Master of Science / Division of Biology / Walter K. Dodds / Contrary to the previous notion that a stream acts primarily as the transporter of materials from land to oceans, research has shown that in-stream processing of organic matter and nutrients is significant and relevant at a global scale. Dissolved organic carbon (DOC) is the most abundant form of organic carbon in streams and has been demonstrated as an important source of energy supporting stream food webs. Understanding the dynamics of DOC in streams is, therefore, important in determining the contribution of flowing waters to global carbon storage and release. However, DOC exists as many different compounds, varying in source, composition, and quality. The composition of DOC that ends up in streams is partly controlled by the surrounding watershed, and landscape effects on DOC quality and quantity in streams have been observed. In the North American Tallgrass prairie, woody encroachment has led to changes in riparian vegetation, potentially altering the DOC received by the stream, and making it important to understand rates of DOC transformation as landscape alterations continue. The heterogeneity of the DOC pool makes it difficult to fully describe its components and to measure transformation rates. DOC uptake, or biological use, has been estimated through several methods including in-stream additions of various DOC sources and bottle incubations of stream water and sediments. One problem with addition methods for calculating uptake is that the DOC pool is difficult to replicate and additions of simple compounds or organic leachates do not represent total dissolved organic carbon (TDOC) dynamics. Another potential issue is that additions of a labile compound could potentially alter microbial activity through a priming effect and therefore distort ambient DOC uptake estimates. Finally, uptake parameters are mostly calculated assuming benthic uptake while recent studies have shown that planktonic uptake of DOC can also be significant. We conducted this study with these three considerations in mind. In the first chapter, we describe our use of in situ additions of glucose and bur oak leaf leachate in prairie stream reaches and concentrations of specific components to determine uptake dynamics of various specific DOC components, from a simple sugar to more complex plant compounds. We calculated uptake parameters of glucose and two different oak leaf components. We found that using glucose concentrations rather than TDOC concentrations, as has been done in previous studies, to measure uptake parameters resulted in higher uptake rates, indicating the importance of measuring the specific component added. Through leaf leachate additions, we found that an amino acid like component was consistently taken up faster than a humic-like component. The second chapter addresses the questions of uptake location and priming through a series of recirculating chamber incubations. We found that benthic uptake of leaf leachate was more important than that in the water column. Finally, elevated uptake of one leaf leachate component in the presence of glucose indicated a priming effect on microbial DOC uptake.

The Bryan/College Station (B/CS) region has been reported to have elevated concentrations of dissolved organic carbon (DOC) in surface water. Increased DOC concentrations are worrisome as DOC has been shown to be an energy source for the recovery and regrowth of E. coli and many watersheds are impaired by high bacteria levels. To examine the sources and fates of DOC in rural and urban regions to better understand DOC movement though the environment, seven watersheds were studied. To investigate source, streams were analyzed using diffuse reflectance near infrared spectroscopy (DR-NIR) and carbon isotopes. Fate of DOC was determined through monthly streams samples, gathered between March 2011 and February 2012, which were incubated for biodegradable DOC (BDOC). Soil in the region was sampled based on land use categories. Soil was analyzed for DOC and BDOC as well as DOC adsorption, the other major fate of DOC. Above ground vegetation was sampled in conjunction with soil and analyzed for BDOC. Data indicated that fecal matter from cliff swallows provided considerable organic material to streams in the B/CS region as shown through DR-NIR. Carbon isotope values in streams ranged from -23.5 +/- 0.7% to -26.8 +/- 0.5%. Stream spectra may be able to predict carbon isotope values in streams (Adj. R2 = 0.88). Mean annual stream DOC concentrations ranged from 11 +/- 3 mg/L to 31 +/- 12 mg/L, which represents a significant decrease in DOC between 2007 and 2011. Concurrent increases in pH and conductivity were also recorded. The decrease in DOC and the increases in pH and conductivity may be due to impacts of high sodium irrigation tap water. Biodegradable DOC was low in streams, which is likely due to DOC being present in streams in refractory forms that are resistant to microbial breakdown. Soil chemistry, including soil adsorption, was greatly influenced by sodium. The elevated adsorption coefficients and release values seen in highly developed and urban open areas can be attributed to frequent exposure to high sodium irrigation water. The results indicate that sodium is a major driver of DOC in the system. Sound management decisions concerning irrigation water chemistry and urban development might eventually emerge to protect water quality as a result of this research.

