Comparison of river and canal water dissolved organic matter fluorescence within an urbanised catchment Elfrida M. Carstea 1 , Andy Baker 2 & Roxana Savastru 1 1 National Institute of R&D for Optoelectronics, Magurele, Romania and 2 Connected Waters Initiative Research Centre, Biological Sciences Building, University of New South Wales, Sydney, NSW, Australia Keywords canal water; dissolved organic matter; fluorescence spectroscopy; urban river. Correspondence E. M. Carstea, National Institute of R&D for Optoelectronics, INOE 2000, 409 Atomistilor Street, P.O. Box MG-5, RO-077125 Magurele, Romania. Email: frida@inoe.inoe.ro doi:10.1111/wej.12062 Abstract Recently, growing interest has been shown in the study of canal water quality, yet no research using continuous fluorescence monitoring to characterise dissolved organic matter (DOM) has been performed. This paper evaluated DOM characteris- tics at hourly resolution. A comparison was made between canal and nearby urban river fluorescence spectra, to emphasise the specific nature of canal water DOM. Results showed that canal water had a significant proportion of microbially derived DOM, while the urban river had a greater proportion of terrestrially derived frac- tions. The microbial character of canal water DOM originated from the low flow of water, the nutrients predominance and continuous DOM processing. Hence, DOM fluorescence is invariant over a timescale of days, and recreational navigation and precipitation events have no major influence on DOM characteristics. Our results are expected to be applicable to future research on highly regulated freshwater systems for DOM quantity estimation or for water quality models. Introduction In the United Kingdom, there are over 3000 km of canals built, starting in 1757 AD, to connect urban and industrial centres with major ports (Harrison & Sutton 2003). In the last decades, canals were turned to leisure and commercial pur- poses (Neal et al. 2006; Eaton 1999). Canals are aquatic systems with special features: extremely low water flow, which under certain meteorological conditions can even change its direction, generating high susceptibility to eutrophication, increasing levels of sediments and slow diffu- sion of pollutants (Swanson et al. 2004). Some of the most important external factors that influence the canal water quality can be specified: industry, precipitation, surface run- off, stormwater drains, groundwater and navigation. Since 1990, periodic dredging of the canal bed is performed in the United Kingdom to remove the excess sediments and reduce the contamination accumulated mostly in the sediments during the industrial revolution (Bromhead & Beckwith 1994; Swanson et al. 2004; Bligh et al. 2007). During the last decades, fluorescence spectroscopy has become a promising tool for water quality detection, by the analysis of the ubiquitous fraction, dissolved organic matter (DOM). The fluorescent fractions of DOM that can be gener- ally identified in water systems are: humic substances, indi- cators of the terrestrial inputs and the amino acid fraction (represented by the fluorescent amino acids, tryptophan and tyrosine), which are indicators of microbial activity. The technique presents numerous advantages in DOM characterisation, including rapid analysis (∼1 min, depending on the set up parameters), high sensitivity and selectivity, little sample pretreatment and small quantities of sample (Hudson et al. 2007; Huo et al. 2009). Furthermore, good cor- relation has been found between DOM fluorescence data and water quality parameters like total organic carbon (TOC) (Cumberland & Baker 2007) and biological oxygen demand (Hudson et al. 2008). In recent studies, fluorescence spec- troscopy has been applied to real-time monitoring of river water (Spencer et al. 2007; Carstea et al. 2009, 2010; Downing et al. 2009). These studies have shown that DOM fluorescence exhibits rapid (hourly to diurnal) variations, depending on the river type, and that are highly influenced by river discharge, and the amount and intensity precipitation. No such studies have been made so far, with fluorescence spectroscopy, to investigate the canal water organic carbon properties at daily scale, which are important for an accurate understanding of the carbon cycle in the water system (Cole et al. 2007). With highly regulated flow, analysis of canal DOM properties would contrast previous studies, and be relevant to our understanding of DOM in other regulated systems. Therefore, the purpose of this study was to evaluate the properties of DOM, using fluorescence, at hourly resolution. Water and Environment Journal. Print ISSN 1747-6585 11 Water and Environment Journal 28 (2014) 11–22 © 2013 CIWEM.