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

Flood waters during October, 1994, ruptured a group of pipelines that relea sed gasoline, diesel fuel and crude oil into the San Jacinto River near Hou ston, Texas. This mixture traveled downstream where it ignited inside a flo oded house. The resulting fire burned for seven days. A petroleum-contamina ted wetland, designated as a research area, received no cleanup during the spill response. Sediment samples collected over a period of one year were a nalyzed for nutrients and petroleum hydrocarbons. Natural levels of the nut rient analytes were estimated by monitoring the values over a year followin g the event. Nutrients monitored include ammonium (plus ammonia), nitrate(p lus nitrite), available phosphorus, total Kjeldahl nitrogen and total phosp horus 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, ammonium, and nitra te, respectively. Average ammonium concentrations were as high as 40 ppm N and average available phosphorus levels were as high as 75 ppm P during Dec ember, 1994. Available nutrient levels declined over the period of the stud y indicating that the system had been enriched. Theories about the source o f enrichment include deposition of either nutrient rich sediments from the flood or ashes from the fire. Also, disturbances due to site construction a ctivities involved in building the sampling structures could have contribut ed to the perturbations observed. During the study, the sum of total petrol eum target analytes decreased from approximately 160 ppm to less than 10 pp m. Correlation coefficients of 0.76, 0.75, -0.67, and -0.63 were found betw een the sum of target analytes and ammonium, available phosphorus, total Kj eldahl nitrogen, and total phosphorus in Kjeldahl digest, respectively. The se correlation coefficients suggest interdependency between nutrient levels and degradation of the petroleum. The data suggest that the naturally elev ated nutrient levels provided favorable conditions for the degradation of t he oil.