Northern peatlands represent a significant carbon reservoir, containing approximately a third of the terrestrial carbon pool. The stability of these carbon stores is poorly understood, and processes of accumulation and degradation appear to be finely balanced. Over the last decade, it has become increasingly clear that losses of dissolved organic carbon (DOC) from peatlands can be of considerable size and this flux appears to have increased substantially over the last 20 years. Despite its significance, the chemical composition of peatland-derived DOC remains poorly understood. This study aimed to characterise dissolved organic matter (DOM) at the molecular level using a novel combination of techniques. The study site (Cors Fochno, Wales, UK) is an ombrotrophic bog on which a number of studies into carbon cycling and hydrology have been carried out, providing a useful context for this project. The size and compositions of the DOC pool was monitored over 18 months, from three banks of piezometers, sampling from depths of 15 cm to 6 m. DOM which is representative of bog runoff was also monitored. DOC concentrations varied considerably between locations, spanning an order of magnitude (11.4 to 114 mgC l-1). Several relationships between DOC concentration and environmental and physical factors were established: DOC levels near the surface of the peatland varied with temperature, those in the runoff were most affected by recent rainfall events and the apparent DOC concentration at depth was related to the hydraulic conductivity of peat at that depth. The annual flux of DOC from the site was estimated at 113 tonnes, or 17.4 gC m-2. Only a small portion of the DOC pool could be characterised by analysis of dissolved combined amino acids (DCAA) and dissolved carbohydrates (as neutral sugars). Non-protein amino acids were most abundant in runoff samples, suggesting microbial reworking of DOM on entering drainage systems. DCAA yields decreased with depth, and the DCAA pool in deeper peat layers was characterised by more hydrophobic compounds. Interpretation of semi-quantitative results from TMAH thermochemolysis GC-MS analysis suggested oxidative degradation of organic matter near the surface of the peatland and photochemical degradation where DOM entered drainage networks, and this was supported by novel interpretation of results from ultrahigh resolution mass spectrometry analysis. The deepest porewaters were dominated by nalkanes, with notable contributions from fatty acids, suggesting a plant wax source for this DOM. The highest DOC concentrations were found at intermediate depth from a site midway between the centre of the bog and the southern boundary where hydraulic conductivities were low, and DOM from these piezometers were characterised by high contributions from a suite of phenolic compounds (with mainly para-hydroxyphenyl structures). These compounds have been linked to Sphagnum species, and are known to be functionally important to the development and maintenance of the unusual chemical environment in peatlands which slows decay rates, reduces microbial activity, and allows the sequestration of the large carbon reservoir. The findings of this study highlight the dynamic nature of peatland derived DOM, both in the size of the carbon pool and its composition which change dramatically with both season and depth.

The effects of predicted future climate change was investigated with special emphasis on the association of organic contaminants with dissolved organic carbon (DOC) in the Baltic Sea. An automated method was developed for the measurements of DOC - water distribution constants at realistic DOC concentrations in brackish water. The method proved to be valid for 30 organic contaminants with different structural elements in the 5 – 100 mg car bon/L DOC concentration range. There were limitations of this method. Firstly, its applicability is limited towards contaminants with lower affinity to DOC. Secondly, at higher (>100 mg carbon/L) DOC concentrations the sorption of contaminants was underest imated. Afterwards, water samples were collected from 15 points within the Baltic Sea in a north - south gradient t o examine the spatial differences in DOC characteristics and sorption properties . The DOC samples were analyzed using proton nuclear magnetic resonance and ultraviolet spectroscopy. Results from both techniques indicated that the aromatic nature of the DOC pool increased towards the northern Baltic Sea. This was expected as the freshwater inflow has high significance in controlling the hydrograp hic conditions in the Bothnian Bay. Sorption of organic contaminants was subsequently measured in the same samples. The results showed decreased sorption from north to south for hydrophobic contaminants such as chlorinated benzenes but for contaminants lik e tributyl - phosphate no spatial tendencies were observed. The data generated was used to determine molecular descriptors of DOC using linear free energy relationships. The results indicated a higher significance of hy drogen bond donor/acceptor functional g roups of the DOC in the south. Changes in contaminant distribution were simulated in model pelagic ecosystems at possible endpoints predicted by future climate change scenarios. Separate and combined effects of temperature a nd DOC were studied in mesocosms. The results indicated interesting tendencies. Increased temperature resulted in increased losses in the amounts of organic contaminants. Increased DOC levels promoted sedimentation and sorption of contaminants to particulate matter and biota. Hi gher amounts of contaminants were retained. The combined effects of the two factors led to and overall decrease in dissolved amounts. Higher losses or increased sedimentation and sorption to particles were also observed depending on contaminant properties. / EcoChange

