The heat budget of a proglacial stream, Phelan Creek, from the Gulkana Glacier, Alaska, is estimated by using the hourly time series of stream water temperature, discharge and meteorology obtained in the summer of 2006. As an analytical result, the net shortwave radiation and bed friction occupied 32.1 and 38.2% of the total thermal input to the stream, respectively. The time series of the water temperature were simulated by a deterministic model with the coupling of the heat budget and the thermal advective diffusion equation. The simulated result is agreeable to the observed one with the Nash-Sutcliffe efficiency (NASH) of 0.747 and the root-mean-square error (RMSE) of 0.2368C over the observation period. However, under condition that the rainfall of more than 1 mm h À1 occurs continually for more than a day, the simulation was less reasonable with NASH ¼ 0.225 and RMSE ¼ 0.2268C. This is probably because the relatively warm subsurface flow input to the stream channel from the non-glacial area.

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The covered-ice breakup in subarctic to arctic rivers in the early snowmelt season often gives any damage to instruments monitoring physical and chemical factors of water. The serious condition has brought few time series data during the snowmelt runoff except the river stage or discharge. In this study, the contribution of snowmelt runoff to the discharge and sediment load is quantified by monitoring water turbidity and temperature at the lowest gauging station of U. S. Geological Survey in the Yukon River, Alaska, for more than 3 years (June 2006 to September 2009). The turbidity was recorded by a self-recording turbidimeter with a sensor of infrared-ray back-scattering type, of which the window is cleaned by a wiper just before a measurement. The turbidity time series, coupled with frequent river water sampling at mid-channel, produce time series of suspended sediment (SS) concentration, particulate organic carbon (POC) concentration and particulate organic nitrogen (PON) concentration (mg?L^–1) by using the high correlation (<i>R</i>² = 0.747 to 0.790; ^P < 0.001) between the turbidity (ppm) and the SS, POC and PON concentrations. As a result, the three-year time series (5 September 2006 to 4 September 2009) indicated that the snowmelt runoff, continuing about 40 days (late April or early May to early June), occupies 14.1% - 24.8% of the annual discharge (1.94 × 10¹¹ to 2.01 × 10¹¹ m³), 8.7% - 22.5% of the annual sediment load (3.94 × 10⁷ to 5.08 × 10⁷ ton), 11.6% - 23.7% of the annual POC flux (4.05 × 10⁵ to 4.77 × 10⁵ ton), and 10.3% - 24.5% of the annual PON flux (2.80 × 10⁴ to 3.44 × 10⁴ ton). In the snowmelt season, the peak suspended sediment concentration preceded the peak discharge by a few days. This probably results from the fluvial sediment erosion in the river channels

In the Bering Sea around and off the Yukon River delta, surface sediment plumes are markedly formed by glacier-melt and rainfall sediment runoffs of the Yukon River, Alaska, in June– September. The discharge and sediment load time series of the Yukon River were obtained at the lowest gauging station of US Geological Survey in June 2006–September 2010. Meanwhile, by coastal observations on boat, it was found out that the river plume plunges at a boundary between turbid plume water and clean marine water at the Yukon River sediment load of more than ca. 2500 kg/s. Grain size analysis with changing salinity (‰) for the river sediment indicated that the suspended sediment becomes coarse at 2 to 5‰ by flocculation. Hence, the plume’s plunging probably occurred by the flocculation of the Yukon suspended sediment in the brackish zone upstream of the plunging boundary, where the differential settling from the flocculation is considered to have induced the turbid water intrusion into the bottom layer.

Sediment plumes, released to the Bering Sea from the delta front of the Yukon River, Alaska, are initiated mainly by glacier-melt sediment runoffs in the glacierized regions of the Yukon River drainage basin. The surface sediment plumes are extended around the fan-shaped Yukon River delta, which is followed by the northwestward dispersion. During continuous measurements of the Yukon River discharge and sediment load, behaviors of the sediment plumes were explored by shipboard and coastal observations in the Bering Sea. At the high river sediment load of ca. 2500 kg/s, the plume partially plunged into the sea bottom layer. The plunging probably originated in the nepheloid-layer formation from the flocculation of river-suspended sediment, of which more than 90% wt. is silt and clay (grain size d < 63 μm). In order to numerically obtain the area of the surface sediment plumes, a satellite image analysis was performed by using three near-infrared bands in MODIS/Aqua or MODIS/Terra. The plume area was significantly correlated (R2 = 0.735, p < 0.01) to the sediment load averaged for the two days with time lags of 20 days and 21 days to the date of a certain satellite image. Hence, the dispersion of plume-suspended sediment appears to be controlled by the sediment runoff events in the Yukon River rather than the northward “Alaskan Coastal Water”.

The nutrient concentration of river water was obtained in the Tokachi River tributaries (Toshibetsu, Satsunai, Otofuke, Shikaribetsu and Sarubetsu) in 200, 200 and 200. Based on the discharge, precipitation and other meteorological data (air temperature, humidity, atmospheric pressure, wind and radiation), a tank model was applied to analyze runoffs of each river. In order to understand the mechanism of nutrient supply from the catchment area, we coupled the land use patterns, soil types and geological distributions with the discharge patterns by the model. From the tank model, the total discharge in winter consisted of more than 0% baseflow. In the snowmelt season, when the discharge increased drastically, the contribution of surface runoff increased up to more than 0% of the total discharge. The contribution of the surface runoff was highly correlated with the effective rainfall in summer, indicating that the rainfall event is immediately reflected by the increase in river discharge. In the Toshibetsu River, the silicic acid concentration varied seasonally with the large amplitude, and was negatively correlated with the discharge. The concentration tended to be high in catchments of the volcanic crust cover. During the winter low discharge, all the rivers showed the highest silicic acid concentration. However, during a spring thaw, the concentration decreased consistently. This suggests that the silicic acid concentration is determined by the mixing between the baseflow of highest concentration and the surface runoff of relatively low concentration. The nitrate concentration differed largely among rivers, which ranged from high concentration (00-00 µmol l-1) in the Sarubetsu River to low concentration (20-0 µmol l-1) in the Toshibetsu River. The concentration was positively correlated with the proportion of the farming area in catchments. This suggests that unutilized excess fertilizer is the major source of nitrate to rivers. The nutrients concentration variations in the Tokachi River tributaries are judged to be affected strongly by the land use, soil and geology rather than discharge patterns.

Characteristics of discharge and suspended-sediment load in a subarctic river, Tanana River, Alaska, were examined by observations in the glacier-melt and permafrost-melt seasons (June to September) of 2002 and 2003. The drainage basin (area: 6.48 10 4 km 2) of the river is occupied by the ca. 96 % permafrost region of the diluvium to alluvium and the ca. 4 % glacier-covered region in the Alaska Range and the Wrangell Mountains. The hydrographs of the Tanana River are explained by the superimposition of rainfall runoffs and baseflow from the permafrost region and glacier-melt runoffs from the glacial region. The suspended-sediment load, meanwhile, varied synchronously with the discharge, but its magnitude nonlinearly responded to the discharge. The nonlinearity of sediment load occurred only under local rainfalls, when the sediment supply from river channels was possibly insufficient. The runoff analyses by a tank model were carried out for the hydrographs of 2002 and 2003. The rainfall onto the whole drainage basin and the meltwater input into the glaciers were estimated by the Thiesen method and the positive degree-day approach (PDDA), respectively. The analytical results reasonably reproducing the hydrographs, indicated that the glacier-melt runoffs occupy 60 % and 66 % of the total discharge in 2002 and 2003, respectively.

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