Application of Stable Isotopes of Water to Study Coupled Submarine Groundwater Discharge and Nutrient Delivery

TY - JOUR

T1 - Application of Stable Isotopes of Water to Study Coupled Submarine Groundwater Discharge and Nutrient Delivery

AU - Duque, Carlos

AU - Jessen, Soren

AU - Tirado-Conde, Joel

AU - Karan, Sachin

AU - Engesgaard, Peter

PY - 2019/9

Y1 - 2019/9

N2 - Submarine groundwater discharge (SGD)-including terrestrial freshwater, density-driven flow at the saltwater-freshwater interface, and benthic exchange-can deliver nutrients to coastal areas, generating a negative effect in the quality of marine water bodies. It is recognized that water stable isotopes ( 18O and 2H) can be helpful tracers to identify different flow paths and origins of water. Here, we show that they can be also applied when assessing sources of nutrients to coastal areas. A field site near a lagoon (Ringkøbing Fjord, Denmark) has been monitored at a metric scale to test if stable isotopes of water can be used to achieve a better understanding of the hydrochemical processes taking place in coastal aquifers, where there is a transition from freshwater to saltwater. Results show that 18O and 2H differentiate the coastal aquifer into three zones: Freshwater, shallow, and deep saline zones, which corresponded well with zones having distinct concentrations of inorganic phosphorous. The explanation is associated with three mechanisms: (1) Differences in sediment composition, (2) chemical reactions triggered by mixing of different type of fluxes, and (3) biochemical and diffusive processes in the lagoon bed. The different behaviors of nutrients in Ringkøbing Fjord need to be considered in water quality management. PO 4 underneath the lagoon exceeds the groundwater concentration inland, thus demonstrating an intra-lagoon origin, while NO 3, higher inland due to anthropogenic activity, is denitrified in the study area before reaching the lagoon.

AB - Submarine groundwater discharge (SGD)-including terrestrial freshwater, density-driven flow at the saltwater-freshwater interface, and benthic exchange-can deliver nutrients to coastal areas, generating a negative effect in the quality of marine water bodies. It is recognized that water stable isotopes ( 18O and 2H) can be helpful tracers to identify different flow paths and origins of water. Here, we show that they can be also applied when assessing sources of nutrients to coastal areas. A field site near a lagoon (Ringkøbing Fjord, Denmark) has been monitored at a metric scale to test if stable isotopes of water can be used to achieve a better understanding of the hydrochemical processes taking place in coastal aquifers, where there is a transition from freshwater to saltwater. Results show that 18O and 2H differentiate the coastal aquifer into three zones: Freshwater, shallow, and deep saline zones, which corresponded well with zones having distinct concentrations of inorganic phosphorous. The explanation is associated with three mechanisms: (1) Differences in sediment composition, (2) chemical reactions triggered by mixing of different type of fluxes, and (3) biochemical and diffusive processes in the lagoon bed. The different behaviors of nutrients in Ringkøbing Fjord need to be considered in water quality management. PO 4 underneath the lagoon exceeds the groundwater concentration inland, thus demonstrating an intra-lagoon origin, while NO 3, higher inland due to anthropogenic activity, is denitrified in the study area before reaching the lagoon.

KW - BEACH AQUIFER

KW - COASTAL LAGOON

KW - EUTROPHICATION

KW - FLUX

KW - HARMFUL ALGAL BLOOMS

KW - INPUTS

KW - MANAGEMENT

KW - RINGKOBING FJORD

KW - RingkObing Fjord

KW - SALINITY DISTRIBUTION

KW - SEEPAGE

KW - freshwater-saltwater interface

KW - nutrients

KW - stable isotopes of water

KW - submarine groundwater discharge

UR - http://www.scopus.com/inward/record.url?scp=85072215834&partnerID=8YFLogxK

U2 - 10.3390/w11091842

DO - 10.3390/w11091842

M3 - Journal article

SN - 2073-4441

VL - 11

JO - Water

JF - Water

IS - 9

M1 - 1842

ER -