Christopher Lundberg - VSP | UCAR Visiting Scientist Programs

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Dissertation AbstractGreenhouse Gas Emissions and Nutrients Dynamics in Restored Wetlands of the MississippiRiver BasinGreenhouse gases were sampled during spring and summer months in 2010 and 2011 at two sitesin the Mississippi River Basin: a riparian forested wetland under restored flood pulsing nearMemphis, TN and a coastal estuarine marsh complex impacted by a river diversion atCaernarvon, LA. Mean methane fluxes at Caernarvon (-0.09 g CH 4 -C m -2 d -1 ) were lower thanthose at Memphis (0.53 g CH 4 -C m -2 d -1 ), and did not differ between seasons. Nitrous oxidefluxes were generally below detection limits. Fluxes were uncorrelated with water depth, soiltemperature, and ambient air temperature, though sampling occurred over a narrow range ofthese variables due to limitations in site accessibility.A water quality dataset spanning 8 years of monthly sampling was analyzed to determine longtermspatial and temporal patterns in nutrient concentrations at Caernarvon. The estuary servedas a source of ammonium, and chlorophyll a and a sink for nitrate, total nitrogen and totalsuspended sediments. Classification of the estuary as a source or sink for phosphate, totalphosphorus and silicate changed with the seasons. Nitrate removal efficiency varied seasonally,with efficiency highest in the fall (98%), summer (92%) and spring (87%) and lowest in thewinter (74%). Removal efficiency was inversely related to loading rate.Water quality samples were collected at Memphis in a secondary channel of the MississippiRiver under restored hydrology during spring and summer 2010-2011. Seasonal variationsexisted in concentrations of nitrate, total nitrogen, total phosphorus and total suspended solids,but not ammonium, phosphate, silicate, dissolved oxygen and chlorophyll a. No parametersvaried longitudinally or laterally within the channel. Nitrate loading rate was high and removalefficiency was low, especially in comparison with Caernarvon and other study sites within theMississippi River Basin, due to the limited size of the receiving wetland.
Project DescriptionThe Effect of Herbivory on Greenhouse Gas Emissions and Carbon Sequestration in WastewaterAssimilation WetlandsWetlands of coastal Louisiana (USA) perform important ecological functions which result ineconomic benefits including improved water quality, nutrient cycling, endangered specieshabitat, fisheries nurseries, recreational hunting and ecotourism (Reed and Wilson, 2004).However, the state of Louisiana has experienced wetland loss on a grand scale (Barras et al.1994, Day et al. 2000, 2007). The majority of the Lake Maurepas wetland complex, located insoutheast Louisiana, is described as degraded or degrading (Shaffer et al., 2009). Maurepaswetlands require restoration efforts that provide a large source of fresh water to prevent longtermsalinity pulses , (<strong>Lundberg</strong>, 2008; Thomson, Shaffer and McCorquodale, 2001). Onepotential source of fresh water for restoration efforts is secondarily-treated wastewater effluent.Wastewater assimilation wetlands (WAWs) have been shown to be an energy- and cost-effectivemeans of improving effluent water quality, increasing accretion, and promoting primaryproductivity (Day et al., 2004; Ko et al., 2004). Assimilation wetlands are currently operationalfor a number of municipalities in south Louisiana (Day et al., 2004). However, greenhouse gasflux and carbon sequestration studies in the region have been sparse. Additionally, the effects ofintensive herbivory by the non-native nutria (Myocaster coypus) on these processes have notbeen explored in WAWs. If selected as a fellow, I would utilize a WAW that has beenoperational for five years to conduct such research.In the fall of 2006, the city of Hammond began discharging municipal disinfected secondarysewage effluent into Four Mile Marsh (Figure 1). A 10-km buried pipeline was installed runningfrom the wastewater facility, where primary and secondary treatment and disinfection of thewater occurs, to the southern assimilation marsh. The pipeline is elevated 2 m at the marsh siteand is situated along a spoil levee separating the treatment marsh from the South Slough canaljust to the north (Figure 2). The wastewater is discharged into the marsh via 900 7.62-cmdiameter polyvinyl chloride (PVC) pipes emanating from the elevated pipe, though only 150PVC pipes are operational at a given time. Discharge pipes can thus be turned on or off, ormoved east or west, depending on environmental management practices or mechanical factors.Since operation began, the marsh has been extensively planted with baldcypress (Taxodiumdistichum) and water tupelo (Nyssa aquatic) seedlings in an effort to regenerate the historicaldominant forested wetland community of the region.This has served as a site for several ecological studies, and a great deal has been learned aboutthe system. For example, the marsh promotes baldcypress growth better than non-assimilationmarshes nearby (Figure 3) (<strong>Lundberg</strong> et al., 2011) and growth varies in response to nutrientavailability, evidenced by decreased growth with increasing distance from the outfall (Figure 4).
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Christopher Lundberg - VSP | UCAR Visiting Scientist Programs

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