Spatio-temporal variation of water salinity in mangroves revealed by continuous monitoring and its relationship to floristic diversity.

Salinity is among the most critical factors limiting the growth and species distribution of coastal plants. Water salinity in estuarine ecosystems varies temporally and spatially, but the variation patterns across different time scales and salinity fluctuation have rarely been quantified. The effects of salinity on floristic diversity in mangroves are not fully understood due to the temporal and spatial heterogeneity of salinity. In this study, we monitored water salinity at an interval of 10-min over one year in three mangrove catchment areas representing the outer part, middle part, and inner part respectively of Dongzhai Bay, Hainan, China. The number of mangrove community types and dominant mangrove species of the three catchment areas were also investigated. We found that the diurnal variation and dry-season intra-month variation in water salinity were driven by tidal cycles. The seasonal variation in water salinity was mainly driven by rainfall with higher salinity occurring in the dry season and lower salinity occurring in the wet season. Spatially, water salinity was highest at the outer part, intermediate at the middle part, and lowest at the inner part of the bay. The intra-month and annual fluctuations of water salinity were highest at the middle part and lowest at the outer part of the bay. The number of mangrove community types and dominant species were lowest at the outer part, intermediate at the middle part, and highest at the inner part of the bay. These results suggest that the temporal variation of water salinity in mangroves is driven by different factors at different time scales and therefore it is necessary to measure water salinity at different time scales to get a complete picture of the saline environment that mangroves experience. Spatially, lower salinity levels benefit mangrove species richness within a bay landscape, however, further research is needed to distinguish the effects of salinity fluctuation and salinity level in affecting mangrove species richness.

Molecularly imprinted ratiometric fluorescence detection of tetracycline based on its fluorescence enhancement effect caused by tungsten trioxide quantum dots.

This paper reports a novel probe developed based on the tungsten trioxide quantum dots (WO3-x QDs) and molecularly imprinted polymers for the detection of trace tetracycline (TC) in the complex food matrix. Tungsten ion (W6+) in WO3-x QDs has a fluorescence enhancement effect on TC, and TC has a fluorescence quenching effect on WO3-x QDs. The blue emission of the WO3-x QDs (λem = 470 nm) as a reference and the yellow emission of the TC (λem = 550 nm) as a response were utilized for the ratiometric fluorescence detection. In order to improve its selectivity, the molecular imprinting technology was combined to construct molecularly imprinted ratiometric fluorescent probes (MIRFPs). Therefore, the MIRFPs can not only selectively detect TC, but also realize the visual detection from blue to yellow. Under the optimal conditions, the linear ranges of 0.01 âˆ¼ 10.0 µmol/L and 20.0 âˆ¼ 80.0 µmol/L were obtained with the limits of detection of 3.23 nmol/L and 6.37 µmol/L, respectively. Furthermore, the MIRFPs had been successfully applied to the detection of TC in milk and eggs. The satisfactory recoveries were in the range of 92.7 âˆ¼ 102.9 % with relative standard deviations (RSD, n = 3) below 1.59 %. This work offers a good strategy for the detection of food hazards.

Niches of nine mangrove species in a Sonneratia apetala-colonized area of Dongzhai Harbor, Hainan Island, China.

The distribution of mangroves is influenced by the environment. We aimed to understand the ecological adaptability of various mangrove species within the range of the exotic species, Sonneratia apetala Buch.-Ham., in Dongzhai Harbor, Hainan Island, China. We used three niche breadth indexes (Simpson, Levins, and Shannon-Weiner) and two niche overlap indexes (Pianka and Levins) to quantitatively determine the niche characteristics of nine mangrove species. The results showed that the order of the niche breadth values of mangrove species was as follows: Aegiceras corniculatum (Linn.) Blanco > Kandelia obovata Sheue et al. > Bruguiera gymnorrhiza (L.) Poir. > Avicennia marina (Forsk.) Vierh. Hailanci > S. apetala > S. caseolaris (L.) Engl. > Rhizophora stylosa Griff > Ceriops tagal (Perr.) C. B. Rob. > B. sexangula (Lour.) Poir. Pearson correlation analysis revealed that the niche breadth of each population was significantly correlated with the importance value of the population in the whole sample (R1 = R2 = 0.771, R3 = 0.644, p < .05). The nine mangrove species were divided into three groups by Bray-Curtis cluster analysis; the groups were similar to the distribution of mangrove species in the natural state as determined by tide level. Niche similarity analysis showed that the niche similarity of most mangroves ranged between 0.5 and 0.8 and that the species pairs A. corniculatum-B. gymnorrhiza, A. corniculatum-Avicennia marina, and K. obovata-S. caseolaris were characterized by large niche similarity ratios. Although it had a moderate niche breadth, S. apetala had a relatively broad niche overlap with mangroves in the mid- and low-tide zones (S. caseolaris, A. corniculatum, K. obovata, and Avicennia marina), a moderate overlap with B. gymnorrhiza and R. stylosa, only a slight overlap with C. tagal, and no overlap with B. sexangular. There was no obvious linear relationship between niche width and niche overlap of mangroves. Due to its inefficiency in utilizing certain resources and relatively high degree of resource selection, it seems likely that S. apetala will not pose a threat to the survival of native plants, let alone completely replace native species.

