B13B-0218 1340h
Nitrogen Additions Affect Root Dynamics in a Boreal Forest Ecosystem
As with many ecosystems, North American boreal forests are increasingly subjected to anthropogenic nitrogen deposition. To examine potential effects on plant growth, we created nitrogen fertilization plots in three sites along an Alaskan fire chronosequence composed of forests aged 5, 17, and 80 years. Each site had been exposed to two years of nitrogen fertilization, with four control plots and four nitrogen plots per site. General observations indicate that aboveground net primary productivity appears to be nitrogen limited in each site. We hypothesized that nitrogen fertilization would positively influence root dynamics as well, with nitrogen additions resulting in an increase in standing root biomass and length. To test our hypothesis, we used a minirhizotron camera to collect sequential images of roots in the top 10 cm of soil in both nitrogen fertilized and control plots in each site. Images were collected monthly during the growing season, with a total of five sampling times between May 2003 and May 2004. We then analyzed the images with WinRhizotron root measurement software. Nitrogen fertilization had varying effects on root biomass among the three sites, with a significant site by N interaction (P = 0.039). A decrease in root biomass was observed in the 5 and 80 year old sites, dropping from 207 g/m2 to 79 g/m2 and from 230 g/m2 to 129 g/m2 for the youngest and oldest sites, respectively. In contrast, root biomass increased from 52 g/m2 to 107 g/m2 in the 17 year old site. (Values are for the top 10 cm of soil only, and likely underestimate total root stocks.) Patterns in standing root lengths diverged from those of root biomass, with a 2.5-fold overall increase under nitrogen fertilization across all sites (P = 0.004). There were no significant differences among sites in nitrogen response. Standing root biomass and length differed from one another in their responses to nitrogen fertilization because nitrogen additions decreased specific root weight (as g per unit length) (P = 0.008). The divergent responses of root biomass and root length under nitrogen addition suggest a shift in root structure to finer roots. One possible mechanism is that phosphorus may have become limiting to plant growth following nitrogen additions. Fine-structured roots can better exploit soil phosphorus due to an increased surface area:volume ratio. Among the sites, standing root biomass was greatest in the oldest site (P = 0.014) but no significant difference occurred in standing root length. This pattern implies that roots become coarser with age, a possible consequence of plant succession from deciduous and annual species in the younger two sites to black spruce in the oldest. Altogether, forest fires could elicit a long-term reduction in carbon stocks in belowground plant biomass; nitrogen fertilization could reduce these stocks even further, but not necessarily at every successional stage.
B13B-0219 1340h
Quantifying Atmospheric N Sources in Major Watersheds of New York State
Human activities have considerably altered nitrogen cycling in the environment, increasing reactive nitrogen (N) inputs to terrestrial and aquatic ecosystems. In the northeastern USA, this enhanced supply of N has been linked to many environmental concerns such as eutrophication, violations of drinking water standards, and forest health decline. Our work concentrates on atmospheric N inputs to ecosystems throughout New York state, which experiences among the highest rates of atmospheric N deposition in the nation. We've focused on a set of measurements at Connecticut Hill, which participates in several national atmospheric deposition monitoring networks (National Atmospheric Deposition Program, Clean Air Status and Trends Network, and the Atmospheric Integrated Research Monitoring Network). There we've co-located a network of 30 passive collectors for sampling multiple N species in dry deposition (HNO$_{3}$, NO$_{2}$, NH$_{3}$). Our preliminary data allow us to address questions of: 1) within-site spatial variability; 2) deployment times and temporal averaging with regard to the frequency of sample collection; 3) how passive sampler concentrations compare to the suite of constituents measured by the national network instrumentation; 4) how local meteorological conditions influence concentrations; and 5) whether the isotopic composition of nitrate-N ($\delta^{18}$O and $\delta^{15}$N) in passively sampled dry deposition can be used to understand the relative contributions of different sources of atmospheric N. Further, we are quantifying sources of N fluxes in surface waters. We make use of a variety of isotopic and chemical tracers in stream water samples to distinguish among atmospheric and other (e.g., fertilizer or wastewater) sources. Our collaborative study aims to characterize atmospheric N sources, which is necessary to develop sound strategies for understanding and managing the effects of these and other N inputs.
