> .nojs { display: none; } ?Athens/Institution Login? Not Registered?? User?Name: > Password: > > > Remember?me?on?this?computer Forgotten?password? ? Home Browse Search My Settings Alerts Help ?Quick Search ??Title,?abstract,?keywords ??Author ? ??Journal/book?title ??Volume ??Issue ??Page ???? ???? ?????? Advanced Search // // Organic Geochemistry Volume 36, Issue 3, March 2005, Pages 463-474 ? Font Size: >?? > Article > >?Article - selected Figures/Tables > >?Figures/Tables - selected References > >?References - selected PDF (477 K) Thumbnails - selected | Full-Size Images Thumbnails - selected | Full-Size Images ? Download PDF??? ? E-mail Article??? ? Cited By??? ? Save as Citation Alert??? ? Citation Feed??? ? Export Citation??? ? Add to my Quick Links??? ? Cited By in Scopus (7) ? ? Related Articles in ScienceDirect Dissolved carbohydrate and microbial ATP in the North A... Deep Sea Research Part A. Oceanographic Research Papers ?Dissolved carbohydrate and microbial ATP in the North Atlantic: concentrations and interactions Deep Sea Research Part A. Oceanographic Research Papers,?Volume 26, Issue 11,?November 1979, Pages 1267-1290 Curtis M. Burney, Kenneth M. Johnson, Dennis M. Lavoie, John McN. Sieburth Abstract A selective and sensitive spectrophotometric assay for monosaccharide (MCHO) before and after a hydrolysis step has permitted the estimation of total carbohydrate (TCHO) and of polysaccharide (PCHO) by difference. The concentrations and diel variations of MCHO, TCHO, PCHO, and dissolved organic carbon (DOC) were estimated on some 90 samples obtained at 15 stations between Rhode Island and Spain. DOC ranged from 570 to 1330 ?g C 1?1 with a mean of 940 ?g C 1?1. MCHO, calculated as hexose, ranged from 65 to 356 ?g 1?1 (mean 163 ?g 1?1), accounting for 3.5 to 13.2% of the DOC. TCHO varied from 175 to 583 ?g 1?1 (mean 348 ?g 1?1), 8.0 to 24.5% of the DOC. PCHO ranged from 0 to 379 ?g 1?1 (mean 184 ?g 1?1), up to 16.0% of the DOC. MCHO, TCHO, and PCHO were positively correlated with DOC at the 0.01 level. PCHO as a % of TCHO decreased significantlyfrom 69% in coastal to 37% in mid-ocean samples. The vertical distribution of the microbial plankton smaller and larger than 3 ?m was determined at 12 of the stations by ATP assay on samples sequentially filtered through Nuclepore membranes. Living biomass for the bacterioplankton (0.2 to 3.0 ?m) calculated from the ATP concentration ranged from 1 to 55 ?g C 1?1 (approx 104 to 106 bacterial cells ml?1) and accounted for 3 to 80% of the total living biomass in the microbial plankton, averaging 30% in the photic and 40% in the aphotic zone. Vertical profiles of bacterial and protist ATP at six stations are compared with those for dissolved carbohydrates, DOC, chlorophyll a, phaeopigments, dissolved oxygen, and temperature. These include four diel drift stations in which a daylight sampling was followed by a predawn resampling on the following day. Carbohydrate peaks were often associated with accumulations of organisms in the > 3-?m size fraction, which were low in chlorophyll a, possibly indicative of collections of protozooplankton. During the day there was evidence of net release of carbohydrate at the depth of the chlorophyll a maxima at oceanic stations but not at neritic stations. Appreciable bacterioplankton maxima (0.2 to 3.0 ?m ATP) occurred most often with carbohydrate minima. PDF (1305 K) Carbohydrates, uronic acids and alkali extractable carb... Organic Geochemistry ?Carbohydrates, uronic acids and alkali extractable carbohydrates in contrasting marine and estuarine sediments: Distribution, size fractionation and partial chemical characterization Organic Geochemistry,?Volume 39, Issue 3,?March 2008, Pages 265-283 Vishwas B. Khodse, Loreta Fernandes, Narayan B. Bhosle, Sugandha Sardessai Abstract Concentration, size fractionation and monosaccharide composition of carbohydrates and uronic acids were investigated in contrasting sediments of the Mandovi estuary (ME), Arabian Sea (AS) and the Bay of Bengal (BOB). Concentrations and monosaccharide composition of carbohydrates and uronic acids varied spatially. Average yields of carbohydrates and uronic acids were higher for the estuarine compared to marine sediments. Interestingly, yields of carbohydrates and uronic acids increased in sediments with water column depth, implying preferential removal of other constituents, selective preservation and/or lateral input of carbohydrate rich material. Analysis of monosaccharide biomarkers indicates that carbohydrates were derived from terrestrial plants, bacteria and phytoplankton, however, the influence of the former was relatively greater in sediments of the ME and BOB, as well as in residual sediments of ME. Approximately 11?21% of total carbohydrates could be extracted using hot alkali extraction followed by sonication. Irrespective of the depositional environment, carbohydrates and uronic acids were greater in the very high molecular weight size fraction (>30?kDa). The abundance of glucose increased with the decrease in molecular size of extracted organic matter. This probably indicates its association with less degradable carbohydrates. PDF (404 K) Distributions of carbohydrate species in the Gulf of Me... Marine Chemistry ?Distributions of carbohydrate species in the Gulf of Mexico Marine Chemistry,?Volume 81, Issues 3-4,?April 2003, Pages 119-135 Chin-Chang Hung, Laodong Guo, Peter H. Santschi, Nicolas Alvarado-Quiroz, Jennifer M. Haye Abstract In