Nitrogen Stimulates Microcystis-Dominated Blooms More than Phosphorus in River Conditions That Favor Non-Nitrogen-Fixing Genera.

Despite the implementation of intensive phosphorus reduction measures, periodic outbreaks of cyanobacterial blooms in large rivers remain a problem in Korea, raising the need for more effective solutions to reduce their occurrence. This study sought to evaluate whether phosphorus or nitrogen limitation is an effective approach to control cyanobacterial (Microcystis) blooms in river conditions that favor this non-nitrogen-fixing genus. These conditions include nutrient enrichment, high water temperature, and thermal stratification during summer. Mesocosm bioassays were conducted to investigate the limiting factors for cyanobacterial blooms in a river reach where severe Microcystis blooms occur annually. We evaluated the effect of five different nitrogen (3, 6, 9, 12, and 15 mg/L) and phosphorus (0.01, 0.02, 0.05, 0.1, and 0.2 mg/L) concentrations on algae growth. The results indicate that nitrogen treatments stimulated cyanobacteria (mostly Microcystis aeruginosa) more than phosphorus. Interestingly, phosphorus additions did not stimulate cyanobacteria, although it did stimulate Chlorophyceae and Bacillariophyceae. We conclude that phosphorus reduction might have suppressed the growth of Chlorophyceae and Bacillariophyceae more than that of cyanobacteria; therefore, nitrogen or at least both nitrogen and phosphorus control appears more effective than phosphorus reductions alone for reducing cyanobacteria in river conditions that are favorable for non-nitrogen-fixing genera.

Relationships between water quality parameters in rivers and lakes: BOD5, COD, NBOPs, and TOC.

Biological oxygen demand (BOD5) or chemical oxygen demand (COD) analysis is widely used to evaluate organic pollutants in water systems as well as the efficiency of wastewater treatment plants. However, both analysis methods have restrictions such as being insensitive, imprecise, time-consuming, and the production of chemical waste. Therefore, total organic carbon (TOC) analysis for organic pollutants has been considered for an alternative analysis instead of BOD5 or COD. Several studies have investigated the replacement of BOD5 or COD with TOC in wastewater samples; however, few studies have investigated the relationships between water quality parameters in rivers and lakes. Therefore, this study evaluated the relationships between BOD5, COD, or NBOPs and TOC by the analysis of national water quality monitoring data of rivers and lakes for 5 years. High correlation coefficients (r) of 0.87 and 0.66 between BOD5 and TOC (p < 0.05) were obtained for rivers and lakes, respectively, and strong correlation coefficients (r) of 0.93 and 0.75 were observed between COD and TOC (p < 0.05) for rivers and lakes, respectively. The correlation coefficient (r) between NBOPs and TOC was 0.93 for rivers and 0.72 for lakes. The coefficients of determination (R 2) were 0.75 and 0.44 between BOD5 and TOC for rivers and lakes as well as were 0.87 and 0.57 between COD and TOC for rivers and lakes, respectively. The coefficient of determination (R 2) between NBOPs and TOC was 0.73 for rivers and 0.52 for lakes.

Stable isotope on the evaluation of water quality in the presence of WWTPs in rivers.

We investigated the distribution of nitrogen compounds in Han River as well as two tributaries of Tancheon and Jungrangcheon. Particularly, we observed the significant releases of NH4 (+)-N from effluent of wastewater treatment plants (WWTPs) in two tributaries that has resulted in the increases of ammonium nitrogen (NH4 (+)-N) in Han River as well as in Tancheon and Jungrangcheon. Due to the increases of NH4 (+)-N in two tributaries, the larger distribution of δ(15)N-NH4 (+) was observed than those of δ(15)N-NO3 (-) in downstream. We calculated the contribution rate of ammonium nitrogen and nitrate nitrogen from effluent to downstream according to the results of stable isotope. The contribution rates of δ(15)N-NH4 (+) from effluent to downstream were significant that ranged between 53 and 100 % in Tancheon and between 27 and 100 % in Jungrangcheon. While the contribution of δ(15)N-NO3 (-) was not significant in Tancheon, it was occasionally observed in Jungrangcheon. These results demonstrated that WWTPs are the major sources of NH4 (+)-N in two tributaries, which caused the distinguishable stable isotope of δ(15)N-NH4 (+). Therefore, the stable isotope of δ(15)N-NH4 (+) could be a useful parameter or tracer for the evaluation of NH4-N released from WWTPs in rivers.