Water chemistry and soil biogeochemistry of Ab-S

The data are from 24 rainfall events of stream flow and water quality fluctuations and 11 soil analyses in Ab-S, a forested watershed in the southern part of Shiga Prefecture, Japan.　
Stream water was sampled for chemical analysis during 24 rainfall events, from the beginning until the post-rainfall decrease in stream water discharge rate. Some collected samples were immediately filtered through cellulose acetate membrane filters (0.45-μm pore size). Both filtered and unfiltered samples were stored in polypropylene bottles at 4°C. The stream water discharge rate was calculated from the overflow water level measured at the weir.
Soil samples were collected every 1–3 months on 11 occasions between June 2012 and December 2013. Soil samples were collected at 0–10 and 20–30 cm at the lower and upper parts of three slopes, respectively. The samples were immediately sieved through a 2.0-mm screen and extracted within 1 day using 2N KCl. The extracts were stored in polypropylene bottles at –25°C. Soil samples used to measure net nitrification rates were incubated for 40 days at the in situ temperature and moisture level, with the net nitrification rate calculated as the difference between the initial and post-incubation NO3– concentrations.
The NO3– concentration in stream water samples was determined by ion chromatography (HIC-6A; Shimadzu, Tokyo, Japan; Compact IC 762; Metrohm, Herisau, Switzerland; ICS-1100; Thermo Fisher Scientific, Waltham, MA, USA). TDN and TN (sum of all nitrogen forms) were measured by UV absorption (UV-2450: Shimadzu) after oxidation of the filtered and unfiltered samples with potassium persulfate. Ammonium (NH4+), NO3–and dissolved silica (SiO2) were colored by treatment with indophenol, naphthylethylenediamine, and molybdenum yellow, respectively, and their absorbance was measured (UV-2450; Shimadzu). The NO3– concentration in the KCl soil solutions was determined by flow injection analysis (OG-F1-300S; Ogawa & Co., Tokyo, Japan).