order to study the role of polysaccharides in the cycling of marine organic matter and transparent exopolymeric particles (TEP), the concentrations of total carbohydrates (p-TCHO), total uronic acids (URA) and total acid polysaccharides (APS) in suspended and sinking particles, as well as carbohydrates in the filter-passing ?dissolved? phase (d-TCHO), were measured in vertical profiles along a N?S transect in the Gulf of Mexico, across a cold core (CCR) and a warm core (WCR) ring (eddy) during both July 2000 and May 2001. The concentrations of d-TCHO in 2000 ranged from 4 to 22 ?M C, with a subsurface maximum, which was located slightly above the depth of chl a maximum, amounting to, on average, 34% of DOC in the CCR, and 13% in the WCR. The concentration of particulate carbohydrates (p-TCHO) in different size fractions (0.7?10, 10?53, and >53 ?m) ranged from 0.04 to 1.1, 0.005 to 0.40, and 0.006 to 0.26 ?M C, respectively, indicating that carbohydrates are mostly concentrated in small particles (0.7?10 ?m). URA and APS were similarly concentrated in small particles, in which, on average, URA accounted for 87% and 57% of total URA, and APS for 92% and 88% of total APS in 2000 and 2001, respectively. URA accounted for 3?9% of carbohydrates in suspended particles, suggesting that URA are a minor component of the p-TCHO pool. Due to its surface-reactive nature, URA could play a major role in the coagulation of particles and macromolecules despite its relatively low abundance. While, on average, p-TCHO and total APS were more enriched in suspended particles than in sinking particles in both 2000 and 2001, the opposite was true for URA in both years. The greater contents of URA that are present in settling particles compared to suspended particles could indicate a mass flow in the direction of sinking particles, either caused by coagulation, by bacterial reworking of particulate and colloidal organic matter, or by their more refractory nature. PDF (509 K) Distributions of nutrients, dissolved organic carbon an... Continental Shelf Research ?Distributions of nutrients, dissolved organic carbon and carbohydrates in the western Arctic Ocean Continental Shelf Research,?Volume 26, Issue 14,?September 2006, Pages 1654-1667 Deli Wang, Susan M. Henrichs, Laodong Guo Abstract Seawater samples were collected from stations along a transect across the shelf?basin interface in the western Arctic Ocean during September 2002, and analyzed for nutrients, dissolved organic carbon (DOC), and total dissolved carbohydrate (TDCHO) constituents, including monosaccharides (MCHO) and polysaccharides (PCHO). Nutrients (nitrate, ammonium, phosphate and dissolved silica) were depleted at the surface, especially nitrate. Their concentrations increased with increasing depth, with maxima centered at 125?m depth within the halocline layer, then decreased with increasing depth below the maxima. Both ammonium and phosphate concentrations were elevated in shelf bottom waters, indicating a possible nutrient source from sediments, and in a plume that extended into the upper halocline waters offshore. Concentrations of DOC ranged from 45 to 85??M and had an inverse correlation with salinity, indicating that mixing is a control on DOC concentrations. Concentrations of TDCHO ranged from 2.5 to 19??M-C, comprising 13?20% of the bulk DOC. Higher DOC concentrations were found in the upper water column over the shelf along with higher TDCHO concentrations. Within the TDCHO pool, the concentrations of MCHO ranged from 0.4 to 8.6??M-C, comprising 20?50% of TDCHO, while PCHO concentrations ranged from 0.5 to 13.6??M-C, comprising 50?80% of the TDCHO. The MCHO/TDCHO ratio was low in the upper 25?m of the water column, followed by a high MCHO/TDCHO ratio between 25 and 100?m, and a low MCHO/TDCHO ratio again below 100?m. The high MCHO/TDCHO ratio within the halocline layer likely resulted from particle decomposition and associated release of MCHO, whereas the low MCHO/TDCHO (or high PCHO/TDCHO) ratio below the halocline layer could have resulted from slow decomposition and additional particulate CHO sources. PDF (704 K) Radiocarbon studies of organic compound classes in plan... Geochimica et Cosmochimica Acta ?Radiocarbon studies of organic compound classes in plankton and sediment of the northeastern Pacific Ocean Geochimica et Cosmochimica Acta,?Volume 62, Issue 8,?April 1998, Pages 1365-1378 Xu-Chen Wang, Ellen R. M. Druffel, Sheila Griffin, Cindy Lee, Michaele Kashgarian Abstract Radiocarbon (?14C) and stable carbon isotopes (?13C) were measured in total hydrolyzable amino acid (THAA), total carbohydrate (TCHO), total lipid, and acid-insoluble organic fractions that had been separated from phytoplankton, zooplankton, sediment floc, and sediment samples from an abyssal site in the northeastern Pacific Ocean. THAA, TCHO, and lipid fractions accounted for 91?99% of the total organic carbon (TOC) in phytoplankton and zooplankton, 57% of TOC in sediment floc, and 18?38% of TOC in sediment. Based on concentration profiles in sediment, first-order degradation rate constants below the bioturbation zone were calculated using a ?multi-G? model considering both labile and refractory organic fractions. The calculated rate constants were in the order THAA ? TCHO > TOC ? TN > lipid, indicating the relative reactivities of these compound classes in the sediment during early diagenesis. Bioturbation affected the distributions of these compound classes in the top few