Several semi-analytical algorithms have been developed to estimate the chlorophyll-a (Chl-a) and phycocyanin (PC) concentrations in inland waters. This study aimed at identifying the influence of algorithm parameters on the output variables and searching optimal parameter values. The optimal parameters of seven semi-analytical algorithms were applied to estimate the Chl-a and PC concentrations. The absorption coefficient measurements were coupled with pigment measurements to calibrate the algorithm parameters. For sensitivity analysis, the elementary effect test was conducted to analyze the influence of the algorithm parameters. The sensitivity analysis results showed that the parameters in the Y function and specific absorption coefficient were the most sensitive parameters. Then, the parameters were optimized via a single-objective optimization that involved one objective function being minimized and a multi-objective optimization that contained more than one objective function. The single-objective optimization led to substantial errors in absorption coefficients. In contrast, the multi-objective optimization improved the algorithm performance with respect to both the absorption coefficient estimates and pigment concentration estimates. The optimized parameters of the absorption coefficient reflected the high-particulate content in waters of the Baekje reservoir using an infrared backscattering wavelength and relatively high value of Y. Moreover, the results indicate the value of measuring the site-specific absorption if site-specific optimization of semi-analyical algorithm parameters was envisioned.
During the summer monsoon, a large amount of the Changjiang River discharge (CRD) extends into Korean coastal waters (KCWs) in the East China Sea, forming Changjiang diluted water (CDW). The harmful dinoflagellate Cochlodinium (=Margalefidinium) polykrikoides frequently causes massive blooms during the monsoon period, and these result in extensive economic losses in southern KCWs. We hypothesized that the scale of C. polykrikoides blooms can be varied depending on the intrusion strength of CDW into KCWs. We analyzed long-term (20 years) data (physicochemical factors and C. polykrikoides bloom area and duration) to test this hypothesis. In confirming the variability in annual salinity, the average Niño 3.4 index in the preceding winter was found to be positively correlated with the CRD in the following summer (R2 = 0.203, p < 0.05). However, the surface salinity in our study area was not significantly correlated with the CRD (p > 0.05), indicating that not all of the CDW volume enters the southern KCWs. This incomplete transfer of CDW into KCWs was related to the path of typhoons in the East Asian region; typhoons are able to moderate the influence of CDW through strong water mixing between the upper and bottom layers. We found that the scale of C. polykrikoides blooms in KCWs was negatively correlated with the strength of the CDW intrusion. Together with previous and present findings, the influx of low salinity CDW can accelerate a rise in surface temperature, and this elevated temperature condition which is unfavorable for C. polykrikoides growth may lead to reductions in the scale of this dinoflagellate blooms. Our findings suggest that intrusion strength of CDW into KCWs plays important role in regulating C. polykrikoides population dynamics by causing inhibitory conditions.
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