Patterns and drivers of change in organic carbon burial across a diverse landscape: Insights from 116 Minnesota lakes

Lakes may store globally significant quantities of organic carbon (OC) in their sediments, but the extent to which burial rates vary across space and time is not well described. Using Pb-210-dated sediment cores, we explored patterns of OC burial in 116 lakes spanning several ecoregions and land use regimes in Minnesota, USA during the past 150-200 years. Rates for individual lakes (across all time periods) range from 3 to 204g C m(-2)yr(-1) (median 33g C m(-2)yr(-1)) and show strong geographic separation in accordance with the degree of catchment disturbance and nutrient enrichment. Climate and basin morphometry exercise subordinate control over OC burial patterns, and diagenetic gradients introduce little bias to estimated temporal trends. Median burial rates in agricultural lakes exceed urban lakes and have increased fourfold since Euro-American settlement. The greatest increase in OC burial occurred prior to the widespread adoption of industrial fertilizers, during an era of land clearance and farmland expansion. Northern boreal lakes, impacted by historical logging and limited cottage development yet comparatively undisturbed by human activity, bury OC at rates 3X lower than agricultural lakes and exhibit much smaller increases in OC burial. Scaling up modern OC burial estimates to the entire state, we find that Minnesota lakes annually store 0.40 Tg C in their sediments, equal to 1.5% of annual statewide CO2 emissions from fossil fuel combustion. During the period of Euro-American settlement (circa 1860-2000), cumulative OC burial amounted to 36 Tg C, 40% of which can be attributed to anthropogenic enhancement.