Environ. Sci. Technol. 1996, 30, 3501-3507
Seasonal Variations in Principal Groups of Organic Matter in a Eutrophic Lake Using Pyrolysis/ GC/MS M A D E L E I N E V . B I B E R , * ,† FAZIL O. GU ¨ L A C¸ A R , ‡ A N D JACQUES BUFFLE† De´partement de Chimie Analytique, Universite´ de Gene`ve, CH-1211 Gene`ve 4, Switzerland, and De´partement de Chimie Physique, Universite´ de Gene`ve, CH-1211 Gene`ve 4, Switzerland
The characteristics of natural organic matter (NOM), which affect its interactions with and therefore the transport of colloids and particles, depend on the evolution of its individual components. Information on the temporal variations of the components of the organic matter of a well-studied eutrophic lake (Bret, VD, Switzerland) was extracted using pyrolysis/ gas chromatography/mass spectrometry. The influence of aquagenic organic matter was found to be at a maximum in summer. The soil-derived organic matter, on the other hand, was found in larger proportions in winter and spring. The appearance of hydroxypropanone in the pyrolysis fragments in the summer months indicates that this portion of the organic matter is aquagenic and very fresh. The dominance of furaldehyde in pyrolysates during the rest of the year indicates the presence of polysaccharides may be of either aquagenic or pedogenic origin. The absence of lignin fragments found in the NOM in this lake suggests that lignin-containing components of terrestrial organic matter are not leached out from the soil in significant quantities. A correlation was found between 3-day cumulative rainfall and the proportion of terrestrial components in the identified organic matter in the spring. This correlation disappeared in the summer, probably because of a higher vegetal cover and the masking effect of the high aquagenic productivity. These factors are also likely to be of importance in more complicated lacustrine systems.
Introduction Organic matter affects the stability of colloids and thus has major implications for transport processes in surface waters and groundwaters. Polysaccharides, for example, play a * Corresponding author e-mail address:
[email protected]. † De ´ partement de Chimie Analytique. ‡ De ´ partement de Chimie Physique.
S0013-936X(96)00171-X CCC: $12.00
1996 American Chemical Society
large role in the inhibition of flocculation in water treatment (1), and waters containing organic matter have been shown to exhibit enhanced colloidal stability (2, 3). Adsorption of organic matter and/or trace elements to particles or colloids affects transport of the latter in surface waters (4), subsurface water (5-7), and bioavailability (8). With its many functional groups acting as ligands, natural organic matter NOM may influence not only the binding of reactive elements or pollutants to the colloid surfaces but also the formation of network-like matrices that stabilize or destabilize these submicron particles (9-13). In doing so, it may affect the aggregation and subsequent sedimentation kinetics, thereby significantly influencing the removal of pollutants from natural water systems. The effect of NOM on aggregation, however, is not very well known and so far has only been studied by treating the organic matter as a single homogeneous group of compounds. Despite the fact that pedogenic organic matter or polysaccharides may influence colloid stability in completely different manners, their individual effects have never been studied separately in the same lake. The size of pedogenic refractory organic matter, for example, is considered to be small (a few nanometers) relative to colloids (∼microns), whose surfaces the carboxylic and phenolic functional groups may coat and charge (10, 14). Due to electrostatic interactions, hydrophobic colloids are qualitatively stable when they are charged (15). Polysaccharides, on the other hand, which tend to have more OH functional groups, are generally larger than colloids (>100 nm) (10, 14). These are more likely to affect colloid stability through steric arrangements (2). Due to these different effects on colloid stability, it is important to study the seasonal evolution of the NOM components individually. Organic matter also affects photochemical processes in lakes by providing electrons (15). Organic electron donors control photocatalytic production of hydrogen peroxide on metal oxide surfaces (16). The specificity of their adsorption determines their capacity as photochemical reductants. Those forming inner-sphere surface complexes are more efficient electron donors than those forming outersphere surface complexes (15). Organic ligands also influence the complexation and cycling of metals in natural waters (e.g., iron). The object of this work is to elucidate the temporal variations of various components of NOM in an eutrophic lake. The NOM in this lake consists of matter of aquagenic and pedogenic origins, which may in turn be divided up into several classes (see Figure 1). Previous studies in this lab using non-perturbing fractionation techniques have shown that the NOM in this lakewater consists mostly of aromatic pedogenic refractory organic matter (PROM), which remains in suspension and is thus largely removed with the lake’s outflow, as well as some largely aliphatic aquagenic organic matter, including polysaccharides, which in turn is removed mainly by sedimentation (17, 18). Highresolution transmission electron microscopy work indicates that a large proportion of submicron colloids is embedded in large organic matrices (19, 20). The detection techniques used (UV absorbance, fluorescence, DOC, TEM) however were not able to discriminate the individual effects and the evolution of polysaccharides. This study attempts to follow
VOL. 30, NO. 12, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
3501
FIGURE 1. Schematic of the natural organic matter constituents and the classes obtained by pyrolysis/GC/MS.