Comparison of methane emissions among invasive and native mangrove species in Dongzhaigang, Hainan Island.

The strength of methane (CH4) source of mangroves is not well understood, especially when including all CH4 pathways in consideration. This study measured CH4 fluxes by five pathways (sediments, pneumatophores, water surface, leaves, and stems) from four typical mangrove forests, including Kandelia candel without pneumatophores and three species with pneumatophores: Sonneratia apetala, Laguncularia racemosa and Bruguiera gymnorhiza-Bruguiera sexangula. The CH4 fluxes from sediments were 4.82±1.46mgCH4m-2h-1 for K. candel and 1.36±0.17mgCH4m-2h-1 for the other three with pneumatophores. Among the three communities with pneumatophores, S. apetala community had significantly greater emission rate than the other two (P<0.05). Pneumatophores in S. apetala were found to significantly decrease CH4 emission from sediments (P<0.01), while those in B. gymnorhiza-B. sexangula were significantly increase it (P<0.05). CH4 fluxes from waters were 3.48±1.11mgCH4m-2h-1, with the highest emission rate in the K. candel community for the duck farming. Leaves of mangroves except for those of K. candel were a weak CH4 daytime sink, but stems were a weak source. The total 72ha of mangroves in the Changning river basin emitted about 8.10Gg CH4 per year, with a weighted emission rate of about 1.29mgCH4m-2h-1. Our results suggested that mangroves are only a small methane source to atmosphere with great contribution from sediments and waters, only slight contribution from leaves and stems. Pneumatophores of different mangrove species played different roles in CH4 fluxes from sediments.

Soil inorganic carbon in mangroves of tropical China: patterns and implications.

Soil inorganic carbon (IC) is neglected in most blue carbon studies despite the globally significant role of the calcium carbonate cycle in ocean C balance and climate change. We sampled soils to 1 m depth from seven mangrove reserves in Hainan Island, China. Only 45 out of 509 samples were rich in IC (greater than 10 mg cm-3). Most of the IC-rich samples were found at the outer part of Qinglan Bay, which is adjacent to the largest coral reef zone of Hainan Island. Soil IC concentration ranged from 0 to 66 g kg-1 (or 0-67 mg cm-3), accounting for 0-92% of total C. IC concentration increased with soil depth where it was abundant. Soil pH was low (2.36-6.59) in IC-depleted soils, but increased to 5.67-7.99 in IC-rich soils. Soil total C stock and IC stock in mangroves of Hainan amounted to 0.76×106 and 0.12×106 Mg, respectively, with IC accounting for 16% of total C. Our study finds that carbonate concentrations can be high in mangrove soils but their spatial distribution indicates they are largely allochthonous in origin. Evidence of carbonate dissolution in mangroves suggests mangroves may increase total alkalinity to buffer acidification in seawater.

Mangrove vegetation enhances soil carbon storage primarily through in situ inputs rather than increasing allochthonous sediments.

The role of soil carbon (C) in coastal wetlands as a net sink is related to the relative abundance of autochthonous versus allochthonous C. We aimed to investigate soil C sources and the pathways by which mangrove vegetation enhances soil C accumulation. We sampled soil to 1 m depth in seven oceanic mangrove forests and an adjacent un-vegetated mudflat at Dongzhai Bay, China. Stable C isotope technique was used to separate autochthonous and allochthonous C sources. Autochthonous C accounted for 27-97% of soil C stock in the top meter. Soil C density was 1.1-3.6 times higher in mangroves than in the mudflat. Among the increased soil C in mangroves relative to mudflat, autochthonous C accounted for 65-100% of the increments. The results suggest that mangrove vegetation enhances soil C storage primarily through in situ inputs, therefore the substantial soil C stocks commonly found in mangroves play an important role in sequestering atmospheric CO2.

