Water chemistry long-term trends

Palmer SM, Driscoll CT, Johnson CE. 2004. Long-term trends in soil solution and stream water chemistry at the Hubbard Brook Experimental Forest relationship with landscape position. Biogeochemistry 68(l) 51-70. 

Figure 14. Stream-water chemistry for control watershed No. 4 at the Fernow Experimental Forest in West Virginia, a, Seasonal pattern in N03 indicates both elevated baseflow concentrations and episodic increases during high-flow events in the spring and thus suggests that this watershed has reached Stage 2 of watershed N loss, b, The long-term trend suggests that substantial changes in N03 export have occurred over the past 2 decades. (Data are from...

Driscoll, C.T., Postek, K.M., Kretser, W. and Raynal, DJ. (1995). Long-term trends in the chemistry of precipitation and lake water in the Adirondack region of New York, USA. Water Air Soil Pollut.. 85, 583-588. 

Husar R. B., Sullivan T. J. and Charles D. F. (1991) Historical trends in atmospheric sulfur deposition and methods for assessing long-term trends in surface water chemistry. In Acidic Deposition and Aquatic Ecosystems (ed. D. F. Charles), pp. 65-82. Springer, Berlin. 

One factor that has been linked with long-term changes in the chemistry of surface waters and soils is the influence of variations in weather, particularly temperature and precipitation. The variability that fluctuations in weather induce in surface water chemistry (Hindar et al. 2003) may obscure the detection of trends resulting from reductions in SO/ deposition. On the other hand, use of long-term data may obscure shorter trends occurring within the series, particularly if the trends are not uni-directional. In this case, the detection of trends may be dependent on the time window used in the analysis, and can affect both the detection of the presence and the direction of a trend (Clair et al. 2002). For example, Clair et al. (1992) found significant decreases in SO/ concentrations in lakes in Nova Scotia, Canada, for the period 1983-1989, but with the addition of two more years of data, many of these trends were reversed (Clair et al. 1995). 

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