the seasonal evolution of some specific NOM classes using pyrolysis/gas chromatography/mass spectrometry to avoid perturbing fractionation. Pyrolysis/mass spectrometry (pyrolysis-MS) and pyrolysis/gas chromatography/mass spectrometry (pyrolysis/ GC/MS) have been used to investigate NOM from soil (2126) and aquatic environments (27-36). A review of the basics of pyrolysis-MS of biomaterials is given in Meuzelaar et al. (37). Information on nitrogen- and phenol-containing compounds is often related to the aquagenic and pedogenic origins, respectively, of the organic matter in suspended material and sediments (38). The pyrolysis of algae, for example, yields nitrogenous byproducts due to their high protein content (32). Pyrolysis/GC/MS has been used to identify seasonal variations in nitrogenous and phenolic compounds in the surface layers of the open ocean, the result of phytoplanktonic blooms and an abundance of fish fecal pellets (38). Here we use pyrolysis/GC/MS to discriminate the source and the temporal variations of the main contributors to NOM in a lacustrine setting.
Experimental Section Materials. All water used for blanks and dilutions was produced by a MilliQ Plus 185 ultrapure water system. TOC samples were acidified with Merck Suprapur HCl. The products used as arbitrary pyrolysis/GC/MS “standards” (bovine serum albumin, dextran, Fluka humic acid, cellulose acetate, and chitin) were from Sigma and Fluka (30). UV/ vis absorption was measured at 280 nm on a Perkin-Elmer Lambda 2 UV/vis spectrophotometer, using a holmium standard. Total organic carbon measurements were done on a Shimadzu TOC-5000 total organic carbon analyzer using acidified 40-mL samples. Appropriate samples were centrifuged in carefully washed 400 -mL polycarbonate tubes at 4000 rpm for 2 h, using a Heraeus 2.0RS centrifuge. Freeze-drying was done using a LSL Secfroid Lyolab B lyophilizer. Weather data for the area surrounding the sampling site were received from the Swiss Meteorological
3502
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 30, NO. 12, 1996
Institute. Rainfall was measured at the Tour-de-Gourze; sunshine was measured at the Pully station from June 14, 1994, to August 18, 1995. Sampling. All samples, unless otherwise noted, were taken from a depth of 3-5 m toward the center of the lake. This sampling depth was chosen so as to remain in the oxic layer of the lake at all times. The water was collected into glass bottles either by a peristaltic pump (250 mL/min) or by using a Plexiglas column with pneumatic closures. The sample bottles were brought back to the laboratory where they were agitated to resuspend any sedimented material. Half of the water was centrifuged 2 h at 4000 rpm, and half was left to sediment for 2 h to remove the largest particles. The 250-mL aliquots of the supernatant were taken from both the sedimented (hereafter referred to as raw) and the centrifuged samples and frozen for subsequent freezedrying. The remaining supernatant was used for UV/vis and TOC analysis. Lyophilization was the method of sample preparation chosen, as with the least amount of sample handling it appeared to present the fewest problems of contamination or artifacts. Sampling Location. Lake Bret is a small eutrophic lake located in Switzerland at an altitude of 672 m, approximately 10 km east of the city of Lausanne. This drinking water supply reservoir has one major inflow, an underground conduit from the Grenet River, and a single outlet. Detailed descriptions of the morphological and hydrological characteristics of the lake are given by Zumstein and Buffle (18). The eutrophic state of the lake is due to agricultural activities in the surrounding area. The lake is thermally and chemically stratified from spring until autumn, and the deeper layers of the lake are anoxic during this time. Pyrolysis/GC/MS. The pyrolysis/GC/MS was performed on a VG Analytical 7070E organic mass spectrometer coupled to a Carlo Erba HRGC 5160 gas chromatograph and a modified CDS pyroprobe 121 pyrolyzer. The GC column used was a 30-m DBWAX fused silica capillary column flushed with helium gas. The pyrolysis probe
FIGURE 2. Example of a pyrochromatogram. The x-axis represents retention time (1 scan ) ∼3 s). The large peak at scan 562, for example, was determined from its mass spectrum to be acetamide and was therefore attributed to the amino sugars category.
