Tidal marshes and biogenic silica recycling at the land-sea interface

We studied the seasonal exchange of biogenic silica and dissolved silica between a freshwater and a saltwater tidal marsh and the nearby coastal waters. From both tidal marshes export of dissolved Si (DSi) was observed, while concurrently biogenic Si (BSi) was imported along with suspended solids. The export of DSi was highest (23.4 % and 123.8 % in the freshwater and saltwater marsh respectively) in summer when dissolved Si concentrations were low in the nearby coastal waters. Combined data from both marshes suggested a logarithmic decrease in DSi export with increasing DSi concentrations in the inundating waters. BSi import was observed year round in the freshwater marsh, but only in summer in the saltwater marsh. The results show that dissolved silica recycling from tidal marshes, both freshwater and saltwater, contributes significantly to estuarine Si availability in summer and provide new insight in the link between tidal marshes and secondary production in nearby coastal waters.