Reconstruction of springs discharge using tree-rings and earlywood vessel chronologies in an alluvial aquifer
Introduction
Springs are a vital source of water for many local communities around the world. During the past decades, population growth, climatic changes, and over-exploitation of groundwater have exerted extra pressure on these valuable resources, especially in the arid and semi-arid regions (Green et al., 2011; Jyrkama and Sykesa, 2007). Spring is a natural outpouring of the groundwater, and it occurs when the water table reaches the ground surface. Springs can be divided into two main types based on geologic structures: alluvial and karst springs. Alluvial springs are found in the alluvial sediments and plains. Karst springs are found in the karst formations located in mountainous areas. The majority of springs in Iran are categorized as Karst springs. However, most alluvial springs are located in densely populated areas and, therefore, they are prone to over-extraction and water pollution (Gholami et al., 2008). Groundwater or springs are one of the main sources of soil moisture, significantly influencing trees that grow in the surrounding environments around water bodies (Mazza et al., 2020; Tulik et al. 2020).
Studies show that groundwater resources have been declining in many parts of the world (Wada et al., 2010). Therefore, it is necessary to record the spring discharge for better management of groundwater resources. Monitoring changes in groundwater is necessary for adopting strategies to mitigate the impacts of water deficiency and climate change. Temporal variation in groundwater depth is tipically monitored on local scales using water table measurements from piezometric wells. Unfortunately, such practices are hampered in many parts of the world by the absence or scarcity of monitoring stations, temporal and spatial gaps in the collected time series data, and data quality issues. Even for the areas with available records, the data commonly span less than one century. Therefore, different models and techniques have been developed to reconstruct past groundwater storage or spring discharge records.
Dendrohydrology is the science of reconstructing past hydrologic variabilities from tree-rings and vessel features (Anderson et al., 2019; Blake et al., 2020; Gholami et al., 2017; Gholami et al., 2019; Tsvetanov et al., 2020; Wigley et al., 1984). Tree-rings and vessel features (dendrohydrology) records have been successfully applied to the reconstruction of rivers discharge and flood occurrence (Hardman and Reil, 1936; Hawley, 1937; Woodhouse, 2000; Pederson et al., 2001; Woodhouse and Meko, 2002; Liu et al., 2010; Edison et al., 2013; Gholami et al., 2017; Anderson et al., 2019; Meko and Therell, 2019; Zhang et al., 2020a, Zhang et al., 2020b). Previous studies have shown that precipitation, soil moisture, soil depth, altitude, and temperature affect tree-ring width, and therefore, these parameters can be investigated using dendrochronological studies (Briffa et al., 1988; Conkey, 1979; Gray et al., 2007; Hidalgo et al., 2000; Meko et al., 2001; Naurzbaev and Sidorova, 2004; Oie et al., 2020; Wise, 2010; Woodhouse et al., 2010; Yin et al., 2008).
Bogino and Jobbágy (2011) investigated the relationship between climate and groundwater fluctuations by studying the growth and death of the Prosopis caldenia species in the lowlands and uplands. They concluded that groundwater depth has a vital role in trees' lives and that the optimum depth of groundwater was ranging from 2 to 8 m. In fact, in areas where trees source their water need from groundwater, they can suffer groundwater level lowering due to climatic change or human impacts because it also affects the water content stored in the upper soil layers (Lewis and Burgy, 1964; Mazza et al., 2020; Williams et al., 1998). Gholami et al. (2017) simulated groundwater level fluctuations using tree-ring and vessel features in the north of Iran. They concluded that vessel features represent the groundwater fluctuations even better than tree-rings. Anderson et al. (2019) successfully reconstructed the streamflow data for the Tennessee Valley using tree-rings chronology. Meko and Therell (2019) used tree-ring and vessel widths for studying floods on the White River of Arkansas, providing results on their potential for precisely modeling the maximum river flows. Previous studies used regression analysis to reconstruct past hydrologic parameters based on tree-rings and vessel features (Robertson et al., 1990; Liu, 2011; Gholami et al., 2017; Tulik et al. 2020). Vessel features are closely related to water absorption and conduction. Therefore, this can be a suitable parameter for evaluating the changes in precipitation, groundwater level, and spring discharge in the alluvial aquifers because there is a correlation between earlywood vessel features and soil moisture during the growing seasons (Garcia Gonzalez and Eckstein, 2003; Fonti and Garcia Gonzalez, 2004; Gholami et al., 2015 and Gholami et al., 2017; Kames et al., 2016; Tulik et al. 2020). In the alluvial aquifers, the water saturates the pore spaces of aquifers. Therefore, the groundwater depth and springs discharge are dependent on groundwater recharge, precipitation, and the amount of groundwater extraction. All the mentioned factors affect the spring discharge fluctuations.