contained a 0.25-in. platinum desorption coil. For analysis, a quantity of dry sample is placed in a quartz sample holder, which in turn is inserted into the pyrolysis coil. The pyroprobe is then inserted into the injection port of the chromatograph, heated in a helium atmosphere to 659 °C at a rate of 20 °C/ms, and held at this temperature for 20 seconds. The final temperature inside an empty glass tube was found to be 610 °C. The pyrolysis products pass directly through a custom-made inlet into the GC column for separation. The column is then heated from 35 to 220 °C at a rate of 3 °C/min and held at this maximum temperature for 20 min. The mass spectrometer is operated in the electron impact mode, at a nominal electron energy of 70 eV, and at a source temperature of 220 °C. Ions in a mass range of 20-200 Da are detected at a scan rate of 3 s/scan. An example of a pyrochromatogram is given in Figure 2. Interpretation of Pyrolysis Data.The interpretation of the pyrochromatograms was carried out based on the methods described in Bruchet et al. (30). A peak appearing on the pyrochromatogram represents the sum of any compounds eluted for a given retention time. These compounds were identified based on their mass spectra by comparing them with library spectra and literature data. The relative amounts of pyrolysis products were determined from the peak areas. The characteristic fragments were assumed to represent the total identified organic matter. Various types of biopolymers usually found in natural waters produce characteristic fragments on pyrolysis (23, 33, 37). The four major types of biomolecules used in this study are carbohydrates (polysaccharides), proteins, amino sugars,
and polyhydroxy aromatics (PHAs). The proportions of these biopolymers are calculated according to Bruchet et al. (30) for a known mixture of dextran, bovine serum albumin, cellulose acetate, Fluka humic acid, and chitin. These calculations are then used to compare the relative proportions of the corresponding major groups found in natural samples. Due to the copious amounts of unquantifiable, small molecules produced during pyrolysis as well as a certain variability in detector response, these percentages do not represent absolute values. The values are relative and should be considered semiquantitative giving proper trends. Pyrolysis of organic matter usually yields higher estimates of polysaccharide and protein content than classical methods. The reason for this is that the pyrolysate is assumed to represent the total organic matter, when in fact the sample may contain some organics whose pyrolysis products are poorly detected by mass spectrometry (35). On the other hand, such classical methods as hydrolysis and monomer analysis generally yield estimates that are too low because hydrolysis is incomplete or monomeric products are destroyed or repolymerized. The true polysaccharide and protein contents in organic matter most likely lie somewhere in between (35). The pyrolysis/GC/MS technique therefore should not be used to obtain absolute values, but rather it should be used on a relative basis to give an indication of the general trends. This method is very effective in evaluating changes in organic matter from a particular location (lake) over time. Reproducibility is estimated to be approximately within (5%. Main Groups of Biopolymers Investigated. Polysaccharides. Reserve and structural polysaccharides contained in microorganisms are released into the water column as metabolic or degradation products. Reserve polysaccharides, such as starch, are readily hydrolyzable and form the energy reservoir of the algae. Structural polysaccharides, on the other hand, are constituents of the cell wall. The cell walls of green algae, for example, consist of an amorphous base matrix, inside which is a crystalline, often fibrillar substance (39). The most common such fibrillar substance is cellulose. Similar fibrillar macromolecules have been observed in waters by TEM (40). These structural polysaccharides are much more resistant to degradation than reserve polysaccharides (39) and therefore are more likely to have a significant residence time in surface waters. Some bacteria are able to produce exopolymers, including insoluble capsular polysaccharides and cellulosic microfibrils, in concentrations of up to 2 g/L (41). The aforementioned polysaccharides released by algae and bacteria in the water are aquagenic. The polysaccharides determined by pyrolysis/GC/M also include those of pedogenic origin (such as plant residues), but the aquagenic input is likely to be more significant (42). Characteristic fragments produced by pyrolysis of the polysaccharide group include hexose and pentose units, furan, and furfural products (42). Proteins. The pyrolytic degradation of proteins often yields nitrogen-containing products such as pyridines, pyrroles, and indoles. Some polypeptides also produce fragments in characteristic relative proportions. Tyrosine, for example, produces phenol and p-cresol in approximately equal proportions (30, 32, 42). This is taken into consideration when assessing the phenol produced by polyhydroxy aromatics. Typically a large portion of the N byproducts come from algal or phytoplanktonic sources (32, 43), which places them in the aquagenic class.
