Zhijian Jiang

Spatial and seasonal characteristics of dissolved heavy metals in the east and west Guangdong coastal waters, South China

Heavy metal concentrations and physicochemical parameters in seawater were measured in Guangdong coastal waters, South China. Results showed that the concentrations and distribution of heavy metals varied spatially and seasonally. Generally, heavy metal concentrations in the east regions were higher than in the west. Concentrations of Pb, Zn, Cd and Cr in wet seasons were generally higher than in dry seasons owing to the seasonal differences of the river discharge, rainfall and seawater intrusion. Principal component (PC) analysis showed that PC1, PC2 and PC3 in the east were correlated to Pb+Cr+Zn+Cd, As+Cd and Cu, respectively, and they were correlated to Pb+Cr, Zn+Cu+Cd and As+Cu, respectively, in the west. That was maybe due to the differences of local heavy metal sources. The anthropogenic activities contributed more to the main sources of heavy metals, and contamination factors indicated that Zn and Pb pollution was serious in study area.

Physiological responses of the seagrass Thalassia hemprichii (Ehrenb.) Aschers as indicators of nutrient loading

To select appropriate bioindicators for the evaluation of the influence of nutrients from human activities in a Thalassia hemprichii meadow, environmental variables and plant performance parameters were measured in Xincun Bay, Hainan Island, South China. Nutrient concentrations in the bay decreased along a gradient from west to southeast. Moreover, the nutrients decreased with an increase in the distance from the shore on the southern side of the bay. Among the candidate indicators, the P content of the tissues closely mirrored the two nutrient loading gradients. The epiphytic algae biomass and the N content in the tissues mirrored one of the two nutrient loading trends. The leaf length, however, exhibited a significant negative correlation with the nutrient gradients. We propose that changes in the P content of T. hemprichii, followed by epiphytic algae biomass and N content of the tissues, may be the useful indicators of nutrient loading to coastal ecosystems.

Distribution and bioaccumulation of heavy metals in marine organisms in east and west Guangdong coastal regions, South China

Heavy metal (Cu, Pb, Zn, Cr, Cd, As) concentrations, distribution and bioaccumulation were studied in marine organisms in Guangdong coastal regions. Heavy metal concentrations and distribution in organisms showed characteristics according to areas and species. Heavy metal concentrations in most organisms were higher in west than in east, tightly related to the local industry structure and the disequilibrium of metal discharge. Generally, high heavy metal concentrations were detected in molluscs and low concentrations were detected in fish. Bioaccumulation factor was used to assess the accumulation level of marine organisms to heavy metals, of which Cd, Cu and As were the most accumulated elements. Accumulation abilities to heavy metals varied among organism species, such as Distorsio reticulate accumulating Cu, Zn, Cd, As, Loligo beka Sasaki accumulating Pb, Cu, Cr, and Turritella bacillum Kiener accumulating Zn, Cd, As. By comparison, Johnius belengeri, Argyrosomus argentatus, Cynoglossus sinicus Wu had relatively low accumulation abilities.

Proteome analysis reveals extensive light stress-response reprogramming in the seagrass Zostera muelleri (alismatales, zosteraceae) metabolism

