Hydrology and Salinity of a Subarctic Coastal Marsh

Abstract

<p>The hydroIogical and salinity characteristics of a James Bay coastaI marsh were studied to determine the processes which govern water and salt movement. A water balance performed between May and August 1984 showed that rainfall (429 mm) and overland flow from Inland marshes (65 mm) were the important inputs, while streamflow (307 mm) and evaporation (293 mm) were the major losses. Streamflow was extremely variable, and was strongly dependent on the marsh water storage level. Evaporation generally occurred at the potential rate, and groundwater flow had no measurable influence on the water balance.</p> <p>Groundwater was very important to the salinity regime, however, because it was found to contain relict salt. Pore waters of the clayey Tyrrell Sea sediments which underlie this marsh, and most of the Hudson Bay Lowland had a relative abundance of the heavy isotopes of oxygen and hydrogen, indicating the deep pore waters do not originate from the present day meteoric or tidaI waters, but were from the ancient Tyrrell Sea. The relatively high salinity of the fossil salt at depth (20 to 25 kg mˉ³) and the low surface salinity (0 to 2 kg mˉ³) causes pronounced upward moIecuIar diffusion. Near the surface of the marsh, the more permeable upper layer of sediment and peat allow salt to be transported by groundwater flow aIso. This causes salt to be leached from the raised beach ridges, and discharged into the interridge depressions. A modeI of the short-term discharge of this salt indicates that the variability of salt export is almost exclusively dependent on rainfall and evaporation, which determine the rate of water outflow, hence saIt export.</p> <p>A model of the long term salt and groundwater transport processes along a transect perpendicular to the coast produced a moderate to good fit with the observed data. The modeI verifies the significant role of the marsh topoqraphy on the rate and direction of saIt transport in groundwater, and thus the spatial distribution of salt.</p>