VOL. 30, NO. 12, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
3503
FIGURE 3. Evolution of the relative proportions of polysaccharides (PS), proteins (PR), amino sugars (AS), and polyhydroxy aromatics (PHA) from June 14, 1994, to August 18, 1995. Raw samples.
Lignins. Lignins are important components of vascular plants. Lignin derivatives such as guaiacol, methyl guaiacol, and vanillic acid (methoxyphenols) are therefore often found in pyrolysates of terrestrial humic substances. In the pyrolysates of algal humic and marine humic substances, however, these derivatives are rarely found (32, 42). The pyrolysates in this study were found to be devoid of such lignin fragments. Amino Sugars. The main source of N-acetylamino sugars in pyrolysates is derived from the pyrolysis of bacterial and fungal cell walls. Bacterial cell walls contain peptidoglycan, with a glycan backbone of N-acetyl functional groups, and these yield acetamide on pyrolysis. Fungal cell walls contain no peptidoglycan; however, they still are a source of acetamide because they contain chitin, a polymer analogous to peptidoglycan (44-46). Polyhydroxy Aromatics. There has been a general consensus that humic substances of terrestrial origin are very aromatic in nature, the extensive humification of higher plants by funghi and bacteria yielding large quantities of phenols (43). More recently, however, there has been some evidence that some pedogenic humic matter may be less aromatic and more aliphatic than previously thought (32, 47). Phenols may also be produced by the pyrolysis of tyrosine; however, these are accompanied by similar amounts of p-cresol fragments and are accounted for as such in the calculations (30, 32).
Results Raw Samples: June 1994-August 1995. The general trend seen in these raw samples shows high proportions of polysaccharides in the summer and a decrease in their contributions during the colder months (see Figure 3). Throughout most of the year, the largest contributor to the polysaccharide fraction is usually furaldehyde. In early summer, however, hydroxypropanone begins to appear (Figure 4). In July, this fragment begins to increase, and in August and into early September it equals or dominates furaldehyde in its contribution to the polysaccharides. In autumn, the hydroxypropanone disappears again for the colder seasons. The proteinaceous material found in the raw samples shows much less variation overall than the polysaccharides (see Figure 3). This component increases to a slight maximum in mid-November and then shows a general decreasing trend back to summer proportions.
3504
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 30, NO. 12, 1996
FIGURE 4. Relative contributions of hydroxypropanone and furaldehyde to the proportion of total polysaccharides in the identified organic matter from June 14, 1994, to August 18, 1995. Raw samples.
FIGURE 5. Evolution of the relative proportions of polysaccharides (cPS), proteins (cPR), amino sugars (cAS), and polyhydroxy aromatics (cPHA) from July 18, 1994, to August 19, 1995. Centrifuged samples.