B13B-0220 1340h
A Novel Approach to Eddy Covariance Fluxes of NO$_{2}$, $\Sigma$PNs, $\Sigma$ANs and HNO$_{3}$
The exchange of reactive nitrogen between the biosphere and atmosphere affects both oxidative atmospheric chemistry and ecosystem nutrient dynamics. Few direct measurements of reactive nitrogen oxide fluxes have been made due to the stringent instrumental requirements for eddy correlation analysis. Thermal dissociation-Laser Induced Fluorescence (TD-LIF) is a sensitive, selective, and fast (5Hz) technique for measuring NO$_{2}$, sum peroxy nitrates, sum alkyl nitrates, and nitric acid. We have deployed a TD-LIF instrument at the University of California - Blodgett Forest Research Station and used it to evaluate the potential for eddy covariance measurements of the fluxes of each of these 4 categories of NO$_{y}$. Here we present preliminary analysis of observed fluxes, and extensive diagnostics of instrument performance using spectral analysis.
B13B-0221 1340h
Nitrogen Addition as a Result of Long-Term Root Removal Affects Soil Organic Matter Dynamics
A long-term field litter manipulation site was established in a mature coniferous forest stand at the H.J. Andrews Experimental Forest, OR, USA in 1997 in order to address how detrital inputs influence soil organic matter formation and accumulation. Soils at this site are Andisols and are characterized by high carbon (C) and low nitrogen (N) contents, due largely to the legacy of woody debris and extremely low atmospheric N deposition. Detrital treatments include trenching to remove roots, doubling wood and needle litter, and removing aboveground litter. In order to determine whether five years of detrital manipulation had altered organic matter quantity and lability at this site, soil from the top 0-5 cm of the A horizon was density fractionated to separate the labile light fraction (LF) from the more recalcitrant mineral soil in the heavy fraction (HF). Both density fractions and whole soils were incubated for one year in chambers designed such that repeated measurements of soil respiration and leachate chemistry could be made. Trenching resulted in the removal of labile root inputs from root exudates and turnover of fine roots and active mycorrhizal communities as well as an increase of available N by removing plant uptake. Since 1999, soil solution chemistry from tension lysimeters has shown greater total N and dissolved organic nitrogen (DON) flux and less dissolved organic carbon (DOC) flux to stream flow in the trenched plots relative to the other detrital treatments. C/N ratio and C content of both light and heavy fractions from the trenched plots were greater than other detrital treatments. In the lab incubation, over the course of a year C mineralization from these soils was suppressed. Cumulative DOC losses and CO$_{2}$ efflux both were significantly less in soils from trenched plots than in other detrital treatments including controls. After day 150 of the incubation, leachates from the HF of plots with trenched treatments had a DOC/DON ratio significantly higher than other detrital treatments. DOC/DON ratio of both LF and bulk soils for the trenched plots did not vary among treatments. In trenched plots, under high N conditions with root-associated labile C inputs gone, there is preliminary evidence that the relative amounts and lability of soil C pools is changing. In particular, the relative concentration of recalcitrant compounds may be increasing and decomposition may be slowing down.
B13B-0222 1340h
Dry Deposition of Fine Aerosol Nitrogen to an Agricultural Field Measured by Eddy-Correlation Mass Spectrometry
In urban areas high emissions of reactive nitrogen species cause an increase in atmospheric aerosol nitrogen formation and deposition. This nitrogen is eventually removed from the atmosphere by wet or dry deposition, with dry deposition often accounting for more than half of the total deposition of particulate nitrate (Lovett, 1994). Total N deposition is not adequately characterized, in part because dry deposition is difficult to measure or model. For example measured fine particle deposition to a forest canopy differs from predicted values by an order of magnitude (Gallagher et al., 1997). The eddy-correlation technique is a micrometeorological method used to directly measure fluxes from measurements made above the surface (Wesely and Hicks, 2000). Eddy-correlation mass spectrometry (ECMS) has been developed to directly measure aerosol particle deposition velocities from fast response aerosol concentration and wind velocity measurements. Using an Aerodyne Aerosol Mass Spectrometer (AMS) (Jayne et al., 2000), the size and composition of ambient aerosols is measured at a high frequency. The AMS signal is proportional to non-refractory PM$_{1.0}$ mass. Aerosol deposition fluxes for a given averaging period are then calculated directly as the covariance of the vertical wind velocity with the AMS signal ($F = -\overline{w'S'}$). A field study was conducted to measure aerosol nitrogen dry deposition to an agricultural field immediately downwind of the Phoenix metropolitan area using eddy-correlation mass spectrometry. The study was supplemented with aerosol composition measurements including bulk deposition collectors and filter bank samplers. Bulk deposition samples and 24-hour filter samples were analyzed for ammonia and nitrogen. Here we compare the results of the flux estimates from bulk collection with inferential measurements (filter samples and modeled deposition velocities) and direct micrometeorological measurements (ECMS) in order to improve N deposition estimates.
