Patos Lagoon Research Articles

Straining and advection contributions to the mixing process in the Patos Lagoon estuary, Brazil

[1] The estuarine area of coastal lagoons and freshwater-influenced regions presents periodically stratified and destratified conditions. The Patos Lagoon, one of the most important hydrological resources in South America, is located in the southernmost part of Brazil and exhibits such variable conditions. Therefore the aim of this study was to investigate the contributions of straining and advection to the modulation of stratification conditions in the Patos Lagoon estuarine region using potential energy anomaly budgets. This study was based a three-dimensional hydrodynamic numerical model that provided information for the potential energy anomaly equation and wavelet analysis. Results from the potential energy anomaly time series revealed strong variability over a timescale of several days following local wind action and the river discharge pattern. Each part of the estuary exhibited contrasting regimes that were spatially distributed with a different balance of terms. The upper part was dominated by along-shore currents associated with east-west wind component and gravitational flux. Contribution from cross-shore advection became important in the middle part of the estuary, where there was an increase in superficial area observed. The lower region was controlled by the north-south wind component being influenced by advection, cross-shore straining, and transversal circulation, suggesting that current velocity maintained transversal pressure gradients and further circulation. Nonlinear interactions between deviations in the dispersion terms and vertical density and velocity were important everywhere but were associated with modulation effects.

Diet and feeding strategy of the dusky grouper Mycteroperca marginata (Actinopterygii: Epinephelidae) in a man-made rocky habitat in southern Brazil

The dusky grouper (Mycteroperca marginata) is a marine species usually associated with rocky bottoms and reefs. The present work investigated the diet and feeding strategy of a dusky grouper population inhabiting a 4.5 km long pair of rocky jetties located in the mouth of Patos Lagoon estuary. No prior research has been conducted in such man-made habitat and the current study provides a basis for comparative studies on the diet of the dusky grouper populations inhabiting natural vs. man-made rocky habitats. Similarly with previous studies on natural substrates, crabs and fishes were the main food categories consumed (%IRI = 85.1 and %IRI = 12.6, respectively), whereas shrimps and mollusks had lower importance in the diet (%IRI = 1.9 and 0.4, respectively). As previously reported for dusky grouper populations inhabiting reefs and rocky bottoms, the present work revealed conspicuous size related dietary shifts. Blue crabs and fishes become increasingly important food items in the diet of larger individuals (> 500 mm, TL). Finally, it was found that the studied dusky population has a generalist feeding strategy with a high between-individual variation in prey consumption. Such strategy remained similar across the size increment of the species. Our findings suggest that man-made rocky substrates provide suitable feeding grounds for the dusky grouper in southern Brazil and could be used as an additional tool in the conservation efforts of this endangered species.

Abundance of bottlenose dolphins, Tursiops truncatus (Cetacea: Delphinidae), inhabiting the Patos Lagoon estuary, southern Brazil: implications for conservation

A new mark-recapture abundance estimate and a photographic census were carried out to investigate the possible decline in the abundance of the bottlenose dolphins, Tursiops truncatus (Montagu, 1821), in the Patos Lagoon estuary due to the high levels of bycatch mortality which occurred between 2002 and 2006 in oceanic coastal areas close to the estuary. Fourteen systematic boat surveys were conducted between August and early December 2005 to photo-identify the bottlenose dolphins. The estimated number of animals, with long-lasting marks, in the population obtained from Chapman's and Mth models were 51 (95% CI = 49-53) and 52 (95% CI = 51-60), respectively. Taking into account the proportion of dolphins with long-lasting marks in the population, the total estimated population size ranged between 84 (95% CI = 76-93) and 86 (95% CI = 78-95) individuals, respectively, which was very similar to the 84 individuals revealed by the population census. Our results did not differ from the abundance estimate carried out in 1998, prior to the high fishing-related mortality event, suggesting that the population is stable. Plausible argument to explain the stability of the population is that some carcasses found on the oceanic coastal beaches near Patos Lagoon estuary come from animals that do not belong to the estuary community. Future studies should investigate fine-scale habitat partition between estuarine and adjacent coastal dolphins. If the existence of different communities living in close proximity (estuarine and coastal areas near to the estuary) is confirmed, a new abundance estimate is needed to access the conservation status of bottlenose dolphins in this region.

