British Columbia Mine Reclamation Symposium

Mine reclamation and surface water balances : an ecohydrologic classification system for mine-affected… Straker, Justin; Baker, Trevor; Barbour, S. L.; O'Kane, Mike; Carey, S.; Charest, D. 2015

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Mine Closure 2015 – A.B. Fourie, M. Tibbett, L. Sawatsky and D. van Zyl (eds) © 2015 InfoMine Inc., Canada, 978-0-9917905-9-3   Mine Closure 2015, Vancouver, Canada 1 J. Straker  Integral Ecology Group Ltd., Canada T. Baker  Integral Ecology Group Ltd., Canada S.L. Barbour  Civil and Geological Engineering, University of Saskatchewan, Canada M. O’Kane  O’Kane Consultants Inc., Canada S. Carey  School of Geography and Earth Sciences, McMaster University, Canada D. Charest  Teck Resources Limited, Canada   Understanding reclamation effects on surface water balances in mine-affected watersheds is critical to both prediction of, and design for, water movement through the post-closure landscape, and for development of appropriate reclamation and revegetation treatments for mine closure. Substantial effort has been invested in increasing knowledge of the effects of mine-waste cover systems on key water-balance terms such as net percolation, but tools to extend that knowledge to effects of cover systems on vegetation establishment and the subsequent effects of these vegetation-substrate interactions on water-balance terms are lacking. The concept of a “soil moisture regime” is used worldwide to understand edaphic conditions and plant communities. However, in most applications, soil moisture regime is a relative or unquantified parameter estimated from the presence of indicator plants or soil properties observed in natural ecosystems. Applications of these approaches to post-mining landscapes are challenging because soils/surficial materials are reconstructed and reference plant communities are often not fully re-established. Some quantitative approaches to estimation of properties that influence soil moisture regime (e.g. available water storage capacity) have been developed, but these are generally based on agricultural soil science, and have limited utility to many post-mining materials. The authors propose new methods for estimating soil moisture regime in post-closure landscapes, using concepts from existing biogeoclimatic ecosystem classification systems and analyses of effects of particle-size distribution on soil water retention. Key variables in the proposed estimation model include regional and local climate, material particle-size distributions (including distributions typical of mine-waste materials), organic-matter accumulation, and topography. This paper discusses methods development of this estimation approach, and presents suggestions for broader application of the approach for quantifying surface-water-balance components (e.g. net percolation) and for reclamation planning (e.g. revegetation species selection) in closure landscapes. One of the principal knowledge gaps in mine reclamation involves characterising soil water dynamics within surficial materials used in reclamation cover systems. The concomitant water balance in these materials is a dominant control on both ecosystem development and watershed performance, and better understanding of these water balances is critical for improved reclamation planning and projection of long-term characteristics of reclaimed ecosystems. It is also critical for improving our understanding of the hydrologic behaviour of reconstructed mine-affected watersheds, including the role of net percolation on flushing of constituents of interest (CIs) from the mine wastes within these watersheds. Although substantial effort has been invested from an engineering perspective in investigating the effects of cover systems on rates of net percolation, this effort has generally not been coupled with understanding soil water dynamics within the Mine reclamation and surface water balances: ecohydrologic classification J. Straker, T. Baker, S.L. Barbour, M. O’Kane, S. Carey and D. Charest 2 Mine Closure 2015, Vancouver, Canada same cover systems for the purposes of reclamation planning and execution. To date most ecological approaches used to address the above knowledge gap, where it has been addressed at all, have been borrowed from ecosystem classification systems, and are limited by the following factors:  they are qualitative or semi-quantitative, and there is limited attempt to evaluate and demonstrate their hydrologic validity;   they rely substantially on the presence of existing natural vegetation communities to provide information on edaphic conditions — these techniques are not applicable to mine-reclamation settings where vegetation communities are absent or introduced; and/or  they have a narrow focus on a single aspect of the surface water balance, such as estimating water retention for revegetation planning. In these approaches, there is no attempt to provide a more comprehensive understanding of surface water balances, or of how water retention and use by vegetation may influence deeper percolation and the water balance of the underlying mine-waste landform. This paper presents a quantitative method to relate the properties of landforms and cover-system materials to plant-available water and surface water balances, based on particle-size distributions (PSDs) and biogeoclimatic ecosystem classification (BEC). BEC is an ecological classification system developed primarily in the western Canadian province of British Columbia (B.C.), in which biogeoclimatic units (“zones”) represent broad geographic areas of similar macroclimate and are recognised as influencing the biological characteristics of the resulting ecosystems (Meidinger and Pojar, 1991). In the BEC system, biogeoclimatic zones can be subdivided into subzones, which can in turn be subdivided into variants, with each subdivision representing a reduction in climatic