Seawater Transparency Research Articles

Analysis of environmental factors impact on water transparency off southeastern Vietnam

Seawater transparency, one of the important parameters to evaluate the marine ecological environment and functions, can be measured using the Secchi disk depth (SDD). In this study, we use multi-source remote sensing data and other fused data from 2011 to 2020 to study the spatial distribution and variation of SDD off southeastern Vietnam. The monthly average of SDD in the study area has obvious seasonal variation characteristics and shows a double peak characteristic. An important observation is a significant decrease in transparency from July to September each year, which is far lower than other nearby seas. To study this low SDD phenomenon, the generalized additive model (GAM) is used to determine the main environmental factors. The response relationship between SDD and environmental factors on different time scales is explained through empirical mode decomposition (EMD) analysis experiments. The results show that the comprehensive explanation rate of the GAM model is 72.1%, and the main environmental factors affecting SDD all have non-linear response relationships with SDD. The contributions are ranked as sea surface salinity (SSS)> offshore current velocity (Cu)> wind direction (WD)> offshore Ekman transport (ETu)> sea surface temperature (SST)> mean direction of wind waves (MDWW). SDD is positively correlated with SSS and SST, and negatively correlated with Cu and ETu. SSS, Cu, ETu, and SST have a significant effect on SDD at interannual scales. Long-term changes in SDD are driven by SSS, Cu, WD, and SST. Generally, SSS has the most comprehensive impact on SDD. WD indirectly has a non-negligible impact on SDD by changing ocean dynamics processes.

Spatial distribution of benthic algae in the South China Sea: Responses to gradually changing environmental factors and ecological impacts on coral communities

AbstractAimIn this study, we investigated whether environmental factors can effectively control the spatial distribution of various benthic algae and examined the critical ecological impacts of algae on corals across the South China Sea (SCS). Relationships between benthic algae and environmental factors were assessed, and potential ecological impacts of algae on coral communities were evaluated across spatial scales.LocationA total of 104 sites at 12 coral reefs in four coral reef regions (CRRs) of the SCS (latitude range of 9–22° N).TaxaTurf algae, macroalgae (including fleshy macroalgae and Halimeda), crustose coralline algae (CCA), coral and juvenile coral.MethodsUsing diver‐based surveys (2015–2018), we investigated four CRRs with different reef distance to mainland (RDM) across the SCS. We obtained field data on benthic algal composition and cover, coral cover and diversity, and juvenile coral density. We also measured and collected the environmental factors (including seawater environmental parameters and reef fish diversity).ResultsThe cover of turf algae and CCA gradually decreased and increased, respectively, with an increase in RDM, which had a strong relationship with the gradually changing environmental factors. Random forest models suggested that nutrients, reef fish diversity, seawater transparency and temperature were the most important factors for predicting turf algae and CCA cover. Linear regression analyses showed a significant relationship between the turf algae, macroalgae, and CCA covers, and juvenile coral density.Main conclusionsOur results showed that gradually changing environmental factors were correlated with the spatial distributions of turf algae and CCA. However, the natural biophysical relationships between macroalgae and environmental factors may be disrupted by turf algal overgrowth and nutrient subsidies. Increases in all benthic algal groups significantly impacted coral recruitment, highlighting the critical role of benthic algae in determining the recovery trajectory of the Indo‐Pacific reefs that are threatened by human activities.

Seagrass distribution using remote sensing along the Ujunggenteng Coastal, Sukabumi

Seagrass beds play an important role in marine ecosystems, primarily as a habitat that supports marine life. This study was undertaken to address the lack of available research regarding changes in seagrass density from year to year along the Ujunggenteng coastal, which is necessary to preserve seagrass beds in this area. More specifically, the purpose of this study was to determine the distribution of seagrass beds along the Ujunggenteng coastal and analyze their physical characteristics over a sixteen year period, from 2000–2016. The method used remote sensing technology that is used to look at the distribution of seagrass beds by performing calculations based on Lyzenga algorithms. Based on the results of data processing, seagrass in the study area was found to be distributed on three coral reefs. From year to year, the area of seagrass along the Ujunggenteng coastal appeared to increase. The physical characteristics affecting the distribution of seagrass along the Ujunggenteng coastal wered found to be sea surface temperature, salinity, and depth of sea water, and the physical characteristics that did not affect the distribution of seagrass were currents and sea water transparency.

