General Overview of GLEAMS
Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) is a continuous simulation, field scale model, which was developed as an extension of the Chemicals, Runoff and Erosion from Agricultural Management Systems (CREAMS) model. GLEAMS assumes that a field has homogeneous land use, soils, and precipitation. It consists of four major components: hydrology, erosion/sediment yield, pesticide transport, and nutrients. GLEAMS was developed to evaluate the impact of management practices on potential pesticide and nutrient leaching within, through, and below the root zone. It also estimates surface runoff and sediment losses from the field. GLEAMS was not developed as an absolute predictor of pollutant loading. It is a tool for comparative analysis of complex pesticide chemistry, soil properties, and climate. GLEAMS can be used to assess the effect of farm level management decisions on water quality.
GLEAMS can provide estimates of the impact management systems, such as planting dates, cropping systems, irrigation scheduling, and tillage operations, have on the potential for chemical movement. Application rates, methods, and timing can be altered to account for these systems and to reduce the possibility of root zone leaching. The model also accounts for varying soils and weather in determining leaching potential. GLEAMS can also be useful in long-term simulations for pesticide screening of soil/management. The model tracks movement of pesticides with percolated water, runoff, and sediment. Upward movement of pesticides and plant uptake are simulated with evaporation and transpiration. Degradation into metabolites is also simulated for compounds that have potentially toxic bi-products. Erosion in overland flow areas is estimated using a modified Universal Soil Loss Equation. Erosion in chemicals and deposition in temporary impoundments such as tile outlet terraces are used to determine sediment yield at the edge of the field.
Some of the features of GLEAMS include:
GLEAMS Publications and Abstracts
automatic irrigation, manual irrigation, and chemigation options
a comprehensive erosion/sediment yield component, allowing the user to describe in detail the topographic features of the field
all channels in the field are assumed to be naturally eroded
the evapotranspiration and canopy interception modules allow simulation of management alternatives in forested area
GLEAMS V3.0 Revisions
Revisions made in V3.0 include:
Forest update: annual leaf drop added to residue
Corrected metric crop height in hydrology parameters
Y2K compliance
simulation of up to 366 pesticides simultaneously
a 2-compartment pesticide degradation component
an increased pesticide database in the pesticide parameter editor
removal of all biomass in the top 1 cm of soil with sod harvest
reduced rainfall energy in northern and southern latitudes
input of metric solar radiation
Y2K compliance
GLEAMS Y2K Update
These programs have been placed here for use of the scientific community; however, no technical support as to use or application can be offered.
GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) was developed to simulate edge-of-field and bottom-of-root-zone loadings of water, sediment, pesticides, and plant nutrients from the complex climate-soil-management interactions. It has evolved through several versions from its inception in 1984 to the present 3.0 version, and has been evaluated in numerous climatic and soil regions of the world. Special studies have resulted in model modifications, and oftentimes the improvements in comprehension resulted in new version releases.
GLEAMS has been revised for year 2000 compliance. It has long been recognized that GLEAMS was not Y2K compliant in that it utilized a 2-digit year and considered leap year every 4 years irrespective of century. Model users requested that the model be made Y2K compliant in order to maintain it's utility beyond 1999. Some additional features had evolved since the release of version 2.10 in 1993. It was decided to incorporate these features and the Y2K revisions into a new version, V3.0.
Technical documentation is available in the user manual.
Change Log:
May 16, 2007
- Soil moisture adjustment constant for nitrification for soil water greater than field capacity. (WGK)
April 27, 2007
- Adjusted soil moisture dissipation constant for pesticide degradation. (WGK)
October 18, 2005
- The calculation of the soil ammonification rate constant was corrected to give a proper nitrogen balance. (WGK)
October 4, 2005
- Precipitation total and nitrogen in precipitation was not printed properly in the plant nutrient output summary. (WGK)
July 26, 2004
- Final soil water was not printed in annual hydrology summary when simulating with metric input units. (WGK)
June 30, 2004
- Soil water adjustment from chemigation/fertigation was not added to the computational layer. (FMD)
June 15, 2004
- The hydrology editor did not convert radiation from English to metric units during import from the climate data base when the metric flag was set. (FMD)
July 18, 2003
- Frozen soil counter decremented only on days of effective rainfall. Consequently, long after soil thaw, model overpredicted runoff and pesticide runoff loss. Frozen soil counter now depends on temperature. (FMD)
Contacts/Links:
Dr. Arlin Nicks climate database is also available at the ARS Hydrology Lab:
http://hydrolab.arsusda.gov/nicks/nicks.htm
Programming modifications to accommodate proper leap-year testing were made, in accordance with recommended procedure, and tested to make sure that years and centuries resulted in leap years. Since some model users may have many parameter files that would require needless change to 4-digit year input, the programming was modified to read those files without changes. This was done by assuming simulation beginning in 19XX since climatic data are not yet available for the year 2000 and beyond. Therefore, NO CHANGES ARE NEEDED IN EXISTING PARAMETER FILES TO RUN THE GLEAMS MODEL VERSION 3.0. However, users CANNOT edit existing parameter files with the presently available parameter editors without making the conversion to 4-digit years.
