Evaluation of Nitrogen Removal in a Soil Trench System after a 10-year Operation

Many studies have confirmed the efficiency of soil trench systems; however, few have systematically studied the distributions of soil temperature, moisture content, and nitrogen in the profile of a soil trench system. In this study, the nitrogen removal in a soil trench system located in Sasagi (Tsukuba, Ibaraki, Japan) was evaluated by incorporating temperature and soil moisture content profile measurements. The results revealed that despite relatively small fluctuations, the soil temperatures at the top layer of soil (depth of 10cm) were greatly affected by air temperature; in comparison, the air temperature had little effect on the soil temperatures of soil layers at deep depth. A similar result was also obtained for soil moisture content, which was mainly affected by precipitation, evapotranspiration, etc. An investigation of the nitrogen distributions revealed a pattern similar to that obtained from the results of a previous simulation. Ammonia can be almost completely removed by using the soil trench system; however, some nitrates still remain in the effluent due to incomplete denitrification that might be caused by an insufficient carbon source.