Discerning natural and anthropogenic organic matter inputs to salt marsh sediments of Ria Formosa lagoon (South Portugal)

Reconstructing Historical Land Use and Anthropogenic Inputs in Lake Victoria Basin: Insights from PAH and n-Alkane Trends

Over the past century, human activities have profoundly transformed global ecosystems. Lake Victoria in East Africa exemplifies these challenges, showcasing the interplay of anthropogenic pressures driven by land use changes, urbanization, agriculture, and industrialization. Our comprehensive study investigates polycyclic aromatic hydrocarbons (PAHs) and n-alkanes in the lake and its catchment to trace their sources and historical deposition. Sediment cores were collected from six sites within the catchment, representing diverse landforms and human activities, ensuring a comprehensive understanding of the basin. The results indicate significant spatial and temporal variations in both PAH and n-alkane profiles, reflecting diverse land use changes and development trajectories in the basin. Urban sites often exhibited higher concentrations of PAHs and short-chain n-alkanes, indicative of anthropogenic sources such as fossil fuel combustion, the input of petroleum hydrocarbons, and industrial emissions. In contrast, rural areas showed low PAH levels and a dominance of long-chain n-alkanes from terrestrial plant waxes. The n-alkane ratios, including the Carbon Preference Index and the Terrigenous-Aquatic Ratio, suggested shifts in organic matter sources over time, corresponding with land use changes and increased human activities. A mid-20th century shift toward increased anthropogenic contributions was observed across sites, coinciding with post-independence development. The mid-lake sediment core integrated inputs from multiple sub-catchments, providing a comprehensive record of basin-scale changes. These findings highlight three distinct periods of organic matter input: pre-1960s, dominated by natural and biogenic sources; 1960s-1990s, marked by increasing anthropogenic influence; and post-1990s, characterized by complex mixtures of pyrogenic, petrogenic, and biogenic sources. This study underscores the cumulative environmental and aquatic ecosystem effects of urbanization (rural vs. urban sites), industrialization, and land use changes over the past century. The combined analyses of PAHs and n-alkanes provide a comprehensive understanding of historical and ongoing environmental impacts, emphasizing the need for integrated management strategies that address pollutant inputs to preserve Lake Victoria's ecological integrity.

Lipid Biomarkers in Urban Soils of the Alluvial Area near Sava River, Belgrade, Serbia

This study focused on the investigation of soil samples from the alluvial zone of the Sava River, located near the heating plant in New Belgrade, Serbia. Using gas chromatography with flame ionization detection (GC-FID), a broad range of alkanes, including linear n-alkanes (C10 to C33) and isoprenoids, was analyzed in all samples. The obtained datasets were effectively made simpler by applying multivariate statistical analysis. Various geochemical indices (CPI, ACL, AI, TAR, etc.) and ratios (S/L, Paq, Pwax, etc.) were calculated and used to distinguish between biogenic and anthropogenic contributions. This approach added a higher level of precision to the source identification of hydrocarbons and provided a detailed geochemical characterization of the investigated soil. The results showed that the topsoil had a high content of TPH (average value, 90.65 mg kg-1), potentially related to an accidental oil spill that occurred repeatedly over extended periods. The uncommon n-alkane profiles reported for the investigated soil samples are probably the result of inputs related to anthropogenic sources, emphasizing that petroleum was the main source of the short-chain n-alkanes. The methodology developed in this study was proven to be efficient for the assessment of the environmental quality of the soil in an urban part of New Belgrade, but it can also be a useful tool for soil monitoring and for a pollution assessment in other (sub)urban areas.

Application of various molecular markers for investigating petrogenic inputs in coastal systems strongly impacted by anthropogenic stressors

In this study, multiple molecular markers [polycyclic aromatic hydrocarbons (PAHs), linear and branched alkanes, unresolved complex mixture (UCM), hopanes, and steranes] were applied to explore petroleum-related inputs in complex coastal systems influenced by various human-induced pressures. To investigate anthropogenic impacts related to petrogenic emissions, we analysed surface sediments from coastal areas of southern Baltic, including harbour/shipyard channels, offshore dumping sites, shipping routes, and major sinks for particulate matter discharged by large rivers. This study indicates a large spatial variability in the contamination degree of examined sites by petroleum-derived chemicals. Hopanes and steranes along with UCM appeared to have the highest potential to identify petroleum sources in studied locations, whereas investigations based on alkanes and PAHs seemed to be considerably affected by inputs of modern biogenic and combustion-derived materials, respectively. However, the combined use of all these markers provides deeper insight into the complexity of sedimentary organic matter in human-impacted environments.

