The legacy of large regime shifts in shallow lakes

Abstract

Ecological shifts in shallow lakes from clear-water macrophyte-dominated to turbid-water phytoplankton-dominated are generally thought of as rapid short-term transitions. Diatom remains in sediment records from shallow lakes in the Prairie Pothole Region of North America provide new evidence that the long-term ecological stability of these lakes is defined by the legacy of large regime shifts. We examine the modern and historical stability of 11 shallow lakes. Currently, four of the lakes are in a clear-water state, three are consistently turbid-water, and four have been observed to change state from year to year (transitional). Lake sediment records spanning the past 150-200 yr suggest that (1) the diatom assemblage is characteristic of either clear or turbid lakes, (2) prior to significant landscape alteration, all of the lakes existed in a regime of a stable clear-water state, (3) lakes that are currently classified as turbid or transitional have experienced one strong regime shift over the past 150-200 yr and have since remained in a regime where turbid-water predominates, and (4) top-down impacts to the lake food-web from fish introductions appear to be the dominant driver of strong regime shifts and not increased nutrient availability. Based on our findings we demonstrate a method that could be used by lake managers to identify lakes that have an ecological history close to the clear-turbid regime threshold; such lakes might more easily be returned to a clear-water state through biomanipulation. The unfortunate reality is that many of these lakes are now part of a managed landscape and will likely require continued intervention.

Environmental filtering and competitive exclusion drive biodiversity‐invasibility relationships in shallow lake plant communities

“…Greater responsiveness to increased resource availability and broader environmental tolerances appear to be attributes of successful invasive plants in general (Davis, Grime, & Thompson, ; Zedler & Kercher, ), and global drivers of change reinforce these advantages (Thompson & Davis, ). In northern shallow lakes, recent findings point to persistent, anthropogenic shifts to more nutrient‐rich, turbid alternative states (Ramstack Hobbs et al., ). Our findings suggest that these changes will exacerbate aquatic plant invasions.…”

Watershed vs. within‐lake drivers of nitrogen: phosphorus dynamics in shallow lakes

“…Almost all of the lake watersheds have been impacted by development since European settlement in this region, complicating the “legacy” of each lake (Ramstack Hobbs et al. ). Indeed, much of the watershed cover now classified as “natural cover” in our analysis is the result of watershed restoration, particularly in the Prairie, Parkland, and Metro study regions.…”

Influence of historical landscape on aquatic plant diversity

“…Scandinavian grassland ecosystems were also found to be impacted by these historical processes (Cousins, 2009;Lindborg & Eriksson, 2004), as well as soil microbes (Hawkes & Keitt, 2015), but studies focusing on the importance of historical factors for aquatic ecosystems are very scarce (Maloney et al, 2008). In freshwater ecosystems, historical factors are often investigated though the use of paleo-limnological records, usually with the aim to reconstruct former ecosystems without testing their influence on current diversity patterns (but see Hobbs et al, 2016).…”