Water extractable organic matter and iron in relation to land use and seasonal changes

Susan Praise; Hiroaki Ito; Takayuki Sakuraba; Dung Viet Pham; Toru Watanabe

doi:10.1016/j.scitotenv.2019.136070

Water extractable organic matter and iron in relation to land use and seasonal changes

Sci Total Environ. 2020 Mar 10:707:136070. doi: 10.1016/j.scitotenv.2019.136070. Epub 2019 Dec 12.

Authors

Susan Praise¹, Hiroaki Ito², Takayuki Sakuraba¹, Dung Viet Pham³, Toru Watanabe⁴

Affiliations

¹ Department of Food, Life and Environmental Sciences, Yamagata University, 1-23 Wakaba-machi, Tsuruoka, Yamagata 997-8555, Japan.
² Center for Water Cycle, Marine Environment and Disaster Management, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan. Electronic address: itohiro@kumamoto-u.ac.jp.
³ Department of Food, Life and Environmental Sciences, Yamagata University, 1-23 Wakaba-machi, Tsuruoka, Yamagata 997-8555, Japan. Electronic address: dphamviet1986@tds1.tr.yamagata-u.ac.jp.
⁴ Department of Food, Life and Environmental Sciences, Yamagata University, 1-23 Wakaba-machi, Tsuruoka, Yamagata 997-8555, Japan. Electronic address: to-ru@tds1.tr.yamagata-u.ac.jp.

PMID: 31863986
DOI: 10.1016/j.scitotenv.2019.136070

Abstract

The soil carbon pool is an essential part of the global carbon cycle although it is sensitive to climatic changes and the local environment. Terrestrial areas are important sources of organic matter for aquatic ecosystems and the fluctuation of different soil minerals and elements is largely influenced by land use and season changes. We studied water-extractable organic matter (WEOM) properties including iron (Fe), water extractable organic carbon (WEOC) and spectral characteristics from forests and arable soils to evaluate the effects of land use and seasonal change on WEOM and Fe in terrestrial areas. We collected soil samples randomly from arable land (AR), broadleaf (BL) and aged needle leaf forests (NL) and extracted WEOM for analysis using rainwater. Results of WEOC and Fe showed similar trend seasonally and were higher in forest sample than in AR. WEOC was high in the upper layer while Fe was independent of the depth and higher in AR. On the other hand, specific ultra-violet absorbance at 254 nm (SUVA₂₅₄) and a proxy for aromaticity significantly varied with both land use and season and was on average two times higher in arable land than forests during spring and summer. Humic-like components significantly varied between the studied sites seasonally while tyrosine-like was affected by season only. The relative abundance of both humic-like and tryptophan-like components were significantly affected by land use while [Fe]: [WEOC] ratio was also high in arable land and negatively correlated with humic-like components in forest sites. As observed from ratio and Fe oxidation rate constant, summer presented ideal conditions for WEOM interactions. The synchronized seasonal WEOC and Fe changes indicate an enhancement of Fe mobility by DOM whereas the differences observed between sites especially from the high humic- and protein-like components in NL and BL reflects the effect of land use.

Keywords: Iron; Land use; Parallel factor analysis (PARAFAC); Seasonality; Water extractable organic matter.