Impact of Damming and Eutrophication on DSi:DIN Variation in River Water, a case study of Yahagi River, Japan

Transcription

1 Impact of Damming and Eutrophication on DSi:DIN Variation in River Water, a case study of Yahagi River, Japan Masashi Kodama* * & Katsuhisa Tanaka** *National Research Institute of Fisheries Science, Fisheries Research Agency, Japan ** Seikai National Fisheries Research Institute, Fisheries Research Agency, Japan

2 Introduction Contents Materials & Methods Variations of DSi,, DIN concentration in Yahagi River Impact of high N loading on DSi:DIN ratio Impact of Damming on DSi:DIN ratio

3 Introduction Profile of Japanese rivers & Importance of Si for marine environment

4 Profile of Japanese Rivers Short (max. length: 367 km) Japanese Rivers World Rivers Rivers Length (km) Yoshimura et al., 2005, Berner & Berner, 1996 Drainage area (km2) Average discharge Location (m 3 s -1 ) Shinano , Honshu Tone , Honshu Ishikari , Hokkaido Yahagi 117 1, Honshu Amzon 8,300 6,150, ,440 America Changjiang 6,380 1,940,000 21,790 China Mississipi 6,019 3,270,000 16,200 America Yellow 5, ,000 1,840 China Zaire 4,380 3,820,000 39,620 Africa Danube 2, ,000 6,400 Europe Rhine 1, ,000 2,200 Europe

5 Profile of Japanese Rivers (cont.) Steep (average slope: 0.44 %) Short residence time Yahagi River J. De Rike (Dutch engineer) remarked This is not a river, but a cataract Longitudinal profiles of major rivers in Japan and continental rivers (Yoshimura et al,. 2005).

6 Importance of Si for Diatoms Dissolved silicate (DSi): Essential for Diatoms frustules Element composition of marine diatoms Si:N:C=1:1:106 (Brzezinski, 1985) Availability of DSi can regulate species composition of phytoplankton Experimental mesocosm (Egge & Aksnes, 1992) Dominance of diatoms cease below DSi = 2 μm

7 Impact of Damming on Marine Environment (case of Danube River & Black Sea) After construction of the dam, DSi : 140 μm 58 μm DSi:DIN : number of phytoplankton bloom Diatoms: 8 19 (2.5-fold) Non-diatoms: 4 23 (6-fold) Winter silicate concentration in the Black Sea (Humborg, et al., 1997)

8 Importance of Si for Marine Silica deficiency (low DSi or high N input) Environment Bloom of non-siliceous phytoplankton species if toxic species Fisheries damage Fish(shellfish) killing Shellfish poisoning paralytic, neurologic, diarrheal, amnestic

9 Nutrient Concentration in World Major Rivers Pristine Developed River Period Si N P Si:N Si:P Amazon Before May-Jun Mackenzie Yukon Zaire Nov May Mississippi Po Rhine Seine Yangtze (Changjiang) Jun Yellow (Hwanghe) Aug Vörösmarty, et al., 1998 Si:N ratio declined in developed rivers

10 Could it happen in Japanese rivers? Environment of Japanese rivers Short residence time of river water Volcanic country High temperature and precipitation However Numerous dams 2,675 dams (fourth highest number) 0.71 per 100km 2 (third greatest density ) No cross-river facilities only 3 rivers (of 113 major rivers) High population density, Industrialization, Agriculture Objective Assess current status and possibility of Si depletion in Japanese river

11 Materials & Methods (Study site) Location of Yahagi River.

12 Materials & Methods (outline of monitoring) About Yahagi River Drainage Area: 1,830 km 2 Length : 117 km Discharge: 35 m 3 s 1 Population: 1.4 million 7 dams in the main stream Stn. M Observation Period Stn. Y: Jun Jun Stn. M: Jun Jun Sampling interval Once or twice a month Measuring subjects Dissolved silicate (DSi) Dissolved inorganic nitrogen (DIN) Dissolved inorganic phosphorus (DIP) Phytoplankton composition Discharge Ministry of Land, Infrastructure and Transport of Japan Stn. Y Study area and sampling stations in the Yahagi River.

