Coastal lagoons are ecologically and economically important environments but a relative low number of studies were carried out in subtropical and permanently closed coastal lagoons. The present study aimed at assessing the temporal and spatial dynamic of trophic relevant water quality parameters in the small, deep and freshwater Peri coastal lagoon, South Brazil. During the 19 sampled months (March/2008-September/2009) spatial homogeneity (horizontal and vertical) was registered in all seasons for all variables, a condition related to the strong wind influence and low human occupation in the lagoon watershed. Seasonal variations of the water quality could be observed and they can be explained mainly by variation on temperature, wind forces and direction and rainfall, characteristic from the subtropical weather. Comparing this study with two others conducted in Peri lagoon in 1996 and 1998, no critical differences that evidence alteration in the water quality were found, but climate differences may have influenced in some small variations observed. The use of four trophic state indices indicated that indices designed for temperate lakes are inappropriate for the subtropical Peri lagoon. The lagoon was classified as oligotrophic for nutrients concentrations and meso-eutrophic for transparency and chlorophyll-a, which can be explained by the high densities and monodominance of the cyanobacterium Cylindrospermopsis raciborskii and the high recycling rates observed in warmer water bodies, when compared to the temperate ones.

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ResumoVariação dos nutrientes e qualidade das águas costeiras da Ilha de Santa Catarina, Brasil. No presente estudo, investigou-se a variação sazonal dos nutrientes e da qualidade da água costeira da Ilha de Santa Catarina (SCI) entre Agosto/2006 e Fevereiro/2008. As amostras de água foram analisadas segundo: temperatura, salinidade, pH, oxigênio dissolvido, material particulado em suspensão, clorofila-a, nitrogênio inorgânico dissolvido (NID) (nitrito + nitrato + amônia), fosfato, silicato, nitrogênio total (NT) e fósforo total (PT). Os resultados mostraram que na Baia Norte a temperatura da água e salinidade apresentam maior variação que no Pântano do Sul. Os valores médios de temperatura e salinidade de 17,6 o C e 34,8 no inverno e 18,1 o C e 34,6 na primavera, bem como a maior concentração de nitrato de 4,12μM neste último período estão fortemente relacionados com as assinaturas da Água de Plataforma Subtropical (APST) e da Água Central do Atlântico Sul (ACAS), respectivamente. As razões N:P (NID:fosfato) e Si:N (silicato:NID) indicam que o nitrogênio é o nutriente limitante para a área. Ademais as concentrações de nutrientes inorgânicos dissolvidos são mais baixas que em outras áreas costeiras urbanizadas da Plataforma Sudeste Brasileira (PSB). A avaliação do estado trófico indica que as águas costeiras da SCI podem em geral ser classificadas como mesotróficas, chegando a eutróficas em alguns períodos do ano.Unitermos: eutrofização, parâmetros físico-químicos, ressurgência, urbanização, zona costeira AbstractIn the present study, seasonal variations of nutrient concentration and water quality of two coastal areas of Santa Catarina Island (SCI) were investigated from August 2006 to February 2008. Water samples were analyzed for temperature, salinity, pH, dissolved oxygen, suspended particulate matter (SPM), chlorophyll-a, dissolved inorganic nitrogen (DIN) (nitrite + nitrate + ammonium), phosphate, silicate, total nitrogen (TN) and total phosphorus (TP). The results showed that water temperature and salinity in the North Bay present greater C and 34.6 in the spring, and the highest nitrate concentrations of 4.12μM (in the spring), are strongly related to the signatures of Subtropical Shelf Water (STSW) and South Atlantic Central Water (SACW) respectively. The low N:P (DIN:phosphate) and high Si:N (silicate:DIN) ratios indicate that nitrogen is the limiting nutrient in the area. In addition, dissolved inorganic nutrient concentrations are lower than in other urbanized coastal areas in the Southeastern Brazilian Bight (SBB). The trophic state evaluation showed that SCI coastal waters can be classified in general as mesotrophic, reaching eutrophic conditions during some periods of the year.

