Resistance to drought affects persistence of alternative regimes in shallow lakes of the Boreal Plains (Alberta, Canada)

Abstract

Summary We examined how lake and landscape factors affected the persistence of alternative regimes in 23 predominantly fishless, shallow lake ecosystems over seven years in the Boreal Plains, Alberta, Canada. The alternative regimes were dominance by SAV (submerged aquatic vegetation) or by phytoplankton. The relationship between alternative regime persistence and a suite of lake and landscape variables were determined using regression tree analysis. We also compared the environmental variables and biological communities among alternative regimes using Kruskal–Wallis nonparametric tests and post hoc tests. Persistence of the SAV‐rich regime was best predicted by water level stability. Switches from a SAV‐rich regime to a phytoplankton‐rich regime have been attributed to drought, which concentrates total phosphorus (TP) and other solutes and increases turbidity, favouring phytoplankton dominance. Lakes with stable water levels are inferred as less sensitive to drought, and presumably experience less evapoconcentration during drought, which helps maintain the SAV‐rich regime. Lakes with more water level drawdown may also delay or inhibit SAV growth through physical disturbance. In contrast, the persistence of the phytoplankton‐rich regime was highest in lakes with higher TP and a lower proportion of surrounding wetlands. We postulate that lakes with less wetland in the buffer are more responsive to variations in precipitation because these systems have a smaller water storage capacity and lack peatlands that otherwise attenuate the effects of drought via shallow groundwater inputs. The relative persistence of lakes in the study area was related to lake and landscape factors that affect the relative sensitivity of the lakes to drought conditions. The biological community in these predominantly fishless lakes appears to play a weak role in maintaining the alternative regimes compared to fish‐bearing lake systems.

Recent Warming, Rather than Industrial Emissions of Bioavailable Nutrients, Is the Dominant Driver of Lake Primary Production Shifts across the Athabasca Oil Sands Region

“…Warmer temperatures can also alter the evaporation-to-precipitation ratio, and concentrate nutrients as well as ions and pollutants, with shallow lakes being particularly sensitive given their high surface area-to-volume ratio [ 29 ]. Precipitation-mediated processes affect transport of allochthonous materials into lakes, and influence water levels, water colour, and nutrient availability [ 11 , 30 , 31 ]. Reduced water levels can concentrate nutrients [ 32 ] and, depending on turbidity, promote light penetration to greater depths, thereby facilitating an expanded zone of aquatic primary production [ 33 ].…”

The legacy of large regime shifts in shallow lakes

“…; sensu Scheffer and Carpenter , Cobbaert et al. ). While top‐down effects, coupled with increased nutrient inputs over time, appear to be the main reason for perturbations in the modern ecology of shallow lakes, is the same true for the long‐term regime shifts in the lakes throughout this region?…”

“…Recent research in northern Alberta, Canada, has highlighted how precipitation and water‐level fluctuations can induce inter‐annual state shifts, however the authors suggest that subsequent change in nutrients is the ultimate driver of ecological change (Cobbaert et al. , ).…”

“…In addition to facilitating fish introductions, increased water level has also been shown to lead to a loss of macrophytes (Wallsten and Forsgren 1989), which could further promote a turbid state. Recent research in northern Alberta, Canada, has highlighted how precipitation and water-level fluctuations can induce inter-annual state shifts, however the authors suggest that subsequent change in nutrients is the ultimate driver of ecological change (Cobbaert et al 2014(Cobbaert et al , 2015.…”

Lake Water Levels and Associated Hydrologic Characteristics in the Conterminous U.S.

“…Water‐level fluctuations have been shown to influence lake temperature and stratification (Furey et al ; Nowlin et al ), which in‐turn affect within‐lake biogeochemical processes. In addition, nearshore habitat in the riparian and littoral zones are affected by water‐level fluctuations that can alter substrate composition (Furey et al ; Evtimova and Donohue ), littoral habitat complexity (Gaeta et al ), macrophyte coverage and composition (Wilcox and Meeker ; Beklioglu et al ; Cobbaert et al ). These habitat changes subsequently affect the structure and composition of macroinvertebrate (Brauns et al ) and fish assemblages (Gaeta et al ).…”