Snowmelt organic acidity episodes

The Chemistry of Weathering—Long-term Control of Acidification SHORT-TERM AND EPISODIC ACIDIFICATION. 4.1 High Discharge from Snowmelt and Rain Pulsed Release of SO4 and NOsfrom Soils Marine Aerosols Organic Acidity... 

Some evidence does exist that mechanisms other than atmospheric deposition contribute to N03" episodes, at least on a small scale. Rascher et al. (43), for example, showed that mineralization of organic matter in the soil during the winter months and subsequent nitrification contribute substantially to snowmelt N03 concentrations at one site in the Adirondacks. Schaefer and Driscoll (83) suggested that a similar phenomenon contributes to N03 pulses during snowmelt at 11 Adirondack lakes and that the contribution from mineralization is greater in low-ANC and acidic lakes. Murdoch and Stoddard (127) presented similar results for streams in the Catskill Mountains. Stottlemyer and Toczydlowski (184) also reported that mineralization contributes to snowmelt NO3" at a site on the upper peninsula of Michigan. It is not currently known how widespread this phenomenon is. 

Seasonal acidification is the periodic increase in acidity and the corresponding decrease in pH and ANC in streams and lakes. Episodic acidification is caused by the sudden pulse of acids due to spring snowmelt and large rain events in the spring and fall. Increases in nitrate are important to the occurrence of acid episodes and tend to occur when trees are dormant and therefore using less nitrogen. Short-term increases in acid inputs to surface waters can reach levels that are lethal to fish and other aquatic organisms. 

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