Paulo Pedrosa

Particulate and dissolved phases as indicators of limnological and ecophysiological spatial variation in Cima Lake system, Brazil: a case study

The spatial distribution and behavior of limnological variables were studied in a fluvial-lacustrine system, in northern Rio de Janeiro State, Brazil. Physical (e.g. temperature, transparency), physico-chemical (e.g. pH, conductivity), chemical (e.g. inorganic nutrients, dissolved oxygen, particulate and dissolved organic carbon), biochemical (water-soluble carbohydrates – SCHO, total proteins – TPROT, chlorophyll a – Chl a and carotenoids – CAR) and biological (phytoplankton taxa composition) variables were assessed in water-column. Results from dissolved and particulate phases varied considerably among sampling sites. The studied variables indicated some relationships, in limnetic zone, between inorganic compounds and organic products (biochemical). In comparison to lake and outflow (channel) waters, the main inflow (stream) body water was characterized by lower concentrations of particulate biochemical variables and higher concentrations of dissolved inorganic-N. Gross biochemical composition of POC and DOC indicated spatial variation in the fluvial-lacustrine system with the minor participation of TPROT-C (total protein carbon) and SCHO-C (water-soluble carbohydrate carbon) in the center of the lake. At the horizontal space of the lacustrine system, at the ends of the lake, it was also observed a shift between the relative participation of TPROT-C and SCHO-C in POC. Ecophysiological state and nature of particulate matter were also evaluated through photosynthetic pigment concentrations, light microscope analysis, (C:N)a, C:Chl a, SCHO:TPROT, TPROT:Chl a and SCHO:Chl a ratios. Spatial variations were recognized in the fluvial-lacustrine system and were linked to a variety of factors such as the nature (detrital vs. living plankton algae) and origin (allochthonous vs. autochthonous) of the suspended particulate matter, hydrological characteristic of the environments (lotic vs. lentic), phytoplankton metabolical responses induced by nitrogen deficiencies, and wind stress. Additionally, based on the present concentrations of Chl a and the high proportion of the cyanobacterium Cylindrospermopsis raciborskii (∼ 90%) in Cima Lake phytoplankton composition we point out that the lacustrine system has suffered profound limnological changes from the last 10 years.

Linking major nutrients (C, H, N, and P) to trace metals (Fe, Mn, and Cu) in lake seston in southern Brazil

We investigated the relationships between major nutrients (C, H, N, and P) and trace metals (Cu, Fe, and Mn) in seston samples from ten lake/lagoon systems in southern Brazil. The systems were characterized by a diverse set of limnological features, including surface areas from 10−1 to 102 km2, water color, aCDOM(440), from 1.4 to 12.9 m−1, and electrical conductivity from 50 to 100 000 μS cm−1. Seston concentrations also varied a great deal, 32-fold. The elemental (C: N, C: P, and N: P) and C: Chl-a ratios in the seston samples indicated, however, common features; i.e., most of the lakes were N-and/or P-limited, and the seston organic fraction was composed of nonvascular plants (e.g., phytoplankton). Our intersystem comparison revealed that the relative content of organic matter in seston and seston concentrations in lake water tended to correlate positively and negatively, respectively, with trace metal concentrations across the seston samples. Possible influences of elemental and C: Chl-a ratios on the association of metals with seston matrices, although theoretically important, were only partially evidenced here; positive correlations were found between C: N and also Org-H: N ratios with trace metal concentrations. We speculate that such results could be circumstantial, as the nature of the seston matrices appeared to be very similar among them. This hypothesis should thus be the theme of further research. In short, our findings suggest that C: N and Org-H: N ratios as well as the relative content of major nutrients in seston and seston concentrations can be importantly related to trace metal concentrations in seston samples. In discussing the results, however, we consider that metal-seston relationships depend on a variety of physical, chemical, and biological factors and/or variables other than those measured in this study, which could also contribute for defining and explaining variations in metal-seston concentrations in lake ecosystems.

