Effects of Winds on Hypoxia Formation in the Pearl River Estuarine Coastal Waters

Transcription

1 The 1th International Estuarine Biogeochemistry Symposium May 19-22, 28, Xiamen China Effects of Winds on Hypoxia Formation in the Pearl River Estuarine Coastal Waters Kedong YIN 1,2,3, Paul J. Harrison 2, Josheph Lee 4, Weihua Zhou 3 1 LED, South China Institute of Oceanology, CAS, Guangzhou, China kdyin@scsio.ac.cn 2 AMCE Program, Hong Kong University of Science and Technology Kowloon, Hong Kong, China 3 Australian Rivers Institute, Griffith University (Nathan Campus) Brisbane, Queensland, Australia 4 Department of Civil Engineering, University of Hong Kong

2 Outline Global and Regional Hypoxia Perspectives Nitrogen Enrichment in the Pearl River Variability of Dissolved Oxygen in Hong Kong Oceanography Processes Monsoons River Outflow Effects of winds in preventing hypoxia formation in Hong Kong

3 Eutrophication Symptoms for Input of Anthropogenic Nutrients Riverine, Atmospheric Nutrient Enrichment River Benthic-Pelagic exchange Algal Biomass Increase Resuspension Benthic Biogeochemical Processes Sinking Decomposition South China Sea O 2 Decrease

4 World Fertilizer Consumption Millions Tons 195 2

5 Global perspective: Dead Zones Source: UNEP, GEO Yearbook 23 (Nairobi: 24) Dead Zone: Dissolved oxygen is < 2 ml/l UNEP (2) estimated, ~2 dead zones in 27.

6 Places suffered from Persistent Hypoxia

7

8 Mississippi River: Average annual concentrations Turner et al Proc. Natl. Acad. Sci. USA ~1 µm Years

9 Northern Gulf of Mexico: a large area of hypoxia dead zone (2, km 2 ) (<2 O 2 mg/l) Science 281, 1998

10 Historic Trend of Nutrients in Yangtze River Maximum DIN Mean Minimum NO 3 -N PO 4 -P N- fertilizer P- fertilizer

11 Persistent Cyanobacterial Blooms in Dianchi Lake in Kunming

12 Harmful Algal Blooms in East China Sea off the Yangtze River Estuary (Satellite View) May 4, 2 About 2 times size of the dead zone Yangtze River

13 The Dead Zone in the Chang Jiang Estuary-East China Sea Li et al., 22 13,7 km 2

14 Pearl River Drainage Basin River-2, 2 km long Area -454, km 2 1 million people 2 km

15 Pearl River Estuary Pearl River 2 nd largest river in China 13 th largest river in the world South China Sea

16 NO 3 (µm) Huo and Yin unpub NO 3 at a PR mouth N 22.8 N 22. N 22.4 N 22.2 N 22. N 21.8 N 21. N 21.4 N 21.2 N 21. N A1 A2 A3 At River Mouth A4 A5 A A7 A8 B1 B2 B3 B5 B4 B B7 B8 C1 C2 C3 C4 C5 C C7 C8 C9 C E E 114. E E 115. E 1 um D1 D2 D3 D4 D5 D D7 E1 E2 E3 E4 E5 E E7

17 NO3 Distribution during summer Guangzhou Guangdong Province Shenzhen Zhuhai Hongkong Latitude Longitude Huo and Yin unpub

18 Monthly Average of total inorganic nitrogen during (Yin 22) N 2 4 Kilom Pearl River Shenzhen, Guangdong Lingdingyang New Territories # Macau Lantau Isl. HK Isl. PR estuary waters Southern Water Mirs Bay TIN 5 Surface Bottom Month 5

19 Nitrogen is high in the Pearl River estuarine coastal waters has increased 3 times in the past comparable to Mississippi and Yangtze which leads to hypoxia What about dissolved oxygen in the Pearl River estuarine influenced coast?