On the Effect of Earth Rotation, River Discharge, Tidal Oscillations, and Wind in the Dynamics of the Patos Lagoon Coastal Plume

The Patos Lagoon is located in the southernmost part of Brazil, between 30°–32° S and 50°–52° W, being connected to the South Atlantic Ocean via a narrow channel that is less than 1 km wide. The lagoon drains a hydrographic basin of approximately 200,000 km2, and its principal rivers contribute with an annual mean discharge of about 2000 m3 s−1. In this work, the dynamics of the Patos lagoon coastal plume was studied considering theoretical situations that determine the relative importance of Earth rotation, river discharge, tides, and winds. To carry out this analysis, the finite element model TELEMAC2D was used for the experiments. The results show that Earth rotation is very important in generating asymmetry in the plume flow. Tides are important for the mixing processes, causing an increase of the plume area and a decrease of the plume penetration offshore. In addition, results also showed that northeast winds displace the coastal plume southward, which is likely to be related to the formation of mud banks south of the Patos Lagoon mouth. During southwest wind events, the mixing zone moves landward, being observed inside the access channel, while part of the coastal plume remains in the coastal zone and is directed northward as a coastal current.

Chemical Speciation and Dissolved Iron in the Pore Water of Patos Lagoon Sediments - Brazil

Sediments can sink or deliver elements to water column. Iron is considered an essential element for the development of cyanobacteria and a limitant to phytoplankton growth. Studies on the chemical speciation of iron in seawater have been conducted, but there is no information about its chemical speciation in pore water, as reported here. This paper presents a voltammetric method to analyze dissolved iron and its chemical speciation in sediment pore water, using adsorptive cathodic stripping voltammetry (AdCSV) and the technique of competitive ligand exchange (CLE-AdCSV), respectively. The limit of detection (LOD = 0.30 10 �6 mol L �1 ), the quantification (LOQ = 0.90×10 �6 mol L �1 ), precision (RSD = 4.9%) and accuracy (98%), were calculated from experiments using certified reference material SLRS-4 (National Research Council Canada). The chemical speciation of pore water from sediment samples collected during April 2009, in the Patos Lagoon Estuary (RS, Brazil), was analyzed for the first time, revealing that the ratio (labile iron to dissolved iron) is significantly lower in pore water extracted from sediments of the upper layer (0 to �5 cm), than from the overlaying water or of the pore water extracted from sediments of the lower layer (�15 to �20 cm).

The Exchange Processes in the Patos Lagoon Estuarine Channel, Brazil

Investigation of process controlling the estuarine-shelf interaction in the Patos Lagoon estuarine channel is accessed using a two-dimensional numerical model. Results obtained suggest this approximation provides good precision level to investigate the advective transport of oceanic waters near the estuarine mouth. The introduction of coastal waters in synoptic time scales is dominated by advection in sub-superficial layers. This process results from the competition between flood currents driven by remote wind effects and gravitational circulation controlled by the intensity of the freshwater discharge. The short term exchange processes follow one most energetic cycle of 8 days and intense flood events occur during periods of low continental discharge and higher intensity winds. Very stratified salinity profiles are found during periods of moderated freshwater discharge. The salt transport is inversely related to the freshwater discharge intensity. It presents a mean rate of the 105 kg.day-1 transported landward during flood events.

Integrated biological responses of zebrafish (Danio rerio) to analyze water quality in regions under anthropogenic influence

This study analyzed water quality in regions around Patos lagoon (Southern Brazil) that are under anthropogenic pressure. Water samples were collected from five different sites, including one used as a source for human consumption (COR) and others known to be influenced by human activities (IP). Danio rerio (Teleostei, Cyprinidae) organisms were exposed for 24h to these water samples, plus a control group. It was observed that: (1) reactive oxygen species levels were lower in COR and IP than in the control group; (2) glutamate-cysteine ligase (catalytic subunit) expression was higher in COR than in other sites; (3) exposure to all water samples affected long-term memory (LTM) when compared to control group. Thus, some water samples possess the ability to modulate the antioxidant system and to induce a decline in cognitive functions, as measured by LTM. The obtained results indicate that a combination of variables of different organization level (molecular, biochemical and behavioral) can be employed to analyze water quality in impacted regions.

