Nakdong River Estuary Barrage 175 175 175 175 350175 ≈ 1983 300 200 Utilizing Pb and Cs Radioisotope Geochronology of 6 Cores

Shifts in Depositional Environments as a Natural Response to Anthropogenic Alterations: Nakdong Estuary, South Korea 0 Shell † †‡ §Sand 25 Silt Joshua Williams , Timothy Dellapenna ,0 Guan-hong Lee Shell Clay Sand 25 Silt 50 연안지형역학실험실 Clay Department of Oceanography , Texas A&M University, College50 Station, Texas 77840 0 75 Shell ‡ Sand 75 Department of Marine25 Sciences,Silt 0 Texas A&M University at Galveston, Galveston, Texas 77554 Clay Shell 100 CEML Sand 100 § 50 25 Silt 0 Department of OceanographyClay , Inha University, Incheon, S. Korea 402-751 Shell 125 125 Sand 75 50 25 Silt *Corresponding Author: [email protected], (409) 740-4746 Clay Abstract: 0 150 Shell 0 150 100 75 50 500 Sand Shell ND 12 ND 12 The Nakdong Estuary, located within the coastal zone of Busan, South ND 14 ND 13 25 ND 12 Silt ND 11 Sand 175 ND 9 ND 19 ND 12 ND 12 0 0 0 0 0 130 cm 25 cm 170 cm 250 cm 355 cm 450 Clay 25 Silt 0 0 125 Shell 100 Shell Shell Shell Shell Shell Korea, has been subjected to a series of engineered alterations typical of Clay 17575 Shell Sand Sand Sand Sand Sand Sand In-situ Alternating )' 400 50 3 25 Silt 25 Silt 25 Silt 25 Silt 20025 Silt 25 SiltSand bivalves Coarse and 50 many eastern Asian estuaries. The construction of two estuarine dams m 150 Clay 125 Clay Clay Clay Clay Fine Intervals 7' 350 Clay 10025 Silt 75 225 200 50 Coarser

Depth (cm) Clay (1934 and 1983) and numerous seawalls associated with land 300 50 50 50 50 50 Grained 175 150 75 125 Minor Section 75 Bioturbation reclamation projects have altered the timing and lux of sediment, and 250 100 50 75 75 75 75 25075 225 100 Depth (cm) 200 200 175 ≈ 1983 Laminations Different resulted in three contrasting discharge energy regimes. Additionally, the 150100 Interspersed Bed Plane 125 Dipping 150 100 100 100 100 275100 75 Directions impoundments have appreciably reduced the tidal prism. Consequently, 225 200 125 Depth (cm) 250 125 100 175 Partial Average'Discharge'(10 150 vast geomorphologic changes have occurred including the development 125 125 125 125 300125 High Degree Preservation 50 250 225 150 100150 of of Laminae Depth (cm) 200 Bioturbation Finer 275 Grained of ive new barrier islands. In order to assess the impacts of these 0 175 325 ≈ 1964 150 150 150 150 150 175 Erosional Section Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. 275 250 175 Surface modiications, the dispersal and accumulation of sediment was evaluated 225125 200 Depth (cm) 210 137 Fig. 2) Average monthly discharge from the Nakdong River Estuary Barrage 175 175 175 175 350175 ≈ 1983 300 200 utilizing Pb and Cs radioisotope geochronology of 6 cores. Average for the period of Jan. 1990 - Aug. 2010. 300 275 200 250 -1 225 225 150Depth (cm) sediment accumulation rates range from 2.19 cm yr adjacent to the irst 200 200 Depth (cm) 200 200 375200 2,000 225 325 -1 325 300 Depth (cm) 275250≈ 1934 50 cm A 195 cm B 275 cm C 380 cm D constructed dam, and were found to be as high as 6.55 cm yr in the 250 1,750 225 225 225 225 400225 Depth (cm) Depth (cm) Depth (cm) Depth (cm) Depth (cm) 175 350 325 250 Fig. 9) Representative X-radiograph sections from core ND 12. Location within core and key central portion of the estuary. These high rates are further supported by 0 0 50 100 350 275 0 50 100 300 1,500 275 Shell features indicated. ) Grainsize Percentage

3 250 250 250 250 250 comparison of bathymetric survey data from 1985 to 2009. Laser 375 350 275 Sand m 200300

7 25 Silt 1,250 325 300 Clay 375 West Nakdong River diffraction grainsize analyses and X-radiographs revealed distinctive 275 275 275 275 275 400 300 325 A 1,000 375 ≈ 1964 changes associated with dam construction, and correlation of events 50 225 Marine-Dominated Mixed 325 Depth (cm) 350 00 5050 100 Very Low 750 300 300 300 300 300 400 350 100 Energy 100 Grainsize Percentage 400 325 Total Energy Energy Environment between cores conveys the episodic sedimentation corresponding to 75