20 Monthly Average of Dissolved O 2 during Dissolved O 2 does not drop to hypoxia! N 2 4 Kilom Pearl River Shenzhen, Guangdong Lingdingyang New Territories # Macau Lantau Isl. HK Isl. Western waters Southern Water Mirs Bay O 2 (mg l -2 ) Month Surface Bottom

21 Lack of the decreasing trend! 12 8 Bottom NM N Pearl River 2 4 Kilom Shenzhen, Guangdong Lingdingyang New Territories 4 # Macau Lantau Isl. HK Isl. Dissolved O 2 (mg L -1 ) SM18 MM Yin et al. 24

22 Bottom Dissolved O 2 in 198s August 1984 July 1981 Summer m mg/l Yin et al. 24 CSR

23 DO in Hong Kong waters, back in (Chau & Abessor 1958, HKU Fish. J. No.2: 43-57, Fig. 11) Bottom August >3 mg/l mg/l ~2 mg/l

24 Seasonal hypoxia does not appear to occur over the coastal scale of the Pearl River estuarine influenced waters in South China Sea However, there are local episodic events of hypoxia

25 Some ecosystems can accommodate a nutrient enrichment without showing apparent eutrophication symptoms. So, what makes the Pearl River Estuary robust to N enrichment? Ecosystem Buffering

26 Ecosystem Buffering Anthropogenic input Ecosystem Buffering Capacity Impacts: Excessive algae Red tides Low DO waters Seasonality: Dry and Wet Spatial and Temporal Variability Climatic events Monsoons River outflow Tidal cycles Rainfall Circulation Stratification Mixing Light Salinity Temperature Nutrients Nutrient Ratios Algal Growth Nutrient utilization Nutrient Limitation DO consumption Drivers Processing Fields Biological responses

27 Ecosystem Buffering Effects of winds Seasonal scale event Episodic events

28 Seasonal Scale Event

29 South China Sea 3 million km 2 Pearl River Estuary South China Sea Largest inland sea after 4 open Oceans 3 times as large as the total of other China coastal seas

30 Pearl River Estuary Pearl River 2 nd largest river in China 13 th largest river in the world South China Sea

31 Northeast Monsoons January Southwest Monsoons July

32 Pearl River Discharge & Rainfall Rainfall in Hong Kong during Monthly Average Rainfall (mm) Dry Season Wet Season Pearl River Discharge (m 3 s -1 ) Month

33 Pearl River Estuarine Coastal Plume

34 Physical processes induced by monsoons and Pearl River discharge

35 Northeast Monsoon Coriolis effect China south coast Coastal Downwelling Southwest Monsoon Coriolis Force Coriolis effect Coastal Upwelling

36 Estuarine Circulation in the Pearl River Estuary and Coastal Waters Two Layer Opposite Flow Circulation River Outflow High N Low P Estuarine/Coastal Plume Salt Wedge Oceanic Water High salinity Cold water Low O 2 Nutrient-poor

37 Pearl Estuary Salinity in Summer South China Sea B1 B4 B7 C1 C4 C7 C1 2 D ept h ( m ) 4 8 River Sea 22 July Cruise (Summer) Vertical Variation of Salinity in Transect B-C A5 E 21. N D4 C A E7 D N1 18C7 2 Relative Distance(km) 23. N 22.8 N 22. N 22.4 N 22.2 N 22. N 21.8 N 21.2 N 21. N Oceanic Waters A1 A2 A3 A4 A7 A8 B1 B2 B3 B5 B4 B B7 B8 C1 C2 C3 C4 C5 C8 C9 C E E 114. E E 115. E D1 D2 D3 D D7 E1 E2 E3 E4 E5

38 Role of Monsoon Induced Physical Oceanographic Processes in Eutrophication Winter Water Masses: Offshore water dominates due to low river discharge Circulation: Downwelling Summer Residence time: Longer Annual flushing mechanism to reduce the accumulative effects of nutrients Water Masses: Circulation: Residence time: Freshwater influence dominates at the surface, oceanic waters dominate at the bottom Two layer flows Shorter Within-season flushing mechanisms

39 Wind Episodic Events

40 Stn Stn Depth (m) A Depth (m) Stn Stn B Distance (km) Local Episodic Hypoxia

41 Localized hypoxia 5 1 Stn Depth (m) A 2 4 8

42 Legend Water sampling stations selected Boundary of Special Administrative Region N Shenzhen MM1 MM2 MM3 MM4 MM7 MM17 MM5 DM2 DM1 DM4 DM3 TM3 TM5 TM4 TM TM7 TM8 MM MM1 DM5 New Territories TM2 NM5 VM14 PM5 PM1 PM4 PM2 PM3 MM15 NM8 NM NM3 NM2 Lantau Island NM1 SM11 SM1 WM4 WM3 VM12 VM8 WM2 SM9 SM7 VM15 WM1 VM7 VM Kowloon VM5 VM4 Hong Kong Island VM2 VM1 JM3 JM4 PM EM1 EM2 PM7 PM8 PM9 PM1N MM14 SM2 SM13 SM17 SM12 SM SM7 SM SM18 5 1km SM5 SM3 SM4 SM2 SM18 SM19 SM1 EM3 MM8 MM8 MM13 Figure showing EPD routine water sampling stations

