TICKET-UWM is a software application that models metals and organics transport in a well-mixed lake with an underlying sediment layer (Farley et al., 2005; Farley et al., 2011). The name TICKET-UWM comes from a merging of the numerical engine for the model calculations (Tableau Input Coupled Kinetics Equilibrium Transport model) from Farley et al. (2008) and the Unit World Modeling approach that has been previously developed for organic chemicals (Mackay et al., 1996; Mackay and Paterson, 1991) and metals (Diamond et al., 1990). Unlike previous models, however, TICKET-UWM simultaneously considers the effects of chemical speciation on metal partitioning, transport and bioavailability in the lake water column and underlying sediments. The initial version of TICKET-UWM was developed to perform steady-state calculations with a continuous load of metal. Recently, the model was upgraded to perform time-variable simulations as well. The user can now assess the dynamic response of a lake to a continuous or instantaneous load of a metal. The metal source can be specified as a soluble salt subject to instantaneous dissolution or as a powder/massive which dissolves according to a user-specified kinetic expression and rate.
The conceptual framework for TICKET-UWM is based on a well-mixed water column with an underlying oxic or anoxic sediment layer. In the model, metals can enter the water column via surface runoff, storm water flow, groundwater flow, atmospheric deposition, and/or direct discharges. The form of the metal released into the environment (e.g. soluble salt, metal powder, massive) is also considered by specifying kinetic expressions to describe dissolution rates in the water column and underlying sediment layer.
Processes that are modeled include:
- Dissolved and particulate phase transport.
- Metal complexation to dissolved and particulate organic matter and inorganic ligands using WHAM V, WHAM VI, or WHAM VII.
- Metal binding to iron and manganese hydroxides using surface complexation submodels.
- Precipitation of metal sulfides, hydroxides and carbonates.
- A description of biogeochemical cycling of carbon, sulfur, iron and manganese in the water column and sediment
- Competitive interactions of metals (i.e. mulit-metal) and major cations on the biological site of action for water and sediment dwelling organisms as described by the Biotic Ligand Model (BLM).
The TICKET-UWM algorithm was constructed as a general solver based upon the Tableau Input Coupled Kinetics Equilibrium Transport (TICKET) numerical engine. Chemical species, chemical equilibrium constants and kinetic rate coefficients stored in external databases that can be edited by the user.
The model is currently able to perform the following calculations:
Steady-State Response: Metal concentrations resulting from an annual average metal load.
Time Variable Response: Concentrations of metals in the water column and sediment as a function of time.
Critical Loads: Calculation of the allowable metal load which would not exceed a water quality standard or critical biotic ligand concentration.
Rapid Removal: Calculation of metal removal from the water column as a function of time (e.g. 28 days) after an instantaneous release.
Biotic Ligand Model with Metal Precipitation: Calculation of metal concentrations on the biotic ligand using WHAM V, VI or VII and the MINTEQA2 precipitation database.