High porewater exchange in a mangrove-dominated estuary revealed from short-lived radium isotopes

Sadat-Noori, Mahmood, Santos, Isaac R., Tait, Douglas R., Reading, Michael J., and Sanders, Christian J. (2017) High porewater exchange in a mangrove-dominated estuary revealed from short-lived radium isotopes. Journal of Hydrology, 553. pp. 188-198.

PDF (Published Version) - Published Version
Restricted to Repository staff only

DOI: 10.1016/j.jhydrol.2017.07.058

View at Publisher Website: https://doi.org/10.1016/j.jhydrol.2017.0...

Abstract

We hypothesise that mangroves play an important role in groundwater exchange processes in sub-tropical and tropical estuarine waters. To investigate this, multiple high resolution time series measurements of radium across a tidal estuary (Coffs Creek, NSW, Australia) were performed as well as a spatial survey in both bottom and surface layers. Results from the spatial survey revealed increasing radium concentrations in parts of the estuary surrounded by mangroves. The average radium concentration in estuary areas lined with mangroves was 2.5 times higher than the average concentration at the mouth of the estuary and 6.5-fold higher than upstream freshwater areas. Additionally, the area enriched in radium coincided with low dissolved oxygen concentrations, implying that porewater exchange may drive anoxia. A radium mass balance model based on 223Ra and 224Ra isotopes at different sections of the estuary confirmed higher porewater exchange rates from areas fringed with mangrove vegetation. Estimated porewater exchange rates were 27.8 ± 5.3 and 13.6 ± 2.1 cm d−1 (0.8 ± 0.1 and 0.4 ± 0.1 m3 s−1) based on 223Ra and 224Ra isotopes, respectively. The average saline porewater exchange was ∼ 10-fold larger than the upstream surface freshwater inputs to the estuary. We suggest that mangrove environments within subtropical estuaries are hotspots for porewater exchange due to the complex belowground structure of crab burrows and the effect of tidal pumping. Because porewater exchange releases carbon and nitrogen from coastal sediments, development and modification of mangrove areas in subtropical estuaries have a significant effect on coastal biogeochemical cycles.


Item ID:	78869
Item Type:	Article (Research - C1)
ISSN:	1879-2707
Keywords:	Permeable sediments, Radon, Seepage, Submarine groundwater discharge
Copyright Information:	© 2017 Elsevier B.V. All rights reserved.
Funders:	Australian Research Council (ARC)
Projects and Grants:	ARC DE140101733, ARC DP150103286, ARC LE140100083
Date Deposited:	20 May 2025 01:45
FoR Codes:	37 EARTH SCIENCES > 3707 Hydrology > 370703 Groundwater hydrology @ 50% 40 ENGINEERING > 4005 Civil engineering > 400513 Water resources engineering @ 10% 41 ENVIRONMENTAL SCIENCES > 4104 Environmental management > 410402 Environmental assessment and monitoring @ 40%
SEO Codes:	18 ENVIRONMENTAL MANAGEMENT > 1803 Fresh, ground and surface water systems and management > 180305 Ground water quantification, allocation and impact of depletion @ 40% 18 ENVIRONMENTAL MANAGEMENT > 1803 Fresh, ground and surface water systems and management > 180305 Ground water quantification, allocation and impact of depletion @ 40% 18 ENVIRONMENTAL MANAGEMENT > 1802 Coastal and estuarine systems and management > 180205 Measurement and assessment of estuarine water quality @ 20%
	More Statistics

Actions (Repository Staff Only)

Item Control Page