Step-wise analysis of precipitation and river chemistry trends in Atlantic Canada

Abstract

Monotonic trends in hydrogen (H⁺), sulfate (SO₄ ⁻²)and nitrate (NO₃ ⁻) were calculated using non-parametric techniques at four Canadian Air and Precipitation Monitoring Network (CAPMoN) sites and six nearby river systems in Atlantic Canada for the period 1983–1991. Over the whole interval, there were increasing nitrate concentrations and deposition trends at three of the four monitoring sites and no trends in SO₄ ⁻² or H⁺ concentrations and deposition. We found that SO₄ ⁻² concentrations increased at three of our six river sites, NO₃ ⁻ increased at one site and H⁺ decreased at one site. River exports showed no trends in the entire study interval. The series were also analyzed in five year time windows, incremented by six months, to see if changes in trend presence or direction would occur, compared to trend analysis over the entire interval. We show that while trends in river chemistry do not contradict deposition patterns, the changes that occurred were not necessarily in step. We also found that the trends which we measured were the result of short-term changes as opposed to long-term continuous monotonic trends. The time lag between precipitation and chemistry trend changes seemed longer in basins dominated by softwoods than by hardwoods.