Abstract
Effects of climatic changes in transitional ecosystems are often not linear, with some areas likely experiencing faster or more intense responses, which something important to consider in the perspective of climate forecasting. In this study of the Venice lagoon, time series of the past decade were used, and primary productivity was estimated from hourly oxygen data using a published model. Temporal and spatial patterns of water temperature, salinity and productivity time series were identified by applying clustering analysis. Phytoplankton and nutrient data from long-term surveys were correlated to primary productivity model outputs. pmax, the maximum oxygen production rate in a given day, was found to positively correlate with plankton variables measured in surveys. Clustering analysis showed the occurrence of summer heatwaves in 2008, 2013, 2015 and 2018 and three warm prolonged summers (2012, 2017, 2019) coincided with lower summer pmax values. Spatial effects in terms of temperature were found with segregation between confined and open areas, although the patterns varied from year to year. Production and respiration differences showed that the lagoon, despite seasonality, was overall heterotrophic, with internal water bodies having greater values of heterotrophy. Warm, dry years with high salinity had lower degrees of summer autotrophy.
Highlights
Current global trends in greenhouse gas emissions will lead to at least 1.5 ◦ C of atmospheric warming by 2030–2050 and at least 3 ◦ C by 2100 [1,2], and half the world’s population already experiences temperatures 1.5 ◦ C warmer than preindustrial [3]
This study shows that in the Venice lagoon in the latest decade, there have been years where high water temperatures were recorded for long periods over the summer while winters had colder values than other years (2012, 2017, 2019) as well as a cluster of years when extremely high summer water temperatures were observed (2008, 2013, 2015, 2018)
We demonstrated warming occurrences in recent years in the Venice lagoon and some concomitant effects on pmax
Summary
Current global trends in greenhouse gas emissions will lead to at least 1.5 ◦ C of atmospheric warming by 2030–2050 and at least 3 ◦ C by 2100 [1,2], and half the world’s population already experiences temperatures 1.5 ◦ C warmer than preindustrial [3]. In recent years (1986–2005), considerably stronger increasing tendencies for SST have been estimated (0.02 ◦ C year−1 [6]). This increase in SST is not homogeneous, with estimates for 1985–2006 in the Mediterranean of circa 0.03 ◦ C (peaking up to increases of 0.16 ◦ C in summer months [7]). Transitional coastal areas are of a heterogeneous nature, meaning that climatic impacts in these areas are context-specific and may be difficult to pinpoint [8] and to generalize depending upon local ecosystem characteristics such as depth and flushing times [9]. According to [9], lagoons were found to be the fastestwarming ecosystem types, falling within the “warm spot” of shallow average depths and short–medium flushing times
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