Modeling the potential effects of atrazine on aquatic communities in midwestern streams

Abstract

The comprehensive aquatic systems model for atrazine (CASM(ATZ)) estimates the potential toxic effects of atrazine on populations of aquatic plants and consumers in a generic lower-order midwestern stream. The CASM(ATZ) simulates the daily production of 20 periphyton and 6 aquatic vascular plant species. The modeled consumer community consists of 17 functionally defined species of zooplankton, benthic invertebrates, bacteria, and fish. Daily values of population biomass (grams of carbon per square meter) are calculated as nonlinear functions of population bioenergetics, physical-chemical environmental parameters, grazing/predator-prey interactions, and population-specific direct and indirect responses to atrazine. The CASM(ATZ) uses Monte Carlo methods to characterize the implications of phenotypic variability, environmental variability, and uncertainty associated with atrazine toxicity data in estimating the potential impacts of time-varying atrazine exposures on population biomass and community structure. Comparisons of modeled biomass values for plants and consumers with published data indicate that the generic reference simulation realistically describes ecological production in lower-order midwestern streams. Probabilistic assessments were conducted using the CASM(ATZ) to evaluate potential modeled changes in plant community structure resulting from measured atrazine exposure profiles in 3 midwestern US streams representing watersheds highly vulnerable to runoff. Deviation in the median values of maximum 30-d average Steinhaus similarity index ranged from 0.09% to 2.52% from the reference simulation. The CASM(ATZ) could therefore be used for the purposes of risk assessment by comparison of site monitoring-based model output to a biologically relevant Steinhaus similarity index level of concern. Used as a generic screening technology or in site-specific applications, the CASM(AT) provides an effective, coherent, and transparent modeling framework for assessing ecological risks posed by pesticides in lower-order streams.

Modeling the effects of thiamethoxam on Midwestern farm ponds and emergent wetlands

“…The taxonomic composition of the farm pond primary producer community paralleled the structure of the previously developed generic Midwestern stream CASM ATZ (Bartell et al 2013). The taxonomic composition of the farm pond primary producer community paralleled the structure of the previously developed generic Midwestern stream CASM ATZ (Bartell et al 2013).…”

“…The approach modified the lower-order Midwestern stream CASM ATZ (Nair et al 2015;Bartell et al 2013) to develop a generic Midwestern farm pond (CASM GFP ) model and an emergent wetland (CASM GWL ) model. Pond and wetland data and information were identified, compiled, and used to 1) define the physical structure and spatial scales of the modeled farm pond and wetland, 2) identify representative aquatic plant and consumer populations that defined a representative food web for each system, 3) estimate the corresponding bioenergetics and habitat quality parameters for the modeled populations, 4) derive d-1 biomass conditions used to begin the 365-d simulations, and 5) develop the daily environmental input data (e.g., depth, temperature, nutrients) required by the models.…”

“…The food web structure defined in the CASM GFP farm pond model (Supplemental Data, Table S1) was developed as a general representation of Midwestern ponds (Deal et al 1997;Guy and Willis 1991). The latter 2 aquatic insects are less characteristic of ponds compared with streams (Bartell et al 2013). Modeled zooplankton populations included generally defined cladocerans, copepods, rotifers, and microzooplankton (e.g., protozoa).…”

“…The CASM GFP and CASM GWL also address life history traits of modeled plant populations as a function of temperature, where populations begin to grow only after experiencing a populationspecific accumulation of degree days (Bartell et al 2013;Best et al 2005). This approach incorporates complex plant phenological events that are known but not readily formulated in terms of bioenergetics.…”

“…Similar to the CASM ATZ (Bartell et al 2013), the primary technical literature describing the life history and population dynamics of the modeled pond populations was used to estimate values of the bioenergetics parameters and factors that define habitat quality for the farm pond and wetland versions of the model. Parameters for the aquatic plant populations and benthic invertebrates were based largely on values reported in Nair et al (2015).…”