Maâmar El-Robrini

Análise faciológica e estratigráfica da planície costeira de Soure (margem leste da ilha de Marajó-PA), no trecho compreendido entre o canal do Cajuúna e o estuário Paracauari

A planicie costeira de Soure, na margem leste da ilha de Marajo (Para), e constituida por areas de acumulacao lamosa e arenosa, de baixo gradiente, sujeitas a processos gerados por mares e ondas. Suas feicoes morfologicas sao caracterizadas por planicies de mare, estuarios, canais de mare e praias-barreiras. A analise faciologica e estratigrafica de seis testemunhos a vibracao, com profundidade media de 4 m, e de afloramentos de campo permitiu a caracterizacao dos ambientes deposicionais, sua sucessao temporal e sua correlacao lateral, a elaboracao de secoes estratigraficas e a definicao de uma coluna estratigrafica. Foram identificadas cinco associacoes de facies: (1) facies de planicie de mare, (2) facies de manguezal, (3) facies de barra de canal de mare, (4) facies de praia e (5) facies de duna. A historia sedimentar da planicie costeira de Soure e representada por duas sucessoes estratigraficas: (1) a sucessao progradacional, constituida pelas associacoes de facies de planicie de mare, manguezal e barra de canal de mare; e (2) a sucessao retrogradacional, formada pelas associacoes de facies de praia e de duna. Essas sucessoes retratam uma fase de expansao das planicies de mare e manguezais, com progradacao da linha de costa (Holoceno medio a superior), e uma posterior fase de retrogradacao, com migracao dos ambientes de praias e dunas sobre depositos lamosos de manguezal e planicie de mare, no Holoceno atual. A historia deposicional da planicie costeira de Soure e condizente com o modelo de evolucao holocenica das planicies costeiras do nordeste paraense.

DINÂMICA SAZONAL DE NUTRIENTES EM ESTUÁRIO AMAZÔNICO

Este artigo mostra a distribuicao dos nutrientes no estuario do rio Paracauari, durante um ciclo hidrologico amazonico (2008), e no final do periodo de La Nina (abril de 2008). Esse estuario e influenciado por clima tropical umido e meso-mares (3 a 4m), semi-diurna. A amostragem foi realizada em 10 estacoes em tres periodos sazonais distintos: chuvoso (marco), intermediario (junho) e menos chuvoso (setembro). Medimos “in situ” os parâmetros fisico-quimicos utilizando uma sonda multiparâmetro; analisamos os nutrientes dissolvidos (nitrato, nitrito, n-amoniacal, fosfato e silicato) por espectofotometria e o material particulado em suspensao por gravimetria. Observamos amplas variacoes sazonais nas concentracoes dos parâmetros estudados. A temperatura da agua (media de 28,58 oC) e bastante homogenea, tipica das aguas tropicais. O pH variou de acido (5,80) a alcalino (7,86) e a salinidade entre 0,06 a 7,56 ambos com valores maximos na foz, devido a maior influencia marinha. As aguas sao mal oxigenadas no periodo chuvoso (2,35 mg.L-1) e bem no menos chuvoso (6,55 mg.L-1). As concentracoes de material particulado em suspensao e de nutrientes foram maximas no periodo chuvoso devido ao aporte natural proveniente das areas adjacentes.

Evolução da linha de costa de Salinópolis, Nordeste do Pará, Brasil

The average rates of change of the shoreline are a good index for determining evolutionary trends in any stretch of the coast. In Salinopolis city, although this trend beis the deposition of sediments on the shoreline, in places where human occupation is consolidating, the coastal erosion has caused significant impacts (decrease of tents, partial loss of houses and breaking the access roads to the beaches). Thus, it was performed with the Digital Shoreline Analysis System , the multitemporal evaluation (25 years) of shoreline change in the urban stretch of Salinopolis from the Landsat satellite images analysis, limiting the study area into three sectors (Western: Corvina and Macarico beaches, Center: Farol Velho beach and Eastern: Atalaia beach). In the period of 07/22/1988 to 08/28/2013, the linear average retreat obtained for the entire study area was -42.25 m, while the linear average increase was 190.26 m, indicating a progradational trend of the coast. The highest rates of change occurred between the 1988-2001 period, with 18.24 m/year in the Western Sector, 0.06 m/year in the Center Sector and 5.08 m/year in the Eastern Sector. The eroding areas are isolated and occur at the edges of the Corvina and Macarico, and Farol Velho and Atalaia beaches, more exposed locations to the ocean and where urbanization is consolidated in a disorderly manner. The depositional trend of sediment in the shoreline predominates since 1988, exclusively on the margins of each beach, derived from high sediment load brought by estuaries that cut the area.

