scholarly journals Turbidity maximum zone index: a novel model for remote extraction of the turbidity maximum zone in different estuaries

2021 ◽  
Vol 14 (11) ◽  
pp. 6833-6846
Author(s):  
Chongyang Wang ◽  
Li Wang ◽  
Danni Wang ◽  
Dan Li ◽  
Chenghu Zhou ◽  
...  
Keyword(s):  
Remote Sensing ◽  
River Estuary ◽  
High Flow ◽  
Turbidity Maximum ◽  
Low Flow ◽  
Distribution Area ◽  
Spatial And Temporal Variation ◽  
Chl A ◽  
Turbidity Maximum Zone ◽  
Novel Model

Abstract. An efficient recognition and extraction of the estuarine turbidity maximum zone (TMZ) is important for studying terrestrial hydrological processes. Although many studies relevant to the TMZ have been conducted worldwide, the extraction methods and criteria used to describe the TMZ vary significantly both spatially and temporally. To improve the applicability of the methods adopted in previous studies and to develop a novel model to accurately extract the TMZ in multiple estuaries and different seasons from remote-sensing imageries, this study estimated the total suspended solid (TSS) and chlorophyll a (Chl a) concentrations in three estuaries. These were the Pearl River estuary (PRE), the Hanjiang River estuary (HRE), and the Moyangjiang River estuary (MRE) of Guangdong Province, China. The spatial distribution characteristics of the TSS and Chl a concentrations were analyzed. A nearly opposite association was found between the TSS and Chl a concentrations in the three estuaries, particularly in the PRE. The regions with high (low) TSS concentrations had relatively low (high) Chl a concentrations and, therefore, a turbidity maximum zone index (TMZI), defined as the ratio of the difference and sum of the logarithmic transformation of the TSS and Chl a concentrations, was firstly proposed. By calculating the TMZI values in the PRE on 20 November 2004 (low-flow season), it was found that the criterion TMZI>0.2 could be used to identify the TMZs of the PRE effectively. The TMZ extraction results were generally consistent with the visual-interpretation results. The area-based accuracy measures showed that the quality (Q) of the extraction reached 0.8429. The same criterion was applied in the PRE on 18 October 2015 (high-flow season), and high accuracy and consistency across seasons were observed (Q=0.8171). The western shoal of the PRE was the main distribution area of TMZs. Extracting TMZs by the newly proposed index performed well in different estuaries and on different dates (HRE on 13 August 2008 in the high-flow season and MRE on 6 December 2013 in the low-flow season). Compared to the previous fixed threshold of TSS or turbidity methods, extracting the TMZ using the TMZI had higher accuracy and better applicability (Q: 0.1046–0.4770 vs. 0.8171–0.8429). Evidently, this unified TMZI is potentially an optimized method for the global monitoring and extraction of TMZs of estuaries from different satellite remote-sensing imageries. It can be used to help the understanding of the spatial and temporal variation in TMZs and estuarine processes at regional and global scales as well as improve the management and sustainable development of regional society and the natural environment.

scholarly journals Turbidity maximum zone index: A novel model for remote extraction of turbidity maximum zone in different estuaries

2021 ◽  
Author(s):  
Chongyang Wang ◽  
Li Wang ◽  
Danni Wang ◽  
Dan Li ◽  
Chenghu Zhou ◽  
...  
Keyword(s):  
Remote Sensing ◽  
River Estuary ◽  
Turbidity Maximum ◽  
Low Flow ◽  
Spatial And Temporal Variation ◽  
Hydrological Process ◽  
Turbidity Maximum Zone ◽  
The World ◽  
Fixed Threshold ◽  
Novel Model

