Water Column Ammonium Concentration and Salinity Influence Nitrogen Uptake and Growth of Spartina Alterniflora

<p>Salt marsh macrophytes, such as <em>Spartina alterniflora, </em>play a<em> </em>critical role in uptake and transformation of inorganic nitrogen before it reaches coastal waters, thereby reducing the potential for eutrophication. Although nitrogen availability typically limits <em>S. alterniflora </em>growth, it may be possible to exceed the nitrogen uptake capacity of <em>S. alterniflora. </em>Increasing either nitrogen concentrations or salinity are key factors regulating <em>S. alterniflora </em>nitrogen uptake. Investigating the effects of nutrients and salinity on <em>S. alterniflora</em> is important given that increases in inorganic nitrogen supply to surface waters from agriculture and urbanization occur simultaneously with freshwater withdrawals that reduce flow and increase salinity. <em>Spartina alterniflora</em> nitrogen uptake in response to increasing inorganic nitrogen (ammonium, NH₄⁺) (0, 10, and 100 µM), and salinity (20, 30, and 40 psu) treatments in a fully crossed factorial design were measured in greenhouse microcosms with tidal simulation in Statesboro, GA from April-October, 2013. Prior to the factorial study, a three month pilot study comparing <em>S. alterniflora </em>growth in novel tidal simulator design and salt marsh field plots revealed tidal simulation did not affect plant height, stem density, or above and belowground biomass. After 48 hours the highest water column NH₄⁺uptake occurred at the lowest salinity (20 psu) and highest ammonium concentrations (100 µM) tested. After 6 months of NH₄⁺-¹⁵N additions, above and belowground <em>S. alterniflora </em>plant tissue δ¹⁵N increased proportionally with NH₄⁺ additions and was reduced by 50% with salinity increases from 20 to 40 psu across all NH₄⁺addition levels. Furthermore, <em>S. alterniflora </em>above and belowground biomass and main shoot height was reduced with increasing salinity from 20 to 40 psu and not significantly affected increasing NH₄⁺ additions. However, at high salinity (40 psu) biomass reductions were mitigated by intermediate (10 µM) NH₄⁺additions by a 50% increase over 0 and 100 µM NH₄⁺additions. Stem density and main shoot height measured weekly also reflected mitigation by intermediate (10 µM) NH₄⁺additions at elevated salinity. That <em>S. alterniflora </em>nitrogen uptake and biomass decrease with increasing water column salinity suggests alteration of coastal salinity may reduce nitrogen uptake capacities of <em>S. alterniflora </em>dominated salt marshes. Thus estuarine water column salinity should be considered when regulating inorganic nitrogen loads in aimed at conserving salt marsh nutrient retention.</p>

Name thesis:degree_name

Master of Science in Biology (M.S.)

Level thesis:degree_level

Thesis (open access)

Discipline thesis:degree_discipline

Department of Biology

Year dc:date.available

2014

Author dc:creator

• MacTavish, Rachel

Contributors dc:contributor

• Daniel Gleason
• Christine Hladik

• ETD
• Ammonium
• Microcosm
• Nitrogen uptake
• Salinity
• Spartina alterniflora
• Tidal simulator
• Biology
• Terrestrial and Aquatic Ecology

Repository record dc:identifier

https://digitalcommons.georgiasouthern.edu/etd/1162

OAI identifier oai:identifier

oai:digitalcommons.georgiasouthern.edu:etd-2210