『Abstract
　Nutrient input through submarine groundwater discharge (SGD) rivals river inputs in certain regions and may play a significant role in nutrient cycling and primary productivity in the coastal ocean. In this paper, we review the key factors determining the fluxes of nitrogen (N) and phosphorus (P) associated with SGD and present a compilation of measured rates. We show that, in particular, the water residence time and the redox conditions in coastal aquifers and sediments determine fluxes and ratios of N and P in SGD. In many coastal groundwater systems, and especially in contaminated aquifers, N/P ratios exceed those in river water and are higher than the Redfield ratio. Thus, anthropogenically driven increases in SGD of nutrients have the potential to drive the N-limited coastal primary production to P-limitation. River input of N and P to the coastal ocean has doubled over the past 50 yr. Results of a dynamic biogeochemical model for the C, N and P cycles of the global proximal coastal ocean (which includes large bays, open water part of estuaries, deltas, inland seas and salt marshes), suggest that this has led to a factor 2 increase in primary production and biomass and a decline in water column N/P ratios, i.e. the system has become more N-limiting. With the same model, we show that an increase of SGD-N fluxes to 〜0.7-1.1 Tmol yr^-1 (with a SGD N/P ratio of 100; equal to 〜45-70％ of pre-human riverine N-inputs) is required to drive the coastal ocean to P-limitation within the next 50 yr.

Keywords: Nitrogen; Phosphorus; Submarine groundwater discharge』

1. Introduction
2. Controls on the SGD flux of N and P to coastal waters
　2.1. Hydrology of coastal aquifers and occurrence of SGD
　2.2. Groundwater redox chemistry
　2.3. Nitrogen and phosphorus in groundwater
　2.4. The saltwater-freshwater mixing zone
　2.5. Nitrogen and phosphorus dynamics and ratios in the mixing zone
3. Rates of submarine groundwater discharge of N and P and the effects on a local and regional scale
4. Effect of SGD inputs of nutrients on a global scale: a model approach
　4.1. Model description
　4.2. Human perturbation of river inputs of nutrients
　4.3. Groundwater input of nutrients
5. Conclusions
Acknowledgements
References

• 『A compilation of world-wide SGD seepage measurements (Tanigichi et al., 2002) shows that rates range from 0.03 to 454 m yr^-1 but mostly fall below 36 m yr^-1.』
• 『Current estimates of the global flux of ground water entering the ocean through SGD vary widely, ranging from 0.01 to 10％ of the surface water runoff (Church, 1996; Garrels and Mackenzie, 1971; Taniguchi et al., 2002; Zektser and Loaiciga, 1993). Our best estimate is 5％ of the total global water flux or 1.85 Tm³ yr^-1.』(67p)

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• Church,T.M.(1996): An underground route for the water cycle. Nature, 380(6575), 579-580.
• Garrels,R.M. and Mackenzie,F.T.(1971): Evolution of Sedimentary Rocks.
• Taniguchi,M., Burnett,W.C., Cable,J.E. and Turner,J.V.(2002): Investigation of submarine groundwater discharge. Hydrological Processes, 16(11), 2115-2129.
• Zekster,I.S. and Loaiciga,H.A.(1993): Groundwater fluxes in the global hydrologic-cycle-past, present and future. Journal of Hydrology, 144(1-4), 405-427.