Research on the chemical element transport characteristics of the larch forest ecosystem of Greater Xing'an Mountain in China

https://doi.org/10.1016/j.pce.2020.102919Get rights and content

Highlights

  • Long-term observation of forest ecosystem on chemical elements of precipitation and runoff in cold temperate regions.

  • Verification of forests in the cold temperate zone will become the sink of nutrients.

  • Integrated analysis of changes in precipitation, forest, and runoff chemical elements.

Abstract

Due to global climate change, forest structure and function have changed significantly. Usually forests are regarded as sinks rather than sources of nutrients. However, in the cold temperate zone, flowing the long-term accumulation of these nutrients on the forest floor could potentially result in forests becoming sources rather than sinks of nutrients. Hence, what effect does the forest have on the transport of chemical elements in precipitation and runoff? It is an important scientific question. To analyse the variability in cold temperate zone larch forest ecosystem chemical transport, we used chemical and instrument analysis methods to monitor the water quality of precipitation and runoff that flowed through the forest system. The results showed that the K, Na, Mn, Zn and Fe chemical element content of precipitation in the Greater Xing'an Mountain region had significant variability in 1997, 2008 and 2015. The Mg, K, Na and Cu contents of runoff differed significantly in 1997, 2008 and 2015. The chemical element content had obvious variability after precipitation flowed through the forest ecosystem of Greater Xing'an Mountain. This showed that the forest ecosystem of Greater Xing'an Mountain had a significant influence on water quality. Therefore, the forest ecosystem in the Greater Xing'an Mountain have increased the retention of nutrients, which is conducive to forest growth. But it will also increase the iron et al. in the water body, which affects the water quality.

Introduction

Since the 19th century, hydrologists, environmentalists, and forest ecologists had begun to study the effects of forests on water quality and water environment, and the earliest research started with soil stability (Xu et al., 2001). During this period, the Coweeta Forest Ecology and Hydrology Research Station in North Carolina in the United States began the study of the ecosystem mineralization cycle, which had a very important impact on the subsequent forest water quality research (Whittaker et al., 1976; Schumacker et al.). In the past 30 years, the forest redistribution of water chemicals in rainfall, migration and diffusion rules, etc., especially in the forest ecosystem, rainfall nutrient input, internal nutrient cycle, runoff nutrient output and other water chemistry characteristics had become one of the focuses of forest water quality research (Xin et al., 2004; Ashley, 2015; Futter et al., 2016). Precipitation flowing through the forest canopy and tree trunks, and finally flowed into the litter layer. The litter layer is the second active surface after atmospheric precipitation enters the forest ecosystem. Similar to the forest canopy, it carried out two opposite processes for various substances carried through it with water, namely, filtration, adsorption and leaching, which changes the concentration and carrying amount of the substances (Chen, 2004; Ashley, 2015). At present, the research on litter layer mainly focuses on the conservation of water sources, the determination of the amount of litter of different tree species, and so on (Yang, 2009; Wondzell et al., 2016). There were little research on the variability of litter layer impact on precipitation chemical cycling. From the perspective of the hydrochemical cycle, the nutrients and nutrients that enter the forest ecosystem circulate inside the forest ecosystem, and were ultimately exported from the forest ecosystem in the form of streams (Chen et al., 2004). Streams were not only an integral part of the forest ecosystem, but are also linked to larger systems such as rivers and urban residents, restricting and affecting the biogeochemical cycle (Xu et al., 2001). The streams from the forest contains a variety of chemical components. Due to atmospheric precipitation, when passing through the forest ecosystem, it can dissolve various organic substances of soil rock weathering and biological remains, thereby increased the chemical composition of the water (Zhu et al., 2019). On the other hand, when the rain passing through the forest ecosystem and becomes a stream, some dissolved components may be removed, and some components in the infiltration may also be absorbed by the soil or removed by exchange (Wondzell et al., 2016). In addition, water can wash away the material on the surface of the plant, and leaches many minerals on the leaf cover into the soil, so that these materials can quickly circulate in the ecosystem (Ashley, 2015). Therefore, there were great significance to strengthen the research on the characteristics of the forest's impact on nutrient input and output of atmospheric precipitation, which is of great significance to the study of the stability of forest ecosystems and the study of regional chemical cycles.

Chemical transport in forest systems is mainly composed of the precipitation input and runoff output and is influenced by plant-atmosphere interactions (Schumacker et al., 1989; Shi et al., 2000; Wang et al., 2012). The chemical composition of precipitation changes dramatically after flowing through the forest system; precipitation is the main source of chemical substances for forest ecosystems (Liu et al., 1995; Tang et al., 2015; Futter et al., 2016). Furthermore, precipitation nutrient input is also the basis of nutrient cycling and nutrient balance in forest ecosystems (Hiratsuka et al., 2014; Zhu et al., 2019). Atmospheric precipitation brings chemicals into the forest ecosystem but also leads to leaching, washes nutrients off of plant leaves and trunks, and promotes the circulation of biological material in the ecosystem (Liu et al., 2007; Erdoğan et al., 2018). The chemical characteristics of precipitation have been analysed in depth, including external nutrient balance and patterns of nutrient cycling and nutrient balance in forest ecosystems (Lidman et al., 2017; Oliveira et al., 2019). Usually forests are regarded as sinks rather than sources of nutrients (Li et al., 2015; Nitschke et al., 2017). However, in the cold temperate zone, the forest growing season is only about 90 days (Zhang et al., 2014), with long-term accumulation of these nutrients on the forest floor could potentially result in forests becoming sources rather than sinks of nutrients (Nitschke et al., 2017). With the growth of forests and the continuous accumulation of precipitation input elements, according to the long-term observing chemical elements of precipitation and the runoff flowed through forests, we would explore whether the forest will become a source of nutrients or a sink.

