Determination and distribution of region-specific background Secchi depth based on long-term monitoring data in the Seto Inland Sea, Japan

Nishijima, Wataru; Umehara, Akira; Sekito, Satoshi; Wang, Feng; Okuda, Tetsuji; Nakai, Satoshi

doi:10.1016/j.ecolind.2017.09.014

Cited by 10 publications

(5 citation statements)

References 18 publications

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“…In addition, random events (e.g., algal blooms) can also have an important impact on SDD (Klemas, 2012;Yang et al, 2022). In past research on SDD, in addition to remote sensing monitoring technology, there is often analysis of the temporal and spatial changes of SDD and environmental driving forces (Philippart et al, 2013;Hayami et al, 2015;Nishijima et al, 2016;Nishijima et al, 2018;Luis et al, 2019;Idris et al, 2022). However, in special sea areas with complex environments, few quantitative studies on the effects of multiple environmental indicators on SDD have been conducted (Alsahli and Nazeer, 2021).…”

Section: Introductionmentioning

confidence: 99%

Analysis of environmental factors impact on water transparency off southeastern Vietnam

Sun

Liu

et al. 2023

Front. Mar. Sci.

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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.

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Section: Introductionmentioning

confidence: 99%

Analysis of environmental factors impact on water transparency off southeastern Vietnam

Sun

Liu

et al. 2023

Front. Mar. Sci.

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“…As for dimension, the Secchi disk is standardized at 30 cm diameter [9,[15][16][17][18]. Some different dimensions are used such as 10 [18], 20 [19][20][21][22], 25 [23,24], 40, and 45 cm [23,24]. The deeper the disk is lowered, the bigger the disk needs to be [25,26].…”

Section: Introductionmentioning

confidence: 99%

Development of a Solar-Powered IoT-Based Instrument for Automatic Measurement of Water Clarity

Pham

Nguyen

et al. 2020

Sensors

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Water clarity is the most common indicator of water quality. The purpose of the study was to develop an instrument which can automatically measure water clarity in place of manual measurement by Secchi disk. The instrument is suspended by buoys at the water surface and uses solar energy to measure the light intensity of LED bulbs after passing through a water column; the result is then converted to Secchi depth by using a regression function. Measurement data are stored in a cloud server so that mobile users can access via an Internet connection. Three experiments were conducted to examine the instrument performance: (i) to ensure light intensity of the LED bulbs is strong enough to pass through the water column; (ii) to determine the regression relationship between the measured light intensity of the instrument and Secchi depth; and (iii) to evaluate the coefficient of variation (CV) of the measured water clarity when using our instrument and a conventional Secchi disk. Experiment results show that the measured values of light intensity are stable with the average CV = 5.25%. Moreover, although there are slight differences between the Secchi depth measured by our instrument and those measured by Secchi disk, the measurements by our instrument can efficiently replace the measurements by conventional Secchi disk, which can be affected by weather conditions as well as by human subjectivity.

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“…A variety of nutrient reduction programmes have been implemented following the deterioration in coastal waters through phytoplankton overgrowth, such as the Grizzle-Figg Act in relation to Tampa Bay, Florida, USA (Greening et al, 2014), the Action Plan for the Aquatic Environment in relation to Danish coastal waters (Riemann et al, 2016), a ban on phosphate-based detergents and the use of biological nitrogen removal in Chesapeake Bay, USA (Williams et al, 2010) and a Total Pollutant Load Control System (TPLCS) in Japanese enclosed waters including the Seto Inland Sea Nishijima et al, 2018). The results, however, have been dependent on the nature of pressures (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…type, magnitude, frequency and timing), connectivity with adjacent systems and differing water quality parameters (Carstensen et al, 2011;Duarte et al, 2015). In successful cases, the improvement appeared in nutrients, Chl.a, dissolved oxygen concentrations and seagrass cover after implementation of the programme (Greening et al, 2014;Riemann et al, 2016;Nakai et al, 2018;Nishijima et al, 2018), whereas little improvement or even worsening were unfortunately reported too (Williams et al, 2010;Riemann et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…One effect of TPLCS implementation on the Seto Inland Sea has appeared in certain ecosystem components (Yamamoto, 2003;Nakai et al, 2018;Nishijima et al, 2018), although it varies in the subareas. The west-central Seto Inland Sea, including Hiroshima Bay and Aki Nada (Figure 1), receives substantial anthropogenic nutrient loading from its watersheds.…”

Section: Introductionmentioning

confidence: 99%

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Management of the west-central Seto Inland Sea, Japan: factors controlling the spatiotemporal distributions of chlorophyll a concentration and Secchi depth

et al. 2019

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Water quality data from 1981 to 2015 were used to elucidate the spatiotemporal distributions of chlorophyll a (Chl.a) concentration and Secchi depth in the west-central Seto Inland Sea, Japan. The results revealed that salinity and distance from the northern coastline were the main factors for predicting Chl.a concentration and Secchi depth, respectively. Significant differences in both of these were observed between subareas in spring, summer and autumn; differences were insignificant in winter. Chl.a concentrations have decreased for the past 35 years, while their extent differed in the subareas. A greater rate of decrease in Chl.a concentration was observed in the innermost Hiroshima Bay in spring, compared with other subareas, while no significant difference in different subareas was found in other seasons. Secchi depth has increased for the past 35 years, but no significant difference in its rate of increase was found among different subareas in all seasons. Total nitrogen loading better explained changes in mean Chl.a concentration than total phosphorus throughout the west-central Seto Inland Sea. Phytoplankton's contributions to light attenuation were low in the west-central Seto Inland Sea, indicating that the nutrient loading reduction programme has been of limited effectiveness in improving water clarity.

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Determination and distribution of region-specific background Secchi depth based on long-term monitoring data in the Seto Inland Sea, Japan

Cited by 10 publications

References 18 publications

Analysis of environmental factors impact on water transparency off southeastern Vietnam

Analysis of environmental factors impact on water transparency off southeastern Vietnam

Development of a Solar-Powered IoT-Based Instrument for Automatic Measurement of Water Clarity

Management of the west-central Seto Inland Sea, Japan: factors controlling the spatiotemporal distributions of chlorophyll a concentration and Secchi depth

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