Rainwater and streamwater chemistry between 2001 and 2014 in the Kahoku experimental watershed no.3, Kyushu

Abstract

We calculated mean annual solute concentrations in rainwater and streamwater between 2001 and 2014 at the Kahoku experimental watershed no. 3 and considered the inter-annual trend. Mean annual non-sea salt Ca²⁺ and Ca²⁺ concentration in rainwater peaked in 2006 and 2007. Other elements in rainwater showed no trend. Mean annual dissolved inorganic nitrogen input through rainwater was 8.9 kg ha⁻¹ y⁻¹, about 60% of which was in the NH₄⁺-N form. Mean annual non-sea salt SO₄²⁻ input was 34.0 kg ha⁻¹ y⁻¹, which was about 90% of the total SO₄²⁻ input. Mean annual K⁺ concentration in streamwater tended to increase gradually over the 15 years of observation. Other elements in streamwater showed no trend. We conducted quality control of the data and evaluated the completeness of the data using the quality assurance/quality control program of the Acid Deposition Monitoring Network in East Asia (EANET). Each year’s completeness of the data was generally high (more than 80%) in both rainwater and streamwater.