Monitoring Off-Shore Fishing in the Northern Indian Ocean Based on Satellite Automatic Identification System and Remote Sensing Data.

Satellite-derived Sea Surface Temperature (SST) and sea-surface Chlorophyll a concentration (Chl-a), along with Automatic Identification System (AIS) data of fishing vessels, were used in the examination of the correlation between fishing operations and oceanographic factors within the northern Indian Ocean from March 2020 to February 2023. Frequency analysis and the empirical cumulative distribution function (ECDF) were used to calculate the optimum ranges of two oceanographic factors for fishing operations. The results revealed a substantial influence of the northeast and southwest monsoons significantly impacting fishing operations in the northern Indian Ocean, with extensive and active operations during the period from October to March and a notable reduction from April to September. Spatially, fishing vessels were mainly concentrated between 20° N and 6° S, extending from west of 90° E to the eastern coast of Africa. Observable seasonal variations in the distribution of fishing vessels were observed in the central and southeastern Arabian Sea, along with its adjacent high sea of the Indian Ocean. Concerning the marine environment, it was observed that during the northeast monsoon, the suitable SST contributed to high CPUEs in fishing operation areas. Fishing vessels were widely distributed in the areas with both mid-range and low-range Chl-a concentrations, with a small part distributed in high-concentration areas. Moreover, the monthly numbers of fishing vessels showed seasonal fluctuations between March 2020 and February 2023, displaying a periodic pattern with an overall increasing trend. The total number of fishing vessels decreased due to the impact of the COVID-19 pandemic in 2020, but this was followed by a gradual recovery in the subsequent two years. For fishing operations in the northern Indian Ocean, the optimum ranges for SST and Chl-a concentration were 27.96 to 29.47 °C and 0.03 to 1.81 mg/m3, respectively. The preliminary findings of this study revealed the spatial-temporal distribution characteristics of fishing vessels in the northern Indian Ocean and the suitable ranges of SST and Chl-a concentration for fishing operations. These results can serve as theoretical references for the production and resource management of off-shore fishing operations in the northern Indian Ocean.

Promoting effect of raft-raised scallop culture on the formation of coastal hypoxia.

The coastal waters around the Yangma Island are an important mariculture area of raft-raised scallop and bottom-seeded sea cucumber in the North Yellow Sea, China. Large-scale hypoxia in the bottom water of this area has caused the death of a large number of sea cucumbers and heavy economic losses. To find out the formation mechanism of hypoxia, the data obtained in each August during 2015-2018 were analyzed. Compared with the non-hypoxic year (2018), the temperature, trophic index (TRIX) and dissolved organic carbon (DOC) in the bottom water were relatively higher, and the water column was stratified causing by continuous high air temperature and low wind speed meteorological conditions in the hypoxic years (2015-2017). These sites with the coexistence of thermocline and halocline, and the thickness of thermocline >2.5 m and its upper boundary >7.0 m deep, were prone to hypoxia. Spatially, the hypoxic place was highly consistent with the scallop cultivating places, and the DOC, TRIX, NH4+/NO3- and apparent oxygen utilization (AOU) at the culture sites were higher, indicating that organic matter and nutrients released by scallops may lead to local oxygen depletion. In addition, the bottom water of the culture sites had higher salinity, but lower turbidity and temperature, indicating that the slowed water exchange caused by scallop culture was a dynamic factor of hypoxia. All sites with AOU >4 mg/L at the bottom had hypoxia occurrence, even if there was no thermocline. In other words, stratification promoted the formation of hypoxia in coastal bottom water, but it was not indispensable. The raft-raised scallop culture could promote the formation of coastal hypoxia, which should arouse the attention for other coastal areas with intensive bivalve production.

Temporal Variation of Chlorophyll-a Concentrations in Highly Dynamic Waters from Unattended Sensors and Remote Sensing Observations.

