A relationship between submarine groundwater borne nutrients traced by Ra isotopes and the intensity of dinoflagellate red‐tides occurring in the southern sea of Korea

Abstract

We measured short-lived radium isotopes ( 223 Ra and 224 Ra), dissolved inorganic and organic nutrients, and photosynthetic pigments during the summers of 2006 and 2007 in the southern sea of Korea, where harmful dinoflagellate blooms occur every year. The Ra tracer measurements reveal that coastal groundwater, rather than other sources previous suggested (i.e., Yangtze River diluted water or Kuroshio currents), is the main source of nutrients that fuel red tides in this region. Although inorganic-nutrient levels are different for different regions and different years, either dissolved inorganic nitrogen or phosphorus is depleted in the red-tide region. This depletion is accompanied by highly elevated levels of dissolved organic nutrients, transformed from groundwaterborne dissolved inorganic nutrients either inside Yeoja Bay or in offshore red-tide areas, thereby creating favorable conditions for the growth of dinoflagellates in competition with diatoms. The intensity of red tides correlates well with the activity of 224 Ra (half life 5 3.66 d) in seawater over daily or yearly time scales. Because the chemically conservative 224 Ra can trace groundwater-borne nutrients, which are utilized by marine biota in this red-tide region, the intensity of red tides seems to be related to the amount of nutrient-enriched groundwater supplied to the offshore red-tide region.

Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

“…In recent years, top-down evidence (i.e., a demonstrated cause-effect) has emerged illustrating clearer links between groundwater inputs and a biogeochemical response in coastal waters. For example, groundwater inputs have been linked to high N:P ratios in estuarine waters , high microphytobenthos production in intertidal flats [Waska and Kim, 2010], and algal blooms in coastal waters [Lee et al, 2010]. To obtain stronger evidence on the importance of SGD to marine budgets, investigations need to combine both bottom-up and top-down approaches.…”

“…Several studies emphasize that SGD is a major source of N and P to the coastal ocean and possibly an overlooked driver of eutrophication [e.g., Hu et al, 2006;Lee et al, 2010]. Other studies highlight that biogeochemical processes occurring in a STE can attenuate high N and P in contaminated terrestrial groundwater prior to discharge to the coastal ocean [Addy et al, 2005;Kroeger and Charette, 2008;Santoro et al, 2008].…”

Temporal variations of groundwater tables and implications for submarine groundwater discharge: a 3-decade case study in central Japan

“…The SGD flux increases over 3 decades; the dissolved inorganic nitrogen (DIN) flux in the SGD to Toyama Bay may increase. Thus, the submarine groundwater discharge is a significant source of nutrition, more than river water, to the coastal marine ecosystem of Toyama Bay (Zhang and Satake, 2003;Lee et al, 2010).…”

Nitrates in Groundwater Discharges from the Azores Archipelago: Occurrence and Fluxes to Coastal Waters

“…The concentration of nutrients from discharging groundwater is often higher than in coastal receiving waters [4], as shown for nitrates which present levels that are two to three orders of magnitude higher than typical coastal waters [5]. Therefore, transport of nutrients toward coastal waters through groundwater discharge can be a driver to the deterioration of water quality in these receiving environments, leading to ecosystem changes [6][7][8][9]. Besides agriculture-derived nutrient loads, sewage fluxes resulting from the increasing average population density in the near coastal-area, which nowadays is three times higher than the global average [10], also results in higher nutrient discharges to the coastal environment, leading toward the widespread eutrophication of coastal waters [11][12][13][14][15], as well as pointing out the need to reduce pollutant fluxes [16,17].…”