masterThesis
Efeitos da reinundação de sedimentos expostos por secas prolongadas sobre as emissões de carbono em reservatórios da região semiárida
Fecha
2019-09-02Registro en:
PINHEIRO, Thaís Lopes. Efeitos da reinundação de sedimentos expostos por secas prolongadas sobre as emissões de carbono em reservatórios da região semiárida. 2019. 67f. Dissertação (Mestrado em Engenharia Sanitária e Ambiental) - Centro de Tecnologia, Universidade Federal do Rio Grande do Norte, Natal, 2019.
Autor
Pinheiro, Thaís Lopes
Resumen
The increased occurrence and intensity of drought events in the semiarid regions has
contributed considerably to the regular and prolonged exposure of reservoir sediment to
the atmosphere. This extreme hydrological scenario may affect the processing of organic
matter and alter greenhouse gas (GHG) emission rates in reservoirs, as these aquatic
ecosystems play an essential role in carbon cycling (C). In addition, during extreme
drought events in the Brazilian semi-arid region, exposed sediment from the dry reservoir
drainage area are transformed into agricultural cultivation sites due to the large amount
of stored phosphorus. This practice defines new biochemically active areas that may
influence the emission rates of two GHGs, carbon dioxide (CO2) and methane (CH4). To
determine how re-flooding events act on C emission rates, we experimentally estimated
CO2 and CH4 flux in exposed sediment from the drainage area of four reservoirs in the
Brazilian semiarid region (Marechal Dutra - Gargalheiras, Passagem das Traíras, Ministro
João Alves - Boqueirão de Parelhas and Cruzeta) with different physicochemical
properties after re-flooding simulation and compared their response with emissions in dry
sediment. The intensity of C emissions varied strongly in and among all reservoirs. The
observed CO2 and CH4 fluxes ranged from 10-40 mg C m-² day-¹ and 0.7-1.3 mg C m-²
day-¹ in dry sediment and from 3-78 mg C m-² day-¹ and 0.4-13.5 mg C m-² day-¹ in
rehydrated sediments, respectively. Nutrient concentrations and organic matter contents
boosted CO2 flux and no variable showed a strong relationship with CH4 flux. In Dourado
reservoir, we compared the responses of CO2 and CH4 flux after re-flooding simulation
in exposed sediment with and without agricultural cultivation. CO2 and CH4 flux in
cultivated areas were about three and two times higher than the flux in the non-cultivated
areas, respectively. Organic matter content and nutrient concentration (nitrogen and
phosphorus) in water and sediment in cultivated areas were found to be drivers of CO2
and CH4 flux. Understanding GHG flux in reservoirs that experience the drying and reflooding cycle is fundamental for the development of management strategies for these
environments. Thus, C emissions from exposed and re-flooded sediment should be
explicitly considered in the total emissions from river networks, particularly under predicted scenarios of global climate change, which should increase the temporality and
spatiality of rainfall.