Resiliency and Recovery of Aquatic Vegetation Following Scouring Floods in Two First-Magnitude Springs, Missouri, USA

Abstract

This study quantifies the loss of vegetative cover in Alley and Big springs, Missouri, following a catastrophic, ‘100 year’ flood, and documents their subsequent recovery. Foliar cover of aquatic vegetation was measured in each spring along six transects, each having three sample cells (1 m2, N = 18). Species diversity analyses included taxa richness, Shannon’s diversity index, and Simpson’s diversity index, which were expressed as the effective number of species (S, He, and De). Species metrics were calculated as individual species frequency (ISF), percent foliar cover (PFC), and species importance value (SIV). Post-flood community diversity metrics (S, He, and De) for the springs were largely not significant for most measures (Epps–Singleton test p > 0.05). This suggests that they may not be sufficiently sensitive for detecting change in springs when the sample size is small. Bare substrate increased significantly at Big Spring post-flood (mean = 87.50%; Epps–Singleton test, p = 0.02), but not at Alley Spring (Epps–Singleton test, p = 0.42). Various alga taxa generally exhibited increased frequency and abundance following the flood, which is reflected in their overall higher SIVs. Most hydrophyte species at Alley Spring showed a marked decline compared to the pre-flood average, only to substantially increase in the last year of sampling, thus maintaining their approximate species important values relative to their pre-flood averages. Several hydrophyte species at Big Spring showed significant decreases (Epps–Singleton test p < 0.05) in their respective community metrics, and recovery had not returned to pre-flood levels on the last sampling date. This study showed that loss and recovery of aquatic vegetation in high-magnitude Ozark springs following flooding are a function of flood intensity as well as substrate size and retention, and proximity to the receiving stream.