In regions with abundant lakes and peatlands, large amounts of carbon (C) accumulate across interconnected upland, wetland, and aquatic ecosystems. Theoretical and empirical studies have characterized vertical C accumulation and its sensitivity to climate variability in both peatlands and lakes; however, few studies have attempted to understand C dynamics across interconnected peat-lake ecosystems. Northern Wisconsin is an ideal location for such studies, because 80% of the fixed C pool in the region is stored in abundant kettle lakes and their surrounding peatlands. Recent evidence indicates that peatland establishment in these basins is rapid and triggered by climate variability, but it remains unclear how the presence and spatial extent of peatland affects carbon accumulation rates (CAR). We hypothesized that peatland establishment around a lake would 1) increase the total CAR in a lake-peatland complex, 2) decrease lake CAR, and 3) decrease the climate sensitivity of total CAR in the lake-peatland basin. To test these hypotheses, we collected a network of peat and lake sediment cores from Fallison Bog in Northern Wisconsin, a well-studied site with established peatland developmental history, and used loss-on-ignition measurements and inferred developmental history to estimate changes in lake, peat, and whole-basin CAR during the Holocene.
Results/Conclusions
The differences in total basin CAR and lake CAR during three developmental stages: an early Holocene lake phase, a dynamic mid-Holocene peatland expansion phase, and isolation of the lake by extensive peatland 2000 years ago, provided support for hypotheses 1 and 2. Consistent with hypothesis 1, prior to peatland establishment the basin accumulated about half as much C per year as it did during the past 2000 years. While total basin CAR was higher during this extensive peatland phase, most C storage was in the form of peat, with lake CAR decreasing during this time, consistent with hypothesis 2. Isolation of the lake from terrestrial nutrients and increased lake acidity may have led to the decreased lake CAR. Interestingly, high variability in lake CAR characterized the interval of rapid peatland expansion, although this was also a climatically dynamic time and the potential influence of peatland development on the climatic sensitivity of CAR remains unclear. However, our results suggest that terrestrial-aquatic interface dynamics are complex and regulate CAR in kettle basins. Lake CAR and peatland developmental trajectories are closely related; the processes controlling this relationship are likely to be influenced by changing climate.