The following provides a quick snapshot of key findings. A more in-depth discussion and references to the scientific literature can be found here.
While estimating nutrient load reductions for hypoxia is relatively straightforward, using fish metrics to estimate load reductions presents a greater challenge because fish species and life stage vary considerably in their sensitivity to changes in oxygen and temperature. In addition, nutrient inputs and hypoxia do not only influence fish health directly; they also affect fish indirectly by altering the availability of quality habitat, which is complicated further because individual- and population-level responses to changes in habitat can be mediated by behaviors we do not fully understand.
However, to illustrate how this could be done, we applied a fish growth rate potential (GRP) model to DO output from the hypoxia model to explore how adult and juvenile yellow perch (a cool water species, relatively tolerant of low oxygen concentrations), rainbow smelt (a cold water species, sensitive to low oxygen), and adult emerald shiner and round Goby respond to changes in temperature and DO.
All species showed a decline with increasing TP loads and temperature, with the sharpest reductions in habitat quality occurring after TP levels exceeded ~5,000 MT/year. This break point is similar to the target TP load for hypoxia described here.
It is interesting to note that the influence of changes in water temperature may have a stronger effect on fish habitat quality than nutrient loading. Under a warmer climate, we may need to reduce loading levels even more dramatically to have meaningful positive effects on habitat quality and Lake Erie fish stocks.