Ponds, puddles, floodplains and dams in the Upper Xingu Basin: could we be witnessing the ‘lentification’ of deforested Amazonia?

Abstract

24Hydrological change is a conspicuous signal of land use intensification in human-dominated 25 landscapes. We hypothesized that land conversion and land use change increase the availability of 26 lentic habitats and associated biodiversity in Southern Amazonian landscapes through at least four 27 drivers. River damming promotes the formation of reservoirs, which are novel permanent lentic water 28 bodies. A rise in the water table driven by local deforestation promotes the expansion of shallow 29 riparian floodplains. Soil compaction and the deliberate construction of cattle and drainage ponds 30 promote the increase in temporary water bodies in interfluvia. We tested these hypotheses using data 31 on habitat characterization and biological surveys of amphibians and fish in forests, pastures and 32 soybean fields in the headwaters of the Xingu River in Mato Grosso, Brazil. Lentic habitat availability 33 sharply increased in deforested land, with consequences to freshwater biodiversity. Reservoir 34 formation influenced both fish and amphibian assemblage structure. Fish species ranged from 35 strongly favored to strongly disfavored by reservoir conditions. Amphibian richness and abundance 36 increased in pasture and soybean streams relative to forests, with a strong positive effect of density of 37 reservoirs in the landscape. Expansion of stream floodplains increased the abundance of 38 Melanorivulus megaroni, a fish species indicator of shallow lentic habitats. Rainwater accumulation in 39 temporary ponds and puddles, entirely absent from well-drained forested interfluvia, allowed the 40 invasion of converted interfluvia by twelve species of open-area amphibians. A literature review 41 indicates that these four drivers of hydrological change are geographically widespread suggesting that 42 we may be witnessing a major yet previously unaccounted form of habitat change in deforested 43 Amazonia. 44 45 Introduction 46 Hydrological change is a conspicuous signal of land use intensification in human-dominated 47 landscapes [1]. The importance of water as a resource for human, livestock and crops, as a source of 48 energy, and as pathway for transportation makes water management a quintessential element of 49 human activities. In addition to the deliberate management of waterbodies, interventions in the 50 terrestrial environment indirectly influence hydrology by altering the partitioning of rainfall among the 51 processes of evapotranspiration, infiltration and runoff [2]. 3 52 Frontier landscapes provide a relevant environmental scenario for testing the occurrence and 53 consequences of anthropogenic hydrological change both because ongoing land use change permits 54 side-by-side comparison of converted and native habitats, and because frontiers are regions where 55 biodiversity change is expected to be highest [3]. The Amazon Basin is the largest area of the world 56 currently undergoing frontier settlement and, within the Amazon Basin, the Brazilian state of Mato 57 Grosso accounts for more than 40% of deforested...