The Venice canal network requires periodic intervention to remove sediments that progressively accumulate. The most recent dredging operation was carried out in the second half of the 1990s and early 2000s. These sediments had accumulated over a period of more than 30 years and were highly contaminated with Cd, Cu, Hg, Pb, Zn and PAHs. Sediments deposited after the dredging work were investigated in 2005, 2009, 2014 and 2017 by analysing sediment cores collected from three sites in the canal network. Arsenic, heavy metal and PAH concentrations were observed to be much lower than past values, although Cu, Hg and PAH levels were still relatively high. The high Cu concentrations (mean 161 mg kg⁻¹) are partly due to the widespread use of Cu-based antifouling paint. Current Italian regulations forbid the disposal of dredged sediments with these concentrations inside the lagoon, thereby increasing the cost of canal network maintenance.

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.

Lagoon sediments have heterogeneous structure and texture, contain shells and plants and are often highly bioturbated and disturbed by human activities. In such sediments, the selection of representative cores and the choice of a subsampling strategy are important but difficult. In this study, we examine the usefulness of X-ray computed tomography (CT) for inferring sediment features that will help in making optimal decisions prior to core opening (24 cores from seven lagoons). Various algorithms (intensity projections, slice thickness, axial and sagittal images, CT number profiles and volumetric region of interest) are tested to visualise low- and high-density volumes or objects and to quantify the relations between the average volumetric CT number and the bulk density of the sediment matrix. The CT number is related mainly to water content and indirectly to total nitrogen and <16-μm grain-size fraction (model R² = 0.94). The outliers are attributed to a weak correspondence between the fraction of sediment sampled for water content determination and the volume of sediment matrix used for CT number measurements in highly heterogeneous sediment slices. In conclusion, CT is a powerful tool for the initial screening of cores recovered from heterogeneous lagoon sediments. The adequate use of available algorithms may provide quantitative information on various sediment features, allowing the purposeful selection of cores and subsamples for further investigation.

The sediment load from the drainage basin may play a key role in sustaining the fragile tidal and subtidal habitats of the Venice Lagoon, which underwent significant erosional losses in recent decades. Freshwater discharge and suspended sediment transport were studied in two estuarine sections of the main tributary of the lagoon, Dese River, employing acoustic instruments and analyzing sediment accumulation in the estuary through bathymetric measurements. The results for 2021 are discussed in terms of discharge, rainfall–runoff relationships, suspended sediment load, and the impact of floods. Compared to previous estimates from 1999, the mean water flow was similar in both years, but the annual suspended sediment load nearly doubled. A single flood event is described, which produced extreme sediment transport and delivered 21.8% of the annual load over a 22 h period. This study provides a framework for assessing whether the sediment load from the Dese River may offset degradation in the morphodiversity of its estuary and the habitats it supports. High-resolution monitoring of sediment delivery from the freshwater tributaries is emphasized as a critical approach for protecting the estuarine areas at the water–land interface of the Venice Lagoon.