Seagrasses are marine ecosystem engineers that are currently declining in abundance at an alarming rate due to both natural and anthropogenic disturbances in ecological niches. Despite reports on the morphological and physiological adaptations of seagrasses to extreme environments, little is known of the molecular mechanisms underlying photo-acclimation, and/or tolerance in these marine plants. This study applies the two-dimensional isoelectric focusing (2D-IEF) proteomics approach to identify photo-acclimation/tolerance proteins in the marine seagrass Zostera muelleri. For this, Z. muelleri was exposed for 10 days in laboratory mesocosms to saturating (control, 200 μmol photons m−2 s−1), super-saturating (SSL, 600 μmol photons m−2 s−1), and limited light (LL, 20 μmol photons m−2 s−1) irradiance conditions. Using LC-MS/MS analysis, 93 and 40 protein spots were differentially regulated under SSL and LL conditions, respectively, when compared to the control. In contrast to the LL condition, Z. muelleri robustly tolerated super-saturation light than control conditions, evidenced by their higher relative maximum electron transport rate and minimum saturating irradiance values. Proteomic analyses revealed up-regulation and/or appearances of proteins belonging to the Calvin-Benson and Krebs cycle, glycolysis, the glycine cleavage system of photorespiration, and the antioxidant system. These proteins, together with those from the inter-connected glutamate-proline-GABA pathway, shaped Z. muelleri photosynthesis and growth under SSL conditions. In contrast, the LL condition negatively impacted the metabolic activities of Z. muelleri by down-regulating key metabolic enzymes for photosynthesis and the metabolism of carbohydrates and amino acids, which is consistent with the observation with lower photosynthetic performance under LL condition. This study provides novel insights into the underlying molecular photo-acclimation mechanisms in Z. muelleri, in addition to identifying protein-based biomarkers that could be used as early indicators to detect acute/chronic light stress in seagrasses to monitor seagrass health.

Effect of nutrient enrichment on the source and composition of sediment organic carbon in tropical seagrass beds in the South China Sea

To assess the effect of nutrient enrichment on the source and composition of sediment organic carbon (SOC) beneath Thalassia hemprichii and Enhalus acoroides in tropical seagrass beds, Xincun Bay, South China Sea, intertidal sediment, primary producers, and seawater samples were collected. No significant differences on sediment δ(13)C, SOC, and microbial biomass carbon (MBC) were observed between T. hemprichii and E. acoroides. SOC was mainly of autochthonous origin, while the contribution of seagrass to SOC was less than that of suspended particulate organic matter, macroalgae and epiphytes. High nutrient concentrations contributed substantially to SOC of seagrass, macroalgae, and epiphytes. The SOC, MBC, and MBC/SOC ratio in the nearest transect to fish farming were the highest. This suggested a more labile composition of SOC and shorter turnover times in higher nutrient regions. Therefore, the research indicates that nutrient enrichment could enhance plant-derived contributions to SOC and microbial use efficiency.

The porewater nutrient and heavy metal characteristics in sediment cores and their benthic fluxes in Daya Bay, South China

Nutrient and heavy metal (Fe, Mn, Ni, Cu, Pb, Zn, Cr, Cd and As) concentrations in porewater in sediment cores and their diffusive benthic fluxes were investigated in Daya Bay, South China, to study the accumulation and transfer of nutrients/metals at the sediment-water interface, and to discuss the impact of human activities on nutrients/metals. Nutrients and heavy metals displayed different profiles in porewater, which was mainly attributed to the distinct biogeochemical conditions in sediments. Total mean fluxes of nutrients (except NO3 and NO2) and metals in study area were positive, indicating nutrients and metals diffused from the sediment to overlying water, and sediment was generally the source of nutrients/metals. Human activities and the weak hydrodynamic force made nutrients/metals accumulate in sediment, so the sediment should be paid more attention to as the endogenesis of contamination in Daya Bay waters.

Effects of nutrient load on microbial activities within a seagrass-dominated ecosystem: Implications of changes in seagrass blue carbon

Nutrient loading is a leading cause of global seagrass decline, triggering shifts from seagrass- to macroalgal-dominance. Within seagrass meadows of Xincun Bay (South China Sea), we found that nutrient loading (due to fish farming) increased sediment microbial biomass and extracellular enzyme activity associated with carbon cycling (polyphenol oxidase, invertase and cellulase), with a corresponding decrease in percent sediment organic carbon (SOC), suggesting that nutrients primed microorganism and stimulated SOC remineralization. Surpisingly, however, the relative contribution of seagrass-derived carbon to bacteria (δ13Cbacteria) increased with nutrient loading, despite popular theory being that microbes switch to consuming macroalgae which are assumed to provide a more labile carbon source. Organic carbon sources of fungi were unaffected by nutrient loading. Overall, this study suggests that nutrient loading changes the relative contribution of seagrass and algal sources to SOC pools, boosting sediment microbial biomass and extracellular enzyme activity, thereby possibly changing seagrass blue carbon.

