Web Release Date: June 19,
Identifying Sources of Nitrogen to Hanalei Bay, Kauai, Utilizing the Nitrogen Isotope Signature of Macroalgae
and
Department of Geological & Environmental Sciences, Stanford University, Stanford, California 94305, U.S. Geological Survey, Menlo Park, California 94025, and P.O. Box 681, Kilauea, Hawaii 96754
Received for review January 7, 2007
Revised manuscript received May 10, 2007
Accepted May 21, 2007
Abstract:
Sewage effluent, storm runoff, discharge from polluted
rivers, and inputs of groundwater have all been suggested
as potential sources of land derived nutrients into
Hanalei Bay, Kauai. We determined the nitrogen isotopic
signatures (
15N) of different nitrate sources to Hanalei Bay
along with the isotopic signature recorded by 11 species
of macroalgal collected in the Bay. The macroalgae integrate
the isotopic signatures of the nitrate sources over time,
thus these data along with the nitrate to dissolved inorganic
phosphate molar ratios (N:P) of the macroalgae were
used to determine the major nitrate source to the bay
ecosystem and which of the macro-nutrients is limiting algae
growth, respectively. Relatively low 15N values (average
-0.5”) were observed in all algae collected throughout the
Bay; implicating fertilizer, rather than domestic sewage,
as an important external source of nitrogen to the coastal
water around Hanalei. The N:P ratio in the algae compared
to the ratio in the Bay waters imply that the Hanalei Bay
coastal ecosystem is nitrogen limited and thus, increased
nitrogen input may potentially impact this coastal ecosystem
and specifically the coral reefs in the Bay. Identifying
the major source of nutrient loading to the Bay is important
for risk assessment and potential remediation plans.
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