Hydrological heterogeneity in Mediterranean reclaimed slopes: runoff and sediment yield at the patch and slope scales along a gradient of overland flow

摘要

Hydrological heterogeneity is recognized as a fundamental ecosystemattribute in drylands controlling the flux of water and energy throughlandscapes. Therefore, mosaics of runoff and sediment source patches andsinks are frequently identified in these dry environments. There is aremarkable scarcity of studies about hydrological spatial heterogeneity inrestored slopes, where ecological succession and overland flow areinteracting. We conducted field research to study the hydrological role ofpatches and slopes along an "overland flow gradient" (gradient of overlandflow routing through the slopes caused by different amounts of run-on comingfrom upslope) in three reclaimed mining slopes of Mediterranean-continentalclimate. We found that runoff generation and routing in non-rilled slopesshowed a pattern of source and sink areas of runoff. Such hydrologicalmicroenvironments were associated with seven vegetation patches(characterized by plant community types and cover). Two types of sinkpatches were identified: shrub Genista scorpius patches could be considered as "deepsinks", while patches where the graminoids Brachypodium retusum and Lolium perenne dominate were classified as"surface sinks" or "runoff splays". A variety of source patches werealso identified spanning from "extreme sources" (Medicago sativa patches; equivalent tobare soil) to "poor sources" (areas scattered by dwarf-shrubs of Thymus vulgaris orherbaceous tussocks of Dactylis glomerata). Finally, we identified the volume of overland flowrouting along the slope as a major controlling factor of "hydrologicaldiversity" (heterogeneity of hydrological behaviours quantified as Shannondiversity index): when overland flow increases at the slope scalehydrological diversity diminishes.