Effects of Groundwater Table Decline on Vegetation Transpiration in an Arid Mining Area: A Case Study of the Yushen Mini
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TECHNICAL ARTICLE
Effects of Groundwater Table Decline on Vegetation Transpiration in an Arid Mining Area: A Case Study of the Yushen Mining Area, Shaanxi Province, China Qiangmin Wang1,2,3 · Shuning Dong1,2,3 · Hao Wang1,2,3 · Jian Yang2,3 · Chunhu Zhao2,3 · Xingling Dong2,3 · Tiantian Wang2,3 Received: 28 September 2019 / Accepted: 1 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We studied the effects of coal mining on the shallow groundwater regime and vegetation in the Yushen mining area (YMA) in northwestern China using a Hydrus-1D numerical model, which was calibrated and validated with field observations, and then used to simulate the effects of groundwater table (GWT) changes on transpiration rates. The actual transpiration ( Ta) was influenced by both GWT depth (GWTD) and precipitation. The ratios of T a and potential transpiration (Tp) vs. GWTD were fitted to a mono-exponential decay of GWTD with correlation coefficients as high as 0.98. Two threshold values, d(Ta/ Tp)/d(H) ≤ − 2% and Ta/Tp = 0.30, were then used to calculate the unaffected and critical depths. The average unaffected and critical water depths were 3.60 and 2.20 m, respectively, which coincided fairly well with the field investigation. The sensitivity analysis showed that although reducing hydraulic conductivity ( Ks) caused the T a/Tp to decline, decreasing the inverse of the air-entry pressure (α) caused the T a/Tp to increase, so variations in K s and α had only a minor effect. Considering that the pre-mining GWTD is between 0 and 4.0 m for about half of the YMA, the vegetation there might be degraded or lost by a GWT decline due to mining. Also, the influence of a GWT decline on transpiration was more obvious during a drought in the YMA. Therefore, effective measures must be taken to avoid a decrease in the GWT. For example, mine water should be reinjected and the mining height reduced to protect the YMA’s shallow groundwater. Keywords Numerical modelling · Unaffected and critical depths · Mitigation strategies · Arid coal mining area
Introduction Transpiration is a key component of the water cycle (Schlesinger and Jasechko 2014) and its precise estimation has a direct influence on water balance analysis (Cheng et al. 2013). However, transpiration is affected by several factors, such as climatic conditions (Meinzer et al. 1999), irrigation * Qiangmin Wang [email protected] * Hao Wang [email protected] 1
China Coal Research Institute, Beijing 100013, China
2
Xi’an Research Institute of China Coal Technology and Engineering Group Corp, Xi’an 710054, China
3
Shaanxi Key Laboratory of Prevention and Control Technology for Coal Mine Water Hazard, Xi’an 710054, China
(Zhang et al. 1998), land-use (Olchev et al. 2008), vegetation type (Springer et al. 2006), and the groundwater table (GWT; Noest 1994; Duan et al. 2011). Most studies have suggested that transpiration is mainly controlled by groundwater depth for phreatophytes (Baird and Iii 2005; Laio et al. 200
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