Composition and sources of sediment organic matter in a western Iberian salt marsh: Developing a novel prediction model of the bromine sedimentary pool

Salt marshes are sensitive highly productive habitats crucial for carbon cycling. This study presents a comprehensive analysis of organic geochemical indicators and geochronology in the Mira salt marsh (SW Portugal) over eight centuries. The closely intertwined carbon and bromine (Br) biogeochemical cycles in these environments can influence the fluxes of volatile compounds such as ozone-depleting methyl bromide, emphasizing the importance of understanding sediment organic matter (OM) origin, budget, and composition in salt marshes. To characterize the strong Br-OM relationship, we used n-alkane signatures, bulk elemental data (total carbon, total nitrogen, Corg/Nat ratio), and stable isotopes (δ15N, δ13C) from a sediment core. Findings revealed a mixed composition of terrestrial and marine OM, posing challenges in distinguishing ex situ higher plant sources from in situ production by marsh vegetation. n-Alkanes (C15 to C31) were found in all the sediment samples, predominantly C25-C29. Changes in their presence were linked to marsh succession, evolving from a vegetation-free tidal flat to a C3 halophyte-dominated high marsh ecosystem. Despite the area's low industrial and population impact, regulation of water flow through the dam affected the balance between continental and marine waters. This study aimed to create a cost-effective predictive model for total Br, enhancing paleoclimatic studies using sedimentary samples. The n-alkane model had limited resolution, but an alternative infrared (IR) spectroscopy-based model, requiring less time and smaller sample sizes, was developed. Combining FT-IR spectra with statistical analysis enabled the creation of a reliable total Br concentration prediction model (mean absolute error = 14.39). These findings have implications for controlling Br enrichment in marsh environments and can be applied in various coastal wetlands with different mineralogical and organic characteristics.

Geochemical records of human-induced environmental changes in two small remote lakes of Songnen Plain, Northeast China

The abundance and composition of aliphatic hydrocarbon biomarkers were determined in dated sediment cores from Lakes Qijiapao (QJP) and Huoshaoheipao (HSH) in the Songnen Plain, Northeast China, to investigate historical environmental changes in these lakes and identify likely controlling factors. Based on these results, the recent environmental history of the two lakes can be divided into three periods. Before 1950, low Paq values (avg. 0.23 and 0.27, respectively) and middle-chain n-alkane abundances (normalized to total organic carbon, avg. 14.82 and 16.01 µg g-1 TOC, respectively) in both lakes suggested low aquatic productivity and the limited input of submerged macrophyte organic matter (OM). However, the significant increase in the abundance of short-chain n-alkanes in Lake HSH (from 8.34 to 16.68 µg g-1 TOC) indicated the emergence of early nutrient enrichment in the lake. From 1950 to 2000, marked increase in the abundance of middle-chain n-alkanes (avg. 21.72 and 22.62 µg g-1 TOC in Lakes QJP and HSH, respectively) and Paq values indicated that both lakes had undergone eutrophication because of the population explosion and agricultural intensification. From 2000 to 2013, the abundance of short- and middle-chain n-alkanes in Lake QJP markedly exceeded those in Lake HSH and indicated a larger eutrophication in Lake QJP, which could be caused by the development of ecotourism in Lake HSH and the concomitant increase in aquaculture in Lake QJP in recent years. The highest abundance of C30 αβ-hopane (~ 10.24 µg g-1 TOC) and the lowest CPIH values in Lake QJP revealed a possible petroleum pollution since 2008. Taken together, lake eutrophication in the Songnen Plain accelerated after 1950 and was influenced primarily by agriculture and aquaculture. This is in contrast to lakes in other regions of China (such as the Yangtze River Basin and Yunnan Province), where urbanization and industrialization have exerted a dominant influence on the lake environment.

