Effects of Land Cover and Atmospheric Input on Nutrient Budget in Subtropical Mountainous Rivers, Northeastern Taiwan

Abstract

The nutrient budget, the difference between the nutrient output via stream and input via precipitation, can provide insights into how environmental processes affect forested ecosystem biogeochemistry. In this study, field measurements of the nutrient budgets—including Na+, Cl−, K+, Mg2+, Ca2+, NO3−, and SO42−—of 19 sites were conducted in Feitsui Reservoir Watershed (FRW) of northeastern Taiwan. A series of power-law regressions were developed to establish the relationship of the nutrient budget to the discharge, nutrient input, agricultural land cover, and slope. The result show that the weekly nutrient budget is significantly affected by agricultural land and input via precipitation (R2 of regression models ≥ 0.90), yet the relationship varies among different nutrient elements. The agricultural land cover is the major factor, while the input via precipitation plays a relatively minor role in the budget of Cl−, Mg2+, Ca2+, and SO42−. These nutrients could be provisioned abundantly from the system, and thus the input via precipitation is not the predominant controlling factor. By contrast, the Na+ and K+ inputs via precipitation are indispensable for accurately estimating the riverine exports. Because weathering is a limited source of K+, the roles of agricultural activities and input via precipitation are likely decisive for transport. Besides, the NO3− budget reveals a strong interplay between the atmospheric input and agricultural land, as expected. Because the nutrient budget model of NO3− is strongly improved, the R2 changes from 0.34 to 0.99 when a larger coefficient in exponent term (10.2) for agricultural land cover (showing that NO3− export is strongly hydrologically controlled) and precipitation input are included. Our analysis is based on one year of data, so extrapolating the result to a long-term period should be done with caution, as there could be substantial inter-annual variation. The nutrient budget approach provides a preliminary assessment to evaluate the impacts of agriculture and atmospheric deposition on nutrient export, which can provide a precursory reference for watershed management for improving water quality and mitigating eutrophication.

Simulation of the Impact of Environmental Disturbances on Forest Biomass in Taiwan

“…Although nutrient cycling and nutrient limitations do play an important role in tree growth in the (sub)‐tropical forest biomes (Houlton et al., 2008), nitrogen (N) and phosphorous (P) cycling are not accounted for in ORCHIDEE r4262. The abundance of dissolved inorganic nitrogen in the river discharge (Chang et al., 2020; Huang et al., 2016) suggests that nitrogen is no longer a factor limiting plant growth over large areas of Taiwan. The primary source of this nitrogen is likely atmospheric deposition from emissions from mainland China, and from local industry and households, estimated to be between 0.8 and 20 kg N ha −1 yr −1 (Zhao et al., 2015).…”

Hydrological Impact of Typhoon on Rivers

“…For nutrient-associated impacts, the nutrient export is strongly affected by the source locality and pathway condition (reaction condition in rivers). Chang et al 2020 and Lee et al 2020 [10,11] attempted to use the nutrient budget and statistical analysis to identify the source locality of different nutrients. Their results showed that agricultural land and atmospheric input are the main sources of nutrients.…”