Spatial and temporal characterisations of dissolved humic substances in freshwater lake

Dissolved organic matter (DOM) is a key component in freshwater ecosystems, strongly influencing the optical, chemical and biological environment. The influence of the organic material on lake water depends on the molecular characteristics of the compounds. In the present study, the spatial distribution of dissolved organic matter and humic concentrations was determined together with the indices for optical colour (a440) and the degradation of high molecular weight organic molecules. By considering these spatial and temporal variations, it was possible to determine the role of hydrological conditions of the lake basin on the lake water quality. The spatially explicit data obtained in a shallow wetland lake were used to determine a series of algorithms that estimate the time dependant relationship between the water optical properties and the residence time in the lake, in particular in relation to the degradation of dissolved organic matter and to the progressive loss of colour and spectrophotometric absorbance.