Temporal trends in mortality and effects of by-catch on common bottlenose dolphins,Tursiops truncatus, in southern Brazil

The mortality of the bottlenose dolphin,Tursiops truncatus, on the southern portion of Rio Grande do Sul State coast was investigated based on 914 beach surveys conducted between 1969 and 2006. A total of 188 stranded bottlenose dolphins were recorded during this period, indicating a 1.8M:1F sex-ratio of those animals sexed (N = 79). Mortality was low in calves, high in juveniles and sub-adults and slightly lower than in adults. The overall mortality was clearly seasonal overlapping with higher fishing efforts in the Patos Lagoon Estuary and adjacent coastal areas, where most individuals washed ashore. Analysis of a continuous 14-year long subset (1993–2006) of the data indicated relatively low levels of mortality between 1995 and 2000 and a marked increase between 2002 and 2005 followed by an apparent drop in 2006. By-catch was responsible for at least 43% of the recorded mortality between 2002 and 2006. Juvenile males were more susceptible to incidental catches. Among females, by-catch of adults represented 75%. Results of a potential biological removal analysis suggest that current levels of fishing-related mortality are unsustainable for the small resident population of bottlenose dolphins that inhabits the Patos Lagoon Estuary, and that this population may be declining.

Influence of ectoparasitism on the welfare of Micropogonias furnieri

The Whitemouth croaker, Micropogonias furnieri, is commonly found in the estuary of Patos Lagoon, RS, Brazil. Like other cultivated Sciaenidae, M. furnieri has potential for aquaculture. However, several difficult-to-control ectoparasites have been shown to be serious fish culture pests. In this study, the parasite influence on M. furnieri is evaluated through examination of the relationship between abundance and host parasitism indexes, relative condition factor (Kn), and the hepatosomatic (RHS) and gonadosomatic relations (RGS). These indexes are qualitative fish welfare indicators. A total of 181 M. furnieri specimens were collected from the pre-limnic and estuarine sites of the Patos Lagoon. The parasites found were Gauchergasilus euripedesi (Copepoda), Myzobdella uruguayensis (Hirudinea), Neomacrovavitrema argentinensis and Neopterinotrematoides avaginata (both Monogenoidea). The relationship between the parasite abundance and the host indexes was verified, but no significant correlation was determined. This result suggests that the found parasite levels are tolerable. On the other hand, sample area differences affected the occurrence and intensity of parasitism, which suggests that the parasites have a preference for different salinities. This result suggests that different saline conditions could determine when the estuary would be optimal for M. furnieri aquaculture.

Dynamics of the Patos Lagoon coastal plume and its contribution to the deposition pattern of the southern Brazilian inner shelf

The southern Brazilian shelf (SBS) is a region influenced by fresh water. The initial deposition of suspended sediments carried by this fresh water presents important ecological consequences for the area. The aim of this study was to investigate the contribution of the Patos Lagoon coastal plume to the deposition pattern observed along the inner continental shelf by providing estimates of estuarine‐shelf suspended sediment exchange. The study was carried out through three‐dimensional numeric modeling experiments on coupled hydrodynamic and morphodynamic processes. Results were analyzed using the dynamic method proposed by Garvine (1995) to study persistent plumes. The results were also analyzed using wavelet analysis. Results showed that the Patos Lagoon coastal plume behaves as a hypopycnal plume covering the first meters of the water column. The Patos Lagoon presents a dominant ebb condition with a mean discharge of 2088 m3 s−1 and an exportation rate of suspended matter of approximately 1.3 × 107 t yr−1. In the adjacent coastal region deposition prevails in sheltered regions up to 10 m deep, with enrichment in silt reaching up to 10% in the deceleration region of the Patos Lagoon coastal plume. The dynamic balance indicates a behavior typical of small to average‐sized plumes, with a well‐developed displacement along the coast that is mainly controlled by the alongshore wind component. The Coriolis force and bed shear stress present significant contributions during periods of moderate to high freshwater discharge when large‐scale plumes are formed. Transversally to the coast the force balance is associated with the Coriolis effect and wind influence, with a less important contribution from bed shear stress. The inner continental shelf adjacent to the Patos Lagoon entrance is dominantly influenced by plume occurrence. In this region northeasterly winds induce the formation of southwestward currents near the coast. These currents deflect around jetties and generate recirculation zones to the south. The formation of a cyclonic eddy occurs in this area and creates convergence zones that intensify the vertical velocities promoting the deposition of suspended sediments.

