what weather conditions causes groundwater level to decrease
The coastline of China is approximately 18,000 km long. In virtually littoral cities, seawater intrusion is a serious threat to groundwater resource. Ix shallow monitoring wells were constructed to written report the dynamics of shallow groundwater level and salinity in the coastal plainly region of Jiangsu province, China. Results showed that atmospheric precipitation, evaporation, and river stage affected the groundwater level in our study area. Positive correlations were observed among the groundwater level, precipitation, and river phase; and then negative correlation existed between the groundwater level and evaporation. The influencing factors on the groundwater level were in the guild atmospheric precipitation > river stage > evaporation. Sufficient precipitation during the wet flavor diluted the groundwater salinity. After the dilution, betwixt two continuous precipitation events, the groundwater salinity increased as the groundwater level decreased. During the dry out flavor, the groundwater salinity chop-chop increased and reached its superlative in December. The groundwater salinity in December was 23 times higher than that in July. The groundwater level and salinity in this written report were generally associated with the flavor. Climate factors led to fluctuation of groundwater levels and salinity during the wet season, and seawater intrusion increased the groundwater salinity during the dry flavour.
one. Introduction
Knowledge of hydrological processes (change of groundwater level, groundwater quality, and tidal level) in coastal aquifers is important because approximately 50 percent of the world population live in coastal zones, peculiarly in low-lying deltaic areas within 60 km of the shoreline [i]. Littoral aquifers typically serve equally a major source of freshwater, such every bit drinking or irrigation water [2].
The groundwater level is a fundamental parameter for evaluating spatial and temporal changes in groundwater environments [3]. The groundwater level is governed by various factors. Climate change, as reflected in precipitation and evaporation rates, influences the groundwater level fluctuation [4]. Chen et al. also constitute that climate trends have loftier correlations with groundwater level variations in southern Manitoba [5]. In plain areas, precipitation infiltration and evapotranspiration in the vertical direction are the major recharge and discharge processes of the water cycle [6]. In our written report surface area, virtually of rainfall falls betwixt July and Oct. Seasonal variation in climate is very obvious. Then we focus on the influence of curt-term seasonal variation in climate on groundwater level in this place. The touch on of climate variability on groundwater levels can be investigated by analyzing the human relationship between climate records and groundwater level fluctuations.
The groundwater salinity is an important groundwater quality indicator, which is controlled by the factors such equally precipitation, evapotranspiration, mineralogy, type of aquifers, topography, and seawater intrusion [vii]. Climatic change and bounding main level ascension exacerbated saltwater intrusion, thereby jeopardizing water employ safety, especially during the dry season [8]. Saltwater intrusion can degrade water quality and reduce available water if bereft freshwater are entering the groundwater organization, and it became more than serious than it was before, specially in delta areas, because of climate alter [8]. Saltwater intrusion occurred globally in more than than 50 countries and regions, particularly Due north Africa, the Middle Due east, the Mediterranean, China, Mexico, and the Atlantic and Gulf Coasts of the United States, including Southern California [ix, 10]. Saltwater intrusion can negatively affect coastal ecosystems in terms of freshwater quality and the dynamics of plant customs. Along with saltwater intrusion, salinization of the groundwater systems may touch on agriculture and domestic and industrial water supplies [11]. Extensive researches were conducted worldwide to understand the mechanisms of saltwater intrusion. Ecology weather condition such as precipitation and evapotranspiration were clustered with hydraulic heads to show that they also influence salinity concentration in groundwater [vii]. In some place, seawater intrusion affects groundwater salinity in item flavour. For example, Rabbani et al. confirmed that saline water starts to penetrate inland during winter months [12]. Information technology is necessary to know the seasonal variations in groundwater salinity.
Groundwater plays a crucial function in the socioeconomic development of Jiangsu coastal plain, a developed area in eastern Cathay. In this place, shallow groundwater is easily afflicted by environment, such as climate change, river stage, and Yellow Sea tidal level. With a growing population, Jiangsu faces an increasing demand for freshwater. For solving this problem, deeply understanding the groundwater system and its influencing factors is necessary. So, the relationships among the groundwater level and climate factors, river stage, Yellow Sea tide level, and variations in groundwater salinity in this area have not been studied.
