Net ecosystem exchange (NEE) of tidal brackish wetlands in urban areas is largely unknown, albeit it is an important ecosystem service. High carbon dioxide (CO2) uptake of estuaries can potentially be achieved by creating conditions that foster CO2 uptake and sequestration. Thus, this study sought to assess NEE in a mesohaline tidal urban wetland that has been restored and determine the biophysical drivers of NEE in order to investigate uptake strength and drivers thereof. Beginning in 2009, NEE was measured using the eddy covariance technique in a restored urban estuarine wetland. Maximum NEE rates observed were −30 µmol m−2 s−1 under high light conditions in the summer. Monthly mean NEE showed this ecosystem to be a CO2 source in the winter, but a CO2 sink in summer. Conditional Granger causality showed the influence of net radiation on half daily to biweekly timescales on NEE and the influence of water level at half daily time scales. The overall productivity of this wetland is within the expected range of tidal brackish marshes and it was a sink for atmospheric CO2 in two out of the 3 years of this study and had a continued increase over the study period.