Multi-method characterisation of natural organic matter isolated from water: characterisation of reverse osmosis-isolates from water of two semi-identical dystrophic lakes basins in Norway

In a “large-scale-catchment-manipulation-research-project”, a dystrophic lake was divided into two halves by means of a plastic curtain, from the middle of the natural outlet to the opposite shore. Since fall 1990, one lake half and the corresponding catchment has been sprinkled with artificial acid precipitation, while the other was left untouched. The catchment acidification experiment took place in an area of Norway receiving little acid rain. During a few day period in October 1994, after four years of acidification, the natural organic matter (NOM) from 2270 l of water was isolated from each of the two sides of the lake, using the following sequential technique: coarse filtration; exchange of cations with Na+; concentrate organic solutes from 2270 l of water to 70 l by means of reverse osmosis membranes; filtration of the 70 l through 0.45 μm membranes; concentration to 4–5 l by evaporation at low pressure and at 30°C; freeze drying (yield 70–75 g). Small portions of both isolates (100–200 mg) were distributed to a number of different laboratories in Europe and North America for analyses. Characteristic data, such as distribution of ions, proton- and copper binding capacity, content of metals, content of organic S, organic N, free- and hydrolysable amino acids are reported here. A number of analytical techniques were used, including UV-VIS, IR and fluorescence spectrophotometry, C-13 NMR; pyrolysis, GC/MS and HPLC. Studies on adsorption- and flocculation abilities of the two “water qualities” and formation of trihalomethanes (THM) upon chlorination, is also included. The results from 10 different laboratories are presented and similarities and differences between the two semi-identical samples are discussed. Some studies of the consequence of the isolation step on the quality of the NOM, are also discussed.