Abstract. Recognizing and extracting estuarine turbidity maximum zone (TMZ) efficiently is important for kinds of terrestrial hydrological process. Although many relevant studies of TMZ have been carried out around the world, the method of extracting and criteria of describing TMZ vary greatly from different regions and different times. In order to improve the applicability of the fixed threshold in previous studies and develop a novel model extracting TMZ accurately in multi estuaries and different seasons by remote sensing imagery, this study estimated the total suspended solids (TSS) concentrations and chlorophyll a (Chla) concentrations in Pearl River Estuary (PRE), Hanjiang River Estuary (HRE) and Moyangjiang River Estuary (MRE) of Guangdong province, China. The spatial distribution characteristics of both TSS concentrations and Chla concentrations were analyzed subsequently. It was found that there was an almost opposite relationship between TSS concentration and Chla concentration in the three estuaries, especially in PRE. The regions of high (low) TSS concentrations are exactly corresponding to the relative low (high) Chla concentrations. Based on the special feature, an index named turbidity maximum zone index (TMZI), defining as the ratio of the difference and sum of logarithmic transformation of TSS concentrations and Chla concentrations, was firstly proposed. By calculating the values of TMZI in PRE on 20 November 2004 (low-flow season), it was found that the criterion (TMZI > 0.2) could be used to distinguish TMZs of PRE effectively. Compared with the true (false) color imagery and the rudimentary visual interpretation results, the TMZs extraction results by TMZI were mostly consistent with the actual distribution. Moreover, the same criterion was further applied in PRE on 18 October 2015. The high accuracy and good consistency across seasons were also found. The west shoal of PRE was the main distribution areas of TMZs. In addition, the good performance in extracting TMZs by this newly proposed index were also found in different estuaries and different times (HRE, 13 August 2008, high-flow season; MRE, on 6 December 2013, low-flow season). Compared to the previous fixed threshold (TSS or turbidity) methods, extracting TMZ by TMZI has a higher accuracy and better applicability. Evidently, this unified TMZI is a potentially optimized method to monitor and extract TMZs of other estuaries in the world by different satellite remote sensing imageries, which can be used to improve the understanding of the spatial and temporal variation of TMZs and estuarial processes on regional and global scales, and the management and sustainable development of regional society and nature environment.

Suaeda Salsa Biomass Remote Sensing in the ShuangTai River Estuary

2012 ◽  
Vol 610-613 ◽  
pp. 3651-3654
Author(s):  
Tao Wu ◽  
Dong Zhi Zhao ◽  
Guo Jun Jiang ◽  
Wei Xu ◽  
Cui Xiao
Keyword(s):  
Remote Sensing ◽  
Linear Regression ◽  
Correlation Coefficient ◽  
Vegetation Indices ◽  
River Estuary ◽  
Quadratic Equation ◽  
Regression Equation ◽  
Suaeda Salsa ◽  
Distribution Area ◽  
Linear Regression Equation

Suaeda salsa is the characteristics vegetation in the wetlands of Northern China. By acquiring Suaeda Salsa biomass, building spectral reflectance curve, probing into the relationship between the vegetation indices and the biomass, and finally achieving Suaeda Salsa’s biomass remote sensing monitor in the ShuangTai river estuary, Conclusions are as follows: 1). Correlation coefficient between the biomass and the vegetation indices (RVI and NDVI) is low, and Linear regression equation (R2) is 0.342 and 0.316, and the Logarithmic regression equation (R2) is 0.319 and 0.21, and the Quadratic equation (R2) is 0.589 and 0.568. Correlation coefficient between the biomass and the vegetation indices (PVI, SAVI and MSAVI) is high, and the linear regression equation is 0.626、0.698 and 0.679, respectively. The logarithmic regression equation is 0.592、0.706 and 0.683 respectively and the quadratic equation is 0.688、0.711 and 0.683. 2). Suaeda salsa’s biomass is consistent with the distribution area in the Shuangtai river estuary. Total biomass maintained at 2.9 × 107- 4.2 × 108kg in 1990, and dropped to 3.4 × 106 ~ 3.5 × 107kg in 1995. In 2000, the quadratic function of vegetation version biomass rebounded, but linear function continues to fall. Biomass increased rapidly, reaching 1.46 ~ 2.4 × 108kg in 2005.

Flow events drive patterns of phytoplankton distribution along a river–estuary–bay continuum

2013 ◽  
Vol 64 (7) ◽  
pp. 655 ◽  
Author(s):  
Emily A. Saeck ◽  
Wade L. Hadwen ◽  
David Rissik ◽  
Katherine R. O'Brien ◽  
Michele A. Burford
Keyword(s):  
Nitrogen Availability ◽  
River Estuary ◽  
High Flow ◽  
Phytoplankton Growth ◽  
Nutrient Loads ◽  
Anthropogenic Pressures ◽  
Phytoplankton Productivity ◽  
Chl A ◽  
Phytoplankton Distribution ◽  
Flow Phase

