OOS 25-2 - Ecological sensitivities to pulse dynamics and antecedent climate: insights from
across US LTER sites

Background/Question/Methods
Understanding pulse dynamics is important to improving prediction in ecology. Climate change is altering hydrologic regimes, but the degree to which ecological responses are coupled to hydrologic pulses likely varies among ecosystems. A pulse is an abrupt change in system variables. Pulses may be isolated, when caused by single disturbances, or recur over variable time scales, including daily to seasonal. We explored patterns and trends in pulse dynamics using time-series analyses of hydrologic and temperature pulses to our understanding of diverse ecosystems within the US Long Term Ecological Research (LTER) Network. Pulse magnitudes and frequencies are changing across ecosystems, largely from altered precipitation, hydrology, and temperature.

Results/Conclusions
Increasing water levels and storms are increasing seasonal and interannual hydrologic pulses in the Florida Everglades, whereas river discharges to coastal Georgia have remained largely seasonal, despite pulsed droughts and storm anomalies. Precipitation pulses in Central Arizona are more frequent in rural than urban areas, but magnitudes of urban rainfall are greater than rural rain pulses. Increases in the frequency and magnitude of discharge pulses from tropical streams in Puerto Rico coincided with amplified rainfall pulses and storms. Declines in seasonal rainfall in central New Mexico reduced the magnitude and seasonality of land-atmosphere fluxes. Sea surface temperatures along coastal California had high interannual and local variability, along with overall warming trends. Days since last ice cover in northern temperate lakes declined with warming water temperature, but decadal oscillations remained detectable. These trends indicate detectable shifts in the seasonality of climate-associated pulses in temperature, precipitation, and hydrology that likely have predictable ecological impacts. Understanding how diverse ecosystems differ in antecedent climate variables, such as hydrology and temperature, that affect pulse dynamics improves our understanding of and predictions on long-term trajectories of populations, communities, and ecosystems undergoing rapid climate changes – an area of focus and exploration ripe for network-level synthesis.