Impact of tsunami Sunda Strait to coastal tourism in Tanjung Lesung Special Economic Zone Pandeglang Regency Banten Province

The coastal area is one of the natural magnificence that is visited by many tourists because it has unique attraction such as white sand, exotic waves, unique coral reef, and beautiful natural scenery. The natural magnificence must be maintained by a variety of damages due to human activities and natural processes such as the tsunami. The impact of the tsunami disaster, in addition to psychological trauma also had an impact on the condition of the objects of tourist attraction, which eventually led to a decline in the number of tourists. Some damage to tourist objects and attractions studied in this paper include spatial conditions, changes in the transparency of seawater on the coast and the condition of existing coral reef. The analysis was carried out by comparing the conditions before and after the impact of the tsunami at Tanjung Lesung Special Economic Zone (SEZ) in December 22th 2018. Through this analysis, it is expected that the management of coastal tourism in the after tsunami Tanjung Lesung SEZ can be carried out more comprehensive and sustainable. Therefore coastal tourism activities will still provide benefits both ecologically and economically for community, government and private administrator of SEZ.

The Estimation of the Main Silting Factors in the Marine Artificial Channel of the Azovstal Port (Mari-upol, Ukraine)

Purpose. The physico-chemical processes in river mouth area, which include the Don and Kuban rivers, limited the transport capacity of the main ports of the Sea of Azov as a result of the silting by suspended matter by the river runoff. The fall of the depths in the the ports and marine channels is one of the key problems of the functioning of the ports. Dredging works and dumping linked with shipping as well as shipping linked with the world economy. It is impossible to abandon shipping, as well it is impossible to abandon the dredging and damping. For this reason, the purpose of the work is to assess the optimal dredging works for the exploitation of the ports of Ukraine in the Sea of Azov. Methods. The comparative analysis of modern hydrometeorological conditions, including the dominant influence of wind activity, the velocity and the direction of currents according to actual data, the transparency of sea water, the runoff the river Kalmius had been done. The available images of DigitalGlobe’s remote sensing satellites and dredging results, which were periodically performed to support the depths on the sea marine channel to the port water area, were examined. Modern and retrospective data of bathymetric surveys using GIS processing technologies for comparing the results, as well as standard methods of statistical data processing were also used. Results. During the investigated period, the images of the Earth's remote sensing satellites from DigitalGlobe were studied. An anthropogenic impact to the silting in the study area was revealed (the turning point between 0 km of the marine channel of the port and the shallow water area of the port of Azovstal). For compare the depths in the investigated area which is under the the river Kalmius influence positions of the surveyed post had been established. As result of analysis of direct measurement data and graphic material the permanent silting of the marine channel was not established as well as the direct statistical relationship between the silting and the river run incoming with suspended matter with Kalmius river. The main process of sedimentation determines by the Don river. The upper limit of maximum sedimentation is 5–7 ‰, coincides with the investigated area, where theoretically one should expect the process of accumulation of bottom sediments. Conclusion. The result of comparing Kalmius river runoff with depths in the marine channel of the port of Azovstal, in the area of area of river mouth, revealed there is not representative statistical relationship. It is necessary monitoring data for a long period of data for representative comparing the runoff Kalmius river and siling processes. In modern period the runoff of the Don river is significantly deformed under the influence of anthropogenic factors and the representative statistical estimation have to be done using only the direct measurements, which are fairly limited. Nevertheless, the reduction of Don river runoff and, thus, the direct impact on the recording capacity of the studied water area determines the need for and technological accessibility of dredging at a significantly lower the cost of wokrs at the present stage.

진해만의 수질과 수산생산량의 경년변동 해석

For the analyzing of annual variation of water quality and fisheries production in Jinhae bay, Korea, we divided three regions and then analyzed water quality and fisheries production of Jinhae bay during 2004 to 2016. Water quality is analyzed by using Water Quality Index(WQI) which is calculating by using Surface; chlorophyll-a, Dissolved Inorganic Nitrogen(DIN), Dissolved Inorganic Phosphorus(DIN), Transparency of seawater, Bottom; Dissolved Saturation(DO). Fisheries production is analyzed by using total fisheries production in Jinhae bay. As a result of this study, WQI of Region Ⅰ was gradually improved 5th grade(2004) to 1st grade(2016) but fisheries production was decreased by 49.2%. Region Ⅱ of WQI was decreased from 2014 and fisheries production was not significant variation. Region Ⅲ of WQI was decreased 1st grade(2005) to 4th grade(2014) but fisheries production was increased by 62.5%.

