Louis A Kaplan

Stroud Water Research Center · Biogeochemistry

A mechanistic understanding of factors that structure spatiotemporal community composition is a major challenge in microbial ecology. Our study of microbial communities in the headwaters of three freshwater stream networks showed significant community changes at the small spatial scale of benthic habitats when compared to changes at mid- and large-...

Respiration of dissolved organic matter (DOM) in streams contributes to the global CO2 efflux, yet this efflux has not been linked to specific DOM sources and their respective uptake rates. Further, removal of DOM inferred from longitudinal concentration gradients in river networks has been insufficient to account for observed CO2 outgassing. We hy...

NMR spectroscopy is widely used in the field of aquatic biogeochemistry to examine the chemical structure of dissolved organic matter (DOM). Most aquatic DOM analyzed by proton NMR (1H NMR) is concentrated mainly by freeze‐drying prior to analysis to combat low concentrations, frequently <100 μM C, and eliminate interference from water. This study...

Exposure of dissolved organic matter (DOM) to sunlight can increase or decrease the fraction that is biodegradable (BDOM), but conceptual models fail to explain this dichotomy. We investigated the effect of sunlight exposure on BDOM, addressing three knowledge gaps: (1) how fractions of DOM overlap in their susceptibility to degradation by sunlight...

Dissolved organic carbon concentrations from White Clay Creek

Abstract Minerals constitute a primary ecosystem control on organic C decomposition in soils, and therefore on greenhouse gas fluxes to the atmosphere. Secondary minerals, in particular, Fe and Al (oxyhydr)oxides—collectively referred to as “oxides” hereafter—are prominent protectors of organic C against microbial decomposition through sorption and...

Dissolved organic matter (DOM) constitutes the largest pool of organic matter in aquatic ecosystems and DOM cycling in inland waters influences the global carbon cycle. This chapter presents our current understanding of DOM in lotic ecosystems, with an emphasis on reactivity to microbial and photochemical oxidation. We review the sources and the hy...

The quantity and chemical composition of dissolved organic matter (DOM) in surface waters influence ecosystem processes and anthropogenic use of freshwater. However, despite the importance of understanding spatial and temporal patterns in DOM, measures of DOM quality are not routinely included as part of large scale ecosystem monitoring programs an...

Dissolved organic matter (DOM) constitutes the largest pool of organic matter in aquatic ecosystems and DOM cycling in inland waters influences the global carbon cycle. This chapter presents our current understanding of DOM in lotic ecosystems with an emphasis on reactivity to microbial and photochemical oxidation. We review sources and the hydrolo...

The quantity and chemical composition of dissolved organic matter (DOM) in surface waters influence ecosystem processes and anthropogenic use of freshwater. However, despite the importance of understanding spatial and temporal patterns in DOM, measures of DOM quality are not routinely included as part of large-scale ecosystem monitoring programs an...

AME prepress abstract - doi: 10.3354/ame01761 Consumption of terrestrial dissolved organic carbon by stream microorganisms Tracy N. Wiegner*, Louis A. Kaplan, Susan E. Ziegler, Robert H. Findlay *Email: wiegner@hawaii.edu ABSTRACT: Terrestrial dissolved organic carbon (DOC) is the largest organic C pool in lotic systems; yet, its role in supporti...

We tested a long-standing hypothesis within river ecology, predicted by the River Continuum Concept, that dissolved organic matter (DOM) diversity decreases with stream order. We measured DOM molecular composition across three stream orders in the headwaters of well characterized forested catchments with ultrahigh-resolution mass spectrometry to as...

We tested a long-standing hypothesis within river ecology, predicted by the River Continuum Concept, that dissolved organic matter (DOM) diversity decreases with stream order. We measured DOM molecular composition across three stream orders in the headwaters of well characterized forested catchments with ultrahigh-resolution mass spectrometry to as...

The bio-reactivity or susceptibility of dissolved organic matter (DOM) to microbial degradation in streams and rivers is of critical importance to global change studies, but a comprehensive understanding of DOM bio-reactivity has been elusive due, in part, to the stunningly diverse assemblages of organic molecules within DOM. We approach this probl...

Riparian soils, rich in organic carbon, act as a source of dissolved organic carbon (DOC) to the adjacent stream, but the hydrologic factors that control the delivery of DOC are not well characterized. A mechanistic two-dimensional, variably saturated flow and reactive transport finite element model (FEM) was developed to explore both biodegradable...