Thus, the purpose of this present study was to investigate the seasonal variations of groundwater level and salinity in Jiangsu coastal obviously. Specific objectives were (i) to observe the dynamics of groundwater level and salinity in wet and dry flavour; (two) to determine the relationships among the groundwater level, salinity content, climate factors (precipitation and evaporation), river stage, and Yellow Sea tide level. This study tin can provide a direction method for littoral plain groundwater past analyzing the factors that influence the groundwater level and the changing trends of groundwater salinity.
two. Materials and Methods
2.one. Study Site Clarification
Observational data on the groundwater level and salinity in Dongtai (120°07′~120°53′ Eastward and 32°33′~32°57′ N), Jiangsu in eastern Cathay were collected and investigated (Figure 1). Jiangsu coastal plain lies to the w of the Yellow Sea at an altitude ranging from 2.half dozen one thousand to four.6 chiliad above body of water level. Dongtai city is in the eastward of Jiangsu province and adjacent to the Xanthous Sea. The plain sandy expanse has a highly permeable soil that consists of mealy sand and extremely fine sand particles. The phreatic surface is at a shallow depth, more often than not 1 chiliad to 3 yard, and even 0.2 m after rainfall below the ground surface. The boilerplate annual temperature, average annual rainfall, and evaporation charge per unit are approximately 15.0°C, 1059.8 mm, and 1006.7 mm, respectively. During the report period in 2013, the annual mean precipitation was approximately 859 mm. The maximum precipitation is recorded in July earlier gradually decreasing. The annual evaporation is approximately 651.5 mm. Over 50% of the rainfall falls between July and October. Most rainfall in the summer is in the grade of local showers and thunderstorms, and in winter the rainfall corporeality is small-scale.
(a)
(b)
Because that most rainfall falls between July and October and very small amount of rainfall falls betwixt November and December in this place, July to October is recognized as the wet flavor and November to December is the dry out season.
two.ii. Experiment Blueprint
A farmland covering an area of 50 m × 100 k was selected equally a typical saline groundwater site with a shallow water tabular array to study the h2o and salt dynamics during different seasons. The farmland was bulldozed by machine to brand sure the country is flat and at that place is no vegetation in the farmland. The farmland is approximately 5 km away from the Yellow Ocean and ii km away from Liangduo River. Nine shallow monitoring wells were constructed and installed to a depth of 5 m in the aquifer of the farmland (Figure 2).
Information on daily precipitation, evaporation, river stage, and the Yellow Sea tide level were gathered from the Liangduo River dam monitoring signal of Jiangsu Province Hydrology and H2o Resources Investigation Bureau, which is located effectually 1.5 km northeast of the farmland. Atmospheric precipitation data were collected using a rain gauge and evaporation was measured using an E601 evaporation pan. Hateful daily river stage and survey of tide data were recorded manually and automatically using a groundwater level monitoring organization at Liangduo River dam. The recorded groundwater levels were based on the 1985 Xanthous Body of water elevation. All data were collected from July 1, 2013, to December 31, 2013.
Manual monitoring logger was set to discover the groundwater table and groundwater samples nerveless daily from the nine wells spread in the expanse. The recorded water levels are below the 1985 tiptop of the Xanthous Ocean. Each sample of 100 mL was nerveless from the upper monitor well. Daily groundwater level and salinity from all wells were monitored manually and analyzed. The groundwater level of ix wells had the same tendency. The average value of the daily groundwater level and salinity of nine wells were obtained from July 1, 2013, to December 31, 2013. The salinity value was calibrated under 25°C.
3. Results
3.1. Variations in Groundwater Level
The boilerplate depth of groundwater in the study area was 1.7 m. In the daily groundwater fluctuation figure, the shallowest groundwater level and the deepest groundwater level were identified. The first situation corresponded to one of the shallowest h2o levels (on October eight) and the other to the deepest one on August 24 (Figure three). The shallowest and deepest water levels were 24 cm and 254 cm, respectively.