Discharge(10 350 375 500 325 32500 5050 100 325 325 25003750 50 100100 lood gate releases. 325 175 cm Waves 0 Grainsize Percentage 350 Grainsize Percentage Shell 100 50 250 375 400400 50 350 Sand 350 350 350 350 Fig. 8) Complete grainsize composition proile and core photograph for 375 275 25 0 50 100 0 Silt 125 130-175 cm section of0 coreGrainsize ND50 19. Percentage A rapid100 increase in silt and clay percentage 400 Grainsize Percentage Tidal Currents 375 Clay 375 375 375 3750 corresponds to the construction of the dam in 1934. 400 Relative Energy % Seoul Shell 300 0 0 Daejeh Dam 00 5050 100 150 Sand 50 Cross Section A-A’ Grainsize Percentage Fig. 3) Time series of total monthly discharge from the Nakdong River Estuary 400 400 400 40000 5050 100 40025 Silt South Grainsize Percentage Table 1) Bathymetric survey data and accumulation rates for cores Noksan Clay Barrier Island Flood-Tidal ± Barrage from Jan. 1990 - Aug. 2010. 175 located a maximum 150 m from survey points. Dam Korea 0 50 1.40100 km 0 50 1001.06 km 0 50 1001.29 km 0 50 1.57100 km0 50 100 325 Delta 75 Grainsize Percentage Grainsize Percentage Grainsize Percentage Grainsize Percentage 50 Grainsize Percentage Central -1 Offshore ± Fig.0 6) Shore normal cross section through the W. Eulsuk Channel. Correlations are based on radiochemically derived data Core Dist. (m) 1985 Depth (m) 2009 Depth (m) SBath (cm yr ) Basin Mokpo Busan Shell 200 with minor depth change interpretations to respect grainsize proiles. Distances between cores are indicated and grainsize ND 11 350112 -1.22 0.06 5.33 Sediments 100 Sand 75 25composition is representedSilt as relative percentages. ND 12 148 -1.01 0.12 4.70 A B 225 ± ± Clay Depth (cm) ND 17 63 -1.46 -0.70 3.18 0 100 Image © 2012 GeoEye Noksan Dam Shell ND 18 37566 -0.61 0.03 2.67 Image © 2012 TerraMetrics 125 50 Image © 2012 DigitalGlobe ND 17 0 ND 15 ND 11 Sand 250 ND 8 ND 6 0 0 0 0 0 West Eulsuk Channel Shell 25 Silt ND 19 ND 19 Shell Shell Shell Shell 125 Shell " ND 14 " ND 14 Sand Clay B " " 75 Sand Sand Sand Sand Sand 400 25 275 Marine-Dominated 150 25 Silt 25 SiltSilt 25 Silt 25 Silt 25 Silt Mixed Discharge-Dominated Clay 50 150 ND 13 ND 13 Clay Clay Clay Clay Clay 100 100 " " ND 18 ND 18 100 0 50 100 Energy West Nakdong " ND 12 " ND 12 50 300 Nakdong River " " 50 50 50 50 50 Grainsize Percentage Total Energy 175 75 ± ND 7 ND 7 175 ND 17 DM " ND 17 " River " ND 15 " ND 15 Waves SH " " ND 11 ND 11 125 210 -1 137 -1 " ND 8 " ND 8 Pb (dpm g ) Cs (dpm g ) ND 19 " JN " XS 325 " ND 16 ND 6 ND 16 ND 6 75 7575 ND 11 75 50 50 " " " " 0.01 0.1 1 10 75 0 0.1 0.2 0.3 0.4 75 ND 14 100 " 200 200 ND 9 JA ND 9 0 0 ND 10 " ND 10 " 150 " ND 5 " ND 5 100 100100 350 Core Dist. (m) A 1985 Depth (m)B 2009 Depth (m) Dam Discharge " " 100 100 100 Tidal Currents Island 125 225 ND 11 112 -1.22 0.06 Relative Energy % ND 1 ND 1 50 50 Depth (cm) ND 2" ND 2" y = -155.89ln(x) + 183.41 " " ND 13 C SN 225 175 ND 12 148 -1.01 " 0.12 0 0 ND 3 ND 3 Depth (cm) R² = 0.823 " " 125 375 ND 18 ND 4 ND 4 125 125 125 125 125 ND 17 63 " -1.46 -0.70 " " Nakdong 100 150100 250 ND 12 1927 Shoreline 1963 Shoreline ND 18 66 -0.61" 0.03 Barrier Island Flood-Tidal Relict Tidal 200 ≈ 1983 Dam WG Kilometers Kilometers 250 150 400 Delta Sand Bar Bay Head 0 0.5 1 2 3 4 0 0.5 1 2 3 4 150 150 150 150150 150 150 ND 7 175 ND 17 " Central 275 " ND 15 Central 0 50 100 " Offshore Delta Fluvial 225 0 50 100 ND 11 Basin Basin Depth (cm) 175 Grainsize Percentage " ND 8 Sediments 175 200 175 -1 175200 -1 175 175 ND#1 5.25 " 275 SAvg = 5.45 cm y 200 SAvg = 5.72 cm y ND 16 ND 6 300 ND#2 " 4.93 " Depth (cm)Depth C D 250 (cm)Depth 250 250 ND#3 3.73 200 200200 200 200 ∼1964 200 Noksan Dam ± ± 225 ND#4 3.60 300 Depth (cm) 325 