A network model shows the importance of coupled processes in the microbial N cycle in the Cape Fear River Estuary

► We constructed a N mass balance network model for the Cape Fear River Estuary. ► Ammonium plays the most central role in N cycling in the Cape Fear River Estuary. ► We estimated the strength of coupling of N cycling processes using environ analysis. ► Coupled nitrification-denitrification comprises nearly half of denitrification loss. ► Coupled nitrification-anammox may be an important N removal pathway in estuaries.