(a)
(b)
The main factors that affected groundwater interaction were the climate parameters (rainfall and evaporation need) [xiii]. Precipitation infiltration was a key recharge source of shallow groundwater likewise equally the major recharge source of groundwater [xiv]. We observed that the groundwater level exhibited multipeak and multivalley curves and the fluctuation bicycle of groundwater synchronized with precipitation events (Figure 3(a)). During the wet season, frequent and sufficient rainfall led to big fluctuations in groundwater level and the shallowest h2o level was reached. As indicated in Figure 3(a), the fluctuation range related to rainfall peaked at 188 cm after heavy rain with 74.iv cm precipitation on Baronial 24 and a day of precipitation infiltration. During the dry out season, the groundwater level fluctuated inside a narrow range with low precipitation. During a nonrainfall period, the groundwater level exhibited a linear down trend because of evaporation and then increased until the adjacent precipitation occurred (Figures iii(a) and 3(b)). The menses from August 1 to xix is characterized past absence of rainfall, together with elevated temperatures and potential evapotranspiration; the longest nonrainfall period during the wet flavour occurred. During this menses, the groundwater level reduced by 175 cm. The groundwater level increased after the precipitation events and and then decreased gradually with evaporation. The groundwater tables varied inside the period from wet to dry out seasons and showed seasonal variations considering of the seasonal distribution of precipitation and evaporation.
In the condition of wake evaporation in December, downward trend of groundwater level was non obvious and even the level on December 31 was 3 cm shallower than December 1. The groundwater level in Dec declined initially and so increased without rainfall recharge which meant that except rainfall in that location were also other factors that afflicted groundwater level. The nearby Liangduo River or the Yellowish Sea may have had an outcome on the fluctuation without atmospheric precipitation events.
Linear regression assay was performed to investigate the relationships among precipitation, evaporation, river phase, sea tide level, and groundwater level. The method was used to identify the effective factors on groundwater level (Figure four). In this method, values were analyzed and the values indicated correlations between groundwater level and the influence factors. The values amidst precipitation, evaporation, river phase, sea tide level, and groundwater level ranged from 0.004 to 0.824. The output showed that precipitation, evaporation, and river stage were significant () effective on groundwater level in the study area. The fitting curve showed positive correlations among groundwater level, precipitation, and river stage, as well as a negative correlation between groundwater level and evaporation. Estimating a dependent variable, which is precipitation, largely contributed to obtaining groundwater level with the highest value. The guild of the influencing factors on groundwater level was precipitation > river stage > evaporation. The sea tide level did not affect the groundwater level ().
The result indicates that precipitation mainly drives dynamic changes in groundwater level in this written report surface area. The groundwater level exhibited multipeak curves and a shallower water level during the moisture season than during the dry flavor because of frequent precipitation events. During the dry out flavor without rainfall, the groundwater level fluctuated because of fluctuations in the Liangduo River stage. River stage had effect on groundwater level. The tide level of the Yellow Sea had no influence on the groundwater level.
3.ii. Variations in Groundwater Salinity
Groundwater salinity was more often than not affected by precipitation. The statistical values of precipitation and groundwater salinity are listed in Table 1, and the results are presented in Figure 5.
| | ||||||||
| Wet flavor | Dry flavour | Standard variance | ||||||
| July | August | September | October | Nov | December | |||
| | ||||||||
| Precipitation (cm) | Monthly | 170.half dozen | 85.1 | 95.2 | 60.six | 19.2 | 0 | threescore.88 |
| Sum | 411.5 | nineteen.2 | ||||||
| | ||||||||
| Evaporation (cm) | Monthly | 94.8 | 101.9 | 62.vi | 61.7 | 37.vii | 17.6 | 32.33 |
| Sum | 321 | 55.three | ||||||
| | ||||||||
| Groundwater salinity (g/kg) | Monthly | 0.87 | i.xx | i.69 | 2.12 | 4.59 | 19.7 | 7.31 |
| Average | 1.47 | 12.15 | ||||||
| | ||||||||
| Groundwater level (cm) | Monthly | 163.3 | 167.1 | 145.0 | 148.9 | 185.5 | 198.3 | 20.69 |
| Average | 156.17 | 191.99 | ||||||
| | ||||||||
The salinity data curve can be divided into two parts. Function I showed the data bend from July to October (wet flavor), wherein the groundwater salinity fluctuated according to precipitating events. The groundwater salinity was reduced later on atmospheric precipitation events, then began to increase gradually until the adjacent effect. Small increases of salinity during major rainfall intervals in Effigy 5 may advise that evaporation fails to accrue salinity due to rainfall washout. The fluctuation in the groundwater salinity could be related to precipitation events. Part II showed the information curve from November to December (dry season), wherein the corporeality of rainfall was lower than that during the moisture season. The groundwater salinity showed increasing trends in early November and so sharply increased in tardily November. The groundwater salinity increased with time and reached its maximum level (24.45 thousand/kg) in Dec.
