Space time evolution of the trophic state of a subtropical lagoon: Lagoa da Conceição, Florianópolis Island of Santa Catarina, Brazil

Abstract

High levels of eutrophication in coastal lagoons due to human activity have been documented worldwide. Among the main impacts observed are anoxia, hypoxia, toxic algal blooms, fish kills, loss of biodiversity and loss of bathing. This study aimed to evaluate the evolution of the trophic state of Lagoa da Conceição, a subtropical lagoon located in an urbanized watershed on the island of Santa Catarina -Brazil. Spatio temporal patterns of stratification and eutrophication were investigated to understand the main biochemical changes over time. The water quality data were obtained from field campaigns supplemented with literature of the last 15 years. The vertical structure of the water column and the trophic state were evaluated by the stratification index and the TRIX index, respectively. Analyses of variance were performed in order to identify possible temporal variations in vertical stratification and trophic level. Eutrophication effects on biogeochemical cycles were verified through a multi-dimensional cluster analysis (MDS) and correlations between variables related to physical, chemical and biological processes were verified by principal component analysis (PCA). The results showed that the water column is homogeneous in all regions except in the central region of the lagoon, and the highest ammonia concentrations and lowest dissolved oxygen concentrations with periods of anoxia are observed in bottom waters. The study looked at the high trophic level of the lagoon and its inability to process the biogeochemical changes imposed by urban development.Keywords: TRIX; Coastal lagoons; Stratification; Hypoxia; Biogeochemical cycles. RESUMONíveis elevados de eutrofização em lagunas costeiras devido à atividade antrópica têm sido documentados no mundo inteiro. Dentre os impactos observados pode-se destacar anoxia, hipoxia, floração de algas tóxicas, mortalidade de peixes, redução da biodiversidade e perda da balneabilidade. O presente estudo teve por objetivo avaliar a evolução do estado trófico da Lagoa da Conceição, uma laguna subtropical localizada em uma bacia hidrográfica urbanizada na Ilha de Santa Catarina -Brasil. Para compreender as principais modificações biogeoquímicas ao longo do tempo foram investigados os padrões espaço-temporais da estratificação e da eutrofização. Os dados de qualidade da água foram obtidos a partir de campanhas de campo complementados com dados da literatura dos últimos 15 anos. A estrutura vertical da coluna da água e o estado trófico foram avaliados pelo o índice de estratificação e o índice TRIX, respectivamente. Análises de variância foram realizadas com o objetivo de identificar possíveis variações temporais na estratificação vertical e no nível trófico. Efeitos da eutrofização nos ciclos biogeoquímicos foram verificados através de uma análise de agrupamento multidimensional (MDS) e correlações entre as variáveis relacionadas a processos físico-químicos e biológicos foram verificadas através da análise de componentes principais (PCA). Os resultados mostraram que há hom...

Phytoplankton Biomass and Environmental Descriptors of Water Quality of an Urban Lagoon

“…Among the aquatic ecosystems, the coastal lagoons stand out for offering important environmental services (e.g., food production, nutrient cycling, recreational activities, and aquaculture). However, they have been degraded worldwide by human activities associated with rapid urbanization [5][6][7][8]. Therefore, coastal ecosystems need constant evaluation to provide the protection of the populations and the improvement of the quality of life.…”

Diversity and space-time dynamics of fish assemblages in a coastal lagoon, western Atlantic

“…The Conceição Lagoon, located in the subtropical western Atlantic, is the target of intense environmental impacts because it is a hub for leisure activities, culture, tourism and recreation (Sierra de Ledo et al 1985). In the 1980s, this lagoon was already considered eutrophic (Odebrecht and Caruso Jr 1987) and in the 1990s, the number of inhabitants in its surroundings tripled (IBGE 2000), increasing nutrient and organic matter intake in this ecosystem.…”

“…Another impact to this Lagoon was the opening of a channel that connects the lagoon to the sea in 1982 (Lisboa et al 2008), which caused an even greater homogenization in its physical and chemical parameters (Silva et al 2017). These impacts vary seasonally and spatially, also influencing the distribution of fish fauna (Pazete de Oliveira and Tejerina-Garro 2010).…”

“…According to Barbosa (2003), in a survey of the fishery data made between 1964 and 1998 in Conceição Lagoon, the catch in the fishery had a linear decrease, decreasing from 326 tons to 5 tons of fish and crustaceans in the course of these years. In the same period, the Conceição Lagoon suffered major changes in water quality due to the eutrophication process (Fonseca 2004), which may lead to impacts such as anoxia, hypoxia, toxic algal blooms, fish mortalities and reduction of the biodiversity of these systems (Silva et al 2017).…”

Bacterioplankton Activity in a Meso-eutrophic Subtropical Coastal Lagoon

“…In coastal ecosystems such as the Conceição Lagoon, a meso-eutrophic coastal lagoon [ 18 ], additional inputs of allochthonous material can stimulate heterotrophic microorganisms and consequently lead to oxygen depletion [ 19 – 21 ]. Anoxia occurrence has increased significantly in the last 15 years in the central area of the lagoon [ 18 ], and its trophic state has changed from oligo-mesotrophic to meso-eutrophic in the same period of time [ 18 ]. Thus, we hypothesized that bacterioplankton activity, determined here by bacterial production and growth, would increase in this meso-eutrophic system if exposed to simultaneous external inorganic nutrients' sources and organic matter.…”