*Minagawa M, Usui T, Miura Y, Nagao S, Irino T, Kudo I, and Suzuki K, Graduate School of Environmental Science, Hokkaido University, Sapporo , Japan *also Faculty of Environmental Earth Science, Hokkaido University, Sapporo , Japan Spatial and temporal variability of nutrient impacts to a coastal biogeochemical systems driven by river water from cultivated land areas Sampling location ● Sapporo Tokachi River Observation and Samples ● Stations off Tokachi (Hydrographic, Nutrients, POM, traps & sediments ) May, August and Nov / April, May, July, Nov. and Dec / March 2005 ▲ River stations (Hydrographic, nutrients, POM, Sediments) from May 2003 to Sept Analyses : temperature, salinity, NO3, NO2, NH4, Si, P, chlorophyll a, POC, PON δ 13 C of POC and δ 15 N of PN in river water and seawater North Pacific 42.8°N 42.2°N 200 m 1000 m 100 m 500 m 143.6°E144°E 144.4°E 42.6°N 42.4°N ▲ ▲ North Pacific Tokachi River Objectives To estimate nutrients impact from Tokachi river water to the coastal system To evaluate origin of carbon and nitrogen of POM off Tokachi coast To elucidate loading pattern of riverine materials from cultivated land To estimate influence of nutrient impact to coastal production Vertical profile of Salinity May Salinity Depth (m) May Salinity Depth (m) Salinity Depth (m) August 2003 Nov ◆ St.T31: river mouth ■St.T33: in plume ▲St.T35: Outside of the plume ▲ ◆ °N 42.2°N 200 m 1000 m 100 m 500 m 143.6°E144°E 144.4°E 42.6°N 42.4°N Tokachi River ■ St.T31 St.T33 St.T35 Conclusions °N 42.2°N 200 m 1000 m 100 m 500 m 143.6°E144°E 144.4°E 42.6°N 42.4°N Tokachi River August °N 42.2°N 200 m 1000 m 100 m 500 m 143.6°E144°E 144.4°E 42.6°N 42.4°N Tokachi River 42.8°N 42.2°N 200 m 1000 m 100 m 500 m 143.6°E144°E 144.4°E 42.6°N 42.4°N Tokachi River Sea surface salinity off Tokachi May 2003 Nov B13A-1053 Tokachi river Flood discharge: m 3 /sec Catchment area: 9010 Km 2 Population: (density= 33 /Km 2 ) °E °N 42°N 144°E 200m 1000m 2000m Water depth (m)  13 C of surface sediments and POC Tokachi River  13 C δ 13 C (‰) ×St.T35 ×St.T33 St.T31 × St.T31(0-5m) POC （ May ） St.T33 POC （ May ） St.T35 POC （ May ） urface Sediments Surface sediments record  13 C pattern indicating terrestrial organic carbon that is rapidly diluted by marine organic carbon on the shelf and most parts of organic carbon are replaced by marine origin toward pelagic (> 200m depth) J F M A M J J A S O N D Month River discharge (m 3 /s) 2003 J F M A M J J A S O N D Month River discharge (m 3 /s) J F M A M J J A S O N D Month Tokachi River (Discharge) August 10 ： 4634 m 3 /s Sept. 8 ： 2072 m 3 /s ●River water sampling ■Seawater sampling Main water sources: Spring-Summer: Snow-melt water Summer-Autumn: Rainfall NO NO 2 - (μM) J F M A M J J A S O N D Month NO NO 2 - (μM) Surface seawater Water quality of the Tokachi River J F M A M J J A S O N D Month POC (μM) Surface seawater J F M A M J J A S O N D Month δ 13 C (‰) δ 13 C of POC (‰) J F M A M J J A S O N D Month δ 15 N of PN (‰) δ 15 N (‰) Surface seawater ■ 2003 ● 2004 ▲ 2005 ■ 2003 ● 2004 ▲ 2005 Sept. 8, 2005 ： 2430 μM ▲ J F M A M J J A S O N D Chl.a (μg/l) Month Chl.a at 0 m depthPOC at 0 m depth POC (μM) J F M A M J J A S O N D Month ■ 2003 ● 2004 ▲ 2005 NO NO 2 - (μM) Nitrate + nitrite at 0 m depth J F M A M J J A S O N D Month Seasonal changes at Stn.T35, (outside of the river plume) J F M A M J J A S O N D Month Phosphate at 0 m depth PO 4 3- (μM) Chl.a (μg/l) POC (μM) Salinity δ 15 N-PN (‰) Salinity Chl.a POC δ 13 C-POC (‰) Salinity Chl.a, POC and isotope ratios vs. Sal May, August, November, 2003 δ 15 N of PNδ 13 C of POC River POC River PN River POC fraction (%) Fraction of riverine POC estimated by δ 13 C ◆ May ◆ August ◆ November  13 C and  15 N of soil, POM and sediments River POM (sinking POM) might supply more than 40 % organic CN sources of coastal sediments in the Tokachi shelf (<200m) ・ River water plays an important role for supplying significant amount of nutrients and POM on the shelf off Tokachi (water depth<200 m) ・ Discharge by snow-melting (in early summer) and heavy rain (in summer and autumn) conveys nutrients to support major production at the coastal area in summer ・ Blooming in spring and autumn are supported by nutrients in the pelagic subsurface seawater (Oyashio current) ・ Annual load of DIN, PO 4 3-, Si(OH) 4 and POC from the Tokachi River to the coastal waters is corresponding to 37, 3.3, 145 and 7.3% of primary production reported in the Oyashio Water, respectively. References: Usui T. et al. (2006) Distribution and sources of organic matter in surficial sediments on the shelf and slope off Tokachi, western North Pacific, inferred from C and N stable isotopes and C/N ratios, Marine Chemistry 98, 241–259