Spatial and temporal patterns of bioindicator mercury in pennsylvania oak forest.

We monitored spatial and temporal patterns of total Hg in forest bioindicators to assess possible local, regional, and global changes in atmospheric Hg deposition. Total Hg concentrations were monitored in leaves and fresh litterfall of northern red oak ( L.), on an epiphytic moss ( Hedw.) on northern red oak stems, and in surface soil organic matter (O and O horizons) in Pennsylvania oak-dominated forests. Variously configured plots were used to monitor Hg deposition near local coal-fired generating stations and an industrial city and along an extended regional transect. Linearly decreasing temporal trends in Hg concentrations occurred in leaves, litterfall, moss, and soil O and O. Mean annual Hg concentrations were often greater near local emissions sources compared with remote areas, especially in the initial monitoring period. Decreasing time trends for different impact areas tended to converge due to greater rates of Hg decrease where initial bioindicator Hg levels were higher. Fresh litter and soil O showed the greatest overall potential as Hg bioindicators. We conclude that Hg deposition has been significantly decreasing over time throughout the study area as a result of locally and regionally declining Hg emissions. Reductions in Hg emissions are likely a co-benefit of the 1990 Clean Air Act regulations and changing industrial activities. Recent leveling of several bioindicator Hg time trends may foretell a shift in Hg depositional patterns. Mercury monitoring studies such as this fulfill a need for documenting local and regional effects of emissions reduction.

Influence of Cryphonectria parasitica Basal Cankers on Radial Growth of Scarlet Oak in Pennsylvania.

Basal cankers induced by Cryphonectria parasitica (=Endothia parasitica) occur throughout the natural range of scarlet oak (Quercus coccinea) within Pennsylvania. Because colonization of scarlet oak is thought to be a long-term host/pathogen relationship, analyses were conducted to investigate effects of basal cankers on radial growth (expressed as area increment) at 1.4 m, breast height (BH). Moderately cankered oaks grew more slowly at BH than did noncankered trees. However, severely cankered scarlet oaks generally exhibited greater radial growth at BH than did noncankered trees. This apparent anomaly likely reflects stimulated growth at BH due to the fungal infection.