A plant‐based index of biological integrity in permanent marsh wetlands yields consistent scores in dry and wet years

Abstract

ABSTRACT Plant‐based assessments can contribute to wetland conservation and management by providing a standardized method to monitor biological communities in relation to human activity. One major challenge, however, is that their measurements must be fairly insensitive to temporal variation in community composition, which can be difficult since marsh plant communities are known to be influenced by natural climatic cycles. Variation in the scores for an index of biological integrity (IBI) was evaluated in relation to plant community changes that occurred between years with differing precipitation inputs throughout the growing season (dry: 240 mm in 2008, 198 mm in 2009; wet: 324 mm in 2010, 329 mm in 2011). Species composition and IBI scores were measured by sampling macrophytes in the centre of the wet meadow zone at 47 semi‐permanent to permanent natural and constructed marshes. Non‐metric multidimensional scaling (NMS) ordinations revealed that although plant community composition shifted between dry and wet years, IBI scores were sensitive to only 21% of the total inter‐annual variation in species composition. The first NMS axis was positively correlated with IBI scores (r = 0.85) as well as several environmental parameters (r2 > 0.2), including dissolved organic carbon, total nitrogen, potassium, shoreline slope, and salinity. The wet meadow IBI also yielded consistent scores between dry and wet years (Spearman's rho = 0.82; Wilcoxon z‐score = 0.53, P‐value = 0.60) and was able to distinguish a change in biological condition among sites against a backdrop of natural variation (F‐test = 3.0, P < 0.001). These findings provide support for the continued use of plants as indicators of wetland condition in permanent northern prairie marshes, providing that the range in water levels is moderate. Copyright © 2013 John Wiley & Sons, Ltd.