Geomorphology of the Anthropocene: Time-transgressive discontinuities of human-induced alluviation

Natural vs anthropogenic streams in Europe: History, ecology and implications for restoration, river-rewilding and riverine ecosystem services

“…Conversely, floodplain deforestation which occurred in broadly two phases (2500-2000 BP and 1500-1000 BP) reduced the supply of wood, seeds and propagules, which would have resulted in increased channel dynamics in reaches of high stream power due to absence of stabilising root systems on river banks, and vegetation of bars and islands. In zones of low stream power these effected were probably cancelled out by the increasing rate of overbank siltation by cohesive sands, silts and clays (Brown et al, 2013).…”

“…To avoid the copy-and-paste approach used in short-term studies which lead too often to truncated specifications and/or failure for restoration projects (Palmer et al, 2009). It is desirable to extend our knowledge on alternative fluvial states and their resilience by including long-term dynamics and evolutionary trajectories (Brierley and Fryirs, 2016;Dearing et al, 2015;Brown et al, 2013;Lespez et al, 2015).…”

“…The principal cause is Holocene overbank sedimentation of sand, silt and clay (Brown and Barber, 1986;Dotterweich, 2008;Pastre et al, 2001;Lespez et al, 2008;Macklin et al, 2010;Broothaerts et al, 2012;Brown et al, 2013;Macklin et al, 2014). It is often an idealised fluvial ensemble of floodplain flats, low or no levées, and sinuous (meandering) stream form to which channels are currently being restored in Europe with the re-engineering of meanders, pools and riffles (Moss and Monsadt, 2008).…”

A stratigraphical basis for the Anthropocene?

“…This is associated with increasing sediment loading in response to erosion due to deforestation, animal grazing and changing agricultural practices, mill development, transport networks, and the influence upon global climate systems including effects such as increased precipitation intensity or desertification and sea-level rise resulting in coastal inundation (Merritts et al 2011;Syvitski & Kettner 2011). In particular, the impact of introduction of intensive agricultural practices is noted as causing a widespread stratigraphical marker across many continents associated with a transition from basal gravels with organic channel fills to a thick capping of sandy silt (Brown et al 2013). In two nearby river systems in the UK, this boundary is dated at 3600 -4400 years cal BP and 1300-220 years cal BP, showing that this boundary is significantly time-transgressive and makes it difficult to consider as a sedimentary boundary for the start of the Anthropocene (Brown et al 2013).…”

“…In particular, the impact of introduction of intensive agricultural practices is noted as causing a widespread stratigraphical marker across many continents associated with a transition from basal gravels with organic channel fills to a thick capping of sandy silt (Brown et al 2013). In two nearby river systems in the UK, this boundary is dated at 3600 -4400 years cal BP and 1300-220 years cal BP, showing that this boundary is significantly time-transgressive and makes it difficult to consider as a sedimentary boundary for the start of the Anthropocene (Brown et al 2013).…”