B13B-0223 1340h
Atmospheric Dust Deposition as a Source of Nutrients and Trace Metals to the Northern Gulf of Aqaba
The deposition of atmospheric dust is a significant but poorly characterized component of nutrient and trace metal input to the euphotic zone of the ocean. Dust deposition is thought to be of particular importance in oligotrophic areas such as the Gulf of Aqaba where other nutrient and trace metal sources are scarce. Our goal is to characterize the magnitude and temporal variability of dust deposition, to evaluate the contribution of this source to the nutrient pool, and to determine the effect of this source on the pelagic ecosystem structure of the Gulf of Aqaba. We collected a multi-season time series of aerosol samples from a coastal station located at the Interuniversity Institute of Marine Sciences in Eilat, Israel, on the northwestern coast of the Gulf. Replicate samples of up to 70 m3 of air (24-hour integrated samples) were collected on 47-mm polycarbonate filters. We will present the results of this time series, including analyses of aerosol concentration and composition, and estimates of the deposition fluxes of N, P, Si, Fe and other trace elements. These data will be related to nutrient and trace metal distributions in the water column and to changes in productivity and ecosystem structure. The effect of aerosols on the growth of the dominant phytoplankton species in the Gulf will also be shown. Finally, a preliminary comparison between dust flux estimates using satellite data and the flux calculated from the aerosol filters will be presented.
B13B-0224 1340h
Atmospheric Transport and Deposition of Nitrogen Compounds From the Asian Continent Over the East China Sea
The growth of economy and population is rapid among in the east Asian countries. Within two decades, emission from east Asia could roughly account for half of the nitrogen released to the atmosphere from all anthropogenic sources worldwide. The Asia/western Pacific region has a unique mixture of aerosols and trace gases because of these distinctive patterns of emissions in combination with the local meteorological conditions affecting the region. Continental outflows can alter bilogical and chemical processes along the coastal Asia and, therefore, modify biogeochemical fluxes and feedbacks that may have serious implications to human health and climate implications. We made atmospheric measurements on board R/V Hakuho Maru over the western North Pacific and the East China Sea from 26 September to 9 October 2002 (the KH02-3 Cruise) in the autumn and from 4 to 20 March 2004 (the KH04-1 Cruise) in the spring. The atmospheric deposition fluxes of nitrogen compounds (ammonium, nitrate, and organic N) to the marine environment were investigated as a part of the IGBP/SOLAS project. Size segregated ambient aerosols (d$<$2.5$\mu$m and d$>$2.5$\mu$m) were collected at every 4-12 hours intervals on a PTFE fiber filter by using a high-volume dichotomous virtual impactor air sampler. Atmospheric average total ammonium concentration over the East China Sea was 2.3 $\mu$g N m$^{-3}$, and that of nitrate was 0.48 $\mu$g N m$^{-3}$. However, $>$90 percent of paticulate ammonium occurred in the fine fraction whereas $>$80 percent of particulate nitrate was in the coarse fraction. By using empirical dry deposition velocities for two size categories, we estimated the ammonium and nitrate dry deposition fluxes over the East China Sea to be 160 Gg N yr$^{-1}$ and 270 Gg N yr$^{-1}$, respectively. Our results clearly show that particle size is critical for different components and flux estimation. The atmospheric inputs of the nitrogen compounds to the East China Sea are found to be comparable to their fluxes of 190 Gg N yr$^{-1}$ and 430 GgN yr$^{-1}$, respectively, by the Changjian River.
B13B-0225 1340h
Disjunct Eddy Accumulation Measurements of Organic Nitrate Fluxes Over a Forest Site in Northern Michigan
Fluxes of organic nitrates have been measured at the PROPHET tower site in northern Michigan by the technique of disjunct eddy accumulation (DEA). This relatively new method involves conditional sampling into up and down cartridge-based reservoirs, from a disjunct sample container. In this experiment, air parcels containing target species were sampled at rates proportional to the magnitude and direction of the vertical wind vector. One disjunct sample was taken every 30 seconds by drawing ambient air into analysis tubes containing a sorbent material (Tenax-TA) for a period of one hour. These sorbet tubes were then analyzed by thermal desorption/GC-ECD. The performance of the DEA instrument and GC during their first field deployment is evaluated and the overall flux for several organic nitrate molecules will be reported. Using these data and the gas phase concentrations, dry deposition velocities of these organic nitrates can be calculated and will be discussed here. The potential role and relative importance (compared to other sources of nitrogen) of these molecules in biosphere-atmosphere exchange within a nitrogen limited forest will also be discussed.
