Water quality and limnology of Korean reservoirs

Reservoirs are the predominant type of lentic ecosystem in Korea, and they account for a considerable proportion (~59%) of the agricultural water uses. There are 18,797 reservoirs in Korea; most (~90%) are small (storage capacity <1,000,000 m³), and most provide irrigation water for paddy farming. Characteristics of Korean agricultural reservoirs are high watershed-reservoir area ratios, shallow depth, unstable hydrodynamics, and eutrophic conditions. Many agricultural reservoirs are relatively old; 54% of all reservoirs were constructed more than 50 years ago. As a result, they have a considerable amount of organic matter accumulation on the sediment, which may contribute to the internal loading of nutrients. Deterioration of water quality and ecosystem health, resulting from cultural eutrophication and harmful algal blooms, are common problems in most Korean agricultural reservoirs. Environmental considerations about reservoirs, especially their ecological functions, have largely been ignored in past management plans. Limnology, the multidisciplinary study of lakes and reservoirs, can provide conceptual models of reservoirs and fundamental information needed to determine causes and potential solutions for environmental stresses. Problems prevailing in Korean reservoirs, such as cultural eutrophication and harmful algal blooms, are complicated ecosystem-level phenomena with many factors interacting with each other. Thus, limnological understanding is a prerequisite to identifying sound solutions and to making wise judgments about reservoir management and restoration. Cooperation with other related disciplines is necessary to establish the proper management plans and applications. Also, international cooperation is suggested to solve environmental problems in agricultural reservoirs, particularly among the countries with similar agricultural practices, climate, geology, and water uses. Electronic Publication     

Pollution control via a dredged pool at the inlet of a reservoir

We investigated the applicability of a dredged pool formed at the inlet of a reservoir for pollution control. To quantify the effect of a dredged pool on the water quality of a reservoir, we monitored the water quality of the Masan Reservoir, located in the city of Asan, Choongnam Province, Korea, before and after dredging. In addition, a completely mixed box model was applied to simulate the water quality of the dredged pool and reservoir. The model included a water balance equation and chemical mass balance equation, into which several interactions among water quality components, such as phytoplankton, total nitrogen (T-N), total phosphorus (T-P), dissolved oxygen, and chemical oxygen demand (COD), were incorporated. The water quality monitoring and modeling results indicated that reservoir water quality was greatly affected by the dredged pool. The loads of T-N and T-P into the reservoir were reduced by the dredged pool, which may have induced the removal of nutrients by settling. However, the dredged pool may have had a negative effect on the reservoir in terms of COD and chlorophyll-a because of the internal production of organic matter and/or algae with water detention. Therefore, a dredged pool may be used for pollution control in a reservoir, as long as it is combined with measures to reduce concentrations of organic matter and/or algae.     

Development of natural and ecological wastewater treatment system for decentralized community in Korea

A pilot study of the natural and ecological wastewater treatment system (NEWS) was performed to treat sewage in decentralized small rural communities in Korea. The absorbent-biofilter system (ABS) provided secondary level pretreatment and demonstrated high removal efficiency especially for SS and BOD₅ showing 88.5 and 82.9%, respectively. The influent and effluent concentrations of TN were 42.1 and 26.2 mg L⁻¹, respectively, with the removal efficiency of 37.8%. In case of TP, the removal efficiency was 45.1% with the influent and effluent concentrations of 3.1 and 1.7 mg L⁻¹. The ABS effluent could not meet the effluent standards, and the further treatment was required. The subsequent up- and down-flow constructed wetland (UDCW) provided further polishing of the ABS effluent and demonstrated effective removal of nutrients as well as SS and BOD₅ with over 70% removal rates. Overall performance of the NEWS, which was composed of ABS and UDCW, demonstrated remarkably high removal rates for BOD₅ (>95.7%), SS (>97.5%), TN (>91.8%) and TP (>90.1%) and met all the effluent standards stably independent of temperature and influent loading in the experimental range. The UDCW used light and porous granular substrate (∅ 5–10 mm, specific gravity of 1.2) with large surface area, and clogging problem was not observed during the study period. The system was cost effective and required minimal maintenance and negligible amount of electricity, and problems associated with noise, odor, files, and sludge were not observed. Considering characteristics of decentralized wastewater treatment systems, the NEWS system was found to be a practical alternative and its application is recommended up to 300 m³ day⁻¹. The NEWS system has an economic problem above 300 m³ day⁻¹, because of complicated equipment, higher operation costs, and maintenance specialists. The NEWS system was coast effective and required minimal maintenance and negligible amount of electricity, and problems associated with noise, odor, files, and sludge were not observed.     

A simplified method for the simultaneous extraction of phytoplanktonic chlorophyll and fecal sterol from water

A simple column method employing Amberlite XAD-1 (60–120 mesh) resin for the simultaneous extraction of coprostanol and algal chlorophyll a was proposed and evaluated. The results showed that the efficiencies of the column extraction for these two water quality indicators were comparable to or better than the conventional hexane liquid/liquid partitioning and aqueous acetone extraction for the respective compounds. Furthermore, the column technique was time-saving and more economical.     

