Global acceleration of lake sediment accumulation rates associated with recent human population growth and land-use changes

Abstract

Sediment Accumulation Rate (SAR; measured as mm yr⁻¹) and Mass Accumulation Rate (MAR; measured as g cm⁻² yr⁻¹) data were collected from published lake core records that spanned the past ~  150 years, from approximately 500 sites worldwide. For each lake, key watershed characteristics including watershed size, slope, land use and climate were extracted, with the goal of quantifying the relative importance of these variables as drivers of SAR and MAR. General additive models provided evidence of accelerated global lake sediment infilling rates after AD 1950. Whereas the onset of sedimentation acceleration varied across ecoregions, global lake MAR values were found to have increased ~  threefold on average, since baseline conditions pre-1900 (i.e. μ_baseline = 0.040 ± 0.044 g cm⁻² yr⁻¹ and μ_modern = 0.13 ± 0.22 g cm⁻² yr⁻¹). The significant drivers, identified through Linear Mixed Effect modeling of MAR time series, were watershed population density (log-transformed) and watershed cropland density (log-transformed). Our results highlight important spatial heterogeneity in SAR and MAR among lakes, precluding the use of simple modeling approaches. SAR and MAR were found to be moderately correlated to one another, despite the potential for post-depositional disparities between segments of the sediment cores. We identified organic matter content (loss-on-ignition, LOI) as a significant co-variate that could be used to correct inflated very recent SAR rates. Our empirical analyses suggest that, despite a wide range of natural variability among lakes, both SAR and MAR increased globally and the increases appear to be mainly the result of enhanced watershed activities associated with agriculture and urbanization.