The role of floods in particulate organic matter dynamics of a southern

Abstract. We investigated the effect of a flood on particulate organic matter (POM) dynamics in the floodplain and active channel of the Little Tennessee River in western North Carolina. We measured litterfall, leaf breakdown, and floodplain litter (before and after the flood) at 12 sites. Annual litterfall (256-562 g m Ϫ2 y Ϫ1 ) was typical of a temperate deciduous forest but lower than lowland floodplain forests in the eastern US. Leaf breakdown rates of 4 tree species (Acer rubrum, Carpinus caroliniana, Juglans nigra, and Platanus occidentalis) ranged from 0.001 to 0.010/d. We separated the 12 sites into 2 groups (inundated and non-inundated) based on the degree of flooding after a flood on 8 January 1998 and determined POM exchange between the active channel and floodplain. Significant transport of leaves from the floodplain to the river occurred at inundated sites, but transport of herbaceous or woody material did not occur. The flood increased leaf breakdown rates of all 4 tree species. Our measurements of litterfall, leaf breakdown, and floodplain litter standing crop suggest that leaves entrained from the floodplain of Little Tennessee River during floods are a source of POM to the active channel. However, flood input of leaves to the river were a small source of POM compared to direct leaffall

Ecosystem function in Appalachian headwater streams during an active invasion by the hemlock woolly adelgid.

Forested ecosystems in the southeastern United States are currently undergoing an invasion by the hemlock woolly adelgid (HWA). Previous studies in this area have shown changes to forest structure, decreases in canopy cover, increases in organic matter, and changes to nutrient cycling on the forest floor and soil. Here, we were interested in how the effects of canopy loss and nutrient leakage from terrestrial areas would translate into functional changes in streams draining affected watersheds. We addressed these questions in HWA-infested watersheds at the Coweeta Hydrologic Laboratory in North Carolina. Specifically, we measured stream metabolism (gross primary production and ecosystem respiration) and nitrogen uptake from 2008 to 2011 in five streams across the Coweeta basin. Over the course of our study, we found no change to in-stream nutrient concentrations. While canopy cover decreased annually in these watersheds, this change in light penetration did not translate to higher rates of in-stream primary production during the summer months of our study. We found a trend towards greater heterotrophy within our watersheds, where in-stream respiration accounted for a much larger component of net ecosystem production than GPP. Additionally, increases in rhododendron cover may counteract changes in light and nutrient availability that occurred with hemlock loss. The variability in our metabolic and uptake parameters suggests an actively-infested ecosystem in transition between steady states

Variable infection of stream salamanders in the southern Appalachians by the trematode Metagonimoides oregonensis (family: Heterophyidae)

Abstract Many factors contribute to parasites varying in host specificity and distribution among potential hosts. Metagonimoides oregonensis is a digenetic trematode that uses stream-dwelling plethodontid salamanders as second intermediate hosts in the Eastern US. We completed a field survey to identify which stream salamander species, at a regional level, are most likely to be important for transmission to raccoon definitive hosts. We surveyed six plethodontid species (N=289 salamanders) from 23 Appalachian headwater sites in North Carolina: Desmognathus quadramaculatus (n=69), Eurycea wilderae (n=160), Desmognathus ocoee (n = 31), Desmognathus monticola (n = 3), Eurycea guttolineata (n=7), and Gyrinophilus porphyriticus (n=19). We found infection in all species except D. monticola. Further analysis focused on comparing infection in the two most abundant species, D. quadramaculatus and E. wilderae. We found that D. quadramaculatus had significantly higher infection prevalence and intensity, probably due to a longer aquatic larval period and larger body sizes and thus greater cumulative exposure to the parasite

Background nutrients in Coweeta streams.

<p>Background nitrogen (µg L⁻¹) in low-order streams at Coweeta Hydrologic Laboratory over the course of this study. Soluble reactive phosphorus was also measured but was always below detection.^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061171#nt102" target="_blank">1</a>}</p>1<p>bd = below detection (5 µg L⁻¹).</p

Metabolic parameters in Coweeta streams.

<p>Changes in gross primary production (GPP), ecosystem respiration (ER), and net ecosystem production (NEP) for low-order streams in Coweeta Hydrologic Laboratory over the years of the study (A–C) and in each stream (D–F). Error bars represent 1 SE of the mean, and different letters represent significant differences (p<0.05) based on Wilcoxon post-hoc multiple comparison tests.</p

Stream characteristics. Physical measures of the 5 study streams in Coweeta during July 2008–2011.

<p>Stream characteristics. Physical measures of the 5 study streams in Coweeta during July 2008–2011.</p

Light penetration in Coweeta streams.

<p>Distribution of July light intensities (lux) at the five study sites in Coweeta Hydrologic Laboratory over the course of the study.</p

Nutrient uptake parameters in Coweeta streams.

<p>Changes in ammonium uptake length (S_w) and areal uptake (U) for low-order streams in Coweeta Hydrologic Laboratory over the years of the study (A–B) and in each stream (C–D). Error bars represent 1 SE of the mean, and different letters represent significant differences (p<0.05) based on Wilcoxon post-hoc multiple comparison tests.</p