Publication Date:
2015-05-17
Description:
Submarine groundwater discharge (SGD) varies significantly across time scales ranging from hours to years, but studies that allow quantitative comparisons between different time scales are few. Most of these studies have focused on beach settings, where the combined variations in fresh and saline SGD can be difficult to interpret. We calculated variations in saline SGD based on a 1-year record of hydraulic head in a salt marsh, where we could isolate variations in saline, tidally-driven SGD. Observed SGD varied by an order of magnitude over the course of the year. Groundwater discharge was proportional to tidal amplitude and varied by at least a factor of two between spring and neap tides. Monthly average SGD was inversely proportional to average sea level; it increased by nearly a factor of two as sea level declined by ∼50 cm from late summer to late winter. This variation was far larger than that predicted by analytic models, owing to the flat topography and inundation of the marsh platform. The effect of short-term (days) variations in sea level associated with wind events and storms was small in comparison. SGD is probably proportional to tidal amplitude in nearly all coastal settings, including beaches. Seasonal variations in sea level may not affect the volume of SGD as significantly in coastal settings where the slope of the intertidal zone is relatively constant, but such variations have the potential to strongly affect the composition of SGD. This article is protected by copyright. All rights reserved.
Print ISSN:
0043-1397
Electronic ISSN:
1944-7973
Topics:
Architecture, Civil Engineering, Surveying
,
Geography
