Total Ecosystem Metabolism Variability in a Subtropical Lagoonal Estuary Channel-Site

Daily, seasonal, and interannual/austral spring (among austral springs only) responses of total ecosystem metabolism (EM) were studied for the first time for the Patos Lagoon estuary using Odum’s Open-Water method. The method was applied from 2016 to 2021 for a channel-site in the inner part of the estuary. The main objective was to determine the driving factors that control EM at different timescales. Net EM (NEM) was heterotrophic throughout the year (mean; standard error: − 193.8; 7.8 mmol O 2 m −2 day −1 ), with gross primary production (GPP) of 89.7 ± 3.7 mmol O 2 m −2 day −1 and community respiration (CR) of − 281.6 ± 10 mmol O 2 m −2 day −1 . Annual GPP was estimated at 298.8 g C m −2 year −1 . Higher EM rates were observed during the austral spring/summer and lower rates during the fall/winter. Smaller timescales and spring/summer exhibited greater fluctuations than long-term and other seasons. The high net heterotrophy was attributed to high turbidity and local depth, in which the majority of water column is below the euphotic zone, where respiration prevails. EM rates were mainly controlled by hydrodynamics: daily by wind-induced short-term salinity changes due to shifts in inflow/outflow of marine/estuarine waters, and photosynthetically active radiation (PAR); seasonally by the freshwater flow regime (drought and flood seasons), which induced changes in the primary production co-limiting factors such as turbidity and nutrient availability, as well as organic matter supply and decomposition (nutrients and organic matter inferred from turbidity); and interannual/austral spring also by the freshwater flow regime, but related to extreme conditions caused by weather/climatic phenomena. In the spring of 2016, an extratropical cyclone occurred with heavy rainfall and freshwater flow, resulting in unusually high EM rates over the following 2 months. The first total EM estimates for the Patos Lagoon estuary, from daily to interannual/austral spring bases, showed the importance of total EM estimates for providing a basis for studies on the effects of climate change on EM of the Patos Lagoon estuary.