43 Wind Speed (m s -1 ) Wind Direction N NW W SW S SE E NE N August September October 22

44 Depth (m) Depth (m) Depth (m) Depth (m) Depth (m) September Sept Oct Salinity MM Temperature 7 DO Light Penetration Chl a

45 Depth (m) Depth (m) Depth (m) Depth (m) Depth (m) September Sept Oct SM Salinity Temperature 5.5 DO Chl a Light Penetration

46 Legend Water sampling stations selected Boundary of Special Administrative Region N Shenzhen MM1 MM2 MM3 MM4 MM7 MM17 MM5 DM2 DM1 DM4 DM3 TM3 TM5 TM4 TM TM7 TM8 MM MM1 DM5 New Territories TM2 NM5 VM14 PM5 PM1 PM4 PM2 PM3 MM15 NM8 NM NM3 NM2 Lantau Island NM1 SM11 SM1 WM4 WM3 VM12 VM8 WM2 SM9 SM7 VM15 WM1 VM7 VM Kowloon VM5 VM4 Hong Kong Island VM2 VM1 JM3 JM4 PM EM1 EM2 PM7 PM8 PM9 PM1N MM14 SM2 SM13 SM17 SM12 SM SM7 SM SM18 5 1km SM5 SM3 SM4 SM2 SM18 SM19 SM1 EM3 MM8 MM8 MM13 Figure showing EPD routine water sampling stations

47 Temperature ( O C) Depth (m) SM SM7 Aug 19 Aug Sep Sep 17 Sep Speed (m.s -1 ) Wind Dir N W S E N 1 15 Augest September

48 Depth (m) Speed (m.s -1 ) Wind Dir SM SM7 Aug 19 Aug 27 Dissolved Oxygen (mg/l) Sep Sep 17 Sep N W S E N 1 15 Augest September

49 Wind (km h -1 ) August Date

50 SM18, 24 h time series, August 2: Temperature Aug Aug Aug Time (hours) Time (hours) Time (hours) Neap tide August 2 Spring tide August 2 Neap tide August Depth (m) Tidal Height (m) T1 T2 T3 T4 T5 T T7 T8 T1 T2 T3 T4 T5 T T7 T8 T1 T2 T3 T4 T5 T T7 T8

51 SM18, 24 h time series, August 2: Salinity Aug Aug Aug Time (hours) Neap tide August 2 Time (hours) Spring tide August 2 Time (hours) Neap tide August 2 Depth (m) Tidal Height (m) T1 T2 1 T3 T4 T5 T T7 T8 T1 T2 T3 T4 T5 T T7 T8 3 2 T1 T2 T3 T4 T5 T T7 T8

52 SM18, 24 h time series, August 2: Dissolved Oxygen Aug Time (hours) Aug Time (hours) Aug Time (hours) Depth (m) Neap tide August 2 Spring tide August 2 Neap tide August Tidal Ht (m) T1 T2 T3 T4 T5 T T7 T8 T1 T2 T3 T4 T5 T T7 T8 T1 T2 T3 T4 T5 T T7 T8

53 Effects of winds during summer : Winds > m s -1 was found to be a wind event, which --mixed the water column and nutrients --caused a phytoplankton bloom in summer in the Strait of Georgia (Yin et al MEPS).

54 Wind speed above m s -1 during July Wind Speed (m s -1 ) August September

55 Frequency for the month during June 4 2 Frequency (days per month) July August Wind Speed (m s -1 )

56 Monthly accumulative frequency during Month Frequency (days) 3 June July August Wind Speed (m s -1 )

57 Effects of winds during summer : Winds > m s-1 frequently interrupts the water column stratification, and mixes oxygen downwards prevents the formation of seasonal hypoxia in the Pearl River influenced coastal waters. However, August is vulnerable to episodic events of hypoxia Climate change wind speed change: may trigger more frequently occurrences of hypoxia events

58 Acknowledgement South China Sea Institute of Oceanology, Chinese Academy of Sciences: Innovative Project for large scale data Hong Kong Research Grant Council Projects HKUST478/5M Hong Kong University Grant Council Project AoE/P-4/4-1 Hong Kong EPD for providing water quality data