The amino sugars vary approximately within the same range as the proteins (Figure 3). Here the maximum levels are achieved around mid-October and are maintained through the winter months. Some fluctuations appear in mid-May and the end of June before returning to normal summer proportions. The proportions of polyhydroxy aromatics are very low, especially in the first summer (Figure 3). Higher relative levels are attained during the winter with some large, unexpected peaks appearing in spring before returning to summer levels. Centrifuged Samples: June 1994-August 1995. The polysaccharides in the centrifuged samples show the same general trend as the raw samples. The summer proportions are very high, followed by fairly sharp decreases throughout the fall and winter (see Figure 5). Fairly low levels are maintained in early spring, followed by the increase back to summer proportions. Here again, as in the raw samples, the largest contributor to the polysaccharide fraction throughout most of the year is furaldehyde. In July, however, hydroxypropanone appears (Figure 6). Through early September it approximately equals furaldehyde in its contribution to the polysaccharides. In autumn, the hydroxypropanone disappears again for the colder seasons. The proportions of proteinaceous material in the centrifuged samples do not vary much. There is a slight
a
b
FIGURE 6. Relative contributions of hydroxypropanone and furaldehyde to the proportion of total polysaccharides in the identified organic matter from July 18, 1994, to August 18, 1995. Centrifuged samples.
FIGURE 8. (a) Evolution of the relative proportions of polysaccharides (cPS) with increasing dissolved organic carbon (DOC). Centrifuged samples from March 28 to July 18, 1995. y ) -33.1 + 17.7x; r 2 ) 0.61. (b) Evolution of the relative proportions of polyhydroxyaromatics (cPHA) with increasing dissolved organic carbon (DOC). Centriguted samples from March 28 to July 18, 1995. y ) 121.3 - 27.8x; r 2 ) 0.66. FIGURE 7. Comparison of 3-day rainfall (from the sampling day plus the two preceding days) and relative proportion of polyhydroxy aromatics in the identified organic matter from June 14, 1994, to August 18, 1995. Centrifuged samples.
increase into autumn and later a return to summer proportions (Figure 5). The relative levels of amino sugars in the centrifuged samples appear to be somewhat higher in the colder months than in the first summer. Several peaks appear in late spring (Figure 5). The polyhydroxy aromatics in the centrifuged samples show a very clear change from very low, initial summer proportions to dominating levels in late winter and early spring. Only in late June do the PHAs cease to dominate the spectrum, returning to lower proportions (Figure 5). Effect of Weather: Raw and Centrifuged Samples. In winter and spring, the polyhydroxy aromatics in the centrifuged samples (cPHA) correlate well with rainfall (rainfall totaled from the sampling day and the two preceding days) measured at a local meteorological station in the spring (Figure 7). This correlation disappears in the summer. When considering the trends with increasing rainfall, the major groups contributing to the organic matter composition are similar for the raw and the centrifuged samples. From the data in this study, the PHA component shows a general increasing trend with increasing rainfall (3-day total) (data not shown). The polysaccharides show
a corresponding decreasing trend. It is also evident from the data that the relative proportions of polysaccharides increase with increasing sunshine (3-day total, data not shown). DOC: Centrifuged Samples. The polysaccharide content of the centrifuged samples as determined by pyrolysis/ GC/MS appears to increase with increasing DOC content in spring and summer (Figure 8a). The amino sugars also appear to increase, although not as markedly as the polysaccharides. The proteins appear to remain unaffected by increasing DOC. As can be seen in Figure 8b, the contribution of PHA to the overall organic matter decreases with increasing DOC. We note that the UV absorbance as well as the DOC of the centrifuged samples appear to be independent of both the sun and the rainfall conditions during the spring and summer of 1995.