13 Variations of DSi,, DIN concentration in Yahagi River

14 Discharge (m 3 s -1 ) DSi (μm) DIN(μM) Variations of Discharge, DSi,, DIN Average: 34.8 m 3 s 1 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/1 Stn. Y Average: 162 μm 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/1 Average: 72 μm Stn. M Stn. Y Stn. M 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/ Higher than world rivers But lower than 1950 s (no dams) 240 μm (Kobayashi, 1960) Higher at Stn. Y (Lower Stn. )

15 Discharge (m 3 s -1 ) DSi (μm) DSi:DIN atomic ratio Variations of Discharge, DSi,, DIN Stn. Y Stn. M Average: 34.8 m 3 s 1 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/1 Average: 162 μm Stn. Y Stn. M 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/1 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/1 9/1 12/1 3/1 6/ Higher than world rivers But lower than 1950 s (no dams) 240 μm (Kobayashi, 1960) Lower at Stn. Y Average at Stn. Y: 2.3 < Danube River ( = 2.8) < 1950 s (= 16 ) (Kobayashi, 1960)

16 DSi,, DIN & DSi:DIN vs Discharge DSi, DIN (μm) DSi DIN DSi: DIN atomic ratio m 3 s 1 Average: Jun - Oct Nov - May Daily average discharge (m 3 s -1 ) Daily average discharge (m 3 s -1 ) Relationships between daily average discharge and DSi, DIN at Stn. Y. Relationship between daily average discharge and DSi:DIN ratio.

17 Impact of high N loading on DSi:DIN ratio

18 Impact of High N Loading from Lower Tributaries Same proportion Q(X10 7 m 3 ),DSi (X10 2 ton), DIN(X10 ton), DIP(ton) Q DSi DIN DIP Stn. M Stn. Y Sewage plant 10 km Annual discharge (Q) and loads of DSi, DIN and DIP in the Yahagi River (blue: from headstream to Stn. M, purple: from Stn. M to Stn. Y, yellow: from sewage plant (from June 2002 to June 2003). Drainage area of Stn. M and Stn. Y High N, P load from lower tributaries & sewage plant

19 Importance of Discharge for DSi:DIN ratio Δ (DSi:DIN) R 2 = 0.51 Decreasing rate of DSi:DIN became smaller with an increase of main stream discharge Daily average discharge (m 3 s -1 ) Main stream discharge is important to dilute high DIN loading Difference of DSi:DIN ratio (=Δ(DSi:DIN)) between Stn. M and Stn. Y versus daily average discharge at Stn. M (from June 2002 to June 2003).

20 Impact of Damming on DSi:DIN ratio

21 Diatom Bloom in Dam Reservoir Diatoms (?0 3 cells ml 1 ) Asterionella formosa relative abundance (%) Stn. M 6/1 7/1 8/1 9/1 10/111/112/1 1/1 2/1 3/1 4/1 5/1 6/1 Temperature Stn. Y A. formosa 6/1 7/1 8/1 9/1 10/111/112/1 1/1 2/1 3/1 4/1 5/1 6/ Asterionella. formosa Planktonic diatom Common in temperate lakes Forms star-shaped colonies Dominant in <10 ºC Water temperature ( ) GES/bacillariophyceae.htm Upper: Variations of diatom cell density at Stn. M and Stn. Y Lower: Variations of Asterionella formosa (diatom) relative abundance and water temperature.

22 Effect of Dam Exchange Rate on Diatom Bloom & DSi:DIN ratio Diatoms (?0 3 cells ml -1 ) Jun.-Oct. Nov.-May DSi:DIN atomic ratio Exchange Rate (%) Diatoms ( 10 3 cells ml -1 ) Relationships between cumulative water exchange at Yahagi Dam reservoir 7 days before sampling and diatom cell density at Stn. M. Relationship between diatom cell density and DSi:DIN ratio at Stn. M.

23 DSi,, DIN Concentration in Coastal Area DSi (μm) Jan.-May. Jun.-Dec. DSi:DIN = 1 DSi = 2.0μM DSi:DIN < 1 Jan-May: 24 %, Jun-Dec: 4 % DSi:DIN < 1 84 % is Jan-May DSi < 2.0 μm Jan-May: 34 %, Jun-Dec: 27 % DIN (μm) DSi:DIN < 1 & DSi<2.0 μm 74 % is Jan-May DIN concentration vs DSi concentration in Chita Bay Surface, 0-4 m (Aichi Fisheries Research Institute)

24 Summary Variations in dissolved silicate (DSi( DSi) ) concentration and ratio to dissolved inorganic nitrogen (DSi:DIN( ratio) ) were investigated in the Yahagi River, Aichi Prefecture, Japan over a three-year period. Regarding the DSi:DIN ratio, there is a possibility of Si depletion in the Yahagi River and Chita Bay during the low flow period. It is suggested that the increased nitrogen loading due to land development and lower river flow induced by water resources development, such as dam construction,, brought about not only a decrease in the DSi supply to the coastal sea but also a reduction in DSi:DIN ratio even in Japan.

25 Acknowledgements Members of Aichi Fisheries Research Institute Tomoki SAWADA Motoi TUZUKI Yuji YAMAMOTO Nobuo KURODA Toyoshige YANAGISAWA