『Abstract
Surface water samples from the St. Lawrence River were collected
in order to study the processes controlling minor and trace elements
concentrations (Al, Fe, Mn, Cd, Co, Cu, Ni ad Zn), and to construct
mass balances allowing estimates of the relative importance of
their natural and anthropogenic sources. The two major water inputs,
the upper St. Lawrence River, which drains waters originating
from the Lake Ontario, and the Ottawa River were collected fortnightly
over 18 months. In addition, other tributaries were sampled during
the spring floods. The output was monitored near Quebec City at
the river mouth weekly between 1995 and 1999. Dissolved metal
concentrations in the upper St. Lawrence River carbonated waters
were lower than in the acidic waters of the tributaries draining
the crystalline rocks of the Canadian shield and the forest cover.
Biogeochemical and hydrodynamic processes occurring in Lake Ontario
drive the seasonal variations observed in the upper St. Lawrence
River. Biogeochemical processes relate to biological uptake, regeneration
of organic matter (for Cd and Zn) and oxyhydroxide formation (for
Mn and Fe), while hydrodynamic processes mainly concern the seasonal
change in vertical stratification (for Cd, Mn, and Zn). In the
Ottawa River, the main tributary, oxyhydroxide formation in summer
governs seasonal patterns of Al, Fe, Mn, Cd, Co and Zn. The downstream
section of the St. Lawrence River is a transit zone in which seasonal
variations are mainly driven by the mixing of the different water
masses and large input of suspended particulate matter from erosion.
The budget of all dissolved elements, except Fe and Zn, was balanced,
as the budget of particulate elements (except Cd and Zn). The
main sources of metals to the St. Lawrence River are erosion and
inputs from tributaries and Lake Ontario.Direct anthropogenic
discharges into the river accounted for less than 5% of the load,
except for Cd (10%) and Zn (21%). The fluxes in transfer of dissolved
Cd,Co, Cu and Zn species from the river to the lower St. Lawrence
estuary were equal to corresponding fluxes calculated for Quebec
City since the distributions of dissolved concentrations of these
metals versus salinity were conservative. For Fe, the curvature
of the dilution line obtained suggests that dissolved species
were removed during early mixing.』
1. Introduction
2. Environmental settings
3. Sampling methods, filtration and analyses
4. Results and discussion
4.1. End-member sources
4.1.1. Hydrograms and sedimetograms
4.1.2. Minor elements (Al, Fe and Mn)
4.1.3. Trace elements (Cd, Co, Cu, Ni and Zn)
4.2. River mouth
4.2.1. Hydrogram and sedimentogram
4.2.2. Minor elements (Al, Fe and Mn)
4.2.3. Trace elements (Cd, Co, Cu, Ni and Zn)
4.3. Mass balances
5. Summary and conclusion
Acknowledgments
Appendix A. Metal flux calculations
A.1. Dissolved metals
A.1.1. Sampled fluxes
A.1.2. Unsampled tributaries
A.2. Particulate metals
A.2.1. Sampled fluxes
A.2.2. Unsampled tributaries
A.3. Suspended matter
References