A redescription of a common euryhaline cumacean from southern Brazil: Diastylis sympterygiae Băcescu & Queiroz, 1985 (Crustacea: Cumacea)

Diastylis sympterygiae Băcescu & Queiroz (1985) has been reported in many ecological studies conducted in the Patos Lagoon, southern Brazil. However, the original description of this species is based on damaged specimens from stomach contents of rays, and therefore insufficient for a confident identification. In the present contribution, based on a large number of well-preserved specimens now available from the type locality area, the description of this common euryhaline species is completed and its range of distribution as far north as São Paulo is extended.

Primeiro registro e aspectos ecológicos de Hoplerythrinus unitaeniatus (Agassiz, 1829) (Characiformes, Erythrinidae) como espécie introduzida na Bacia do Rio dos Sinos, RS, Brasil

A espécie Hoplerythrinus unitaeniatus é conhecida popularmente como jeju ou aimara. Possui ampla distribuição geográfica, ocorrendo em diversas bacias hidrográficas da América Central e do Sul, com sua localidade tipo, o Rio São Francisco. No Brasil o registro mais ao Sul da espécie é a bacia do Rio Uruguai, Rio Grande do Sul. O presente estudo reporta a primeira ocorrência de H. unitaeniatus no Sistema da Laguna dos Patos, Região Hidrográfica do Guaíba, Estado do Rio Grande do Sul, Brasil. A captura ocorreu em um banhado adjacente ao Rio dos Sinos no Município de São Leopoldo (29° 44' 14,04" S e 51° 05' 11,08" W). Dois exemplares foram coletados com redes de arrasto em maio de 2008. Um dos espécimes foi anestesiado com 2-phenoxy-ethanol, fixado em formalina 10%, identificado e incluído na coleção de peixes do Museu de Ciências e Tecnologia da Pontifícia Universidade Católica do Rio Grande do Sul. O segundo espécime foi mantido vivo em aquário durante dez meses, vindo a óbito por debilidade devido a infestação por Lernaea cyprinacea (Crustacea, Copepoda). A presença de lérnea e a facilidade de criação em cativeiro da espécie fazem factível pensar que os peixes escaparam de alguma piscicultura da região. A captura acidental não reflete na proliferação de uma população auto-sustentável, mas direciona à falta de fiscalização para a criação e comercialização de espécies alóctones e exóticas, que futuramente tendem a gerar a homogeneização da biota aquática.

Chave ilustrada para identificação das zoés de Brachyura do estuário da Lagoa dos Patos (RS) e região costeira adjacente

O objetivo do presente estudo é a elaboração de uma chave de identificação ilustrada das espécies de Brachyura que ocorrem no estuário da Lagoa dos Patos e sua região costeira adjacente. A chave abrange espécies as quais foram coletadas mensalmente, usando uma rede de plâncton (165 cm de comprimento, 60 cm de boca e 330 µm de malha). As amostragens foram realizadas na superfície e fundo. Os especimens foram identifcados mediante comparação com larvas cultivadas em laboratório e com descrições já existentes. A chave utiliza caracteres que não sofrem grandes transformações ao longo do desenvolvimento, e a utilização de figuras para ilustrar a chave permite a não especialistas facilmente identificar as espécies.

Attributes of irrigated rice and soil solution as affected by salinity levels of the water layer

In the State of Rio Grande do Sul, Brazil, flooded rice fields using Patos Lagoon as the source of water for irrigation are subject to be damaged by salinity, since this source is bound to the sea on its southern end. The sensitivity of rice is variable during plant development, being higher in the seedling and reproductive periods. However, there is not enough information about the behavior of plants under salt stress during the course of its development, especially in the vegetative stage. This study evaluated the effect of different levels of salinity of irrigation water on the salinity of soil solution over time and on some plant attributes, during the vegetative stage of rice. The study was conducted in a greenhouse, where seeds of the variety IRGA 424 were sown in pots and irrigated with water with electrical conductivity (ECi) levels of: 0.3, 0.75, 1.5, 3.0 and 4.5 dS m-1; from the tillering initiation (V4) until the panicle initiation (PI). The evaluations made were the electrical conductiviy of soil solution (ECe), the dry biomass of plants and stems, tillering, height and the transpiration of plants. The ECe increased with the ECi over time, and was determined by water transpiration flux in pots. The ECe values at the end of the experiment were high and, in most cases, higher than the critical values for flooded rice. The growth attributes of rice were negatively affected from ECi of 2.0 dS m-1 and ECe of 4.0 dS m-1.