A study of the environmental factors influencing the growth phases of Ulva prolifera in the southern Yellow Sea, China

Macroalgal blooms of U. prolifera in the southern Yellow Sea (SYS) have become an ecological disaster. In this study, we attempt to explore the influence of environmental factors and human activity on the annual development of U. prolifera during 2011–2016, combining geostationary ocean color imager images and monitored environmental factors. Blooms of U. prolifera were mainly distributed in the central SYS, drifting from the southern Yellow Sea Radial Sand Ridges. Three growth phases were defined (initial phase, outbreak phase and dissipation phase) to facilitate analysis of the relationship between the environmental factors and growth conditions of U. prolifera. Seaweed cultivation, sea surface temperature (SST) and available radiation influenced the algal biomass during the initial phase; the seawater transparency, precipitation and wind activity affected the algae during the outbreak phase; and SST, intense radiation and cleanup operations increased the rate of algal extinction in the dissipation phase.

An overview of Cuban seagrasses

Here, we present an overview of the current knowledge of Cuban seagrasses, including distribution, status, threats, and efforts for their conservation. It has been estimated that seagrasses cover about 50% of the Cuban shelf, with six species reported and Thalassia testudinum K. D. Koenig being the most dominant. Seagrasses have been studied primarily in three areas in Cuba (northwest, north-central, and southwest). Thalassia testudinum and other seagrasses exhibit spatial and temporal variations in abundance, and updating of their status and distribution is needed. The main threat to Cuban seagrass ecosystems is low seawater transparency due to causes such as eutrophication and erosion. High salinities limit their distribution in the Sabana-Camaguey Archipelago, partly the result of freshwater dams and roads. Seagrass meadows play important ecological roles and provide many ecosystem services in Cuba, with efforts underway to preserve this ecosystem. Research and management projects are directed toward integrated coastal zone management, including a ban on trawl fisheries and the extension of marine protected areas to contain more seagrass meadows. In addition to updating species distributions, it is urgent that managers and researchers in Cuba examine the resilience of this ecosystem in the face of climate change.

MODIS-Based Mapping of Secchi Disk Depth Using a Qualitative Algorithm in the Shallow Arabian Gulf

Regionally calibrated algorithms for water quality are strongly needed, especially for optically complex waters such as coastal areas in the Arabian Gulf. In this study, a regional qualitative algorithm was proposed to retrieve seawater transparency, with Secchi disk depth (SDD) as a surrogate, in the Arabian Gulf. A two-step process was carried out, first estimating the diffuse attenuation coefficient of downwelling irradiance at 490 nm (Kd_490) from MODIS/Aqua imagery and then SDD based on empirical correlations with Kd_490. Three satellite derived Kd products were tested and assessed against a set of in situ measurements, and one from a semi-analytical algorithm based on inherent optical properties gave the best performance with a R2 of 0.62. Comparisons between the performances of SDD models developed in this study and those established in other regions indicated higher accuracy of our proposed model for the Gulf region. The potential factors causing uncertainties of the proposed algorithm were also discussed. Seasonal and inter-annual variations of SDD over the entire Gulf were demonstrated using a 14-year time series of MODIS/Aqua data from 2002 to 2015. High SDD values were generally observed in summer while low values were found in winter. Inter-annual variations of SDD did not shown any significant trend with exceptions during algal bloom outbreaks that resulted in low SDD.

Reproductive periods of Lucina pectinata (BIVALVE; LUCINIDAE) in the Paranaguá Estuarine Complex, Paraná - Brazil.

The objectives of the present study is to describe the size for exploitation and gonadal maturation of L. pectinata in Peças Island in Paraná coast. Twenty two individuals were sampled every month, from an intertidal flat of the Peças River, Municipality of Guaraqueçaba, during two periods - summer/autumn and winter of the 2009. Environmental parameter data was obtained at the same time of the biological sampling: temperature, salinity and seawater transparency at the Peças River mouth. The animals' height, length, width, gross weight, wet weight of meat and dry weight of meat were measured at the lab. The gonad development stages (GDS), condition index (CI) and yield index (Y) were calculated. Sex identification was conducted by direct observation of the gonads and gametes under an optic microscope. Individuals were classified as males (M), females (F) or undetermined (U). The medium height observed was of 49.62 ± 6.84 mm. Period of more expressive gonad repletion were observed in summer when water temperature was higher. Results of GDS in both periods showed a predominance of partially filled gonad stages. This may be related with the fact that L. pectinata has intense gametogenesis activity, that is, the organisms do not have a resting interval, but go back to gonad restructuring rapidly after releasing the gametes. The continuity of the reproductive cycle of the specimens found in both studied periods could demonstrate a possible continuous reproduction of the species and a size for exploitation above 40.00 mm of height.