Monitoring of water quality changes in highly dynamic inland lakes is frequently impeded by insufficient spatial and temporal coverage, for both field surveys and remote sensing methods. To track short-term variations of chlorophyll fluorescence and chlorophyll-a concentrations in Poyang Lake, the largest freshwater lake in China, high-frequency, in-situ, measurements were collected from two fixed stations. The K-mean clustering method was also applied to identify clusters with similar spatio-temporal variations, using remote sensing Chl-a data products from the MERIS satellite, taken from 2003 to 2012. Four lake area classes were obtained with distinct spatio-temporal patterns, two of which were selected for in situ measurement. Distinct daily periodic variations were observed, with peaks at approximately 3:00 PM and troughs at night or early morning. Short-term variations of chlorophyll fluorescence and Chl-a levels were revealed, with a maximum intra-diurnal ratio of 5.1 and inter-diurnal ratio of 7.4, respectively. Using geostatistical analysis, the temporal range of chlorophyll fluorescence and corresponding Chl-a variations was determined to be 9.6 h, which indicates that there is a temporal discrepancy between Chl-a variations and the sampling frequency of current satellite missions. An analysis of the optimal sampling strategies demonstrated that the influence of the sampling time on the mean Chl-a concentrations observed was higher than 25%, and the uncertainty of any single Terra/MODIS or Aqua/MODIS observation was approximately 15%. Therefore, sampling twice a day is essential to resolve Chl-a variations with a bias level of 10% or less. The results highlight short-term variations of critical water quality parameters in freshwater, and they help identify specific design requirements for geostationary earth observation missions, so that they can better address the challenges of monitoring complex coastal and inland environments around the world.

Key drivers of hypoxia revealed by time-series data in the coastal waters of Muping, China.

Coastal hypoxia (low dissolved oxygen in seawater) is a cumulative result of many physical and biochemical processes. However, it is often difficult to determine the key drivers of hypoxia due to the lack of frequent observational oceanographic and meteorological data. In this study, high-frequency time-series observational data of dissolved oxygen (DO) and related parameters in the coastal waters of Muping, China, were used to analyze the temporal pattern of hypoxia and its key drivers. Two complete cycles with the formation and destruction of hypoxia were captured over the observational period. Persistent thermal stratification, high winds and phytoplankton blooms are identified as key drivers of hypoxia in this region. Hypoxia largely occurs due to persistent thermal stratification in summer, and hypoxia can be noticeably relieved when strong wind mixing weakens thermal stratification. Furthermore, we found that northerly high winds are more efficient at eroding stratification than southerly winds and thus have a greater ability to relieve hypoxia. This study revealed an episodic hypoxic event driven by a phytoplankton bloom that was probably triggered by terrestrial nutrient loading, confirming the causal relationship between phytoplankton blooms and hypoxia. In addition, we found that the lag time between nutrient loading, phytoplankton blooms and hypoxia can be as short as one week. This study could help better understand the development of hypoxia and forecast phytoplankton and hypoxia, which are beneficial for aquaculture in this region.

Scallop farming impacts on dissolved organic matter cycling in coastal waters: Regulation of the low molecular weight fraction.

To elucidate the impacts of scallop farming on the biogeochemical characteristics of low molecular weight (LMW, <1 kDa) dissolved organic matter (DOM), samples collected from a bay scallop mariculture area (MA) and its surrounding areas were determined for absorption and fluorescence spectroscopy after microfiltration and centrifugal ultrafiltration. The values of absorption coefficient a350 showed a spatial variation trend of inshore area (IA) > MA > non-mariculture area (NMA) for both bulk (<0.7 µm) and LMW fractions. Four fluorescent components, namely two protein-like components (tryptophan-like C1 and tyrosine-like C2) and two humic-like components (microbial humic-like C3 and terrestrial humic-like C4), were identified. Scallop farming influenced DOM transformation by altering phytoplankton abundance and promoting microbial degradation. In July, the net contributions of phytoplankton to the spectroscopy parameters of LMW-DOM in the surface seawater were 11.0% for a350, 4.3% for C1, 0.8% for C2, 0.6% for C3 and 3.0% for C4, respectively; the corresponding values of bulk DOM in the surface seawater were 24.3% for a350, 20.1% for C1, 5.9% for C2, 2.0% for C3, 2.9% for C4, respectively. Compared with NMA, the contributions of microbial degradation to a350 in MA's surface seawater increased by 9.0% for LMW-DOM and 6.9% for bulk DOM in July; however, the effects on different fluorescent components varied. In August, compared with NMA, the contributions of microbial degradation to spectroscopy parameters in the bottom water of MA decreased by 35.7% for a350, 6.3% for C2, 1.3% for C3, and 4.4% for C4 for LMW-DOM fraction; for bulk DOM, the corresponding contribution decreased by 10.8% for C1. These variations indicate that protein-like substances from scallop aquaculture are easily degraded into LMW substances, while humic-like substances degradation diminishes over time.

