First Matthew R.

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Matthew R.
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  • Preprint
    Water quality and planktonic microbial assemblages of isolated wetlands in an agricultural landscape
    ( 2011-07) Atkinson, Carla L. ; Golladay, Stephen W. ; First, Matthew R.
    Wetlands provide ecosystem services including flood protection, water quality enhancement, food chain support, carbon sequestration, and support regional biodiversity. Wetlands occur in human-altered landscapes, and the ongoing ability of these wetlands to provide ecosystem services is lacking. Additionally, the apparent lack of connection of some wetlands, termed geographically isolated, to permanent waters has resulted in little regulatory recognition. We examined the influence of intensive agriculture on water quality and planktonic microbial assemblages of intermittently inundated wetlands. We sampled 10 reference and 10 agriculturally altered wetlands in the Gulf Coastal Plain of Georgia. Water quality measures included pH, alkalinity, dissolved organic carbon, nutrients (nitrate, ammonium, and phosphate), and filterable solids (dry mass and ash-free dry mass). We measured abundance and relative size distribution of the planktonic microbial assemblage (< 45 μm) using flow cytometry. Water quality in agricultural wetlands was characterized by elevated nutrients, pH, and suspended solids. Autotrophic microbial cells were largely absent from both wetland types. Heterotrophic microbial abundance was influenced by nutrients and suspended matter concentration. Agriculture caused changes in microbial assemblages forming the base of wetland food webs. Yet, these wetlands potentially support important ecological services in a highly altered landscape.
  • Article
    Stream nutrient enrichment has a greater effect on coarse than on fine benthic organic matter
    (Society for Freshwater Science, 2013-09-17) Tant, Cynthia J. ; Rosemond, Amy D. ; First, Matthew R.
    Nutrient enrichment affects bacteria and fungi associated with detritus, but little is known about how biota associated with different size fractions of organic matter respond to nutrients. Bacteria dominate on fine (<1 mm) and fungi dominate on coarse (>1 mm) fractions, which are used by different groups of detritivores. We measured the effect of experimental nutrient enrichment on fungal and bacterial biomass, microbial respiration, and detrital nutrient content on benthic fine particulate organic matter (FPOM) and coarse particulate organic matter (CPOM). We collected FPOM and CPOM from 1 reference and 1 enriched stream. CPOM substrates consisted of 2 litter types with differing initial C:nutrient ratios (Acer rubrum L. and Rhododendron maximum L.). Fungal and bacterial biomass, respiration, and detrital nutrient content changed with nutrient enrichment, and effects were greater on CPOM than on FPOM. Fungal biomass dominated on CPOM (99% total microbial biomass), whereas bacterial biomass dominated on FPOM (95% total microbial biomass). These contributions were unchanged by nutrient enrichment. Bacterial and fungal biomass increased more on CPOM than FPOM. Respiration increased more on CPOM (up to 300% increase) than FPOM (50% increase), indicating important C-loss pathways from these resources. Microbial biomass and detrital nutrient content were positively related. Greater changes in nutrient content were observed on CPOM than on FPOM, and changes in detrital C:P were greater than changes in detrital C:N. Threshold elemental ratios analyses indicated that enrichment may reduce P limitation for shredders and exacerbate C limitation for collector-gatherers. Changes in CPOM-dominated pathways are critical in predicting shifts in detrital resource quality and C flow that may result from nutrient enrichment of detritus-based systems.
  • Preprint
    Comparison of techniques used to count single-celled viable phytoplankton
    ( 2010-10-14) Steinberg, Mia K. ; First, Matthew R. ; Lemieux, Edward J. ; Drake, Lisa A. ; Nelson, Bruce N. ; Kulis, David M. ; Anderson, Donald M. ; Welschmeyer, Nicholas A. ; Herring, Penny R.
    Four methods commonly used to count phytoplankton were evaluated based upon the precision of concentration estimates: Sedgewick Rafter and membrane filter direct counts, flow cytometry, and flow-based imaging cytometry (FlowCAM). Counting methods were all able to estimate the cell concentrations, categorize cells into size classes, and determine cell viability using fluorescent probes. These criteria are essential to determine whether discharged ballast water complies with international standards that limit the concentration of viable planktonic organisms based on size class. Samples containing unknown concentrations of live and UV-inactivated phytoflagellates (Tetraselmis impellucida) were formulated to have low concentrations (<100 ml-1) of viable phytoplankton. All count methods used chlorophyll a fluorescence to detect cells and SYTOX fluorescence to detect non-viable cells. With the exception of one sample, the methods generated live and non-viable cell counts that were significantly different from each other, although estimates were generally within 100% of the ensemble mean of all subsamples from all methods. Overall, percent coefficient of variation (CV) among sample replicates was lowest in membrane filtration sample replicates, and CVs for all four counting methods were usually lower than 30% (although instances of ~60% were observed). Since all four methods were generally appropriate for monitoring discharged ballast water, ancillary considerations (e.g., ease of analysis, sample processing rate, sample size, etc.) become critical factors for choosing the optimal phytoplankton counting method.
  • Preprint
    Leaf litter nutrient uptake in an intermittent blackwater river : influence of tree species and associated biotic and abiotic drivers
    ( 2014-12) Mehring, Andrew S. ; Kuehn, Kevin A. ; Thompson, Aaron ; Pringle, Catherine M. ; Rosemond, Amy D. ; First, Matthew R. ; Lowrance, R. Richard ; Vellidis, George
    Organic matter may sequester nutrients as it decomposes, increasing in total N and P mass via multiple uptake pathways. During leaf litter decomposition, microbial biomass and accumulated inorganic materials immobilize and retain nutrients, and therefore both biotic and abiotic drivers may influence detrital nutrient content. We examined the relative importance of these types of nutrient immobilization and compared patterns of nutrient retention in recalcitrant and labile leaf litter. Leaf packs of water oak (Quercus nigra), red maple (Acer rubrum) and Ogeechee tupelo (Nyssa ogeche) were incubated for 431 days in an intermittent blackwater stream and periodically analyzed for mass loss, nutrient and metal content, and microbial biomass. These data informed regression models explaining temporal changes in detrital nutrient content. Informal exploratory models compared estimated biologically-associated nutrient stocks (fungal, bacterial, leaf tissue) to observed total detrital nutrient stocks. We predicted that (1) labile and recalcitrant leaf litter would act as sinks at different points in the breakdown process, (2) plant and microbial biomass would not account for the entire mass of retained nutrients, and (3) total N content would be more closely approximated than total P content solely from nutrients stored in leaf tissue and microbial biomass, due to stronger binding of P to inorganic matter. Labile litter had higher nutrient concentrations throughout the study. However, lower mass loss of recalcitrant litter facilitated greater nutrient retention over longer incubations, suggesting that it may be an important long-term sink. N and P content were significantly related to both microbial biomass and metal content, with slightly stronger correlation to metal content over longer incubations.