Observations of presumable groundwater seepage occurrence in Puck Bay (the Baltic Sea)

Abstract We report the results of recent field measurements of seawater thermohaline structure and transparency carried out in early summer 2014 in Puck Bay. Near-bottom, less saline waters occurred almost in the entire study area. Their occurrence in the shallow part of Puck Bay was accompanied by an increase in the seawater transparency. The most likely explanation of these observations is a submarine fresh groundwater discharge.

Simulation of seagrass bed mapping by satellite images based on the radiative transfer model

Seagrass and seaweed beds play important roles in coastal marine ecosystems. They are food sources and habitats for many marine organisms, and influence the physical, chemical, and biological environment. They are sensitive to human impacts such as reclamation and pollution. Therefore, their management and preservation are necessary for a healthy coastal environment. Satellite remote sensing is a useful tool for mapping and monitoring seagrass beds. The efficiency of seagrass mapping, seagrass bed classification in particular, has been evaluated by mapping accuracy using an error matrix. However, mapping accuracies are influenced by coastal environments such as seawater transparency, bathymetry, and substrate type. Coastal management requires sufficient accuracy and an understanding of mapping limitations for monitoring coastal habitats including seagrass beds. Previous studies are mainly based on case studies in specific regions and seasons. Extensive data are required to generalise assessments of classification accuracy from case studies, which has proven difficult. This study aims to build a simulator based on a radiative transfer model to produce modelled satellite images and assess the visual detectability of seagrass beds under different transparencies and seagrass coverages, as well as to examine mapping limitations and classification accuracy. Our simulations led to the development of a model of water transparency and the mapping of depth limits and indicated the possibility for seagrass density mapping under certain ideal conditions. The results show that modelling satellite images is useful in evaluating the accuracy of classification and that establishing seagrass bed monitoring by remote sensing is a reliable tool.

The features of transparency field generation in the upper sea layer of the northwestern Black Sea in the winter-spring period

The features of transparency field generation in the upper sea layer of the northwestern Black Sea in the winter-spring period are analyzed on the basis of long-term data of specific marine observations from 1978–1995. The statistical assessments of the seasonal variations of the beam attenuation coefficient associated with fluctuations of river discharge and open sea water characteristics are calculated for the region under study. It is shown that the amount of suspended matter, which is most responsible for seawater transparency, depends both on rivers’ discharge volumes, the area of their interaction with seawater over the northwestern Black Sea shelf, and regional hydrometeorological conditions, which in turn depend on the hydrometeorological conditions in the catchment areas of the European rivers of the Black Sea basin.

Seawater Quality, Suspended Solids, and Settling Particles in the Wood Pool Area of Shimizu Port, Japan

Abstract The transport and contamination of suspended solids in a wood pool were quantitatively studied as a case study for the environmental assessment of an enclosed sea area. To assess the present contamination of Shimizu Port (Japan), seawater, suspended solids, and settling particles were collected from three rivers, the wood pool, and Shimizu Port. Physical and chemical properties of the samples were analyzed. In addition, tidal currents were observed to investigate the transport process of chemical substances by suspended solids. The results showed that the amount of lithogenic particles discharged into Shimizu Port was approximately 12 000 kg/day. Suspended solids discharged from rivers and the biological particles produced in the port caused a reduction in seawater transparency and an increase in chemical oxygen demand. Trace metals, such as Mn, Co, and Pb, were highly concentrated in suspended solids. Tributyltin adsorbed onto settling particles was approximately 300 µg/kg. Concentration factors for Mn, Fe, Cd, and Pb from water and settling particles are comparable to those of plankton. Hydroxides were found in suspended solids from the wood pool, which locates in the inner part of Shimizu Port. The results showed that these suspended particles could accumulate metals from seawater as effectively as biogenic particles. After particle deposition, trace metals are regenerated into seawater under anaerobic conditions. This process plays an important role in the accumulation of chemicals in seawater and sediments, especially in enclosed sea areas.

