The impact of submarine groundwater discharge on nutrient dynamics in a sub-polar mudflat

Abstract

Submarine groundwater discharge (SGD) plays a major role in the hydrological and biogeochemical cycles controlling nearshore nutrient availability. The Northern Gulf of Alaska coastline is highly diverse, ranging from rocky beaches, sandy beaches, and mudflats; SGD varies according to sediment permeability, strength of wave pumping, and slope of the water table. SGD has been previously estimated at a rocky beach in the NGA, but this thesis sought to quantity SGD in an extensive mudflat using well-established tracers (radium and radon) and determine the major sources of nutrients to the bay. The rate of SGD was comparable between the mudflat and rocky beach (233 ± 245 and 260 ± 360 cm day⁻¹, respectively), and both locations were significant sources of nitrate and silicic acid, and sinks of phosphate. Offshore water also provides a major input of nitrate and phosphate to the bay. Thus, there is no single dominant source for all macronutrients, consequently, multiple processes must be considered when predicting nutrient cycling.