Potential for shoreline recession to accelerate discharge of groundwater
pollutants to coastal waters
Abstract
Discharge of groundwater-derived pollutants to inland and marine coastal
waters is influenced by the transport and reactive processes occurring
in nearshore aquifers. The effect of shoreline change on these processes
and subsequent discharge of pollutants to coastal waters is unclear. The
objective of this study was to evaluate the impact of shoreline
recession (landward movement of the mean shoreline) on the transport of
nitrogen [N] and phosphorus [P] in a nearshore aquifer and their
discharge to coastal waters. Field investigations were conducted on a
permeable unconfined nearshore aquifer on Lake Huron, Canada, in years
coinciding with historically low and high lake water levels. At the
site, a septic system-derived nutrient-rich (N and P) groundwater plume
is moving towards the lake and the mean shoreline position moved
~30 m landward between sampling years due coastal
erosion and mean lake water level increase. Data indicate PO4-P fluxes
to the lake were higher following shoreline recession due to shortened
travel pathways. In contrast, NO3-N fluxes were governed by the specific
geochemical conditions near the sediment-water interface, which are not
only a function of the shoreline position. Further, findings show
shoreline recession may modify mineral phases that tend to sequester
pollutants (e.g., iron oxides) near the sediment-water interface and
this may possibly mediate release of sediment-bound pollutants. The
findings provide new insights into potential impacts of shoreline change
on chemical discharge to coastal waters as needed to inform long-term
water quality predictions and management.