Vegetation and arthropod responses to wastewater enrichment of a pine forset.

The effects of spraying secondary-treated wastewater on a young pine forest were studied in South Carolina, U.S.A. Soil, herb-shrub layer vegetation and arthropods were analyzed in control, low-spray and high-spray areas to determine the overall impact of four years of chronic nutrient and water enrichment. Spraying had no significant effect on soil organic matter and cation exchange capacity. Soil cation buildups did not occur and cation leaching was evident.Wastewater application produced a more mesic environment and the herb-shrub layer vegetation shifted to an earlier stage in succession. Plant diversity decreased significantly as a few rapidly-growing opportunistic species (e.g., Erechtites hieracifolia, Polygonum pensylvanicum) replaced the more diverse perennial herbshrub layer vegetation of the pine forest. Peak vegetation biomass levels doubled and net primary production rates were 10 times greater in high spray areas. Litter biomass levels, however, did not change significantly. Litter decomposition rates were significantly greater in treated areas which apparently offset the added litter resulting from increased plant production.Arthropod production increased 3-fold in treated areas. All herbivore guilds had higher biomasses that reflected seasonal changes in producer phenology. Total arthropod diversity increased despite the lower vegetation diversity in spray areas. Arthropod diversity apparently increased because of greater resource availability in treated areas.