Diffuse nutrient export dynamics from accumulated litterfall in forested watersheds with remote sensing data coupled model

Wei Ouyang; Zeshan Wu; Pengtao Wang; Xintong Cui; Xin Hao; Weihong Zhu; Ri Jin

doi:10.1016/j.watres.2021.117948

Diffuse nutrient export dynamics from accumulated litterfall in forested watersheds with remote sensing data coupled model

Water Res. 2022 Feb 1:209:117948. doi: 10.1016/j.watres.2021.117948. Epub 2021 Dec 8.

Authors

Wei Ouyang¹, Zeshan Wu², Pengtao Wang², Xintong Cui², Xin Hao², Weihong Zhu³, Ri Jin³

Affiliations

¹ School of Environment, State Key Laboratory of Water Environment Simulation, Beijing Normal University, Beijing 100875, China; Advanced Interdisciplinary Institute of Environment and Ecology, Beijing Normal University, Zhuhai 519087, China. Electronic address: wei@itc.nl.
² School of Environment, State Key Laboratory of Water Environment Simulation, Beijing Normal University, Beijing 100875, China.
³ School of Geographic and Ocean Sciences, Key laboratory of Wetland Ecological Functions and Ecological Security, Yanbian University, Yanji, Jilin 133000, China.

PMID: 34952486
DOI: 10.1016/j.watres.2021.117948

Abstract

Nutrients exported from forest litterfall significantly contribute to the global cycling of elements and the water quality in watersheds. Simulating the watershed discharge load is challenging because of the combined effects of the decomposing litterfall and topographic heterogeneity. We quantified the contribution of diffuse nutrient export from forest litterfall in a low temperature watershed using artificial rainfall experiments and watershed territorial modeling with remote sensing data, and therefore, the critical spatial factors and corresponding nutrient export dynamics were identified. Rainfall intensity and terrain slope were found to be the key factors for nutrient export under different litterfall decomposition conditions. Based on the moderate resolution imaging spectroradiometer data and field observations, the temporal patterns of litterfall biomass of two types of dominant forests (broad-leaved and mixed) were interpreted. The spatial patterns of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) exports from watershed litterfall were simulated by coupling the observed discharge parameters under artificial rainfall conditions and watershed surface flow modeling with the hydrological characteristics of the forested areas. The average watershed TOC, TN, and TP loads exported from the litterfall were approximately 58.22, 7.89, and 0.37 kg ha^-1 a^-1, respectively. The exported loads of TOC, TN, and TP varied with the forest types, and the loads from the litterfall of deciduous broad-leaved forest were found to be ∼50-70% of loads from the litterfall of mixed forest. A comparison with similar studies worldwide also indicated that low temperature decreased the litterfall decomposition rate and diffuse nutrient export. This study indicated that litterfall nutrients were a key contributor to watershed water pollution, and their spatial discharge trend varied intensively with the terrestrial conditions. The modified simulation methods were found to accurately assess the cycling of nutrients from the forest litterfall on a watershed scale.

Keywords: Artificial rainfall; Forest litterfall biomass; MODIS; Nutrient export; Watershed diffuse pollution.