Assessment of bottom sediment quality in Niterói harbor (Brazil, South America) through ecological indexes concerning nutrients and trace metals

Assessment of eutrophication from phosphorus remobilization after resuspension of coastal sediments from an urban tropical estuary

Dredging activities cause sediment resuspension, which can change the bioavailability of nutrients such as phosphorus (P) in aquatic ecosystems due to remobilization. This study evaluated the remobilization of P in the solid and dissolved phase before and after sediment resuspension in the Meriti and Iguaçu River estuaries and the Rio de Janeiro and Niterói harbor in Guanabara Bay (Rio de Janeiro, Brazil). Three water and sediment samples were collected at each point. Dissolved phosphorus (DP), total phosphorus (TP), organic phosphorus (OP), and inorganic phosphorus (IP) were analyzed before and after resuspension. Resuspension directly impacted the fine-grained samples, causing the release of P into the water column after resuspension, increasing eutrophication of the estuary and risk to biota. The phosphorus enrichment index (PEI) was calculated in the four areas, and in all areas, the index was above 1, which means high ecological risk. The area with sandy granulometry and a lower percentage of organic matter showed an increase in the index after resuspension. The resuspension may impact the increase of eutrophication in some areas, due to the remobilization of the sediment and the adsorbed contaminants.

Biomass and species composition of green macroalgae in the Binhai Harbor intertidal zone of the Southern Yellow Sea

Green tides have occurred in the Southern Yellow Sea (SYS) for 16 consecutive years, causing widespread concern. Attached and floating green macroalgae have been observed in Binhai Harbor, Jiangsu Province, China, in the SYS. This study used morphological analysis, and internal transcribed spacers and rps2-trnL molecular identification methods, to analyze the species composition and biomass of green macroalgae along the Binhai Harbor coast. Six species of green tide algae (Ulva prolifera, Ulva meridionalis, Ulva linza, Ulva flexuosa, Ulva californica, and Ulva intestinalis) were identified, in addition to Blidingia sp. The discovery of U. californica is the first report of this species off the coast of Jiangsu Province. The floating green macroalgae along the Binhai Harbor coast originated from attached green macroalgae in Binhai Harbor, and a small number of the attached algae were closely related to the large-scale floating U. prolifera in the SYS. Moreover, in December 2021, February 2022, and April 2022, the total biomass of attached green macroalgae in Binhai Harbor was 25.600, 10.767, and 25.867 t, respectively, of which the U. prolifera biomass was 10.697, 8.709, and 4.185 t, respectively. This study proved Binhai Harbor may not be an important source of green tide in the SYS.