Asynchronous multitrophic level regime shifts show resilience to lake browning

Area of Science:

• Paleolimnology
• Freshwater Ecology
• Climate Change Science

Background:

• Lake browning, driven by increased dissolved organic carbon, climate warming, and nitrogen deposition, poses a widespread environmental challenge.
• Understanding multitrophic level responses to lake browning is crucial for effective ecosystem management.
• Sedimentary records offer valuable insights into long-term ecological changes in lakes.

Purpose of the Study:

• To investigate multitrophic level responses to lake browning in a remote Chinese headwater lake.
• To analyze shifts in diatoms, chrysophyte stomatocysts, and chironomids as indicators of ecological change.
• To determine the driving forces behind these shifts and their relative importance.

Main Methods:

• Sedimentary core analysis from a remote headwater lake in the Three Gorges Reservoir region.
• Dating of sediment layers to establish temporal shifts in biotic communities.
• Analysis of diatoms, chrysophyte stomatocysts, and chironomids as biotic proxies.
• Correlation of biotic shifts with environmental factors like temperature, nitrogen deposition (δ¹⁵N), and littoral moss expansion (δ¹³C).

Main Results:

• Distinct timing of community shifts observed: chironomids (1886 ± 18 CE), chrysophytes (∼1914 ± 10 CE), and diatoms (∼1941 ± 6 CE).
• Shifts were linked to rising temperature, nitrogen deposition, littoral moss expansion, and biotic interactions, with varying driver importance across taxa.
• Zoobenthos grazing emerged as a potentially dominant factor over bottom-up pathways in humic conditions.
• Coexistence of diverse algae post-1950s suggests mixotrophic chrysophytes mitigate browning via heterotrophy.

Conclusions:

• Lake browning regime shifts necessitate multitrophic level analyses for comprehensive understanding.
• Heterotrophic processes by mixotrophic chrysophytes can sustain ecological equilibrium in brownified lakes.
• Heterotrophy's role in carbon cycling is likely to increase in montane lakes experiencing water brownification.