The impact of pond aquaculture on the composition of organic carbon and nitrogen in suspended matter: an evidence from the Tam Giang-Cau Hai lagoon system in Central Vietnam.

Using empirical evidence from sites in Tam Giang – Cau Hai (TG–CH) Lagoon, Central Vietnam, this book chapter establishes an understanding of how small-scale fishers (SSF) become aware and respond to climate shocks that influence their livelihoods. This chapter focuses on documenting and analyzing the various response strategies that fishery households employ in the face of climate shocks and stressors. This provided a better understanding of the adaptive capacity of fishery households in the TG–CH Lagoon. Research data were gathered from five fishing villages in two coastal communes in Thua Thien Hue province and included a survey (n = 181 households), four focus group discussions (FGDs), and seven in-depth interviews with the head of fisheries associations, commune officers, policymakers and researchers. In general, fishers were proactive in seeking solutions and employing coping strategies to face shocks induced by climate change. The timely assistance and support of local authorities and other organizations helped fishers at the research sites to recover effectively. Also, diversified livelihoods had brought stability to people’s livelihoods and lives. Such solutions provided positive results and promised to help people adapt to long-term climate change and the increased disaster risk situation in the TG–CH Lagoon. The assessment of SSF resilience to climate change and risks is also an essential step towards enhancing understanding and decision making to reduce the vulnerable situation for fishery communities in the TG–CH Lagoon in particular and in Vietnam in general.

The Tam Giang - Cau Hai lagoon is the biggest one in Southeast Asia of 70 kilometers long and the total area of 248 square kilometers. It plays a very important role in the economy, culture and ecotourism in Thua Thien - Hue province and especially, it is of a great scientific value. However, it has been being threatened due to over exploiting and aquaculture. Many constructions, such as, hydroelectric Plant on Huu Trach branch and in A Luoi district, water reservoir in Ta Trach branch, Thao Long salt water prevention dyke will have affect on its ecosystem. Analyzing fish specimens collected from 2005 to 2007 in Tam Giang - Cau Hai lagoon, we revealed 177 species belonging to 129 genus of 73 families in 18 orders, of those the Perciformes are the most abundant order with 100 species (56.50%); the next is Cypriniformes with 15 species (8.47%), Anguilliformes with 12 species (6.78%), Clupeiformes with 9 species (5.08%); Pleuronectiformes order with 8 species (4.52%); each of Scorpaeniformes and Tetraodontiformes order with 5 species (2.82%); Siluriformes and Beloniformes with 4 species (2.26%); Rajiformes and Synbranchiformes with 3 species (1.69%); each of Elopiformes and Syngnathiformes with 2 species (1.13%); and the others with 1 species (0.56%). Of the total 177 fish species recorded in Tam Giang - Cau Hai lagoon, there are 21 species of the local economic value and 8 species listed in Red Data Book of Vietnam (2007) at different levels (VU - Vulnerable and EN - Endangered).

Carbon and nitrogen stable isotopes in suspended matter and sediments from the Schelde Estuary

Metals and arsenic in sediment and fish from Cau Hai lagoon in Vietnam: Ecological and human health risks

This study investigated the occurrence of microplastics (MPs) in the gastrointestinal tracts (GT) and tissues of four common shrimps (including two wild-caught shrimps and two farmed shrimps) collected from a high-diversity lagoon in central Vietnam. The numbers of MP items in greasy-back shrimp (Metapenaeus ensis), green tiger shrimp (Penaeus semisulcatus), white-leg shrimp (Litopenaeus vannamei), and giant tiger shrimp (Penaeus monodon), determined per weight and individual, were 0.7 ± 0.3, 0.6 ± 0.2, 1.1 ± 0.4, and 0.5 ± 0.3 (items/g-ww), and 2.5 ± 0.5, 2.3 ± 0.7, 8.6 ± 3.5, 7.7 ± 3.5 (items/individual), respectively. The concentration of microplastics in the GT samples was significantly higher than that in the tissue samples (p < 0.05). The number of microplastics in the farmed shrimp (white-leg shrimp and black tiger shrimp) was statistically significantly higher than the number of microplastics in the wild-caught shrimp (greasy-back and green tiger shrimps) (p <0.05). Fibers and fragments were the dominant shapes of the MPs, followed by pellets, and these accounted for 42-69%, 22-57%, and 0-27% of the total microplastics, respectively. The chemical compositions determined using FTIR confirmed six polymers, in which rayon was the most abundant polymer, accounting for 61.9% of the MPs found, followed by polyamide (10.5%), PET (6.7%), polyethylene (5.7%), polyacrylic (5.8%), and polystyrene (3.8%). As the first investigation on the MPs in shrimps from Cau Hai Lagoon, central Vietnam, this study provides useful information on the occurrences and characteristics of the microplastics in the gastrointestinal tracts and tissues of four shrimp species that live in different living conditions.

