『Abstract
This paper presents an uncomplicated approach to improve estimates
of groundwater nutrient load to marine embayment. A two-dimensional
chemical profile of shallow groundwater was analysed in a sandy
beach in three seasons (early summer, late summer and mid winter)
and an adjusted estimate of groundwater nutrient discharge was
derived that accounts for a complex biogeochemical environment
and non-conservative behaviour of nutrients in the pre-discharge
beach groundwater. The study was conducted at Cockburn Sound,
Western Australia, where there has been significant groundwater
contamination and associated marine ecological degradation. Losses
in nitrogen and increases in phosphorus were observed along the
discharge pathway beyond that expected from mixing with marine
water, and the changes were attributed to chemically and biologically
mediated reactions. A slow groundwater velocity (0.14-0.18 m day-1),
high organic carbon (TOC=0.35-4.9 mmol l-1, DOC=0.28-4.6
mmol l-1) and low to sub-oxic conditions (DO=0.4-24%
saturation) were deemed suitable for chemically and biologically
mediated reactions to occur and subsequently alter regional estimates
of groundwater nutrient concentration. Accounting for this environment,
groundwater loads were calculated that were 1-2 orders of magnitude
less than previous regional-based estimates: 0.4-13 kg NOx-
day-1, 0.2-24 kg NH4+
day-1 and 0.004-0.8 kg FRP day-1. This paper
applies knowledge of recent research and presents scope to marine
managers or modellers to account for groundwater inputs to the
marine environment.
Keywords: Groundwater nitrogen; Permeable sand; Coastal aquifer;
Submarine groundwater discharge』
Introduction
Materials and methods
Study site
Sample collection
Beach sediment characterisation
Results
Beach sediment profile
Sea water
Integrated and deep groundwater
Shallow groundwater
Discussion
Controls on beach groundwater quality
Water level
Salinity
Temperature
Chemistry
Conclusion
Acknowledgments
References