Large scale nutrient, wetland vegetation and

morphodynamic modeling of the lower Mississippi

Delta and surrounding receiving basins PART 2

Ehab Meselhe and Johannes Smits

November 2014

Contents

• The modeling framework

• Wetland vegetation sub-model

• Present models, preliminary results

• Work to come

The modeling framework: Delft3D 4

Delft3D-FLOW,

SED-ONLINE Delft3D-WAQ LAVegMod

Delft3D-FLOW for transport, salinity, temperature, silt, clay and sand

Delft3D-WAQ for silt, nutrients, phytoplankton, detritus, oxygen, vegetation biomass

LAVegMod (ULL) for vegetation types (dominant species) distribution

grid, bathymetry,

flow, temperature

flow resistance

depth, salinity,

temperature,

nutrients (?)

veg. distribution

BIOMASS above/belowground

distribution

distribution

function

Delft3D-WAQ modules “layered sediment’

Processes in Delft3D-WAQ

o If water is below residual depth water quality processes except reaeration are

stopped, whereas sediment diagenesis and vegetation processes continue

o Sediment bed in open water and soil bed in wetland have the same processes

Delft3D-WAQ, processes

LAVegMod (Duke-Sylvester & Visser, ULL)

LAVegMod habitat conditions

LAVegMod for Barataria - Breton sound

Focus on 7 taxa

• Spartina alterniflora (oyster grass)

• Spartina patens (wiregrass)

• Sagittaria latifolia (arrowhead)

• Sagittaria lancifolia (bulltongue)

• Zizaniopsis miliacea (cutgrass)

• Typha spp. (cattail)

• Phragmites spp. (common reed)

Submerged Aquatic Vegetation (SAV)

• Use Delft3D-WAQ module to simulate total

biomass

• Aim to quantify nutrient store, flow resistance and

enhanced settling

VEGMOD in Delft3D-WAQ

2 of 5 biomass compartments are used for herbaceous wetland vegetation

VEGMOD, starting points for extension

• All species are in all grid cells with small biomass, but only those will

grow that are predicted by LAVegMod

• Vegetation types distribution is fixed as delivered by LAVegMod

• Biomass develops seasonally towards target biomasses (input)

• Growth is limited by available nutrients

• Mortality for scenescence, herbivory and inundation

• Nutrient (N,P,S) uptake and detritus production as in present

VEGMOD (allocated to layers)

VEGMOD extension, growth

Mass balance:

Initial biomass:

Growth rate:

Biomass incr. ≤ BMt: 𝐵𝑀𝑢𝑛𝑙 ,𝑖 = 𝐵𝑀𝑎𝑐𝑡 ,𝑖 ∗ 1 + 𝐺𝑎𝑐𝑡 ,𝑖 ∗ ∆𝑡

- Ratios of aboveground and belowground biomasses are calculated on

the basis of nutrient availability

- Ratios are determined from a look-up table or function from biomass

allocation model (ULL)

- Changing ratios require “correction” nutrient uptake fluxes due to

different nutrient content of aboveground and belowground biomasses

𝑅𝑔𝑟 𝑖 = 𝐵𝑀𝑙𝑖𝑚 ,𝑖 − 𝐵𝑀𝑎𝑐𝑡 ,𝑖

∆𝑡

VEGMOD extension, mortality

Biomass decr.:

Mortality rate:

𝐵𝑀𝑚𝑜𝑟 ,𝑖 = 𝐵𝑀𝑎𝑐𝑡 ,𝑖 × 1 − 𝑀𝑠𝑖 × ∆𝑡−𝑀𝑖𝑖 × ∆𝑡 −𝑀𝑔𝑟𝑖

𝑅𝑚 𝑖 = 𝐵𝑀𝑚𝑜𝑟 ,𝑖 − 𝐵𝑀𝑎𝑐𝑡 ,𝑖

∆𝑡

Multi-domain models

Tentative 2D test models

(7 layers)

Why aggregation? o Horizontal gradients of WQ substances in water and

sediment are relatively small compared to hydrodynamics

o Reduces computational time

Tentative results salinity

Work to come

• Implementation of new VEGMOD and the SAV module in Delft3D-WAQ

• Modification of BLOOM input

• Formulation/implementation of flow resistance output

Delft3D-WAQ-LAVegMod

• Step-wise calibration Delft3D-FLOW in combination with SED-ONLINE

and Delft3D-WAQ

• Prediction of wetland accretion, vegetation and eutrophication according

to scenarios on the timescale of decades