[Using in-situ reflectance to monitor the chlorophyll concentration in the surface layer of tidal flat].

An optical monitoring method is proposed for the rapid, non destructive measurements of chlorophyll concentration (Chl-a) in the surface sediments of emerged tidal flat, and it can be further applied in remote sensing work. Hyperspectral reflectance of intertidal sediments were measured in day time at the tidal flats of the Sishili Bay, the Northern Yellow Sea, and surface sediments (3 mm) were sampled for the in-door measurements of Chl-a. On the basis of the reflectance at 650, 675 and 700 nm, the indices of normalized difference index of microbenthos (NDI-MPB) and trough depth (T-depth) were proposed for the measurements of microphytobenthos biomass. T-depth can be used to remove the linear background spectral noises and indicate the existence of microphytobenthos; Good linear relationship was observed between NDI-MPB and Chl-a content in sediments (2.22-49.36 mg x m(-2), r > 0.99), which may be used to monitor the biomass of microphy to benthos.

The joint effects of atmospheric dry and wet deposition on organic carbon cycling in a mariculture area in North China.

In this research, the atmospheric dry and wet deposition fluxes of particulate organic carbon (POC) over the coastal waters around the Yangma Island in North Yellow Sea were investigated. Combining the results of this research and previous reports about the wet deposition fluxes of dissolved organic carbon (DOC) in precipitation (FDOC-wet) and dry deposition fluxes of water-dissolvable organic carbon in atmospheric total suspended particles (FDOC-dry) in this area, a synthetic assessment of the influence of atmospheric deposition on the eco-environment was conducted. It was found that the annual dry deposition flux of POC was 1097.9 mg C m-2 a-1, which was approximately 4.1 times that of FDOC-dry (266.2 mg C m-2 a-1). For wet deposition, the annual flux of POC was 445.4 mg C m-2 a-1, accounting for 46.7 % that of FDOC-wet (954.3 mg C m-2 a-1). Therefore, atmospheric POC was mainly deposited through dry process with the contribution of 71.1 %, which was contrary to the deposition of DOC. Considering the indirect input of organic carbon (OC) from atmospheric deposition, that is, the new productivity supported by nutrient input from dry and wet deposition, the total OC input from atmospheric deposition to the study area could be up to 12.0 g C m-2 a-1, highlighting the important role of atmospheric deposition in the carbon cycling of coastal ecosystems. The contribution of direct and indirect input of OC through atmospheric deposition to the dissolved oxygen consumption in total seawater column was assessed to be lower than 5.2 % in summer, suggesting a relatively smaller contribution to the deoxygenation in summer in this region.

Effects of suspended particles and dispersants on marine oil snow formation of crude oil/diesel oil.

Marine oil snow (MOS) potentially forms after an oil spill. To fully understand the mechanism of its formation, we investigated the effects of suspended particles (SP) and dispersants on MOS formation of crude oil and diesel oil by laboratory experiments. In the crude oil experiment, the SP concentration of 0.2 g L-1 was more suitable for crude oil MOS formation. The addition of dispersants significantly stimulated N and TV during MS/MOS formation of SP at 0.4 g L-1 and 0.8 g L-1 concentration (p < 0.05). Without SP, the dispersants also stimulated crude oil MOS formation. Furthermore, the concentration of SP had a significantly positive effect on the reduction of the total amount of N-alkanes (p < 0.05). In the diesel oil experiment, after adding dispersants to diesel oil, the maximum N, Dm, and TV values at a SP concentration of 0.2 g L-1 were significantly higher than those at 0.4 g L-1 and 0.8 g L-1 (p < 0.05). Besides, we found that dispersants stimulated MOS formation in diesel oil at a SP concentration of 0.2 g L-1. However, the dispersants had an inhibitory effect on diesel oil MOS formation without SP. Notably, the MOS formed by diesel oil appeared white, unlike the black MOS associated with crude oil. These findings are important for the environmental impact of oil spills and elevated SP concentrations.

Atmospheric deposition as a direct source of particulate organic carbon in region coastal surface seawater: Evidence from stable carbon and nitrogen isotope analysis.

