Dissolved Organic Matter Dynamics in Natural and Human-Modified Watersheds I Posters
Presiding: W H McDowell, University of New Hampshire; B A Pellerin, U.S. Geological Survey
B33A-01 1330h
Driving Forces behind Organic Matter and Nutrient Dynamics in a Mangrove Forest Ecosystem in South India
Organic matter is primary carbon source and energy for micro and macro fauna inhabiting in the mangroves, either derived from autochthonous or allochthonous sources. Species composition and sorption capacity of the sediment may alter the organic matter distribution in the mangrove forests. Salinity may also have some impact over the organic matter composition. To understand the organic matter dynamics in the mangrove forest, we conducted a survey on the Pichavaram mangroves lying on the southeast coast of India. We have observed a wide variation in the concentrations of nutrients in the mangrove water in time and space scale. An annual concentration of DOC is 4.19 mg L-1, POC 2.97 mg L-1, DON 3.23 mg L-1 and DOP 0.35 mg L-1. Nutrient dynamics in the mangrove water is significantly influenced by seasonal effects and internal microbial mechanisms. Among the plant species Rhizophora mucronata, R. apiculata and Avicennia marina are the dominant and contributing around 43.41%, 39.55% and 18.13% litter per year respectively. Benthic microbial mineralization of organic matter and total carbon oxidation were studied and found that in Avicennia zone was higher than Rhizophora zone. This was further supported by sulfate reduction. The relationship between salinity and nutrients were analyzed by plot of nutrients versus salinity for different seasons. It has been observed that the net gain of DIN (1.14% m-1) was more than (0.84% m-1), which suggests that conversion of inorganic to organic form was minimal in premonsoon. And the same trend was also observed in monsoon. But the reverse trend was observed in post monsoon (1.5% m-1) and summer (0.65% m-1). Mean C:N ratio increased from 13.6 to 30.2 reflecting the relatively losses of N from the mangrove ecosystem. This is supported by N:Si ratio reduced from 2.49 to 0.33, this may be attributed to relative contribution of diatoms production. Interchanges between nutrient pools were apparent throughout the system. Sediment, and even surface-water, concentration of nutrients seemed to respond to plant root zone oxidation and uptake and release of nutrients. Pore water biogeochemical processes were linked to surface-water nutrient dynamics as well. Based on these findings, tidal effects, pore water concentrations, seasonal variation and microbial transformations were identified as driving forces behind coastal outwelling of nutrients and organic matter from mangroves.
B33A-02 1330h
DOC, Color and Disinfection By-Product Precursor Dynamics along an Urbanization Gradient, Croton Water Supply System, New York, USA
Hydrologic processes in suburban watersheds and their effects on water quality warrant investigation. Biweekly and storm samples were collected and analyzed for base cations, selected anions, and DOC over a one-year period at the outlet of three small (37 - 55 ha) watersheds (one forested, two with different degrees of suburban development) in the Croton Watershed, southeastern New York. Less frequent sampling for Pt/Co color and disinfection by-product precursors (DBPs) were also conducted. Median baseflow concentrations (>3 days since rainfall) of DOC were similar, ranging from 2.1 to 1.8 to 1.7 mg L -1 for the most urbanized to the forested watershed, respectively. On a unit area load basis (kg ha-1 yr-1), the range was from 8.9 to 6.4 to 5.1, again from most urbanized to forested watershed. All three watersheds showed similar storm responses, with evidence for a flushing mechanism in that DOC concentration increased with increasing discharge. Pt/Co color and DBPs (determined as both total trihalomethane and total haloacetic acid formation potentials) showed similar storm behavior, although the range of response was greater than observed for DOC, suggesting a labile DOC fraction was mobilized during storm events. The more urbanized watersheds tended to favor brominated over chlorinated forms of DBPs; the reasons for this are unclear.
