Julann A. Spromberg

Modeling the effects of chronic toxicity on fish populations: the influence of life-history strategies.

Five life-history scenarios were composed to simulate fish population adaptations for survival under various environmental conditions. The scenarios encompassed differences in stage-specific survival, fecundity and hatch success, number of spawning events, and life-span effect response to chronic toxic impacts. The strategies represent a good survivor/generalist (GS), a species exhibiting high young-of-the-year survival, a species exhibiting high adult survival, a species with no parental care or guarding behavior, and an anadromous salmonid strategy. Although the modeled scenarios were similar in population growth rate and imposed toxic effects, differences concerning the influence of various traits were found. Scenarios characterized by a short life span, short time to reproductive maturity, moderate to high survival to reproductive maturity, large number of spawning events, and parental guarding behaviors experienced less perturbation from the imposed chronic stresses. The GS scenario, modeled after the round goby (Neogobius melanostomus), exemplified these characteristics. Scenarios exhibiting little difference between reproductive effort for younger and older adults recovered quickly from stressors on fecundity and adult survival rates. Greater population decline in response to commensurate impacts was seen for life-history strategies with long life span, no parental guarding behaviors, semelparity and annual iteroparity, high adult survival rates, and moderate to low fecundity.

Predicted transport of pyrethroid insecticides from an urban landscape to surface water

The authors developed a simple screening-level model of exposure of aquatic species to pyrethroid insecticides for the lower American River watershed (California, USA). The model incorporated both empirically derived washoff functions based on existing, small-scale precipitation simulations and empirical data on pyrethroid insecticide use and watershed properties for Sacramento County, California, USA. The authors calibrated the model to in-stream monitoring data and used it to predict daily river pyrethroid concentration from 1995 through 2010. The model predicted a marked increase in pyrethroid toxic units starting in 2000, coincident with an observed watershed-wide increase in pyrethroid use. After 2000, approximately 70% of the predicted total toxic unit exposure in the watershed was associated with the pyrethroids bifenthrin and cyfluthrin. Pyrethroid applications for aboveground structural pest control on the basis of suspension concentrate categorized product formulations accounted for greater than 97% of the predicted total toxic unit exposure. Projected application of mitigation strategies, such as curtailment of structural perimeter band and barrier treatments as recently adopted by the California Department of Pesticide Regulation, reduced predicted total toxic unit exposure by 84%. The model also predicted that similar reductions in surface-water concentrations of pyrethroids could be achieved through a switch from suspension concentrate-categorized products to emulsifiable concentrate-categorized products without restrictions on current-use practice. Even with these mitigation actions, the predicted concentration of some pyrethroids would continue to exceed chronic aquatic life criteria.

Population survivorship index for fish and amphibians: Application to criterion development and risk assessment

Criterion development currently focuses on physiological responses when determining permitted chemical concentrations in environmental media. Losses of biodiversity attributed to chemical pollution may be related not only to physiological sensitivity but also to inherent population characteristics that are not included in risk assessment or criterion development. In the present study, we proposed a process and a tool for summarizing population- and species-level information that contributes to long-term survivorship. We investigated the influences of life-history strategies of fish and amphibians that contribute to variations in population sensitivity or resiliency. A life-history survivorship index for application in criterion development and risk assessment was developed to help identify which species in a study system possess life-history strategies inherently sensitive to chemical stressors. It includes life-history characteristics of fecundity, number of spawning events, life stages, parental care, attrition rates, time to reproductive maturity, and other factors. Survivorship index values may be used as multipliers to permitting criteria, resulting in toxicological-ecological guidelines that incorporate toxicological information with regional ecological and population characteristics for local or regional application. We intended the procedure to serve as a step toward incorporating population and ecological information into regulatory procedures with the goal of protecting biodiversity from chronic toxic impacts.