Nutrient dynamics in marsh sediments contaminated by an oil spill following a flood

Flood waters during October 1994, ruptured a group of pipelines that released gasoline, diesel fuel and crude oil in to the San Jacinto River near Houston, Texas, This mixture travelled downstream where it ignited inside a flooded house. The resulting fire burned for seven days. A petroleum-contaminated wetland, designated as a research area, received no cleanup during the spill response. Sediment samples collected over a period of one year were analysed for nutrients and petroleum hydrocarbons. Natural levels of the nutrient analytes were estimate by monitoring the values over a year following the event. Nutrients monitored include ammonium (plus ammonia), nitrate (plus nitrite), available phosphorus, total Kjeldahl nitrogen and total phosphorus in Kjeldahl digest. Available nutrient concentrations were initially high and then declined to presumable background levels of approximately 10 ppm P, 5 ppm N, and 0.5 ppm N for available phosphorus, phosphorus levels were as high as 75 ppm P during December, 1994. Available nutrient levels declined over the period of the study indicating that the system has been enriched. Theories about the source of enrichment include deposition of either nutrient rich sediments from the flood or ashes from the fire. Also, disturbance due to site construction activities involved in building the sampling structures could have contributed to the perturbations observed. During the study, the sum of total petroleum target analytes decreased from approximately 160 ppm to less that 10 ppm. Correlation coefficients of 0.76, 0.75, -0.67, and -0.63 were found between the sum of target analytes and ammonium, available phosphorus, total Kjeldahl nitrogen, and total phosphorus in Kjeldahl digest, respectively. These correlation coefficients suggest interdependency between nutrient levels and degradation of the petroleum. The data suggest that the naturally elevated nutrient levels provided favourable conditions for the degradation of the oil. (Author)