An Approach for In Situ Rapid Detection of Deep-Sea Aromatic Amino Acids Using Laser-Induced Fluorescence.

Amino acids are the material basis of almost all life activities. An improved understanding of the source, state, and cycle of amino acids is essential for determining the energy flow and material circulation of marine ecosystems. In the present study, an in situ rapid detection method of ultraviolet (UV; 266 nm) laser-induced fluorescence (LIF) technology was used to detect three natural, aromatic amino acids in the seawater. The laser-induced fluorescence peaks of aromatic amino acids tryptophan, tyrosine, and phenylalanine were located at 350 nm, 300 nm, and 280 nm, respectively. High, linear correlations between the concentrations of the aromatic amino acids and the fluorescence peak heights were observed, and the lowest detectable concentrations of tryptophan, tyrosine, and phenylalanine were 4.70 × 10-9 mol/L, 2.76 × 10-8 mol/L, and 6.05 × 10-7 mol/L, respectively, which allowed us to quantify their concentrations by using laser-induced fluorescence. This paper not only provides a practical method for the detection of aromatic amino acids in seawater, but a new means to further understand the biogeochemical processes of carbon cycles in the deep sea.

Water optical properties over or around coral reefs in the coastal region: implications for coral reef remote sensing.

Coral reefs inhabit clear oceanic-type waters to turbid coastal regimes. For shallow coastal water environments, the coral reefs from remote sensing will be substantially influenced by the complexity and heterogeneity of the optical properties of water. Through a set of bio-optical and chemical measurements in July 2019 around Xidao Island, Sanya, China, we explored spatial variations of water components' concentrations (including suspended solids, phytoplankton, and dissolved organic carbon) and the optical absorptions (i.e., particulate pigments, detritus, and colored dissolved organic matter) in waters over or around coral reefs; further analysis of their influences upon the remote sensing reflectance (Rrs(λ)) of water was performed. It was observed that the bio-optical and chemical properties of the waters over or around coral reefs were spatially and vertically heterogeneous for different sampling sites. As expected, the suspended solids dominated the optical properties of coral reefs waters in areas of Xidao Island, which evidently influenced the Rrs(λ), especially for the surface waters (Pearson r > 0.60, p < 0.01). In addition, the dissolved organic carbon concentrations exhibited significant relations to the Rrs(λ) both in surface and bottom water layers, whereas the colored dissolved organic matter showed a weak negative correlation with the Rrs(λ). These findings will support the mapping and monitoring benthic habitats with remote sensing imagery in coastal regions, especially when a removal of the influence by particulate sediments was available.

The Ecological Status and Change in High-Latitude Coral Assemblages at the Xuwen Coral Reef, Northern South China Sea: Insight into the Status and Causes in 2020.

Taking the coral communities of the Xuwen coral reef in 2020 as the research object, we analyzed the species composition, diversity, and interspecific Spearman correlation of the scleractinian coral communities, investigated the features and spatial distribution of the scleractinian coral community, and discussed the correlation between the community composition and environmental factors to identify the affecting factors and their sources. These results showed that (1) compared with the survey in 2004, the coverage of corals in 2020 had significantly decreased, while the dominant genera were still Goniopora and Porites. The coral morphology was massive, and the diversity of the coral community (Shannon-Wiener index, H') was 2.87. The distribution of coral was uneven. The competition among some dominant species of coral was intense. (2) The mass coral bleaching event in the NSCS in August 2020 did not cause severe coral death in the short term on the Xuwen coral reef. (3) The growth of the coral community in 2020 might be greatly affected by high suspended solids and nutrient levels, which were related to the current, mariculture, and coastal erosion. (4) Anthropogenic activities such as coastal aquaculture and fishing were the major factors leading to the reduction in coral coverage on Xuwen coral reef in the past 10 years.

Effective upwelling irradiance depths in turbid waters: a spectral analysis of origins and fate.

The spectral distribution of upwelling and downwelling irradiance were used to estimate the effective upwelling irradiance depth as well as examine the angular distribution of the downwelling radiance. The effective upwelling depth was seen to undergo spectral "shifts" in wavelength maxima in relation to elevated particulate concentrations. Wavelengths of the UVA minimum and mid visible maximum depths were found to be shifted to higher wavelengths (red shifted) at high particulate concentrations, while expected minimums at chlorophyll and phycocyanin absorption peaks and in the NIR were shifted to lower wavelengths (blue shifted). By comparing upwelling and downwelling irradiance profiles, the wavelength limits of the asymptotic angular radiance distribution were found to correspond to the visible spectral domain (390-740 nm).

[Comparison of methods for estimating soybean chlorophyll content based on visual/near infrared reflection spectra].