centimeters of the sediment. The ?14C values of all organic fractions decreased in the order plankton in surface water to sediment floc to sediments at 4100 m depth. Distinct differences in ?14C exist among THAA, TCHO, and lipid fractions in sediment floc and sediments. The lipid fraction exhibited lower ?14C signatures than THAA and TCHO fractions. Differential decomposition of organic matter and sorption and/or biological incorporation of ?old? DOC into sediment appear to be the major processes that likely control the observed ?14C signatures and abundances. ?13C values of the organic compound classes in sediment are similar to their values in plankton indicating that organic matter input to sediment in the northeastern Pacific is mainly from marine sources. Also, distinct ?13C signatures were found in each of the four organic fractions. PDF (443 K) View More Related Articles ? View Record in Scopus ? doi:10.1016/j.orggeochem.2004.09.004???? > Copyright ? 2004 Published by Elsevier Ltd. A seasonal survey of carbohydrates and uronic acids in the Trinity River, Texas Chin-Chang Hung , , Kent W. Warnken1, and Peter H. Santschi Laboratory for Oceanographic and Environmental Research (LOER), Department of Marine Sciences, Texas A&M University at Galveston, 5007 Ave. U, Galveston, TX 77551, USA > Received 3 October 2003;? revised 1 March 2004;? accepted 14 September 2004.? Associate Editor?George Wolff.? Available online 8 December 2004. > Abstract Due to their potential significance as indicators of ecological health, the biogeochemical cycling of carbohydrates and uronic acids was investigated in the Trinity River Texas, during 2000?2001. Concentrations of dissolved organic carbon (DOC), total carbohydrates (TCHO), polysaccharides (PCHO), monosaccharides (MCHO), uronic acids (URA), as well as of oxygen, suspended particulate matter, nutrients and trace metals (Cu, Pb, Cd) were assessed at various stages of discharge. TCHO/DOC ratios, as well as nutrient and hydrogen ion concentrations, were inversely related to temperature, which suggests that biological processes in Lake Livingston, the largest freshwater reservoir along the Trinity River, are not only regulating nutrient concentrations but also the preferential degradation of carbohydrates over that of bulk DOC. However, uronic acids were selectively preserved during this temperature controlled biological process, as is evident from the positive correlation of URA/TCHO ratios and temperature. Thus, uronic acids are more refractory compounds than bulk TCHO. Significant correlations between TCHO and dissolved Cu, Pb and Cd suggest that their pathways and cycles are linked through common sources or removal processes. Article Outline 1. Introduction 2. Materials and methods 2.1. Sample collection and measurement 2.2. Analysis of carbohydrates and uronic acids 3. Results and discussion 3.1. Discharge and ancillary hydrographic data 3.2. DOC and carbohydrates 3.3. Effect of biological activity on CHO and URA concentrations 3.4. Relationship between trace metals and carbohydrates 4. Conclusions Acknowledgements References 1. Introduction Carbohydrates are among the most important biopolymers in freshwater systems ( Thurman, 1985, Buffle, 1990, Sigleo, 1996 and Mannino and Harvey, 2000). Previous research has shown that the composition of carbohydrates in fresh waters is similar to that in seawater ( Repeta et al., 2002). However, only a minor fraction of carbohydrates is characterized at the molecular level. For example, glucose, galactose, arabinose, xylose, mannose, fucose, and rhamnose, identified by HPLC or GC?MS, are the main components of carbohydrates in rivers and lakes ( Sweet and Perdue, 1982, Cheng and Kaplan, 2001 and Repeta et al., 2002). Since it has been shown that acid polysaccharides such as uronic acids (URA) can be excreted by algae and bacteria in response to low nutrient or high metal stress ( Costerton, 1984 and Leppard, 1993), they can also play a significant role in heavy metal detoxification in aquatic environments ( Leppard, 1997). Hung et al. (2001) reported that the concentrations of dissolved URA, acid polysaccharides with a carboxylic group, can make up a significant fraction of carbohydrates, i.e., up to 12% in the waters of the Gulf of Mexico. Recent studies have shown that URA compounds also exist in both suspended and sinking particles as well as in sediments ( Bergamaschi et al., 1999 and Hung et al., 2003), but their biogeochemical cycling in river, estuarine and oceanic environments is still poorly understood. Recent studies have shown that trace metals in natural waters are complexed by natural organic ligands ( van den Berg et al., 1987, van den Berg et al., 1991, Kozelka and Bruland, 1998, Muller, 1999 and Tang et al., 2002) and the distribution of trace metals in natural waters is strongly affected by the production of organic ligands ( Sholkovitz, 1976 and Santschi et al., 1997). Some organic ligands, such as phytochelatins, thiols and extracellular polysaccharides, have been found in metal stress experiments ( Leppard, 1993, Leppard, 1997, Ahner and Morel, 1995, Leal et al., 1999 and Rozan et al., 2000), but the chemical compositions of organic ligands in natural waters are largely unknown. In order to better understand the processes that control the biogeochemical cycling of carbohydrate and URA compounds, and their interaction with trace metals, concentrations of carbohydrates and URA were measured during the calendar years 2000?2001 in the Trinity River, Texas. The Trinity River is the primary freshwater input source to Galveston Bay, contributing, on average, approximately 83% of the gauged input. Lake Livingston, the second largest lake in Texas, with a 84,800-acre (34,300-ha) reservoir, is located around 80 miles (130 km) north of the mouth of the Trinity River. Lake Livingston?s dam was built in 1969 to modulate the flow of the Trinity River. Detailed information about organic carbon is reported separately ( Warnken and Santschi, 2004). 