Navegando por Autor "MELO, Odilon Teixeira de"

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Acesso aberto (Open Access)
Comportamento biogeoquímico de nutrientes no estuário do Rio Bacanga, Ilha de São Luís-MA
(Universidade Federal do Pará, 1998-10-08) MELO, Odilon Teixeira de; LIMA, Waterloo Napoleão de; http://lattes.cnpq.br/1229104235556506
The Bacanga River is a sub-estuary of the São Marcos Bay and is located in the metropolitan region of São Luís. It is a region that has multiple uses (fishing, drinking water collection, domestic sewage disposal, recreation and leisure, etc.). The cycle of essential nutrients has been studied in several estuarine systems, interactions with biota (primary production), with suspended and bottom sediments, influence of river runoff, enrichment of coastal waters, fertilization by domestic sewage, constitute the main lines of research in these environments. In the Bacanga estuary, the enrichment of nitrogen and phosphorus has contributed to the eutrophication process of the estuarine zone. On the other hand, the construction of a dam downstream (Figure 2.1), reduced the inflow of coastal waters during the ebb and flow of the tide and, on the other hand, an upstream dam reduced the flow of fresh water to the mixing zone. The main objective of this work was to characterize the biogeochemical behavior of essential nutrients (C, N, P and Si), through a spatio-temporal distribution, interaction with primary production and phytoplankton biomass (chlorophyll “a”) and its relationships with some physical, physical-chemical and chemical parameters. Six field campaigns were carried out during 1997, three in the rainy season (February, April and June) and three in the dry season (August, October and December), with sampling, in each campaign, in twelve collection stations in a profile horizontal and in an extension of 12 km between upstream and downstream. A vertical profile was also carried out at collection stations number 2, 8 and 11 in order to observe the existence of stratification in the estuarine zone. In the field, temperature, conductivity and transparency were measured and water samples were collected for the different physical-chemical and chemical parameters. In the laboratory, classical titrimetric methods, ultraviolet-visible and atomic absorption spectrophotometry were used. The results showed (downstream) the following values for the chemical species: ammonium 4 to 100µM, nitrite 0.6 to 9.7µM, nitrate 1.3 to 7.3µM, urea 2.9µM, phosphate 2 to 14.5µM and silicate 19 to 89µM; and, upstream 0.3 to 3µM ammonium, 0.2 to 1.2µM nitrite, 0.8 to 2.8µM nitrite, 1 to 2µM urea, 0.15 to 1.96µM phosphate and 82 to 196µM silicate. These high values, in the downstream part of the estuarine system, show that the main source of these nutrients is domestic sewage, since the sewage discharge points are concentrated in this area of the estuary. The values found in the upstream part can be considered as natural (background) for the region. Dissolved oxygen ranged from 2 to 5.5ml/L, considering the longitudinal profile, from downstream to upstream, depending on the biogeochemical processes in which it participates. In the downstream part, the values are low (1.9 to 3ml/L) due to weak turbulence and low primary production. On the contrary, in the downstream part, the greater turbulence and the influence of the coastal waters richer in oxygen, justifies those higher values (above 4ml/L). Hydrogen sulfide gas was determined only in the months of April and October and ranged from 1 to 3.4mg/L, also in the longitudinal profile. Primary production showed maximum values (26 to 138mgC/m3/h) in August and considering three depth levels (1, 50 and 100%) of the euphotic zone and chlorophyll “a” from 10 to 44mg/m3 in the longitudinal profile. . This high primary production in this zone of the estuarine system can be explained by several factors, such as low turbulence, the availability of nutrients and sunlight that month. The major ions (Na+, K+, Ca2+, Mg2+ and SO42-) showed the following values: sodium from 12 to 9400mg/L, potassium from 2.6 to 340mg/L, calcium from 10 to 360mg/L, magnesium from 15 to 1143mg/L and sulfate from 5.8 to 2375mg/L, considering the variation between the months of April and October, which correspond to the dry and rainy seasons. The salinity ranged from 0 to 32%, the temperature from 24.5 to 31.3°C, both in the longitudinal profile. This shows that the spring waters are cold and of zero salinity. The vertical profiles showed that there is a thermal, haline and chemical stratification (dissolved gases: oxygen and hydrogen sulphide) that can lead to bottom waters and a deficiency or absence of oxygen. This oxygen deficiency can be induced by thermohaline stratification and by the decomposition of organic matter of natural (mangrove and river runoff) and anthropogenic (domestic sewage) origin. Conservative behavior was evidenced for salinity, temperature, conductivity and major ions and non-conservative for essential nutrients (N, P and Si). Fertilization of Bacanga's estuarine waters occurs mainly through domestic sewage, allowing the environment to present high rates of primary production. However, excessive fertilization can lead to anoxia of the water column with possible death of fish and animals.
