Contrasting human versus climatic impacts on erosion

Abstract

Both human activity and climate change can influence erosion rates and initiate rapid landscape change. Understanding the relative impact of these factors is critical to managing the risks of extreme erosion related to flooding and landslide occurrence. Here we present a 2100 year record of sediment mass accumulation and inferred erosion based on lacustrine sediment cores from Amherst Lake, Vermont, USA. Using deposition from August 2011 Tropical Storm Irene as a modern analogue, we identified distinct event deposits indicative of destructive erosion events. These deposits record a prolonged (multidecadal) interval of enhanced erosion following the initial storm‐induced landscape disturbance. The direct impact of human land cover alteration is minimal in comparison to the more recent twentieth century increase in the occurrence of catastrophic erosion linked to overall wetter conditions that favor high erosion rates and more easily trigger landslides during periods of extreme precipitation.

Historically unprecedented erosion from Tropical Storm Irene due to high antecedent precipitation

“…The cesium‐137 ( 137 Cs) onset at 26 cm (Figure ) in AL 13‐4 indicates a post‐1954 sedimentation rate of 0.36 cm/yr., excluding 5 cm of clastic deposition comprising three short‐lived event deposits. Applying this deposition rate to pre‐1954 background sediments, with the implicit assumption of similar deposition rates prior to 1954, the bottom of the 50 cm core corresponds to roughly the beginning of the twentieth century, consistent with timing of results in Cook et al (. As observed in Keeney Cove, the Irene event deposit in Amherst Lake stands out as anomalous from all other twentieth century sediments.…”

“…Population in the town of Plymouth, Vermont, where Amherst Lake is located, peaked in the 1840s (Ward et al, 1983). Historical photography from the early twentieth century shows a predominantly reforested landscape in the immediate vicinity of the lake (Cook et al, 2015). Thus, Irene flooding and anomalous erosion on low-order streams occurred during a period of maximum historical upland forest cover.…”

“…Core transects revealed a high degree of spatial coherence at both Keeney Cove (Fallon et al , ) and Amherst Lake (Cook et al , ). Here we focus on reconstructions from the primary core site along respective transects.…”

Evidence for elevated coastal vulnerability following large‐scale historical oyster bed harvesting

“…Kirwan et al ., ). Further, recent studies find little direct evidence in north‐eastern watersheds for a deforestation‐induced increase in sediment load for regional rivers (Cook et al ., ; Yellen et al ., ). It is possible that background increases in MS at our three sites is due to land clearance.…”

Hydro‐geomorphic behavior of contrasting tropical landscapes and critical zone response to changing climate

“…Hillslope erosion is controlled by rainfall-triggered landslides, the propensity for which depends on a multitude of non-climatic factors including slope morphology and soil and forest properties (Roering et al, 1999;Simoni et al, 2008;Hales et al, 2009;De Rose, 2013;Formetta et al, 2016;Moos et al, 2016), and on the frequency of extreme hydro-meteorological events (Casadei et al, 2003;Chen et al, 2013;von Ruette et al, 2014;Arnone et al, 2016). Clarifying the relative contribution of climatic vs non-climatic factors to the hillslope erosion rates of diverse landscapes is no trivial task (Riebe et al, 2003;Cook et al, 2015). Understanding the interrelations among different erosional processes within the complex structure of the critical zone remains a challenge (Anderson et al, 2007;Brantley et al, 2007).…”