Seasonal changes of a dynamic macrotidal beach: Case Study of Marieta Beach (Amazon Coast/Brazil)

ABSTRACT Guerreiro, J.S., Ranieri, L. A., El-Robrini, M., Vila-Concejo. Seasonal changes of a dynamic macrotidal beach: Case Study of Marieta beach(Amazon Coast/Brazil) The Amazon Atlantic Coast is a very dynamic area due to the large discharge associated to a large network of rivers that include the Amazon River. Many of the beaches in this area are located within the area of influence of macrotidal range. There is a large sediment availability that creates extensive tidal flats. Waves are moderate with average offshore of 1.8m. The area has a tropical climate with two seasons, rainy and dry, and is under influence of moderate SE/NE trade winds. This paper presents topographic and hydrodynamic data from one of these beaches, Marieta Beach, and shows that while it undergoes severe erosion during the rainy season, accretion and recovery occurs during the dry season. Erosion seems to be associated to the large river discharge in the rainy season (10 3 to 10 4 m3/s−1), high water levels coupled with strong ebbing currents that remove the sediment from the beach. The beach accumulates large volumes of sediment during the dry season (averaging 15.2 m3); the processes that drive sediment transport are not clear but given that onshore winds occur during this period, it is hypothesized that locally wind- generated waves are capable of transporting sediment back to the beach. Seasonal behavior in this case is associated to the tropical seasonality of the rivers instead of traditional storm/fair weather conditions cycles that are often found in the literature.

Salinity variation in the macrotidal mixing zone: the Paracauari River estuary, Marajó Island (Northern Brazil)

ABSTRACT Monteiro, S.M. and Robrini, M., 2016. Salinity variation in the macrotidal mixing zone: the Paracauari River estuary, Marajó Island (Northern Brazil). In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 93–97. Coconut Creek (Florida), ISSN 0749-0208. The objective of this study is to delineate the estuarine zones (Riverine Zone – RZ, under river influence; Mixing Zone – MZ, under marine influence) across different seasonal periods in the macrotidal Paracauari River estuary – Marajó Island (Northern Brazil). We measured salinity (S) and electric conductivity (EC) in the water column using a multi-parameter probe. We also collected data on suspended particulate matter (SPM – gravimetric estimation) along 40 km of the estuary during higher rainfall (660 mm), transitional (260 mm), and lower rainfall (10 mm) periods in 2008. The first sampling station was located at the river mouth (marine domain) and the last sampling station was in riverine domain. Due to La Niña phenomenon, the Paracauari River estuary showed mean EC and S ranging from 256 μS.cm−1 and 0.1, respectively, in the higher rainfall period, to 11002 μS.cm−1 and 6.1 in the lower rainfall period. Maximum SPM concentrations (93.72 mg.L−1) occurred during the higher rainfall period and minimum values (15.49 mg.L−1) occurred during the lower rainfall period. Therefore, RZ (oligohaline, S < 1.0) prevails during higher rainfall period; during the transitional period, an eight km-wide MZ (oligohaline, S = 1.5) is present and the RZ is upstream; in the lower rainfall period, marine waters penetrate as far as 40 km from the mouth, thus characterizing this stretch as MZ (mesohaline, 2.5 < S < 7.5). Hence, the zonation of the Paracauari River estuary is influenced by river waters during periods of higher rainfall rates and by marine waters during periods of lower rainfall rates.