2-17474 p151-157 APMdj

Expansion of cattail, Typha domingensis , is perhaps the most conspicuous indicator of long-term degradation of the Florida Everglades. The spread of cattail in the Everglades has been tracked at a landscape scale through photointerpretation of aerial and satellite photography (Rutchey and Vilchek 1994, Jensen et al. 1995, Rutchey and Vilchek 1999 and Rutchey et al. 2008) and has provided an impetus for observational and experimental investigations of the causes and implications of this alteration of the wetland plant community and associated habitat (Davis 1991, Urban et al. 1993, Doren et al. 1997, Newman et al 1998, Hagerthey et al. 2008). These studies indicate elevated phosphorous inputs from agricultural runoff have been a primary driver of cattail expansion and associated replacement of the natural sawgrass and slough communities of the Everglades system. While expansive growth of T. domingensis is undesirable in the remnant Everglades (i.e., the Water Conservation Areas and Everglades National Park), this species is a vital component of stormwater treatment areas (STAs) that have been constructed to reduce the phosphorus inputs (Guardo et al. 1995) that have impacted the structure and function of the Everglades ecosystem. The STAs consist of compartmentalized flow ways with multiple cells ranging in size from 1001400 ha, and currently are managed to support either emergent or submerged aquatic vegetation (Burns and McDonnell 2003). Typha domingensis is the dominant species in emergent cells, where it provides for phosphorus uptake and storage primarily through the production of leaf litter biomass. Phosphorus inputs are removed from the water column by microbial communities associated with the slow decomposition of this cattail leaf litter, which simultaneously accumulates in a soil building process that buries the stores of sequestered phosphorus (Kadlec 2006, Richardson et al. 1997). Based on performance models and analyses (Burns and McDonnell 2003) the preferred configuration of Everglades STAs has emergent cells that discharge into cells with expansive beds of submerged aquatic vegetation (SAV). The SAV cells, which consist primarily of southern naiad, Najas quadalupensis , Chara spp. and pondweed, Potamogeton illinoensis, provide for phosphorus removal through direct uptake, an associated periphyton complex and by a coupled calcium coprecipitation/adsorption pathway (Dierberg et al. 2002b, Scinto and Reddy 2003). When positioned downstream of emergent cells that provide initial treatment of stormwater runoff with high P loads, SAV cells have the capability of reducing P concentrations to the low levels (Dierberg et al. 2002a, Knight et al. 2003) that are needed to achieve Everglades restoration goals (Davis and Ogden 1994). Establishment and maintenance of SAV cells has required frequent herbicide applications to control invasion by floating and emergent vegetation, including spread of T. domingensis from linear stands (emergent vegetation strips) that are maintained to buffer wind and wave energy, which can generate catastrophic disturbances to the SAV beds, particularly during tropical storm events. The SAV cells of Everglades STAs have shown evidence of phosphorus removal efficiencies (Juston and DeBusk 2006) that are desired (i.e., outflows of ≈ 10 μg/L), but have characteristics that may compromise their sustainability. For example, due to the relatively rapid rates of decomposition (i.e., 10 × faster than cattail) (Chimney and Pietro 2006) and the precipitation and deposition of calcium carbonate in SAV beds (Dierberg et al. 2002a,b), SAV cells accrete unstable, flocculent substrates that could eventually inhibit their ability to support growth of rooted SAV. Potential consolidation of these sediments is precluded by permanent inundation of SAV cells, which is needed to maintain SAV growth and to provide for sustained treatment of stormwater runoff. Alternative management strategies would allow for expanded growth of T. domingensis within SAV beds, or potentially in a managed rotation. Incursion of T. domingensis could help stabilize soils through more substantive root and rhizome growth and with the deposition of more recalcitrant (Osborne et al. 2007) and slowly decomposing leaf litter (Chimney and Pietro 2006). Thus, population growth characteristics of T. domingensis, including rates of expansion and associated attained densities, provide a basis for the formulation of management needs and potential alternatives for SAV cells of the Everglades STAs. 1 Vegetation and Land Management Department, South Florida Water Management District, 3301 Gun Club Road, West Palm Beach, FL 334164680, [email protected]. Received for publication April 17, 2009, and in revised form August 5, 2009.