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Yearly above-ground production estimates in natural, ditched, and impounded high salt marshes along the Indian River Lagoon in east central Florida ranged from 834.9 g/m2 in the impounded marsh to 2.316.5 g/m2 in the natural one. Mosquito control activities in the impounded marsh prior to the start of this study resulted in larger stocks of dead and litter biomass there during the first year than at the other two marshes. High soil temperature and salinity during the summer may have caused a decrease in production during that season. Annual tumover rales varied from 5.8 at the impounded marsh during the first year to 1.1 at the impounded marsh and at a nearby ditched marsh during the second year. Prduction was inversely correlated with flooding frequency. No significant differences were found in the rates of litter loss from any of the sites, but litter from the impounded marsh had greater organic content than litter from the open and the ditched marshes. The data suggest that flooding for mosquito control during the summer can curtail production, but the effects upon yearly production are minor, as production during the summer is naturally low.

The effects of reestablishing a marsh-lagoon connection through culverts upon the fish populations and the physical conditions of two impounded sub-tropical marshes are examined. After installation of the culverts, mean salinities in the two marshes increased from approximately 13 ppt to 25 ppt and pH from 7.1 to 7.3. The abundance of marsh resident species, particularly those that forage in the upper marsh, decreased significantly after connection, but utilization of the marshes by transient species increased by almost two orders of magnitude. Modification of the marsh hydroperiod seems to be most important in influencing the changes in the patterns of fish utilization, abundance, and diversity observed at the study sites.