Winter to spring variations of chromophoric dissolved organic matter in a temperate estuary (Po River, northern Adriatic Sea)

Occurrence and distribution of microbial pollutants in coastal areas of the Adriatic Sea influenced by river discharge

The transport of a variety of pollutants from agricultural, industrial and urbanised areas makes rivers major contributors to the contamination of coastal marine environments. Too little is known of their role in carrying pathogens to the coast. We used DNA-based metabarcoding data to describe the microbial community composition in seawater and sediment collected in front of the estuary of the Tronto, the Chienti and the Esino, three Italian rivers with different pollution levels that empty into the north-central Adriatic Sea, and to detect and measure within these communities the relative abundance of microbial pollutants, including traditional faecal indicators and alternative faecal and sewage-associated pollutants. We then applied the FORENSIC algorithm to distinguish human from non-human sources of microbial pollution and FAPROTAX to map prokaryotic clades to established metabolic or other ecologically relevant functions. Finally, we searched the dataset for other common pathogenic taxa. Seawater and sediment contained numerous potentially pathogenic bacteria, mainly faecal and sewage-associated. The samples collected in front of the Tronto estuary showed the highest level of contamination, likely sewage-associated. The pathogenic signature showed a weak but positive correlation with some nutrients and strong correlations with some polycyclic aromatic hydrocarbons. This study confirms that rivers transport pathogenic bacteria to the coastal sea and highlights the value of expanding the use of HTS data, source tracking and functional identification tools to detect microbial pollutants and identify their sources with a view to gaining a better understanding of the pathways of sewage-associated discharges to the sea.

Time resolved data unveils the complex DOM dynamics in a Mediterranean river

In this study, dissolved organic carbon (DOC) data and optical properties (absorbance and fluorescence) of DOM, weekly collected in the Arno River for 2 years, are used to investigate the main processes determining DOM temporal dynamics in a small Mediterranean river, with torrential hydrology and medium-high human impact, and to quantify the contribution of this river to Med Sea carbon budget. A clear seasonal cycle of DOM, with DOC values ranging between 170 and 490 μM, was observed. Optical properties indicates that DOM quality in the river is different depending on the season; terrestrial humic-like substances prevail in winter, when discharge and floods are the main drivers of DOM concentration and quality, whereas autochthonous protein-like substances prevail in spring and summer, when biological processes dominate. Our results provide a robust estimate of the DOC flux to the Med Sea (9.6 · 10⁹ g DOC yr^-1) and of its range of variability (12.95 · 10⁹-5.12 · 10⁹ g DOC yr^-1). The 80% of this flux was generally delivered during autumn/winter with significant amounts ascribed to single flood events (up to 26% in 2014). This study, by providing a rich dataset on water quantity and quality and by quantifying the importance of the hydrological regime on DOC transport, represents an important step toward a quantitative modeling of the Arno River.

Dissolved organic carbon as potential indicator of global change: A long-term investigation in the northern Adriatic

Dissolved organic carbon (DOC) is an essential component of the biogeochemical marine system, effecting biological and chemical reactions that take place in the sea. DOC represents a dynamic component of the global carbon cycle. This paper reports 25years of measurements of DOC content and distribution at seven stations along the transect Po River delta - Rovinj in the northern Adriatic (NA). The results show strong temporal and spatial variability: (1) The highest average DOC concentrations were observed in 1998 and 2002 (143μmol/L and 137μmol/L, respectively); (2) The minimum average DOC was recorded in 2006 (88μmol/L) and (3) The short-term DOC accumulation (up to 203, average 102μmol/L) for the years 2009 to 2012, was observed during the summer and autumn months followed by unusually low DOC concentrations during the winter and spring. The DOC results from the more recent monitoring at the same stations indicate primarily oligotrophic characteristics of the NA seawater (88μmol/L). The results of DOC variability and distribution in the NA appears to be strongly influenced by complex circulation patterns. This paper provides a "link" between the Ionian circulation and the NA ecosystem as a part of the recently identified Adriatic-Ionian Bimodal Oscillating System (BiOS). A good agreement between the BiOS oscillation and other variables related to the DOC concentration, like the NA A and B winter types, the Po River discharge, salinity, chlorophyll a, occurrence of hypoxic-anoxic conditions, eutrophication and oligotrophication, suggests that DOC might be a good tool and indicator of global change.

Insights on the Optical Properties of Estuarine DOM - Hydrological and Biological Influences

Dissolved organic matter (DOM) in estuaries derives from a diverse array of both allochthonous and autochthonous sources. In the estuarine system Ria de Aveiro (Portugal), the seasonality and the sources of the fraction of DOM that absorbs light (CDOM) were inferred using its optical and fluorescence properties. CDOM parameters known to be affected by aromaticity and molecular weight were correlated with physical, chemical and meteorological parameters. Two sites, representative of the marine and brackish water zones of the estuary, and with different hydrological characteristics, were regularly surveyed along two years, in order to determine the major influences on CDOM properties. Terrestrial-derived compounds are the predominant source of CDOM in the estuary during almost all the year and the two estuarine zones presented distinct amounts, as well as absorbance and fluorescence characteristics. Freshwater inputs have major influence on the dynamics of CDOM in the estuary, in particular at the brackish water zone, where accounted for approximately 60% of CDOM variability. With a lower magnitude, the biological productivity also impacted the optical properties of CDOM, explaining about 15% of its variability. Therefore, climate changes related to seasonal and inter-annual variations of the precipitation amounts might impact the dynamics of CDOM significantly, influencing its photochemistry and the microbiological activities in estuarine systems.