2. Materials and methods 2.1. Sample collection and measurement Samples were collected from the Trinity River (29?48?N, 94?45?W, Fig. 1), Texas, using clean Teflon bottles during the period beginning September 2000 through August 2001. After collection, samples were immediately brought to the lab and filtered through GF/F filters. Carbohydrate samples were stored in a freezer (?20?C) until analysis. Water temperature, conductivity and dissolved oxygen (DO) were measured during the sampling period. DO was measured using a dissolved oxygen electrode sensor (YSI 90 MEA). Additionally, samples were collected for the analysis of suspended particulate matter (SPM), dissolved organic carbon (DOC), nutrient, and trace metal concentrations. DOC samples were collected by filtration of 50 ml aliquots of river water using a 25 mm GF/F filter, precombusted at 450 ?C for 5 h and the filtered solution was measured by catalytic high temperature combustion using a Shimadzu TOC 5000 analyzer ( Guo and Santschi, 1997). Nutrients were analyzed by a flow-injection spectrophotometric method ( Grasshoff et al., 1983). Dissolved trace metal (Cu, Cd and Pb) concentrations were measured by on-line ICP-MS ( Warnken et al., 2000). Briefly, river samples were collected by ultra-clean techniques, filtration using acid-cleaned prefilters and filters (0.45 ?m, MSI) in acid-cleaned Teflon bottles. These samples were stored in a cooler in double plastic bags (the inner bag acid-cleaned) and stored in a refrigerator until measurement ( Warnken, 2002). The daily discharge of the Trinity River was recorded by the United States Geological Survey (2002). Full-size image (96K) Fig. 1.?The sampling location of Trinity River in Texas. > View Within Article > 2.2. Analysis of carbohydrates and uronic acids Dissolved carbohydrates, including total carbohydrates (TCHO), monosaccharides (MCHO), and polysaccharides (PCHO) were analyzed using a modification ( Hung et al., 2001) of the TPTZ method ( Myklestad et al., 1997). Briefly, the concentrations of TCHO were determined as follows: 3 ml of river sample and 0.3 ml of 1 N HCl were added to a 10 ml glass ampoule. The sealed ampoules were hydrolyzed at 150?C for 1 h. Then, 1 ml of hydrolysate, after neutralization with sodium hydroxide, was pipetted to a dark glass bottle containing 1 ml of 0.7 mM potassium ferricyanide, and the well-mixed solution was placed in a boiling water bath for 10 min. After that, 1 ml of 2 mM ferric chloride solution and 2 ml of 2.5 mM TPTZ (2,4,6-tripyrridyl-s-triazine, Sigma) solution were added and mixed on a Vortex mixer. The absorbance was measured at 595 nm. The reagent blank in Milli-Q was subtracted before calculating the concentration of the monosaccharide (e.g., glucose). The MCHO concentration in samples was directly measured without hydrolysis. The PCHO concentration in samples was equal to the difference between TCHO and MCHO ([PCHO]?=?[TCHO]???[MCHO]). The concentrations of TCHO, MCHO and PCHO are expressed as ?M C. The concentrations of dissolved uronic acids (URA) were analyzed according to Filisetti-Cozzi and Carpita (1991) and Hung and Santschi (2001). Briefly, 10 ml of river water were concentrated to 0.4 ml using lyophilization and was pipetted to a glass vial. Then, 40 ?l of sulfamic acid was added and the solution was stirred on a vortex mixer. Subsequently, 2.4 ml of 75 mM sodium tetraborate in concentrated sulfuric acid was added to the vial and heated at 100?C for 10 min in a boiling water bath. After cooling, 30 ?l of 0.15 % m-hydroxydiphenyl was added and the absorbance was measured at 525 nm. Glucuronic acid was used as a standard compound. For the control experiment, a UV-irradiated river water sample (24 h) was used, following the same procedures as for the samples. The river water blank was subtracted from the measured concentrations and the concentration of uronic acids were reported as total uronic acids (URA, ?M C). 3. Results and discussion 3.1. Discharge and ancillary hydrographic data Discharge rates, water temperature, conductivity, concentrations of dissolved oxygen and SPM in the Trinity River are shown in Table 1 and Fig. 1 and Fig. 2. Trinity River discharge was low during the months of September and October of 2000, but showed a high variability beginning in November 2000. A high discharge event began in mid-February 2001, with a crest in mid-March that eventually declined by the end of April. Discharge rates remained below average throughout the remainder of the study period, with the exception of an additional high discharge event during the month of June, associated with tropical storm Allison. This storm made landfall over Galveston, Texas, on June 8, 2001, and dumped up to 30 inches of rain, flooding the city of Houston and its surrounds based on the rainfall information from the National Weather Service Forecast Office (www.srh.noaa.gov/hgx/projects/allison01.htm). > > Table 1. Trinity River discharge (TRD) and water temperature (T ), dissolved oxygen (DO) concentration, conductivity (Cond.), and suspended particulate matter (SPM) concentrations Sample # Date TRD (m3 s?1) T (?C) DO (mg L?1) SPM (mg L?1) Cond. (?S cm?1) 1 6-Sep-00 32 31.6 6.2 13.2 454 2 6-Nov-00 617 23.6 7.4 69.1 413 3 11-Nov-00 592 18.2 8.7 68.7 390 4 21-Nov-00 309 13.4 9.4 64.6 369 5 9-Dec-00 63.7 12.8 9.9 18.3 365 6 18-Dec-00 248 11.3 11.3 41.5 360 7 28-Dec-00 671 9.5 11.9 108.0 358 8 2-Jan-01 742 7.5 12.1 127.0 353 9 16-Jan-01 436 9.2 11.9 44.6 332 10 20-Jan-01 1008 8.0 11.9 196.0 272 11 12-Feb-01 189 10.7 11.4 41.6 293 12 22-Feb-01 558 13.1 11.3 75.5 291 13 28-Feb-01 1138 15.1 10.4 130.0 290 14 4-Mar-01 1699 14.8 10.7 219.0 288 15 16-Mar-01 1781 15.6 9.2 101.0 285 16 21-Mar-01 1532 15.3 8.8 99.1 269 17 26-Mar-01 1283 16.0 8.8 93.6 276 18 9-Apr-01 821 20.0 8.0 76.6 293 19 23-Apr-01 268 22.4 7.7 62.6 316 20 9-May-01 259 25.3 7.3 61.0 336 21-TS 11-Jun-01 2033 26.0 6.7 292.0 329 22 24-Jun-01 60.6 28.3 6.4 21.2 294 23 17-Jul-01 62.3 32.7 6.1 15.9 320 24 6-Aug-01 41.6 32.0 6.1 15.6 292 Full-size table > View Within Article > > > Full-size image (22K) Fig. 2.?Temporal variation of (A) water temperature, (B) SPM, DOC, (C) > , > , (D) TCHO/DOC and URA/TCHO in the Trinity River, Texas. > View Within Article > Water temperature ranged from 7.5 to 31.6?C, reflecting a remarkably seasonal variation (Fig. 2A). The low value was recorded just after one of the coldest Decembers on record for this region of Texas. Elevated temperatures during the summer result in increased respiration rates, leading to oxygen undersaturation, while low temperatures in winter are the cause of reduced photosynthesis and respiration rates and increased gas solubility, leading to higher dissolved oxygen concentrations. Dissolved oxygen concentrations varied by a factor of two, and ranged from a summertime low of 6.15 mg l?1 to a high value of 12.1 mg l?1 ( Table 1) in winter. A simple linear correlation to temperature was not observed during the study period, suggesting that oxygen concentrations were not simply controlled by equilibration with ambient atmospheric oxygen concentrations, but were modified further by in situ bacterial respiration and phytoplankton photosynthesis. For instance, Trinity River water was supersaturated or at saturation during the winter months and became increasingly undersaturated (as low as 83%) with increasing temperature during the summer months of both 2000 and 2001. The concentrations of SPM ranged from 13 to 219 mg l?1 ( Table 1), with an extremely high value of 292 mg l?1 appearing in June, 2001, caused by Tropical Storm Allison. Conductivity showed a general decrease during the study period, with values as high as 454 ?S cm?1 measured in September 2000. Generally, Trinity River water had increased and highly variable conductivity levels at low discharge rates, possibly due to evapotranspiration effects ( Oktay et al., 2001) and reached higher but nearly constant conductivity levels at intermediate and high discharge rates. Observations in a Wisconsin watershed (Milwaukee River) by Shafer et al. (1997) for stream flows up to 50 m3 s?1 were similar to ours, in that a significant linear decrease in conductivity was observed with increasing discharge. The pH of Trinity River water ranged from a high value of 8.22 to a low of 7.56 ( Table 1) remaining on the alkaline side of neutral throughout the study period. Generally, the pH is controlled by the CO2 dissolution of CaCO3, producing Ca2+ and 2 > , the major component of alkalinity at the pH of 7.9???0.3 in Trinity River water. This equilibrium with CaCO3 is the main reason why Ca concentrations in Trinity River water are constant ( Warnken, 2002). A strong inverse relationship between dissolved oxygen concentrations and those of nitrate (Fig. 3A, R?=?0.90; n?=?24; p? > Full-size image (12K) Fig. 3.?Linear correlation of (A) nitrate and (B) phosphate with dissolved oxygen. (C) The TIN: > ratio measured for samples collected between September 2000 and September 2001. > View Within Article > N:P ratios of between 30 and 50 were determined for the winter months (Fig. 3C). However, strong removal of total inorganic nitrogen (TIN), likely in Lake Livingston and the other upstream reservoir lakes, resulted in N:P ratios of approximately one during the summer months in both 2000 and 2001 (Fig. 3C). Lake Livingston has a significant effect on phosphorus and nitrogen in the lower watershed, accounting for a 60% decrease in phosphorus and a 30% decrease in nitrogen or a 2:1 decrease in phosphorus relative to nitrogen, which helps to explain the observations during winter ( GBNEP, 1994). In other words, the average concentrations of TIN and P in Trinity River samples are 45 and 1.87 ?M, respectively. The ratio of TIN/P in the winter should be 42 due to a 30% and 60% decrease in N and P, respectively. Nitrate was the nitrogen species present at the highest concentration during much of the year, followed by ammonium, urea and nitrite, respectively. Only at elevated temperatures (low nitrate concentrations) did ammonia reach levels similar to or greater than those of nitrate. A source of nitrate could be from soil leaching. However, ammonium and urea are derived mostly from washout of fertilizers and other biological nitrogen sources from agricultural soils. In summer time (at elevated temperatures), agricultural activity could result in higher ammonium and urea discharges and recycling of biological nitrogen sources. Normalized carbohydrates (e.g., TCHO and URA) also have a striking seasonal variation (Fig. 2D), similar to that of the nutrients. Thus, the concentrations of nutrients may be an important factor that affects the distribution of autochthonous and allochthonous sources of dissolved carbohydrates in the Trinity River. 