『Abstract
Hydrologists have long been concerned with the interface of groundwater
flow into estuaries, but not until the end of the last century
did other disciplines realize the major role played by groundwater
transport of nutrients to estuaries. Mass balance and stable isotopic
data suggest that land-derived NO3, NH4, and dissolved organic N do enter estuaries
in amounts likely to affect the function of the receiving ecosystem.
Because of increasing human occupancy of the coastal zone, the
nutrient loads borne by groundwater have increased in recent decades,
in spite of substantial interception of nutrients within the land
and aquifer components of watersheds. Groundwater-borne nutrient
loads have increased the N content of receiving estuaries, increased
phytoplankton and macroalgal production and biomass, decreased
the area of seagrasses, and created a cascade of associated ecological
changes. This linkage between land use and eutrophication of estuaries
occurs in spite of mechanisms, including uptake of land-derived
N by riparian vegetation and fringing wetlands, “unloading” by
rapid water removal, and direct N inputs to estuaries, that tend
to uncouple the effects of land use on receiving estuaries. It
can be expected that as human activity on coastal watersheds continues
to increase, the role of groundwater-borne nutrients to the receiving
estuary will also increase.』
1. Background
2. Nutrient transport by groundwater
2.1. Concentrations of N in groundwater
2.2. Volume of groundwater flow
2.3. Nitrogen loads from land
3. Effects of land use on groundwater nutrients
3.1. Concentrations
3.2. Nitrogen stable isotopic signatures
4. Effects of land-derived nitrogen loads on estuaries
4.1. Effects on nitrogen concentrations in water of receiving
estuaries
4.2. Effects on estuarine biota
5. Modifications to degree of coupling between land and estuary
5.1. Riparian vegetation
5.2. Fringing wetlands
5.3. Estuarine water residence times
5.4. Other direct nitrogen inputs
Acknowledgements
References