A method to estimate chlorophyll-a concentration in the surface layer of a stratified lake from surface layer temperature time series, meteorogical fluxes, a knowledgeof blue-to-red peak absorption ratio and dissolved organic matter concentration / Sri Adiyanti

2008

In maintaining lake water quality, primary productivity has been a growing interest to lake managers for many years. One commonly used primary productivity parameter is chlorophyll-a (chl a) concentration as a proxy for phytoplankton population, which may vary diurnally. A practical, calibration-less, cost-effective, non-labour intensive method and yet capable producing a real-time and accurate chl a concentration is important. This study aims to provide an alternative method to estimate chl a concentration in the surface layer of a stratified lake using surface layer temperature time series data and meteorological fluxes (physical properties), as well as a knowledge of the blue-to-red peak absorption ratio, the dissolved organic matter concentration and relative composition of four major phytoplankton groups (biological properties). The intention of the method is to produce a better resolution of chl a concentration in between biological properties measurements; hence it can minimize the monitoring cost to produce a time series of chl a concentration. The method consists of a model which derives the light attenuation coefficient from surface layer temperature time series data and water surface flux measurements, and a model that relates the light attenuation coefficient to the total chl a concentration in the surface layer. The one-dimensional surface mixed-layer model, which is the base of the first model, was tested under wind-dominated deepening events in Lake Como (Italy) during which the surface layer deepened as a onedimensional slab-like layer. The simulated and observed surface layer deepening characteristics are shown to agree well over conditions characterized by a range of Richardson number from O(10-1) to O(102). The test was also conducted under lowwind stratifying condition, which is one of the necessary criteria for the method. In the second model,

phytoplankton absorption spectra are assumed to vary as a function of the community structure, which distinguishes the method from other similar approaches. The method was valid for cases where the horizontal pressure gradient in the surface layer was negligible, the photic depth was deeper than the diurnal surface layer and the increment in temperature in photic region was considerably larger than the thermistor's precision. The method was validated using data sets measured in Lake Kinneret (Israel), Valle de Bravo (Mexico), and Winamp Gulf (Kenya). The estimated values of the light attenuation coefficient (first model) and the total chl a concentration (second model) were mostly within 10% error of the actual direct measurements. The dissolved organic matter concentration is a critical parameter for the method; hence it is important to have good estimates of this parameter. The method uses fresh phytoplankton footprint (i.e. accumulation of heat), therefore it is useful for a quick assessment of the total chl a concentration in a water body of interest. The sensitivity analyses, possible improvement, as well as the application of the method as a management tool are discussed.

Thesis (Ph.D.)--University of Western Australia, 2008

http://repository.uwa.edu.au:80/R/-?func=dbin-jump-full&object_id=9768&silo_library=GEN01