ND 9 ND#5 6.07 ND 10 " 275 300 300 " Coring Sites " Hwachun ID 225 ND#6 4.57 ND 5 Nakdong Dam Depth (cm) East Eulsuk Channel 225 225 225 " Depth (cm) Depth (cm) 225 225 Depth (cm) Depth (cm) Depth (cm) Accumulation Rate 250 350 ND#7 4.82 WG ND 19 ND 19 350 350 C " C " 8.0 cm/yr ND 14 ND 14 325 300 ND#8 5.00 ND 1 CG " " 250 ND 2" Marine-Dominated Mixed Discharge-Dominated MFG Nakdong Dam 250 250 250 250 ≈ 1964 250 ND#9 6.78 " Myungjido ± 275 Hwachun ID Shinho ID and Seawall 375 ND#10 1.5 cm/yr 9.07 100 Energy 100 ND 13 400 400 ND 3 " Eulsukdo " Noksan ID ND 13 " ND 19 ND 18 " 325 ND#11 5.59 Limit of " ND 18 350 Kilometers " ND 12 " 210 275 -1 137 -1 ND 4 Total Energy ND 14 " " ND 12 275 275 275 275 275 " W. Nakdong Tidal Influence ND 19 Myungji RD " PbXS (dpm g ) ND 30012 Cs (dpm g ) 210Pb (dpm g-1) ND#120 0.5 1 2 3 6.554 137 -1 W. Eulsuk " ND 7 400 XS ND 15 Cs (dpm g ) Waves River E. Eulsuk ND 17 ND 14 " ND 7 0.01 0.1 1 10 0 0.1 0.2 0.3 0.4 " ND 15 ND 17 " Shinpyung- ND#13 4.12 Channel " " ND 15 0.01 0.1 1 10 0 0.1 0.2 0.3 Dam Discharge Shinho ID Channel ND 11 " ND 11 MG 350 " ND 8 " ND 8 Changlim ID 0 0 ND#14 4.07 Myungji RD " " 300 00 50 100 Fig. 10) Interpolated sediment accumulation rates. Known values are based on 50 50 ND 16 ND 6 ND 6 375 300 300 300 300 3000 50 100 0 " " " ND 16 " Noksan ID ND 13Kilometers " 325 Grainsize Percentage radioisotopeND#15 analyses. Correlations4.91 of isochrons between cores were used to " Shinpyung- y = -181.40ln(x) + 59.75 y = -154ln(x) + 41.56 ND 18 " ND 9 ND 9 BH 375 50 50 ND#16 4.90 ND 13ND 10 " " 50 50 0 0.5 1 2 3 " 4 Changlim ID " ND 10 R² = 0.844325 calculate unknown rates. Letters correspond to conceptual model in Fig. 11. " R² = 0.825 Tidal Currents ND 12 " ND 5 ND 5 325 325 325 325 325 ND#17 3.36 ND 18 " " 350 NM 400 0 Relative Energy % " ND 1 ND#18 2.86 " ND 12 " ND 1 0 ND 2 " 100 100 100 0 "ND 17 ND 7 " ND 2 100 " DM " 400 Shell ND#19 2.19 ND 15 MG ND 3 ND 3 350 " " 350 350 350 350 350 " "ND 7 ND 4 Sand Table 2) Comparison of radioisotope accumulation rates derived from Nakdong ND 11 " " " ND 4 0 50 100 375 Barrier Island Flood-Tidal ND 8 ND 17 "ND 15 " 00 150 5050 100 150 150 210 137 150 JN " " 1971 Shoreline 1998 Shoreline Grainsize Percentage 25 Silt Pbxs and Cs proiles. Averaged rates were used for correlation. Bay Head Dam CG/MFG ND 16 ND 6 "ND 11 Grainsize Percentage -1 -1 Delta Kilomete"rsND 8 Kilometers SAvg = 6.25 cm375 y SAvg = 6.85 cm y 375 375 375 375 375 Clay -1 0 0.5 1 2 3 4 " 0 0.5 1 2 3 4 200 210 -1 137 -1 Delta JA BH "ND 16 ND 6 200 400200 Core Pb SAvg200 (cm yr ) Cs SAvg (cm yr ) Average∼1964 (cm yr ) Offshore Fluvial SN -1 " SAvg = 4.91 cm y Dredged " ND 9 50 ND 11 5.45 5.72 5.59 Sediments Depth (cm)Depth Depth (cm)Depth 400 0 50 100 Cross Section B-B’ Fig. 4) Historical shoreline changes of the Nakdong Estuary compiled from KHOA marine charts. 0 50 100 (cm)Depth 250 ND 10 400 400 400 400 400 (cm)Depth 250 X X X X NM "ND 5 "ND 9 250 250 Grainsize Percentage ND 12 6.25 6.85 6.55 Construction" and initiation of current islands occurring between publication dates of charts are ND 10 00 5050 100 ND 13 4.26 3.98 4.12 DY "ND 1 " 0 50 100 0 50 100 0 50 100 0 50 100 3000 50 100 300 " " Coring Sites indicated on the respective chart.ND 5 1.14 km Grainsize Percentage 2.5 km 1.45 km 1.12 km -1 2012 Shoreline Grainsize300 Percentage Grainsize Percentage 300 Grainsize Percentage Grainsize Percentage75 Grainsize Percentage SAvg = 4.48ND cm 15 y 4.48 4.91 4.69 ND 3 ND 2 1964 Kilometers " Cross Section A-A' "ND 1 ∼ ND 18 2.91 2.82 2.86 " 350 350 0 1 2 3 4 "ND 4 Cross Section B-B' ND 2 Fig. 7) Shore350 parallel cross section across the central portion of 350the Nakdong Estuary. Isochron identiication is maintained from ND 19 2.03 2.36 2.19 Fig. 11) Conceptual model for relative energy and facies distribution depending on dam discharge " 100 ND 3 Cross Section A-A’. 