Assessing the vulnerability of small-scale fishery communities in the estuarine areas of Central Vietnam in the context of increasing climate risks

The Tam Giang - Cau Hai lagoon in Thua Thien-Hue province is the largest lagoon in South East Asia and also one of the places having the largest area of seagrass in Vietnam. The study results from 2009 to 2017 showed that 6 seagrasses species were identified (Halodule uninervis is a newly recorded species, however, Halophila minor is not recorded) and there were 8 freshwater grass species (with the exception of Potamogeton maackianus), with a total area of 2,840 ha. In particular, the area of seagrass has been recovering significantly from 1,000 hectares in 2009 to 2,037 hectares in 2017.

The Tam Giang - Cau Hai lagoon system plays an important role in the economic development of the Thua Thien Hue area. In this project, the study and analysis of several heavy metals, such As, Cd, Pb, Zn, Hg, Cr, and Cu contained in the lagoon system were taken to assess pollution levels and ecological risk. Thirty-five sediment samples were collected in the research area in January 2024 (rainy season). Metals’ concentration was analyzed by (Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The assessment method is based on comparisons with the national technical regulation on sediment quality (QCVN 43:2017). It includes the geo-accumulation index (Igeo), enrichment factor (EF), pollution load index (PLI), and ecological risk index (RI). Results indicate the concentration of heavy metals were As (4.65); Cd (0.08); Pb (11.93); Zn (33.66); Hg (0.07); Cr (12,88) and Cu (4.97) mg/kg that within the allowed limits for surface water and brackish water sediments in QCVN 43:2017/BTNMT (national technical regulation on sediment quality). The geo-accumulation index (Igeo) for the heavy metals (As, Cd, Pb, Zn, Hg, Cr and Cu) confirmed that the sediment was not polluted. The enrichment factor (EF) proved that human activities are the primary source of increasing concentration of As, Cd, Hg, and Pb in sediment. Based on PLI, the pollution level of Tam Giang - Cau Hai lagoon is considered good, and the ecological risk (RI = 20.75) in the study area is low.

We developed an empirical approach to consider social-ecological system change and transformation by drawing on resource users’ knowledge and perceptions. We applied this approach in the Cau Hai lagoon, a coastal area dominated by small-scale fisheries in central Vietnam. Nine focus groups with more than 70 fishers were used to gather information about key social-ecological system elements and interactions, historical social-ecological dynamics, and possible thresholds between distinct social-ecological system identities. The patterns of change in livelihoods and resource exploitation in the Cau Hai lagoon are similar to those seen in other coastal lagoon and small-scale fishery contexts. Our findings show some promise for the use of local knowledge and the perceptions of resource user communities to understand and characterize social-ecological transformations. Importantly, however, we also demonstrate how social-ecological transformations are complicated processes driven by many factors beyond the control of any singular individual or group. We argue that (1) the occurrence of social-ecological transformations can result in either positive or negative outcomes and (2) that we need to direct our thinking away from drawing tidy conclusions about if and when social-ecological transformations take place. Our research also encourages scholars to carefully consider how we frame the benefits of participatory, community-based governance initiatives. Importantly, we need to examine the ways that governance initiatives will be beneficial for some people and detrimental for others, and we need to be fully aware of locally contested interests and acknowledge competing priorities for fisheries management and human well-being. Community-oriented assessments informed by resilience thinking can help to open up questions about economic, political, cultural, and environmental aspects of undesirable path dependencies and traps.

The origin and distribution of suspended organic matter, the trophic features and the stable carbon isotopic composition of particulate organic carbon (POC) were studied monthly in a Western Mediterranean semi-enclosed basin. Sampling stations were selected as a function of wind-exposure and the degree of vegetation cover and then compared with an adjacent unvegetated site. the predominant vegetation was seagrass (Posidonia oceanica and Cymodocea nodosa) and Caulerpa prolifera. Water samples were analyzed for total suspended matter (inorganic and organic fractions), photosynthetic pigments (chlorophyll-a and phaeopigments), dissolved organic carbon, particulate organic carbon and their isotopic composition. Temperature and salinity were also measured at the same sampling sites within range of Mediterranean limits. the suspended organic matter concentration was 1.77 ± 1.55 mg l−1; the chlorophyll-a concentration was low (0.35 ± 0.24 μg l−1); the disolved organic carbon concentration was 2,140 ± 2,010 μg l−1; the particulate organic carbon concentration was 212 ± 106 μg l−1 and the isotopic composition was 18.77 ± 2.51%°. There were significant temporal differences except for phaeopigments, POC and its POC isotopic composition, and there were no spatial differences other than for δ13C. This picture highlighted a general seasonal trend and trophical features similar to adjacent sea. Spatial differences in δ13C showed that the source of suspended organic matter was different between stations as that between sources and wind-hydrodynamic constraints. In

