Eutrophication history and organic carbon burial rate recorded in sediment cores from the Mar Piccolo of Taranto (Italy)

Abstract

During the second half of the twentieth century, coastal lagoons in densely populated regions experienced eutrophication due to excessive nutrient inputs. Detrimental effects, including hypoxia/anoxia and harmful algae blooms, have occurred in many Mediterranean lagoons, but their trophic evolution is poorly documented. The lack of adequate monitoring data can partly be offset by examining sedimentary records. In the Mar Piccolo, a lagoon comprising two basins near Taranto (Italy), eutrophication has followed population growth and pollution resulting from naval activities and massive industrialisation. Based on 210Pb-dated sediment cores, continuous in situ density profiles obtained with computed tomography, organic carbon (OC) and total nitrogen (TN) content and OC and TN isotopic signatures, this paper reconstructs the history of eutrophication, discusses the sources of organic matter and provides an estimate of the OC burial rate before and during the eutrophic period. OC burial increased in the period 1928–1935 and peaked in the decade 1960–1970. OC and TN content were still high in the surface sediments collected in 2013, despite partial diversion of sewage outfalls in the period 2000–2005. The divergent δ13C and δ15N signatures of the two basins during the eutrophic period suggest they were affected by different nutrient sources. The OC burial rate during the eutrophic phase (≈ 46 g m−2 y−1) was close to the world median value for lagoon sediments, and was about twice the burial rate recorded in the preceding oligotrophic phase.

Invertebrate diversity associated with a shallow rhodolith bed in the Mediterranean Sea (Mar Piccolo of Taranto, south‐east Italy)

“…Although there is no clear interpretation of the relationship between rhodolith shape and water energy (Aguirre, Braga & Bassi, 2017; Braga, 2017; O'Connell et al, 2020), large boxwork rhodoliths seem consistent with a lower hydrodynamic regime (Basso, 1998; Basso, Nalin & Nelson, 2009; Sañé et al, 2016). However, the higher frequency of spherical shapes suggests that, in the Mar Piccolo, tidal currents or their combination with wind and coastal conformation (Dominik et al, 2023) ensure the regular overturning of rhodoliths. Disturbance by large living organisms (bioturbation) has also been shown to play a primary role in overturning rhodoliths, where hydrodynamic forces are insufficient to move them (Marrack, 1999; Millar & Gagnon, 2018).…”

Spatial Distribution of Trace Elements in Sub-Surficial Marine Sediments: New Insights from Bay I of the Mar Piccolo of Taranto (Southern Italy)

“…The appli investigation approach is synthesized in the flowchart in Figure 2. From the analysis of the most recent literature data [31,32], it emerged that Bay I of the Mar Piccolo basin is characterized by quite high sediment accumulation rates, with values ranging from 1 mm/year to 3 mm/yr. With regards to the granulometric composition, results obtained by Dominik et al [32] highlight that sediments from the I Bay are mainly clayey silt, with the silt fraction accounting for 60%, followed by clay (30%) and sand (10%).…”

“…From the analysis of the most recent literature data [31,32], it emerged that Bay I of the Mar Piccolo basin is characterized by quite high sediment accumulation rates, with values ranging from 1 mm/year to 3 mm/yr. With regards to the granulometric composition, results obtained by Dominik et al [32] highlight that sediments from the I Bay are mainly clayey silt, with the silt fraction accounting for 60%, followed by clay (30%) and sand (10%). Furthermore, as emerged from the sediment core described in Valenzano et al [31], the upper part of the sediment layer in the Mar Piccolo basin corresponds to specific lithofa-cies, consisting of very soft, grey, structureless silts with an abundant organic content and bioclasts whose deposition occurred in a semi-enclosed basin with low hydro-dynamicity.…”