Using Submerged Aquatic Vegetation to Establish Minimum and Maximum Freshwater Inflows to the Caloosahatchee Estuary, Florida

Species of submerged aquatic vegetation (SAV) are frequently used in the management of estuarine systems to set restoration goals, nutrient load reduction goals, and water quality targets. As human need for water increases, the amount of freshwater required by estuaries has become an increasingly important issue. While the science of establishing the freshwater needs of estuaries is not well developed, recent attempts have emphasized the freshwater requirements of fisheries. We evaluate the hypothesis that SAV can be used to establish freshwater inflow needs. Salinity tolerance data from laboratory and field studies of SAV in the Caloosahatchee estuary, Florida, are used to estimate a minimum flow required to maintain the salt-tolerant freshwater species, Vallisneria americana, at the head of the estuary and a maximum flow required to prevent mortality of the marine species Halodule wrightii at its mouth. For V. americana, laboratory experiments showed that little or no growth occurred between 10‰ and 15‰. In the field, lower shoot densities ($600\ \text{blades}\ {\rm m}^{-2}$) tend to occur at salinities greater than 12‰. Relationships between salinity in the estuary and discharge from the Caloosahatchee River indicated that flows $>8.5\ {\rm m}^{3}\ {\rm s}^{-1}$ would produce tolerable salinity (< 10‰) for V. americana and flows $