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Nitrogen Sources and Fluxes to Indian River Lagoon: A Two Part Research Proposal. Alisa Britt Kepple. Why Should We Care About DIN and PON Concentrations Leaving the St. Lucie Inlet?. * The National Academy of Sciences has proposed that the eutrophication

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Nitrogen Sources and Fluxes to Indian River Lagoon: A Two Part Research Proposal

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Nitrogen sources and fluxes to indian river lagoon a two part research proposal l.jpg

Nitrogen Sources and Fluxes to Indian River Lagoon:A Two Part Research Proposal

Alisa Britt Kepple

Why should we care about din and pon concentrations leaving the st lucie inlet l.jpg

Why Should We Care About DIN and PON Concentrations Leaving the St. Lucie Inlet?

* The National Academy of Sciences has proposed that the eutrophication

caused by accelerated nitrogen inputs is the biggest threat to coastal resources in the world.

The Indian River lagoon provides an opportunity to study the direct

effects of agricultural rich - population growth on a regional estuary.

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St. Lucie Inlet: South Eastern Florida Last stop on the Intercoastal Waterway

HUC 03080202

“Cape Canaveral”

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Questions to be answered with this study:

  • What is the major source of anthropogenically introduced nitrogen to this system and who is responsible?

    • Fertilizer

    • Manure

    • Boat Pump out

      Positive source identification of nutrients to the lagoon using Arc Hydro GIS stream tracing and multi-stable isotope tracers for positive source identification

  • Has the EPA’s Baffle Box Solution Solved the Eutrophication Problem? Or made it worse?

  • Arc Hydro time series analysis of storm surge events

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The problem at St. Lucie:Storm Water Run-off disrupts the natural ecosytem

  • Due to increased population, deforestation, agriculture and industrialization periods of heavy rain lead to:

    • Influx of nutrients

      • Sustained algal blooms

        • Reduced dissolved oxygen concentrations- Fish Kills

        • Obstruct Sunlight - Sea Grass Beds destroyed

    • Erosion- Influx of Fine Grained Sediment

      • Sea Grass Beds and benthic fauna populations destroyed

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Part One: Nitrogen Sources to the lagoonThe riverine flux increases in direct proportion to

  • Anthropogenic Sources

    • Fertilizer

    • Atmospheric pollution

    • Nitrogen fixation by crops

    • import/ export of food and feedstocks

    • Sewage effluent

    • Riverine input of introduced vegetation

  • Natural Sources

    • In-situ N fixation (absent from most estuaries)

    • Riverine input of indigenous vegetation

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Trying to identify the SOURCE of nutrient pollution is a problem:

Phytoplankton uptake and assimilation of the N-15 enriched nitrate




Euphotic Zone




15 DON

15 NH4+

PON (original signal)

N-15 enriched PON incorporated in the sediment record

14 N2



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However, By Running an Additional Isotope on NO3-

Multi-isotope studies offer a direct means of source identification

because different sources of nitrate and PON have isotopically distinct C, N, O signatures

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Anthropogenically Introduced Sources collected for C, N, O Isotope Analysis

  • Ammonium Nitrate Fertlizer- Fast release (golf courses)

  • Ammonium Sulfate Fertilizer- Slow release (crops)

  • Cow Manure

  • Sewage Efluent (Different localities will have different signatures)

  • Boat Pump-out (Expect wide range of signatures)

  • Non-indigenous grass clippings (Kentucky Blue Grass)

  • Non-indigenous tree leaves

  • Pineapples

  • Citrus (Orange, Grapefruit, tangerine, lemon, lime)

  • Papaya

  • Winter Vegetables (tomato, peppers, eggplant)




Native plants of st lucie county to be collected for s c n o isotope analysis l.jpg

