Oil bioremediation in salt marsh mesocosms as influenced by nitrogen, phosphorus, and bacterial seeding

Abstract

Glasshouse experiments were conducted to determine the effects of N and P fertilization and bacterial seeding on crude oil degradation in salt marsh mesocosms containing marsh soil and Spartina alterniflora. Fertilization with urea, NH4, and N03 applied at 75 or 150 kg N ha-1 did not enhance oil degradation during 82 d of experimentation in continuously flooded mesocosms during winter (temperature range of 17-30'C). Phosphorus applied at 40 kg P ha-' with or without N significantly enhanced oil degradation during winter. Phosphorus applied alone led to 46% of the applied total petroleum hydrocarbons (TPH) remaining in mesocosms while 57% of the applied TPH remained in the treatment not receiving P. Two slow-release fertilizers containing N and P, Max Bac and Inipol, enhanced oil degradation more than other N fertilizers applied with P. During summer (temperature range of 27-42'C), Max Bac and P applied at 100 kg N ha-' and 40 kg P ha-' did not enhance oil degradation in continuously or alternately flooded mesocosms during the 40 d of experimentation. Continuously flooded mesocosms averaged 28% TPH remaining while alternately flooded mesocosms averaged 49%. Bacterial seeding proved ineffective in enhancing oil degradation. Five commercial bioremediation products did not enhance oil degradation compared to uninoculated controls in continuously flooded mesocosms during 33 d of experimentation during spring (temperature range of 27 42'C) or in alternately flooded mesocosms during 41 d of experimentation during summer. Max Bac and P applied at 100 kg N ha-] and 40 kg P ha-I enhanced oil degradation during spring but not during summer. The use of 15 N techniques during winter revealed that approximately 23% of the applied urea-N and NH4-N was taken up by S. alterniflora compared to 8% of the applied N03-N. Further studies may be needed to assess the effectiveness of N and P fertilization in natural field conditions.