H072-03
The relation between age and transit time of biogeochemical cycling in ecosystems
The relation between age and transit time of biogeochemical cycling in ecosystems
Wednesday, 9 December 2020: 16:06
Virtual
Abstract:
The concepts of age and transit time can be used to characterize overall system behavior for biogeochemical cycling.
They can inform us about the range of timescales of biological activity, and the degree of heterogeneity and complexity in ecosystems. They are also useful diagnostics to compare models with observations.
Based on a review of different models and a compilation of observations, we show here that 1) ages of carbon in terrestrial ecosystems are much higher than transit times, with ages in the order of centuries and millennia, and transit times on the order of decades. This implies that carbon entering ecosystems returns to the atmosphere very quickly, but the small proportion of carbon that remains, can stay for very long times. 2) Large ecosystem disturbances such as land-use change can drastically shift the relation between ages and transit times, particularly for soils. Observations from tropical and temperate ecosystems show that after land-use, soil microorganisms rely more on older carbon for their metabolism, with a decrease in mean age and an increase in mean transit time.
With these results, we advance the hypothesis that shifts in the age and transit time relation can be an important diagnostic to characterize major shifts in ecosystem behavior, for example to assess changes after permafrost thawing or due to changes in climatic regimes.
Furthermore, the observed relations between age and transit time in ecosystems suggest that carbon sequestration may require large amounts of inputs sustained for very long times to be meaningful for climate change mitigation.
There is also a large potential to combine estimates of ages and transit times for water and different biogeochemical elements in ecosystems to better understand system-level properties and their response to environmental change.
They can inform us about the range of timescales of biological activity, and the degree of heterogeneity and complexity in ecosystems. They are also useful diagnostics to compare models with observations.
Based on a review of different models and a compilation of observations, we show here that 1) ages of carbon in terrestrial ecosystems are much higher than transit times, with ages in the order of centuries and millennia, and transit times on the order of decades. This implies that carbon entering ecosystems returns to the atmosphere very quickly, but the small proportion of carbon that remains, can stay for very long times. 2) Large ecosystem disturbances such as land-use change can drastically shift the relation between ages and transit times, particularly for soils. Observations from tropical and temperate ecosystems show that after land-use, soil microorganisms rely more on older carbon for their metabolism, with a decrease in mean age and an increase in mean transit time.
With these results, we advance the hypothesis that shifts in the age and transit time relation can be an important diagnostic to characterize major shifts in ecosystem behavior, for example to assess changes after permafrost thawing or due to changes in climatic regimes.
Furthermore, the observed relations between age and transit time in ecosystems suggest that carbon sequestration may require large amounts of inputs sustained for very long times to be meaningful for climate change mitigation.
There is also a large potential to combine estimates of ages and transit times for water and different biogeochemical elements in ecosystems to better understand system-level properties and their response to environmental change.