Lakes play an important role in the global carbon (C) cycle as they process carbon from terrestrial (allochthonous) and within lake (autochthonous) sources and may store C over long periods of time. Some arctic lakes contain high concentrations of dissolved organic carbon (DOC) that does not absorb light and thus remains colourless. The origin of this DOC remains unknown, but the sediment of these lakes have been suggested to accumulate primarily autochthonous (algal) C. I developed an experimental chamber for hydrogen (H) isotope pre-treatments and applied a novel H isotope tracing approach to determine the origin of the DOC and sediment C of a lake on SW Greenland known to contain colourless DOC. I hypothesized that autochthonous C was the prime source of DOC and sediment C, in line with previous theories. Analyses of algae and soil samples from the catchment revealed that local allochthonous and autochthonous C sources had a δ2H composition of -139 ‰ and -209 ‰, respectively. In contrast to my hypothesis, the analysed DOC had a mean δ2H isotopic composition of -147 ‰ indicating a dominance (ca 80-90 %) of allochthonous C. Similarly, the sediment had a mean δ2H isotopic composition of -155 ‰, suggesting that about 84 % of the C accumulating in the sediment was derived from terrestrial sources. The terrestrial origin was supported by field observations of high DOC seepage water (up to 70 mg L-1) with uncharacteristically low light absorption values entering the lake during high precipitation events. My results indicate that terrestrial processes are fundamental C sources for arctic lakes, even in regions with very low precipitation.

Dissolved organic carbon (DOC) is one of the largest pools of carbon in the ocean, and is of the same size as the carbon dioxide in the atmosphere. Estuaries connecting the land and the ocean are one of the most important DOC sources to the ocean, and play an important role in the global carbon cycle. Because of their complex chemical, physical, geological and biological properties, estuaries have become rich ecological environment. In this study, we investigated the seasonal distributions of DOC in the Taiwan Strait (TS) and Taiwanese rivers, aiming to understand the distributions and variations of DOC in different seasons. The results show that DOC concentrations are generally the highest in the upper estuary, and then decrease downstream due to mixing with the low DOC seawater. The process of river flow constantly accumulates terrestrial material, and the DOC shows positive correlations with Chl. a, CH4 and BOD (Biochemical Oxygen Demand), suggesting that biological activities and pollutions could be sources of DOC in the estuary. The DOC concentrations (salinity<1) varied in dry (Nov.-Apr.) and wet (May-Oct.) seasons with ranges of 42-1185 £gM (mean=245¡Ó254£gM; n=32) and 18-565 £gM (mean=183¡Ó151£gM; n=24), respectively. The total DOC flux of 25 rivers is 87.8 Gg C/yr, which can be translated to the fluxes of all rivers in Taiwan to be 101.9 Gg C/yr. The amount of DOC flux in Taiwan is only about 0.07% of the tropical area, but the per unit area flux (3.92 gC /m2 /yr) is almost twice those of the tropical rivers (2.13 gC /m2 /yr). In Taiwan, the population density and land use are higher than the world average. Consequently, the impacts of the environment by human activities reveal the utmost export of DOC, and need further investigation. Next, in the TS, the DOC shows significant negative correlations with Sigma-T, and the distributions of DOC are mainly controlled by physical mixing in both winter and summer. In the western TS, DOC concentration is relatively high, compared to the eastern part, and is because of low temperature and salinity, but high DOC coastal China current flowing from north to south. DOC concentration decreases with increasing depth owing to the intrusion at depth by the Kuroshio, which contains relatively low DOC. In winter, the import of coastal China current brings more nutrients from north to south, and supports the growth of bacteria which depletes the DOC and oxygen. As the result, DOC decomposition rate is higher in winter than in summer. The TS¡¦s DOC fluxes in summer (northern TS: 3.85¡Ñ1012mol C/yr¡Fsouthern TS: 3.75¡Ñ1012mol C/yr) are higher than in winter (northern TS: 3.69¡Ñ1012mol C/yr¡Fsouthern TS: 2.84¡Ñ1012mol C/yr). Main differences are due to the prevailing southwest monsoon winds in summer transporting more water from the South China Sea to the TS, and the river discharge brings more terrigenous organic matters into the TS. Therefore, the DOC export in summer is higher than in winter.