3.2. DOC and carbohydrates Temporal variations of DOC, MCHO, PCHO, TCHO and URA concentrations in the Trinity River are shown in Fig. 2. DOC concentrations exhibited low but variable concentrations at low discharge, increasing with increasing discharge, and ranging from 350 to 560 ?M. The range of our DOC data is in agreement with previous investigations from the Trinity River mouth ( Benoit et al., 1994, Guo and Santschi, 1997 and Tang et al., 2001). Most importantly, DOC was inversely related to conductivity ( Warnken and Santschi, 2004), suggesting a watershed influence on the transport pathway of DOC, demonstrating the different effects of lower ionic strength surface runoff, enrichment by chemically eroded major ions, both coupled to the retention of DOC compounds during percolation through the saturated zone (see Table 2). > > Table 2. Concentrations of dissolved monosaccharides (MCHO), polysaccharides (PCHO), total carbohydrates (TCHO), uronic acids (URA) and dissolved organic carbon (DOC) in the Trinity River Sample # MCHO (?M C) PCHO (?M C) TCHO (?M C) URA (?M C) DOC (?M C) 1 n.d. n.d. n.d. n.d. n.d. 2 44.5 13.5 58.0 8.7 370 3 29.3 6.3 35.6 5.2 382 4 82.3 2.9 85.3 11.2 392 5 107.4 2.7 110.1 11.6 454 6 84.8 3.4 88.2 11.5 460 7 84.8 11.9 96.7 14.3 425 8 132.2 23.2 155.4 25.7 429 9 125.9 12.2 138.1 23.8 430 10 92.4 11.1 103.6 15.3 557 11 87.8 12.8 100.6 11.4 479 12 65.3 7.6 72.8 8.1 461 13 88.1 10.7 98.8 9.1 534 14 88.3 16.3 104.7 15.5 559 15 105.6 13.7 119.3 15.8 534 16 73.2 10.7 83.9 17.2 552 17 115.7 9.6 125.3 22.8 519 18 89.3 4.0 93.3 12.5 510 19 90.3 9.0 99.3 13.9 484 20 79.8 4.4 84.2 13.3 457 21-TS 37.5 4.9 42.4 9.8 444 22 69.5 6.2 75.7 19.2 444 23 42.0 13.3 55.3 14.4 393 24 38.1 4.7 42.8 12.8 450 Full-size table > View Within Article > Concentrations of MCHO in the Trinity River showed large irregular variations, ranging from 27 to 112 ?M C. PCHO concentrations were much lower than those of MCHO, accounting for only 10?20% of TCHO. MCHO was thus a major component of TCHO, ranging from 80% to 90% of TCHO. This high proportion of MCHO to TCHO is in contrast to that found in marine environments, where PCHO compounds are the major fraction of TCHO ( Pakulski and Benner, 1994, Hung et al., 2001 and Hung et al., 2003). For instance, Hung et al. (2003) reported that PCHO is about 3?4 times higher than MCHO in the Gulf of Mexico. This difference between riverine and marine systems is due to in situ production of high molecular weight PCHO compounds by phytoplankton or bacteria in pelagic systems, while in river systems, most carbohydrates as MCHO originate from decomposition products of soil litter and plant leaves that are leached into surface waters ( Hedges et al., 1994). The temporal variation in TCHO/DOC ratios was inversely related to water temperature, with maximum ratios (>30%) in winter time and low ratios (on average, 13%) in summer time (Fig. 2D). In addition, the temporal variation of URA/TCHO roughly paralleled that of water temperature, i.e., was lower (on average, 14%) in the winter and higher (on average, 26%) in the summer. In order to compare our data to that from other rivers and lakes, it is necessary to take into account geographic locations (mainly latitude and climate conditions). Table 3 lists relevant literature data on carbohydrates from rivers and lakes, indicating that the ratio of total carbohydrates to total organic matter ranges from 5% to 72% of DOC. Since different analytical methods for measuring total carbohydrates appear to give different results, one can only compare data acquired using similar methods. With that in mind, our data are in good agreement with those measured by spectrophotometric methods ( Buffle, 1990, Wilkinson et al., 1997, Paez-Osuna et al., 1998 and Gu?guen et al., 2004), but appear higher than data obtained using other methods ( Ding et al., 1999, Guo et al., 2003, Benner and Opsahl, 2001 and Bianchi et al., 2004). For example, TCHO concentrations, determined as the sum of individual identifiable monosaccharide compounds determined by HPLC-PAD or GC?MS methods appear to be significantly lower. The significantly higher values obtained by the spectrophotometric technique, when compared to chromatographic methods are, however, to be expected, since a large fraction of the carbohydrate-type structures in natural organic matter has not been characterized at the molecular level by current chromatographic methods ( Benner and Kaiser, 2003). In addition, humic substances (mainly humic and fulvic acids) also contain carbohydrate structures that are determined by the TPTZ method ( Buffle, 1990), but not yet adequately by chromatographic techniques. In fact, we have tested the reaction of humic matter for TPTZ method and the result is 8:10:100 for humic acid:fulvic acid:glucose in terms of carbon. It supports that humic matter also provides a part of the TPTZ chemical reaction. > > Table 3. Relative concentrations of bulk carbohydrates (TCHO), colloidal polysaccharides (CCHO, 1 kDa), total monosaccharides (MCHO) and uronic acids (URA), normalized to dissolved organic carbon (DOC), in dissolved and colloidal samples from fresh