TY - JOUR
T1 - Dynamics of Groundwater-Derived Nitrate and Nitrous Oxide in a Tidal Estuary From Radon Mass Balance Modeling
AU - Wong, Wei Wen
AU - Grace, Michael
AU - Cartwright, Ian
AU - Cardenas, M. Bayani
AU - Zamora, Peter
AU - Cook, Perran
PY - 2013
Y1 - 2013
N2 -
We monitored submarine groundwater discharge (SGD) into the Werribee Estuary, Australia, using both chemical and physical methods. SGD occurred at hotspots where
222
Rn persisted through a 12 month survey period. A significant correlation between
222
Rn and NO
3
-
(r
2
= 0.8, p < 0.01), as well as between
222
Rn NO
3
-
and N
2
O (r
2
= 0.6, p < 0.01) at a
222
Rn NO
3
-
hotspot, and much higher and N
2
O concentrations in groundwater relative to surface water suggest that elevated and N
2
O concentrations in the estuary were derived from SGD. Two sampling campaigns over 24 h revealed that variations of
222
Rn, and N
2
O were controlled by tide-induced hydraulic-head gradient fluctuations and, possibly to a much lesser extent, by tidal pumping and density-driven convection. A two-box
222
Rn mass-balance model was used to calculate the rate of SGD into two different layers across the pycnocline of the estuary. A higher total groundwater discharge rate of 0.12 ± 0.09 m d
-1
was observed in the surface layer during ebb tide compared with 0.10 ± 0.08 m d
-1
during flood tide. Fluxes of groundwater-derived and N
2
O were higher than the riverine flux at baseflow by more than 30 fold and 20 fold, respectively. SGD derived fluxes exceeded the mean annual riverine NO
3
-
and TN fluxes by a factor of ~ 5 and ~ 3 respectively. SGD-derived N
2
O fluxes were 170 μmol m
-2
d
-1
, which are among the highest N
2
O fluxes observed in estuaries.
AB -
We monitored submarine groundwater discharge (SGD) into the Werribee Estuary, Australia, using both chemical and physical methods. SGD occurred at hotspots where
222
Rn persisted through a 12 month survey period. A significant correlation between
222
Rn and NO
3
-
(r
2
= 0.8, p < 0.01), as well as between
222
Rn NO
3
-
and N
2
O (r
2
= 0.6, p < 0.01) at a
222
Rn NO
3
-
hotspot, and much higher and N
2
O concentrations in groundwater relative to surface water suggest that elevated and N
2
O concentrations in the estuary were derived from SGD. Two sampling campaigns over 24 h revealed that variations of
222
Rn, and N
2
O were controlled by tide-induced hydraulic-head gradient fluctuations and, possibly to a much lesser extent, by tidal pumping and density-driven convection. A two-box
222
Rn mass-balance model was used to calculate the rate of SGD into two different layers across the pycnocline of the estuary. A higher total groundwater discharge rate of 0.12 ± 0.09 m d
-1
was observed in the surface layer during ebb tide compared with 0.10 ± 0.08 m d
-1
during flood tide. Fluxes of groundwater-derived and N
2
O were higher than the riverine flux at baseflow by more than 30 fold and 20 fold, respectively. SGD derived fluxes exceeded the mean annual riverine NO
3
-
and TN fluxes by a factor of ~ 5 and ~ 3 respectively. SGD-derived N
2
O fluxes were 170 μmol m
-2
d
-1
, which are among the highest N
2
O fluxes observed in estuaries.
UR - http://www.scopus.com/inward/record.url?scp=84894468560&partnerID=8YFLogxK
U2 - 10.4319/lo.2013.58.5.1689
DO - 10.4319/lo.2013.58.5.1689
M3 - Article
SN - 0024-3590
VL - 58
SP - 1689
EP - 1706
JO - Limnology and Oceanography
JF - Limnology and Oceanography
IS - 5
ER -