Extrinsic vs. Intrinsic Regimes Shifts in Shallow Lakes: Long-Term Response of Cyanobacterial Blooms to Historical Catchment Phosphorus Loading and Climate Warming

Abstract

To evaluate the relative influence of intrinsic and extrinsic factors on ecosystem dynamics and regime shifts, we examined the algal response to historical catchment phosphorus loading from two shallow lakes located in Quebec, Canada. Roxton Pond is a eutrophic shallow lake with submerged macrophytes, and Lake Petit Saint-François (PSF) is a hypereutrophic shallow lake with no submerged macrophytes. Specifically, we inferred past cyanobacteria dynamics using pigment analyses, and tested whether the most parsimonious response model for cyanobacteria dynamics was congruent with the response model for phosphorus loading to the catchment. For both lakes, we found that an abrupt increase in cyanobacteria concentration lagged behind the initial increases in agricultural phosphorus use in the catchment as well as climate warming by over a decade. The delayed cyanobacterial response to these external drivers, observed in both lakes, suggests that intrinsic factors more than likely played important roles in ecosystem dynamics. These results show that cyanobacteria dominance in shallow lakes can be brought on by intrinsic responses to catchment phosphorus loading, climate warming, or both, but the timing depends on the antecedent conditions and the magnitude of the external forcing.

Molecular and Pigment Analyses Provide Comparative Results When Reconstructing Historic Cyanobacterial Abundances from Lake Sediment Cores

“…Differences in the cyanobacterial community over time were evident in Lake Pounui, where echinenone was more abundant than myxoxanthophyll in the top of the core, and in Lake Rototoa where myxoxanthophyll was more abundant from the middle of the core. These types of shifts in specific cyanopigments have been well documented in other lakes in the literature [21,24,25] and have been theorized to be associated with changes in the cyanobacterial community.…”

“…However, unlike diatoms, cyanobacteria have soft cell walls, which degrade quickly once the cell dies; therefore, the only proxies available to study them in sediment cores are the molecules they produce. Studies to date have targeted their pigments [10,[20][21][22][23][24][25], toxins (anatoxin, microcystin [24,26]), lipid biomarkers (e.g., 2-methylbacteriohopanetetrol as a possible biomarker for a freshwater strain of Synechococcus [27]), and now, their DNA [22,24,[27][28][29][30].…”

The Effectiveness of Global Constructed Shallow Waterbody Design Guidelines to Limit Harmful Algal Blooms

“…The theory of regime shifts in shallow lakes considers abrupt changes between clear and turbid water states (Scheffer & van Nes, 2007). Once a waterbody has shifted to a turbid state, it is difficult to reverse to the clear state (Groffman et al., 2006; Scheffer et al., 2001; Vermaire et al., 2017). Assuming that the same behavior applies for constructed waterbodies, it becomes critical to design the waterbody correctly to minimize the likelihood of HABs because, once HABs begin to occur, a new cyanobacteria‐dominated regime may be initiated.…”

Can we detect ecosystem critical transitions and signals of changing resilience from paleo‐ecological records?

“…Roxton Pond is a eutrophic, shallow lake (maximum depth 6.2 m) in the Eastern Townships of Quebec, Canada, that experienced a pronounced increase in nutrient loading during the 1970s as a result of agricultural activities (Vermaire et al 2017). According to the paleolimnological record, this was followed by a change in the zooplankton and phytoplankton community and an increase in cyanobacterial pigment concentrations in the 1990s.…”

“…To provide a range of regime shift time series, we cross-examined the published literature and identified core records with (1) an abrupt onset of a eutrophic state (Roxton Pond; echinenone pigment used as a proxy of total cyanobacteria abundance; Vermaire et al 2017); (2) a noisier eutrophication signal (Lake Anarry; myxoxanthophyll pigment used as a proxy of colonial cyanobacteria abundance; Stevenson et al 2016);and (3) possible flickering between alternate states (Lake Geneva; a composite proxy reconstructed from multiple intercorrelated varved cores tracking the inferred volume of hypolimnetic hypoxia; Jenny et al 2014). Cyanobacterial dominance and hypolimnetic hypoxia are wellestablished symptoms of anthropogenic disturbances and increased nutrient loading to lakes (Edmondson 1961, Reckhow 1977; thus, both paleolimnological proxies are used here as indicators of a shift from oligotrophic to eutrophic conditions (Taranu et al 2015, Jenny et al 2016).…”