Caracterização das atividades econômicas tradicionais no entorno das marismas no estuário da Lagoa dos Patos (RS)

As marismas são ecossistemas entremarés predominantes na costa brasileira em latitudes maiores que29º S. No estuário da Lagoa dos Patos (RS), 6.837 ha de margens e ilhas são recobertos por marismasque vêm sendo utilizadas pela atividade agrícola e pecuária extensiva desde o século XVII. Este estudovisou caracterizar os usos das marismas pelas atividades econômicas tradicionais (agricultura e pecuáriaextensiva) desenvolvidas no estuário da Lagoa dos Patos. O trabalho foi efetuado nos municípios deRio Grande e São José do Norte por meio de entrevistas semiestruturadas com pessoas envolvidas coma pecuária, a agricultura e a área urbana vivendo no entorno das marismas. As propriedades rurais compecuária possuem uma área média de 306 ha, com uma lotação de 1 animal.ha-1. O pastejo por bovinosocorre sobre Spartina densiflora (inverno) e Scirpus olneyi (verão), podendo consumir 4,6% e 15,3%da produção de biomassa anual, respectivamente. As propriedades agrícolas são de pequeno porte (áreamédia de 19 ha, com 4,2 ha cultivados), produzindo principalmente cebola e hortigranjeiros. Os agricultoresutilizam 6,4% da biomassa anual de S. densiflora e 20,5% de Juncus kraussii como coberturavegetal, adubação e construção de pequenos galpões. A maioria dos agricultores e pecuaristas relatou aexpansão nos últimos 50 anos de J. kraussii sobre campos, áreas cultivadas e marismas recobertas porS. densiflora, bem como os moradores urbanos observaram a erosão das margens no mesmo período.As técnicas agropecuárias tradicionalmente utilizadas nas últimas décadas na região estuarina da Lagoados Patos permitiram a reprodução social da atividade econômica conjuntamente com a conservação das marismas.

Straining and advection contributions to the mixing process of the Patos Lagoon coastal plume, Brazil

The Southern Brazilian Shelf is a region influenced by freshwater, and the evolution of stratification can present important ecological consequences in this area. The aim of this paper was to investigate the importance of straining and advection processes that affect the stratification and destratification of the water column along the Southern Brazilian inner shelf, a region that is influenced by the Patos Lagoon coastal plume. The study was carried out through 3‐D numerical modeling experiments and the results were analyzed using the potential energy anomaly equation and wavelet analysis. Results showed that the potential energy anomaly showed strong variability over a time scale of several days and followed the wind pattern over the study region, and was accompanied by the monthly modulation of river discharge and remote effects associated with variability in oceanic circulation. However, the most important events in synoptic time scales occurred in periods shorter than 20 days and were coincident with the passage of meteorological systems over the study region. Straining and advection were the most important mechanisms for the evolution of stratification in the adjacent coastal region. Nonlinearities and dispersion terms were as important as modulation effects, mainly during periods of high fluvial discharge. Close to the Patos Lagoon mouth, vertical advection explained most of the stratification evolution, due to the morphological characteristics in this region. In the frontal region and far field of the plume, the following two regions must be considered: the northeast part, which is characterized by the convergence of the coastal currents and ebb flows associated with the freshwater discharge that promote the domination of the cross‐shore straining and advection, and the southwest part, which is controlled by the coastal currents that result in the domination by alongshore straining and advection and cross‐shore advection terms. Close to the mouth of the Patos Lagoon, the occurrence of downward velocities generated downward displacement of the isopycnals, which decreases the potential energy anomalies, and vice versa. Near the frontal region, the anomalies were dependent on the intensity of the fluvial discharge. During moderate to high discharge events, the northeastward currents intensified mixing along shore, which decreased the potential energy anomalies. In the same way, the southwestward currents intensified the spreading of freshwater and increased the stratification and the potential energy anomalies.