The estimation of crop chlorophyll content could provide technical support for precision agriculture. Canopy spectral reflectance was simulated for different chlorophyll levels using radiative transfer models. Then with multiperiod measured hyperspectral data and corresponding chlorophyll content, after extracting six wavelet energy coefficients from the responded bands, an evaluation of soybean chlorophyll content retrieval methods was conducted using multiple linear regression, BP neural network, RBF neural network and PLS method. The estimate effects of the three methods were compared afterwards. The result showed that the three methods based on wavelet analysis have an ideal effect on the chlorophyll content estimation. R2 of validated model of multiple linear regression, BP neural network, RBF neural network and PLS method were 0. 634, 0. 715, 0. 873 and 0.776, respectively. PLS based on Gaussian kernel function and RBF NN methods were better with higher precision, which could estimate chlorophyll content stably.

Remote sensing of particulate organic carbon dynamics in a eutrophic lake (Taihu Lake, China).

A two step approach was developed to estimate POC concentrations in a shallow eutrophic lake, where dissolved carbon and inorganic particulate matter strongly influence optical properties. The approach was based on the identification of a co-variability of POC concentrations with one or more inherent optical properties (IOPs). In the present case, a relationship between POC and absorption at 620 nm was identified and was combined with a reflectance based algorithm for case II waters. Compared with other published POC algorithms, this approach provided better estimates over a wide range of POC concentrations in two hypereutrophic lake waters with the predominance of cyanobacteria (R(2) > 0.80). While it is unlikely that a single POC algorithm can be created that is independent of the variability of POC sources, this approach allows for a common method to identify appropriate algorithms with which POC dynamics can be explored.

[Estimation of DOC concentrations using CDOM absorption coefficients: a case study in Taihu Lake].

Dissolved organic carbon (DOC) is the largest organic carbon stock in water ecosystems, which plays an important role in the carbon cycle in water. Chromophoric dissolved organic matter (CDOM), an important water color variation, is the colored fraction of DOC and its absorption controls the instruction of light under water. The available linkage between DOC concentration and CDOM absorptions enables the determination of DOC accumulations using remote sensing reflectance or radiance in lake waters. The present study explored the multi-liner relationship between CDOM absorptions [a(g) (250) and a(g) (365)] and DOC concentrations in Taihu Lake, based on the available data in 4 cruises (201005, 201101, 201103, 201105) (totally 183 sampling sites). Meanwhile, the results were validated with the data of the experiment carried out from August 29 to September 2, 2011 in Taihu Lake (n = 27). Furthermore, a universal pattern of modeling from remote sensing was built for lake waters. The results demonstrated that this method provided more satisfying estimation of DOC concentrations in Taihu Lake. Except the data obtained in January 2011, the fitted results of which were not conductive to the winter dataset (201101) in Taihu Lake, due to the diverse sources and sinks of DOC and CDOM, the multi-liner relationship was robust for the data collected in the other three cruises (R2 = 0.64, RMSE = 14.31%, n = 164), which was validated using the 201108 sampling dataset (R2 = 0.67, RMSE = 10.58%, n = 27). In addition, the form of the statistic model is universal, to some extent, for other water areas, however, there is difference in the modeling coefficients. Further research should be focused on the parameterization using local data from different lakes, which provides effective methodology for the estimation of DOC concentrations in lakes and other water regions.

[Aerosol optical thickness of the atmospheric aerosol over Taihu Lake and its features: results of in-site measurements].

Based on the data measured in situ by an automatic sun tracking photometer (CE-318), the aerosol optical thickness (AOT) and the corresponding Angström coefficient alpha of the atmospheric aerosol over Taihu Lake from November 2005 to October 2010 were collected. The results showed that high values of AOT over Taihu Lake were measured in summer (June to July) whereas low values were detected in autumn and winter (October to January). However, the low and high values of a appeared in spring (March to April) and in autumn (September to November), respectively. The variations of AOT and a over Taihu Lake may be related to weather patterns in this region. Based on the frequency distribution, AOT (500 nm) had only one peak value, with a maximum frequency of 0.4-0.6 and a yearly average value of 0.80, accounting for 26% of the total sample. Calculated from the mean AOT (500 nm), the solar radiation reduction was reduced by at least 50% by the atmospheric aerosol, resulting in more turbid atmosphere in this region and consequently heavy fog and haze. There were two peak values of the Angström coefficient alpha, with the maximum frequency ranging from 1.1-1.3 and 1.3-1.5 and a yearly average value of 1.17, accounting for 30% of the total sample. Significant variations were also observed in the daily average values of AOT (500 nm) and a, indicating the coexistence of different types of aerosols over Taihu Lake. The mean value of AOT (500 nm) declined when a increased. To sum up, values of AOT (500 nm) over Taihu Lake changed greatly with time, and the aerosol should be classified as an urban-industrial aerosol.