Response of Typha x glauca to Phosphorus, Hydrology, and Land Use in Lake Ontario Coastal Wetlands

Abstract

A combination of field sampling, a greenhouse growth experiment, and GIS was used to quantify the effects of phosphorus, hydroperiod, watershed land use, and wetland hydrogeomorphic classification on the invasive cattail Typha x glauca Godron across 18 Lake Ontario coastal wetlands. To determine T. x glauca density and frequency in coastal wetlands, vegetation was sampled in 1 - m2 quadrats along stratified random transects, each of which crossed three wetland vegetation zones when present ( submergent, emergent, and wet meadow). In each wetland, water samples were collected and shipped for laboratory analysis to determine total phosphorus concentrations in wetland waters. For each wetland, ESRI ArcGIS was used to determine its watershed area, watershed land use as croplands, and length of lotic surface waters. A greenhouse growth experiment using a full factorial random block design was used to investigate the effects of variable hydroperiod and phosphorus concentrations on T. x glauca biomass allocation. Multiple linear regressions revealed that frequency of occurrence of T. x glauca cannot be predicted by the individual and combined effects of wetland water mean total phosphorus (mg/L) or croplands in wetland watersheds (p = 0.345), However, these variables were predictors of increases in cattail density (p = 0.021). Increases in mean water total phosphorus concentrations can be predicted by the combined effect of wetland watershed croplands and total length of watershed lotic waters (p = 0.002), but individually, croplands were the only significant predictor (p = 0.001; lotic waters,p = 0.414). Wetland hydrogeomorphic classification did not predict cattail density (ANOVA, p = 0.389) or frequency (p = 0.665). Wetland mean total phosphorus concentrations increased from lacustrine to riverine wetland systems (p = 0.040) but there were no differences between riverine and barrier wetlands (p = 0.598) or between lacustrine and barrier wetlands (p = 0.169). A full factorial T. x glauca growth experiment with variable hydroperiods and phosphorus concentrations was performed over the course of eight weeks. As assessed by MANOVA, there was an increase in above- and below-ground biomass allocation for the simple main effects of hydroperiod (p < 0.000), phosphorus concentrations (p < 0.000), and their interaction (p < 0.000). Multiple pairwise interaction comparisons within block hydrology between nutrient treatments results revealed that as hydroperiod and phosphorus concentrations increased, the more pronounced the differences in their interaction became. Overall, results of this study demonstrated that increasing concentrations of phosphorus positively influenced cattail growth in a controlled setting as well as in Lake Ontario coastal wetlands. Although phosphorus positively influenced growth, hydrologic regime had the greatest influence on cattail growth and biomass allocation, with increased biomass as hydroperiod increased. Results could be used by Lake Ontario stakeholders or other land managers to craft policies that reduce phosphorus inputs into wetlands and manage hydrologic regimes in a manner that limits or reverses the spread of this invasive species.