Water quality modeling in waterbodies involves simulating the biochemical transformation of nutrients and their movement through several water layers, sediment bed layers, and the aquatic biota. Each available modeling package simulates the biological and chemical processes occurring in waterbodies in different ways, depending upon the level of complexity of the model, and the modeling domain. The usefulness of these models mostly depends upon the final objective of the modeling exercise and the availability of data.

Some notable models are listed below.

HSPF – HSPF is a hydrologic and water quality simulation program, typically used at the watershed scale. It simulates the waterbody as a unidirectional mixed reach, and biochemical processes are simulated in three different routines.

1. Phytoplankton – free-floating photosynthetic material
2. Benthic algae – photosynthetic materials attached to the waterbody bed
3. Zooplankton – zooplankton that feed on the phytoplankton

This formulation is simplistic and does not include any further species breakdown beyond these general categories.

EFDC+ – EFDC+ is a 1-, 2-, and 3-dimensional fully coupled hydrodynamic model that includes a water quality component derived from CE-QUAL-ICM. Until version 10.2, EFDC+ was limited to simulating up to three phytoplankton types (cyanobacteria, diatoms and green algae) and one macroalgae group. In addition, it has a sub-model for aquatic rooted plants and epiphytic algae growing on plant shoots. EFDC+ also includes a full sediment diagenesis model to simulate nutrient cycling among the biota and sediment bed.

In the natural world, however, multiple dominant species of algae, plants, and animals (e.g., zooplankton) may be present in a waterbody and require detailed modeling. The original limits of EFDC on the number of algal species and animals that could be modeled was not practical in some situations. To eliminate these issues, EFDC+ version 10.3 will now include a generic formulation for “macrophytes and algae” groups and zooplankton groups. This will give users the flexibility to model unlimited algal species and consider the role of zooplankton both as grazers that control algal population and as a food source for higher trophic-level organisms in a waterbody.

In EFDC+ 10.3, these “macrophytes and algae” interact with each other in their competition for nutrients and light. The model considers the preferences of zooplankton species with respect to other macrophyte and algae species. To verify these enhancements to EFDC+, a model of Pearl Lake, Minnesota, was built using EFDC+ and compared to a 2014 study carried out by USGS which used CE-QUAL-W2 (Smith et al, 2017).  This earlier study assessed the algal community dynamics, water quality, and fish habitat suitability in Pearl Lake, which is an agricultural land-use dominated lake. The CE-QUAL-W2 study had successfully predicted water temperature, dissolved oxygen, as well as captured algal dynamics with four general groups: (1) diatoms, (2) green algae, (3) cyanobacteria, (4) haptophyta. These results were also replicated in the model simulated using EFDC+10.3.