Century-scale stream network dynamics in the Russian Plain in response to climate and land use change Valentin Golosov * , Andrey Panin Faculty of Geography, Moscow State University, 119992, Vorobiovy Gory, Moscow, Russia Abstract The spatial and temporal dynamics of stream net density (SND) within the Central and Southern parts of the Russian Plain during the last two centuries are studied by comparison of historical cartographic sources. A significant decrease of SND is observed in the forest – steppe and steppe zones. The maximum SND decrease is detected at the northern edge of the steppe zone, where SND values in the middle of the 20th century were only 50–60% of those at the beginning of the 19th century. Two stages of permanent stream disappearance were found within the study area: (1) The end of the 18th century to the first half of the 19th century, where the SND decrease was associated with a high frequency of droughts, that coincided with an expansion of the area of arable land, and (2) the last quarter of the 19th century, where the SND decrease can be explained by the extreme erosion rates resulting from the expansion of cultivation over steep slopes during the expansion of arable cultivation after the 1861 land reform. The roles of regional climate dynamics and land use change are confirmed by hydrological and meteorological data coupled with data on anthropogenic gully formation. Detailed studies of SND dynamics in a number of key basins provide a basis for understanding the mechanisms of SND reduction. D 2005 Elsevier B.V. All rights reserved. Keywords: Valley order; Stream net density; Erosion; Aggradation; Russian Plain 1. Introduction A drainage network is composed of linked erosion forms of varying dimensions and age. It may change noticeably due to development of gullies, but here we emphasise the older component of the drainage network — the valley net, which in most cases is considered stable at century-to- millennial time scales within plain and lowland areas. In its lower reaches the valley network is occupied by perennial streams but first-order valleys often have only ephemeral or seasonal water flow and stay dry at other times. After its introduction by Horton (1945), the term ‘‘drainage density’’ has been used in the literature both in relation to the total valley network (e.g., Carlston, 1965) and to the stream network only (e.g., Gregory and Walling, 1968). To avoid misunderstanding, in this paper we use the terms ‘‘valley net density’’ (VND) and ‘‘stream net density’’ (SND), respectively. Interest in the various aspects of drainage network composition reached a peak in the 1960–70s. Most research focussed on the geographical distribution of drainage density, its controlling factors and its relationship with water discharge. Thus, it was found that base flow is inversely related to VND (Carlston, 1965) but is directly related to SND (Gregory and Walling, 1968). Using examples from south-west England, Gregory (1966) showed that the network of present stream channels conforms more closely to Horton’s first two laws than the valley network, the reason being that valley net includes elements of different ages and origin and some valleys were active under former hydrological conditions and are fossil in the present network. Gregory (1966) also suggested that the existence of dry valleys may in some situations reflect a reduction of discharge similar to that associated with the occurrence of underfit streams, and that the valley net is representative of the former stream 0341-8162/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2005.07.011 * Corresponding author. Fax: +7 95 9395044. E-mail address: golosov@river.geogr.msu.su (V. Golosov). Catena 66 (2006) 74 – 92 www.elsevier.com/locate/catena