To assess the source characteristics of coastal aerosols and evaluate the contribution of atmospheric deposition to particulate organic matter in surface seawater, total suspended particulates (TSP) were collected at a shore-based site on the south coast of North Yellow Sea from December 2019 through November 2020. The samples were analyzed for total organic carbon (TOC) and nitrogen (TN) as well as stable carbon and nitrogen isotope (δ13C and δ15N). The results showed that the annual mean concentrations of TOC and TN were 5.36 ± 4.74 and 5.12 ± 6.52 µg m-3, respectively. δ13C fluctuated between -25.1 ‰ and -19.2 ‰ with an annual mean of -24.0 ± 1.0 ‰ and a significant seasonal variation (P < 0.05) characterizing by the enrichment in winter (-23.4 ± 0.6 ‰) compared to other seasons, which was probably related to the massive coal combustion. Besides, δ15N ranged from 7.9 ‰ to 21.1 ‰ with an annual mean of 12.5 ± 2.9 ‰ and a less pronounced seasonal pattern (P = 0.23). The Bayesian isotope-mixing model showed that, annually, the most important source of TSP was biogenic and biomass source (55.5 ± 10.8 %), followed by fossil fuel combustion (31.9 ± 9.0 %), while the marine contribution was less (12.6 ± 2.3 %). For TOC and TN, the dominated sources were fossil fuel combustion (47.7 ± 3.4 %) and biogenic and biomass source (57.3 ± 11.7 %), respectively. Furthermore, the model results indicated that the contribution of atmospheric deposition to suspended particulate matter in surface seawater was 18.0 ± 11.0 %, 17.1 ± 6.7 % and 10.2 ± 2.0 % in autumn, spring and summer, respectively. For particulate organic carbon in surface seawater, the contribution of atmospheric deposition was 35.2 ± 3.5 % in spring, highlighting the huge impact of atmospheric deposition on particulate carbon cycling in coastal waters.

Biogeochemical properties and fate of dissolved organic matter in wet deposition: Insights from a mariculture area in North Yellow Sea.

To address the potential roles of atmospheric wet deposition in carbon cycling in coastal waters, a comprehensive study of the biogeochemical properties of dissolved organic matter (DOM) in precipitation and the resulting implication in a mariculture area in North Yellow Sea was conducted. The annual mean concentrations of dissolved organic carbon (DOC), chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) were 1.52 ± 1.52 mg C L-1, 0.36 ± 0.66 m-1 and 0.38 ± 0.35 QSU, respectively. The concentrations of most DOM proxies exhibited significant negative correlations with the corresponding precipitation amount (R2 = 0.15-0.40, P < 0.01), but the dilution effects became less significant when the precipitation amount exceeded 10.2, 10.7, 10.2 and 2.4 mm for DOC, CDOM, highly­oxygenated and hypoxic structured humic-like substances, respectively. Seasonally, the dominant precipitation type in winter was snowfall, in which the DOM contained more high-molecular-weight compounds with higher aromaticity and humification degree, while the characteristics of DOM in intensive rainfall in summer were contrary to those in winter. The wet deposition flux of DOC to this region was estimated to be 6.31 × 108 g C a-1, which was 3.3 and 1.4 times that of the dry deposition and local riverine input, thereby contributing to 4.0 % of the DOC storage in the study area. In summer, the intensive input of DOC through wet deposition (0.43 g C m-2) to surface seawater could enrich its bioavailable DOC by 10.7 µmol L-1, the complete aerobic decomposition of which would cause an obvious dissolved oxygen depletion in the surface seawater by 21.4 µmol L-1, demonstrating the influence of wet deposition on summer deoxygenation in coastal waters.

Atmospheric wet deposition serves as an important nutrient supply for coastal ecosystems and fishery resources: Insights from a mariculture area in North China.

To determine the ecological effects of atmospheric wet deposition of dissolved nutrients on the coastal waters around the Yangma Island, rain and snow samples were collected and analyzed at a shore-based site for one year. The wet deposition fluxes of dissolved inorganic nitrogen and phosphorus (DIN and DIP) and dissolved organic nitrogen and phosphorus were 69.2, 0.136, 13.3 and 0.143 mmol m-2 a-1, respectively. In summer, the new production fueled by wet deposition accounted for 19.3 % of that in seawater and 16.4 % of the amount of particulate organic carbon ingested by the scallops cultivated in the study area, indicating the potential contribution of wet deposition to fishery resources. Meanwhile, precipitation increased the seasonal average DIN/DIP ratios in surface seawater by 17.7 %, 16.3 %, 23.4 % and 6.5 % in spring, summer, autumn and winter, respectively, which could change the composition of ecological community and cause obvious negative impact on the ecosystem and mariculture.

