Abstract
Groundwater-surface water interactions drive water quality in both streams and the coastal ocean, where groundwater discharge occurs in streams as baseflow and along the coastline as submarine groundwater discharge (SGD). Groundwater contributions to streams and to the coastal ocean were quantified in three urban streams in Kāneʻohe Watershed, Hawaiʻi. We used radon as a groundwater tracer to show that baseflow contributions to streams ranged from 22 to 68% along their reaches leading to the coast of Kāneʻohe Bay. Total SGD was 4,500, 18,000, and 23,000 m3/day for the northwest, central, and southern sectors of the bay, respectively. Total groundwater (stream baseflow + SGD) dissolved nutrient fluxes were significantly greater than those sourced from stream surface runoff. The studied streams exhibited increasing nutrient levels downstream from groundwater inputs with high nutrient concentrations, negatively impacting coastal water quality. SGD dynamics were also assessed during the anomalously high perigean spring tides in 2017, where SGD was four times greater during the perigean spring tide compared to a spring tide and resulted in strong shifts in N:P ratios, suggesting that rising sea level stands may disrupt primary productivity with greater frequency. This study demonstrates the importance of considering baseflow inputs to streams to coastal groundwater budgets and suggests that coastal water quality may be improved through management and reduction of groundwater contaminants.
Highlights
Groundwater-surface water interactions impact nutrient and pollutant transport and directly affect water quality in streams and coastal ecosystems
We have shown increased nutrient fluxes, and higher nutrient concentrations during perigean spring tides, highlighting the importance of conducting more studies that investigate the relation of sea level to submarine groundwater discharge (SGD) composition
The approach used in this study led to an improved understanding of nutrient delivery and contaminant flow paths to streams and the coastal ocean in Kāne‘ohe Watershed and Bay, and highlighted the importance of considering groundwater discharge via stream baseflow
Summary
Groundwater-surface water interactions impact nutrient and pollutant transport and directly affect water quality in streams and coastal ecosystems. Gaining reaches of streams receive groundwater, which affects stream discharge as well as its water quality [1]. Polluted groundwater discharge to streams and coastline is a common problem for island watersheds with densely populated coastal plains, which in addition are often upstream of coral reefs and other sensitive coastal ecosystems that. Stream and coastal water quality driven by groundwater. The views expressed are those of the authors and do not necessarily reflect the views of NOAA or any of its subagencies. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of this manuscript
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