Geochemical properties of blue carbon sediments through an elevation gradient: study of an anthropogenically impacted coastal lagoon

Global research is showing that coastal blue carbon ecosystems are vulnerable to climate change driven threats including accelerated sea-level rise and prolonged periods of drought. Furthermore, direct anthropogenic impacts present immediate threats through deterioration of coastal water quality, land reclamation, long-term impact to sediment biogeochemical cycling. These threats will invariably alter the future efficacy of carbon (C) sequestration processes and it is imperative that currently existing blue carbon habitats be protected. Knowledge of underlying biogeochemical, physical and hydrological interactions occurring in functioning blue carbon habitats is essential for developing strategies to mitigate threats, and promote conditions to optimise C sequestration/storage. In this current work, we investigated how sediment geochemistry (0-10 cm depth) responds to elevation, an edaphic factor driven by long-term hydrological regimes consequently exerting control over particle sedimentation rates and vegetation succession. This study was performed in an anthropogenically impacted blue carbon habitat along a coastal ecotone encompassing an elevation gradient transect from intertidal sediments (un-vegetated and covered daily by tidal water), through vegetated salt marsh sediments (periodically covered by spring tides and flooding events), on Bull Island, Dublin Bay. We determined the quantity and distributions of bulk geochemical characteristics in sediments through the elevation gradient, including total organic carbon (TOC), total nitrogen (TN), total metals, silt, clay, and also, 16 individual polyaromatic hydrocarbon's (PAH's) as an indication of anthropogenic input. Elevation measurements for sample sites were determined on this gradient using a LiDAR scanner accompanied by an IGI inertial measurement unit (IMU) on board a light aircraft. Considering the gradient from the Tidal mud zone (T), through the low-mid marsh (M) to the most elevated upper marsh (H), there were significant differences between all zones for many measured environmental variables. The results of significance testing using Kruskal-Wallis analysis revealed, that %C, %N, PAH (µg/g), Mn (mg/kg), TOC:NH₄ ⁺ and pH are significantly different between all zones on the elevation gradient. The highest values for all these variables exists (excluding pH which followed a reverse trend) in zone H, decreasing in zone M and lowest in the un-vegetated zone T. TC content is 16 fold higher overall in vegetated (3.43 -21.84%) than uninhabited (0.21-0.56%) sediments. TN was over 50 times higher (0.24-1.76%), more specifically increasing in % mass on approach to the upper salt marsh with distance from the tidal flats sediments zone T (0.002-0.05%). Clay and silt distributions were greatest in vegetated sediments, increasing in % content towards upper marsh zones The retention of water, metals, PAHs, mud, chloride ions, NH₄ ⁺, PO₄ ^3- and SO₄ ^2- increased with elevated C concentrations, concurrently where pH significantly decreased. Sediments were categorized with respect to PAH contamination where all SM samples were placed in the high polluted category. The results highlight the ability of Blue C sediments to immobilise increasing levels of C, N, and metals, and PAH with over time and with both lateral and vertical expansion. This study provides a valuable data set for an anthropogenically impacted blue carbon habitat predicted to suffer from sea-level rise and exponential urban development.

GRAPHICAL ABSTRACT

Summarized results from this study demonstrating the geochemical changes through an elevation gradient, with a transect encompassing intertidal sediments through supratidal salt marsh sediments within Bull Island's blue carbon lagoon zones.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10533-022-00974-0.

Contemporary pollution of surface sediments from the Algarve shelf, Portugal

The present-day human footprint is traceable in all environments. Growing urban centers, tourism, agricultural and industrial activities in combination with fishery, aquacultures and intense naval traffic, result in a large output of pollutants onto coastal regions. The Algarve shelf (Portugal) is one exemplary highly affected coastal system. With this study the contemporary pollution was followed in eighteen offshore surface sediment samples. Heavy metals (e.g., Cr, Pb, Cu, Hg) and organic contaminants, such as linear alkylbenzenes, dichlorodiphenyltrichloroethane metabolites, polycyclic aromatic hydrocarbons, and hopanes, have been identified and quantified, that pose hazardous effects on the marine environment and biota. This study correlates spatial distribution patterns with the pollutant composition, potential sources and pathways, each sample's grain size, and local influences, such as discharging river systems and ocean currents. This study presents a blueprint-study that allows the methodological adaption to new shelf systems with regionally different ocean current-driven distribution patterns of anthropogenic pollutants.