Abstract
Over the last 40 years, declining spring water flow rates have become a typical feature of karst springs in Northern China. Wavelet analysis, the Mann-Kendall trend test and the mutation test were used to analyze dynamic monitoring data of groundwater levels and atmospheric precipitation in the Jinan karst spring area, from 1956 to 2013, to study hydrological responses to atmospheric precipitation over one-year periods. Results from this analysis show that: (1) Atmospheric precipitation and the spring water level displayed multi-scale change characteristics, having two very similar cycles of change of 16 and 12 years. This finding shows that atmospheric precipitation generates a direct impact on the level of spring water. (2) From 1956 to 2013, the groundwater level in the Jinan spring area had a significant downward trend (0.65 m/10a). Precipitation recorded an increasing trend (12.65 mm/10a), however this was not significant. The weight of the influencing factors of the spring dynamic therefore changed due to the influence of human factors. (3) A mutation of atmospheric precipitation occurred in 1999, after which annual precipitation increased. Results for the mutation of the groundwater level showed an initial change in 1967. After this change the water level continued to decrease before rapidly increasing after 2004. The future trend of the spring water level should be maintained with consistent precipitation (having an upward trend), indicating that atmospheric precipitation is not the only factor affecting the dynamics of the spring. (4) Different periods were identified on the multiple regression model. The main influencing factors on groundwater level over the past 58 years were identified as a transition from precipitation to artificial mining. These results also validate the suitability and reliability of using wavelet analysis and the Mann-Kendall test method to study groundwater dynamics; these results provide a reference for the future protection of the Jinan City spring.
Highlights
Atmospheric precipitation is an important factor affecting groundwater dynamics and periodic precipitation affects groundwater levels by ensuring a certain period of change [1,2,3,4,5]
Analysis of these four phases indicated that factors influencing groundwater level in the Jinan spring area are dynamic and changeable
The main causes of groundwater level changes in the early study period were found to be was in a state of high flow and had a high water level, 1965 to 1989: Flow from the spring declined and the groundwater level recorded a significant decline, 1990 to 2002: This period was regarded as the spring seasonal outflow/low water level fluctuation stage, 2003 to 2013: This stage recorded recharge of the artificial groundwater and was characterized by the spring flowing during this period
Summary
Atmospheric precipitation is an important factor affecting groundwater dynamics and periodic precipitation affects groundwater levels by ensuring a certain period of change [1,2,3,4,5]. Baotu spring, located in Jinan city, is historically very important in China, it is renowned across the world. Karst water from the springs in the Jinan area has historically been the main water source. Water 2018, 10, 698 with economic and population development, the volume of groundwater exploitation has sharply increased in this area since the early 1970s, and artificial exploitation has had a tremendous impact on spring water supply. In 1972 Baotu spring seasonal stopped flowing, creating great concern for local inhabitants. In order to resume spring flow it was stipulated in 2003 that large-scale exploitation of groundwater should be prohibited near the spring area. With issues relating to flow levels in the spring not being resolved with the substantial reduction in exploitation, we can infer that influencing factors on spring dynamics due to anthropogenic activities have changed
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