400 400 for a wave-dominated estuary. A) No discharge released B) Periodic (weekly to monthly), low Kilometers " 0 0.5 1 2 3 4 ND 4 400 400 energy discharge C) Consistent (daily to weekly), high energy discharge. Energy regimes are indicated as being either marine, mixed, or dam discharge dominated, and relative energy inputs Fig. 1) Detailed study area map showing core sampling locations and cross sections. 210Pb (dpm g-1) 137Cs (dpm g-1) 210 -1 137Cs (dpm g-1) 125 210Pb (dpm g-1) 137Cs (dpm2.193839357 g-1) XS ND 11 PbXS (dpm g ) ND 13 XS ND 18 are time averaged. Relative amounts of wave and tidal energy are assumed constant throughout Noksan, Nakdong, and Daejeh Dam locations, channel names, barrier islands, and 0.01 0.1 1 10 0 0.1 0.2 0.3 0.4 0.01 0.1 1 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.01 0.1 1 10 0 0.1 0.2 0.3 industrial (ID) and residential districts (RD) are indicated (WG=Western gate, 0 0 0 0 0 0 the estuary. 150 CG=Control gate, MFG=Main loodgate, JN=Jinudo, DM=Daemadeung, JA=Jangjado, y = -91.19ln(x) + 63.47 y = -105.12ln(x) + 58.71 50 50 50 50 BH=Bakhabdeung, SN=Sinjado, DY=Doyodeung, NM=Namutsitdeung, and y = -155.89ln(x) + 183.41 R² = 0.816 R² = 0.913 MG=Maenggeummeorideung). R² = 0.823 50 50 Conclusions: 175 100 100 100 100 ∼1964 The construction of two estuarine dams and numerous seawalls have greatly -1 -1 150 150 100 SAvg = 4.26 cm y 100 SAvg = 3.98 cm y 150 150 200 modiied the sediment transport dynamics of the Nakdong Estuary. These 200 200 200 200 Methods: -1 -1 modiications have eliminated large areas of intertidal zone, and SAvg = 5.45 cm y SAvg = 5.72 cm y 150 150 Depth (cm)Depth Depth (cm)Depth Depth (cm)Depth Depth (cm)Depth Depth (cm)Depth Depth (cm)Depth 225 19 Vibracores of 7.6cm diameter were collected between Oct. Depth (cm) • 250 250 ∼1964 ∼1964 250 250 appreciably reduced the tidal prism and river discharge. Sediment lux to 9-12, 2012. 200 -1 -1 300 300 200 300 SAvg = 2.91 cm y 300 SAvg = 2.82 cm y the estuary is restricted to loodgate releases which produce high low 250 velocities and episodic deposition. •X-radiographs taken at 64 kV for 1.6 mAS with a Medison X-ray 350 350 350 350 250 250 The implications of these alterations are evident in a rapid geomorphologic source and a Varian PaxScan® Amorphous Silicon Digital 275 400 400 400 400 shift from tide-inluenced to wave-dominated. High sediment Imager. 210 -1 137 -1 210 -1 137 -1 PbXS (dpm g ) Cs (dpm g ) Pb (dpm g ) Cs (dpm g ) 210Pb (dpm g-1) 137Cs (dpm g-1) ND 12 XS ND 15 300 XS ND 19 accumulation rates within the central estuary are due to a reduction in 0.01 0.1 1 10 0 0.1 0.2 0.3 0.4 0.01 0.1 1 10 0 0.1 0.2 0.3 0.01 0.1 1 10 0 0.1 0.2 0.3 0.4 •Grainsize analyses done via laser diffraction using a Malvern 0 0 0 0 0 0 accommodation space in the upper estuary. Additional evidence for this y = -154ln(x) + 41.56 y = -181.40ln(x) + 59.75 50 325 y = -63.02ln(x) + 37.79 Mastersizer 2000 Particle Size Analyzer. 50 50 R² = 0.825 50 R² = 0.844 R² = 0.935 reclassiication occurs as a series of barrier islands that have developed 50 50 210 210 100 100 100 100 post-dam construction accompanied by a redistribution of facies. • Pb activities were measured indirectly using Po and 350 150 counted by α-spectroscopy using a Canberra surface barrier 150 150 150 100 ∼1964 The increase in sediment trapping eficiency that has ensued resulting -1 -1 100 SAvg = 6.25 cm y SAvg = 6.85 cm y 200 200 ∼1964 375 from extensive coastal construction provides the basis for detector. 200 200 -1 SAvg = 4.91 cm y 150