waters Location sample type TCHO (C %) CCHO (C %) MCHO (C %) URA (C %) Reference Williamson River, USA (D) 2 Sweet and Perdue (1982) Chena River, USA (C, D) 5.6 1.8 Guo et al. (2003) Mississippi River (C) 8.5 Guo et al. (2003) Amazon River (C) 4 Hedges et al. (1994) Yukon River, USA (D) 22?27 Gu?guen et al. (2004) Lake Bret, Switzerland (D) 14?24 Wilkinson et al. (1997) River (D) 6-24 Buffle (1990) Stream, USA (D) 6?8 Cheng and Kaplan (2001) Mississippi River (C) 1?4 Benner and Opsahl (2001) Trinity River, USA (C, D) 17 15 2 Hung et al. (2001) Mississippi River, USA (C) 6-8 Bianchi et al. (2004) Santa Ana River, USA (D) 5?13 Ding et al. (1999) Delaware River, USA (C ) 15 Repeta et al. (2002) Mississippi River, USA (C ) 9 Repeta et al. (2002) Lake Superior, USA (C ) 30 Repeta et al. (2002) Culiacan River, Mexico (D) 17 Paez-Osuna et al. (1998) Natural waters, UK (D) 5?31 Boult et al. (2001) Trinity River, USA (C) 9?36 ? 8?31 1?5 This study Full-size table Abbreviation: D: dissolved, C: Colloid (>1 kDa), total monosaccharides (MCHO): the summation of 5?7 monosaccharides, glucose, galactose, rhamnose, fucose, arabinose, xylose, and mannose. > View Within Article > URA concentrations in the Trinity River also showed large variations, ranging from 5.2 to 25.7 ?M C, without any marked seasonal variation in absolute concentrations ( Table 3). However, relative amounts, as a percentage of TCHO, were strongly influenced by temperature. The average concentration of URA in the Trinity River was two to three times higher than in Galveston Bay ( Hung et al., 2001), which receives its water mainly from the Trinity River. For example, these authors reported URA concentrations in Galveston Bay that ranged from 1.0 to 8.3 ?M C. However, it is likely that some of the URA in the Trinity River were contained in humic acids, as glucuronic acids have been documented as parts of humic acids ( Buffle, 1990). The URA/TCHO ratios in the Trinity River range from 0.1 to 0.3 and URA/DOC ratios from 0.01 to 0.05. Because data of URA and total acid polysaccharide (APS) concentrations in aquatic systems are scarce, it is difficult to directly compare our data with literature data. Buffle (1990) reported that URA made up 0.01?0.05 of soil organic matter and Bergamaschi et al. (1999) reported that uronic acids normalized to organic carbon in sinking and sedimentary particles ranged from 0.01 to 0.1. Recently, Aluwihare et al. (2002) reported that URA, mainly glucuronic and galacturonic acids, accounted for less than 2% of OC in the high molecular weight fraction. This comparison demonstrates, however, that our values of URA fall within the range of previously reported data. 3.3. Effect of biological activity on CHO and URA concentrations The majority of riverine DOC compounds have been shown to be easily degradable by microorganisms ( Benner and Opsahl, 2001, Hedges et al., 1997 and Raymond and Bauer, 2001). Microbial activity increases with increasing water temperature, preferentially utilizing specific and more labile DOC compounds, e.g., structural carbohydrates ( Wil?n et al., 2000). Sweet and Perdue (1982) observed during a short-term investigation (5 months) that dissolved polysaccharide concentrations in rivers and lakes of Oregon appeared to decrease from winter to spring. They attributed this decrease to microbial activity. Findlay et al. (1991) reported that bacterial abundances and production were significantly correlated with temperature in the Hudson River with higher bacterial abundances and production in summer. Leff and Meyer (1991) measured the bioavailability of DOC along the Ogechee River, Georgia, and the results showed that bioavailability of DOC changes temporally, resulting in lower concentrations at high discharge (March) and higher values at low discharge (January). These authors concluded that the causes for these changes were related to the composition and physiological state of the bacterial assemblage, as well as the nature of the DOC. They also pointed out that both organic matter and bacteria are also washed into the river from the floodplain during high discharge rates but many of these bacterial cells might be inactive. We did not measure bacterial production and bacterial biomass during this investigation, but based on previous research, we postulate that the higher temperatures resulted in higher bacterial activity and abundance. Indeed, the negative linear relationship between in situ water temperature and the TCHO/DOC ratios, which coincides with that between O2 and nutrients, suggests selective biodegradation of more labile organic carbon compounds (i.e., carbohydrates) at elevated temperatures (Fig. 4A) that also coincide with increased oxygen consumption and nutrient uptake. The most important known compounds of DOC in freshwaters, humic acids also contain a significant fraction of carbohydrates (e.g., Buffle, 1990; and references therein). Despite the documented degradability of the carbohydrate fraction of DOC, DOC concentrations did not correlate with temperature. The cause is unlikely related to the small temperature difference between the region where production and degradation processes might be most active, i.e., Lake Livingston, and 80 miles (130 km) downstream where it was recorded, as climatic differences are very small (www.weather.com/weather/climatology/monthly). > > Full-size image (8K) Fig. 4.?The relationship between (A) water temperature and TCHO/DOC, (B) water temperature and