Changes in ecosystem resilience detected in automated measures of ecosystem metabolism during a whole-lake manipulation

Abstract

Environmental sensor networks are developing rapidly to assess changes in ecosystems and their services. Some ecosystem changes involve thresholds, and theory suggests that statistical indicators of changing resilience can be detected near thresholds. We examined the capacity of environmental sensors to assess resilience during an experimentally induced transition in a wholelake manipulation. A trophic cascade was induced in a planktivoredominated lake by slowly adding piscivorous bass, whereas a nearby bass-dominated lake remained unmanipulated and served as a reference ecosystem during the 4-y experiment. In both the manipulated and reference lakes, automated sensors were used to measure variables related to ecosystem metabolism (dissolved oxygen, pH, and chlorophyll-a concentration) and to estimate gross primary production, respiration, and net ecosystem production. Thresholds were detected in some automated measurements more than a year before the completion of the transition to piscivore dominance. Directly measured variables (dissolved oxygen, pH, and chlorophyll-a concentration) related to ecosystem metabolism were better indicators of the approaching threshold than were the estimates of rates (gross primary production, respiration, and net ecosystem production); this difference was likely a result of the larger uncertainties in the derived rate estimates. Thus, relatively simple characteristics of ecosystems that were observed directly by the sensors were superior indicators of changing resilience. Models linked to thresholds in variables that are directly observed by sensor networks may provide unique opportunities for evaluating resilience in complex ecosystems.regime shift | alternative stable states | early warning signals | sonde | high-frequency time series

Land use affects temporal variation in stream metabolism

“…This statement does not mean that anthropogenic disturbance cannot affect such ecosystems, as evidenced by the effect of land use on dryland river metabolism (Fellows et al 2009). Last, as an ecosystem-level measure, stream metabolism integrates variability observed at lower hierarchical levels (sensu Pickett et al 1989), and may not provide an early warning tool of an impending state change (Batt et al 2013). However, as demonstrated by the increased mean rates and metabolic variability, the streams in our study are clearly stressed by human land use, and this stress may make them vulnerable to cumulative press or pulse disturbances arising from future landuse intensification or climate change.…”

Reversal of a cyanobacterial bloom in response to early warnings

“…Hence, the range of DO %sat was more limited than that of the pigments. Nonetheless, DO %sat can be useful as an indicator of an impending regime shift (35), although in some cases, DO %sat alarms are delayed compared with those derived from other resilience indicators (36).…”

Evaluating early-warning indicators of critical transitions in natural aquatic ecosystems

“…The development of early-warning indicators (EWIs) derived from bifurcation theory has drawn considerable interest for their ability to detect critical transitions, particularly given their promise of generalizability. These EWIs have been shown to precede critical transitions in modeled time series (8)(9)(10), experimental time series (11)(12)(13), reconstructed paleo-climate records (14,15) and whole-lake experiments (16). Until now, however, an assessment of the generality and the detection power of EWIs on long-term monitoring data in aquatic systems is lacking (17).…”