Modelagem simplificada do fósforo total em lagos e reservatórios brasileiros

Abstract

Resumo O fósforo é considerado o principal fator responsável pela eutrofização de lagos e reservatórios. No presente estudo, utilizou-se um modelo transiente de mistura completa para analisar a dinâmica do fósforo em 40 lagos e reservatórios localizados nas regiões Nordeste, Sudeste e Centro-Oeste do Brasil. Os resultados con- firmaram a dependência do coeficiente de decaimento de fósforo com o inverso da raiz quadrada do tempo de residência hidráulica. No entanto, em virtude da elevada temperatura da água dos lagos e reservatórios do Nordeste, esse coeficiente assumiu valores cerca de duas vezes superiores àqueles observados em regiões de clima tropical. Por outro lado, devido à alta variabilidade de temperatura dos lagos e reservatórios do Sudes- te, o coeficiente oscilou entre valores extremos observados em regiões de clima temperado e semiárido. Em virtude disso, propôs-se uma equação geral para calcular o coeficiente de decaimento de fósforo como uma função não apenas do tempo de residência hidráulica, mas também da temperatura da água. Após validação e análise de sensibilidade do modelo proposto, o mesmo foi aplicado a um reservatório hipotético sujeito a variações temporais de volume, vazão, carga e temperatura da água. Espera-se que este modelo simplificado possa auxiliar na gestão de lagos e reservatórios brasileiros. Palavras-chave: Eutrofização. Temperatura. Qualidade da água. Abstract Phosphorus is considered the main factor responsible for eutrophication of lakes and reservoirs. In the present study, a transient complete mixing model was used to analyse phosphorus dynamics in 40 lakes and reservoirs located in the Northeast, Southeast and Central-West regions of Brazil. The results confirmed the dependence of the phosphorus decay coefficient on the inverse of the square root of the hydraulic residence time. However, due to the high-water temperature of the lakes and reservoirs of the Northeast, this coefficient assumed values about two times higher than those observed in regions of tropical climate. On the other hand, due to the high temperature variability of the lakes and reservoirs in the Southeast, the coefficient oscillated between extreme values observed in temperate and semiarid regions. As a result, a general equation was proposed to calculate the phosphorus decay coefficient as a function not only of the hydraulic residence time, but also of the water temperature. After valida- tion and sensitivity analysis of the proposed model, it was applied to a hypothetical reservoir subject to temporal variations of water volume, flow, load and temperature. This simple model will potentially assist in the management of Brazilian lakes and reservoirs. Keywords: Eutrophication. Temperature. Water quality.

Coupling Hydrological and Hydrodynamic Models for Assessing the Impact of Water Pollution on Lake Evaporation

“…where: TP(t) = total phosphorus at time t (mg•L −1 ); TP o = total phosphorus at time t − 1 (mg•L −1 ); t = time step (year); w = phosphorus load at the entrance to the water body (g•year −1 ); V = volume (m 3 ); Q o = outlet flow (m 3 •year −1 ); and k = phosphorus decay coefficient (year −1 ). It is noteworthy that the k-values applied in Equations ( 2) and (3) were the same as those previously calculated [24] (Equation ( 1)). The volumes (V) were obtained through the water balance performed by the CE-QUAL-W2 model.…”

“…Furthermore, with the values of the hydraulic residence time for the mentioned years, the decay coefficient of phosphorus in the lake, k (year −1 ), was also evaluated. To this end, the model shown in Equation (1) [24] was applied, which was validated by several authors [4]. The k-values obtained were also used in the complete-mix transient water quality model [35], later applied for several studies [36,37], as described in Section 2.6.…”

“…Subsequently, two water quality models were applied and compared to obtain the concentration at the outlet of the lake: the transient model of complete mixing [24,35], later validated [36], Equations ( 2) and (3); and the empirical model that relates average wind speed, v m (m•s −1 ) and TP (mg•L −1 ) [10], as shown in Equation (4).…”

“…Some have studied the impact of climate on hydrodynamics, including the thermal stratification patterns of lakes [19][20][21][22][23]. Others estimated pollutant loads and modeled water quality in different environments [2,13,24]. Additionally, several studies have coupled hydrological models to hydrodynamic models [21,25,26].…”

Zero-dimensional modelling as tool for reservoir water quality planning and management

“…Pintilie et al (2007) also applied a zero-dimensional model considering the mass balance and complementary equations for metals, under several scenarios with steady conditions. Also, Toné (2016) applied and calibrated the CSTR model to 33 reservoirs of Brazil's northeast semiarid region and validates the model with data from 8 reservoirs of the South African semiarid.…”