Soil carbon storage in mangroves is primarily controlled by soil properties: A study at Dongzhai Bay, China.

Coastal wetlands are well known for their considerable capacity to store carbon (C). However, the spatial patterns and major controls of soil C concentration and C density in coastal wetlands remain poorly known. We measured soil total C concentration up to one meter depth and assessed environmental and biological factors influencing soil C input and decomposition processes across various geomorphologic settings and mangrove forest types at Dongzhai Bay, China. Structural equation modeling (SEM) was used to determine the causal pathways of influencing factors on soil C concentration. We found that the variation pattern of soil C concentration across geomorphologic settings and forest types was mirrored by soil properties. From 68 to 94% (varying with soil depth) variations of soil C concentration were explained by the inter-related influencing factors included in SEM. In the upper 60cm soil layers, soil moisture was the most important factor affecting soil C concentration. In the 60-100cm subsoil zone, the proportion of finer soil particles was the primary control of soil C concentration variation. In contrast, aboveground biomass and nearness of sampling site to the open water, which affect autochthonous and allochthonous C inputs, had relatively weak effects on soil C concentration compared to soil properties, which affect C decomposition. Soil C concentration was a good predictor of soil C density at all soil depths. The results suggest that top- and subsoil C concentrations in mangroves are subjected to different environmental controls, but taken together, mangrove soil C storage may be primarily controlled by soil property-mediated C decomposition rate. Subsoil C deserves more attention since it may respond differently to environmental changes than the better-known topsoil C.

Carbon stocks and potential carbon storage in the mangrove forests of China.

Mangrove forests provide important ecosystem services, and play important roles in terrestrial and oceanic carbon (C) cycling. Although the C stocks or storage in terrestrial ecosystems in China have been frequently assessed, the C stocks in mangrove forests have often been overlooked. In this study, we estimated the C stocks and the potential C stocks in China's mangrove forests by combining our own field data with data from the National Mangrove Resource Inventory Report and from other published literature. The results indicate that mangrove forests in China store about 6.91 ± 0.57 Tg C, of which 81.74% is in the top 1 m soil, 18.12% in the biomass of mangrove trees, and 0.08% in the ground layer (i.e. mangrove litter and seedlings). The potential C stocks are as high as 28.81 ± 4.16 Tg C. On average, mangrove forests in China contain 355.25 ± 82.19 Mg C ha(-1), which is consistent with the global average of mangrove C density at similar latitudes, but higher than the average C density in terrestrial forests in China. Our results suggest that C storage in mangroves can be increased by selecting high C-density species for afforestation and stand improvement, and even more by increasing the mangrove area. The information gained in this study will facilitate policy decisions concerning the restoration of mangrove forests in China.

[Wind-attenuation effect of Sonneratia apetala and Kandelia obovata plantations].

A field monitoring was conducted to examine the wind-attenuation effect of mangrove plantations at the Sanjiang Bay of Dongzhai Harbor, Hainan Province of South China. The wind speed and wind direction were measured at a site 50 m away from the offshore forest fringes of Sonneratia apetala and Kandelia obovata plantations and 2 m above the ground. Both the S. apetala and the K. obovata plantations had obvious effect in attenuating the speed of the wind from northerly to the shore, with the mean wind speed decreased by > 85% and the better effect of K. obovata plantation. With the increase of the wind speed, the wind-attenuation effect of the plantations presented a trend of decreasing first and remained stable then. At 50 m away from the offshore forest fringe of S. apetala plantation, the wind-attenuation rate was higher than 89.8% when the mean wind speed was lower than 5 m x s(-1), tended to be stable when the mean wind speed was 10 m x s(-1), and turned to be 58.9%-63.6% when the mean wind speed was higher than 15 m x s(-1). The S. apetala plantation had better wind attenuation effect in warmer season than in colder season. Under the extremely adverse weather like typhoon, the mean wind speed and extreme wind speed at 50 m away from the offshore forest fringe of S. apetala plantation were decreased by 59.4% and 53.2%, respectively.

Physiological responses of mangrove Sonneratia apetala Buch-Ham plant to wastewater nutrients and heavy metals.

