Episodic nature of wet deposition of acidic material at a site in south-east England

Abstract

The causal factors for episodic deposition of acidic material in rainfall cannot be fully understood from conventional daily network data. A brief review of the meteorological conditions leading to episodes is given. A definition of 'episodicity' was considered and applied to a 6 month data set collected at high temporal resolution using a microprocessor based acid rain monitor at a site in south-east England. The deposition was highly episodic for all of the measured variables when data from individual rain events were considered. Combining the data into daily averages resulted in changes of episodicity classification for several chemical species. A large percentage of the total deposition recorded during the field experiment occurred in a 5 day period when there was an independent report of ecological damage at other locations in England. Nitrate deposition showed the highest degree of episodicity with 51% of the 6 month total occurring during the 5 day episode. Meteorological details of the transport and wet deposition processes during this period were examined. Back trajectory analysis indicated that the episode was the result of pollutant loading in eastern and central Europe of the air masses reaching the site together with an absence of upwind precipitation scavenging

An Experimental Study of Factors Underlying Differential Ecosystem Recovery From Acidification of Upland Waters

“…In addition to these four explanatory frameworks it is possible to add another: 5. The "episodicity" hypothesis: that chemical-biological differentials can be explained in terms of infrequent but extreme events, so that sites that are prone to great fluctuations in acid deposition over time may have retarded recovery from acidification (Beverland et al, 1997;Jamieson, 1998). Each of these five hypotheses will be discussed in turn.…”