Investigation of temperature regimes for air, streamflow and topsoil layers in a riparian area of harpen Creek

Primary important temperatures in forest ecosystems are associated with the air, topsoil, and streamflow. However, previous studies mostly examined these factors individually. Limited studies investigating these temperatures in the same plot can be found especially in a forest environment. We recorded temperatures of the air, topsoil layers and streamflow in a riparian area of Harpen Creek of the Fushan Experimental Forest from 2005, and we accumulated more than 5 yr of continuous records. The analytical results showed that the average yearly temperatures for air, streamflow, and 5-, 30-, and 50-cm soil layers during the monitoring period were 17.7, 17.6, 17.9, 18.0, and 18.1℃, respectively. The highest average monthly temperature for air and streamflow occurred in July, while those for the soil layers occurred in August. The minimum monthly average temperatures for all monitoring items occurred in January. Air, streamflow, and topsoil layers had nearly the same monthly average temperature of about 16.5℃ in the month of April for the Harpen Creek drainage basin. When the air temperature was < 15.5℃, the streamflow had the highest temperature among all monitored items, and the second highest was the 30-cm soil layer. Yearly temperature fluctuations for all monitoring items were significant, and the descending rank of ranges of yearly temperature changes was air, 5-cm soil layer, 30-cm soil layer, 50-cm soil layer, and streamflow. Air temperature had the maximum magnitude of changes within a day for all months, and the second was the temperature of the 5-cm topsoil layer. However, the maximum magnitude of daily changes was < 0.5℃ for soil layers deeper than 30 cm, and this indicated that there was only a small and insignificant diurnal change in temperatures of deeper soil layers. The magnitude of changes of streamflow temperature within a day was less than that for the 5-cm soil layer except for the period from September to December. In addition, the linear regression relationships for air temperature versus streamflow temperature and air temperature versus temperature of the monitored topsoil layers were also established in this report. Hopefully those investigations will provide knowledge of the riparian ecosystem of Harpen Creek.