Gaoping River Research Articles

Tidal and flood signatures of settling particles in the Gaoping submarine canyon (SW Taiwan) revealed from radionuclide and flow measurements

Sediment transport and sedimentation processes in the Gaoping submarine canyon were studied using sediment trap and current meter moorings deployed at a location during the winter (January–March) and the summer (July–September) months in 2008. At the end of each deployment, sediment cores were also collected from the canyon floor at the mooring site. Samples from sediment traps and sediment cores were analyzed for 210Pb and 234Th by gamma spectrometry. In conjunction with particle size and flow measurements, the datasets suggest that sediment transport in the canyon is tidally-modulated in the drier winter season and flood (river)-dominated in the wetter summer season. From the magnitude and temporal variation of sediment flux in the canyon with respect to the burial flux and sediment budget on the open shelf and slope region, we reaffirm that, on annual or longer timescales, the Gaoping submarine canyon is an effective conduit transporting sediments from the Gaoping River's drainage basin (the source) to the deep South China Sea (the ultimate sink).

Partition of suspended and riverbed sediments related to the salt-wedge in the lower reaches of a small mountainous river

A month-long comprehensive field experiment during the beginning of the flood season of a small mountainous river in southern Taiwan was carried out in 2004. The major goal of the study was to investigate the effect of hydrodynamic sorting related to the salt-water intrusion on the spatial variability of suspended and riverbed sediments and their coupling of different sizes. The experiment included the deployment of an instrumented tetrapod near the river mouth with an upward-looking ADCP and two CTDs mounted at 50 and 100 cm above the bed (cmab), respectively. On three different days along the river, turbidity, salinity and temperature of the water column were profiled; and water samples were taken from the surface and near the bed at different stations. Additionally, one sediment sample was also taken from the riverbed. Suspended sediment concentrations (SSC) were analyzed for five different sizes, i.e. > 500, 250–500, 63–250, 10–63 and 1.2–10 μm by filtration. For each riverbed sample the size-composition was analyzed for the subsample that contained lithogenic and nonlithogenic components; and the subsample having major nonlithogenic components (organic matter, carbonates, and biogenic opal) was removed. The grain-size frequency distributions of the riverbed samples were analyzed using a laser particle analyzer. The results were grouped into the following size classes: > 473, 249–473, 62–249, 10–62, and < 10 μm for comparison with those of the suspended sediments near the riverbed. Some suspended sediment samples were analyzed for POC and PON. Some riverbed samples were analyzed for TOC. Statistical methods of linear regression and Empirical Orthogonal (Eigen) Function (EOF) were used in the data analysis. Two-layered estuarine circulation pattern was observed at the tetrapod site. The tidally-driven salt-water intrusion is the major factor influencing the hydrodynamics of the Gaoping River, which in turn, affect the longitudinal and vertical distribution of the suspended sediments and the longitudinal distribution of the riverbed sediments. During the flood, the intrusion front of the salt-wedge creates a dynamic barrier. Upriver from this barrier, the riverbed substrate is coarser, composed of sediments mostly coarser than 249 μm. Within the salt-wedge the riverbed substrate is finer, consisting of mostly mud (< 62 μm). The barrier creates a trap on the riverbed immediately seaward from the intrusion front, retaining higher percentages of clay-sized sediments and TOC. The barrier also creates partition in the terrestrial and marine sources of organic matter in the suspended and riverbed sediments. Within the salt-wedge the major contributor of riverbed TOC is the clay-sized marine sediment transport upriver by the intruding seawater. The terrestrial POC is a minor contributor to the riverbed TOC. The riverbed and suspended sediments are coupled. Most size-classes in corresponding suspended and riverbed sediments have a reciprocal relationship (negative feedback) through resuspension and deposition on the water–bed interface. The only size-class of 62–473 μm on the riverbed and 63–250 μm in the suspension are co-varying (positive feedback). This size class contains largely a transient floc population that is formed and disintegrated in-situ both on the riverbed and in the suspension in the course of a tidal cycle.

