Response of Typha to Phosphorus, Hydrology, and Land Use in Lake Ontario Coastal Wetlands and a Companion Greenhouse Study

Abstract

Loss of Great Lakes wetlands due to changes in land use, hydrology, nutrient inputs, and invasive species led to the need for studies involving physical factors that influence growth of invasive cattails (Typha). Thus, in 18 Lake Ontario coastal wetlands, we sampled vegetation along stratified random transects and collected water samples for total phosphorus (TP) analyses. We used GIS to determine watershed area, percent land use as croplands, and length of lotic surface waters entering wetlands. A greenhouse growth experiment with a full factorial random block design was used to investigate the effects of variable hydroperiod and phosphorus concentrations on T. × glauca biomass changes. Correlation analyses of wetland data revealed that TP in field studies was related to percent croplands but not lotic length; mean percent Typha was not related to TP. In the growth experiment, above- and below-ground biomass increased significantly for simple main effects of hydroperiod and phosphorus concentrations. Multiple pairwise interaction comparisons between hydrology and nutrient treatments showed that effects of phosphorus concentration were present only at longer hydroperiods. Lack of correlation between Typha and phosphorus concentrations in the field was likely due to the overwhelming effect of water-level regulation on Lake Ontario. The greenhouse study demonstrated that increasing concentrations of phosphorus positively influenced cattail growth in a controlled setting. Although phosphorus positively influenced growth, hydrologic regime had the greatest influence on cattail growth, with increased biomass as hydroperiod increased. More natural hydrology and management of phosphorus inputs may help limit spread of Typha.