Skip to main content

Some review on the fate of dissolved organic carbon in terrestrial ecosystem

My recent modeling work involves some rewind of the process happened near the land surface, which causes some issue to the estimate of dissolved organic carbon (DOC) dynamics in terrestrial ecosystem.

I will skip the importance of DOC because you can find plenty of literatures online but instead I will focus on the challenge from a modeler's perspective.

First, we need to understand the source of DOC. Generally we think DOC is produced due to decomposition process and water flux. As we know, microbial decomposition occurs within nearly all places within the ecosystem: litter, soil and aquatic systems, etc. But water may not be present all the times in some ecosystem components.

In litter, decomposition is a continuous process through which fresh vegetation is transferred into organic carbon and enter into soil. However, a portion of the organic carbon may be transported through water flux in form of DOC during snowmelt, runoff and surface leaching. In this case, it is almost certain that the amount of DOC is influenced by not only the stage of decomposition, but also the amount of water flow.

As DOC flows into soil layer, it becomes part of soil DOC dynamics. Unlike litter, both decomposition and water flux are nearly always present even though the magnitude may be different.

When DOC enters into aquatic ecosystems (stream and lake, etc.), it may be consumed by the living organism within the systems. Also DOC may be directly produced within aquatic ecosystems.

Let's now consider the water movement, because of the hydrologic processes, DOC flows within the whole system. In each area, DOC is produced and consumed by various microbial activities. At the same time, there will be DOC flow in/out the domain (surface runoff, subsurface runoff, groundwater movement and surface leaching).

Taking all the above into consideration, DOC dynamics is each domain is a complex system (mixing of various concentration, microbial activity, biochemistry, etc.). As a result, modeling the fate of DOC dynamics in soil is difficult.

To tackle the difficulty, there are several steps we must take. First, we need to simulate the hydrological process with confidence; Second, we need to simulate all the flux of DOC within a domain (grid cell, etc.). Third, we need to simulate the DOC solute transport.

I will demonstrate how we did it in my future post.


Popular posts from this blog

Spatial datasets operations: mask raster using region of interest

Climate change related studies usually involve spatial datasets extraction from a larger domain.
In this article, I will briefly discuss some potential issues and solutions.

In the most common scenario, we need to extract a raster file using a polygon based shapefile. And I will focus as an example.

In a typical desktop application such as ArcMap or ENVI, this is usually done with a tool called clip or extract using mask or ROI.

Before any analysis can be done, it is the best practice to project all datasets into the same projection.

If you are lucky enough, you may find that the polygon you will use actually matches up with the raster grid perfectly. But it rarely happens unless you created the shapefile using "fishnet" or other approaches.

What if luck is not with you? The algorithm within these tool usually will make the best estimate of the value based on the location. The nearest re-sample, but not limited to, will be used to calculate the value. But what about the outp…

Numerical simulation: ode/pde solver and spin-up

For Earth Science model development, I inevitably have to deal with ODE and PDE equations. I also have come across some discussion related to this topic, i.e.,

In an attempt to answer this question, as well as redefine the problem I am dealing with, I decided to organize some materials to illustrate our current state on this topic.

Models are essentially equations. In Earth Science, these equations are usually ODE or PDE. So I want to discuss this from a mathematical perspective.

Ideally, we want to solve these ODE/PDE with initial condition (IC) and boundary condition (BC) using various numerical methods.

Because of the nature of geology, everything is similar to its neighbors. So we can construct a system of equations which may have multiple equation for each single grid cell. Now we have an array of equation…

Watershed Delineation On A Hexagonal Mesh Grid: Part A

One of our recent publications is "Watershed Delineation On A Hexagonal Mesh Grid" published on Environmental Modeling and Software (link).
Here I want to provide some behind the scene details of this study.

(The figures are high resolution, you might need to zoom in to view.)

First, I'd like to introduce the motivation of this work. Many of us including me have done lots of watershed/catchment hydrology modeling. For example, one of my recent publications is a three-dimensional carbon-water cycle modeling work (link), which uses lots of watershed hydrology algorithms.
In principle, watershed hydrology should be applied to large spatial domain, even global scale. But why no one is doing it?  I will use the popular USDA SWAT model as an example. Why no one is setting up a SWAT model globally? 
There are several reasons we cannot use SWAT at global scale: We cannot produce a global DEM with a desired map projection. SWAT model relies on stream network, which depends on DEM.…