Nitrification, Anammox and Denitrification along a Nutrient Gradient in the Florida Everglades

The Florida Everglade wetland had been historically oligotrophic system. However, Everglade have received drainage water enriched with phosphorus (P) fertilizer over past 40 years, which has created the gradient of P content, TN:TP ratio, the pool and size of microbial population in the Water Conservation Area 2A (WCA-2A) in the northern part of Everglade ecosystem. Until recent, there was little information on how the nutrient change caused by P enrichment affected the inorganic N transformation rates and relationships between them in the Everglade wetland ecosystems. Thus, we studied the relationships between nitrification, anammox and denitrification rates in along a sediment P gradient in WCA-2A, a nutrient affected area of the Florida Everglades. The P-enriched site exhibited higher nitrification rates than did the transitional and un-impacted sites, and their activities were regulated by ammonium concentrations. Bacterial ammonia monooxygenase subunit A ( amoA : AOB) nitrifiers were more numerous than archaeal amoA (AOA) nitrifiers and likely contributed most to sediment nitrification rates, which had positive correlations with ammonium concentration. Enhanced nitrification rate might supply more nitrite to anammox bacteria and enhance their activities, implying the possibly presence of coupled nitrification-anammox processes in wetland ecosystems. For nitrate reduction, labile organic carbon contents were positively correlated with sediment denitrification rates and abundances of nirS and nirK genes, and their activities and gene abundances were higher in the P-impacted and transitional sites than in the un-impacted site. Denitrification rates were much higher than anammox rates in sediment samples; however, the reverse was true in the water column. In summary, this study demonstrated that P-enrichment might enhance inorganic N transformation rates in wetland sediment ecosystem; however denitrification and anammox rates in the water ecosystems was not significantly affected by P-enrichment factors. In addition, the relative importance for N removal between denitrification and anammox was different from the water and sediment ecosystems in the Everglades wetland.