Table 1 shows that the groundwater salinity increased equally monthly precipitation decreased. In July, with abundant atmospheric precipitation, the groundwater salinity was but 0.87 g/kg, the lowest salinity level in the study time serial. The groundwater salinity increased each month until the maximum monthly average was reached in December. The groundwater salinity in December was approximately 23 times college than that in July.
Table ii shows the 27 atmospheric precipitation events that occurred during the study series. Irresolute percentage is a ratio which is the differential value betwixt groundwater salinity before and later rainfall divided by groundwater salinity earlier rainfall. The value between precipitation and changing percentage of groundwater salinity is 0.653, which is significant at the 0.01 level. Atmospheric precipitation influenced salt dilution in groundwater. A sufficient amount of rainfall diluted salt in groundwater and decreased the groundwater salinity. Inadequate rainfall had no result on decreasing the groundwater salinity. The highest rainfall of 74.iv cm did not cause a high percentage of change. The highest modify per centum of groundwater salinity was caused past a 60.3 cm precipitation event, and the 3.3 cm precipitation event the next day resulted in a 45.22 change per centum. The changing pct was related not but to rainfall just also to groundwater level and the initial value of groundwater salinity. The private and small amount of rainfall had minimal or no issue on decreasing the groundwater salinity, particularly during the dry flavor. Rainfalls were all less than viii.5 cm during the dry flavor and no rainfall recharged the groundwater in December; groundwater salinity increased. The groundwater salinity sharply increased during the dry flavor, when no precipitation consequence occurred.
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| + means groundwater salinity increasing percent; − means groundwater salinity decreasing pct. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
three.3. Variations in Groundwater Salinity with Groundwater Level
Every bit analyzed in the preceding sections, rainfall caused the groundwater level and salinity to fluctuate, and groundwater salinity was depression when the corporeality of rainfall was large. After the decreasing of groundwater salinity acquired by rainfall, between two continuous precipitation events, groundwater salinity increased with the lowering of water levels. Our findings propose that salt movement is closely related to the groundwater table.
In different seasons, the groundwater salinity exhibited different trends every bit the groundwater level inverse, every bit shown in Figure vi. Praveena et al. indicated that high evaporation in areas with shallow groundwater tables may also lead to salinization [vii]. During the wet season, with high precipitation and evaporation, the groundwater level fluctuated frequently in a wide range and the groundwater salinity fluctuated synchronously with the groundwater level, just the trend appeared inversely.
During the observation menses, the correlation coefficient betwixt the groundwater level and salinity was 0.324 and was significantly correlated at the 0.01 level. The correlation coefficients from wet to dry out seasons were 0.259 and 0.529, respectively, and both were significantly correlated at the 0.01 level. This finding suggested that the groundwater salinity is associated with the groundwater level. The correlation coefficient during the wet season was lower than that during the dry season. Without the influence of precipitation events, a higher correlation between groundwater salinity and level was observed.
From November to Dec, the total rainfall was only xix.2 cm, which occurred in early on November. These precipitation events resulted in small-scale groundwater level fluctuations (Figure 6). The groundwater salinity curve did not exhibit any noticeable fluctuation, suggesting that the small amount of rainfall did not affect the groundwater salinity. After the precipitation events, the groundwater table remained relatively stable. The groundwater level fluctuation interval was 172 cm to 210 cm. During this nonrainfall menstruation, the variations in groundwater salinity were not similar to those at the groundwater level. The groundwater salinity increased suddenly in late Nov before entering a catamenia of sustained and rapid growth. Linear fits were conducted on groundwater salinity in early November and from late November to December. The linear fit equations were and , respectively. The growth rates of salinity were compared, with the latter menstruation showing college levels than the one-time. Without precipitation dilution, shallow groundwater salinity increased continuously during the dry out season.
four. Give-and-take
The precipitation, evaporation, and groundwater level values are reported in Tabular array 1. The time series shows that the wet season precipitation is significantly college than that during the dry out season, bookkeeping for 95 percentage of full precipitation. The evaporation and groundwater levels in the wet season are 5 times and 35 cm higher than those in the dry flavor, respectively.
