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Hypersaline spring water (TDS ~ 85 g/L) and gas are escaping from the top of a calcite travertine mound on Anticosti Island. This mound is located in the Chaloupe River area above the Jupiter Fault which cuts through the Ordovician formations in the subsurface, including the oil and gas-rich Macasty Shale Formation. The CI content is approximately 3 times that of seawater, but the geochemical profile indicates it to be a Paleozoic basin brine (geogenic He = 2E-7 cc/cc) evaporatively enriched beyond halite saturation (Br:Cl molar ratio = 0.0022 [+ or -] 0.00013) that has been diluted by some 73 [+ or -] 6% with meteoric waters. Measurable tritium (3.4 TU) indicates this to be a mixture of modern and Holocene recharge. The radioiodine ([.sup.129]I < 10 million atoms/L) is a three-component mixture of geogenic and post-nuclear contributions with low levels in pre-nuclear Holocene recharge. Degassing at the vent (1% to 2% C[O.sub.2], PC[O.sub.2] = 0.02 arm, >90% [CH.sub.4]) provokes calcite precipitation and travertine mound formation. Methane comprises a thermo-catalytic component and a biogenic component produced at depth in the organic-rich Macasty Formation by reduction of surface-derived dissolved inorganic carbon (DIC; a[.sup.14]C = 3.5 pMC), producing enriched [delta][.sup.13][C.sub.DIC] values recorded in the travertine. The occurrence of basin-derived brine and gas discharging in association with the surface expression of the Jupiter fault implies that this fault provides a pathway for deep circulation of meteoric waters, likely driven by the relief on the island. Key words: hypersaline spring, basin brine, travertine mound, methane discharge, Jupiter fault, Anticosti De l'eau de source hypersaline et du gaz s'échappent au sommet d'un monticule de travertins composé de calcite sur l'île d'Anticosti. Ce monticule se trouve dans le secteur de la rivière Chaloupe au-dessus de la faille de Jupiter qui recoupe les formations ordoviciennes seulement en sous-surface, y compris les shales de la Formation de Macasty riche en pétrole et en gaz. La teneur en Cl est environ 3 fois supérieure à celle de l'eau de mer, mais le profil géochimique indique qu'il s'agit d'une saumure de bassin paléozoïque (He géogénique = 2E-7 cc/cc) enrichie par évaporation au-delà de la saturation en halite (rapport Br:Cl = 0, 0049) qui a été diluée par des eaux météoriques à 73%. Le tritium mesurable (3,4 TU) indique qu'il s'agit d'un mélange de recharge moderne et holocène. L'iode radioactif ([.sup.129]I < 10 millions atomes/L) est un mélange à trois composants de contributions géogéniques et postnucléaires avec de faibles niveaux dans la recharge holocène prénucléaire. Le dégazage à l'évent (1% à 2% C[O.sub.2], [P.sub.CO2] = 0.02 atm, >90% [CH.sub.4]) provoque la précipitation de la calcite et de la formation du monticule de travertins. Le méthane comprend un composant thermocatalytique dérivé du Macasty et un composant biogénique produit en profondeur dans la Formation de Macasty riche en matière organique par réduction du DIC dérivé de la surface (a[.sup.14]C = 3.5 pMC), produisant des valeurs [delta][.sup.13][C.sub.DIC] enrichies enregistrées dans le travertin. La présence d'une résurgence de saumure et de gaz provenant du bassin en association avec l'expression de surface de la faille de Jupiter implique que cette faille fournit une voie de circulation profonde des eaux météoriques. Mots-clés : source hypersaline, saumure de bassin, monticule de travertin, décharge de méthane, faille de Jupiter, Anticosti, 1. Introduction Discharges of saline water and gas in terrestrial settings are unusual geological features and considered to be the surface expression of deeply circulating fluids with a complex origin [...]

We use a long-term chemical and hydrologic record in combination with longitudinal sampling and high-frequency nitrate (N[O.sup.-.sub.3]) measurements from in situ sensors to describe temporal and spatial patterns of nitrogen (N) inputs and removal in the spring-fed Ichetucknee River (Columbia County, Florida) and to determine the hydrological, geomorphic, and biological factors that influence those dynamics. Over a 20-yr period of record, N[O.sub.3]-N removal averaged 118 kg N [d.sup.-1] (0.77 g N [m.sup.-2] [d.sup.-1]) over the upper 5 km of the Ichetucknee River. Three independent estimates of gross autotrophic N assimilation (from gross primary production, diel N[O.sup.-.sub.3] variation, and standing biomass) agreed closely but accounted for less than 20% of observed N removal. Longitudinal surveys indicate negligible or negative dissolved organic nitrogen and ammonium (N[H.sub.4.sup.+]) production, suggesting that denitrification is the predominant mechanism of N removal in this river. A positive relationship between discharge and the magnitude of N[O.sub.3]-N removal shows that interactions with the surrounding floodplain exert considerable influence at high flows, and longitudinal N[O.sup.-.sub.3] patterns indicate that N removal may be influenced by channel morphology. These results suggest a greater role for dissimilatory processes and hydrologic connectivity with hyporheic and floodplain sediments than has been previously recognized in highly productive spring-fed rivers of north Florida. While hydrologic variation is the primary determinant of variation in N[O.sup.-.sub.3] removal within the Ichetucknee River, comparison across systems indicates that biotic characteristics can cause significant deviation from predictions based on purely physical models of relationships between river size and N removal.

Abstract.--Large springs in the southwestern United States and northern Mexico have endemic spring-adapted fishes that have congeners, which are found inhabiting more eurythermal streams. In Texas, Gambusia nobilis, G. heterochir, [...]