variability and geographic area (Lloyd et al., 1990). Within each subzone or variant, there are sequences of distinct ecosystems (“site series”), with associated vegetation communities reflecting differences in topography and soil depth, texture, drainage, moisture regime and nutrient regime. In this system, soil water availability is believed to have the greatest influence on ecosystem development. This availability is in part determined by climate, but since climate is relatively uniform within a biogeoclimatic subzone or variant, variation in soil water availability at this level of classification results from influences of soil and topography on surface water balances (Lloyd et al., 1990). These influences are manifested in the resulting plant associations, that is, each site series has an assemblage of plants adapted to its edaphic conditions — a fundamental principle of the BEC system is that sites with similar physical properties have similar vegetation potential (Meidinger and Pojar, 1991). A subset of plants on a site — “indicator plants” — are diagnostic of edaphic conditions owing to their adaptation to narrow ranges of conditions such as soil water availability. In the BEC system, soil water availability is estimated using a concept termed “soil moisture regime” (SMR), which reflects “the average amount of soil water annually available for evapotranspiration by vascular plants over an extended period of time (several years)” (Pojar et al., 1985). The BEC system incorporates nine SMR classes ranging from driest (Class 0, or very xeric) to wettest (Class 8, or hydric); this spectrum is referred to as a hygrotope (Pojar et al., 1985; Meidinger and Pojar, 1991). The most common classifications of hygrotope — and those used in the BEC system — are classifications of potential hygrotope based on subjective inferences from site and/or vegetation features (e.g. source of water, rate of water removal, slope position, soil textural class), and represent a relative ranking of sites in terms of potential soil water availability. Meidinger and Pojar (1991) provide a common example of this approach, although more complex and semi-quantified examples exist in the BEC system (e.g. Lloyd et al., 1990). Actual hygrotopes integrate the above Ecosystem Reconstruction Mine Closure 2015, Vancouver, Canada 3 information with climate and surface-water-balance inputs and losses such as precipitation and evapotranspiration to provide estimates of absolute rather than relative water availability. Quantified estimates of both potential and actual hygrotope or SMR are uncommon, and those that exist are limited in their application to specific geographic regions and/or ecosystems (e.g. Waring and Major, 1964). In B.C., Green et al. (1984, summarised in Pojar et al., 1985) used a water-balance approach to develop an actual hygrotope, but it is based on intra-annual duration of water deficits and on presence of water tables, and although the authors provide defining features for their classes, methods for classifying sites according to this system are not provided. Various land-capability classification systems in Canada — beginning with agricultural land-capability systems — have used available water storage capacity (AWSC) as an index of potential soil-water availability. AWSC is defined as the volume of water per unit area held within the active or rooting zone of the soil profile between the volumetric water content (VWC) at field capacity (FC) and the permanent wilting point (PWP). The FC is the VWC at which the rate of gravitational drainage becomes negligible relative to the current rate of evaporation or evapotranspiration (Zettl, 2014). This water content is often taken to be the water content at negative pore-water pressures of 10–33 kPa, depending on soil texture. The PWP is the VWC at which soil water is no longer available for plant uptake. Although this water content varies by plant species, by convention it is defined as the water content at a negative pore-water pressure of 1500 kPa. AWSC is generally expressed as a depth of water (mm) over a specified soil depth, or as a depth of water per unit depth of soil (mm water/cm soil). A common practice has been to assign AWSC values based on soil texture: for example, the document Land capability classification for agriculture in British Columbia (B.C. Ministry of Environment, 1983) provides AWSC values in mm water/cm of soil depth for soils of different textural classes. However, these systems, being initially focused on agriculture, do not link AWSC to SMR or to the occurrence of typical natural ecosystems and/or larger hydrologic performance.  In northeast Alberta, the Land capability classification system for forest ecosystems in the oil sands (or “LCCS” — Cumulative Environmental Management Association, 2006; first published in 1996) attempted to use earlier concepts (and values) of assigning AWSC to textural classes for application to mine-reclamation and forest-ecosystem settings. The LCCS equates a potential hygrotope to numeric values calculated from texture-class-based AWSC and some topography and surficial-material-depth modifiers such as slope position and depth to impermeable layers. This approach represents an advancement in producing an objective and quantified relative hygrotope, but still has limitations for broader application. First, texture-based AWSC values in the LCCS apply uniformly across texture or material classes, and do not recognise or account for variation in PSDs within these classes. For instance, the LCCS applies an AWSC value of 1.0 mm/cm to oil sands tailings, regardless of actual PSD and whether these tailings are complete or are cyclone overflow or underflow products. Second, although there has been substantial investigation and validation of the LCCS AWSC values (e.g. Barbour et al., 2010), and thus of their use as a relative hygrotope, there has been limited evaluation of the