Environmental monitoring is essential to assess and, if possible, anticipate the consequences of various marine economic developments. This study describes progress in environmental monitoring by developing and applying a eutrophication index (EI) for marine protected areas (MPAs). The EI combines available data, such as biological oxygen demands, dissolved inorganic nitrogen and phosphorus, and chlorophyll-a, with the weighting factors calculated from principal component analysis to assess environmental quality. Its effectiveness was tested using nearly three decades of environmental data (since 1996) from the Nha Trang MPA in Vietnam. The EI revealed clear trends in environmental quality. In the period 1996–2006, environmental conditions deteriorated, negatively impacting aquaculture. In the later period, 2007–2024, improved environmental protection policies, technological developments, expanding tourism, and heightened public awareness contributed to a reversal of this trend. During the earlier period, the EI indicated poor environmental quality (Level V), while in the later years, it improved significantly, approaching Level II. This study also identified the spatial eutrophication patterns and helped to determine the causes of specific eutrophication levels. These included port development, aquaculture activities, and domestic waste discharge. These findings highlight the close relationship between environmental quality and economic activities in the bay. Overall, the new EI and its sensitivity maps enhance environmental monitoring capabilities. They provide valuable tools for decision-makers, aiding in the strategic planning of marine economic development, ecosystem protection, and sustainable resource use. The approach supports long-term environmental stewardship and more informed, adaptive management of coastal and marine areas.

Heavy metal concentration in the aquatic environment of estuaries is a significant environmental concern with potential consequences for ecosystems and human health. Heavy metals are naturally occurring elements that can enter aquatic environments through both natural processes and human activities. The interplay between natural processes and human activities, particularly urbanization and industrialization, often exacerbates heavy metal pollution in aquatic ecosystems. Some of the most common heavy metals of concern in estuarine pollution include arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb), zinc (Zn), and iron (Fe). Based on the results of two surveys in rainy and dry seasons, the paper aims to assess the concentrations of heavy metals in the estuarine environment of Ba Ria - Vung Tau Province, Vietnam, to understand the extent of contamination and its potential impacts on the ecosystem and human health. The average concentrations As, Cd, Hg, Pb, Zn, and Fe were 2.01, 0.024, 0.028, 1.63, 4.71, and 492.9 µg/L in water, and 6.70, 0.175, 0.060, 11.78, 41.94, and 3,108.9 mg/kg in sediment, respectively. Heavy metal concentrations in water have an increased trend during the rainy season. In contrast, values in sediment exhibit an opposite pattern, which can be explained by various environmental factors and processes. For water and sediment quality, individual metals, and overall metal contamination levels (the contamination factor - Cf, contamination degree - Cd, and metal pollution index - MPI) may appear to be low, whereas the assessment of the combined effects of multiple metals (Metal quality index - MI > 1) indicates that there is a potential risk to aquatic life in the estuaries. This assessment may underscore the importance of considering not only individual metal concentrations but also their cumulative effects when evaluating water and sediment quality and making decisions regarding protecting aquatic ecosystems. Further investigations and measures may be needed to mitigate potential harm to aquatic organisms and for sustainable management in estuaries.

Contamination by heavy metals in coastal and marine environments is an increasingly serious threat to both marine ecosystems and humans. The numerous marine cultivation and industrial zones along the coast of Khanh Hoa may influence the heavy metal contamination in the seawater and marine sediments. In this study, 36 seawater and 36 marine sediment samples were collected along the coast of Khanh Hoa to evaluate the levels of eight heavy metal elements. The results indicated that heavy metal concentrations in the surface seawater at Khanh Hoa were much lower than the national technical regulatory limits. The comprehensive pollution index of the heavy metals averaged less than 1. Therefore, heavy metal pollution in the seawater along the coast of Khanh Hoa is slight. Among the eight heavy metals (Cd, Co, Cu, Cr, Mn, Ni, Pb, and Zn) analyzed in the sediments, Cu concentration in the sediment at Cam Ranh Bay is much higher than the national technical regulatory limit. Ecological risk assessment of the sediments also indicated a possible combined biological effect of Cu, Pb, and Zn at Cam Ranh. Therefore, heavy metals in the marine environment at Khanh Hoa should be monitored yearly. Decision-makers should consider the Cu content in seafood because bioaccumulation of heavy metals may occur in marine organisms.

Microplastic (MP) pollution has emerged as a critical environmental concern, posing ecological risks across various aquatic systems. In this study, sediment samples from the Han River estuary (Vietnam) were analyzed during the 2023 rainy season and the 2024 dry season to evaluate the spatial and...