Land management impacts on runoff sources in small Amazon watersheds

Abstract

Abstract:Forest clearing and conversion to cattle pasture in the lowland Amazon region has been linked to soil compaction and increased soil water storage, which combine to diminish soil infiltration, enhance quick lateral flows and increase the stream flow response to precipitation. Quantifying the importance of quick surficial flow in response to this land use change requires identification of water sources within catchments that contribute to stream flow. Using an end member mixing analysis approach, potential contributing sources of stream flow were evaluated during an entire rainy season in a forest and a pasture watershed drained by ephemeral-to-intermittent streams in the south-western Amazon. Water yield was 17% of precipitation in the pasture and 0Ð8% of precipitation in the forest. During the early rainy season, throughfall, groundwater, and soil water contributed 79%, 18%, and 3%, respectively, to total forest stream flow. Over the entire rainy season, throughfall, groundwater, and shallow soil water provided 57%, 24%, and 19%, respectively, of stream flow. In the pasture watershed, overland flow dominated stream flow both in the early (67%) and late (57%) rainy season, with a mean contribution of 60% overland flow, 35% groundwater, and 5% soil water. The uncertainty associated with those estimates was studied using a Monte Carlo approach. In addition to large changes in total surface flow, marked differences were found in the proportions of total stream flow in the second half of the rainy season between the forest and pasture watershed. These results suggest that (1) there is great potential for alteration of the hydrological budgets of larger watersheds as the proportion of deforested land in the Amazon increases, and (2) as more rainfall is diverted into fast flowpaths to streams in established pastures, the potential to deliver water with higher solute concentrations generated by erosion or by bypassing sites of solute removal increases.

Groundwater quality comparison between rural farms and riparian wells in the western Amazon, Brazil

“…[25][26][27] In fact, Williams et al and Chaves et al studying intact forests in Central Amazonas and Rondônia, respectively, found more acidic pH values (4.7 and 5.2) than those observed in the Urupá basin. 15,16 In addition to the above mentioned factors influencing acidity in groundwater, in rural and urban areas, domestic and industrial sewage disposal and soil alteration through corrective products and fertilizers can also influence pH. 28 Hence, the proximity of wells to septic tanks could have led to the differences observed between the two riversides, mainly for the shallower wells.…”

“…Other studies conducted in forest ecosystems in the Amazon region have also found low conductivity values. 15,16 Concentrations of chemical constituents in groundwater showed high spatial variability, especially for anions ( Figure 1). The general order of dominance of cations in the groundwater of the studied area is Na + >> K + ≈ Ca 2+ > Mg 2+ and Ca 2+ > Na + > Mg 2+ > K + for right and left margins, respectively, whereas for anions it is Cl -> HCO 3 -≈ NO 3 ->> SO 4 2-(right) and HCO 3 ->> NO 3 -≈ Cl ->> SO 4 2-(left).…”

“…10 Little information is available on groundwater quality in the Amazon region, most of it focusing on urban wells and a few on forest and pasture areas. [11][12][13][14][15][16] The lack of reliable data on groundwater quality is currently a serious limiting in rural water-supply project designs and an effective monitoring program should be developed in order to improve rural drinking-water supply. 17 Hence, in order to increase the knowledge about the chemistry of this important water resource, this study focused the comparison of groundwater chemistry dynamics in more pristine riparian wells against those located in rural areas, both located in an intensively deforested area in the Amazon region.…”

Análise morfométrica e socioambiental de uma bacia hidrográfica Amazônica, Carlinda, MT

“…Segundo Chaves et al (2008), o desmatamento e a conversão em pastagem na região amazônica estão diretamente relacionados à compactação do solo e ao aumento de armazenamento hídrico, o que combina com a diminuição da infiltração da água no solo e com o aumento da inundação lateral e da velocidade de resposta do escoamento à precipitação. Assim, para mitigar os efeitos da pecuária extensiva na bacia hidrográfica, pode ser empregada a técnica de terraceamento ou sulcamento para permitir melhor infiltração da água e, com isso, a recarga do lençol freático e a diminuição da inundação.…”

Impact of selective logging and an intensive line planting system on runoff and soil erosion in a tropical Indonesian rainforest

“…The effect of human activities on runoff regimes has been proven by a number of experimental studies from various parts of the world. Much research has focussed on monitoring the influence of changes in land cover, mainly deforestation and afforestation processes [4,5,11,26], the influence of cultivated areas [13,15,20] and the impact of logging [6,22,28].…”