Freshwater flow events drive phytoplankton productivity in subtropical coastal river systems. However, few studies have the necessary temporal and spatial resolution to fully characterise the effect of events on the distribution of phytoplankton across the full river–estuary–bay continuum. The present study characterised the response of phytoplankton to high-flow events in an Australian subtropical system; and identified the primary drivers of this response. During high-flow events, the concentration of phytoplankton chlorophyll a (Chl a) initially declined in the estuary, a response primarily driven by the shortened water-residence time. In the bay, phytoplankton growth in the near-shore zone was light limited; however, nutrients stimulated phytoplankton growth on the seaward edge of the river plume. During the post-high-flow phase, the concentration of Chl a in the freshwater reaches peaked downstream, where catchment-derived nutrients accumulated. In the estuary, elevated nutrient loads stimulated phytoplankton growth upstream and downstream of the light-limited zone. In the bay, nitrogen availability declined, and Chl a declined with an increasing distance offshore. The phytoplankton response to events documented in the present study can be used to identify when and where phytoplankton in subtropical systems may be strongly influenced by changes in the magnitude of nutrient, sediment and freshwater loads associated with high-flow events which result from anthropogenic pressures within the catchment.

Dynamic sedimentation process of the turbidity maximum zone in the Yangtze River Estuary under the influence of human activities

2020 ◽  
Author(s):  
Weihua Li ◽  
Xiaohe Zhang ◽  
Zhanhai Li ◽  
Jiufa Li
Keyword(s):  
River Estuary ◽  
River Mouth ◽  
Turbidity Maximum ◽  
Yangtze River Estuary ◽  
The Yangtze River ◽  
The South ◽  
Turbidity Maximum Zone ◽  
The North ◽  
The Yangtze River Estuary ◽  
Mouth Bar

<p>Due to the impact of the Three Gorges Dam on water and sediment storage, the sediment flux into the Yangtze River Estuary has dropped sharply by 70%, and the suspended sediment concentration in the estuary has responded accordingly. From the comparison of the measured suspended sediment concentration data of the Yangtze River estuary for many years, it is known that the suspended sediment concentration in the South Passage has been reduced by about 60% recently, and that in the middle and upper reaches of the North Channel and the South Channel has been reduced by about 40%. On the other hand, A series of artificial engineering has been completed in the past 20 years, such as the 12.5m Deep-Waterway Regulation Engineering, the Nanhui Shoal Slush-enclosure Engineering, and the Hengsha Shoal Slush-enclosure Engineering, etc. These engineering have significantly changed the original water and sediment transport pattern of the Yangtze River Estuary. It resulted in a significant change of the estuarine turbidity maximum zone and the corresponding river mouth bar topography. This paper intends to discuss the impact of human activities on the dynamic sedimentation process of the maximum turbidity zone in the Yangtze River Estuary based on field measured data. Results are as follows:</p><p>(1) Compared to two decades ago, the suspended sediment concentration in the North Passage, the South Passage and the North Channel, and the middle and lower reaches of the North Branch is still high, which is related to the existence of the turbidity maximum zone and river mouth bar in these river sections.</p><p>(2) The implementation of man-made engineering such as the submerged diversion dike between the North Passage and the South Passage and the Nanhui Shoal Slush-enclosure Engineering changed the flow structure in the upper section of the South Passage, leading to the turbidity maximum zone and the corresponding river mouth bar have completely disappeared.</p><p>(3) Affected by the 12.5m Deep-Waterway Regulation Engineering, the turbidity maximum zone and the corresponding river mouth bar originally located at the upper section of the North Passage have also disappeared.</p><p>(4) The longitudinal circulation flow structure, salt water wedges, and stagnation points in the middle and lower sections of the North Passage and the South Passage still exist. The positions of the turbidity maximum zone and the corresponding river mouth bar topography are not significantly affected by the engineering. And the core area of ​​the obvious turbidity maximum zone and the river mouth bar (only in the South Passage) still exist. Due to the artificial dredging of the navigation channel in the North Passage, it actually appeared as an invisible river mouth bar that has been dredged by continuous dredging.</p><p> (5) The drastic reduction of sediment flux from the basin has caused seabed erosion adjacent to the Yangtze River Estuary, and the corresponding eroded sediment has become one of the main sediment budget sources of the turbidity maximum zone.</p>

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