Periodic signals of climatic variables and water quality in a river-eutrophic pond-wetland cascade ecosystem tracked by wavelet coherence analysis

摘要

Lakes are sensitive to changes in their environmental boundary conditions that can be indicated in the periodic behavior of water quality variables. The present work aims to assess the degree to which common annual periodic behavior is present (1994-2010) in the meteorological parameters (global radiation, air temperature, cloud cover), streamflow; and five primary nutrients (e.g. total phosphorus, nitrate-nitrogen) as possible indicators of ecosystem vulnerability in four different ecosystems using wavelet coherence analysis. The cascade system is located in the mouth of a shallow river where the water flows through a eutrophic pond then a disturbed/undisturbed macrophyte covered wetland reaching a large shallow lake. The results highlight the differing abilities of the elements of the cascade of ecosystems to follow seasonality. The changes in water quality (nutrient cycle) in the eutrophic pond most closely mirror meteorological seasonality. The vulnerability of the wetland ecosystem was expressed by its decreased capacity to follow seasonal changes due to high algae loads and additional inflows. Moreover, the wetland proved to be weak and unstable regarding phosphorus and nitrogen retention. With the successful application of wavelet coherence analysis to the "black-box" cascade system the study sets an example for the implications of the method in such combined or stand-alone natural/partially-constructed ecosystems.