Concentrations of N and P in floodwater and uptake of 15N by Spartina alterniflora in oilcontaminatd mesocosms

Fertilization of salt marshes to enhance oil biodegradation may not be effective if nutrients in floodwater are rapidly removed by plants or adsorbed to sediments. Three 15N labeled fertilizers and two commercial nitrogen (N) and phosphorus (P) slow-release fertilizers were applied at rates of 75–210 kg N ha−1 with and without 40 kg ha−1 of supplemental P to oil-contaminated, flooded mesocosms growing Spartina alterniflora. Phosphorus concentrations in floodwater ranged between 0.05 and 2.82 μg P ml−1 39 days after P application. Urea and NO3−1 concentrations in floodwater were below detection limits by 2 weeks after N application, but NH4+ remained detectable for approximately 3 weeks. Approximately 20% of N from urea and ammonium fertilizers was recovered in shoots of Spartina, but only 7% from nitrate fertilizer was recovered. Frequent applications of fertilizers may be needed to maintain desirable nutrient concentrations in floodwater for enhancing oil biodegradation.