New Approaches to Watershed Modelling Using STELLA® · Modelling in Complex Systems in STELLA®...

New Approaches to Watershed Modelling Using STELLA®

WeSMART Conference, December 11, 2014

Heather Cray & Michael McTavish

Ecosystem Modelling

What are models and ecosystem models? • Broadly, a model is a tool used to represent some feature of a larger, more complex system

to help us better understand that system

• An ecosystem model generally studies the complex interactions between the biotic and abiotic features of ecological systems

• Generally interested in the movement of material and energy through the system (e.g. water, nutrients, organisms, etc.)

Modelling in Complex Systems in STELLA®

This model was constructed using STELLA® (V.10.0.4) from isee systems. • “Modeling and Simulation Software for

Education and Research”

• A tool for understanding systems dynamics (a methodology and modelling approach for exploring complex systems)

• Users construct models through a visual interface (equation layer generated automatically)

The visual layer of a STELLA® model consists of 3 main elements:

Stocks: state variables representing reservoirs of material, energy, populations, etc. Flows: movements between stocks Converters: auxiliary variables representing algebraic relationships, additional parameters, constants, etc., which typically modify how stocks/flows interact


Information that we possess:

• Initial population size

• Estimated birth rate individual-1

• Estimated survivorship/death rate


An example of a simple population model constructed in STELLA® using stocks, flows, and converters…

Information that we possess:

• Initial population size

• Estimated birth rate individual-1

• Estimated survivorship/death rate

Population(t) = Population(t - dt) + (Births -

Deaths) * dt

INIT Population = 50

INFLOWS:

Births = Population*Birth_Rate

OUTFLOWS:

Deaths = Population*Death_Rate

Birth_Rate = 0.3

Death_Rate = 0.2





With sufficient data, future conditions can be (cautiously) extrapolated through time.

(In this example we follow the growth of an initial population N0 = 50 through 20 years)

The Pine River Watershed

• Located in Southern Ontario along the eastern shore of Lake Huron in Bruce County • Sub-watershed of the Lake Huron Basin

• 160 km2 of mixed land cover dominated by agriculture with smaller areas of forest,

wetlands, and urban infrastructure

The Pine River Watershed – Land Use

• Historically over 90% forest cover consisting of mixed upland stands

• Current forest cover is below 5%

• Soil is primarily till with a few bands of sandy deposits

• Due to its high agricultural productivity, much of the land has been cleared of wetlands and forests and remaining woodlots are fragmented

Overall Model Structure

When asked to construct an ecosystem model for the Pine River Watershed, we went looking for existing environmental data…


…decades of monitoring data exist for the Pine River Watershed, mostly in disconnected datasets.

Soils

Urbanization

Riparian Cover

Nutrient Loading

Biodiversity

Invasive Species

Wetlands

Forest Cover

Drainage

Habitat

When asked to construct an ecosystem model for the Pine River Watershed, we went looking for existing environmental data…

Etc.

Etc.

Etc.


We selected key parameters of interests and organized them into connected Modules (model components which can run independently or jointly with other modules):

“Background Modules” provide user-controlled inputs which modify the behaviour of the “Primary Modules”.


The Calendar Module tracks the progression of months (the basic time step for the model) and is used to cue seasonally-specific events.

Modules Month

Counter Month Hydrology

Turkey Demographics

Deer Demographics

1 January Precipitation; Evapotranspiration;

Stream Discharge - -

2 February Precipitation; Evapotranspiration;


3 March Precipitation; Evapotranspiration;


4 April Precipitation; Evapotranspiration;

Stream Discharge Nest Initiation -

5 May Precipitation; Evapotranspiration;

Stream Discharge Spring Hunting -

6 June Precipitation; Evapotranspiration;


7 July Precipitation; Evapotranspiration;


8 August Precipitation; Evapotranspiration;


9 September Precipitation; Evapotranspiration;


10 October Precipitation; Evapotranspiration;

Stream Discharge Fall Hunting -

11 November Precipitation; Evapotranspiration;

Stream Discharge -

Breeding; Hunting Season A

12 December Precipitation; Evapotranspiration;

Stream Discharge - Hunting Season B

Land Use Module

• Land use change and habitat loss have been identified as leading threats to biodiversity and sustainability within the Pine River Watershed

• Different land classes have various consequences for animal habitat, hydrology, etc. • Wetlands • Impervious surfaces • Cropland vs pasture (erosion, fertilizer, pesticide…)

• 5 classes used: Wetland, Woodland, Urbanized, Cropland,

and Pasture

Land Use Module

The Land Use Module provides the breakdown of all land within the modelled area across 5 land use classes.

