Terrestrial sedimentation and the carbon cycle: Coupling weathering and erosion to carbon burial

Abstract

The terrestrial sediment cycle is not in equilibrium. Agriculture, civil engineering, and mining mobilize vast quantities of soils, unconsolidated sediment, and bedrock, perhaps more than all natural geomorphic processes combined [Hooke, 1994]. The hydraulic architecture of the land has been transformed to serve agriculture, water supplies, land reclamation, navigation, and power generation. Few rivers lack dams and reservoirs; large rivers are confined to their channels by levees; normal floodplains are converted to paddy lands and aquiculture; water is mined; irrigation raises soil moisture and creates artificial distributary systems, and so forth. Agriculture has transformed a large Ëaction of the 231

Storage and Turnover of Organic Matter in Soil

“…Erosion by wind and water affects roughly 10×10 12 m 2 of land worldwide (Jacinthe and Lal 2001) and moves 1-5 Pg C y -1 , with more than 70% deposited terrestrially (Stallard, 1998). As a result of the erosion effects on decomposition and NPP described above, recent studies have suggested that erosion results in a global terrestrial C sink of 0.25-1 Pg C y -1 (Stallard 1998;Smith et al 2005;Berhe et al 2007;van Oost et al 2007). …”

“…In terms of total watershed C stock, recent empirical and modeling studies conclude that erosion-and the balance between its effects on productivity and decomposition in eroding and depositional sites-tends to lead to an increase in stock, even if there are local decreases in the eroding sites themselves (Stallard 1998;Smith et al 2005;Berhe et al 2007;Harden et al 1999).…”

“…During the past two centuries, agricultural expansion has led to large losses of soil C. Soils may lose a significant portion of their C when native ecosystems are replaced by less productive ones; these changes represent a loss of fast-cycling C rather than passive C pools (Davidson and Ackerman 1993;Trumbore et al 1995;Stallard 1998). Tillage leads to substantial losses of old soil C due physical disruption of soil aggregates and enhanced aeration of the soil that exposes organic matter to microbes and oxidization (e.g., Tisdall and Oades 1982;Tiessen and Stewart 1983b;Baisden et al 2002;Ewing et al 2006).…”

Carbon source/sink function of a subtropical, eutrophic lake determined from an overall mass balance and a gas exchange and carbon burial balance

“…However, in some area of the world where lakes occupy 10e20% of the land surface area, such as Wuhan City, China, lake carbon budget is potentially a very important component of the whole area carbon budget. Studies on carbon burial in lake sediments have shown that lakes are disproportionately important carbon sinks (Dean and Gorham, 1998;Einsele et al, 2001;Mulholland and Elwood, 1982;Stallard, 1998), with the sedimentation mass of organic carbon in lakes about half that of oceans, which cover 71% of the earth's surface (Dean and Gorham, 1998). Compared to large lakes, small lakes are proportionally more important for carbon burial (Kortelainen et al, 2004).…”

Holocene carbon burial by lakes in SW Greenland

“…For example, Dean & Gorham (1998) estimated global C burial by small lakes to be on the order of 70 g C m −2 yr −1 , based on C accumulation rates in three lakes. Stallard (1998) suggested a lower rate of 4.5 g C m −2 yr −1 . The most comprehensive study is that of Kortelainen et al (2004), who took advantage of the Nordic Lake Survey database and used C standing stock determinations from 122 lakes (mean burden 19 kg m −2 ) to estimate that Holocene C burial by all Finnish lakes is 1.8 g C m −2 yr −1 .…”