Modifications of the model are such that running existing parameter files will result in the appropriate 7-digit year/day in daily output. That is, an old file parameter HBDATE of 73001 will result in storm output date 1973001 if there is rainfall on January 1, 1973. This applies to all components.
Increased Number of Pesticides to Simulate Simultaneously
The number and size of arrays in GLEAMS increased, and some special modifications evolved over time that required special considerations for compiling, such as with OS2 Fortran Compiler, Microsoft Fortran Compiler for Windows 3.1 or Windows NT. These executable files could be transported to other DOS-based P/Cs or operating systems. One such special feature was a modification to run up to 366 pesticides simultaneously for pesticide screening instead of the nominally maximum of 10. Such changes can be accommodated by compilation with Microsoft Developer Studio, a 32-bit Fortran compiler for Windows 95, Windows 98, or Windows NT. It is assumed that all current GLEAMS users have P/Cs with Windows 95, Windows 98, or Windows NT systems. Thus, the available executable program, GLEAMS30.EXE will not run on DOS-based computers. It will operate efficiently under the DOS-Prompt in the Windows-based P/Cs. Those users who want to make changes in the source code made available MUST have a 32-bit Windows-based compiler in order to not exceed storage limitations.
2-Compartment Pesticide Degradation Component
A 2-compartment pesticide degradation component was developed for GLEAMS. It better describe the degradation process of those compounds that have a rapid initial degradation but slows considerably in the latter stages. Use of the component requires flow rates between the two compartments which are known for only a few pesticides. It results in continued pesticide runoff and leaching whereas the usual first-order process shows no compound remaining. The pesticide parameter editor includes input capability for those rates. If they are left blank by GLEAMS users, it defaults to the usual first-order process. The feature is incorporated in version 3.0 mainly as a research tool.
Increased Pesticide Database in the Pesticide Parameter Editor
In the earlier version of GLEAMS, there were 243 pesticides built into the pesticide database (parameter editor). Those were from the ARS-NRCS-EXT database. An additional 93 compounds from the Hornsby, Wauchope, and Herner publication (Hornsby, A.G., R.D. Wauchope, and A.E. Herner. 1995. Pesticide Properties in the Environment. Springer-Verlag,
New York. 217 pp.) Foliar characteristics were added in accordance with the procedures by Willis and McDowell (see references in GLEAMS 2.1 publication). The complete list of compounds and their properties are given in an Excel table available herewith.
Removal of all Biomass in the Top 1-cm of Soil with Sod Harvest
At the request of Dr. A. B. Bottcher, Soil & Water Engineering Technology, Inc., Gainesville, Florida, GLEAMS 2.10 was modified to remove all biomass (residue on the surface and roots) as well as any nutrient pools to represent sod harvest on turf farms. Since this is becomming an increasingly common practice, the feature is incorporated in this version 3.0. If the model user sets the dry matter ratio, DMY in the plant nutrient component, to 100.0, it signals the model to remove the biomass on harvest date. It shows up in the output as a harvest and removal.
Reduced Rainfall Energy in Northern and Southern Latitudes
Rainfall energy is considerably lower in the upper latitudes of the Northern and Southern hemispheres. Studies in Finland were reported by Drs. S. Rekolainen and M. Posch, Ministry of the Environment, Helsinki (Rekolainen, S., and M. Posch. 1994. Adapting the CREAMS model for Finnish conditions. Nordic Hydrology, 24:309-322). Their procedures were adapted in GLEAMS 2.10 for further studies, and the modifications are incorporated GLEAMS 3.0. The procedure is to be published in the Journal of Agricultural Water Management (Knisel, W.G., and E. Turtola, GLEAMS model application on a heavy clay soil in Finland).
Input Metric Solar Radiation
Earlier versions of GLEAMS required user input of the 12 mean monthly values of solar radiation in Langleys/day even for those who use metric input. In GLEAMS 3.0, radiation can be input in MJ/square meter/day. The model will convert to Langleys/day for model calculation. THIS IS THE ONLY KNOWN EXCEPTION WHERE EXISTING PARAMETER FILES CANNOT BE RUN WITH GLEAMS 3.0. IF SOLAR RADIATION IS IN LANGLEYS/DAY, AND THE PARAMETER FLGMET=1, THE MODEL WILL MULTIPLY LANGLEYS/DAY BY 23.9 TO GIVE AN ERRONEOUS VALUE. For developing new parameter files, the metric values can be entered in the parameter editor.