Discussion Based on previous studies of this lake, a high DOC content, with more aliphatic compounds, carbohydrates, and proteins is expected during the summer months as compared to the rest of the year. The content of pedogenic matter, leached from the watershed by rainfall, is expected to remain fairly constant (18). The relative proportions of aquagenic matter are expected to decrease during the colder months, with a corresponding relative increase in contribution from the allochthonous pedogenic substances. In Zumstein and Buffle (18), the aliphatic compounds are considered to be
VOL. 30, NO. 12, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
3505
of aquagenic origin, with the possible inclusion of some polysaccharides and proteins of pedogenic origin. Other studies on river water and an eutrophic lake elsewhere also showed maxima in dissolved carbohydrate content in spring and early summer and a corresponding minimum in autumn (30, 48). In the Seine River water study, the main changes in the organic matter were found to be an inverse variation in polysaccharide and PHA fragment content (30). Raw Samples: June 1994-August 1995. The extremely high level of polysaccharides in the summer of 1994 may be explained by the very sunny and very hot weather ideal for microbial productivity during this time. From the pyrolysis of several standards, it can be seen that hydroxypropanone is a dominant characteristic peak in dextran pyrolysates, while the furaldehyde is typical of cellulose. The input of cellulose into the water may come either from a pedogenic source or, more likely, from the degradation of the aquagenic microorganisms (algae, bacteria, etc.) and their cell walls. The presence of dextran-like material is probably the result of microbial production and, considering dextran’s degradability, indicates that the organic matter is fresh. This portion of the organic matter is without a doubt aquagenic in nature. The slight increase from September to November seen in the proportion of protein corresponds to a time, according to Zumstein and Buffle (18), of maximum flux of NOM by sedimentation as the lake turns over. The major source of amino sugars is microbial cell walls. Pyrolysis of microorganisms such as phytoplankton and bacteria therefore yields amino sugars as well as proteinaceous material. Since the seasonal amino sugar profile is similar to that of the proteins, the sources in the organic matter are most likely of aquagenic origin. Very low proportions of polyhydroxy aromatics in the first summer reflect the importance of the aquagenic material produced by microorganisms in the total identified organic matter. The proportions of polyhydroxy aromatics appear to vary almost inversely with polysaccharides. An increase in the relative proportions of PHA may be caused by an actual increase in pedogenic input; however, it may also sometimes be the result of a respective decrease in actual polysaccharide content. For instance, when the growth of microorganisms is high and the polysaccharides are by far the largest contributors to the total identified organic matter, the relative proportion of terrestrial material is small regardless of actual PHA content. The higher proportions of PHA in the winter and spring, however, still reflect an increase in the absolute concentration of pedogenic organic matter in the lake during the colder months. Centrifuged Samples: June 1994-August 1995. Again the cellulose source represented by the furaldehyde seen all year most likely comes either from a pedogenic source or from the degradation of microorganisms and their cell walls. The presence of the rather degradable dextran in the summer, as indicated by the hydroxypropanone fragments, is probably the result of microbial production and is both aquagenic and fresh. Though the protein proportion does not vary much, the levels of proteins are somewhat higher in early spring, usually a period of high production of microorganisms. The pyrolysis of such algae is known to produce the nitrogen-rich byproducts associated with the protein and amino sugar categories. Though algae are generally considered to be somewhat larger than 1 µm, some may be insufficiently dense to be removed from the sample by the
3506
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 30, NO. 12, 1996
centrifugation.The polyhydroxy aromatics in the centrifuged samples dominate the organic matter in the winter and spring. In the summer, the pedogenic contribution to the organic matter is masked by the high autochthonous activity producing polysaccharides. Raw vs Centrifuged Samples. Aside from several points in late winter, the general trends seen in the raw and centrifuged samples for the various groups of biopolymers are fairly similar. The raw samples contain all except the large, dense particles or aggregates that sediment out within 2 h. The centrifuged samples, on the other hand, are expected to contain mostly dissolved components and any particulates insufficiently dense to be removed by the centrifugation. According to calculations, the centrifugation should remove particles larger than approximately 1 µm, although in reality some larger particles may still remain (49). The similarity in trends of the biopolymers in both samples indicates that the NOM identified by pyrolysis/ GC/MS is not usually removed by sedimenting particles or aggregates under the conditions used in this study. Effect of Weather: Raw and Centrifuged Samples. Zumstein and Buffle (18) found a correlation between rainfall and the pedogenic organic matter in the river leading to the lake when using the rainfall from the sampling day added to the rainfall from the two preceding days (3-day total). In the present study, there is a quite good correlation of the PHA in the centrifuged lake sample with 3-day integrated rainfall in spring. This may be explained by the fact that the Grenet River water comes mainly from superficial drainage of the surrounding agricultural basin (18). Thus after prolonged rainfall, more of the water coming into the lake has leached through the soil, and more organic matter of terrestrial origin can be found the lake. The correlation between cPHA and rainfall is no longer present in the summer months. This is attributed to the high activity of microorganisms in summer, producing levels of polysaccharides high enough to mask any effect of rainfall on the input of pedogenic matter into the lake. Another contribution might come from a higher vegetal cover in summer, which could then result in a lower leaching potential. These effects should be taken into account when studying more complicated lacustrine systems. DOC: Centrifuged Samples. An increase seen in the polysaccharide proportion of the centrifuged samples with increasing DOC content is in good agreement with the findings of Zumstein and Buffle (18). The polysaccharide proportion is strongly influenced by the production and release of reserve and structural polysaccharides of the cell walls of microorganisms. The degradation of these microbial cell walls is also the likely cause of the increase in amino sugars. The proteins appear to remain unaffected by increasing DOC. This suggests that the main changes in DOC are caused by either polysaccharide production in the lake or polyhydroxy aromatics leaching from the soil. Further work should be done either in conjunction with tracers or detailed microbiological studies.
