Optical approaches to examining the dynamics of dissolved organic carbon in optically complex inland waters

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SPATIAL DISTRIBUTION AND THE POSSIBLE SOURCE OF CDOM FOR INLAND WATER IN SUMMER IN THE NORTHEAST CHINA

The availability of underwater light is a critical factor in the growth and abundance of primary producers in shallow embayments. The aim of this study was to examine the spatial distribution and the possible source of CDOM for inland water in summer in the northeast china. Absorption spectra of inland water samples were measured from 200nm to 800nm. Highest mean-value of a(375) occurred in Chagan Lake. A significant spatial difference was found among four different inland waters, and evident spatial variation was in Chagan Lake. A consistent negative non-linear relationship was recorded between S value and CDOM absorption coefficient. Furthermore, S value was used as a proxy for CDOM composition and source. Fulvic acids is primary contribution for CDOM absorption in Songhua Lake and Shitoukoumen Reservoir, but humic acids in Nanhu Lake and Chagan Lake. The relationships between CDOM absorption and total suspended matter concentration and chlorophyll-a concentration were analyzed. It demonstrated the biological processes source for Nanhu Lake, Shitoukoumen Reservoir and Chagan Lake. But for Songhua Lake, the dominating source is from river inputs, but biological process was also an important portion for CDOM concentration

Spectral Absorption Properties of Colored Dissolved Organic Matter (CDOM) and Total Suspended Matter (TSM) of Inland Waters

Spectral absorption properties of total suspended matter (TSM) and colored dissolved organic matter (CDOM) are important for the use of the bio-optical model to estimate water quality parameters. This study aims to investigate the variation in the absorption coefficients of TSM and CDOM of inland waters. A total of 92 water samples were collected from Shitoukoumen Reservoir and Songhua Lake in Northeast China, analyzed for TSM and Chl-a, and measured for the absorption coefficient of TSM, CDOM and total pigments using a laboratory spectrophotometer. The absorption coefficient of TSM has been decomposed for phytoplankton and inorganic sediments. The results show that for Shitoukoumen Reservoir, CDOM has strong absorptions with shallow absorption slopes (i.e., the coefficient S in a(lambda)=a(lambda(0))exp[-S(lambda- lambda(0))]) and large absorption at 355 nm; and for Songhua Lake, CDOM follows similar spectral absorption curves but less variation in the S value. The results also show TSM has the average absorption coefficient 5.7 m(-1) at 440 nm and 0.93 m(-1) at 675 nm, and their concentration is well correlated to TSM with R-2 larger than 0.85 at 440 nm over both Songhu Lake and Shitoukoumen Reservoir. In summer, CDOM was mainly terrigenous and had a high proportion of humic acid derived from the decomposition of phytoplankton and there were no obvious difference of S value. The results indicate that inorganic sediments contributed much more absorption than phytoplankton pigments in Shitoukoumen Reservoir than that in Songhua Lake, and there is strong association of TSM concentration to absorption coefficient at 440 nm

An absorption-specific approach to examining dynamics of particulate organic carbon from VIIRS observations in inland and coastal waters

An absorption-based approach was used to determine surface particulate organic carbon (POC) concentrations in both inland and coastal waters. The improved performance of this approach was based on the specification of local POC absorption characteristics based on dominant POC sources; phytoplankton or detritus based. This specification was made using a new POC-Index (PI), developed and tested across a range of POC (300-10,000 mg/m(3)) conditions in temporally and spatially heterogeneous inland and coastal waterbodies. The POC model was based on remote sensing reflectance (R-rs, sr(-1)) in four wavebands: R-rs(751), R-rs(488) and R-rs(R/G), where R is the red band [R-rs(672)] for detritus dominated waters and G is the green band [R-rs(555)] in the phytoplankton dominated waters. The model provided a high R-2 (0.74) and relatively low r(RMSE) (42.0%, N = 136, p < 0.01). Validation with independent datasets from Chaohu Lake and the Yangtze River Estuary produced a larger positive bias (R-2 = 0.59, r(RMSE) = 83%, delta = 634 mg/m(3), S = 0.63, I = 1439 mg/m(3)); nevertheless, the bias was reduced when tuned with local data (R-2 = 0.80, r(RMSE) = 45%, delta = 72 mg/m(3), S = 0.81, I = 327 mg/m(3)). Additionally, HydroLight simulations presented an independent correlation between PI and CDOM conditions and reasonable POC estimates from the new approach developed in this study. The approach was tested using data from Visible Infrared Imaging Radiometer Suite (VIIRS) in a range of optically complex conditions to quantify carbon dynamics. We indicate the advantages and challenges of using this approach in ecosystems where multiple organic carbon sources are present

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

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 620nm 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 (R2>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