A comparative examination of recent changes in nutrients and lower food web structure in Lake Michigan and Lake Huron

Abstract

The lower food webs of Lake Huron and Lake Michigan have experienced similar reductions in the spring phytoplankton bloom and summer populations of Diporeia and cladocerans since the early 2000s. At the same time phosphorus concentrations have decreased and water clarity and silica concentrations have increased. Key periods of change, identified by using a method based on sequential t-tests, were 2003-2005 (Huron) and 2004-2006 (Michigan). Estimated filtration capacity suggests that dreissenid grazing would have been insufficient to directly impact phytoplankton in the deeper waters of either lake by this time (mid 2000s). Despite some evidence of decreased chlorophyll:TP ratios, consistent with grazing limitation of phytoplankton, the main impact of dreissenids on the offshore waters was probably remote, e.g., through interception of nutrients by nearshore populations. A mass balance model indicates that decreased phosphorus loading could not account for observed in-lake phosphorus declines. However, model-inferred internal phosphorus dynamics were strongly correlated between the lakes, with periods of increased internal loading in the 1990s, and increased phosphorus loss starting in 2000 in Lake Michigan and 2003 in Lake Huron, prior to dreissenid expansion into deep water of both lakes. This suggests a limited role for deep populations of dreissenids in the initial phosphorus declines in the lakes, and also suggests a role for meteorological influence on phosphorus dynamics. The high synchrony in lower trophic level changes between Lake Michigan and Lake Huron suggests

Ice‐Free Radiative Convection Drives Spring Mixing in a Large Lake

“…While Lake Michigan experiences partial ice cover (Figure ), the comparatively low latitude (i.e., high winter irradiance) means that ice cover is generally small, and getting smaller with climate change (Wang et al, ), negating the ice albedo effect described above. Additionally, the invasion and profundal expansion of quagga mussels in the past two decades has increased water clarity in both lakes to the point where secchi depths now regularly exceed 20 m (Barbiero et al, ), allowing sunlight to penetrate and directly heat the water to great depths. Together, these factors dramatically increase the overwinter heat input to the lakes, allowing ice‐free radiative convection to play a potentially larger role in winter mixing for Lakes Michigan and Huron than for other large lakes around the world.…”

“…This is especially true during the vernal turnover in dimictic lakes, when near-surface waters below the temperature of maximum density (T MD ≈ 4°C) experience radiative convection; as daily radiative (solar) heating increases water temperatures throughout the photic zone, these heavier, gravitationally unstable surface waters sink, driving enhanced turbulent mixing. Large radiative heat fluxes in the Laurentian Great Lakes, attributed to high water clarity (Barbiero et al, 2018) and low ice cover (Wang et al, 2011), make them particularly susceptible to this phenomenon. Large radiative heat fluxes in the Laurentian Great Lakes, attributed to high water clarity (Barbiero et al, 2018) and low ice cover (Wang et al, 2011), make them particularly susceptible to this phenomenon.…”

“…Recent work has established radiative convection as a dominant mixing mechanism in ice‐covered lakes (Bouffard et al, ; Jonas, Terzhevik, et al, ; Yang et al, ), but its potential importance in nearly ice‐free dimictic lakes has been largely speculative (e.g., Boyce et al, ). Large radiative heat fluxes in the Laurentian Great Lakes, attributed to high water clarity (Barbiero et al, ) and low ice cover (Wang et al, ), make them particularly susceptible to this phenomenon. Although ice‐free radiative convection has been observed throughout the spring heating period (March–June; see Figure ) in the Laurentian Great Lakes (Lake Michigan: Church, ; Beletsky & Schwab, ; Lake Superior: Bennett, ; Austin, ; and Lake Ontario: Scavia & Bennett, ), there have been, to the best of our knowledge, no direct observations of the turbulence characteristics associated with this mixing mechanism, despite its potential importance for both biological and chemical properties, including phytoplankton and zooplankton biomass (Sommer et al, ; Vanderploeg et al, ), dissolved oxygen (Yang et al, ), and nutrients (Hampton et al, ).…”

Zebra or quagga mussel dominance depends on trade-offs between growth and defense—Field support from Onondaga Lake, NY

“…Zhulidov et al [76,77] did observe a shift from quagga mussel dominance to zebra mussel dominance in the lower Don River system, and speculated that selective predation on quagga mussels by roach (Rutilus rutilus) adapting to mussel feeding could explain the return of zebra mussel dominance. In addition, twelve years of annual data from lakes Erie, Ontario, Michigan and Huron have recently been published [11,78] and the data from western Lake Erie where round goby is abundant (but not from the deeper lakes Ontario, Michigan and Huron) show coexistence of the two dreissenid species. The two species also continue to coexist in the shallow water of Oneida Lake [12,79].…”

Food‐web structure and ecosystem function in the Laurentian Great Lakes—Toward a conceptual model

“…Dreissenids have acted to modify relative nutrient and energy inputs into basal resource zones across lakes (with minimal effects in Lake Superior) (Barbiero et al., ; Hecky et al., ; Kao et al., ). Dreissenids also change the physical habitat of an invaded site by making unstable bottoms more colonisable by Cladophora (Brooks, Grimm, Shuchman, Sayers, & Jessee, ).…”