Submarine groundwater discharge and nutrient addition to the coastal zone and coral reefs of leeward Hawai'i |
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| Authors: | Joseph H Street Karen L Knee Eric E Grossman Adina Paytan |
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| Institution: | aDepartment of Geological & Environmental Sciences, Stanford University, Bldg. 320, Rm. 118 450 Serra Mall, Stanford, CA 94305, USA;bCoastal and Marine Geology Program, U.S. Geological Survey Pacific Science Center, 400 Natural Bridges Dr. Santa Cruz, CA 95060, USA |
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| Abstract: | Multiple tracers of groundwater input (salinity, Si, 223Ra, 224Ra, and 226Ra) were used together to determine the magnitude, character (meteoric versus seawater), and nutrient contribution associated with submarine groundwater discharge across the leeward shores of the Hawai'ian Islands Maui, Moloka'i, and Hawai'i. Tracer abundances were elevated in the unconfined coastal aquifer and the nearshore zone, decreasing to low levels offshore, indicative of groundwater discharge (near-fresh, brackish, or saline) at all locations. At several sites, we detected evidence of fresh and saline SGD occurring simultaneously. Conservative estimates of SGD fluxes ranged widely, from 0.02–0.65 m3 m− 2 d− 1at the various sites. Groundwater nutrient fluxes of 0.04–40 mmol N m− 2 d− 1 and 0.01–1.6 mmol P m− 2 d− 1 represent a major source of new nutrients to coastal ecosystems along these coasts. Nutrient additions were typically greatest at locations with a substantial meteoric component in groundwater, but the recirculation of seawater through the aquifer may provide a means of transferring terrestrially-derived nutrients to the coastal zone at several sites. |
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| Keywords: | Submarine groundwater discharge Coastal zone Nutrients Tracers Radium isotopes Hawai'i |
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