The circulation of chemical elements such as N, P, K and other element in forests is an important indicator of ecosystem structure and function variability, and strengthening our understanding of the transport characteristics of these elements is helpful for further understanding the response of relevant ecological processes to the overall changes in ecosystems (Liu et al., 1995; Wang et al., 2012). Precipitation plays an important role in forest ecological processes and the nutrient cycle. Forest N:P decreases with decreasing rainfall, and the total nitrogen and total phosphorus of the forest decrease with decreasing rainfall. Previous studies have found that increased rainfall may accelerate the decomposition of forest litter, shorten the nutrient soil-plant-litter cycling rate, and accelerate the loss of nutrients such as N, P, and K in forests (Futter et al., 2016). At the same time, an increase in rainfall also affects the microbial community structure and enzyme activity by changing the water content and pH of the forest humus layer and soil, thus affecting the accumulation process of chemical elements such as N, P, K and Mg in forest soil (Lidman et al., 2017). The water chemistry characteristics of forest ecosystems reflect the ecological and physiological characteristics of forest growth and the eco-hydrological cycle (Zhang et al., 2007; Luke et al., 2017). Usually, the different chemical elements have different functions in forest systems and water quality management (Liu et al., 2007). The different contents of chemical elements in precipitation have different influences on forest ecosystems. High nutrient content accelerates tree growth but pollutes water in forest regions. Low nutrient content in precipitation not only decreases tree growth but also removes nutrients from forest ecosystems (Mclaughlin et al., 2014). Therefore, research on the variability of chemical elements in precipitation in a forest system can explore the nutrient input and output characteristics of the eco-hydrological cycle of forest ecosystems (Zhang et al., 2014; Burja et al., 2014; Vincent et al., 2016).

The larch forest system (Larix gmelinii) in the cold temperate zone of Greater Xing'an Mountain in China is a special forest ecosystem. Larch forests have a very close interdependence with permafrost. The larch forest ecological environment is also called the “frozen forest” and is a main type of light coniferous forest; it is a representative forest ecosystem in China (Zhang et al., 2014). Due to global climate change and human activities, the temperature of the region is becoming warmer, the precipitation is increasing, and the boundaries of permafrost have begun to move northward. The environment is gradually deteriorating in ways that have seriously affected the forest hydrological processes and the stability of permafrost. Larch forests are sensitive to climate change, including changes in the chemical element input from precipitation (Zhang et al., 2014). Therefore, the further study of the chemical transport characteristics of forests has important significance for larch forest protection in Greater Xing'an Mountain. The objectives of this paper include (1) to analyse the chemical elements in precipitation in different years and (2) to quantify the long term chemical variability of the runoff after precipitation flowed through the forest ecosystem. Furthermore, the relationship between the chemical nutrient input from precipitation and output in runoff is discussed.

Section snippets

The study area

The Greater Xing'an Mountain National Forest Ecological Station (Fig. 1) is located at Greater Xing'an Mountain in Inner Mongolia, with geographical coordinates 50°49′N ~ 50°51′N, 21°30′E ~ 121°31′E. The test site area is 11000 hm2, representing a typical forest of the cold temperate coniferous forest region in China (Fig. 1). The station belongs to the China Forest Ecosystem Network (CFERN) and the National Ecosystem Network (CNERN). The site has also been selected for the Global Terrestrial

The chemical element difference of the precipitation in 1997, 2008 and 2015

Fig. 3 shows that the chemical element contents in precipitation on Greater Xing'an Mountain were in the order ofCa > K > Na > Zn > Mg > Fe > Cu > Mn (Fig. 3). This shows that Ca, Na, K, Mg and Zn were the main input elements in rainfall in the Greater Xing'an Mountain region. The Fe in 1997 were significantly different from those in 2008 and 2015, based on a 95% confidence interval, and they showed a significant decrease. The K and Na in 1997 and 2008 were significantly different from in 2015,

Discussion

Research on chemical settlement in precipitation and runoff is very important for water resource management and ecosystem services function assessment. In our study, the K, Na, Mn, Zn and Fe contents of the precipitation varied across 1997, 2008 and 2015. The chemical element content of precipitation has a direct relationship with the precipitation source. Precipitation in the Greater Xing'an Mountain region mainly consists of two parts: external input and internal circulation. The external

Author statement

Chuanfu Zang: Investigation, Data curation, Software, Writing—original draft preparation, Writing—review and editing, Visualization, Conceptualization, Methodology, Validation, Formal analysis, Supervision, Project administration. Mingwan Wu: Investigation, Data curation, Original draft preparation, Formal analysis, Software. Junmao Zhang: Investigation, Data curation. Yongjie Yue: Validation, Visualization, Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was supported by the National Natural Science Foundation of China [31660233]. We thank Professors Qiuliang Zhang and Mei Zhou from the Inner Mongolia Agricultural University for their support and help with this research. We thank the Greater Xing'an Mountain National Forest Ecological Station. We also thank native English-speaking editors at American Journal Experts for language polish.

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