• Journal of Environmental Impact Assessment
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• v.29 no.5
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• pp.323-337
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• 2020

Long-term continuous data were used to investigate changes in air and water temperature and temperature hysteresis at Lake Paldang, the largest source of drinking water in South Korea. Based on the temperatures at Yangpyeong, near Lake Paldang, using a seasonal Mann-Kendall test, the rate of change of increase in temperature over the last 27 years (0.060℃/yr, 1993-2019) was higher than that of during 47 years (0.048℃/yr, 1973-2019). The air and water temperatures in Lake Paldang and its influent rivers had a high correlation (R > 0.9, p < 0.005); however, the water temperature increased at rate slower than the river water temperature, and the water temperature decreased slowly as the air temperature fell. The depth-averaged water temperature also changed more slowly than the surface water of the lake both when the air temperature was high and when it was low. This is likely because the lake has a larger area and a longer heat retention time than rivers, resulting in a greater hysteresis of water temperature at lake.

• Journal of Wetlands Research
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• v.24 no.4
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• pp.301-311
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• 2022

The purpose of this study is to analyze the seasonal characteristics of water quality using long-term water quality monitoring data. Seasonal characteristics of water quality were analyzed using monitoring data from 34 tributaries where long-term monitoring was performed in the Nakdong River system, and average data analysis of water quality, coefficient of variation analysis, and trend analysis were performed for seasonal analysis. For seasonal analysis, average data analysis of water quality, coefficient of variation analysis, and trend analysis were performed. As a result of the evaluation of the coefficient of variation, tributaries were larger than main streams, and BOD, T-P, and TOC were larger in autumn and T-N were larger in spring. Trend analysis was analyzed using Mann-Kendall and Sen's Slope. BOD, T-N, and T-P tended to decrease, but TOC had a lot to increase. Through this study, it was possible to evaluate the availability of long-term water quality monitoring data and analyze seasonal characteristics, and to analyze the stabilization period of water quality and changes in pollutant sources for watershed management.

• Current Research on Agriculture and Life Sciences
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• v.32 no.3
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• pp.135-143
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• 2014

The variability and temporal trends of the annual and seasonal minimum and maximum temperature, rainfall, relative humidity, wind speed, sunshine hours, and runoff were analyzed for 5 major rivers in Korea from 1960 to 2010. A simple regression and non-parametric methods (Mann-Kendall test and Sen's estimator) were used in this study. The analysis results show that the minimum temperature ($T_{min}$) had a higher increasing trend than the maximum temperature ($T_{max}$), and the average temperature increased by about $0.03^{\circ}C\;yr.^{-1}$. The relative humidity and wind speed decreased by $0.02%\;yr^{-1}$ and $0.01m\;s^{-1}yr^{-1}$, respectively. With the exception of the Han River basin, the regression analysis and Mann-Kendall and Sen results failed to detect trends for the runoff and rainfall over the study period. Rapid land use changes were linked to the increase in the runoff in the Han River basin. The sensitivity of the evapotranspiration and ultimately the runoff to the meteorological variables was in the order of relative humidity > sunshine duration > wind speed > $T_{max}$ > $T_{min}$. Future studies should investigate the interaction of the variables analyzed herein, and their relative contributions to the runoff trends.

• Journal of Environmental Science International
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• v.27 no.11
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• pp.1029-1048
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• 2018

In this study, seasonal Mann - Kendall test method was applied to 12 stations of the water quality measurement network of Nam-River based on data of BOD, COD, TN and TP for 11 years from January 2005 to December 2015 The changes of water quality at each station were examined through linear trends and the tendency of water quality change during the study period was analyzed by applying the locally weighted scatter plot smoother (LOWESS) method. In addition, spatial trends of the whole Nam-River were examined by items. The flow-adjusted seasonal Kendall test was performed to remove the flow at the water quality measurement station. As a result, BOD, COD concentration showed "no trand" and TN and TP concentration showed "down trand" in regional Kendall test throughout the study period. BOD and TP concentration in "no trand", COD, and TN concentration showed an "up trand" tendency in Nam-River dam. LOWESS analysis showed no significant water quality change in most of the analysis items and stations, but water quality fluctuation characteristics were shown at some stations such as NR1 (Kyungho-River 1), NR2 (Kyungho-River 2), NR3 (Nam-River), NR6 (Nam-River 2A). In addition, the flow-adjusted seasonal Kendall results showed that the BOD concentration was "up trand" due to the flow at the NR3 (Nam-River) station. The COD concentration was "up trand" due to the flow at NR1 (Kyungho-River 1) and NR2 (Kyungho-River 2) located upstream of the Nam-River. The effect of influent flow on water quality varies according to each site and analysis item. Therefore, for the effective water quality management in the Nam-River, it is necessary to take measures to improve the water quality at the point where the water quality is continuously "up trand" during the study period.

