Spatial and temporal dynamic of trophic relevant parameters in a subtropical coastal lagoon in Brazil

Abstract

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.

Determining the high variability of pCO2 and pO2 in the littoral zone of a subtropical coastal lake

“…Spatial homogeneity of nutrients and chlorophyll a, elevated densities of the cyanobacteria Cylindrospermopsis raciborskii (Woloszinska) Seenayya and Subba-Raju, and low phosphorus concentration have been observed in the lake (Hennemann and Petrucio 2011;Tonetta et al, 2013). The system has two main tributaries (Cachoeira Grande and Ribeirão Grande Streams) and it is the largest source of drinking water in Santa Catarina Island (Figure 1).…”

Considerations regarding the dominance of Cylindrospermopsis raciborskii under low light availability in a low phosphorus lake

“…The lake has a surface area of 5.07 km 2 , maximum depth of 11.0 m, and showed spatial homogeneity, both horizontally and vertically, concerning chlorophyll-a and nutrients (Hennemann & Petrucio 2011). The lake has been considered polymictic and light limited, according to Tonetta et al (2013).…”

“…) -1 ) and a potential P limitation to phytoplankton growth (Reynolds 2006). A previous study in the lake showed that traditional trophic state indices do not represent conditions in Peri Lake appropriately (Hennemann & Petrucio 2011). According to the authors, the indices developed for temperate lakes indicate a mesotrophic condition concerning total P concentration, while indices adapted for warmer water bodies considered the lake oligotrophic.…”

“…According to the authors, the indices developed for temperate lakes indicate a mesotrophic condition concerning total P concentration, while indices adapted for warmer water bodies considered the lake oligotrophic. Additionally, the classification considering Secchi disk depth (water transparency) and chlorophyll-a concentration also differed significantly (from mesotrophic to hypertrophic), according to the index used (see Hennemann & Petrucio 2011 for an extended discussion about application of trophic state indices in the lake). The relative high chlorophyll-a concentration (17.7 μg.L -1 ), mostly due to the high C. raciborskii density, reflects on low water transparency (Secchi depth ~ 1.0 m).…”

“…It is well recognized that Cylindrospermopsis has been extending its distribution to colder regions (Vidal & Kruk 2008;Sinha et al 2012), although always in systems with high nutrients concentration. Here we focus on trying to understand the features leading to C. raciborskii dominance in an environment with low P concentration, light limitation, constantly mixed, and showing C. raciborskii dominance even at low temperatures (Hennemann & Petrucio 2011;Tonetta et al 2013).…”