Critical Loads - Monitoring Strategy

During the process of conducting the critical loads (CLs) assessment for Land Management Planning, additional monitoring may be recommended to enable the calculation of specific types of CLs and CL exceedances, or to refine, and therefore improve, the reliability of the existing CLs and CL exceedances available for your forest. For example, you may find that:

  • You have very few (or no) surface water chemistry samples and therefore no CLs of acidity for surface waters,
  • The CLs for nutrient nitrogen or terrestrial acidification are not reliable enough to serve as the basis for land management decisions, and/or
  • Better estimates of deposition are needed for your forest in order to calculate more reliable CL exceedance estimates.
  • Forests in Alaska and Puerto Rico have limited CL exceedance information due to the lack of available geospatial deposition estimates and/or resource information.

All of these situations will require collection and analysis of site-specific information on resource condition and/or pollutant deposition. This Monitoring Strategy will help the forest identify and prioritize data collection and analysis needs in order to develop monitoring recommendations for the Plan with the intention of improving CL and CL exceedance estimates in future planning efforts.

The Monitoring Strategy is broken into three main parts:

  1. The introduction table, below, helps users locate the appropriate monitoring response to issues from the steps in the Critical Load Implementation Strategy.
  2. The first section focuses on improving pollutant deposition estimates.
  3. The second section addresses how to improve critical load estimates and is presented in four parts:

Responses to issues identified at steps in the CL Implementation Strategy

From Step 1 of the CL Strategy
Forests in Alaska and Puerto Rico will not see any information in the National Forest Exceedance Table. Alaska and Puerto Rico were not included due to the lack of geospatial deposition estimates. Go to Improving Deposition Estimates.
Fields in the NF Exceedance Table are blank, indicating unavailable CLs. Go to the part of Section 2 that corresponds to the missing values for your forest.
Only a few data points were relied upon to make a “No Exceedance” determination of aquatic ecosystem CLs of acidity for your forest. May not be representative of larger area. Go to Monitoring Acidification Effects – Aquatic Ecosystems and consider developing a surface water monitoring plan to increase coverage across your forest.
There is concern that the deposition values used in the national exceedance calculations do not adequately represent conditions on the forest.Go to Improving Deposition Estimates.
From Step 7 of the CL Strategy
CL exceedance information indicates low risk of detrimental effects, but deposition trends are increasing.

(See CL Strategy Step 2 to help define forest concerns between acidification and nutrient nitrogen saturation.)
Assessment showed exceedance of CLs, but information is not considered reliable enough to support development of Target Loads (TL). Monitoring recommended to improve reliability of CLs.
Surface water CL exceedances rated as unreliable due to an insufficient number of water sample sites.Go to Monitoring Acidification Effects – Aquatic Ecosystems and develop a surface water monitoring plan.
CLs of acidity for forested ecosystems are exceeded.
Water samples are not available or are insufficient for a reliable surface water CL exceedance calculation.
Indicates area is at risk of acidification. First step is to acquire reliable surface water CLs.  Go to Monitoring Acidification Effects – Aquatic Ecosystems and develop a surface water monitoring plan using the terrestrial CLs to prioritize sample locations.
CLs of acidity for forested ecosystems are exceeded AND surface water CLs of acidity are exceeded (and considered reliable).Go to Monitoring Acidification Effects - Forested Ecosystems and consider soil chemistry monitoring to improve terrestrial CL calculations, contribute to dynamic modeling for setting target loads, or better understand the severity and extent of the problem before making management recommendations.
Empirical CLs of nutrient nitrogen are exceeded. Go to Monitoring Nutrient Nitrogen Effects.
  • Consider improving lichen CL estimates.
  • Next consider other receptors that have exceeded these CL's. Work with appropriate scientists to determine whether an N gradient or addition study will improve the reliability of these CLs for your forest.