Characteristics of Stream Water Nutrient Concentrations during Snowmelt Period in a Headwater Catchment in the Central Chugoku Mountains: A Comparison between No-Snow Period and Snowmelt Period Based on Weekly Sampling for One Year

To characterize stream water nutrient concentrations during snowmelt period (Jan-Apr) in a forested headwater catchment in the central Chugoku Mountains, hydrological observations and weekly stream water sampling were conducted for one year. Even in the coldest period (Jan-Feb), snow melting progressed temporally and generated a relatively large streamflow in the catchment. Compared with those during the no-snow period (May-Aug and Sep-Dec), the dissolved nitrogen (DN) and phosphorus (DP) concentrations during snowmelt period were high, whereas the particulate nitrogen (PN) and phosphorus (PP) concentrations were the same or slightly low. The DN and DP concentrations during the snowmelt period might have been strongly influenced by melting water from accumulated snow rather than by leaching water from the soil layer. On the other hand, the PN and PP concentrations during the snowmelt period seemed to reflect the decrease in the extent of accumulation of mobile sediments within the stream channel. In conclusion, in areas of the Chugoku Mountains around the catchment studied, 1) the use of DN, DP and TN concentrations measured during no-snow periods as substitutes for those measured during snowmelt period can underestimate the annual export load of the nutrients, and 2) stream water sampling at shorter intervals, i.e., every 1~3 days, is necessary for accurate nutrient load evaluation based on field investigation during snowmelt periods.