Assuming that the first Chilia lobe was partially built during its first depositional cycle, the estimated rate of sediment deposition for the entire lobe must have been less than 5.9 MT/year (see Supplementary data). Subsequently, during the Chilia II lobe growth to completion, the depositional rate remained similar PD0332991 solubility dmso at ∼4.5 MT/year but it increased by an order of magnitude to over 60 MT/year during the open coast Chilia III lobe growth phase (Table 2 in Supplementary data). Thus, Danube’s partial avulsion that reactivated
the Chilia branch was gradual since the 8th century BC and its discharge reached its maximum only around 1700 AD. This sustained increase in sediment load brought down by the Danube to the delta was explained by Giosan et al. (2012) by an increase in erosion in the lower watershed. Ecological changes in the Black Sea best constrain the age of the maximum sediment load to the last 700–600 years, when an upsurge in soil-derived nutrients (i.e., Si, N) lead to the makeover of the entire marine ecosystem (Giosan et al., 2012 and Coolen et al., 2013). Past hydroclimate changes in
the lower Danube basin are currently little known but detailed reconstructions http://www.selleckchem.com/products/AZD2281(Olaparib).html in the Alps (Glur et al., 2013) document repeated intervals of higher precipitation in the last thousand years associated with cooler periods in Central Europe (Büntgen et al., 2011). Stronger and higher floods during this period may help explain the successive Danube avulsions, first toward the St George, and then toward the Chilia branch. However, the lack of a strong sensitivity to changes in discharge in a large river like Danube (McCarney-Castle et al., 2012) leaves the dramatic increase in sediment load unexplained without a late deforestation
of the lower watershed (Giosan et al., 2012), which provides the bulk of the Danube’s load (McCarney-Castle et al., 2012). Similar increased sensitivity to land use for continental scale rivers have been documented in other cases, whether through modeling (e.g., for Ebro River by Xing et al., 2014) or field-based studies (e.g., Rhine GPX6 by Hoffmann et al., 2009). However, climate variability expressed as floods probably contributed to this intense denudation as the erosion sensitivity of landscapes increases on deforested lands (Lang et al., 2003). What could explain the rapid deforestation in the lower Danube basin since the 15th century (Giurescu, 1976), hundreds of years later than in the upper watershed of Central Europe (Kaplan et al., 2009)? The Columbian Exchange (Crosby, 2003), which led to the adoption of more productive species such as maize probably led to “a demographic revival” ( White, 2011), which certainly required the expansion of agricultural lands. However, this alone cannot explain the extensive clearing of forest in agriculturally marginal highlands of the Carpathian and Balkan mountain ranges (e.g., Feurdean et al., 2012).