iv.1. Furnishings of Precipitation, River Phase, and Evaporation on Dynamics of Groundwater Level
The dynamics of groundwater level in the study area are affected mainly past precipitation, water level of nearby river, and evaporation. Information technology was affected past precipitation, evaporation, and river stage. Dogan et al., Apaydin, Jan et al., Hong and Wan, and Carretero and Kruse constitute that atmospheric precipitation was ane of the dominant factors that contributed to groundwater level fluctuation [thirteen, fifteen–xviii]. In our report, the groundwater levels quickly changed post-obit each precipitation event. Later on rainfall, the groundwater level presented a linear downward trend considering of evaporation until the side by side precipitation effect occurred. The groundwater level was affected not only by precipitation and evaporation but also by the river stage.
4.2. Effects of Precipitation Dilution on Dynamics of Groundwater Salinity
The groundwater salinity tin can exist reduced afterwards the recharge of precipitation events. Research showed that the groundwater salinity changes according to precipitation events. Wang et al. pointed out that the precipitation infiltrated and leached down to recharge groundwater, which could refresh and dilute the salt of the soil h2o or groundwater during the rainy season [half-dozen]. Wang et al. observed that, during dry out seasons, shallow groundwater would be sanitized because of the evaporation and condensation furnishings in the north China plainly [half-dozen]. Rabbani et al. confirmed that saline h2o starts to penetrate inland during winter months when river menses is low and groundwater level decreases as a effect of climate change in Bangladesh [12]. These studies indicated that the shallow groundwater salinity would increase past evaporation in the status of no precipitation or saline h2o penetrating. In our study, loftier precipitation decreased the salinity concentration in groundwater during the wet season, and continues evaporation increase salinity dramatically during the dry season. The amount of atmospheric precipitation serves an of import function in table salt dilution. Taking advantage of atmospheric precipitation can be a expert method to control groundwater salinity in a littoral apparently.
4.3. Variations in Groundwater Level Influence on Groundwater Salinity
According to the entire written report time series, groundwater salinity changed according to the fluctuation of groundwater level. During the dry season, the correlation coefficient between the groundwater level and salinity was higher than that during the moisture flavour. The fluctuations of groundwater level were mainly caused by atmospheric precipitation and evaporation in wet season, while in dry season the groundwater level was mainly affected by the water level of Liangduo River and groundwater salinity concentration was increased sharply past seawater intrusion. Zhou et al. establish that the saltwater intrusion is mainly controlled by river belch and tidal current in Zhujiang River Estuary [19]. It is also related to wind aamplitude and management and sea level rising. A deep mechanism of saltwater intrusion should be investigated. For a clearer mechanism of saltwater intrusion in this study surface area, not only climate factors just as well more influencing factors as above can be researched. And spatial assay should be focused on.
v. Conclusions
In coastal plainly of eastern China, the average depth of groundwater level is shallow and easily affected by climate factors (precipitation and evaporation) and river stage. The influencing factors on the groundwater level were in the order atmospheric precipitation > river stage > evaporation. The groundwater salinity is influenced by climate factors, groundwater level, and seawater intrusion. Precipitation infiltrated into groundwater and diluted the salinity, then the groundwater salinity fluctuated with precipitation events. Between two precipitation events, groundwater salinity increased with evaporation. Groundwater salinity changed with the fluctuation of groundwater level and pregnant correlation was found betwixt them (). In the study period, the groundwater salinity fluctuated frequently. During wet flavour it maintained in a low salinity level. It increased continuously and reached a maximum value in December during the dry flavour. The issue indicated that seawater intrusion occurred in the coastal manifestly in dry season.
Conflict of Interests
The authors declare that in that location is no conflict of interests regarding the publication of this paper.
Acknowledgments
This study was financially supported by the Public Welfare Industry Special Funds for Scientific Research Projects of the Ministry of H2o Resources (Grant no. 200801025) and the Innovative Project of Scientific Enquiry for Postgraduates in Ordinary Universities in Jiangsu Province (Grant no. CXZZ13_0267). The authors thank Jiangsu Province Hydrology and Water Resource Investigation Bureau for providing them with climate data.
Copyright
Copyright © 2015 Shao-feng Yan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted utilise, distribution, and reproduction in whatever medium, provided the original work is properly cited.
Source: https://www.hindawi.com/journals/jchem/2015/905190/
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