Protocol for the Derivation of Environmental and Human ... - CCME

Appendix A
Appendix A
Nutrient and Energy Cycling Check
1.0 Using Soil Nutrient and Energy Cycling Data to Derive Effects-based
Guidelines
Soils are dynamic, open, systems characterized by fluxes of energy and nutrients. The ability of soils to
support plant life depends on the coordinated activities of a myriad of invertebrates and microorganisms
that mediate nutrient and energy cycles. Decomposition, respiration, and organic nutrient cycles are
examples of measurable soil processes whose rates may be adversely affected by contaminants.
In theory, these processes should be good indicators of soil quality. In practice, however, it is difficult
to integrate currently available literature into the derivation process because of:
• uncertainties in interpretation of results, including variability seen in dose-response relationships
(Denneman and van Gestel 1990),
• frequent lack of a reference toxicant, and
• uncertainty over appropriate controls ("acceptability criteria") (Environment Canada 1992).
On the other hand, soil process data have the desirable property of ecological relevance -- the use of
these measures as indicators or predictors of ecosystem performance is well established (see Paul and
Clark 1989). Furthermore, data on effects of common contaminants on some soil microbial processes
is abundant (see, for example, Bååth 1989). A balance is struck among these considerations by using
qualifying nutrient and energy cycling data as a check against preliminary soil quality guidelines derived
from single-species bioassay.
The microbial ecology relevant to the cycling of organic nutrients indicates that contaminant data from
nitrogen fixation, nitrification, nitrogen mineralization, decomposition, and respiration studies are all
potentially acceptable for use in a checking role against guidelines derived from single species bioassay
(See Section 2.0). Of these, N-fixation and nitrification data are preferred, but carbon cycling and
nitrogen mineralization measures may be used when the former are unavailable or insufficient for
guideline derivation.
2.0 Nutrient and Energy Cycling Processes as Indicators of Soil Quality
Because biological activity in soils is dominated by the detrital food chain, energy flow is closely linked
to carbon cycling, which is normally observed through measurements of decomposition and respiration.
Other elements whose cycling rates in soils are mainly functions of biological activity include the plant
macroelements nitrogen, sulfur and phosphorus. Activities of microorganisms are primarily responsible
for liberating these elements from organic forms (mineralization), and making them available for uptake
by plants.
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