The priming effect refers to quantitative changes in microbial decomposition of recalcitrant organic matter upon addition of labile organic matter and is a phenomenon that mainly has been reported and debated in soil science. Recently, priming effects have been indicated in aquatic ecosystems and have received attention due to the potential signifi...

Storms dominate solute export budgets from catchments and drive hydrogeochemical changes in the near-stream environment. We captured near-stream hydrogeochemical dynamics during an intense storm (Hurricane Sandy, October 2012), by instrumenting a riparian-hyporheic zone transect of White Clay Creek in the Christina River Basin Critical Zone Observa...

Evapotranspiration (ET) plays a crucial role in catchment water budgets, typically accounting for more than 50% of annual precipitation falling within temperate deciduous forests. Groundwater ET is a portion of total ET that occurs where plant roots extend to the capillary fringe above the phreatic surface or induce upward movement of water from th...

Terrestrial sources of dissolved organic C (DOC) provide energy for stream microbial heterotrophs. Hydrologic conditions alter flow paths to the stream and influence terrestrial source quantity and quality. We used bioreactors to measure biodegradable DOC (BDOC) in water from soils, shallow wells, and spring seeps under baseflow conditions, overlan...

We studied the influence of spent mushroom substrate (SMS) land application on water resources. Four study sites, including mushroom farms with low or high density land applications of SMS, and two controls, an alfalfa field and a woodland, were instrumented with soilwater lysimeters and groundwater monitoring wells. Water samples were collected du...

Integrated carbon budgets of terrestrial and aquatic ecosystems indicate that particulate organic carbon (POC) plays an important role in the transport, storage, and turnover of carbon during its transit from land to sea. However, little is known about the rates at which POC in suspension is metabolized during downstream transport. We address this...

We investigated the biological lability of fluorescent dissolved organic matter (FDOM) from a temperate Piedmont stream. Plug-flow bioreactors, colonized and maintained with natural stream water, were used to determine the concentrations of stream-water biodegradable dissolved organic carbon (BDOC) and relative concentrations of FDOM within operati...

The downward flux of dissolved organic carbon (DOC) in the vadose zone was examined using "artificial rain" experiments on a soil lysimeter at the White Clay Creek watershed in southeastern Pennsylvania. Refractory DOC (RDOC) and labile biodegradable DOC (BDOC) were transported from the organic rich soil layer and eluted from the base of a soil lys...

Background/Question/Methods Many streams export large amounts of nitrate due to increases in anthropogenic loadings, and these nitrate fluxes can cause eutrophication and drinking water violations. Denitrification, a respiratory process in which heterotrophic microbes use nitrate as the electron acceptor and organic carbon as an electron donor, i...

A 34-year record of dissolved organic carbon (DOC) concentrations and compositions was used to assess the role of hydrologic variability in the carbon cycle of a headwater stream. The DOC concentration record is characterized by sharply increasing values during storms and annual minima associated with soil freezing in winter (Fig. 1). Baseflow disc...

Physically based, distributed models can provide much more detailed information about the mechanisms surrounding the fate and transport of dissolved organic carbon (DOC) than can lumped models. We present such a model of soil and stream water DOC. The Penn State Integrated Hydrological Model (PIHM) was adopted as the framework and coupled with a co...

Background/Question/Methods The quality of DOC is important to in-stream heterotrophic production, and the amount of biodegradable DOC (BDOC) regulates both microbial biomass as well as nutrient cycling. For example, carbon quality influences nitrogen transformations because heterotrophic denitrification requires a carbon source and autotrophic ni...

The microbial pesticide Bacillus thuringiensis var. israelensis (B.t.i.) was applied aerially to suppress larval black fly populations in the Susquehanna River, Pennsylvania. We quantified (1) the passage and retention of B.t.i. spores through a 1.5-km reach and (2) changes in black fly and nontarget macroinvertebrate abundances in the drift and be...

Dissolved organic carbon (DOC) dynamics were measured in a second-order stream located in a pasture in southeastern Pennsylvania. In situ measurements made at six stations in early summer showed a diel patern of net DOC release from the streambed communities with predawn minima and afternoon maxima. When an 18-m section of the stream was covered wi...

Aerobic cellulolytic bacteria were ranked according to ability to degrade cellulose azure and to clear cellulose agar. Cellulomonas uda NRRL B404 and Cellulomonas sp. NRC 2406 showed greater clearing of cellulose agar than other isolates, but differences in cellulose azure decomposition were not statistically significant. Isolates were tested for a...