URA/TCHO. > View Within Article > Carbohydrate concentrations are a function of the rates of production and degradation processes. TCHO compounds in the Trinity River, like in most rivers, have several sources: soil erosion of humic substances and in situ production, especially in reservoir lakes such as Lake Livingston, as well as point source discharges from waste water treatment plants. While soil erosion is most active at high discharge rates, treatment plant discharges are independent of discharge rates and temperature making this a relatively constant source. Our results suggest that carbohydrate concentrations decrease in response to temperature-dependent uptake and degradation reactions by bacteria and photochemical processes, leaving more refractory compounds behind. Recent work by Repeta et al. (2002) has suggested that organic carbon in freshwaters mostly consists of terrestrially derived humic substances and in situ microalgal production, with degradation resistant compounds being transferred into the ocean. However, one of the carbohydrate compound classes, URA, seems to be more resistant to degradation. This interplay between production and degradation, resulting in the formation of refractory URA compounds, is exemplified by the positive correlation between water temperature and URA/TCHO (but not URA/DOC) ratios in our data set, with a positive intercept (Fig. 4B). The positive intercept suggests that about 8???2% of TCHO consisted of pre-existing URA compounds. This either indicates that extra URA compounds are produced in situ at elevated temperatures, or that they are more refractory than more labile bulk TCHO compounds. While it is possible that bacterial activity, which increases with temperature ( Shiah and Ducklow, 1997), can produce certain uronic acids, such as mannuronic acid and glucuronic acid ( Kenne and Lindberg, 1983), the data would suggest biomass build-up at elevated temperatures being less important than increased degradation of bulk carbohydrates. This is supported by the significant negative correlation between TCHO/DOC and temperature. Thus, this positive correlation between URA/TCHO and temperature more likely indicates that URA compounds are more stable compounds than the neutral carbohydrates that make up the bulk of TCHO. Indeed, recent research has also shown that uronic acids exist in the water column, as well as in sediment trap material and in sediments ( Bergamaschi et al., 1999, Hung et al., 2001 and Hung et al., 2003). 3.4. Relationship between trace metals and carbohydrates It is well known that a large fraction of trace metals in aquatic environments may be complexed by natural organic ligands ( Donat et al., 1994, Tang et al., 2001 and Ndung?u et al., 2003). However, it is difficult to directly measure the type of organic ligands binding trace metals in natural waters. In watersheds, both metals and potential organic ligands can have similar sources: waste water treatment plants and soil erosion. Any correlation between organic ligands and individual trace metals (e.g., Cu, Pb, and Cd), and potential ligand compounds that are present in constant proportion to some major fractions, such as TCHO (Fig. 5A?C) suggests that these trace metals and organic ligands have similar sources, e.g., soil leaching or waste water treatment plant discharges. The significant correlation found during this study between URA and dissolved Cu (p?=?0.02) and Pb (p? > Full-size image (12K) Fig. 5.?The relationship between [TCHO] vs. (A) Cu, (B) Pb and (C) Cd, respectively. > View Within Article > > > Full-size image (6K) Fig. 6.?The relationship between [URA] vs. (A) Cu and (B) Pb, respectively. > View Within Article > 4. Conclusions A seasonal investigation of carbohydrate species and related chemical parameters at one station in the lower reaches of the Trinity River shows that biological activity and photo-chemical reactions may significantly affect the production and consumption of organic matter in freshwater systems, especially in rivers with reservoir lakes. The significant and negative correlation between TCHO/DOC and temperature suggests that carbohydrate compounds are more easily utilized by bacteria or decomposed by photo-chemical reactions than bulk DOC. Conversely, the positive correlation between URA/TCHO and temperature indicates that uronic acids (URA), which are generated by microbial activities, are more resistant to degradation than bulk carbohydrates. More research is needed to test the relative degradability of individual acid polysaccharides, such as mannuronic acid, glucuronic acid, and galacturonic acid, etc., as compared to labile sugars. 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Buffle, Different roles of pedogenic fulvic acids and aquagenic biopolymers on colloid aggregation in freshwaters, Limnology and Oceanography 42 (1997), pp. 1714?1724. Corresponding author. Tel.: +409 740 4772; fax: +1 409 740 4786 1?Present address: Lancaster University, Department of Environmental Science, Institute of Environmental and Natural Science (IENS), Lancaster, LA1-4YQ, UK. Tel.: +44 (0)1524 510212; fax: +44 (0)1524 593985. Organic Geochemistry Volume 36, Issue 3, March 2005, Pages 463-474 ? Home Browse Search - selected My Settings Alerts Help About ScienceDirect ?|? Contact Us ?|? Information for Advertisers ?|? Terms & Conditions ?|? Privacy Policy Copyright ? 2008 Elsevier B.V. All rights reserved. ScienceDirect? is a registered trademark of Elsevier B.V.