『Abstract
Submarine Groundwater Discharge (SGD) has been frequently ignored
as a nutrient source to marine ecosystems because it is difficult
to identify and quantify. However, recent studies show its ubiquity
and ecological importance to the coastal zone, particularly when
associated with contaminated continental aquifers. The Ria Formosa
is a coastal lagoon located in the south of Portugal and surrounded
by an intensely farmed area. Following a 12-month field study
using seepage meters, we identified groundwater discharge in the
intertidal zone of the lagoon. The seepage fluid was a mixture
of two water types: one with low salinity and high nitrate concentration
and another similar to local seawater. Based on the integration
of monthly seepage rate measurements throughout the year, we estimate
the mean discharge of submarine groundwater into the lagoon to
be 3.6 m3 day-1 per linear meter of coastline
with freshwater contributions (per volume) ranging from 10％ to
50％. The results of this study suggest a continental origin for
the freshwater component, thus linking the biogeochemial cycles
in the lagoon to anthropogenic activities taking place in the
neighboring coastal plain. We further identify SGD as an important
nutrient source to the Ria Formosa, estimating annual loads of
36.2mol (0.507 kg) of Nitrogen, 1.1 mol (0.034 kg) of Phosphorous
and 18.6 mol (0.522 kg) of silicon per meter of coastline. Based
on these results, we suggest that SGD is a potential contributor
to the observed nutrification status of the Ria Formosa lagoon.
Keywords: Submarine Groundwater Discharge; Seepage meters; Nutrification;
Permeable sediments; Ria Formosa; Nitrate』
Introduction
Study area
Methods
Results and discussion
Identification and behavior of SGD
Presence of two water masses
Freshwater origin and contribution
Periodic pattern of water seepage rates and associated nutrient
fluxes
Implications and future research
Acknowledgments
References