Our research objectives were to (i) determine the persistence of an introduced surrogate (Cellulomonas sp. NRC 2406) for a genetically engineered microorganism in sediments, growths of Cladophora glomerata (Chlorophyta), and leaf packs, (ii) test community and ecosystem structural and functional responses to the introduced bacteria, and (iii) evalu...

Heterotrophic members of the biofilm community play a critical ecological role in lotic ecosystems. They take up, degrade, and mineralize organic carbon, often dominate community respiration, and are a critical link to higher trophic levels through the microbial loop. The goal of our study was to identify who within the stream biofilm community act...

The temporal variation of the delivery of dissolved organic carbon (DOC), a complex mixture of compounds, from hillslopes to the adjacent streams is determined by hydrological and biogeochemical processes that have not been completely quantified. In particular, processes involving differences in the fate and transport of the easily biodegradable fr...

Dissolved organic carbon (DOC) is an important constituent of soil solution that plays a role in many chemical and biological processes in soils; it is also an important energy source for bacteria in the soil ecosystem. Hydrology has a significant control on the transport and fate of dissolved organic carbon in the soil but mechanisms that affect s...

Metabolism of terrestrial organic carbon in freshwater ecosystems is responsible for a large amount of carbon dioxide outgassing to the atmosphere, in contradiction to the conventional wisdom that terrestrial organic carbon is recalcitrant and contributes little to the support of aquatic metabolism. Here, we combine recent findings from geophysics,...

The terrestrial biosphere is assumed to take up most of the carbon on land. However, it is becoming clear that inland waters process large amounts of organic carbon and must be considered in strategies to mitigate climate change.

We measured the baseflow concentration and composition of seston and suspended particulate organic carbon (POC) over a 1-yr period in White Clay Creek, a third-order stream in the southeastern Pennsylvania Piedmont, to assess temporal variability in seston concentration and quality at seasonal and diel timescales. Each month, we sampled stream wate...

A field study was conducted to determine the microbial community structures of streambed sediments across diverse geographic and climatic areas. Sediment samples were collected from three adjacent headwater forest streams within three biomes, eastern deciduous (Pennsylvania), southeastern coniferous (New Jersey), and tropical evergreen (Guanacaste,...

1. We estimated uptake of stream water dissolved organic carbon (DOC) through a whole-stream addition of a 13C-DOC tracer coupled with laboratory measurements of bioavailability of the tracer and stream water DOC. 2. The tracer, a leachate of 13C-labelled tree tissues, was added to the head waters of White Clay Creek, Pennsylvania, U.S.A., over a 2...

Anthropogenic influences on the global carbon cycle have affected terrestrial, aquatic, and atmospheric carbon pools and flows. Accumulation of carbon in the atmosphere is recognized as a global environmental threat that is altering weather patterns, melting glaciers, changing season length and affecting species distribution. Increasing evidence su...

Metabolism in freshwater ecosystems of terrestrial organic carbon provides a major source of CO2 outgassing to the atmosphere. This contradicts the conventional wisdom that terrestrial organic carbon is recalcitrant and contributes little to the support of aquatic metabolism. We combine recent progress from geophysics, microbial ecology and organic...

BRIDGES BRIDGES is a recurring feature of J-NABS intended to provide a forum for the interchange of ideas and information between basic and applied researchers in benthic science. Articles in this series will focus on topical research areas and linkages between basic and applied aspects of research, monitoring, policy, and education. Readers with i...

Organic matter (OM) in streams that provide drinking water is a potential energy source for bacterial regrowth in distribution systems and a precursor for disinfection byproducts. Baseflow concentrations of OM were measured over a 3-y period in 60 streams divided evenly between water-supply regions east and west of the Hudson River (EOH or WOH) in...

Ecosystem metabolism was measured in 10 streams flowing into New York City drinking- water-supply reservoirs. Six of the streams were located west of Hudson River (WOH) in the Catskill Mountains and 4 were in the Croton River watershed east of Hudson River (EOH). Measurements were made for 3-d periods between June and November in each of 3 y using...

Macroinvertebrate communities were examined in conjunction with landuse and water- chemistry variables at 60 sites in the NYC drinking-water-supply watersheds over a 3-y period. The watersheds are in 2 adjacent regions of New York State (east of Hudson River (EOH) and west of Hudson River (WOH)) that are geographically distinct and have unique macr...

Uptake of nutrients and organic C was measured once annually between 2000 and 2002 in each of 10 streams within the water-supply source areas for New York City. Nutrients (PO4 3- and NH4 þ ) and organic C (glucose and arabinose) were injected into the streams for 1 to 2 h, and uptake lengths were estimated from the longitudinal declines in downstre...