The drinking water treated by water treatment plant (WTP) usually has an excess of assimilable organic carbon (AOC) in distribution systems in south Taiwan. They will cause the growth of heterotrophic plate count (HPC) and deterioration of water quality in pipeline of distribution systems. Recently, part of traditional purification processes were changed into advanced processes in WTP. The past researches showed the combined advanced processes ultrafitration (UF) / reverse osmosis (RO) in south WTP in Taiwan has the removal problems of AOC in above UF / RO processes because the organic compounds in raw water caused a fouling layer which was formed on the membranes surface. These problems made the back-wash frequency increasing, short membrane life and raising cost. The study combines activated carbon and membrane bioreactor (MBR) to explore the removal efficiency of drinking water in laboratory. The system showed the removal efficiencies of dissolved organic carbon (DOC) and AOC were 57% and 36%, respectively in average. More, the system showed the removal efficiencies of DOC and AOC were 81% and 66%. The results of this research showed good removal efficiency was found in AOC and DOC. Good quality of biological stability, removal of organic compounds, low cost in building and maintaining were reached.

The aim of this study was to investigate the importance of winter season for the production of carbon dioxide (CO2) and methane (CH4) in humic and clear-water boreal aquatic systems. The study was conducted in 16 experimental ponds in northern Sweden during the winter of 2013. Half of the ponds had a higher concentration of dissolved organic carbon (DOC). CO2, CH4, DOC and dissolved inorganic carbon (DIC) were measured repeatedly under the ice from January to April. The results show that CO2 was accumulated continually during winter. No difference in winter accumulation were found between humic and clear ponds. CH4 was rarely accumulated in neither humic nor clear ponds, and was not an important part of the gas flux at spring ice melt. At ice melt, the flux from humic ponds accounted for 1.6 g C m-2 and 1.7 g C m-2 from clear ponds, which was equivalent for 15.6% respective 100% of the annual gas emissions. On a whole-year basis humic ponds acted as a source of 10.3 g C m-2, while clear ponds acted as a sink of 14.7 g C m-2. 76 mg m-2 d-1 DOC was consumed in humic and 59 mg m-2 d-1 DOC in clear ponds while the DIC accumulation was 125 mg m-2 d-1 in humic and 118 mg m-2 d-1 in clear ponds. This study stresses the importance of ice-covered boreal aquatic systems as a significant parts of the global carbon cycling.

Dissolved Organic Carbon accounts for many different functions in the boreal forest ecosystem. It is the main vehicle for organic carbon transport from the litterfall to the forest soil profile and together with water drainage it can be transported to streams. In boreal forests, the DOC transport have gain attention because of recently documented rise in concentration. Several models have been proposed, first to gain understanding in the main cauces of this increase in concentration, and then to simulate the transport of DOC in the landscape. An exploratory work was made to identify the extent of physical control and hydrological pathways for DOC discharge and the long-term biological control over DOC production, transport in the soil profile and discharge in 2 different situations. A 22-year dataset from the Krycklan Catchment site was used. Meteorological data was used as driving variables to calibrate DOC concentration and runoff in a small catchment (Site C7). The CoupModel was set up to represent the described vegetation and documented soil characterization and then calibrated to fit the measured variables. A stepwise calibration process was preferred to promote the understanding of the different components of the landscape in the organic carbon cycle. Results point to soil heat and water transfer processes as the most relevant group to explain both water runnof and DOC discharge, with increasing relevance in the deeper layers, explaining up to 97% of short-term variability in DOC discharge for the 27-35 cm layer. Soil organic carbon pools showed to have relevance in organic carbon stock balance along the soil profile. Conclusions state that, In concordance with other authors, there is a hydrological primary control over DOC discharge, but that soil organics and especially vegetation perform a relevant role in long-term balance of the organic carbon cycle. Further studies with this model could include time-series of atmospheric deposition of Sulphur and nitrogen and running the model in cascade.

Allochthonous organic carbon is increasing and leading to browning of freshwaters in the northern hemisphere. It is already known that an increase in allochthonous dissolved organic carbon (DOC) affects benthic primary production and respiration negatively via light limitation, however, little is known about the impact on benthic bacteria. This report aims at examining how DOC and other environmental variables affect the production and growth of benthic bacteria. This was done by analyzing data from 18 lakes in northern Sweden with different DOC concentrations. This analysis was divided into two datasets: one including data at the whole lake scale and the other including data over depth within the lakes. The result showed that DOC, average depth, and the light extinction coefficient all had a negative impact on bacterial production on a whole lake scale. The light extinction coefficient was also affecting the whole lake bacterial growth efficiency (BGE) negatively. Over depth within the lakes a higher light input increased the bacterial production. In the same dataset, light was also affecting the BGE positively, while temperature had a negative effect. The results can thus be linked to the increase in allochthonous carbon and brownification. Because allochthonous DOC have a negative effect on benthic primary production, there will be less autochthonous DOC available for benthic bacteria. Allochthonous DOC is considered less degradable than autochthonous DOC. The increase in allochthonous DOC therefore has a negative impact on benthic bacterial production, likely connected to a decrease in production of autochthonous DOC by benthic algae.