Quantifying submarine groundwater discharge to Indian River Lagoon, Florida

Abstract

Each submarine groundwater discharge technique has individual strengths and weaknesses. Seepage meters provide a direct measurement of localized flow. They can also easily provide 'clean' seep water samples. However, seep meters may be susceptible to possible artifacts caused by interaction of tides and waves, although such limitations have not been thoroughly tested. The radioisotopes are less difficult to sample in the field than using seepage meters, but their measurement requires sophisticated laboratory equipment that is not widely available. One important characteristic of the radioisotope techniques is that they provide an integrated value of seepage rates across the entire lagoon. They are thus complementary to the seepage meter technique. Chloride concentrations indicate that only a minor component (1 -5%) of seep water originates from meteoric ground water. This implies that 95 -99% of the interstitial water has to be recycled lagoon seawater. The isotopic concentration of strontium (87Sr/86Sr) was nearly identical in the seep water and lagoon water, yet was measurably lower than that in modern seawater. The 87Sr/86Sr ratios were also systematically lower during the rainy season, reflecting the greater influx of seep water into lagoon water and short groundwater residence times. Nutrient concentrations were 3-5 times elevated in the seep water over the lagoon water, and suggest that sediment/water interface exchange processes, such as submarine groundwater discharge, are critical components of coastal nutrient budgets (Johannes, 1980; Krest et al., 2000). References

Hurricanes, El Niño and harmful algal blooms in two sub-tropical Florida estuaries: Direct and indirect impacts

“…The relationship is functionally tied to the positive relationship between nutrient concentrations and rainfall 14,56 . External nutrients enter the northern Indian River Lagoon from a variety of sources, including surface water runoff, groundwater discharge, direct rainfall inputs, septic system leakage, and permitted and accidental releases from sewage treatment systems [60][61][62][63][64][65] . All of these processes can be enhanced by high rainfall, although the relative importance of the sources can vary by nutrient type.…”

Cyclical Patterns and a Regime Shift in the Character of Phytoplankton Blooms in a Restricted Sub-Tropical Lagoon, Indian River Lagoon, Florida, United States

“…The pattern results in above and below average watershed inflows to coastal aquatic ecosystems (Kahya and Dracup, 1993;Dracup and Kahya, 1994). Nutrients enter NIRL from a variety of external sources, including surface water runoff, tributary inflows, groundwater inputs, rainfall, septic system seepage, and periodic permitted and accidental releases from sewage treatment systems (Swarzenski et al, 2001;Adkins et al, 2004;Steward and Green, 2007;Gao, 2009;Lapointe et al, 2015;Trefry and Fox, 2021). All of these inputs can be exacerbated by high rainfall levels.…”