Lichen, herbaceous plants, trees, and aquatic systems can develop negative responses to atmospheric pollution once deposition thresholds are exceeded. The threshold at which a negative change begins to occur is known as a critical load and each ecosystem component has a unique critical load value based on their sensitivity. While the relationship between pollution and ecosystem change is clear, the application of critical load science to land management can be challenging when each critical loads within an area of interest is different. Here we integrated all relevant critical load data within two federal land management areas to communicate the risks to their ecosystems to change at current and future deposition levels. Agencies manage a broad range of resources impacted by disturbance and changing gradients, therefore it is imperative to be clear about the risk of impact, the amount of change expected, and where the change is expected to occur.

We evaluated critical loads of nitrogen deposition for herbaceous species (richness decline), tree species (growth and survival decline), and lichen species (detectability), and critical loads of sulfur deposition for aquatic systems (decreased ANC and fish species richness decline). We calculated the exceedance of each critical load based on the average nitrogen and sulfur deposition from 2014-2016 modeled using the NADP Total Deposition Model. Exceedances and responses to deposition were presented to land managers as graphs, maps, and tables. Exceedance values were identified as valid indicators for managers, but we not actionable without showing expected impact to the system. Critical load exceedances that could be tied to predetermined management priorities were more relevant to managers; e.g. the loss of basal area of harvestable tree species. Ecosystem components that are not directly connected to a resource priority, linking the change to downstream effects was useful for communication; e.g. the loss of forage lichen impact deer and rodent communities. Tying responses to management priorities allowed managers to not only justify action, but allowed them to integrate the new data into preexisting management plans.

Disclaimer: Views expressed are the authors’ and not views or polices of the U.S.EPA.