The microbial heterotrophic utilization of dissolved organic matter (DOM) was determined experimentally in microcosms using stream water and stream‐bed sediments from a third order reach of White Clay Creek (Pennsylvania, U.S.A.). Sources of DOM for the experiments included White Clay Creek water at baseflow and stormflow and cold water extracts of...

The adenylate energy charge (EC A ) of microbial communities from streambed sediments was measured during three different seasons, under experimental manipulation and in culture. The EC A values of sediments ( x ±S.E.) in the autumn, winter and spring were low and constant; 0.22±0.03 ( n =12), 0.32±0.04 ( n = 12) and 0.28±0.03 ( n =6) respectively....

Studies were performed to assess the acclimation of the stream‐bed heterotrophic microflora to sources of dissolved organic matter (DOM) typical of its environment and microfloral responses to pulses of DOM. Microcosm measurements of dissolved organic carbon (DOC) uptake, dissolved oxygen uptake. ATP concentration and epitluorescence microscopic co...

Recurring seasonal patterns of microbial distribution and abundance in three third-order temperate streams within the southeast Pennsylvania Piedmont were observed over 4 years. Populations associated with streambed sediments and rocks (epilithon) were identified using terminal restriction length polymorphism (tRFLP) and sequencing of 16S rRNA gene...

We investigated dissolved organic matter (DOM) metabolism by employing plug-flow biofilm reactors and ultra-high resolution mass spectrometry of DOM isolated by C, extraction in two forested stream ecosystems, a low DOM tropical stream sampled at baseflow and a higher DOM temperate stream sampled during a storm. On passage through the bioreactors,...

Questions related to transport of DOC from catchment soils to streams are vexed. Observed variation of DOC in streams over storm events may be due to "flushing" of DOC that builds up in unsaturated soils between events and also may be due to the timing of water delivery from riparian areas versus hillslopes. Furthermore, the rates at which DOC is p...

Ecosystem tracer-level additions would benefit from a stable isotope-labeled source of complex organic molecules. We tested a method to label tree C with 13C and create a stable isotope tracer for stream dissolved organic carbon (DOC) using tulip poplar (Liriodendron tulipifera L.) seedlings. In 2000, seedlings were grown with 0.82 moles of 13CO2 t...

Natural organic matter (NOM) in drinking water supplies can provide precursors for disinfectant byproducts, molecules that impact taste and odors, compounds that influence the efficacy of treatment, and other compounds that are a source of energy and carbon for the regrowth of microorganisms during distribution. NOM, measured as dissolved organic c...

The uptake of nutrients was measured in each of ten streams within the water supply source areas for New York City, once each year between 2000 and 2002. Uptake lengths were estimated from the conservative-tracer-corrected downstream attenuation of short-term (1-2 h) nutrient releases. Uptake lengths correlated with stream size and were converted t...

Chironomidae are diverse and abundant in streams and rivers and are often included in water quality and pollution evaluations. We examined distribution patterns of chironomid genera from 60 sites in the 2 regions (East and West of the Hudson River) that are the source of New York City's drinking water. These watersheds range from forested to urbani...

Little is known about the molecular composition of the biodegradable fraction of dissolved organic matter (BDOM) in stream ecosystems. We combined plug-flow biofilm reactors, tetramethylammonium hydroxide (TMAH) thermochemolysis GC-MS, and 13C-labeled TMAH thermochemolysis GC-MS to study the molecular composition of BDOM from two stream ecosystems....

Dissolved organic C (DOC) is metabolically important in streams, but its contribution to ecosystem metabolism is not well known because it is a complex mixture of mostly unidentified molecules. The uptake of bioavailable DOC in White Clay Creek (WCC), a 3rd-order stream in Penn- sylvania, was estimated from the results of an experiment using 13C-la...

Understanding the role of black carbon (BC) in the natural environment is very important because of the potential impacts of black carbon on human health, global carbon cycling, and pollutant transport. There has been circumstantial evidence for the existence of black carbon molecules in dissolved organic matter (DOM); however, direct evidence has...

A study of 16 streams in eastern North America shows that riparian deforestation causes channel narrowing, which reduces the total amount of stream habitat and ecosystem per unit channel length and compromises in-stream processing of pollutants. Wide forest reaches had more macroinvertebrates, total ecosystem processing of organic matter, and nitro...

A technique for measurement of the stable isotope composition of dissolved organic carbon (DOC) in stream water, using an elemental analyzer (EA) coupled to an isotope ratio mass spectrometer (IRMS), is described. Stream water samples were concentrated by rotary evaporation, acidified to remove dissolved inorganic carbon (DIC), and dried in silver...