Land class areas were calculated for current conditions but can be modified by: 1) setting new fixed values; or 2) setting fixed rates of land use change between classes

(e.g. 2% “cropland” to “urbanized” per year).

Land Use Module

• Where do we find data? • Stats Canada agricultural census • Spatial analysis of satellite imagery • Local studies and reports

• How is this useful?

1. Set stocks to current state of land cover 2. Simulate change by increasing or decreasing proportions 3. Use the land use module to provide input into hydrology and population

• Other modules respond dynamically to changes in land use

Hydrology Module

• Models the hydrology of the Pine River Watershed, as well as the total phosphorus exported into Lake Huron at the Pine River outflow

• Calculates runoff, precipitation, evaporation, transpiration, subsurface flow, and river discharge into Lake Huron

• As each land use will have different effects on how precipitation moves through the watershed, Land Use proportions inform the runoff calculations

• The Hydrology module is subdivided into five subsystems:

1. Precipitation (Environment Canada data) 2. Evapotranspiration (nearby weather station) 3. Runoff 4. Subsurface Flow 5. River Flow

Hydrology Module - Runoff

Runoff

• Runoff was calculated for each Land Use soil type based on surficial geology and vegetation cover Runoff curve value

• Runoff term used for Subsurface Flow and River Flow subsystems

Hydrology Module – Flow and discharge

Flow and discharge

For the purposes of this model, we have assumed that runoff associated with agricultural land use and fertilizer addition is the primary source of phosphorous loading into the watershed

Hydrology Module – Customization

1. Evaluating habitat suitability for benthic and fish communities • By including a more spatially-correlated dataset to represent the waterways (i.e.

tributary versus main channel, water depths and widths, substrate, water temperature, velocity)

• This could be within habitat brackets (high : low quality) or for particular target species, such as trout or bass

2. Total Suspended Solids (TSS) in the water column based on the velocity and volume of water at peak flood periods • Would require estimates of surface runoff which are spatially correlated to particular

crop types and periods of fallow versus exposed soil

3. Potential Erosion based on topographic and slope variables, water velocity and volume, presence/absence/quality of riparian vegetation, and livestock access to stream • Estimate topsoil loss and facilitate modelling various management schemes, including

ongoing and potential riparian restoration options

4. E. coli and waste treatment options • Point sources and mitigation options for the management of E. coli could be

incorporated into the model using bacteria life cycle data and current/future manure and fertilizer regimes

Demographics Modules

Two of the Primary Modules are demographic models for two species of interest within the watershed:

Eastern Wild Turkey (Meleagris gallopavo silvestris)

White-Tailed Deer (Odocoileus virginiana)

Both modules are designed to provide insight into how human activities (land use change & hunting) impact animal populations.

Demographics Modules

Population model for Pine River Watershed White-Tailed Deer

Demographics Modules – Eastern Wild Turkey

• 3 age classes (poult subadult adult)

• Primary flows: birth, maturation, death (hunting & natural)

• Details such as maturation rates, sex ratio, clutch size, habitat requirement, mortality rates, etc., can be set manually or modelled from existing datasets

An age- and sex-structured demographic model for the eastern wild turkey

• Approximate carrying capacity estimated based on habitat requirements and land use

• Spring and fall hunting seasons contribute differently according to age class and sex (based on available harvest records)

• Model users may manipulate numbers of hunters, licenses, etc.

• Easily adapted to different species of interest (e.g. fish and fishing regulations)

Demographics Modules – Eastern Wild Turkey

Structure & Function

Prediction & Sensitivity

What can we do with an ecosystem model?

Applications of Ecosystem Modelling



Identify Key Features






Identify Missing Features








Identify Missing Features

Interactions & Connectivity

Conclusions

Ecological Monitoring… What does ecosystem modelling have to offer?

Conclusions


• Improve understanding of ecosystem structure & function

Conclusions



• Organize and categorize existing data

Conclusions




• Identify gaps in data

Conclusions





• Identify connectivity between elements

Conclusions





• Identify connectivity between elements

• Visual representation of a complex system

New Approaches to Watershed Modelling Using STELLA® · Modelling in Complex Systems in STELLA®...

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