Upper Midwest Environmental Sciences Center
Identifying and quantifying environmental thresholds for ecological shifts in a large semi-regulated river
Giblin, Shawn. 2017. Identifying and quantifying environmental thresholds for ecological shifts in a large semi-regulated river. Journal of Freshwater Ecology, 32:1, 433-453, DOI: 10.1080/02705060.2017.1319431
Ecological shifts, between a clear anadensis-dominated state and a turbid state dominated by phytoplankton and high inorganic suspended solids, have been well described in shallow lake ecosystems. While few documented examples exist in rivers, models predict regime shifts, especially in regulated rivers with high water retention time. Here I quantiﬁed ecological shifts in a large, semi-regulated ﬂoodplain river during a transition from a turbid- to a clear-water state using water quality, aquatic vegetation and ﬁsheries data from a rigorous, standardized long-term data set. My ﬁndings indicate that signiﬁcant changes occurred in total suspended solids concentration, aquatic anadensis abundance, native and non-native ﬁsh biomass, ﬁsh functional feeding guild patterns, ﬁsh habitat guild assemblages and ﬁsh spawning guild assemblage patterns over a nearly 20-year period in Navigation Pool 8 of the Upper Mississippi River. Transitions in physical and biological indicators were examined to identify mechanisms underlying the ecological shifts. Environmental variables driving ﬁsh assemblage changes were identiﬁed (total suspended solids and aquatic vegetation) and management-relevant thresholds are presented. Awareness of management thresholds is critical for resource managers to implement measures to prevent the river from moving to a degraded state characterized by high non-native ﬁsh abundance and low predatory ﬁsh species abundance.
Aquatic macrophytes; ﬁsheries guilds; trophic shifts; Mississippi River; total suspended solids; ecological shift; alternative stable state