This chapter presents a rationale for distinguishing between the metabolism of monomeric and polymeric DOM; reviews the sources, concentration, and composition of the monomeric organic carbon pool in aquatic environments; discusses factors that contribute to the biodegradability of DOM; and describes contrasting views of DOM molecules support bacte...

In many aquatic ecosystems, most microbes live in matrix-enclosed biofilms and contribute substantially to energy flow and nutrient cycling. Little is known, however, about the coupling of structure and dynamics of these biofilms to ecosystem function. Here we show that microbial biofilms changed the physical and chemical microhabitat and contribut...

The tetramethylammonium hydroxide (TMAH) thermochemolysis method was recently introduced for the qualitative characterization of organic matter from natural waters (NOM). Such characterizations were usually of a qualitative nature, and any semiquantitative assessments of individual compounds were often achieved by measuring relative areas and assum...

Current velocity affected the architecture and dynamics of natural, multiphyla, and cross-trophic level biofilms from a forested piedmont stream. We monitored the development and activity of biofilms in streamside flumes operated under two flow regimes (slow [0.065 m s(-1)] and fast [0.23 m s(-1)]) by combined confocal laser scanning microscopy wit...

In this study, we determine concentrations of neutral and amino sugars and a sugar alcohol in freshwaters using high-performance liquid chromatography and pulsed amperometric detection with a single isocratic analysis. Coeluting arabinose, galactosamine, and mannosamine are separated with a mobile phase of 22.8 mM NaOH-KOH at a temperature of 17 de...

Our nation’s network of rivers, lakes and streams originates from a myriad of small streams and wetlands, many so small they do not appear on any map. Yet these headwater streams and wetlands exert critical influences on the character and quality of downstream waters. The natural processes that occur in such headwater systems benefit humans by miti...

1. We monitored streamwater and streambed sediment porewaters from White Clay Creek (WCC), SE Pennsylvania, for dissolved organic carbon (DOC), dissolved oxygen (DO) and conductivity to investigate organic matter processing within the hyporheic zone. Dissolved organic carbon and DO concentrations were higher in the streamwater than in the porewater...

Ecologically significant properties of wild-type and genetically engineered bacteria capable of degrading 3-chlorobenzoate (3-CB) were compared in the laboratory, and isolates were introduced into streambed sediments in microcosms to observe their population dynamics. 3-CB metabolism, growth on algal extract, temperature optima, and ingestion by pr...

The presence of natural organic matter (NOM) strongly impacts drinking water treatment, water quality, and water behavior during distribution. Dissolved organic carbon (DOC) concentrations were determined daily over a 22 month period in river water before and after conventional drinking water treatment using an on-line total organic carbon (TOC) an...

Accurate determinations of total (TOC), dissolved (DOC) and particulate (POC) organic carbon concentrations are critical for understanding the geochemical, environmental, and ecological roles of aquatic organic matter. Of particular significance for the drinking water industry, TOC measurements are the basis for compliance with US EPA regulations....

This paper describes improvements made to the determination of dissolved carbohydrates in stream water with high-performance liquid chromatography and pulsed amperometric detection (HPLC-PAD). We eliminated interference from dissolved oxygen, separated xylose and mannose along with other molecules, reduced the chromatographic peak shift associated...

A molecular tracer method was developed for identifying organic matter sources to surface waters. We targeted wastewater treatment plant (WWTP) effluent, agricultural and feedlot runoff, urban and suburban runoff, and wildlife. Tracers included fecal steroids, caffeine, consumer product fragrance materials (FMs), and petroleum and combustion byprod...

Using samples from a variety of US water sources, a study finds that different methodologies for analyzing total organic carbon yield equivalent data. The Stage 1 Disinfectants/Disinfection By‐products Rule requires analyses of total organic carbon (TOC) in drinking water sources. In this study, water samples from 102 watersheds across North Americ...

1. Riparian zones hold a central place in the hydrological cycle, owing to the prevalence of surface and groundwater interactions. In riparian transition zones, the quality of exfiltrating water is heavily influenced by microbial activities within the bed sediments. This paper reviews the role of micro-organisms in biogeochemical cycling in the rip...

Procedures for the extraction of aquatic humic substances and analysis of their lignin-derived phenols were assessed and altered to simplify and shorten XAD-8 resin cleaning, reduce losses due to sorption, and optimize oxidative release of phenols without increasing their transformation. The revised cleaning procedures require 5 rather than 120h an...