In constructing water budgets and mass flux
estimates for the coastal margins, submarine
groundwater discharge is often overlooked
because it represents a non-point source,
occurs over a broad subterranean area, and
is therefore more difficult to quantify.
However, our investigations in Alabama and
the Bengal Basin have shown that
groundwater discharge can be substantial
and can influence oceanic chemistry through
the discharge of nutrients from fertilizers and
trace metals from the weathering of the
aquifer protoliths.

We estimate that the mature siliceous aquifer
of Baldwin County, AL has a groundwater flux
to the Gulf of Mexico of 1.9+/-0.8x10^9 m^3/yr
and its submarine nitrate discharge is 1.1+/-
0.01x10^8 mol/yr or 0.8% of the annual
Mississippi River input. If other coastal zones
have similar submarine fluxes, then
groundwater discharge would effectively
double the nitrate discharge to the Gulf. In the
Bengal Basin, the groundwater fluxes of Sr
and Ba to the global ocean are estimated to
be 3.9% and 1.5%, respectively, of the global
continental flux. This strongly suggests that
groundwater discharge into the coastal
oceans can be a significant source of trace
metals such as Sr and Ba and influences the
global Sr isotopic balance and its evolution
through time. In coastal floodplains with high
precipitation rates and rapid accumulation of
immature sediment, such as the Bengal
Basin, submarine discharge can make
significant contributions to global oceanic
budgets equal to or greater than the surface
river flux.

Within the Bengal Basin, a significant portion
of the population suffers from arsenic
poisoning. The sediments appear capable of
supplying the dissolved arsenic to the
groundwater. The microbial mediated
reductive dissolution of iron oxy-hydroxides
liberates arsenic from the sediment into the
moderately reducing groundwater used by
over 40 million people. The strong
correlations between high levels of dissolved
arsenic with iron, methane, and ammonia
links the bacterial breakdown of As-bearing
FeOOH to the Holocene deposits of the
Ganges-Brahmaputra Rivers floodplain.