HY-1C ultraviolet imager captures algae blooms floating on water surface.

Some species of algae such as cyanobacteria can vertically migrate through water during a day, which is a notable floating feature of harmful algae blooms. To date, this process has been observed and quantified using visible and near-infrared (VNIR) bands from spaceborne sensors with high temporal resolution (i.e., Geostationary Ocean Color Imager; GOCI). In this study, we conducted an in-situ measurement at Taihu Lake in China to investigate the ultraviolet (UV) reflection spectra of floating cyanobacteria blooms, and identified that they have significant UV reflection features (higher than that of background water) associated with their floating status. This has been demonstrated using spaceborne UV images at both 355 and 385 nm from the Ultraviolet Imager (UVI) onboard Haiyang-1C (HY-1C) of China. Compared with synchronous optical images from the Chinese Ocean Color and Temperature Scanner (COCTS), we found that UVI has a special ability to distinguish cyanobacteria floating on water surface. Additionally, the intensity of the UV signals obtained is positively correlated with the cyanobacterial equivalent density. Ultraviolet remote sensing, therefore, can work as a new approach for the detection of harmful algae blooms and help determine the floating status of them, which deserves further research.

The impacts of intensive scallop farming on dissolved organic matter in the coastal waters adjacent to the Yangma Island, North Yellow Sea.

In-situ field investigations coupled with incubation experiments were conducted in the coastal waters adjacent to the Yangma Island to explore the impacts of intensive bay scallop farming on the quantity and composition of dissolved organic matter (DOM). During the scallop farming period, the values of dissolved organic carbon (DOC), chromophoric dissolved organic matter (CDOM) and fluorescence dissolved organic matter (FDOM) in the mariculture area (MA) were generally higher than those in the non-mariculture area (NMA). Bay scallops released a large amount of DOM with the characteristics of high molecular weight and low degree of humification into the water column through excretion, which altered the DOM biogeochemical cycle. The DOM excretion fluxes by scallop were calculated based on incubation experiments. The results showed that, without considering the DOM transformation in the water, the excretion process of bay scallops in a growth cycle can increase the concentration of DOC, CDOM and fluorescent components C1-C4 in the seawater in MA by 19.7 µmol l-1, 0.048 m-1, 0.065 QSU, 0.164 QSU, 0.017 QSU and 0.015 QSU, respectively. Assuming that the labile part of DOM excreted by scallops was completely aerobic decomposed, it could reduce DO and pH in the seawater by ~13.4 µmol l-1 and ~ 0.018 in MA. This study highlights the impact of human activities (scallop farming activities) on DOM cycle in coastal waters, which can help guide future policy formulating of mariculture and ecological protection.

Atmospheric dry deposition of water-soluble organic matter: An underestimated carbon source to the coastal waters in North China.

Water-soluble organic matter (WSOM) is a ubiquitous group of organic compounds in the atmosphere, which plays an important role in the biogeochemical cycle. To determine the quantity and chemical composition of the dry deposition of WSOM and assess its ecological effects on the coastal waters around the Yangma Island, North Yellow Sea, total suspended particulates (TSP) samples collected at a coastal site for one year from December 2019 to November 2020 were analyzed. The concentration of water-soluble organic carbon (WSOC) and the spectroscopy of chromophoric dissolvable organic matter (CDOM) and fluorescent dissolvable organic matter (FDOM) in the samples showed highly temporal variability with higher values in winter and spring than in summer and autumn. In addition, the correlation analysis revealed that the content of WSOM in the TSP as well as its chemical composition were greatly influenced by the sources and aging processes of aerosols. Moreover, the dry deposition flux of WSOC to the study area was calculated to be 0.79 ± 0.47 mg C m-2 d-1, namely 1.91 × 108 g C yr-1, which could increase the annual average concentration of dissolved organic carbon in surface seawater by 10.2 µmol L-1, implying that the dry deposition could sustain the secondary production and affect the carbon cycle of the coastal waters. Besides, the complete decomposition of bioavailable WSOC of dry deposition could reduce the annual average concentration of dissolved oxygen in surface seawater by 4.8 µmol L-1, which could contribute partly to the seawater deoxygenation in the coastal area around the Yangma Island.