Spirulina maxima Derived Pectin Nanoparticles Enhance the Immunomodulation,Stress Tolerance,and Wound Healing in Zebrafish

In this study, Spirulina maxima derived pectin nanoparticles (SmPNPs) were synthesized and multiple biological effects were investigated using in vitro and in vivo models. SmPNPs were not toxic to Raw 264.7 cells and zebrafish embryos up to 1 mg/mL and 200 µg/mL, respectively. SmPNPs upregulated Il 10, Cat, Sod 2, Def 1, Def 2, and Muc 1 in Raw 264.7 cells and tlr2, tlr4b, tlr5b, il1β, tnfα, cxcl8a, cxcl18b, ccl34a.4, ccl34b.4, muc5.1, muc5.2, muc5.3, hamp, cstd, hsp70, cat, and sod1 in the larvae and adult zebrafish, suggesting immunomodulatory activity. Exposure of larvae to SmPNPs followed by challenge with pathogenic bacterium Aeromonas hydrophila resulted a two-fold reduction of reactive oxygen species, indicating reduced oxidative stress compared to that in the control group. The cumulative percent survival of larvae exposed to SmPNPs (50 µg/mL) and adults fed diet supplemented with SmPNPs (4%) was 53.3% and 76.7%, respectively. Topical application of SmPNPs on adult zebrafish showed a higher wound healing percentage (48.9%) compared to that in the vehicle treated group (38.8%). Upregulated wound healing markers (tgfβ1, timp2b, mmp9, tnfα, il1β, ccl34a.4, and ccl34b.4), enhanced wound closure, and restored pigmentation indicated wound healing properties of SmPNPs. Overall, results uncover the multiple bioactivities of SmPNPs, which could be a promising biocompatible candidate for broad range of aquatic and human therapies.     

Water quality monitoring and multivariate statistical analysis for rural streams in South Korea

South Korea is located in the Asian monsoon region, and paddy rice farming is one of the important agricultural activities, which may contribute to the non-point source pollution of inland water bodies along with rainfall runoff. The status of water quality in rural streams located throughout South Korea was examined in this study by water quality monitoring and statistical analysis. Totally six surveys were conducted in 2003 and 2005 to monitor 300 streams located in rural subwatersheds; these streams are affected by agricultural activities and water supply for agricultural practices. The monitoring was performed at the terminal point of each subwatershed. In each study year, the streams were monitored in the three hydrological periods (April, July, and October) to observe differences in the impacts of agricultural activity and rainfall pattern. During the surveys, 15 water quality parameters were measured and interpreted using multivariate statistical methods including factor analysis and cluster analysis. Results show that the water quality of the rural streams monitored in this study appeared to meet the Korean water quality criteria for agricultural use, which are 8.0 and 100 mg/L for biochemical oxygen demand and suspended solids, respectively. In terms of organic contamination and suspended solids, the best stream water quality was observed in October compared to other periods. This can be attributed to the fact that October follows the rice-harvesting period and has low rainfall; thus the streams are probably less affected by agricultural activities and surface runoff. The three hydrological periods did not show much variation in the nitrogen and phosphorus parameters related to stream water nutrient conditions. Factor analysis indicates that the first five factors for April explained about 67% of the total sample variance. In July, the first four factors explained about 60% of the total variance, while the first four factors for October explained about 65%. Cluster analysis reveals that the streams could be divided into four groups in April and October and five groups in July. The box-and-whisker plots of the physicochemical variables indicate that Group A had the best water quality among the groups. This study demonstrates that the rural stream water quality of South Korea in the Asian monsoon region can be greatly affected by agricultural activities such as paddy rice farming and rainfall patterns.     

Estimation of pollutant loads in an estuarine reservoir considering pollution source characteristics and seasonal variation

The Total Maximum Daily Load (TMDL) program is an integrated process of watershed assessment and management to address surface water quality impairment. The management of organic contaminants and nutrients is a primary concern in conserving surface water bodies. Watershed-scale pollutant loads simulation can assist stakeholders and watershed planners in making decisions on immediate and long-term land use schemes to improve water quality. However, the behavior of contaminants in a watershed needs to be characterized prior to such model applications. The objectives of this study were to characterize point and nonpoint pollutants runoff at a watershed scale and to develop a Pollutant Load Calculation Model (PLCM), which facilitates the estimation of pollutant delivery to a watershed outlet. The developed model was applied for the six sub-watersheds of the Saemangeum estuarine watershed in Korea, where a large tidal reclamation project has been underway. Two years stream flow and water quality data were used for the model calibration, while 1 year data were utilized for the model validation. The model calibration resulted in the R ² values of 0.58, 0.53, and 0.35 for BOD, TN, and TP, respectively. Overall performance for the validation period was similar with that for the calibration period although the R ² values were slightly decreased. The PLCM tends to substantially under or overestimate delivery pollutants loads during the summer rainy seasons when most rainfall events occur. This is probably because once-a-month-measured water quality data, which might not represent appropriately monthly water quality, particularly, for rainy seasons, were used for the loads calculation. Thus, more frequently monitored water quality data should be used for the delivery loads estimation at least for a rainy season in order to improve the PLCM performance. Nevertheless, the developed model took the pollutant reduction process into account, which is not allowed with the conventional unit loading method, and furthermore temporal variations of pollutant loads based on stream flows were also incorporated into the pollutant loads estimation. The developed PLCM can be a useful tool to assess pollutants delivery loads at a watershed scale and thus assist decision makers in developing watershed pollution management schemes.