Multi-temporal scale characteristics of algae biomass and selected environmental parameters based on wavelet analysis in Lake Taihu, China

Abstract

It is widely accepted that algal blooms are a result of eutrophication processes. Water temperature, total phosphorus and total nitrogen are the main environmental parameters impacting Chlorophyll-a (Chla) in aquatic ecosystems. To elucidate the variability of these parameters in Lake Taihu, China, we analyzed their multi-temporal characteristics using wavelet power spectrum. We evaluated the non-stationary statistical association between algal biomass (as Chla) and the selected environmental parameters using wavelet coherence and wavelet phase difference. Our results indicate that these variables presented periodic oscillations in frequency domain and localization along time axis. Significant 3–4 month and annual bands are identified in both algal and environmental parameters variations. Chla responded quickly to variation in water temperature but showed a delayed response to variation in total nitrogen; it also showed a delayed response to variation in total phosphorus during 1995–1997, but responded more quickly in recent years. The intensity of oscillation power in frequency domain resulted in non-stationary statistical association, and the phase difference in time domain resulted in time-lag correlations between Chla and the selected environmental indices. These results contribute to elucidate the nonlinear eutrophication dynamic process and provide information for algal bloom prediction and lake management.