[Monitoring "green tide" in the Yellow Sea and the East China Sea using multi-temporal and multi-source remote sensing images].

Landsat-TM (Theme Mapper) and EOS (Earth Observing System)-MODIS (MODerate resolution Imaging Spectrora-diometer) Terra/Aqua images were used to monitor the macro-algae (Ulva prolifera) bloom since 2007 at the Yellow Sea and the East China Sea. At the turbid waters of Northern Jiangsu Shoal, there is strong spectral mixing behavior, and satellite images with finer spatical resolution are more effective in detection of macro-algae patches. Macro-algae patches were detected by the Landsat images for the first time at the Sheyang estuary where is dominated by very turbid waters. The MODIS images showed that the macro-algae from the turbid waters near the Northern Jiangsu Shoal drifted southwardly in the early of May and affected the East China Sea waters; with the strengthening east-asian Summer Monsoon, macro-algae patches mainly drifted in a northward path which was mostly observed at the Yellow Sea. Macro-algae patches were also found to drift eastwardly towards the Korea Peninsular, which are supposed to be driven by the sea surface wind.

Summer deoxygenation in a bay scallop (Argopecten irradians) farming area: The decisive role of water temperature, stratification and beyond.

During 2015-2020, 26 cruises were carried out in a bay scallop farming area, North Yellow Sea, to study the dissolved oxygen (DO) dynamics and its controlling factors. Significant DO depletion (deoxygenation) was observed in the summertime with the decrease rates of 0.31-0.55 and 0.96-2.10 µmol d-1 in the surface and bottom waters, respectively, which were comprehensively forced by temperature, photosynthesis and microbial respiration. Seasonally, temperature was the main driver of the deoxygenation processes. In the surface water, DO dynamics were dominated by temperature-induced solubility changes, while the photosynthesis offset the effects of physical processes to a certain extent; in the bottom water, its dynamics were mainly attributed to the comprehensive control of temperature-induced solubility changes and biological respiration. Overall, the results suggested that the occurrence of hypoxia and acidification in the coastal waters were highly associated with the formation of temperature-induced stratification under complex hydrodynamic processes.

Potential linkage between sedimentary oxygen consumption and benthic flux of biogenic elements in a coastal scallop farming area, North Yellow Sea.

Surface sediments were collected from a mariculture area adjacent to the Yangma Island suffering from hypoxia in summer, and a laboratory static incubation was conducted to study the sedimentary oxygen consumption (SOC) and the benthic fluxes of nutrients and fluorescent dissolved organic matter (FDOM). Compared with some coastal areas, the SOC of the studied area was relatively low in summer with the value of 2.34-6.03 mmol m-2 d-1. Sediment acted as an important source of nutrients (except for nitrate) and FDOM for the overlying water. Dissolved oxygen (DO) in the overlying water could affect the decomposition mode of sedimentary organic matter (SOM), i.e. aerobic and anaerobic decomposition and subsequently dominated the release of nutrients and FDOM. When DO > 50 µmol l-1, it was beneficial to the release of ammonium, silicate and FDOM. In contrast, low oxygen conditions, i.e. DO < 100 µmol l-1, stimulated sediment phosphate efflux. In addition, scallop farming activities also affected the SOC and benthic flux of nutrients and FDOM mainly through biological deposition.

Massive shellfish farming might accelerate coastal acidification: A case study on carbonate system dynamics in a bay scallop (Argopecten irradians) farming area, North Yellow Sea.

