nutrients Across the Hawaiian Islands

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This project is a collaboration between the University of California, Santa Barbara, the University of Hawaii, and Cornell University. It was submitted to the Environmental Geochemistry and Biogeochemistry Program (EGB) and supported by the Atmospheric Chemistry, Petrology and Geochemistry, and Hydrologic Sciences Programs. The interdisciplinary team includes an ecosystem ecologist, a pedologist, an atmospheric chemist, and an isotope geochemist. The objective is to evaluate the sources and fates of elements deposited to Hawaiian ecosystems. Well characterized gradients in substrate age and precipitation will be utilized. Preliminary analyses of certain of these gradients suggest that atmospherically derived elements are crucial to the functioning of both older and wetter systems. This project will: (1) determine rates of atmospheric deposition of elements by wet, dry, and cloudwater deposition; (2) use elements in the lanthanide series, particularly the europium anomaly and neodymium isotopes, to trace the integrated contribution of continental dust to pools of more immobile elements; (3) determine the mineralogy, element pools, and weathering status of soils in all sites, and measure mineralogic indicators of dust inputs from continental sources; (4) analyze directly the cumulative contribution of atmospheric versus weathering sources to plant and soil strontium pools in all sites, and evaluate the sources of that strontium; and (5) integrate these measurements to estimate the contribution of atmospheric inputs to the pools and availability of all major elements, as these vary with substrate age and climate. Atmospheric wet, dry, and cloud deposition will be directly monitored at two sites representing the end members of the Hawaiian physical climate system. Deposition of mineral aerosols derived from Asia will be inferred by measuring the concentration of unique materials such as quartz in soils and the concentration of continentally derived trace element patterns (rare earth elements and Th, Hf) and neodymium isotopes. Further, the relationship between Nd and P will be explored to determine whether it is possible to use Nd isotopes as an indicator of mineral aerosol contributions of P to Hawaiian ecosystems. Measurements of soils will be used to determine patterns of mineralogy and element pools in space and time; because the sites are arrayed on well defined gradients, these can be used to calculate weathering inputs. Strontium isotope measurements will make use of the difference in isotopic ratio between the marine source of most atmospheric deposition and the rock source of weathering; both of these are well defined and consistent in the Hawaiian system. Measurements of quartz and trace elements will allow an estimate of Sr input from highly radiogenic continental sources.