Effects of the detention pond on sediment condition in estuary zone on Takahashi River

Abstract

In order to clarify the influence of the discharge from the detention pond on the estuary zone in Takahashi river, flowing to the Straits of Bisan, we researched the sediment conditions and analyzed the distributions of carbon and nitrogen stable isotope (δ¹³C and δ¹⁵N). In the upper reach of the estuary zone, sediment conditions were good, on the otherhand, the lower each became worse rapidly. The concentrations of DIN in the surface water and COD value in the sediment of the detention pond were 144.6±34.6 μM and 58.1±9.1mg・dg^-1, individually. These scores were higher than the mean value of the estuary zone (13.7±5.3 μM and 12.2±9.9mg・dg^-1). The value of the δ¹³C and δ¹⁵N on riverzone, sea zone and detention pond zone were -26.6‰・11.1‰, -23.2‰・6.7‰ and -26.7‰・2.3‰, individually.The stable isotope values in the three stations around the detention pond showed similar results to the detention pond.These results suggested that sediment conditions in the estuary zone were aggravated by the mud discharge from the detention pond.