Seven cruises were carried out in a bay scallop (Argopecten irradians) farming area and its surrounding waters, North Yellow Sea, from March to November 2017 to study the dynamics of the carbonate system and its controlling factors. Results indicated that the studied parameters were highly variability over a range of spatiotemporal scales, comprehensively forced by various physical and biological processes. Mixing effect and scallop calcification played the most important role in the seasonal variation of total alkalinity (TAlk). For dissolved inorganic carbon (DIC), in addition to mixing, air-sea exchange and microbial activity, e.g. photosynthesis and microbial respiration processes, had more important effects on its dynamics. Different from the former, the changes of water pHT, partial pressure of CO2 (pCO2) and aragonite saturation state (ΩA) were mainly controlled by the combining of the temperature, air-sea exchange, microbial activity and scallop metabolic activities. In addition, the results indicated that massive scallop farming can significantly increase the DIC/TAlk ratio by reducing the TAlk concentration in seawater, thereby reducing the buffering capacity of the carbonate system in seawater especially for ΩA. Preliminary calculated, ~75.7 and ~45.5 µmol kg-1 of TAlk were removed from the surface and bottom waters respectively in one scallop cultivating cycle. If these carbonates cannot be replenished in time, it is likely to accelerate the acidification process of coastal waters. This study highlighted the control mechanism of the carbonate system under the influence of bay scallop farming, and provided useful information for revealing the potential link between human activities (shelled-mollusc mariculture) and coastal acidification.

The influence of summer hypoxia on sedimentary phosphorus biogeochemistry in a coastal scallop farming area, North Yellow Sea.

In situ field investigations coupled with laboratory incubations were employed to explore the surface sedimentary phosphorus (P) cycle in a mariculture area adjacent to the Yangma Island suffering from summer hypoxia in the North Yellow Sea. Five forms of P were fractionated, namely exchangeable P (Ex-P), iron-bound P (FeP), authigenic apatite (CaP), detrital P (De-P) and organic P (OP). Total P (TP) varied from 13.42 to 23.88 µmol g-1 with the main form of inorganic P (IP). The benthic phosphate (DIP) fluxes were calculated based on incubation experiments. The results show that the sediment was an important source of P in summer with ~39% of the bioavailable P (BioP) recycled back into the water column. However, the sediment acted a sink of P in autumn. The benthic DIP fluxes were mainly controlled by the remobilizing of FeP, Ex-P and OP under contrasting redox conditions. In August (hypoxia season), ~0.92 µmol g-1 of FeP and ~0.52 µmol g-1 of OP could be transformed to DIP and released into water, while ~0.36 µmol g-1 of DIP was adsorbed to clay minerals. In November (non-hypoxia season), however, ~0.54 µmol g-1 of OP was converted into DIP, while ~0.55 µmol g-1 and ~0.28 µmol g-1 of DIP was adsorbed to clay minerals and bind to iron oxides. Furthermore, scallop farming activities also affected the P mobilization through biological deposition and reduced hydrodynamic conditions. The burial fluxes of P varied from 11.67 to 20.78 µmol cm-2 yr-1 and its burial efficiency was 84.7-100%, which was consistent with that in most of the marginal seas worldwide. This study reveals that hypoxia and scallop farming activities can significantly promote sedimentary P mobility, thereby causing high benthic DIP flux in coastal waters.

[Quantitative analysis of chlorophyll-a reflectance spectrum in red spectral region of water].

The chlorophyll-a concentration in waters is one of the main parameters of water color remote sensing in case II waters. There is a reflectance peak in red band region because of inherent optical properties. Based on the coefficients of absorption and backscattering of waters, colored dissolved organic matter (CDOM), tripton and chlorophyll-a, the reflectance of remote sensing was simulated according to the forward radiation transfer model without the consideration of fluorescence peak. The reflectance peak intensity and reflectance peak position at different wavelengths in red band region were analyzed with different chlorophyll-a concentration. There is a good linear relationship between the red reflectance peak intensity and chlorophyll-a concentration when the chlorophyll-a concentration is 1-50 microg x L(-1). But the linear relationship between the reflectance peak intensity and chlorophyll-a concentration will decrease with the increasing chlorophyll-a concentration. When chlorophyll-a concentration is up to 1 000 microg x L(-1), the logarithm relationship between the reflectance peak intensity and chlorophyll-a concentration is better than linear relationship. The wavelength position of reflectance peak in red band region will shift towards larger wave-length at logarithmic growth rate with increasing chlorophyll-a concentration, and the logarithm relationship will be more apparent with the inoreasing chlorophyll-a concentration. The same trend happens to the reflectance peak intensity and the wavelength position of peak in red region with different in-water constituents, such as CDOM, tripton and so on. Furthermore, according to the comparison with fluorescence peak, the authors also found that the reflectance peak intensity and the wavelength position of peak in red region are different from those of the fluorescence peak.