Using satellite observations of ocean color to categorize the dispersal patterns of river-borne substances in the Gaoping (Kaoping) River, Shelf and Canyon system

Mapping the water constituents from remotely sensed ocean color data enables a better understanding of the dispersal patterns of river-borne substances in the Gaoping (formerly spelled Kaoping) River, Shelf and Canyon (KPRSC) system. Based on twelve MODIS-Aqua images in the KPRSC region taken in 2005, we apply a newly developed GA-SA approach to derive maps of chlorophyll- a concentration ( Chl- a), colored dissolved organic matter (CDOM) and non-algal particle/detritus/mineral (NAP). The results demonstrated that the different characteristics of Chl- a, CDOM and NAP make them ideal tracers for observing large-scale dispersal patterns. With ancillary information of averaged daily precipitation, the daily wind field obtained from QuikSCAT (Quick Scatterometer), and the 8-day composite of the temperature field obtained from MODIS-Aqua, we categorized the surface dispersal patterns as coastal, northwestward and frontal patterns. Also, for the first time, we observed a sudden increase of biomass on a large scale from a pair of ocean color images taken over only a 2-day interval. Another remarkable feature is the interaction between the southeastward flow and the intrusion of the Kuroshio Branch, resulting in complicated patterns with various scales of vortex structures and current fronts. The observed features could be used for model validation of the flow field of the KPRSC system.

Tectonically active sediment dispersal system in SW Taiwan margin with emphasis on the Gaoping (Kaoping) Submarine Canyon

The sediment dispersal system in southwestern Taiwan margin consists of two main parts: the subaerial drainage basin and the offshore receiving marine basin. In plan view, this sediment dispersal system can be further divided into five geomorphic units: (1) the Gaoping (formerly spelled Kaoping) River drainage basin, (2) the Gaoping (Kaoping) Shelf, (3) the Gaoping (Kaoping) Slope, (4) the Gaoping (Kaoping) Submarine Canyon and (5) the Manila Trench in the northernmost South China Sea. The Gaoping River drainage basin is a small (3250 km 2), tectonically active and overfilled foreland basin, receiving sediments derived from the uprising Central Range of Taiwan with a maximum elevation of 3952 m. The Gaoping Submarine Canyon begins at the mouth of the Gaoping River, crosses the narrow Gaoping Shelf (~ 10 km) and the Gaoping Slope, and finally merges into the northern termination of the Manila Trench over a distance of ~ 260 km. The SW Taiwan margin dispersal system is characterized by a direct river-canyon connection with a narrow shelf and frequent episodic sediment discharge events in the canyon head. In a regional source to sink scheme, the Gaoping River drainage basin is the primary source area, the Gaoping Shelf being the sediment bypass zone and the Gaoping Slope being the temporary sink and the Manila Trench being the ultimate sink of the sediment from the Taiwan orogen. It is inferred from seismic data that the outer shelf and upper slope region can be considered as a line source for mass wasting deposits delivered to the lower Gaoping Slope where small depressions between diapiric ridges are partially filled with sediment or are empty. At present, recurrent hyperpycnal flows during the flood seasons are temporarily depositing sediments mainly derived from the Gaoping River in the head of the Gaoping Submarine Canyon. On the decadal and century timescales, sediments temporarily stored in the upper reach are removed over longer timescales probably by downslope-eroding sediment flows within the canyon. Presently, the Gaoping Submarine Canyon serves as the major conduit for transporting terrestrial sediment from the Taiwan orogen to the marine sink of the Manila Trench. Seismic data indicate that the Gaoping Submarine Canyon has been eroding the Gaoping Slope intensely by presumed hyperpycnal flows and transporting sediments from the canyon head to the middle and lower reaches of the canyon. The middle reach is a sediment bypass zone whereas the lower reach serves as either a temporary sediment sink or a sediment conduit, depending on relative prevalence to deposition or erosion during canyon evolution. Contrast differences in channel gradient and travel length between the Gaoping and Amazon sediment dispersal systems suggest that the Gaoping (Kaoping) River-Canyon system is an active sediment dispersal system for transporting terrestrial materials to the deep sea. The fate of the Gaoping River sediment is the northern Manila Trench.

