EFFECTS OF IN-SITU OIL BURNING ON COASTAL WETLANDS: SOIL TEMPERATURES AND REGROWTH OF MARSH PLANT SPECIES

摘要

Twenty-one full-scale in-situ burn experiments examined soil temperatures which marsh plants experience during insitu burning. Two hundred sixty four plant sods, including Spartina alterniflora, Spartina patens, Distichlis spicata, and Sagittaria lancifolia plants, were exposed in a 6 m diameter tank to burning diesel fuel or crude oil for intervals ranging from 400 s to 1400 s. Individual sods were instrumented with thermocouples to track soil temperatures throughout each burn. After the burns, the sods were returned to the greenhouse where plant recovery was monitored for up to a year. The water depth over the soil surface during in-situ burning was a key factor controlling plant recovery. For either 400 s or 1400 s burn exposures, soil temperatures did not exceed 50 °C and 70 °C for 10 cm and 2 centimeters of water overlying the soil surface, respectively. Ten and 2 centimeters of water overlying the soil surface were sufficient to protect all 3 types of marsh plants from burning impacts. In contrast, 2 cm of soil exposure to the fire during the burn resulted in high soil temperatures, with 80 °C to 100 °C at 0 cm to 0.5 cm below the soil surface. The effect of thermal stress on plant survival differed with species as 2 cm of soil exposure during burning impeded the post-burn recovery of the salt marsh grass, S. Alterniflora, and fresh marsh species, S. lancifolia. However, 2 cm of soil exposure during in-situ burning did not detrimentally affect the post-burn recovery of the brackish marsh grasses, S. patens and D. Spicata. For plants positioned 10 cm above the water level, peak surface soil temperatures ranged from 350 °C to 800 °C for 400 s and 1400 s burns, respectively. Thermal stress almost completely inhibited the post-burn recovery of S. alterniflora in this water level treatment.