This stock and flow diagram is a working draft of a conceptual model of a dune-lake system in the Northland region of New Zealand.

This stock and flow diagram is a working draft of a conceptual model of a dune-lake system in the Northland region of New Zealand.

Interactions between wolves and livestock depending on abundance
Interactions between wolves and livestock depending on abundance
Examining the population growth of a species and how reproductive technology influences its population as an endangered species.
Examining the population growth of a species and how reproductive technology influences its population as an endangered species.
Just recently, there was a huge problem that ended about C8, a deadly chemical, that was poured into lakes and rivers by DuPont, a company that sold nylon. This chemical caused a huge consensus, many birth defects, and cows with green insides spraying blood from many places.
Just recently, there was a huge problem that ended about C8, a deadly chemical, that was poured into lakes and rivers by DuPont, a company that sold nylon. This chemical caused a huge consensus, many birth defects, and cows with green insides spraying blood from many places.
Primitives for Watershed modeling project. Click Clone Insight at the top right to make a copy that you can edit.  The converter in this file contains precipitation for Phoenix only.
Primitives for Watershed modeling project. Click Clone Insight at the top right to make a copy that you can edit.

The converter in this file contains precipitation for Phoenix only.
Simple mass balance model for lakes based on the Vollenweider equation:  dMw/dt = Min - sMw + pMs - Mout  The model was first used in the 1960s to determine the phosphorus concentration in lakes and reservoirs for eutrophication assessment.  This version considers mercury, and adds diagenesis, using
Simple mass balance model for lakes based on the Vollenweider equation:

dMw/dt = Min - sMw + pMs - Mout

The model was first used in the 1960s to determine the phosphorus concentration in lakes and reservoirs for eutrophication assessment.

This version considers mercury, and adds diagenesis, using an extra state variable (mercury in the sediment), and incorporates desorption processes that release mercury trapped in the sediment back to the water column.

The temporal dynamics of the model simulate the typical development of pollution in time.

1. Low loading, low Hg concentration in lake
2. High loading, increasing Hg concentration in lake
3. Desorption rate is low, Hg in sediment increases
4. Measures implemented for source control, loading reduces
5. Hg in lake gradually decreases, but below a certain point, desorption increases, and lake Hg concentration does not improve
6. Recovery only occurs when the secondary load in the sediment is strongly reduced.
 From Jay Forrester 1971 Book  World Dynamics , the earlier, simpler version of the  World 3   Limits to Growth  Model. adapted from Mark Heffernan's ithink version at  Systemswiki .  An element of Perspectives: The Foundation of Understanding and Insights for Effective Action. Register at  http://w

From Jay Forrester 1971 Book World Dynamics, the earlier, simpler version of the World 3 Limits to Growth Model. adapted from Mark Heffernan's ithink version at Systemswiki.

An element of Perspectives: The Foundation of Understanding and Insights for Effective Action. Register at http://www.systemswiki.org/

32 6 months ago
This model depicts a very simplified series of interactions between water quality inspectors and cannabis cultivators in northern California.
This model depicts a very simplified series of interactions between water quality inspectors and cannabis cultivators in northern California.
M.Sc. in Environmental Engineering SIMA 2018 New University of Lisbon, Portugal   Model to represent oyster individual growth by simulating feeding and metabolism. Model (i) partitions metabolic costs into feeding and fasting catabolism; (ii) adds allometry to clearance rate; (iii) adds temperature
M.Sc. in Environmental Engineering SIMA 2018
New University of Lisbon, Portugal

 Model to represent oyster individual growth by simulating feeding and metabolism. Model (i) partitions metabolic costs into feeding and fasting catabolism; (ii) adds allometry to clearance rate; (iii) adds temperature dependence to clearance rate; (iv) illustrates how coupled model requires a substantial volume of water (a single oyster typically clears 20-30 m3 of water in one growth cycle)
This diagram provides a stylised description of important feedbacks within a shallow-lake system.     Mahinga Kai
This diagram provides a stylised description of important feedbacks within a shallow-lake system.
Mahinga Kai
Clone of Pesticide Use in Central America for Lab work        This model is an attempt to simulate what is commonly referred to as the “pesticide treadmill” in agriculture and how it played out in the cotton industry in Central America after the Second World War until around the 1990s.     The cotto
Clone of Pesticide Use in Central America for Lab work


This model is an attempt to simulate what is commonly referred to as the “pesticide treadmill” in agriculture and how it played out in the cotton industry in Central America after the Second World War until around the 1990s.