Modern accumulation rates and a budget of sediment off the Gaoping (Kaoping) River, SW Taiwan: A tidal and flood dominated depositional environment around a submarine canyon

Ninety-two box cores collected during 2004–2006 from an area of ~ 3000 km 2 off the Gaoping (formerly spelled Kaoping) River, SW Taiwan, were analyzed for fallout radionuclides ( 210Pb, 137Cs and 7Be) to elucidate sedimentation rates and processes, and for the calculation of a sediment budget. The study area is located at an active collision margin with a narrow shelf and a submarine canyon extending essentially into the river's mouth. The results indicate fairly constant hemipelagic sedimentation in much of the open margin and for most of the time except in the inner shelf and along the axis of the canyon where sediment transport is more dynamic and is controlled by tidal current and wave activities constantly, and by fluvial floods or gravity-driven flows episodically. Sedimentation rates in the study area derived from 210Pb and constrained by 137Cs vary from 0.04 to 1.5 cm/yr, with the highest rates (> 1 cm/yr) flanking the Gaoping canyon over the upper slope (200–600 m) and the lowest rates (< 0.1 cm/yr) in the distal basin beyond the continental slope. The depocenter delineated from 210Pb-based sedimentation rates overlaps with the area covered by a flood layer resulting from super-typhoon Haitang in July 2005. Such correspondence supports the notion that the processes operating on event timescale have bearing on the formation of the sediment strata over centennial or longer timescales. From the distribution of sedimentation rates, sediment deposited in the study area annually is estimated to be 6.6 Mton/yr, accounting for less than 20% of Gaoping River's sediment load. The calculated budget, coupled with the presence of the short-lived 7Be and non-steady-state distribution of low levels of 210Pb in sediments along the canyon floor, suggests rapid transport of sediment from Gaoping River's mountainous watershed (the source) via the Gaoping (Kaoping) Submarine Canyon and adjacent channels (as the conduit and temporary sink) to the abyssal plain and the Manila Trench in the South China Sea (the ultimate sink).

Geochemical controls on distributions and speciation of As and Hg in sediments along the Gaoping (Kaoping) Estuary–Canyon system off southwestern Taiwan

Surface and box-cored sediments were collected along the Gaoping (formerly spelled Kaoping) Estuary–Canyon system and analyzed for As and Hg contents and speciation, 210Pb-based sedimentation rates and various geochemical parameters to elucidate the mechanisms that control natural and anthropogenic inputs of As and Hg from the Gaoping (Kaoping) River (KPR). The contents of As and Hg in surface sediments ranged from 1.84 to 20.7 mg kg − 1 and from 0.07 to 2.15 mg kg − 1 , respectively, in the estuary and canyon. The concentrations generally decreased from the lower river toward the mixing boundary and then increased toward the estuarine mouth, followed by a slight variation in the canyon. Both As and Hg concentrations correlated strongly with clay, total organic carbon (TOC), Al, Fe and Mn contents in estuarine sediments but not necessary the same cases for canyon surface sediments. The factor analysis of surface sediments shows that the first two factors, which account for 75.6% of the variance, may represent major roles of carriers (clay, Al and Fe–Mn oxides) and TOC in controlling As and Hg distributions, respectively. Accordingly, the spatial patterns of the enrichments of As (1.9–16.2) and Hg (1.8–30.8) with reference to the crust levels follow the individual element's distribution patterns, likely because of deposition variability following inputs from the river. The contents of mobile As and Hg correlated substantially with the contents of both metals that were extracted with 0.1 M HCl. In addition to the major pool in the residual fraction (65–87%), As was relatively abundant in Fe–Mn oxides/hydroxides, whereas Hg was abundant in the organic/sulfide fraction. The deposition and accumulation rates of As and Hg in the canyon clearly decreased as the depth of water increased. The depth distributions of both metals are likely controlled primarily by TOC and Fe–Mn oxides associated factors followed by a contribution from anthropogenic pollution. The metal pollution appears to have increased substantially around 1970, following the economic boom in Taiwan, suggesting that modern sediments in the Gaoping (Kaoping) Canyon were derived from the Gaoping (Kaoping) River (KPR).

Weathering sources in the Gaoping (Kaoping) river catchments, southwestern Taiwan: Insights from major elements, Sr isotopes, and rare earth elements