Increased delivery of particulate organic matter (POM) to coastal lagoons has caused disturbance in nutrient cycling, water quality and aquatic biodiversity. Therefore, the major concern in coastal management is assessment of sources and pathways of POM in order to maintain ecosystem health. Elemental and isotopic of POM compositions are being increasingly used as useful markers for sources of POM in coastal ecosystems to obtain understanding of the nutrient sources and anthropogenic influences. In this study, variation in elemental and stable isotope compositions of carbon (C) and nitrogen (N) were measured in Cau Hai lagoon, Central Vietnam to characterize the possible sources of C and N. Variations in values of C/N ratios (8.17 ± 0.14) and 13C (-22.00‰ ± 0.13) indicated that POM was mainly of autochthonous origin due to high microalgae productivity. The values of 15N (3.83‰ ± 0.08) were likely inferred from potential input of POM from aquaculture practices. These results suggest that main sources of POM in the lagoon were derived from autochthonous microalgae and slightly anthropogenic impacts through aquaculture activities. Control POM load should be taken into account in maintaining water quality and biodiversity in the lagoon to inhibit microalgae biomass and shading due to nutrient enrichment.

Oxic–anoxic conditions in the water column of a tropical freshwater reservoir (Peña-Larga dam, NW Venezuela)

Sustainability assessment of traditional fisheries in Cau Hai lagoon (South China Sea)

Diversity and productivity of primary producers are known to be influenced simultaneously by resource availability and resource ratio, but the relative importance of these two factors differed among studies and so far only entire phytoplankton communities were investigated which might ignore specific nutrient requirements and stoichiometric plasticity of different functional groups. We measured nutrient availability (DIN, total N [TN], total P [TP]), nutrient imbalance (TN:TP, DIN:TP, N:Pseston), species richness, and abundance of the whole phytoplankton community, as well as those specific for cyanobacteria, diatoms, and dinoflagellates in Cau Hai lagoon in Vietnam. We determined the correlation among these variables, using structural equation modeling. The models applied to the whole phytoplankton community indicated that the nutrient availability (particularly TP and DIN) drove variation in phytoplankton abundance and richness, and that abundance also depended on species richness. The models applied to different functional groups differed considerably from the entire community and among each other, and only a part of the models was significant. The relationship between nutrient availability (mainly TP) and abundance was driven by cyanobacteria, and the relationship between nutrient imbalance (only with N:Pseston) and species richness was driven by diatoms. Remarkably, the positive relationship between species richness and abundance, as consistently observed for the whole phytoplankton community, was only observed for one of the three functional groups (diatoms), indicating that resource complementarity occurs particularly among species of different functional groups. Our results emphasized that nutrient availability (TP and to a lesser extent DIN) as well as nutrient imbalance (albeit only with N:Pseston as proxy) were driving factors for the phytoplankton community in the Cau Hai lagoon and hence alterations in both of these factors leading to a shift in phytoplankton species composition and productivity.

By applying of regression methods to assimilate data for suspended particulate matter as the input data to mathematical model, the paper presents the results on the distribution and carrying capacity of suspended particulate matter in Cau Hai lagoon, Thua Thien-Hue province during the dry season (7/2013) and rainy season (10/2013). The initial simulation show that the water exchange in Cau Hai lagoon is weak in comparsion with that in Thuy Tu lagoon as well as Tam Giang lagoon, leading the distribution of suspended particulate matter to be dominated by seasonal and the suspended particulate matter from Truoi river. The overall mean concentration of suspended particulate matter is 30 g/m3 during dry season and 48 g/m3 in the rainy season. Notably, the carrying capacity of suspended particulate matter in Cau Hai lagoon is very low in the rainy season, with the remaining capacity of receiving being only 4%. Therefore, a small increase in the suspended particulate matter can result in the overload of suspended particulate matter in Cau Hai region.