Aim: the present study aimed at assessing the response of phytoplankton biomass (as chlorophyll-a) to simulated conditions of increased water temperature and phosphorus (P) inputs in Peri lagoon, a subtropical coastal lagoon dominated by Cylindrospermopsis raciborskii most of the year; Methods: microcosm experiments were conducted in thermostatic light chambers during 3 and 7 days in austral summer, autumn and winter 2009. Control temperatures were tested against 3 and 5 °C rises in water temperature in each season. In each temperature treatment, three P concentrations were tested: control (non-enriched, ~1.5 µg.L -1 PO 4 3+ ) and enrichments of four (+6 µg.L -1 PO 4 3+ ) and eight (+12 µg.L -1 PO 4 3+ ) times natural concentrations; Results: the results showed that P enrichments alone did not increase chlorophyll-a concentrations, but temperature increases significantly elevated phytoplankton biomass in autumn and winter microcosms. Water temperature increases were followed by significant elevations in the oxygen saturation levels in all microcosms and seasons. The combined effect of increased temperature and P enrichments resulted in the highest chlorophyll-a levels also in autumn and winter. Summer microcosms seem to have been negatively affected by the experimental conditions (too high water temperatures); Conclusions: the bioassays showed that global temperature rises can significantly elevate the phytoplankton biomass in Peri coastal lagoon, especially in colder months and if followed by increased P inputs, what can lead to major ecological consequences to the water body and to water supply issues in the region.

with higher chlorophyll a and lower N concentration in the last three years sampled. The lake was considered potentially P limited during the majority of the study period and a positive correlation was found between chlorophyll a and total and dissolved P concentration. Phytoplankton biomass (as chlorophyll a) was apparently controlled by water temperature and P availability (TN:TP ratio and dissolved P). Water transparency (as Secchi depth) was strongly and negatively influenced by chlorophyll a concentration.Cylindrospermopsis raciborskii abilities to compete for P and light seem to be important factors determining its success and dominance in this low P coastal ecosystem. The fluctuating P supply, probably associated to sediment resuspension by wind in this shallow waterbody, is an advantageous factor for cyanobacteria and has an important role in chlorophyll a dynamics. Thus, high chlorophyll a concentration in this subtropical lake seems to be related to the P-limited condition, shallowness and low water column transparency, which are probably favouring the dominance of C. raciborskii, especially in higher summer temperatures, and leading to high chlorophyll a concentration even in a low dissolved nutrient environment.

Paleolimnology of lake sediments can be a powerful tool to assess various aspects of lake history and catchment change through elemental, isotopic and molecular analysis of the sedimented organic matter (OM). In this sense, the objective of the present study was to investigate the source, depositional history and preservation of OM in the sediments of two different sites in Peri Lake (southern Brazil) to better understand the nature and direction of environmental changes. Therefore, two sediment cores were sampled and analysed for total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) concentrations and elemental ratios, and stable isotope ratios of C and N (δ(13)C and δ(15)N). Both cores showed similar general tendencies, with increasing amounts of OM (range 1-35%), TOC (2.55-258.40 mg g(-1)), TN (0.30-25.97 mg g(-1)) and TP (0.03-4.72 mg g(-1)) from the bottom toward the top more recent layers. TOC:TN ratios (range 8.1-14.7) showed a slight decrease in recent times and indicated a mixture of allochthonous and autochthonous contribution to the OM, with predominance of the last source. TN:TP (range 0.2-51.3) indicated a condition of potential limitation by P in general. Both δ(13)C (range -25.58 to -20.85) and δ(15)N (range 2.6 to 7.1) showed a decreasing pattern toward the top of the cores, in opposition to macronutrient concentration. Differences in the depth variation pattern between the two cores were associated to the marginal location of one of the cores. The results suggest that nutrients and primary production are increasing in the lake.

Although many studies have shown that the dispersion, increased abundance and dominance of cyanobacteria can be attributed to nutrient enrichment, we discuss features contributing to the dominance of Cylindrospermopsis raciborskii in a shallow, polymictic, subtropical coastal lake with low phosphorus and light limitation (Peri Lake). The presence and dominance of C. raciborskii in an environment with such characteristics emphasizes the idea that nutrients alone do not explain the high density of this cyanobacterium. Other features should be considered in explaining this species dominance, such as phosphorus storage and physiological flexibility, which seem to be key features to high densities in low phosphorus systems.

Temporal and spatial variations of organic and inorganic forms of phosphorus in the sediments of a subtropical oligo-mesotrophic shallow lake were investigated in relation to water column parameters, sediment characteristics and benthic fauna. The main results found were: 1) Phosphorus (P)  concentration varied seasonally, with organic P and total P  increasing in the sediments in warmer periods; 2) Sediment spatial variation, in terms of grain size composition and organic matter content, influenced P concentrations; 3) quantities and qualities of P in the sediments were positively correlated with water parameters, especially DO and NO3, Chl-a,  water temperature, pH, and total P. Negative correlations were observed between %OP and DO in sites 1, 3 and 4, and with NO3 in sites 2, 3 and 4; 4) benthic functional feeding groups showed significant relationships with temporal variation in sediment P concentration, including gathering-collectors, shredders, filterers and filtering-collectors. The results suggest a high importance of temperature mediated control of sediment-P release, both directly, through its direct effects on primary production and decomposition rates, and indirectly through its effects on other water and sediment parameters, especially dissolved oxygen concentration.