Developing a Soil-Quality Index

 The severe disturbance that surface mining often causes has the potential to drastically alter a soil’s physical, chemical, and biological properties (Insam and Domsch, 1988). In particular, metals associated with mining deposits present obstacles to ecosystem recovery (Nielsen and Winding, 2002), as their residence time in soils can be quite extensive (Brookes, 1995). Quantifying soil quality can be useful for evaluating the impact of such disturbances and can improve the understanding of the mechanisms behind ecosystem processes. Definitions of soil quality generally involve soil function [for example, a soil’s ability to support vegetative diversity and biomass or to sustain itself through nutrient cycling (Doran and Parkin, 1994)]. SQIs are generally composed of biological (and sometimes physicochemical) parameters that reduce a system’s complexity to a metric that indicates the soil’s ability to carry out one or more functions (Papendick and Parr, 1992; Halvorson and others, 1996).
 
Simple ratios, such as the metabolic quotient, qCO2 (quantity of mineralized substrate/unit of microbial biomass carbon/unit of time) and enzyme activity/total carbon, are generally too simplistic and often difficult to interpret (Gil-Sotres and others, 2005); thus, many SQIs combine these parameters with other microbial indicators, such as organic matter (TOC and TN) and microbial activity. Specifically, estimates of carbon and nitrogen mineralization, respiration, and enzyme activity (assays of enzymes, such as arylsulfatase and phosphatase, are recommended in other papers on soil quality indicators) can be very useful in evaluating soil recovery in surface-mining situations (Insam and Domsch, 1988; Mummey and others, 2002). Identifying sensitive soil-quality indicators in mineralized terrane (terrain), therefore, and incorporating them into an SQI, could aid long-term monitoring of reclamation efforts in areas impacted by surface mining. 

The work of this task is to extend ongoing efforts to develop an SQI that represents a soil ecosystem’s ability to incorporate organic carbon and nitrogen, as many SQIs combine many different data types, including TN and TOC, into one metric. Methods include sampling field sites of varying climate, vegetation, and trace metal chemistry that have been impacted by mining (Blecker and others, 2010). The first step entails identifying the microbial indicator variables that correlate with soil organic carbon and nitrogen for a variety of ecosystems and types of geological mineralization. Soil samples were collected at a few WLCI sites during spring 2010. Meanwhile, work to develop an SQI from existing chemical data (without microbial indicator variables) continued; the SQI will be a cumulative metric representing diverse indicator data such as pH, salt content, nutrient content, and concentration of metals. Although this number will demonstrate the data variability across the WLCI region, it will not provide any information on soil or ecosystem function. The addition of the microbial indicator variables to the SQI calculation will greatly improve the utility of the SQI and help to integrate scientific and management objectives. 

Blecker, S.W., Stillings, L.L., Amacher, M.C., Ippolito, J.A., and DeCrappeo, N., 2010, Ecosystem health in mineralized terrane -- Data from podiform chromite (Chinese Camp mining district, California), quartz alunite (Castle Peak and Masonic mining districts, Nevada/California), and Mo/Cu porphyry (Battle Mountain  mining district, Nevada) deposits: U.S. Geological Survey Open-File Report, 2010-1040, 38 p. (Also available at http://pubs.usgs.gov/of/2010/1040/.) 
Brookes, P.C., 1995, The use of microbial parameters in monitoring soil pollution by heavy metals: Biology and Fertility of Soils, v. 19, p. 269-279. 
Doran, J.W., and Parkin, T.B., 1994, Defining and assessing soil quality, in Doran, J.W., and others, eds., Defining soil quality for a sustainable environment:  Madison, Wis., Soil Science Society of America Special Publication 35, p. 3-21. 
Gil-Sotres, F., Trasar-Cepeda, C., Leiros, M.C., and Seoane, S., 2005, Different approaches to evaluating soil quality using biochemical properties: Soil Biology and Biochemistry, v. 37, p. 877-887. 
Halvorson, J.J., Smith, J.L., and Papendick, R.I., 1996, Integration of multiple soil parameters to evaluate soil quality -- A field experiment example: Biology and Fertility of Soils, v. 21, p. 207-214. 
Insam, H., and Domsch, K.H., 1988, Relationship between soil organic carbon and microbial biomass on chronosequences of reclamation sites: Microbial Ecology, v. 15, p. 177-188. 
Mummey, D.L., Stahl, P.D., and Buyer, J.S., 2002. Soil microbiological properties 20 years after surface mine reclamation -- Spatial analysis of reclaimed and  undisturbed sites: Soil Biology and Biochemistry, v. 34, p. 1717-1725. 
Nielsen, M.N., and Winding, A., 2002, Microorganisms as indicators of soil health: Copenhagen, Denmark, National Environmental Research Institute, Technical Report 388, 85 p., accessed September, 2008, at http://www.dmu.dk/1_viden/2_Publikationer/3_fagrapporter/rapporter/FR388.pdf. 
Papendick, R.I., and Parr, J.F., 1992, Soil quality -- The key to a sustainable agriculture: American Journal of Alternative Agriculture, v. 7, p. 2-3. 

• Chemical analyses of soil samples and preliminary results.
• Blecker, S., Stillings, L.L., Amacher, M.C., Ippolito, J.A., Gough, L., and DeCrappeo, N., 2010, Indicators of ecosystem health and the impact of mineralized terrane, in Briggs, K.M., ed., Proceedings of the U.S. Geological Survey Interdisciplinary Microbiology Workshop, Estes Park, Colorado, October 15-17, 2008: U.S. Geological Survey Scientific Investigations Report 2010-5146.
• Blecker, S.W., Stillings, L.L., Amacher, M.C., Ippolito, J.A., and DeCrappeo, N., Development of vegetation-based soil-quality indices for mineralized terrane in arid and semi-arid ecosystems: Ecological Indicators (in review). 

• Blecker, S.W., Stillings, L.L., Amacher, M.C., Ippolito, J.A., and DeCrappeo, N., 2010, Ecosystem health in mineralized terrane -- Data from Podiform Chromite (Chinese Camp mining district, California), Quartz Alunite (Castle Peak and Masonic mining districts, Nevada/California), and Mo/Cu porphyry (Battle Mountain mining district, Nevada) deposits: U.S. Geological Survey Open-File Report, 2010-1040, 38 p.
• Blecker, S.W., Stillings, L.L., Amacher, M.C., Ippolito, J.A., and DeCrappeo, N., Development of an SQI from data for soil organic matter and microbiological activity, in mineralized terranes (manuscript to be submitted to a peer-reviewed journal).