RECONSTRUCTING THE BIOGEOCHEMICAL OUTCOMES OF LANDSCAPE DISTURBANCES USING LAKE SEDIMENT RECORDS

Recent advances in laboratory and quantitative methods now enable robust reconstructions of past environmental conditions. Retrospective studies focusing on vegetation composition and disturbance regimes are frequently assessed from depositional archives, which are analyzed for ecological proxy data such as subfossil charcoal and pollen. The biogeochemical responses to landscape disturbances are reconstructed using stable isotopes (e.g. δ¹⁵N) and microscanning X-Ray Fluorescence (XRF), though few published paleoecological studies consider these metrics alongside charcoal and pollen records. This is due in part to a lack of consensus on the characteristics of disturbances and/or ecosystem properties that would lead to a change in a biogeochemical signal. For instance, following a disturbance event one might expect a biogeochemically sensitive site to exhibit significant shifts in the bioavailability of key macronutrients, such as N, P, and K, relative to pre-disturbance conditions. On the other hand, the absence of change in a biogeochemical proxy following disturbance may suggest biogeochemical complacency. In published biogeochemical reconstructions, both sensitivity and complacency have been observed and the factors that influence the biogeochemical signal include sediment subsampling strategy, edaphic conditions, disturbance and vegetation type, and catchment connectivity. This talk provides an overview of strategies for detecting biogeochemical responses to disturbance in forested landscapes using lake sediment records. Specific examples of sensitive (and complacent) biogeochemical records are discussed within an ecological context provided by high-resolution charcoal and pollen records for fire and bark beetle disturbances in western North America.