Environmental sustainability at the hierarchical level of lake systems

This paper argues that some determinants of environmental sustainability may be illuminated by examining temporal and geographic variation across lake systems. Typically, lakes respond to both transient and more permanent environmental changes, natural or anthropogenic, and the results of these variations are usually recorded by a diverse set of in-lake indicators. Cause and effect relationships from such complex environmental interactions can be evaluated from physical, chemical and biological data related to lake structure and function. Given the wide distribution of such systems over the planet, we emphasise their potential application not only to local/regional, but also to global scales. Objectively, a local case study is described (Cima Lake, Brazil), and we highlight the potential contribution of lake ecosystems as a repository of extensive environmental information. The method has the potential to be useful to analyse environmental sustainability and to improve the knowledge base for land-use policies.

4 – HIDROQUÍMICA, CARBONO ORGÂNICO E NUTRIENTES DISSOLVIDOS E PARTICULADOS NA BACIA DE CAMPOS*

RESUMO Aguas oceânicas tropicais sao conhecidas por apresentar valores minimos de nutrientes dissolvidos e valores maximos de material particulado na camada eufotica, onde ha maior producao primaria (camada biogenica), ocorrendo incremento da concentracao de nutrientes dissolvidos e declinio de particulados nas massas de agua da camada afotica (biolitica). Nesta pesquisa, a hidroquimica da area de abrangencia da Bacia de Campos foi avaliada atraves de amostragens em 72 estacoes de coleta, em ate seis profundidades (superficie, segunda profundidade, e os nucleos das massas de agua mais profundas), nas estacoes chuvosa e seca de 2009. As distribuicoes verticais de nutrientes dissolvidos e de material particulado apresentam padroes de concentracao tipicos de aguas tropicais permanentemente estratificadas e, como esperado, maiores valores foram encontrados nas aguas da plataforma continental em relacao a regiao de talude. Estes resultados confirmam o papel do continente como fonte de materiais para a zona pelagica. Adicionalmente, tambem sugerem a ocorrencia de processos fisicos advectivos com sinais nas aguas de areas mais rasas da plataforma, em funcao da atividade de ondas e correntes. Finalmente, as variacoes na distribuicao espacial observadas para nitrato, ortofosfato e silicato possivelmente estao relacionadas a intrusao da Agua Central do Atlântico Sul (ACAS) na plataforma continental na regiao de Cabo Frio e a formacao de vortices na regiao do Cabo de Sao Tome, regioes onde foram encontradas as maiores concentracoes de nutrientes dissolvidos e material particulado.

5 – MATÉRIA ORGÂNICA DISSOLVIDA CROMÓFORA*

RESUMO A materia orgânica dissolvida constitui o maior pool de carbono orgânico marinho, sendo comparavel aos estoques globais de carbono associado a biomassa viva de plantas terrestres e ao CO2 atmosferico. Parte da materia orgânica dissolvida presente nas aguas marinhas, cerca de 50-70%, e representada por material cromoforo, absorvedor de luz, sendo denominada materia orgânica dissolvida cromofora (MODC). Atraves dessa propriedade optica e possivel caracterizar variacoes quantitativas e qualitativas da fracao cromofora de pools orgânicos dissolvidos e, por extensao, avaliar a dinâmica da materia orgânica dissolvida como um todo. Neste estudo, a materia orgânica dissolvida cromofora foi caracterizada na area de abrangencia da Bacia de Campos (RJ, Brasil). Foram determinados os coeficientes opticos de absorcao, absorcao especifica e de inclinacao espectral, considerando duas campanhas de amostragem, em um periodo chuvoso e outro seco de 2009, distribuidas em 72 estacoes de coleta e profundidades que variaram entre 1 m (superficie) e 2.500 m. De um modo geral, tomando por base os dados referentes a superficie, foi possivel observar uma maior quantidade de cromoforos no periodo chuvoso, na regiao costeira e na porcao sul da area de estudo. Na regiao de talude, os perfis verticais indicaram uma tendencia de aumento de cromoforos com o aumento da profundidade. Os nossos resultados parecem relacionados a diferentes fontes (autoctones e aloctones) e estados (e.g. tamanho molecular, labil-recalcitrante) da materia orgânica dissolvida no sistema. Nesse sentido, alguns fatores ambientais regionais, como as transferencias pontuais (Rio Paraiba do Sul) e nao pontuais de materia orgânica na interface continente-mar, o padrao de circulacao das correntes marinhas na regiao, as diferentes caracteristicas termohalinas das massas de agua em associacao a processos de degradacao microbiana e foto-oxidativa, sao discutidos como provaveis fontes de variacao optica inerente da materia orgânica dissolvida cromofora na Bacia de Campos.