Colored dissolved organic matter dynamics and anthropogenic influences in a major transboundary river and its coastal wetland

Most transboundary rivers and their wetlands are subject to considerable anthropogenic pressures associated with multiple and often conflicting uses. In the Eastern Mediterranean such systems are also particularly vulnerable to climate change, posing additional challenges for integrated water resources management. Comprehensive measurements of the optical signature of colored dissolved organic matter (CDOM) were combined with measurements of river discharges and water physicochemical and biogeochemical properties, to assess carbon dynamics, water quality, and anthropogenic influences in a major transboundary system of the Eastern Mediterranean, the Evros (or, Марица or, Meriç) river and its Ramsar protected coastal wetland. Measurements were performed over three years, in seasons characterized by different hydrologic conditions and along transects extending more than 70 km from the freshwater end-member to two kilometers offshore in the Aegean Sea. Changes in precipitation, anthropogenic dissolved organic matter (DOM) inputs from the polluted Ergene tributary, and the irregular operation of a dam were key factors driving water quality, salinity regimes, and biogeochemical properties in the Evros delta and coastal waters. Marsh outwelling affected coastal carbon quality, but the influence of wetlands was often masked by anthropogenic DOM contributions. A distinctive five-peak CDOM fluorescence signature was characteristic of upstream anthropogenic inputs and clearly tracked the influence of freshwater discharges on water quality. Monitoring of this CDOM fluorescence footprint could have direct applications to programs focusing on water quality and environmental assessment in this and other transboundary rivers where management of water resources remains largely ineffective.

Biophysical processes affecting DOM dynamics at the Arno river mouth (Tyrrhenian Sea)

Dissolved organic carbon (DOC) and optical properties (absorption and fluorescence) of chromophoric dissolved organic matter (CDOM) were measured in October 2012, at the Arno river mouth and in a coastal station close to it. The data reported indicates that the Arno river represents an important source of DOC and CDOM to this coastal area, with a total DOC flux of 11.23-12.04 · 10(9)g C · y(-1). Moving from the river to the sea, CDOM absorption and fluorescence decreased, while the spectral slope increased, suggesting a change in the molecular properties of CDOM. Mineralization experiments were carried out in order to investigate the main processes of DOM removal and/or transformation in riverine and coastal water. DOC removal rates were 20 μM · month(-1) in the river and 3 μM · month(-1) in the seawater, while CDOM was released during the first 30 days and removed in the following 40 days.

Colored dissolved organic matter signature and phytoplankton response in a coastal ecosystem during mesoscale cyclonic (cold core) eddy

Chromophoric dissolved organic matter (CDOM) and hydrochemical parameters were measured in the nearshore region of the western Bay of Bengal with and without significant terrestrial influence. A meso-scale cyclonic eddy that occupied the northern part of the study area set up a nutrient enriched distinct ecosystem in April (premonsoon) attended with increased levels of DOM fluorescence, particularly the protein tyrosine like fluorescence (B). A new (minor) fluorescence component, attributed to land source was revealed which contained two fluorophores, the red-shifted tryptophan-like (TU) hypothesized as the "unfolded protein" and the petroleum hydrocarbon-like (P). During the eddy, pennate diatom population increased, bringing the centric:pennate diatom ratio to half of what it was during the remaining period (monsoon season). The nutrients distribution suggested that when pennates are favored (premonsoon), orthophosphate and silicate are the limiting nutrients and that when centric diatoms are favored (monsoon season), the limitation is by nitrate.

Photochemical and microbial alterations of DOM spectroscopic properties in the estuarine system Ria de Aveiro

The chromophoric dissolved organic matter (CDOM) of marine (MZ) and brackish water (BZ) zones of Ria de Aveiro showed different spectral characteristics and susceptibility to photochemical alterations, reflecting the different amounts and prevailing sources of organic matter.

Revealing sources and distribution changes of dissolved organic matter (DOM) in pore water of sediment from the Yangtze estuary

Dissolved organic matter (DOM) in sediment pore waters from Yangtze estuary of China based on abundance, UV absorbance, molecular weight distribution and fluorescence were investigated using a combination of various parameters of DOM as well as 3D fluorescence excitation emission matrix spectra (F-EEMS) with the parallel factor and principal component analysis (PARAFAC-PCA). The results indicated that DOM in pore water of Yangtze estuary was very variable which mainly composed of low aromaticity and molecular weight materials. Three humic-like substances (C1, C2, C4) and one protein-like substance (C3) were identified by PARAFAC model. C1, C2 and C4 exhibited same trends and were very similar. The separation of samples on both axes of the PCA showed the difference in DOM properties. C1, C2 and C4 concurrently showed higher positive factor 1 loadings, while C3 showed highly positive factor 2 loadings. The PCA analysis showed a combination contribution of microbial DOM signal and terrestrial DOM signal in the Yangtze estuary. Higher and more variable DOM abundance, aromaticity and molecular weight of surface sediment pore water DOM can be found in the southern nearshore than the other regions primarily due to the influence of frequent and intensive human activities and tributaries inflow in this area. The DOM abundance, aromaticity, molecular weight and fluorescence intensity in core of different depth were relative constant and increased gradually with depth. DOM in core was mainly composed of humic-like material, which was due to higher release of the sedimentary organic material into the porewater during early diagenesis.