Long-term Changes of Water Level Associated with Chlorophyll a Concentration in Lake Baiyangdian, North China

In this study, periodic structures of water level and chlorophyll a (Chl a) concentration in Lake Baiyangdian and their correlations were analyzed using Morlet wavelet transform, wavelet power spectrum and cross wavelet transform analyses. Monthly data of water level (from 1950 to 2009) and Chl a concentration (from 2000 to 2009) were obtained from the Anxin county water conservancy and environmental bureaus, respectively. Results from the Morlet wavelet transform analysis show that water level fluctuations follow intra-annual and 60-month periodicity. In contrast, the wavelet transform analysis shows a water level variation structure of 6 and 16 month periodicity at a high confidence level (>95%). The periodic structure of Chl a concentrations shows 6 and > 12 month patterns in continuous wavelet transform analysis whereas the periodic structures generated using wavelet power spectrum analysis exhibit 4 and > 12 month variance, with the 4 month periodic change above the 95% confidence level. Comparative cross wavelet and coherence and phase analysis of water levels and Chl a concentrations in the lake results in a 16-month periodic structure that displays a complicated nonlinear relationship between the two parameters. Several short-term periodic nonlinear relationships also appear at other time intervals. In conclusion, we show for the first time that a 16-month periodic structure demonstrates the most robust influence of water level on Chl a concentrations in Lake Baiyangdian. Our results can help in understanding the interactions between specific hydrological changes and their corresponding ecological effects. (C) 2011 Published by Elsevier B. V. Selection and/or peer-review under responsibility of School of Environment, Beijing Normal University.