Cross-walking state and federal macrophyte assessment methodologies for determining wetland condition

Background/Question/Methods

The US Environmental Protection Agency with additional federal, state and tribal partners initiated the National Wetland Condition Assessment (NWCA) 2011 in an effort to establish a baseline for wetland condition across the US.  Florida assessed 67 wetlands from coastal mangroves in the Florida Keys to bottomland swamps in the western panhandle. A subsample of these wetlands (n=19) were identified for additional analysis. The Florida Wetland Condition Index (FWCI), an index of biological integrity, compares wetland plant community structure to reference standard condition. Applying quantitative indices developed for FWCI evaluates macrophyte presence and absence to determine wetland condition. The wetland subsets were identified as palustrine emergent or forested and were stratified across a gradient of anthropogenic influence, embedded in landscapes dominated by silviculture (n=6), agriculture (n=3), urban (n=2), mining (n=1) and reference (n=7) land use categories. Under NWCA protocol, assessment areas (AAs) are 40 meter radius circles randomly selected from an existing wetland Geographic Information System data layer.  NWCA data were collected in nested quadrats totaling an area of 500 m². FWCI utilized belted transects within the boundary of the NWCA AA for a total area of 160m².

Results/Conclusions

While many sites had similar total richness values, the two assessments shared less than 75% of the same species 50% of the time. One site had as many as 47 unique species detected and 30% of sites had over 20 unique species per method. The difference in total area analyzed between the two methods is 340m²; however, pairwise wetland condition was significantly linearly correlated (R² = 0.87).  Bray-Curtis distance measures further emphasized wetland condition scores were not impacted by differences in species detection. This suggests using FWCI indices can provide consistent analysis results even when macrophyte detection is inconsistent. One site had differences in total richness when a transect crossed an ecotone yielding different condition values by assessment method. This suggests placement of the AA can significantly affect results. This study is important to applied aspects of wetland assessment for tracking compliance with Florida’s policies concerning no net loss of wetland function.  By finding statistically similar results between the two assessment methods, recommendations can be made to stream line field efforts by minimizing area sampled and time.