Observations on the mode and seasonality of reproduction in Furcellaria lumbricalis (Gigartinales, Rhodophyta) populations in the northern Baltic Sea

The life cycle of the red alga, Furcellaria lumbricalis, is poorly known in the northern part of the brackish water Baltic Sea, even though it is one of the most common red algal species in the region. To study its life cycle and reproduction, monthly sampling (n=30/sampling site) was carried out for one year on the coast of Finland at four locations spanning 500 km along a salinity gradient (3.6–5.4 psu). In three of the populations studied, only tetrasporangia and spermatangia were produced. In the fourth population, at the lowest (3.6 psu) salinity, all algae examined were vegetative. Winter months were the main season for tetrasporangial production, when sori with masses of sporangia were present. Smaller sori with only a few tetrasporangia were observed during spring at higher salinities, and some sporangia were detected in the population at 5 psu salinity, even during the summer months. The timing and intensity of reproduction was regulated by a combination of factors including seawater salinity, along with seawater transparency, temperature and photoperiod. In conclusion, we hypothesise that three of the populations, living at salinities between 4.9–5.4 psu reproduce by thallus fragmentation and possibly by asexual tetraspore-to-tetraspore cycling without meiosis, and the fourth population, at a salinity of 3.6 psu, survives by thallus fragmentation and reattachment.

Study of the seawater transparency field in the Crimea-Caucasus shelf area

This paper discussesin situ observational data on the directed light attenuation index in the near-surface layer, collected in September 1987. The absolute light attenuation index has been evaluated for a near-shore strip of water 10–15 miles in width. When multidisciplinary research is conducted in the open sea, this part of the sea surface remains unstudied, as the observational grid for it is made larger than the spatial-temporal parameters of the biophysical processes producing optical inhomogeneities.

Florisphaera profunda, a possible nannoplankton indicator of late Quaternary changes in sea-water turbidity at the northwestern margin of the Pacific

Three piston cores from the Ryukyu Trench slope, northwestern margin of the Pacific Ocean, contain nearly continuous paleoceanographic records of the last 320, 165 and 105 kyr. Ages of the cores are constrained by plankticδ 18O stratigraphy and roughly substantiated by the presence of two calcareous nannofossil events. Spectral analysis of the changes in relative abundance of Florisphaera profunda, a nannoplankton species presently living in the lower euphotic zone, reveals a maximum power at ∼0.01 cycles/kyr, corresponding to the ∼ 100 kyr/cycle of orbital eccentricity. Much lower power is observed at the ∼ 23 kyr precessional band. This differs from the equatorial Atlantic Ocean variations, which show dominant power in the ∼ 23 kyr precessional band in the changes of F. profunda abundances ( Molfino and McIntyre, 1990a). Besides, our cores were taken outside the equatorial divergence zone. We also show a rather close relationship between F. profunda abundance and sea-water transparency (Secchi depth) in the present northwest Pacific, based on data from 204 sites of surface sediment samples. Because sea-water transparency is primarily affected by bio-productivity change in open ocean, stratigraphic changes of F. profunda abundances in our cores seem to have been caused by productivity change as well pointed out by Molfino and McIntyre (1990a,b). A mechanism proposed by them for its change, however, is not applied to our cases due to differences in spectral analysis results and in geographic situation. Alternatively, we suggest that geographic change of the northwestern margin of the Pacific during the late Quaternary caused F. profunda abundance change through the sea-water turbidity change which has been affected not only by bio-productivity but also by land-origin particles supply.

Long-term study of heterotrophic bacteria as indicators of eutrophication of the open middle adriatic sea

Results of the 20-year study, from 1968 to 1988, indicate a trend of increasing density of heterotrophic bacteria in the open middle Adriatic Sea. An identical trend has been observed for primary production resulting in an increase of oxygen saturation in the layer of maximum primary production. Transparency of seawater decreased during the investigated period. This suggests that fluctuations of hydrographic, chemical and biological parameters in the open middle Adriatic Sea are not only a result of the influence of natural factors but are influenced by coastal eutrophication as well. Eutrophication rapidly extended towards the open Adriatic Sea after the late 1970s.

Influence of Suspended and Dissolved Matter on the Transparency of Sea Water

The transparency at different levels in the sea as recorded by means of a transparency-meter is compared with the distribution of suspended particles studied with the aid of a Tyndall-meter. A simple procedure is used to distinguish between different components of light extinction and to derive values of the content of the dissolved yellow substance. The distribution of yellow substance is illustrated for the transition area between the Baltic and the Skagerrak and for the outflow of the Gota Alv. It is emphasized that the content of yellow substance may often be considered as a characteristic property of a water mass. DOI: 10.1111/j.2153-3490.1953.tb01036.x

A Theory on the Transparency of Sea Water

The present author de r i ved theoretically the equation for the transparency of water as follows,and by the above equation discussed the relation between transparency and the oceanographical elements which have e f f e c t s on it.