This study aims at quantifying the distribution of REEs associated with chemical weathering processes, as well as investigating weathering mechanisms and source regions of the Gaoping (formerly spelled Kaoping) River (KPR) catchment basin located at southwestern Taiwan. Spatial distributions of dissolved rare earth elements, as well as major ions, trace elements and Sr isotopes in river waters were analyzed using SF-ICPMS and TIMS. Our results indicate that REE concentrations and patterns predominantly reflect sources and intensity of chemical weathering along the river's catchment. Most specimens have high Na/Cl (4.2–30.1 mol/mol) ratios due to strong weathering intensity in the upper stream. The Na/Ca and Mg/Ca ratios suggest the main contribution is from weathering of silicates and carbonates. Total concentrations of REEs are rather low in the Gaoping (Kaoping) River (6.7–15.4 ng/L), possibly influenced by adsorption onto suspended particles. The REE patterns also reflect source heterogeneity in weathering minerals with large LREE depletion and MREE enrichment. Europium is strongly enriched in the Gaoping (Kaoping) River water, as a result of its preferential dissolution from suspended particles. Unique Gadolinium anomaly is present in all specimens, likely related to contamination due to clinic waste disposal. Small fractionations of LREE/HREE have occurred along the KPR and can be used as a distinct signature for source identification. The main stream samples exhibit a relatively wide range of 87Sr/ 86Sr, 0.71265–0.71360, with a systematical increase downstream due to source mixing of dissolved basalt (less radiogenic) and sedimentary rocks. Each tributary shows distinct Sr isotope signatures due to different rock types and ages. These isotopic and elemental compositions provide important information on weathering source and erosion budget.

Seasonal variability of dissolved major and trace elements in the Gaoping (Kaoping) River Estuary, Southwestern Taiwan

To gain a better understanding of the geochemical behavior of trace elements in estuary and to examine seasonal variations in associated chemical fluxes, more than 50 water samples were collected near the mouth of the Gaoping (formerly spelled Kaoping) River, a major river in southwestern Taiwan. These samples, collected in typical dry and wet tropical monsoon seasons during 1999–2004, were analyzed for dissolved major and trace elements and Sr isotopes. Our results show that dissolved Na, Mg, Ca and Cl behave conservatively along the salinity gradient and display significantly larger fluxes in the wet seasons. Vertical profiles of the major elements reveal mainly two end-member mixing between the riverine freshwater and the seawater. Trace elements of B, Sr and U also display conservative distribution in the vertical profiles. In contrast, dissolved Ba and Mn were affected by uptake/release processes involving groundwater, benthic flux and water/sediment interactions. 87Sr/ 86Sr ratios also support a scenario of mixing between a more radiogenic continental source and the seawater. It appears that the wet season samples have higher trace element concentrations due to inputs from topsoils and atmospheric dusts. This implies that chemical compositions in river waters respond sensitively to regional climatic changes. The observed high fluxes of B and Sr in the Gaoping (Kaoping) River emphasize the potential impact of mountainous rivers on the global oceanic mass balance of these constituents.

From suspended particles to strata: The fate of terrestrial substances in the Gaoping (Kaoping) submarine canyon

The river–sea system consisting of the Gaoping (new spelling according to the latest government's directive, formerly spelled Kaoping) River (KPR), shelf, and Submarine Canyon (KPRSC) located off southern Taiwan is an ideal natural laboratory to study the source, pathway, transport, and fate of terrestrial substances. In 2004 during the flood season of the KPR, a system-wide comprehensive field experiment was conducted to investigate particle dynamics from a source-to-sink perspective in the KPRSC with the emphasis on the effect of particle size on the transport, settling, and sedimentation along the pathway. This paper reports the findings from (1) two sediment trap moorings each configured with a Technicap PPS 3/3 sediment trap, and an acoustic current meter (Aquadopp); (2) concurrent hydrographic profiling and water sampling was conducted over 8 h next to the sediment trap moorings; and (3) box-coring in the head region of the submarine canyon near the mooring sites. Particle samples from sediment traps were analyzed for mass fluxes, grain-size composition, total organic carbon (TOC) and nitrogen (TN), organic matter (OM), carbonate, biogenic opal, polycyclic aromatic hydrocarbon (PAH), lithogenic silica and aluminum, and foraminiferal abundance. Samples from box cores were analyzed for grain-size distribution, TOC, particulate organic matter (POM), carbonate, biogenic opal, water content, and 210Pb ex. Water samples were filtered through 500, 250, 63, 10 µm sieves and 0.4 µm filter for the suspended sediment concentration of different size-classes. Results show that the river and shelf do not supply all the suspended particles near the canyon floor. The estimated mass flux near the canyon floor exceeds 800 g/m 2/day, whose values are 2–7 times higher than those at the upper rim of the canyon. Most of the suspended particles in the canyon are fine-grained (finer than medium silt) lithogenic sediments whose percentages are 90.2% at the upper rim and 93.6% in the deeper part of the canyon. As suspended particles settle through the canyon, their size-composition shows a downward fining trend. The average percentage of clay-to-fine-silt particles (0.4–10 µm) in the water samples increases from 22.7% above the upper rim of the canyon to 56.0% near the bottom of the canyon. Conversely, the average percentage of the sand-sized (> 63 µm) suspended particles decreases downward from 32.0% above the canyon to 12.0% in the deeper part of the canyon. Correspondingly, the substrate of the canyon is composed largely of hemipelagic lithogenic mud. Parallel to this downward fining trend is the downward decrease of concentrations of suspended nonlithogenic substances such as TOC and PAH, despite of their affinity to fine-grained particles. On the surface of the canyon, down-core variables (grain size, 210Pb ex activity, TOC, water content) near the head region of the canyon show post-depositional disturbances such as hyperpycnite and turbiditic deposits. These deposits point to the occurrences of erosion and deposition related to high-density flows such as turbidity currents, which might be an important process in submarine canyon sedimentation.