Dynamics of nonstructural carbohydrates in seagrass Thalassia hemprichii and its response to shading

A field survey was performed to examine nonstructural carbohydrate (NSC) dynamics in seagrass Thalassia hemprichii at the Xincun Bay in southern China. An indoor experiment to investigate the response of NSC in T. hemprichii to shade was conducted. Belowground tissue of T. hemprichii was the dominant site of NSC reserves, and soluble sugar was the primary storage compound. The starch content of belowground tissue was lower in high intertidal areas than in low intertidal areas, indicating that the longer air exposure in high intertidal areas resulted in less NSC synthesis and less accumulation of NSC in T. hemprichii. The lowest level of soluble sugar and its proportion to NSC in belowground tissue were observed near the cage culture area, where the nutrient concentration in water and sediment was the highest; while the highest level of that was observed near the coastal shrimp farm, Where salinity was the lowest. Soluble sugar in belowground tissue showed the following trend: summer>spring>winter>autumn. This corresponded to seasonal changes in the intensity of light. Leaf sugar accumulated during the autumn-winter period, providing a carbon and energy source for flower bud formation and seed germination. Short-term shading decreased NSC accumulation. Collectively, these results suggest that nutrient enrichment, freshwater discharge and exposure to air affect NSC dynamics in T. hemprichii. Light intensity, flower bud formation, and seed germination were all found to induce seasonal variations in NSC in T. hemprichii.

Sediment microbes mediate the impact of nutrient loading on blue carbon sequestration by mixed seagrass meadows

Recent studies have reported significant variability in sediment organic carbon (SOC) storage capacity among seagrass species, but the factors driving this variability are poorly understood, limiting our ability to make informed decisions about which seagrass types are optimal for carbon offsetting and why. Here we show that differences in SOC storage capacity among species within the same geomorphic environment can be explained (in part) by below-ground processes in response to nutrient load; specifically, differences in the activity of microbes harboured by morphologically-different seagrass species. We found that increasing nutrient load enhanced the relative contribution of seagrass and algal sources to SOC pools, boosting sediment microbial biomass and extracellular enzyme activity within mixed seagrass meadows composed of Thalassia hemprichii and Enhalus acoroides, and thus possibly weaken the seagrass blue carbon sequestration capacity. The relative contribution of seagrass plant material to sediment bacterial organic carbon (BOC) and the influencing SOC-decomposing enzymes in E. acoroides meadows were half that of T. hemprichii meadows living side-by-side, even though the mixed seagrass meadows received SOC from the same sources. Overall this research suggests that microbial activity can vary significantly among seagrass species, thereby causing fine-scale (within-meadow) variability in SOC sequestration capacity in response to nutrient load.

Atmospheric deposition of trace elements to Daya Bay, South China Sea: Fluxes and sources

This study was conducted from October 2015 to March 2017, with the aim of providing the first data on the fluxes and sources of wet and dry deposition of trace elements (TEs) in Daya Bay, South China Sea. Wet deposition flux of TEs was always preponderant and orders of magnitude higher than that of dry deposition owing to the high rainfall frequency in Daya Bay. The total deposition fluxes of TEs in the target area were higher than in most places worldwide, but at a moderate level within China. Wet deposition was highest in summer and lowest in winter, whereas dry deposition showed an opposite seasonal trend. The main sources of TEs in wet deposition were seasalt/dust, fossil fuel combustion, and crustal sources, and in dry deposition, they were dust/metallurgic, fossil fuel, petrochemical industry and crustal sources.