Analysis of dynamic characteristics and driving factors of Jinan spring water on a long-time scale

Springs of Jinan City in Shandong Province are typically large karst ones in Northern China. With 136 mouths of springs, there are four major spring groups, namely, Baotu Spring, Heihu spring, Wulongtan spring and Pearl spring, distributed around the moat in the urban area. Springs are the lifeblood of Jinan City and play an important role in the development of this city. However, since the dry season in 1972, the springs had witnessed seasonal cutoffs. Baotu Spring even experienced complete cutoffs throughout the respective year of 1982, 1988 and 1989. From 1999 to 2002, the cutoff of this spring spanned 926 days, the longest cutoff time in history. Until September 2003, thanks to a series of measures taken by the government, the four major springs began to gush all year-round, but the spring flow is much less than before.

Currently, studies usually focus on short-time-span spring dynamics in Jinan instead of long-term comparative studies on spring dynamics in different periods. Especially, the strong human influence on spring dynamics after springs gushed again needs further research. Few analyses of the influence factors of complex human activities, such as the impact of urban construction are relatively few. In these studies, the whole built-up area has been taken as the object, which ignores the fact that the runoff discharge area itself does not have the condition of infiltration, resulting in the overestimation of hardening area in statistics. In order to comprehensively explore the dynamic evolution of the four major spring groups and the main control factors affecting spring gushing, we have conducted a study on the dynamic characteristics and causes of springs over the past 60 years for the development and utilization of karst groundwater resources and environmental protection in the Jinan region.

To identify the dynamic change pattern of the four spring groups in Jinan, we have studied the dynamic change characteristics of the springs and their influencing factors such as natural-human activities, etc. through correlation analysis, partial correlation analysis, regression analysis, and water balance analysis, based on a series of monitoring data for a long term. The results indicate that the dynamics of the four springs in Jinan City have experienced four stages: stage 1 from 1959 to 1967, at which the springs gushed spectacularly with a large amount of flow at a high water level; stage 2 from 1968 to 1980, at which the landscape of springs attenuated with a small amount of flow at a low water level; stage 3 from 1981 to 2002, at which the springs experienced long-term intermittent cutoff with a very small amount of flow at a rather low water level; stage 4 from 2003 up till now, at which the springs gushed again because of the regulated restoration. At stage 4, the average flow rate of springs decreased from 366.6 thousand m³·d⁻¹ to 142.0 thousand m³·d⁻¹, then to 46.9 thousand m³·d⁻¹, but subsequently recovered to 170.6 thousand m³·d⁻¹; the average water level of springs decreased from 30.48 m to 27.91 m, then to 26.25 m, but afterward, recovered to 28.24 m.

In addition, this study quantitatively identifies the influencing factors and the degree of impact in each stage. The main control factors at stage 1 are precipitation and extraction, with an average impact degree of 581.7 thousand m³·d⁻¹ and −95.8 thousand m³·d⁻¹; the main control factors at stage two are precipitation, extraction and water engineering, with an average impact degree of 520.1 thousand m³·d⁻¹, −426.1 thousand m³·d⁻¹ and −59.8 thousand m³·d⁻¹; the main control factors at stage 3 are extraction, precipitation, water engineering, and urban construction, with an average impact degree of −518.2 thousand m³·d⁻¹, 514.2 thousand m³·d⁻¹, −69.2 thousand m³·d⁻¹ and −24.0 thousand m³·d⁻¹; the main control factors at stage 4 are precipitation, extraction, ecological replenishment sources, urban construction, and water engineering, with an average impact degree of 553.8 thousand m³·d⁻¹, −254.4 thousand m³·d⁻¹, 103.6 thousand m³·d⁻¹, −89.9 thousand m³·d⁻¹ and −65.6 thousand m³·d⁻¹. In general, precipitation and extraction control the spring flow, but other driving factors gradually increased with the development at the four stages. Before the springs gushed again, the impact of precipitation gradually weakened, but the influence of extraction, urban construction and water conservancy projects gradually increased by degrees. After the springs gushed again, the impact of the government's regulation and control played a dominant role.

To keep a continuous gush of spring, first of all, we should ensure that Baotu Spring area 3-type water conversion can be effectively carried out. Besides, we should strengthen dynamic monitoring and regulation, rationally coordinate major factors such as groundwater mining, ecological replenishment and water conservancy projects, etc., and formulate an optimal groundwater development program in a scientific and elaborate way, relying on the sharing mechanism among different departments. Finally, in order to reduce the impact of urbanization on springs, we should strengthen the protection and restoration of ecological environmental in the recharge area of southern springs so as to improve the capacity of water resources conservation. The research results can provide basis for spring runoff protection.