Acknowledgments We are indebted to Dr. A. Bruchet and his colleagues for invaluable advice, Dr. W. Kloeti for assistance with the experiments, the Schweizerische Meteorologische Anstalt for the weather data, and Prof. W. Stumm and two anonymous reviewers for helpful comments on the manuscript. M.V.B. gratefully acknowledges Prof. W. Wildi for financial support. This work was supported by Projects
5001-036780 and 5001-40013 of the Swiss National Science Foundation.
Literature Cited (1) Lochtman, J.; Reichert, J.; Bernhardt, H. Vom Wasser 1978, 50, 7-19. (2) O’Melia, C.; Tiller, C. In Environmental Particles, Volume 2; Buffle, J.; van Leeuwen, H., Eds.; Lewis Publishers: Boca Raton, FL, 1993; pp 353-386. (3) Weilenmann, U.; O’Melia, C.; Stumm, W. Limnol. Oceanogr. 1989, 34, 1-18. (4) Sigg, L. In Chemical Processes in Lakes; Stumm, W., Ed.; Wiley & Sons: New York, 1985; pp 283-311. (5) McCarthy, J.; Degueldre, C. In Environmental Particles, Volume 2; Buffle, J.; van Leeuwen, H. Eds.; Lewis Publishers: Boca Raton, FL, 1993; pp 247-316. (6) Ryan, J.; Gschwend, P. Water Resour. Res. 1990, 26, 307-322. (7) McCarthy, J.; Zachara, J. Environ. Sci. Technol. 1989, 23, 496503. (8) Bouwer, E.; Zehnder, A. Trends in Biotechnol. 1993, 11, 360367. (9) Stumm, W.; Morgan, J. Aquatic Chemistry, 3rd ed.; Wiley Interscience: New York, 1996. (10) Buffle, J.; Leppard, G. Environ. Sci. Technol. 1995, 29, 21692175. (11) Filella, M.; Buffle, J. Colloids Surf. 1993, 73, 255-273. (12) Tipping, E.; Ohnstad, M. Colloid stability of iron oxide particles from a freshwater lake. Nature, 1948, 308, p 266-268. (13) Davis, J. A. Geochim. Cosmochim. Acta 1982, 46, 2381-2393. (14) Wilkinson, K.; Ne`gre, J.-C.; Buffle, J. J. Contam. Hydrol. Submitted for publication. (15) Stumm, W. Chemistry of the Solid-Water Interface; John Wiley & Sons: New York, 1992. (16) Hoffmann, M. In Aquatic Chemical Kinetics: Reaction Rates of Processes in Natural Waters; Stumm, W., Ed.; John Wiley & Sons: New York, 1990. (17) Zumstein, J. Ph.D. Thesis No. 2401, Universite´ de Gene`ve, Gene`ve, Switzerland, 1989. (18) Zumstein, J.; Buffle, J. Water Res. 1989, 23, 229-239. (19) Filella, M.; Buffle, J.; Leppard, G. Water Sci. Technol, 1993, 27, 91-102. (20) Perret, D.; Leppard, G.; Mu ¨ller, M.; Belzile, N.; De Vitre, R.; Buffle, J. Water Res. 1991, 25, 1333-1343. (21) Sorge, C.; Schnitzer, M.; Schulten, H.-R. Biol. Fertil. Soils 1993, 16, 100-110. (22) Saiz-Jimenez, C. Sci. of the Total Environ. 1992, 117/118, 13-25. (23) Schulten, H.-R.; Schnitzer, M. Soil Sci. 1992, 153, 205-224. (24) Saiz-Jimenez, C.; de Leeuw, J. J. Anal. Appl. Pyrolysis 1986, 9, 99-119. (25) Saiz-Jimenez, C.; Haider, K.; Meuzelaar, H. L. C. Geoderma 1979, 22, 25-37. (26) Bracewell, J.; Roberston, G.; Williams, R. J. Anal. Appl. Pyrolysis 1971, 2, 53-62.