B33A-03 1330h
The Contribution of Labile Organic Matter in Groundwater to Carbon Sources Fueling CO2 Evasion From River Surfaces
Labile dissolved organic matter (DOM) transported from land to river channels via groundwater may be an important source of carbon fueling CO2 evasion from river surfaces in the Amazon basin. The importance of DOM transported to rivers via groundwater will vary with hydrologic regime. We measured metabolism, DOM size fractions, pCO2 and dissolved O2 in various flow paths at two locations with contrasting hydrologic regimes in the Amazon basin. In Oxisol soils located north of Manaus, hydraulic conductivity is constant with depth and vertical infiltration of rainfall dominates during storm events. At our Ultisol-dominated site, stream flow is more event-dependent due to decreasing hydraulic conductivity with depth and subsequently more lateral surface flow during rainfall events. At this site, we found high in-stream respiration rates with a sharp decrease to one-fourth of the initial rate during the first thirty minutes of stream flow-generating precipitation events. A second peak in respiration rate occurred after about one hour. The two peaks suggest that two different pools of labile DOM are flushed into the river and respired to CO2 during storms by time-dependent, surface flow paths. In contrast, stream flow in Oxisol-dominated regions is less event-dependent due to more infiltration of rain water. In these regions, labile DOM in groundwater may be a larger part of the carbon pool contributing to CO2 evasion from river surfaces.
B33A-04 1330h
Stable Isotopic Tracking of Autocthonous Carbon in Two Contrasting Ozark Streams
The central role of microbes in biogeochemical processes makes the identification of carbon (C) sources fueling microorganisms critical to our understanding of stream ecosystems. The Δ13C of biofilm phospholipid fatty acids (Δ13CBPLFA) were determined in experiments conducted from July 2002 through July 2003 using 13C-labeled bicarbonate to track autochthonous C in two streams. In Moore Creek (MC), an agricultural stream, and Huey Hollow (HH), a forested stream, dissolved organic carbon (DOC) was released in light incubations during all seasons and represented >10% biofilm net primary production. The DOC from light incubations was enriched in 13C relative to DOC from dark incubations suggesting algal exudates were a major source of the DOC. The Δ13CBPLFA suggest that 13C enriched exudates were not utilized by heterotrophic bacterial components in MC. Autotrophic PLFA from light incubations were more enriched in 13C while heterotrophic bacterial Δ13CBPLFA were similar between light and dark incubations. By contrast, both heterotrophic and autotrophic biomarkers were significantly enriched in 13C in light incubations relative to dark incubations conducted in spring and summer in HH. Results suggest the exchange of C between autotrophic and heterotrophic components of biofilm communities differs between nutrient-enriched and depleted streams.
B33A-05 1330h
A National Survey of TOC Trends in Relation to Watershed Characteristics and DBP Formation Potential
All drinking water supplies contain some background organic matter. Usually these organics are naturally-occurring plant product or their derivatives. In the early 1970s NOM became a focus of concern as its central role in the formation of potentially carcinogenic disinfection byproducts (DBPs) was recognized. Different watershed are known to result in waters with different levels of NOM, however the factors that lead to these differences are not understood. It's now clear that more attention must be paid to the upstream processes that give rise to NOM in raw waters. The total organic carbon (TOC) is one of the most widely used measures for quantifying the amount of NOM in water. Impacts of man made changes in the watershed effect NOM quantity and quality. To understand what watershed characteristics most affect NOM quantity and quality, and therefore the threat of increased DBPs, we are seeking out long term, broad range data on TOC concentrations. This project has initiated the development of a comprehensive database on TOC in raw waters. TOC data has been collected and analyzed from existing database sources (STORET, USGS stations) in order to represent large-scale trends across ecoregions and land use types. TOC and DBP data has been collected from participating water treatment plants, spread across North America, to analyze the observed TOC trends against the water quality management of the water plants. Results are presented first as visual spatial and temporal trends of existing TOC values across the nation, second as a correlation of land cover types to shown TOC values, and third as potential correlation to TOC values observed at participating water treatment facilities and its relation to DBPs. Select results will be presented.
B33A-06 1330h
Navigating the NMR Maze: The Application of NMR to the Study of Natural Organic Matter.
Nuclear magnetic resonance (NMR) is one of the most powerful tools to study natural organic matter (NOM). There is a plethora of NMR methods that can be, and have been, applied to NOM. However, the vastness of the array of available NMR techniques can lead to confusion among non-experts even though the information provided by NMR is unique and highly applicable to geochemical and biogeochemical process. The work presented here will show the information available from a series of different NMR techniques including both solid and liquid state on samples ranging from NOM fractions to whole soils. This discussion will focus on how to obtain desired information in the shortest time and simplest manner. Finally, how NMR information can be used to study geochemical and biogeochemical processes will be discussed.