COI Funded Project: An Isotopic Tracer Investigation of Organic Nitrogen Cycling Within the Subterranean Estuary and Groundwater Seepage face
Project Funded: 2002
Proposed Research
Increases in the supply of land-derived nitrogen to receiving
waters, on Cape Cod and on a global scale, has led to eutrophication
of many coastal waterbodies. On Cape Cod, delivery of land-derived
N to the coastal zone occurs primarily through groundwater transport.
However, little information is currently available on the influence
of nitrogen cycling processes in the mixing zone of fresh and saline
groundwater or on processes in the sediments of the seepage zone
on the transport of land-derived nitrogen to coastal waters. In
addition, our past studies and those of others have shown that a
large fraction of these nitrogen loads to coastal waters are often
composed on organic nitrogen. To our knowledge there have been no
field experiments on the reactivity of the organic nitrogen and
on the role of land-derived organic nitrogen in the nitrogen cycle
and eutrophication of coastal waters. The goal of the proposed research
is to quantify nitrogen transformations, retention and losses in
aquifers at the margin between watersheds and coastal waters, with
a particular focus on the role of the organic nitrogen.
We propose to utilize anthropogenically generated variations in
the isotopic signatures of N exported from the watersheds of Waquoit
Bay to obtain isotopically labeled dissolved organic nitrogen of
natural chemical composition. We will use ultrafiltration to concentrate
the organic nitrogen from a sample of groundwater collected from
an urbanized watershed, spike the sample with isotopically labeled
inorganic nitrogen and a conservative tracer and inject the sample
into the nearshore aquifer of a forested watershed. This is an innovative
technique and, in contrast to past studies using additions of only
inorganic nitrogen isotope tracers, will allow quantification of
organic nitrogen cycling, in addition to the cycling of the other
major forms of nitrogen.
This study will provide both basic and applied information on the
influence of poorly studied segments of the aquatic cascade from
land to sea on the magnitude and species composition of nitrogen
loads transported to receiving waters. The results will improve
management of coastal waters by updating nitrogen transport models
and by providing a more accurate link between land-derived nitrogen
loads and the eutrophication of receiving waters.
Originally published: January 25, 2002