Mangroves play an important role for removing nutrients, heavy metals, and other pollutants in wetland ecosystems. This study investigated the physiological responses of a mangrove plant (i.e., Sonneratia apetala Buch-Ham) to different wastewater pollution levels. Four different treatments, namely three concentration levels (i.e., normal, five-time-greater than normal, and ten-time-greater than normal) of wastewaters and one control (i.e., salted water), were used to grow the mangrove plants. Results showed that the height and biomass of the plant increased with wastewater pollution levels. No significant differences in root and catalase activities were observed among different treatments, whereas the increases in peroxidase and superoxide dismutase activities were attributed to the need for detoxification. In general, leaf chlorophyll content increased with wastewater pollution levels due to the increase in nutrient contents.

[Adaptability of mangrove Avicennia marina seedlings to simulated tide-inundated times].

A laboratory test on the effects of differents simulated tide-inundated times with 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 h x d(-1) on the growth of Avicennia marina seedlings was conducted. The ten growth information indices including chlorophyll, root vigor, growth, biomass and photosynthetic rate were mensurated. The principal components analysis was made combining the ten growth information indices. The 210 d experimental results showed that the chlorophyll, root vigor, growth and biomass would rise first and then fall as the extension of the inundate time; and they changed suddenly at the threshold inundate time 16 h x d(-1). The growth and biomass of Avicennia marina seedlings with more than 16 hours tide-inundated time per day were less than them with no more than 16 hours tide-inundated time per day. The maximum value of stem increment each month, leaf blade increment each month, dry weight of stem, dry weight of root and total biomass were under the 10 hours tide-inundated time per day. It concluded that Avicennia marina seedlings would grow adaptively with less than 16 hours tide-inundated time per day, 8-12 hours of tide-inundated time per day is the most suitable for the growth of Avicennia marina seedlings, while 16 h x d(-1) is a critical tide-inundated time when the plant responded to be obviously inadaptable.

[Niches of several mangrove species in Dongzhai Harbor of Hainan Island].

Employing the succession series of Kandelia candel-Aegiceras corniculatum community in non-indigenous species Sonneratia apetala extension area as resource axes, and with three axes, commonly used calculation formulae, this paper determined the niche breadth and overlap of mangrove populations. The results showed that the niche breadth decreased in order of Aegiceras corniculatum (3.8357) > Kandelia candel (3.3421) > Bruguiera gymnorrhiza (3.3180) > Avicennia marina (3.0975) > Sonneratia apetala (2.9137) > Sonneratia caseolaris (2.5724) > Ceriops tagal (1.8523) > Rhizophora stylosa (1.6897) > Bruguiera sexangula (1.0000), which could indicate the ecological adaptability and distribution range of the species. The niche overlap among K. candel, A. corniculatum, B. gymnorrhiza and A. marina was the largest, suggesting the intense competition among them, followed by the niche overlap of S. apetala with S. caseolaris, A. corniculatum, K. candel and A. marina, S. apetala with R. stylosa and B. sexangula, S. apetala with C. tagal, and S. apetala with B. sexangula.

[Dynamics and species-diversities of artificial Sonneratia apetala, Sonneratia caseolaris and Kandelia candel communities].

Studies on the dynamics and species-diversities of artificial Sonneratia apetala, Sonneratia caseolaris and Kandelia candel communities showed that the arbor layer of S. apetala and S. caseolaris communities contained two distinctive sub-layers. The upper layer was composed of S. apetala or S. caseolaris, and the medium layer was composed of K. candel and Aegiceras corniculatum. The dominant population S. apetala or S. caseolaris in S. apetala and S. caseolaris communities only had old-aged individuals but no regenerations appeared recently, while K. candel and A. corniculatum were actively progressive populations, which would possibly become dominant populations during the course of community development, showing that S. apetala and S. caseolaris were pioneer species for plantation, which could promote natural colonization of regional mangrove species when planted at open mudflat. K. candel was the actively progressive population in K. candel community, its natural regeneration and succession could be successful, while A. corniculatum and B. sexangula were initially progressive populations. The species composition and species-diversities of S. apetala and S. caseolaris communities were similar, both contained the main species in K. candel community, namely, K. candel, A. corniculatum and Bruguiera sexangula, showing that S. apetala and S. caseolaris could co-exist with these regional species. To introduce and plant them could help to form complicated and diversified mangrove communities. During the early stage of the development, the species-diversities of S. apetala and S. caseolaris communities were higher when their planting density was high. The species-diversities grew slightly higher when the communities became older.