Efeitos da engorda artificial das praias do Meireles e de Iracema (Fortaleza, Ceara) na qualidade das aguas marinhas da area de influencia da obra

Abstract

Despite the widespread use of artificial beach nourishment to mitigate coastal erosion, this intervention can cause temporary or permanent changes in the marine ecosystem, including alterations in water quality, sediment, and biota. In this context, the present study evaluates the effects of artificial nourishment at Meireles and Iracema beaches in Fortaleza, Ceará, on marine water quality within the project's area of influence. Five oceanographic campaigns were conducted between 2019 and 2022, covering the start of the works (Ti), the dredging period (T1), and three post-construction phases (T2, T3, and T4). Sampling was conducted at two depths (subsurface and bottom) at twelve oceanographic stations distributed between the direct influence area of the nourishment site and the borrow area. All inorganic and organic parameters were evaluated, as well as the Class 1 saline water quality criteria established by CONAMA Resolution No. 357/2005. Analyses followed the procedures described in Standard Methods for the Examination of Water and Wastewater (APHA, 2005). The results for inorganic parameters showed that, overall, water quality was consistent with natural environmental variability across the monitoring campaigns. However, isolated exceedances of the maximum permissible values (MPVs) established by CONAMA Resolution No. 357/2005 were observed, particularly for total residual chlorine (TRC), which exceeded the 0.01 mg/L limit in all phases, reaching maximum values of 0.57 mg/L (standard deviation, SD = 0.31) in T3 and 0.64 mg/L (SD = 0.13) in T4. Total fluoride showed a mean concentration of 2.4 mg/L (SD = 0.24) in T2, above the 1.4 mg/L limit, while polyphosphates reached 0.085 mg/L (SD = 0.192) in Ti, exceeding the 0.031 mg/L limit, and sulfides showed a mean of 0.0023 mg/L (SD = 0.0066) in Ti, slightly above the 0.0020 mg/L limit. In marine sediments, the evaluated inorganic elements, including metals, metalloids, and nutrients, remained below the Level 1 and Level 2 guideline values of CONAMA Resolution No. 454/2012 throughout all study phases. For organic parameters, exceedances of the maximum permissible values established by CONAMA Resolution No. 357/2005 were recorded in marine water, occurring more frequently during T2 and T3 and mainly within the nourishment area. Concentrations above regulatory limits were observed for DDT and heptachlor epoxide + heptachlor (both with a maximum permissible value of 1 ng/L), for methoxychlor above 30 ng/L, and for polychlorinated biphenyls (PCBs) above 30 ng/L. Among polycyclic aromatic hydrocarbons (PAHs), benzo[a]pyrene and dibenzo[a,h]anthracene exceeded the maximum permissible value of 18 ng/L, particularly during T3. In marine sediments, organic contaminants were generally below the limits established by CONAMA Resolution No. 454/2012, with only one exceedance recorded for DDT. The human health risk assessment for dermal exposure indicated no non-carcinogenic risk, while carcinogenic risk was mainly associated with benzo[a]pyrene and dibenzo[a,h]anthracene. Ecotoxicological assays in marine water using the sea urchin Echinometra lucunter did not indicate persistent chronic toxicity during the study period. However, an isolated episode of generalized embryo-larval toxicity was observed during T2, followed by episodic and spatially restricted effects in subsequent phases, associated with environmental dynamics. Overall, the integrated results indicate that the artificial nourishment of Meireles and Iracema beaches did not cause permanent negative effects on the environmental quality of the study area. The observed changes were predominantly localized and associated with local environmental dynamics and the influence of pre-existing anthropogenic sources.