Characterization and composition of heavy metals and persistent organic pollutants in water and estuarine sediments from Gao-ping River, Taiwan

The objective of this study was to determine the concentrations and possible sources of heavy metals and persistent organic pollutants (POPs) in water and estuarine sediments from Gao-ping River in order to evaluate the environmental quality of aquatic system in southern Taiwan. High concentrations of heavy metals including Cr, Zn, Ni, Cu and As, ranging from 10.7 to 180 mg/kg-dry weight (dw), were detected in sediments from Gao-ping River. When normalized to the principal component analysis (PCA), swinery and electroplating wastewaters were found to be the most important pollution sources for heavy metals. Of various organochlorine pesticide (OCP) residues detected, aldrin and total-hexachlorocyclohexane (HCH) were frequently found in sediments. The total concentrations of OCPs were in the range 0.47–47.4 ng/g-dw. Also, the total-HCH, total-cyclodiene, and total-dichlorodiphenyltrichloroethane (DDT) were in the range 0.37–36.3, 0.21–19.0, and 0.44–1.88 ng/g-dw, respectively. The polychlorinated biphenyl (PCB) concentrations in sediments from Gao-ping River ranged between 0.37 and 5.89 ng/g-dw. The PCB concentrations are positively correlated to the organic contents of the sediment particles. α-HCH was found to be the dominant compound of HCH in the sediments, showing that long-range transport may be the possible source for the contamination of HCH in sediments from Gao-ping River. In summary, trace amounts of POPs in estuarine sediments from Gao-ping River were detected, showing that there still exist a wide variety of POP residues in the river sediments in Taiwan. These POP residues may be mainly from long-range transport and weathered agricultural soils, while heavy metal contamination is primarily from the swinery and industrial wastewaters.

Characterization and distribution of polycyclic aromatic hydrocarbon contaminations in surface sediment and water from Gao-ping River, Taiwan

The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) in water and sediment samples collected from 12 locations in Gao-ping River, Taiwan were analyzed. Molecular ratios and principal component analysis (PCA) were used to characterize the possible pollution sources. Concentrations of total 16 PAHs (ΣPAHs) in water samples ranged from below method detection limits (<MDLs) to 9.4 μg/L with the mean value of 0.43±0.75 μg/L ( n=48), which were predominated by two- and three-ring PAHs. The ΣPAH concentrations in sediments ranged from 8 to 356 ng/g-dry weight with the mean value of 80.6±31.8 ng/g ( n=48). Three- and four-ring PAHs including phenanthrene, anthracene and pyrene were the dominant species in sediment samples. High contents of PAHs were found in the estuary of the river and in the vicinity of industrial areas. Ratios of specific PAH compounds including phenanthrene/anthracene (Phe/Ant), fluoranthene/pyrene (FL/Pyr), chrysene/benzo[a] anthracene (Chr/BaA), low-molecular-weight PAH/high-molecular-weight PAH (LPAH/HPAH) were calculated to evaluate the possible sources of PAH contamination. These ratios reflect a mixed pattern of pyrolytic and petrogenic inputs of PAHs in Gao-ping River. The petrogenic PAHs may be mainly from the leakage of crude oil and the refined products from urban vehicle traffic, while the pyrolytic PAH input is located in the proximity near the mouth of estuary of the River. The PCA analysis confirmed that petrochemical industrial parks located in the vicinity of estuary of Gao-ping River might be the possible source for the PAH input.