  • Botanical NameCommon Name

  • Acrostichum danaeifolium Giant Leather Fern

  • Avicennia germinans Black Mangrove

  • Baccharis halimifolia Saltbush,

  • Groundsel Batis maritima Saltwort

  • Borrichia frutescens Sea-ox-eye Daisy

  • Cassia chamaecrista Partridge Pea

  • Cocoloba uvifera Sea Grape

  • Conocarpus erectus Buttonwood Mangrove

  • Eugenia axillaris White Stopper

  • Flaveria linearis Yellow Top

  • Forestiera segregata Florida Privet

  • Helioptropium angiospermum Scorpion-tail

  • Hymenocallis latifolia Spider Lily

  • Juniperus silicicolaSouthern Red Cedar

  • Kosteletzkaya virginica Saltmarsh Mallow

  • Laguncularia racemosa White Mangrove

  • Lysinium carolinianumChristmas Berry

  • Parthenocissus quinquefolia Virginia Creeper

  • Paspalum repens Water Paspalum

  • Passiflora suberosa Corky Stem Passion Flower

  • Rapanea punctata Myrsine Rhizophora

  • MangleRed Mangrove

  • Rhus copalllina Southern Sumac

  • Sabal palmetto Cabbage Palm

  • Serenoa repens Saw Palmetto

  • Sesuvium portulacastrum Sea Purslane

  • Solidago sp. Goldenrod

  • Spartina alternaflora Spartina grass

  • Spartina bakeri Sand Cordgrass

  • Spartina patens Salt-Meadow

  • Cordgrass Verbesina virginica Frostweed

Native Plants of St. Lucie County to be collected for S, C, N, O Isotope Analysis




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1. Water Quality Sample Collection and Stream Networks:Arc Map Layers

  • Ideal sample collection sites will be chosen after completion of base map and query analysis – (base map to show idealized collection sites within proximity of most highly populated, commercialized and farmed areas and areas exhibiting highest nutrient concentrations).

  • Interactive query and trace function analysis to determine most likely point source of highest nutrient concentrations along the stream network

    • Cylindrical transverse mercator projection

    • Base map of the Indian river lagoon and stream flow data

    • Stream networks and basin (EPA River Reach Files, EPA basin files)

    • Nutrient concentrations (USGS national water information system)

    • Grid Polygons:

    • Indian River citrus industry – (Ammonium Sulfate Fertilizer)

    • Indian River golf courses – (Ammonium nitrate fertilizer)

    • Population of residential regions

    • Point Feature Classes connected on network:

    • Marina locations

    • Sewage treatment plants

    • EPA baffle box locations

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The EPA’s Solution: A Baffle Box

  • Concrete Sediment Trap

    • Designed to trap leaves, sediment and litter

    • Installed inside drainage systems along the developed shorelines

    • Baffle Box System:

      • Estimated 46,000 pounds sediment per month per box

Baffle Boxes and Drainage Canals

The gradient in St. Lucie is from SL - 85 feet above SL

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Why I think this is a BIG problem rather than a Solution:


Baffle Box





Estuary and Coast

INCREASED Primary Productivity

DECREASED Sedimentation Rate

DECREASED oxygen concentration



 Surface Area =  Bacterial Colonization

 Oxygen =  Nitrification

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2. Arc HydroTime Series Events

  • Three separate time series events will be modeled of suspended sediment, nutrient and oxygen concentrations through the stream network to the lagoon during:

    • Dry Season

    • Storm surge event prior top the EPA’s implementation of the baffle box

    • Storm surge event following the EPA’s implementation of the baffle box

  • Results from the three models will be queried and an analysis of the effectiveness of the EPA baffle box will be assessed regarding turbidity (fine grained sediment) and nutrient concentrations

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  • Federally Endangered Species

  • American Alligator

  • Atlantic Hawksbill Turtle

  • Atlantic Green Sea Turtle

  • Eastern Indigo Snake

  • Leatherback Sea Turtle

  • Loggerhead Sea Turtle

  • Short Nosed Sturgeon

  • West India Manatee

  • Southeastern Beach Mouse

  • Bachman’s Warbler

  • Bald Eagle

  • Florida Scrub Jay

  • Kirtland’s Warbler

  • Peregrine Falcon

  • Piping Plover

  • Red Woodpecker

  • Roseate Tern

  • Snail Kite

  • Wood Stork

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Interpreting the Bulk Sediment Record : Additional Information from C/N and 13C and 15N isotopes

Milder, Montoya, Altabet (1999)

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Core and POM/DOM/DIN/ Grab Sample STATION

Core/ Grab Sample Station


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Interpreting the C and N Isotope Record

Kao and Liu (2000)

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The Determination and Relation Between Nitrate Concentrations in Rivers and the Marine Environment

  • How much nitrate or PON was introduced from a particular source is complicated by:

    • The occurrence of multiple possible sources of nitrate and PON

    • Overlapping N isotopic composition between point and non-point sources

    • Co-existence of biogeochemical processes that alter the stable isotopic signature and concentrations of nitrate which is then incorporated into PON

