Critical Loads - Monitoring Strategy - Section 2b

Monitoring Acidification Effects - Aquatic Ecosystems

While there are many different sensitive receptors for aquatic ecosystems that can be affected by air pollution (e.g., water chemistry, fish, macrobenthic invertebrates, and diatoms), the receptor used to develop these CLs for Forest Planning is surface water chemistry.  The following recommendations focus on improving CLs of acidity for surface waters.  

The CLs of acidity for surface waters provided on the Air Quality Portal were only calculated for sites where surface water samples were collected and analyzed and the data reported in NRM Air.  Even if a forest has several surface water CLs calculated within its boundary, the number of monitoring sites might be insufficient to warrant developing a target load; additional measurements might be needed.  Fortunately, surface water chemistry is relatively easy to obtain.  The Air Program supports surface water chemistry monitoring by developing national protocols, maintaining a laboratory equipped to analyze chemically dilute waters for air pollutants, and supporting NRM Air, a module within the national database, NRM, to store and report results.   

Forests should follow the Forest Service National Protocols for Sampling Pollution-Sensitive Waters RMRS-GTR-278WWW (April 2012). The protocols provide a consistent framework for deciding where, when, and how to conduct water sampling for the purpose of evaluating and monitoring air pollution effects on aquatic ecosystems.  The Missoula Technology and Development Center has developed stream and lake sampling videos to support field implementation of the protocol.  The Protocol document and training videos are available online at: //

Sample analysis support is provided by the Forest Service Air Program Biogeochemistry Lab.  This lab specializes in analyzing dilute lake and stream water (which are highly sensitive to effects of air pollution), their procedures have been aligned with National Protocols, and data reporting into the national database, NRM AIR, is facilitated.  Forests should therefore use this lab for air pollution related monitoring projects. 

Create a clear objective for monitoring before developing a monitoring plan to support the objective.  In this case you are either collecting the first surface water chemistry measurements for a forest, or expanding/updating existing data.  In both cases, the terrestrial CLs of acidity for forested ecosystems can be used to identify watersheds at highest risk.  If resources are limited, streams in these watersheds can be measured first.  This is possible because the soils of the watershed influence the buffering capacity of the stream water