Banca de DEFESA: RENNAN CABRAL NASCIMENTO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : RENNAN CABRAL NASCIMENTO
DATE: 20/08/2021
TIME: 08:30
LOCAL: Defesa remota pelo Google Meet
TITLE:

THORIUM FLUX AND SEDIMENT SOURCE APPORTIONMENT IN THE IPOJUCA RIVER WATERSHED

KEY WORDS:

Natural radionuclides. Soil erosion. Semiarid. Fingerprinting of sediment sources. Sediment transport. Elementary geochemistry. Alternative tracers.

PAGES: 114
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Ciência do Solo
SUMMARY:

The Ipojuca River is the third most polluted river system in Brazil. High concentrations and fluxes of metals in sediments indicate the contamination pattern, compared with values from catchments impacted by mining. Recent hydrological and morphological changes in the estuarine-marine zone increased the susceptibility of fine particle and metal sedimentation in these environments. It is assumed here that other elements may be transferred, such as radionuclides, and that the identification of sources and controlling soil erosion and sediment transport can reduce the distribution of contaminants to the outlet and the local coastal environment. Accordingly, the objectives of this study were (1) to evaluate the natural contents in soils and the distribution of Th in suspended (SS) and bed (BS) sediments, (2) to evaluate the patterns of delivery of sediments based on the combination of different classifications of potential sources of the fingerprinting method and (3) to evaluate the dynamics of delivery of different sediment sources from the semiarid portion of the Ipojuca River. (1) The mean Th concentration in soils was 28.6 mg kg-1. The estimated quality reference values were at 21 mg kg-1 and 86.3 Bq kg-1. The Th concentration in suspended and bed sediments ranged from 2.8 to 32.9 mg kg-1. The suspended sediments transported 3.42 t year-1 of Th, equivalent to more than 99% of the flux of this element. In the downstream cross section, suspended sediment samples exhibited Th concentrations similar to those observed in rivers impacted by mining activities. However, there was no evidence of anthropogenic impacts on Th concentrations. The flux of sediments from the study area to the ocean is mainly triggered by soil erosion processes in the mid-lower course region. (2) The downstream region (SS = 80.5% and BS = 86.7%), the Oxisols (SS = 65% and BS = 30.8%) and sugarcane cultivation (SS = 62% and BS = 63.6%) were the dominant sediment sources. Combined, the Oxisols and sugarcane areas controlled about 63.5% of the SS and 47.2% of the BS transported, i.e., less than 8% or approximately 280 km² of the catchment. Approaches combining potential sources, based on robust discriminations, tend to provide greater detail of areas under dominant erosion and reduce the scale of containment of these processes. (3) The semiarid lower catchment presented significantly higher contributions than the other regional sources (middle and upper), approximately 69% and 56% of the SS and BS, respectively. There was no dominant source of land use. The Caatinga (SS = 49%; BS = 47%) expressed a mild superiority in relation to the channel bank (SS = 35%; BS = 39%). Therefore, the recovery and conservation of vegetation in the Caatinga and the stabilization of channel banks, especially in the lower stretch, are fundamental for controlling the transport of river sediments in the outlet of this semi-arid catchment. More studies are needed to better assess the conservative patterns of color parameters in semiarid environments. Here, we provide some of the first information on sediment contributions from the main land uses and land cover in the semiarid region of northeastern Brazil.

BANKING MEMBERS:
Externo à Instituição - CRISTIANO POLETO - UFRGS
Externo à Instituição - TALES TIECHER - UFRGS
Externo ao Programa - 1250263 - CLISTENES WILLIAMS ARAUJO DO NASCIMENTO
Externo ao Programa - 1048872 - YGOR JACQUES AGRA BEZERRA DA SILVA
Presidente - 053.385.794-56 - YURI JACQUES AGRA BEZERRA DA SILVA - UFPI