The loading history of trace metals and nutrients in Altata-Ensenada del Pabellón, lagoon complex, northwestern Mexico

Potentially toxic elements fluxes in 210Pb-dated sediment cores from a large coastal lagoon (southern Gulf of Mexico) under environmental stress

Terminos Lagoon (TL), in the southern Gulf of Mexico, has been under intensive anthropogenic pressure (e.g., oil-industry development) since the 1970s. Historical changes in flux ratios of potentially toxic elements (PTEs; As, Cd, Cr, Cu, Ni, Pb, V, Zn) were, for the first time, assessed inside TL by using 210Pb-dated sediment cores. Sediments showed minor enrichments for Cd, Ni, Pb, and V. However, according to international benchmarks, the As, Cr, Cu, and Ni concentrations could pose a risk for benthic biota. Sedimentary processes involved in the accumulation of PTEs were identified through a chemometric approach. Increments in PTEs flux ratios concur with the recent (⁓50 years) and extensive land-use changes, particularly the transport and deposit of materials delivered by rivers. These findings are expected to be used in managing this crucial natural resource, the larger Mexican coastal lagoon ecosystem, to mitigate the effects of global change.

Microbial Origin of the Organic Matter Preserved in the Cayo Coco Lagoonal Network, Cuba

The southern part of the tropical Cayo Coco Island (Cuba) hosts a complex, highly evaporative and marine-fed lagoonal network. In the easternmost lagoon of this network, hypersaline conditions favour the development of complex sedimentary microbial ecosystems within the water column at the bottom water-sediment interface and on the shore. Some of these ecosystems are producing microbial mats and biofilms with variable mineralisation rates, depending on their location. Since the mineralisation of these microbial deposits is rare, the sedimentary record does not provide a direct window on the evolution of these ecosystems or their distribution through space and time. However, microbial deposits also produce copious amounts of organic matter, which may be used to decipher any microbial-related origin within the sedimentary record. Microbial mats and biofilms were identified as the potential source of organic material in addition to the surrounding mangrove, soils and suspended particulate matter (SPM). The origin and evolution of the sedimentary organic matter preserved within the lagoonal sediments has been analysed using geochemical parameters such as elemental (TOC, TN and [C/N]atomic ratio) and isotopic (δ13Corg and δ15NTN) signals on four sedimentary cores retrieved from different locations in the lagoon and compared with the geochemical signatures of the potential sources. Despite the high potential for organic matter accumulation in the studied lagoon, the TOC and TN downcore values in sediments that were analysed (i.e., micritic muds and bioclastic sands) remain very low compared to the sediment-water interface. The relative contributions of the different potential sources of organic matter were estimated using [C/N]atomic ratios and δ13Corg values. The δ15NTN signature was discarded as a source signature as it records synsedimentary, early diagenetic, secondary evolution of the nitrogen signal associated with OM remineralisation (i.e., denitrification). Finally, among the microbial deposits, the slime recognised in the permanently submersed zone of the waterbody appears to be the main contributor to the organic matter preserved within the sediments of the lagoon. SPM, mainly composed of microbial-rich particles, also contribute and cannot be ruled out as a source.

Spatio-temporal distribution of organic and inorganic pollutants from Lake Geneva (Switzerland) reveals strong interacting effects of sewage treatment plant and eutrophication on microbial abundance

Variation with depth and time of organic matter (carbon, nitrogen, phosphorus), inorganic pollutant (mercury), as well as bacterial abundance and activity, were investigated for the first time in sediment profiles of different parts of Lake Geneva (Switzerland) over the last decades. The highest organic contents (about 32%), mercury concentration (27 mg kg(-1)), bacterial abundance (in order of 9×10(9) cell g(-1) dry sediment), and bacterial activity (1299 Relative Light Units (RLU)) were found in the highly polluted sediments contaminated by the waste water treatment plant (WWTP) discharge, which deposited during the period of cultural eutrophication. Such data, which contrast with the other sampled sites from deeper and more remote parts of the lake, prove that the organic matter and nutrients released from the municipal WWTP have considerable effects on bacterial abundance and activities in freshwater sediments. In fact, the relatively unpolluted deepwater sites and the coastal polluted site show large synchronous increases in bacterial densities linked to the anoxic conditions in the 1970s (lake eutrophication caused by external nutrient input) that subsequently increased the nutrient loading fluxes. These results show that the microbial activities response to natural or human-induced changing limnological conditions (e.g., nutrient supply, oxygen availability, redox conditions) constitutes a threat to the security of water resources, which in turn poses concerns for the world's freshwater resources in the context of global warming and the degradation of water quality (oxygen depletion in the bottom water due to reduced deep waters mixing). Moreover, the accumulation of inorganic pollutants such as high mercury (methyl-mercury) concentration may represent a significant source of toxicity for sediment dwelling organisms.

Heavy metal inputs evolution to an urban hypertrophic coastal lagoon, Rodrigo De Freitas Lagoon, Rio De Janeiro, Brazil

This work discusses the temporal variation of metal concentrations in a hypertrophic coastal lagoon located in the metropolitan area of Rio de Janeiro (Brazil). The lagoon watershed includes one of the mostly densely urbanized areas of the city but without industrial activities. Six sediment cores were collected in the lagoon between May and July 2003 and analyzed for the concentration of metals (Fe, Al, Mn, Zn, Pb, Cu, Cr, and Ni). Typical sedimentation rate was calculated as being 0.75 cm year( - 1) and was uniform for at least the past 70 years. Therefore, the alterations in the dynamics of the lagoon caused by changes in its watershed were clearly indicated in sediment cores. The construction of an artificial canal to the sea and the increasing urbanization and soil use changes were the major factors affecting metal accumulation in the lagoon sediments. Metals typical of anthropogenic urban sources (Pb, Zn, and Cu) showed increasing loads following urbanization.