Biogeochemistry and water balance of the Ottawa River basin.
Creators: name: Telmer, Kevin H.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1997
Subjects: subject: Physical Geography.

description: A physicochemical database is constructed by linking chemical and stable isotope analyses of the Ottawa River and its tributaries to properties of their catchment basins by overlaying maps of the properties and maps of the catchments utilizing a Geographic Information System (SPANS). Data include bedrock geology, forest type and extent, soil properties such as the organic carbon content of soils, land use, elevation, discharge, precipitation, and temperature. Deuterium ($\delta$D) and oxygen ($\delta\sp $O) isotopes for the Ottawa River and its tributaries in the spring range from $-$71 to $-$92$\perthous$ and $-$9.4 to $-$12.7$\perthous$ VSMOW, respectively. In the fall these values are $-$51 to $-$89$\perthous$ and $-$5.1 to $-$11.7$\perthous$ and the discharge weighted average at the mouth of the river, based on monthly samples, is $-$82 and $-$10.9$\perthous$. From these data, the average isotopic composition of precipitation that falls in the Ottawa River basin is calculated to be $-$103.8 and $-$14.5$\perthous$ for $\delta$D and $\delta\sp $O, respectively. Based on forty years of daily meteorological and discharge data and utilizing GIS, annual evapotranspiration for the Ottawa River basin is calculated to be 51%. Due to climatic and soil conditions, the upland silicate basins and lowland carbonate basins average 40 and 65% evapotranspiration, respectively. Combined evaporation and evapotranspiration calculations apportions 43% of the water losses in the Ottawa River basin to transpiration plus interception. Peaks in discharge occur in the spring due to snow melt, and in the late fall due to the cessation of transpiration by frost and are directly out of phase with precipitation inputs which are greatest during the summer. This implies that riverine baseflow is maintained exclusively by groundwater recharge during the non-growing season. Both the susceptibility of minerals to weathering and soil respiration rates increase downstream such that low-elevation-low-latitude tributaries, draining easily weathered carbonate terrains with thick productive high-pCO$\sb2$ soils, and containing areas with relatively high population density and intense agricultural land use, are characterized by: (1) high concentrations of total dissolved solids (TDS), DIC, Ca$\sp{2+}$, Mg$\sp{2+}$, Sr$\sp{2+}$ have $\delta\sp $C$\rm \sb{DIC}$ of approximately $-$8$\perthous$, and low $\rm \sp‡Sr/\sp†Sr$ ratios, representing a geogenic signal; and (2) high concentrations of Na$\sp+$ Cl$\sp-$, and K$\sp+$, representing a mixed anthropogenic and geogenic signal. Conversely, the sparsely, populated, high-elevation-high-latitude, chemically resistant, silicate shield catchments are characterized by low TDS, DIC, SO$\sb4\sp{2-}$, Ca$\sp{2+}$, Mg$\sp{2+}$, NO$\sb3\sp-$, Sr$\sp{2+}$, higher Si and Fe$\rm \sb{total}$, have $\rm \delta\sp C\sb{DIC}$ of roughly $-$16$\perthous$ and high $\sp‡$Sr/$\sp†$Sr ratios, and their anthropogenic signal is subdued to non-existent. Isotopic composition of dissolved inorganic carbon ($\rm \delta\sp C\sb{DIC}$) for the lowland carbonate and upland silicate tributaries is about $-$8 and $-$16$\perthous$, respectively. This suggests that (1) the source of DIC to the Ottawa River is soil respiration and carbonate weathering, (2) exchange with the atmosphere is unidirectional or volumetrically unimportant, and (3) in-river respiration and photosynthesis are not significant influences on the river carbon budget. (Abstract shortened by UMI.)