• Journal of Korea Water Resources Association
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• v.46 no.6
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• pp.667-681
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• 2013

In this study, monthly and seasonal dissolved oxygen trends of 19 water quality measurement stations in Sapgyo stream watershed were analyzed using monthly dissolved oxygen (DO) data measured for 16 years (1995~2010). Mann-Kendall trend test and Sen's slope estimator were carried out for trend analysis. Furthermore, Sapgyo stream watershed was divided into four different sections (Sapgyo stream, Muhan stream, Gykgyo stream, and Sapgyo lake) and chi-square test of homogeneity for DO trend was carried out for four different sections. The study results indicated that most of water quality measurement stations showed increasing or non-significant trend of DO on a monthly and seasonal basis. The chi-square test of homogeneity for each water quality measurement station showed the statistical homogeneity in seasonal DO trend; however, the test results showed the statistical non-homogeneity in monthly DO trend for the stations located in the reservoir. Overall, the dissolved oxygen trend in each water quality measurement station showed different patterns depending on the location of each station and season.

• Korean Journal of Ecology and Environment
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• v.48 no.2
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• pp.95-107
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• 2015

In order to identify long-term trends of water quality parameters in Lake Kyeongpo, Mann-Kendall test, Sen's slope estimator and linear regression were applied on data, with 15 parameters from three different sites and rainfall, monitored once in every two months from March to November during 1998~2013. Seasonal variation analysis only used Mann-Kendall test and Sen's slope estimator. Analysis result showed that salinity, transparency and nutrient variables (total phosphorus, dissolved inorganic phosphorus, total nitrogen, nitrate nitrogen, ammonia nitrogen) were only parameters having statistically significant trend. In linear regression analysis, salinity (surface and bottom layer of all sites) and transparency (only at site 1), were figured out with statistically significant increasing trend, while in non-parametric statistical method, salinity and transparency in all sites (surface, middle, deep) were figured out with statistically significant increasing trend. Water quality parameters showing statistically significant decreasing trends were dissolved oxygen (surface layer of site 1 and bottom layer of sites 2 and 3), total phosphorus (sites 1 and 2), dissolved inorganic phosphorus, total nitrogen, nitrate nitrogen and ammonia nitrogen in the linear regression analysis and, dissolved oxygen (bottom layer of all sites), total phosphorus, dissolved inorganic phosphorus, total nitrogen, nitrate nitrogen and ammonia nitrogen in the non-parametric method. Seasonal trend analysis result showed that salinity, turbidity, transparency and suspended solids in spring, salinity, transparency, nitrate nitrogen and suspended solids in summer and temperature, salinity, transparency and suspended solids in fall were the variables depending on the season with increasing trends. In general, rainfall during the research period showed decreasing trend. The significant reduction trends of nutrients in Lake Kyeongpo were believed to be related to lagoon restoration and water management project run by Gangneung city and under-water wear removal, but further detailed studies are needed to know the exact causes.

• Environmental Engineering Research
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• v.21 no.1
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• pp.58-68
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• 2016

The study explored droughts using the Standardized Precipitation Index (SPI) in the northwestern region of Bangladesh, which is the drought prone area. In order to assess the trend and variability of monthly rainfall, as well as 3-month scale SPI, non-parametric Mann-Kendall (MK) tests and continuous wavelet transform were used respectively. The effect of climatic parameters on the drought in this region was also evaluated using SPI, with the Southern Oscilation Index (SOI) by means of the wavelet coherence technique, a relatively new and powerful tool for describing processes. The MK test showed no statistically significant monthly rainfall trends in the selected stations, whereas the seasonal MK test showed a declining rainfall trend in Bogra, Ishurdi, Rangpur and Sayedpur stations respectively. Sen's slope of six stations also provided a decreasing rainfall trend. The trend of the SPI, as well as Sen's slope indicated an increasing dryness trend in this area. Dominant periodicity of 3-month scale SPI at 8 to 16 months, 16 to 32 months, and 32 to 64 months were observed in the study area. The outcomes from this study contribute to hydrologists to establish strategies, priorities and proper use of water resources.