(27) Gadel, F.; Charrie`re, B.; Serve, L. Estuarine Coastal Shelf Sci. 1993, 37, 211-236. (28) van Loon, W. M. G. M.; Boon, J.; de Groot, B. Environ. Sci. Technol. 1993, 27, 2387-2396. (29) Charrie`re, B.; Gadel, F.; Serve, L. Hydrobiologia 1991, 222, 89100. (30) Bruchet, A.; Rousseau, C.; Mallevialle, J. J. Am. Water Works Assoc. 1990, Sep; 66-74. (31) Abbt-Braun, G.; Frimmel, F.; Schulten, H. Water. Res. 1989, 23, 1579-1591. (32) Gadel, F.; Bruchet, A. Water Res. 1987, 21, 1195-1206. (33) Bruchet, A. Ph.D. Thesis No. 1050, Universite´ de Poitiers, Poitiers, France, 1985. (34) Saliot, A.; Ulloa-Guevara, A.; Viets, T.; de Leeuw, J.; Schenck, P.; Boon, J. Org. Geochem. 1984, 6, 295-304. (35) van de Meent, D.; Los, A.; Leeuw, J. W.; Schenck, P. A.; Haverkamp, J. In Advances in Organic Geochemistry; Wiley: New York, 1983, pp 336-349. (36) Wilson, M.; Philip, R.; Gillam, A.; Gilbert, T.; Tate, K. Geochim. Cosmochim. Acta 1983, 47, 497-502. (37) Meuzelaar, H. L. C.; Haverkamp, J.; Hileman, F. In Pyrolysis Mass Spectrometry of Recent and Fossil Biomaterials, compendium and atlas; Elsevier: New York, 1982. (38) Gadel, F.; Alcan ˜ iz, J.; Charrie`re, B.; Serve, L. Cont. Shelf Res. 1990, 10, 1039-1062. (39) Lochtman, J. Ph.D. Thesis No. 82, Technische Hochschule Aachen, Aachen, Germany, 1977. (40) Leppard, G.; Burnison, B.; Buffle, J. Anal. Chim. Acta 1990, 232, 107-121. (41) Breedveld, M.; Zevenhulzen, L.; Canter Cremers, H.; Zehnder, A. Antonie van Leeuwenhoek 1993, 64, 1-8. (42) Bracewell, J.; Haider, K.; Larter, S.; Schulten, H.-R. In Humic Substances II, Hayes, M.; MacCarthy, P.; Malcolm, R.; Swift, R., Eds.; Wiley: New York, 1989; pp 181-369. (43) Gadel, F.; Charrie`re, B.; Serve, L.; Comellas, L. Oceanol. Acta 1992, 15, 61-74. (44) Gutteridge, C. S. Methods Microbiol. 1987, 19, 227-272. (45) Eudy, L.; Walla, M.; Hudson, J.; Morgan, S. J. Anal. Appl. Pyrolysis 1985, 7, 231-247. (46) Hudson, J.; Morgan, S.; Fox, A. Anal Biochem. 1982, 120, 59-65. (47) Oades, J. In Minerals in soil environments, 2nd ed.; Dixon, J.,Weed, S., Eds.; Soil Science Society of America: Madison, WI, 1989; pp 89-159. (48) Hama, T.; Handa, N. Arch. Hydrobiol. 1983, 98, 443-462. (49) Perret, D.; Newman, M.; Ne`gre, J.-C.; Chen, Y.; Buffle, J. Water Res. 1994, 28, 91-106.
Received for review February 22, 1996. Revised manuscript received August 2, 1996. Accepted August 7, 1996.X ES960171X X
Abstract published in Advance ACS Abstracts, October 15, 1996.
VOL. 30, NO. 12, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
3507