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Sumultaneous Equations

  • δ15N = δ15N (Fertilizer) + δ15N (manure) + δ15N (sewage) + δ15N (boat pump out) + δ15N (grass-indig) + δ15N (grass-intro) + δ15N (mangrove) + δ15N (tree-intro) + δ15N (N fix crop)

  • 13C = 13C (Fertilizer) + 13C (manure) + 13C (sewage) + 13C (boat pump out) + 13C (grass-indig) + 13C (grass-intro) + 13C (mangrove) + 13C (tree-intro) + 13C (N fix crop)

  • 18O = 18O (Fertilizer) + 18O (manure) + 18O (sewage) + 18O (boat pump out) + 18O (grass-indig) + 18O (grass-intro) + 18O (mangrove) + 18O (tree-intro) + 18O (N fix crop)

  • 1 = δ15N (Fertilizer) + δ15N (manure) + δ15N (sewage) + δ15N (boat pump out) + δ15N (grass-indig) + δ15N (grass-intro) + δ15N (mangrove) + δ15N (tree-intro) + δ15N (N fix crop)




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Collection of water Samplesfor Isotopic Analysis

  • Samples biologically labile- filter immeadiately 0.1 u filter - refrigerate

  • Ammonium: “Micro-diffusion method”

    • NH4 is slowly diffused into an acid solution to produce ammonium sulfate and then combucted to form N2 gas for the MS

  • Nitrate: “Kjeldahl Reaction”

    • Distill off existing ammonium- reduce nitrate to ammonium

  • Nitrate 18O: Farquhar Method

    • NO3--> KNO3

    • Combust with Hg(CN)2 --> CO2 gas for the MS

  • DON (Amino Acids and Phenols) “Feuerstein Method”

    • Freeze Dry, ion chrmoatography, rotovap, dialysis through resins

  • Filtered Fraction: POM

    • Pre-combusted glass fiber filter (GF/F)

    • Combust to N2 --> MS

    • Can also be analyzed for C, O, S isotopes

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  • Pre-1565 horizons in sediment cores will provide an isotopic baseline that reflects natural sources of nitrogen

  • Post 1565 to present horizons will show

    • an increase in anthropogenically introduced nitrogen (manure, sewage and fertlizer)

    • an increase in sedimentation rate

    • a bimodal sedimentation pattern (fine and coarse grained)

    • An increase in terrestrial vegetation run-off

    • significant decrease in indigenous vegetation

    • a spatial increase in denitrification (due to eutrophism)

  • Post 1990 (Baffle Box)

    • Decreased sedimentation rate

    • Decreased terrestrial derived PON

    • An increase in marine PON deposition laterally

    • Increased denitrification laterally

  • IF The EPA baffle box HAS been successful- it will be possible to differentiate between St. Lucie Canal fertilizers (Citrus Industry) and fertilizers introduced by the general public

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How the Baffle Box Works

  • Storm-Water is forced through:

    • A : Oil collection booms

    • B: Sediment falls through grills

    • C: Sediment is retained behind baffles

    • D: Deflectors help maintain sediment despite water flow through

    • F: (not shown) over-flow bypass area

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  • OK… So why THREE isotopes?????????

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Rayleigh FractionationAssume: Products are removed from the Reactants

Denitrification Reactant

Denitrification Product

Kendall and McDonnel, 1998

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The Nitrogen Cycle: Can’t Assume the Products have been removed:Associated Isotopic Fractionations

Capone, 2000

Interpretation is complicated because of multiple cycles

Most fractionation occurs during the “rate determining step”

* Large reservoir

Little or No fractionation Occurs

* Small Reservoir

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Interpreting the 13C Record

  • - Two source model

    • A.) Sample has an intermediate composition

    • B.) Correction Factors Applied: Metabollic Processes have changed the isotopic composition of the sample

  • Three Source Model- Need for an additional Isotope

    • C.) Is sample a mixture of two components or the result of only one component?

Fry and Sher, 1984

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In Regions where it is likely that Denitrification has Occurred

A= Fertilizer

B= Manure

  • The Effects of Mixing can be distinguished from the effects of denitrification

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Under idealized conditions, it is possible to tell NO3- generated

from fertilizer versus sewage

But in most situations

there are Source- Overlap Identification Problems………

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