Depth (cm)Depth The Depth (cm)Depth reevaluating traditional facies models for unaltered estuaries. Depth (cm)Depth 250 Depth (cm)Depth Depth (cm)Depth 137 250 (cm)Depth 150 •Activity of Cs measured by gamma spectroscopy (662 keV) 250 250 400 observations made within this study have allowed the development of a 300 300 -1 -1 200 -1 using a semi-planar intrinsic germanium detector coupled with 300 300 SAvg = 4.48 cm y SAvg = 2.03 cm y SAvg = 2.36 cm y ∼1964 0 50 100 conceptual model for facies distribution according to relative discharge 350 350 Grainsize200 Percentage CANBERRA DSA-1000 16K channel integrated multichannel 350 350 250 energy of the adjacent loodgate. analyzer. 400 400 400 400 250 210 137 210 Fig. 5) Excess Pb and Cs proiles. Error bars for activity are137 indicated or-1 occur within the range of the plot symbol.210 Regression-1 line for Pbxs 137 -1 210Pb (dpm g-1) Cs (dpm g ) PbXS (dpm g ) ND 18 Cs (dpm g ) and respective averageXS accumulation ratesND (S Avg13) are shown within plot. Note different depth scales depending on core. 0.01 0.1 1 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.01 0.1 1 10 0 0.1 0.2 0.3 0 0 0 0 y = -105.12ln(x) + 58.71 y = -91.19ln(x) + 63.47 50 R² = 0.913 50 R² = 0.816 50 50 100 100 ∼1964 -1 -1 100 SAvg = 4.26 cm y 100 SAvg = 3.98 cm y 150 150

200 200 150 150 Depth (cm)Depth Depth (cm)Depth Depth (cm)Depth Depth (cm)Depth ∼1964 250 250 -1 -1 200 200 300 SAvg = 2.91 cm y 300 SAvg = 2.82 cm y

350 350 250 250 400 400

210 -1 137 -1 PbXS (dpm g ) ND 19 Cs (dpm g ) 0.01 0.1 1 10 0 0.1 0.2 0.3 0.4 0 0

y = -63.02ln(x) + 37.79 R² = 0.935 50 50

100 ∼1964 100

150 Depth (cm)Depth Depth (cm)Depth 150

-1 -1 SAvg = 2.03 cm y 200 SAvg = 2.36 cm y 200

250