Hidrogeoquímica do escoamento superficial no solo de uma mesobacia no nordeste paraense

Abstract

The hydrogeochemical of the overland flow can assist in decision-directed management of water resources in river wathershed, especially in areas with agricultural activities, such as the northeast of Pará, that sustainability is compromised by inadequate management and land use. In face of this we elaborated the following question: What is the effect of different agricultural production systems on the runoff in a northeastern Pará watershed? It was evaluated some hydrogeochemical variables of the overland flow at different agricultural systems in the watershed of Timboteua and Buiuna streams situated in the northeast of Pará state, a region where family farming is the main land use. Physico-chemical variables and dissolved inorganic anions concentrations were measured in the material transported by rainwater and overland flowat soils of agricultural fields with different management types (chop-and-mulch and slash-and-burn) in the following ecosystems: i) 20 years Secondary forest (“Capoeira”)(CP), ii) Agroforestry system (SAF) - slash-and-burn (SQ), iii) Agroforestry System (SAF) - chop-and-mulch (ST), iv ) Agroecosystem - chop-and-mulch (RT), v) Agroecosystem - slash-and-burn (RQ), vi) Cattle Pasture Agroecosystem - slash-andburn (PQ). The experiment consisted of three overland flow plots (1m2) in each one of the six ecosystems (totaling 18 plots). Also it were installed three collectors of rainwater and two rain gauges near by the ecosystems. Monitoring was done from January to June 2010, being collected 234 samples rainwater and runoff. In the first chapter, assessing the influence of land use and soil management to water losses by overland flow, we measured the highest runoff total volumes at [PQ] (34,79 mm) and SAF [ST] (15,25 mm). In the Chapter 2, monitoring the physico-chemical aspects of the overland flow, we could see that rainwater samples where the most acid ones , followed by [CP] and [SQ] samples, what can be related to organic matter sources. Finally at Chapter 3, regarding to the anions (Cl- , NO3 - , PO4 3- , SO4 2-) concentrations in the rainwater and overland flow, it is likely a moderate and positive correlation of pH with the anions, being stronger with the nitrate (ρ = 0.448 **), as well as a positive correlation of electrical conductivity with chloride (ρ = 0.625 **) and sulfate (ρ = 0.629 **) and a negative one with the volume (ρ = -0, 531 **). In summary it was observed the influence of land use and management types at the different studied ecosystemsto the overland flow volume, and its physico-chemical parameters (pH, EC) and anions concentrations.