The tree-rings width and the vessel's features vary by environmental factors during the growing season. The wood produced at the beginning of the growing season is called earlywood or springwood and is characterized by coarse vessels and a thin wall. The wood produced in the late growing season is called the latewood or summerwood, and it can be identified by its relatively small vessels and thick walls. The combination of earlywood and latewood forms the annual tree-ring. At the beginning of the growing season, water absorption in trees increases due to increased precipitation, spring discharge, groundwater level, and increased vessel size (Campelo et al., 2010). The change in vessel size is attributed to water availability, where larger vessels have larger space for water transportation (Gholami et al., 2017; Hacke and Sperry, 2001). Therefore, tree-rings and vessel features can be used in the spring discharge modeling as an alternative in measuring groundwater and spring discharge.
Caucasian elm (a binomial and ring-porous tree) is a mesophytic deciduous species that grows mainly in the riverside, mixed lowland, and ravine forests. These species are suitable for evaluating the effects of soil moisture and groundwater changes during the growing season and have been used for dendrohydrology in previous studies (Davis et al., 2012; Gholami et al., 2017; Gholami et al., 2019; Grissino-Mayer, 1993). Previous dendrohydrology studies were mainly focused on surface water (e.g., reconstruction of river discharge, flood occurrence). To our knowledge, dendrochronology has not yet been used in the reconstruction of spring discharge. It is assumed that.
by identifying the relationship between the spring discharge and the tree-ring widths and vessel features, we can reconstruct the historical spring discharge (Gholami et al., 2017; Mazza et al., 2020; Williams et al., 1998). In this research, a new approach for reconstructing spring discharge is introduced. For this purpose, tree-rings, vessel features, and hydrogeologic variables were used to reconstruct the discharge of two alluvial springs during the three temporal sections (early spring, mid-growing season, and late-summer) of the growing season in the past decades. This study aimed to predict the historical spring's discharge using dendrohydrology and ANN.
Section snippets
Study area
The study area is a portion of the southern coastal plains of the Caspian Sea in Iran, extending between 48° 59′ E and 37° 39′ N (Fig. 1). The mean annual precipitation is approximately 1000 mm, which creates a humid climate in the region. Major land-use types in the study area are forest lands, rice field lands, and residential areas. The lithology of the site is mainly Quaternary sediments (alluvial sediments) that host alluvial springs. This study focused on two springs within the study site
Results
The monthly discharge during the growing season (from 1982 to 2018) ranged from 1.7 to 11.8 l per second for Vardem spring and 2 to 20 l per second for the Khanekenar spring. The mean monthly springs discharge during the growing season in Vardem and Khanekenar springs are 4.1 and 6.4 lit per second, respectively. Both of the studied springs have permanent discharge in the growing season. The mean monthly vessel diameters vary from 47 to 232 μm, and the mean tree-rings width range from 1.4 to
Discussion
The number of vessels did not show a significant relationship with the springs' discharge. We can not be sure that all of the small vessels were counted carefully. Therefore, the number of vessels is not a suitable parameter compared to the other vessel features (Gholami et al., 2019; Kames et al., 2016; Tulik et al. 2020). Also, earlywood vessels' size decreases significantly during the growing season. The maximum and minimum vessel size was observed in the early spring and late summer,
Conclusions
The results show that dendrohydrology can be used for reconstructing the past springs' discharge in the unconfined aquifers within the alluvial formations. The performance of the dendrohydrology-based spring discharge modeling is dependent on environmental conditions such as the distance from rivers, the aquifer's properties, the tree species, and the discharge regime of the springs.
Dendrohydrology performs better for those springs that the flow fluctuates a lot during growing seasons. It is
Declaration of Competing Interest
None.
Acknowledgments
We would like to express our appreciation to the Regional Water Company of Guilan for providing the spring discharge data and helping us with the data preprocessing.
References (63)
- et al.
Tree-ring reconstructions of streamflow for the Tennessee Valley
J. Hydrol.
(2019) - et al.
Climate and groundwater effects on the establishment, growth and death of Prosopis caldenia trees in the Pampas (Argentina)
Forest Ecol. Manag.
(2011) - et al.
Summer temperature patterns over Europe: a reconstruction from 1750 ad based on maximum latewood density indices of conifers
Quat. Res.
(1988) - et al.
Modeling of groundwater depth fluctuations using dendrochronology in alluvial aquifers
J. Hydrol.
(2015) - et al.
Dendrohydrogeology in paleohydrogeologic studies
Adv. Water Resour.
(2017) - et al.
Annual precipitation in the Yellowstone National Park region since AD 1173
Quat. Res.
(2007) - et al.
Beneath the surface of global change: impacts of climate change on groundwater
J. Hydrol.
(2011) - et al.
Functional and ecological xylem anatomy
Perspect. Plant Ecol. Evol. Syst.
(2001) - et al.
Modeling effects of changing land use/cover on daily stream flow: an artificial neural network and curve number based hybrid approach
J. Hydrol.
(2013) - et al.
The impact of climate change on spatially varying groundwater recharge in the Grand River watershed (Ontario)
J. Hydrol.
(2007)