OUTLINES. Ruey-Chy Kao 1, Peter O. Zavialov 2, Chung-Feng Ding 1 MOTIVE METHODOLOGY CONCLUSION

Transcription

1 INVESTIGATION AND ASSESSMENT OF SUBMARINE GROUNDWATER DISCHARGE OF PING-TUNG NEAR SHORE AREA IN SOUTHWESTERN TAIWAN Ruey-Chy Kao 1, Peter O. Zavialov 2, Chung-Feng Ding 1 1.Tainan Hydraulics Laboratory, National Cheng kung University, Taiwan ROC 2.Shirshov Institute of Oceanology, Russian Academy of Sciences, Russia OUTLINES MOTIVE METHODOLOGY CONCLUSION 1 1

2 MOTIVE Submarine Groundwater Discharge (SGD) will carry pollutants into the sea, and will induce, Near shore ecosystem variation Inland sectors development How to increase the fresh water usage efficiency before SGD flows into sea? 2 Land subsidence prevention Surface water and ground water conjunctive utilization Groundwater flow regime in Ping-Tung Plain STUDY AREA 3 2

3 FIELD WORK - Station s Location Ping Tung County 4 METHODLOGY DATA ACQUISTION & DISCUSSION 5 3

4 FIELD SURVEY ITEMS and PURPOSES Hydrographic measurements: CTD (flow-through and profiling): temperature; salinity; density; dissolved oxygen; fluorescence, turbidity ADCP: velocity yprofiles UV-lidar: chlorophyll; DOM; suspended matter Transmissometer: light extinction SeaHorse current meters: velocity at bottom Water samples: (NOT Shown in this paper) Dissolved oxygen; Suspended solids; Total phosphorus; Phosphates; Nitrate; Nitrite; Ammonia; Metals. Analyses are done at THL and SIO RAS. Bottom sediment samples: (NOT Shown in this paper) Organic carbon; N-alkane composition (Chromo-mass spectrography) Benthic samples Analyses are done at SIO RAS TOTAL OF 16 STATIONS AND 24 STATIONS WERE OCCUPIED DURING 6 THE FEBRUARY AND OCTOBER CRUISES IN 2009 Boat for investigation 7 CTD profiling 4

5 Flow-through system Flow-through CTD Pump 8 Remover of bubbles Laser Flow-through Fluorometer LFF mounted onboard 9 Data registartion 5

6 Submersible transmissometer PUM-A PUM-A measures vertical profiles of the seawater light attenuation coefficient (closely related to concentration of suspended particles) and of seawater temperature Vertical profiles of the seawater light attenuation (blue) 10and seawater temperature (red) at Station 11 Lidar UFL-8 Mounting onboard Measurement 11 Laser flash at the sea surface at night time 6

7 Seawater sampling Sampling the surface and bottom sample of water column 12 Current measurements Work with the novel Sea Horse instrument to measure currents in the near-bottom layer 13 ADCP instrument 7

8 Sediment sampling 14 Stratification type 1: Impact of river discharges Locations

9 Stratification type 2: Fully mixed bottom layer Locations 9,10,12,13 16 Stratification type 3: Groundwater influence? Locations 11,14-16! The bottom layer is fresher than the above laying water 17 9

10 SGD influence Sea bottom Sea bottom 18 BLUE: Salinity RED: Temperature BLACK: Extinction 19 10

11 20 Possible SGD signal 21 11

12 22 SALINITY AT BOTTOM FEBRUARY 2009 Suspected SGD area 23 12

13 SUSPECTED SGD LOCATIONS FEBRUARY Second Survey 25 13

14 Stratification of SGD October 2009 On historical records, SGD found in this area, around station G the water column is almost fresh BLUE: Salinity RED: Temperature BLACK: Extinction

15 SALINITY AT BOTTOM OCTOBER 2009 Suspected SGD area 28 FLUORESCENCE AT BOTTOM OCTOBER 2009 Suspected SGD area 29 15

16 30 SUSPECTED SGD LOCATIONS OCTOBER 2009 Station 11 February 2009 October

17 Station 11 February 2009 STRUCTURE APPEARS ROBUST! October SGD 33 SUSPECTED SGD LOCATIONS BOTH CRUISES 17

18 Approximate estimation of the SGD volume rates Advection-diffusion balance: ws = k ds/dh, S = S 0 exp(wδh/k), wδz/k = ln(1 + ΔS/S 0 ) ΔS/S 0, w = k/s 0 ΔS/ ΔH Considering S 0 =30 psu, k=3x0-4 m 2 /s, w 10-5 ΔS/ ΔH [m/s] S(H) W: velocity of groundwater seepage S : salinity H : vertical coordinate K : eddy diffusivity ΔH : thickness of salinity drop ΔS : maximum salinity drop ΔH ΔS 34 Station 11 February 2009 October 2009 Summary of data on SGD-affected near-bottom layer at different locations in February and October 2009 February October Station ΔH, m ΔS, psu ΔH, m ΔS, psu G Unknown Unknown

19 Station 11 February 2009 February: y October 2009 ΔS=0.04 psu, Δz=2 m W = 2x10-7 m/s Q 0.2 g/ s m 2 October: ΔS=0.02 psu, Δz=0.5 m W = 4x10-7 m/s Q 0.4 g/ s m 2 36 October: ΔS= psu, Δz=0.2 2 m W = 10-6 m/s Q 1 g/ s m 2 estimated volume rate: ~ g/s/m / 2 360~3600 ml/hr/m

20 Measurement of the SGD volume rates drum type seepage meter Deployed 4 sets of seepage meter nearby suspected area, extending from 8 m to 11 m isobaths on January 27, Seepage p g collecting devices had been retrieved on February 8, Average seepage rate is about 6.0 ml/m 2 /hr during dry season. 2011/01/27~02/08 12 days, Drum Diameter: 60 cm St. ID V t A seepage rate (L) (hr) (m 2 ) (L/m 2 /hr) SGD E-03 SGD E-03 Average 5.96E-03 V: volume of water in the collection bag of drum type seepage meter (liter) t: measured time interval (hour) A: cross-section of drum type seepage meter (square meter) SGD4 38 CONCLUSION The survey detect SGD signals in Ping Tung shelf by oceanographic measurements, and quantify SGD influence on sea water column. There do exist distinctive features in Ping Tung shelf restricted to the very near-bottom layer that are very likely associated with SGD. These features are typically small-scale patches, but their locations seem to be robust. The plausible locations of SGD have been identified, and the corresponding anomalies quantified. The SGD influence is shown to be confined to the bottom up 0.2 to 1.5 m of the water column, and produce observable anomalies in Salinity (0.01~0.05 psu maximum), turbidity and fluorescence. The average measured rate of SGD discharge in study area is 6.0 ml/hr/m 2 in dry season. More data is needed to fully describe the spatial and temporal pattern of SGD of Ping-Tung shelf

21 SGD