A drenagem pretérita do Rio Camaquã na costa do Rio Grande do Sul

A análise de registros sísmicos de alta resolução (3,5 e 7,0 kHz), obtidos na Lagoa dos Patos, revelou a presença de diversos canais soterrados que dissecaram profundamente a zona costeira do Rio Grande do Sul (Sul do Brasil) antes do estabelecimento da superfície baixa e levemente ondulada daplanície costeira atual. Em direção ao continente, o sistema de paleodrenagem mapeado de registros sísmicos pode ser vinculado ao curso atual do Rio Camaquã. À jusante, ele pode ser conectado com sistemas de paleocanais da plataforma continental adjacente e talude continental, reconhecidos em trabalhos anteriores através de estudos sísmicos e morfoestruturais. À montante, a drenagem foi escavada no prisma costeiro depositado durante eventos prévios de nível de mar alto do Quaternário. O caminhoda paleodrenagem, reconhecida na planície costeira e plataforma continental adjacente, representa um sistema fluvial-plataformal ligando a bacia de drenagem continental aos depocentros da bacia marginal, atravessando a plataforma continental exposta durante um evento de regressão forçada.

Evaluation of surface sediment contamination by polycyclic aromatic hydrocarbons in colony Z3—(Patos Lagoon, Brazil)

This paper describes the extraction and analysis of Polyaromatic Hydrocarbons (PAHs) in five points of the Patos Lagoon Estuary. These points were in the area named “colony Z3”, which is a craft fishermen community in Pelotas City (southern Brazil). Samples were collected in July of 2007, and the concentrations of 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) were determined by gas chromatography coupled to a mass spectrometry detector (GC/MS). The PAH concentrations ranged from 4.7 to 112.5 µg kg − 1 dry weight. Sediment samples with the highest PAH concentrations appeared at point 2, which is a pier. The correlation between the total organic material (TOM) and the total PAH concentration suggests that TOM plays an important role in controlling the PAH levels in sediments. According to the observed ratios of individual PAHs, the contamination in the studied areas originated both from high-temperature pyrolytic processes and petrogenic sources. The levels of PAHs at the studied sites in the Z3 colony (Patos Lagoon) were low enough that they should not exert adverse biological effects.

Building adaptive capacity to climate variability: The case of artisanal fisheries in the estuary of the Patos Lagoon, Brazil

The vulnerabilities of fishing communities to climate and environmental change represent major issues for the governance of fisheries resources which have a direct effect on human security, livelihoods and rights. This paper explores the dynamics of social-ecological systems in the estuary of the Patos Lagoon in southern Brazil. The paper identifies key factors that increase and/or minimize the vulnerabilities of the fishing communities in this lagoon with the objective of understanding: (a) the degree to which fishing communities are able to build adaptive and learning capacities to minimize/reduce vulnerabilities and maintain their livelihoods; and (b) how and under what circumstances external and internal factors may influence and disrupt the social-ecological resilience in this lagoon system. Results show that fishing communities with a higher degree of self-organization are able to create ways to minimize their vulnerability to adverse climatic conditions. However, only a few communities have developed adaptive mechanisms to cope with the influence of climate on resource abundance and availability. Little external institutional support for small-scale fishing communities, erosion of their traditional resource use systems and decreasing fish stocks in recent decades have all led to a gradual increase in the vulnerability of fishing livelihoods in this lagoon. The uncertainties associated with climate are related to increasing vulnerability and influence the degree of resource conservation and exploitation. The lack of public policies to deal with the impact of climate variability on the livelihoods of fishing communities and the presence of weak institutions in resource governance represent major threats to the social security of fishers in this region.

Pisces, Perciformes, Gobiidae, Ctenogobius stigmaticus (Poey, 1860): new species record at Patos Lagoon estuary, state of Rio Grande do Sul, Brazil

The present note records for the first time the gobiid fish Ctenogobius stigmaticus (Poey, 1860) at Patos Lagoon stuary, state of Rio Grande do Sul, southern Brazil. The known distribution of this species is therefore extended 600 km southwards.