Spectrophotometric discrimination of river dissolved organic matter

Abstract

Abstract:There is a need to be able to differentiate the dissolved organic matter (DOM) fraction in river waters. Research in the 1970s and 1980s has attempted to utilize both absorbance and fluorescence to distinguish between DOM fractions in river waters, but both were limited by the available technology. Total organic carbon content has, therefore, been widely used as a standard method of measuring DOM concentration, although it has little power to differentiate DOM fractions. Recent advances in fluorescence spectrophotometry enable rapid and optically precise analysis of DOM. Here, we show how a combination of both fluorescence and absorbance can be used to discriminate statistically between spatial variations of DOM in tributaries in a small catchment of the Ouseburn, NE England. The results of the discriminant analysis suggest that about 70% of the samples can be correctly classified to its tributary. Discriminant function 1 explains 60Ð8% of the variance in the data and the fulvic-like fluorescence intensity has the largest absolute correlation within this function; discriminant function 2 explains a further 21Ð5% of the variance and the fulvic-like fluorescence emission wavelength has the largest absolute correlation within this function. The discriminant analysis does not correctly classify all tributaries every time, and successfully discriminates between the different tributaries 70% of the time. Occasions when the tributary waters are less well discriminated are due to either episodic pollution events (at two sites) or due to tributaries that have strong seasonal trends in spectrophotometric parameters, which allows the sites to be misclassified. Results suggest that spectrophotometric techniques have considerable potential in the discrimination of DOM in rivers.

Runoff- and erosion-driven transport of cattle slurry: linking molecular tracers to hydrological processes

“…This "protein" fluorescence can be a useful tracer for slurry as proteins form a significant part of the organic nitrogen pool, which can be derived from plant, animal or bacterial sources (Jones et al, 2005;Vinolas et al, 2001). It is well documented that fluorescence at an excitation at 270 nm can be linked to farm wastes (Baker, 2002a;Hudson et al, 2007;Naden et al, 2010) and the lack of a signal in the control samples supports the hypothesis that the slurry is the source in these experiments. The assumed higher molecular weight compounds that fluoresce at longer wavelengths are most likely derived from soil DOM rather than from the slurry.…”

“…The slurry was only applied to the top 1 m strip of the slope and therefore the signal was rapidly diluted both by the rainfall and the additional signal from the soil-derived DOM. Furthermore, the 270 : 360 ratio of the slurry was calculated at 1.7, which is lower than the range cited in the literature (∼ 2-5) for cattle slurries (Baker, 2002a). This could be because when the slurry was collected (during April 2008), it had been a very wet spring and as a result the farm slurry store had received higher than average volumes of rainwater, potentially diluting the slurry before application.…”

“…However, the larger total load exported during highintensity storms will result in greater total losses of nutrients from the soil and could result in pressures on receiving waters, such as increased biological oxygen demand (BOD). It is estimated that input of cattle slurry can produce a BOD of between 10 000 and 30 000 mg L −1 , leading to reduced oxygen levels and ultimately the death of aquatic life (Khaleel et al, 1980;Baker, 2002a;Foy and Kirk, 1995).…”

Cross-connection detection in Australian dual reticulation systems by monitoring inherent fluorescent organic matter

“…Fluorescence EEM spectroscopy has been successfully utilized to monitor natural organic matter in a number of freshwater applications, such as for the characterization and classification of spatially separated rivers and other surface waters [96,97], identification of DOM variability in estuaries [98], and the monitoring of organic fluxes through groundwater [99,100] amongst others. …”

Catchment tracers reveal discharge, recharge and sources of groundwater-borne pollutants in a novel lake modelling approach

“…Tracing FDOM has been done in both rivers and open waters (Baker, 2002(Baker, , 2001Stedmon and Markager, 2005b) but only a few studies have been conducted in groundwater. These studies have focused on changes in FDOM from deep groundwater wells (Lapworth et al, 2008) or tracing FDOM using samples that are taken very far apart (Chen et al, 2010).…”