Acesso aberto (Open Access)
Dinâmica de nutrientes e da matéria orgânica no manguezal do Igarapé Nunca Mais - Ilha de São Luís (MA)
(Universidade Federal do Pará, 2002-11-22) MELO, Odilon Teixeira de; LIMA, Waterloo Napoleão de; http://lattes.cnpq.br/1229104235556506
It is well known that the State of Maranhão has more than fourty percent of the Brazilian mangroves covering an área with almost 4800km2 and along of 640km of coastline. These mangrove swamps border a number of tidal channels, bays, gulfs, and others estuarine systems, where the macro-tidal system gives a singular condition to this environment, that it is different from the others Brazilian áreas. The exportation of macro-particles from the mangroves to the coastal waters is well known. However, there is a discussion if the mangroves import or export micro-particles and dissolved nutrients to the coastal areas. Few studies have been developed in this subject due to the methodological complexities of the flow calculations. The choice of the pilot-area for this study is the igarapé Nunca Mais, a tidal channel surrounded by an area of 1.22km2 of mangrove ecosystem, situated in the Northeastern portion of the São Luís Island. This choice is due bay the fact that in this area occurs exchanges with the coastal waters from the Maranhão Gulf take place. This tidal channel is the main transport pathway between the mangrove and the coastal waters. During the spring tides this mangrove is completly flooded. The main aim of this study was to evaluate the role of a mangrove region — Maranhão Gulf — in a macro-tidal area in exchanging of materials with the coastal waters. The characterization and quantification of the dissolved inorganic nutrients and the organic matter were the main focuses of this study. For this purpose were utilized flows calculations from "Eulerian" method. During the period of 13 months (from April 2000 to April 2001), in the neap and spring fluxes of the dissolved inorganic nutrients (ammonium, nitrite, nitrate, phosphate, and silicate) and those of the organic matter (organic carbon, organic nitrogen, and organic phosphorus) were determined along 52 tidal cycles. For the characterization of organic matter were used elemental ratio C/N, isotopes 13C and 15N ratio, and by the identification of dissolved humic substances as tracers for organic matter sources. The differences on day clear and orvernight show average values from 0960 for the pH and salinity, positive values of 5, 6, 8 and 11%, respectively, for nitrate, phosphate, ammonium, and silicate, and negative values for the oxygen (-10%), and for the dissolved and particulate organic matter (-1% to -6%). The dissolved nutrients and organic matter varies such as tidal ranges showing maximum values in the low tile, indicating flow from intersticial water of the mangrove for the tidal channel. Particulate organic matter values show variations relationships with current velocity showing resuspension and sediment transport. This fact confirms that the biological processes, such as nutrient consumption and organic matter deposition, in the tidal channel, and the tidal dynamics were relevants in the lief variations. The results obtained in this study show a seasonal variation with minium values in the dry season, except for the silicate, and maximum values in the rainy season, showing the raro precipitation influence in the transport from mangrove for the coastal waters. In addition, in the dry period, occurs maximum consumption of nutrient by phytoplancton, as well as, observed on primary production. It was evidencied also lower values in the concentration of particulate organic matter during this dry season due the lower fluxes values from the mangrove. The net exportation of inorganic nutrients and the organic matter in the mangroves of the São Luís Island (Maranhão State, Brazil), in the tidal channel Igarapé Nunca Mais, is evidencied in this study by interpretation of the flows calculations and the values from C/N. rations, elemental and isotopic. The isotopes of C and N used here as tracers lead to the identification of the primary sources of the organic matter in the tidal channel, i.e., the originated from mangroves, the coastal waters, and the resulting from allochthonous production. During the rainy period there are dominance of the organic matter (dissolved and particulate) transported from the mangrove, while in the dry period the marine and autochthonous sources are more considerables. The photosynthesis of the phytoplancton, in the tidal channel, justifies the autochthonous production. The net exportation of the dissolved organic matter for the coastal waters is slightly superior to the particulate organic matter (DOM, 14mM-2.day-1; POM, 20mM.m.-2.day-1). Perhaps this difference is due a fast sedimentation in the intermediary zune of the tidal channel that have the biggest profundity; this fact leads a minor quantity of particulates exported for coastal waters. It infers that this organic matter is constititued, dominantly, by humic substances because they are more refractory to the bacterial activity and consequently they can be transported by tidal currents for the adjacent coastal waters. Of course, the tidal amplitude ranges and pluviometric precipitation are relevant factors in these exportation processes. By this exposition, this study confirms the important role of mangrove for the fertilization of the coastal waters of Maranhão Gulf.