The cotton industry expanded dramatically in Central America after WW2, increasing from 20,000 hectares to 463,000 in the late 1970s. This expansion was accompanied by a huge increase in industrial pesticide application which would eventually become the downfall of the industry.

The primary pest for cotton production, bol weevil, became increasingly resistant to chemical pesticides as they were applied each year. The application of pesticides also caused new pests to appear, such as leafworms, cotton aphids and whitefly, which in turn further fuelled increased application of pesticides. 

The treadmill resulted in massive increases in pesticide applications: in the early years they were only applied a few times per season, but this application rose to up to 40 applications per season by the 1970s; accounting for over 50% of the costs of production in some regions. 

The skyrocketing costs associated with increasing pesticide use were one of the key factors that led to the dramatic decline of the cotton industry in Central America: decreasing from its peak in the 1970s to less than 100,000 hectares in the 1990s. “In its wake, economic ruin and environmental devastation were left” as once thriving towns became ghost towns, and once fertile soils were wasted, eroded and abandoned (Lappe, 1998). 

Sources: Douglas L. Murray (1994), Cultivating Crisis: The Human Cost of Pesticides in Latin America, pp35-41; Francis Moore Lappe et al (1998), World Hunger: 12 Myths, 2nd Edition, pp54-55.

Here is an average representation of Earth today. Enjoy!
Here is an average representation of Earth today. Enjoy!
Modeling the change in concentration of O2 in a lake with a continuous loading of BOD, modeled as a CSTR
Modeling the change in concentration of O2 in a lake with a continuous loading of BOD, modeled as a CSTR
 for more information, contact Dr. Ann Stapleton at: stapletona@uncw.edu     Description:    A simple model for breeding plants from generation to generation, with one "yield" variable (e.g. height) and 4 combinations of plants from the parents. Simulation tracks the frequencies of each combination
for more information, contact Dr. Ann Stapleton at: stapletona@uncw.edu

Description:

A simple model for breeding plants from generation to generation, with one "yield" variable (e.g. height) and 4 combinations of plants from the parents. Simulation tracks the frequencies of each combination in each generation as well as the overall average height by generation.

Adjust all sliders before beginning simulation. Make sure the A1A2 parameters are equal to the A2A1 parameters.
Simple model to illustrate Michaelis-Menten equation for nutrient uptake by phytoplankton.  The equation is:  P = Ppot S / (Ks + S)  Where:  P: Nutrient-limited production (e.g. d-1, or mg C m-2 d-1) Ppot: Potential production (same units as P) S: Nutrient concentation (e.g. umol N L-1) Ks: Half sat
Simple model to illustrate Michaelis-Menten equation for nutrient uptake by phytoplankton.

The equation is:

P = Ppot S / (Ks + S)

Where:

P: Nutrient-limited production (e.g. d-1, or mg C m-2 d-1)
Ppot: Potential production (same units as P)
S: Nutrient concentation (e.g. umol N L-1)
Ks: Half saturation constant for nutrient (same units as S)

The model contains no state variables, just illustrates the rate of production, by making the value of S equal to the timestep (in days). Move the slider to the left for more pronounced hyperbolic response, to the right for linear response.
This diagram provides a stylised description of important feedbacks within a shallow-lake system.
This diagram provides a stylised description of important feedbacks within a shallow-lake system.

This model uses simple functions (converters, cosine) to simulate the water balance inside a reservoir.
This model uses simple functions (converters, cosine) to simulate the water balance inside a reservoir.
This model describes the flow of energy from generation to consumption for neighborhoods in the metro Atlanta area. It also calculates the cost of energy production and the number of years it will take to recover that cost.
This model describes the flow of energy from generation to consumption for neighborhoods in the metro Atlanta area. It also calculates the cost of energy production and the number of years it will take to recover that cost.