The Analysis of the Seasonal, Spatial, and Compositional Distribution of Humic Substances in a Subtropical Shallow Lake

Abstract

The spatial and temporal distribution of humic substances in aquatic ecosystems can have Biosystem Sciences and important effects on ecosystem productivity, negatively impacting primary productivity Technology, University of Siena, while positively impacting secondary productivity. In the present investigation, a large shal-53100 Siena, Italy low lake ecosystem was studied to determine the spatial and seasonal variation of the b Central Laboratory of composition and concentration of humic substances. Concentrations of total dissolved orHydrobiology, ganic matter, humic acid, and fulvic acid were found to display significant spatial distriMinister of Agriculture, butions (1.3...13.5 mg/L, DOM; 0.1...5.4 mg/L, HA). The distribution is described by using 00147 Roma, Italy mapping techniques and the analysis of the spatial distribution of the lake. An analysis of the seasonal variations also indicated the dependence of the occurrence of these compounds on meteorological and hydrological conditions. To identify the potential sources of these organic materials, an analysis was made of the ratio of humic and fulvic acid fractions and total DOM. It was found that areas of high DOM concentration coincided with the areas of highest HA percentage of total DOM. Furthermore using the ratio of the normalised concentrations of HA, FA, and residual DOM (< 5000 g/mol) it was found that areas dominated by each are spatially distinct. This confirms the hypothesis that in these shallow lakes, photodegradation and bacterioplankton activity will create a residence time dependent zonation of each component of the total DOM.

The optical characterization of chromophoric dissolved organic matter using wavelength distribution of absorption spectral slopes

“…To examine changes in CDOM optical properties due to photodegradation and conservative mixing, a specific experiment was performed using Sigma Aldrich humic acid, following standard solution preparation (Mazzuoli et al 2003) at a concentration of 30 mg L 21 . One aliquot of the prepared solution (filtered through 0.22-mm filter, Millex GP filter unit, Millipore) was placed in a sterile acid-washed quartz bottle for exposure to solar radiation for 8 d in November 2007 for a total dose of 2800 kJ m 22 UVA and 200 kJ m 22 UVB.…”

Penetration of Solar Radiation into the Waters of Messina Strait (Italy)

“…17 Chromophoric dissolved organic matter (CDOM) concentrations were calculated by using the absorbance value at 272 nm of water samples at different depths. 18,19 …”

Extensive spatial analysis of the light environment in a subtropical shallow lake, Laguna Iber�, Argentina

“…Millipore filter) on site and stored in hermetic containers in the dark at 4°C. The filtered samples were analysed without further modification by UV/V1S spectroscopy (Pharmacia Biotech Ultrospec 2000 Ò UV/V1S Spectrophotometer, spectral bandwidth 3 nm) in 0.01 m path length quartz curvettes (Hautala et al, 2000;Mazzuoli et al, 2004). The calibration curve for the DOM measurement was determined by preparing a stock DOM solution with commercial humic acid (Aklrich, Na+ form).…”

“…The calibration curve for the DOM measurement was determined by preparing a stock DOM solution with commercial humic acid (Aklrich, Na+ form). The stock solution was analysed to determine its relative molecular distribution and compared with that of the lake obtained in previous campaigns (Mazzuoli et al, 2004). The stock solution was found to have a similar range of molecular weights to that found in the lake, and therefore considered an appropriate standard for aquatic DOM.…”

“…To the south, Rio Mirin˜ay connects the lake to a long and narrow wetland area that is surrounded by cultivated areas. The average flowrate of the river over the measurement period was estimated to be 15 000-29 000 m 3 /h (Mazzuoli et al, 2004). Seasonal measurements, during 1999-2000, demonstrated a wide spatial variation in physico-chemical properties and phytoplankton concentrations, particularly between lake basins (Co´zar et al, 2003).…”