B13B-0226 1340h
Biogenic emission of nitric oxide and nitrous oxide from arid and semi-arid soils: update of measurements, processes, controlling factors and the potential role of soil texture
Recently it became evident, that arid and semi-arid soils may be a significant source of nitrogen oxide (NO) (and to a lesser extent also of nitrous oxide (N$_{2}$O)). Particularly, desert soils may provide rather high NO emissions just after seasonally limited and/or sporadical rain events due to the accumulation of nitrate and/or ammonium. N emissions from semi-arid and arid lands particularly contribute to the high error margins of global N emissions from soils, simply because of a very small number of corresponding measurements being available (both in the laboratory and in the field). We present (a) a summary of the underlying mechanisms of N emissions (chemodenitrifictaion, denitrification, nitrification), (b) a very recent update of available NO and N$_{2}$O measurements from semi-arid and arid soils worldwide, and (c) a review of those factors which control the N emissions (N availability and fertilization, soil moisture and temperature). We will particularly address the potential role of soil texture in the partitioning of NO vs. N$_{2}$O fluxes. The global importance of NO vs. N$_{2}$O from semi-arid and arid soils will be discussed.
B13B-0227 1340h
Measurement of Wet Deposition of Inorganic and Organic Nitrogen in a Forest Environment
Nitrogen is often the limiting nutrient for tree growth. Wet deposition is a major source of nitrogen to a forest. Few previous studies have included organic nitrogen as part of the assessment of atmospheric inputs of nitrogen to forest ecosystems. A significant fraction of wet and dry deposited nitrogen is organic, and several studies have shown that organic nitrogen can thermally or photochemically degrade into inorganic nitrogen as well as be directly taken up by leaves, thereby making it a viable source of nitrogen to forests. Our hypothesis is that organic nitrogen is a significant fraction of nitrogen deposited via wet deposition to a forest, and that this nitrogen can be utilized by the trees. Dissolved inorganic and organic nitrogen were measured in precipitation at the University of Michigan Biological Station (UMBS) in an open field and under the forest canopy. Precipitation was collected on an event basis. The rainwater collectors were deployed just prior to a rain event and were retrieved immediately after the rain finished. The collection bottles were surrounded with dry ice to freeze the precipitation upon collection, preventing degradation of any nitrogen species either by bacteria or by chemical reactions. The samples were analyzed for nitrate, ammonium, and organic nitrogen content. The results of the frozen, single event sampling were compared with samples collected unfrozen over a one-week period in order to investigate sample stability issues. Canopy retention of nitrogen in precipitation will also be discussed.
B13B-0228 1340h
Determining Impacts of Confined Animal Feedlot Operations (CAFOs) on the Water Quality and Periphyton Community in two Mid-Michigan Streams
Confined Animal Feedlot Operations or CAFOs are suspected of having serious impacts on adjacent streams either from direct discharges of animal wastes or from surface runoff carrying animal wastes after rain events. These inputs often contain high levels of nutrients, particularly nitrogen and phosphorus. In some cases other particular chemical constituents in the animal waste, like ammonia nitrogen may adversely affect resident stream biota. We investigated two streams adjacent to two CAFOs in mid-Michigan. Sites were sampled upstream of the CAFO influence and downstream of each facility. Geochemical analyses showed high concentrations of nitrate nitrogen and total nitrogen at both upstream and downstream locations of both streams. This indicates that upstream nutrient inputs had already impacted the study streams, making separation of CAFO inputs hard to separate from the already existing high inputs of nutrients from other routine agricultural practices. Coliform bacteria concentrations were also determined throughout the summer, using the Coliscan rapid detection method to separate E.coli from total coliforms. E.coli is the bacterium associated with human fecal contamination and is routinely measured to determine compliance with Michigan's Water Quality Standard of 130 cfu's/100ml. E.coli are also routinely found in warm-blooded animal waste. High levels of E.coli were enumerated from both downstream CAFO locations. Measured E. coli concentrations downstream of the CAFOs were well above the State of Michigan's standard. At one site over 80% of samples exceeded the state's standard and 20% of samples exceeded the standard at the other downstream location. The attached periphyton community was sampled using glass slides as artificial substrates exposed for 28 days at each sampling location. Dramatic changes were reported in diatom species dominance and in community species composition. For example the diatom species, Cocconeis placentula var. euglypta, comprised over 40% of the upstream diatom community, yet comprised $< $5% of the downstream CAFO impacted diatom community. This study indicates the usefulness of associating a biological component with simultaneous measurements of traditional water quality parameters. CAFOs may have a much greater impact on the stream periphyton community than just accelerating plant growth from excess nutrients. Changes in stream water chemistry had significant impacts on the species and structure of the attached algal community. The chemical parameters; total phosphorus, ortho-phosphorus and ammonia nitrogen appeared to be the most sensitive of those measured, in detecting the possible influences of feedlot inputs on overall stream water quality