• Journal of The Korean Society of Agricultural Engineers
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• v.62 no.5
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• pp.15-26
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• 2020

There are fifteen non-point pollution management areas in Korea and three of them (Doam lake, Daegi district and Golji-cheon) are located in the upstream of the Namhan river watershed. Many efforts to reduce non-point sources (NPS) pollution have been conducted, however, water quality pollution in the watershed is still serious. To solve these problems, it is a priority to grasp water quality using statistical techniques. In this study, a trend analysis was conducted to evaluate the effect of NPS management in the watershed. The long-term trends from 1996 to 2018 of water quality properties were analyzed using data collected from the water environment information system. Seventeen monitoring stations were selected along the main stream in Namhan river basin. Monthly water quality properties (BOD, COD, TN, TP, TN/TP ratio, Conductivity, SS and Chlorophyll-a) were collected and analyzed by Mann-Kendall test and LOWESS. The results showed that the Conductivity tended to increase in all regions and was the highest level in Jijangcheon. Organic pollution such as BOD and COD tended to increase in the Jungseon area. SS did not show a large tendency, but it showed high concentration in the Doam watershed. In all regions, 40% of water quality properties showed a tendency to 'UP', 15% of water quality properties tended to 'DOWN', and 46% indicated no tendency. In order to determine the cause of this, additional research and measures for improvement are necessary. This study will be used for the establishment of water quality policy in the future.

• Journal of Korean Society on Water Environment
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• v.33 no.1
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• pp.15-33
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• 2017

Based on the existing pollutant emissin standards which are armed at the pollutant concentration of each pollution source, government formulated and implemented new management system of total water pollutant emission. By virtue of this new management system, pollution loading amount of individual watershed could be controlled, which achieved the requirement of water quality management such as TP and BOD. In initiate stage of it's implement, BOD was selected as object of water quality management, While it's necessary to consider the continuity of water quality data and established pollutant management laws and policy. During the ongoing management, TP management was added into the system while simply BOD management was not enough. However, the frequency of algae bloom in Han-river showed a trend of same, even though TP was treated as additional control target. Therefore, this paper will analyze different water quality parameters and characteristic of water quality, so that this study can be provide as reference for watershed management of water quality, by which the applicable management period and target pollutant can be selected in the future.

• Korean Journal of Ecology and Environment
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• v.35 no.1 s.97
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• pp.36-44
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• 2002

The spatial and temporal trends of water qualities in Lake Soyang was statistically analyzed in this study. The water qualities include nutrients, ionic contents and chlorophyll-a (Chl-a) measured during 1993${\sim}$2000. The rainfall intensity and runoff from the catchment appeared to play an important role in water quality trends in the lake. According to seasonal Mann-Kendall test, conductivity, TP, and Ctl-a did not show any trends of increase or decrease over the 8 year period, while TN declined slightly. It was found that the variation of TP was a function of interannual inflow and rainfall. In the analyses of spatial trend, conductivity, based on the mean by site, showed a downlake decline over the eight year period. Minimum conductivity was found in the headwaters during summer monsoon of July to August and near the dam during October. This result indicates a time-lag phenomenon that the headwater is diluted by rainwater immediately after summer monsoon rain and then the lake water near the dam is completely diluted in October. During summer period, TP and TN had an inverse relation with conductivity values. Concentrations of TP peaked during July to September in the headwaters and during September in the downlake. Also, TN increase during the summer and was more than 1.5 mg/L regardless of season and location, indicating a consistent eutrophic state. Values of Chl-a varied depending on location and season, but peaked in the midlake rather than in the headwaters during the monsoon. Regression analyses of log-transformed seasonal Chl-a against TP showed that value of $R^2$ was below 0.003 in the premonsoon and monsoon seasons but was 0.82 during the postmonsoon, indicating a greater algal response to the phosphorus during the postmonsoon. In contrast, TN had no any relations with Chl-a during all seasons.