relationship between these values and actual soil water contents (i.e. the actual hygrotope), and of the relationship between these values and ecosystem development and landscape/watershed hydrologic performance. The concept of SMR has been applied globally based on duration or magnitude of growing-season water deficits but typically involves relatively broad classes that can be mapped at a continental scale (e.g. Soil Survey Staff, 1999) rather than applied to differentiate between ecosystems and hydrologic behaviours at a local or regional scale. The classification system proposed here is substantially informed by the biogeoclimatic, hygrotope/SMR, and land-capability classifications described above, but is intended to derive estimates of plant-available water, surface-water-balance performance, and associated ecosystem characteristics from landscape, landform and Mine reclamation and surface water balances: ecohydrologic classification J. Straker, T. Baker, S.L. Barbour, M. O’Kane, S. Carey and D. Charest 4 Mine Closure 2015, Vancouver, Canada surficial-material properties using objective and quantified methods that can be consistently and easily applied. Further, the proposed system is designed to be broadly applicable to a range of climatic, physiographic and surficial-material conditions (i.e. globally), yet have sufficient resolution to differentiate ecosystem characteristics and hydrologic performance on a local scale. Additional goals for the classification system are that it  be capable of derivation solely from information on material properties, topography and climate, and not rely on observations of intact above-ground ecosystems for diagnosis;  be capable of evaluation and validation or adjustment through analysis of related empirical observations, including relationships with non-mine ecosystems classified through standard BEC methods; and  provide useful interpretations for a range of mine-planning and reclamation-management considerations, including both cover placement/revegetation and understanding hydrologic behaviour on the mine landform-landscape-watershed scale. The proposed classification framework is based on three primary factors with decreasing geographic scales of application (Table 1, adapted from Devito et al., 2005). For the first classification factor, AWSC is determined from PSDs of materials in the upper one metre of surficial material. This determination can be applied globally, as it is based on universal principles of soil physics. The next classification factor involves modification of the profile AWSC estimate for a topography-based energy regime.  These modifications are specific to latitudinal ranges and thus must be developed specifically on the continental to sub-continental scale. The final classification factor applies regional and local climate information to the potential hygrotope resulting from application of the first two factors to generate an actual hygrotope and identify ecosystems associated with this hygrotope. Thus, application of the first classification factor (AWSC) requires only information contained in this paper; application of the second factor (topography/energy) may require modification of information contained in this paper, depending on latitude of application; and application of the third factor (climate) requires information on climate local to the application site and biogeoclimatic or similar classification information. AWSC is estimated from PSD of the sub-100-mm fraction, using the following classes: clay (<0.005 mm), silt (0.005–0.05 mm), sand (0.05–2 mm), Unified System of Soil Classification (USSC) sand (2–4.75 mm), and coarse fragments (>4.75 mm). To facilitate more cost-effective and reliable classification, low-technology field equipment has been developed to allow rapid determination of the cobble-and-gravel separate (>4.75 mm) based on a large volume of material, with subsequent determination of the finer fractions based on laboratory analyses of smaller subsamples.   Ecosystem Reconstruction Mine Closure 2015, Vancouver, Canada 5 Factor Range of factor Scale of applicability Classification outputs PSD of surficial materials High silt and clay contents, low sand, gravel and cobble contents: higher AWSC High sand, cobble and gravel contents, low silt and clay contents: lower AWSC Global Profile AWSC in surface 1 m Topography and energy High latitude: slope and aspect significantly affect energy distribution Tropical and sub-tropical: slope and aspect do not significantly affect energy distribution Continental to sub-continental Adjusted AWSC; relative SMR or potential hygrotope Regional and local climate Dry, arid to sub-humid (P < PET) storage and ET dominant runoff and NP may be reduced Wet, humid (P > PET) runoff and NP dominant  Regional to local Actual SMR and hygrotope; identification of associated ecosystems  The AWSC of each material profile is calculated in two steps from PSD data. First, the AWSC of the fine fraction (<2 mm) is calculated using the empirically derived soil-water-characteristic equations developed by Saxton and Rawls (2006). (Bulk density for these equations is assumed to be 1.44 T/m3, which is based on a database of mine-waste material properties, as is the estimated rock particle density of 2.71 T/m3.) These equations include adjustment for organic matter content, which is measured at all sites. In the second step, additional AWSC is assigned to the USSC sand fraction (2–4.75 mm) in recognition of the potentially substantial volume of water held within the pores of rocks, particularly those of sedimentary origin (Waring and Major, 1964; Flint and Childs, 1984; Childs and Flint, 1990). Rock porosity is calculated using measured rock bulk-density values, which are converted to AWSC estimates based on Flint and Child’s (1984) work that shows 50% of the internal porosity of rocks is released at suctions between 10 and 1500 kPa. Coarse fragments (>4.75 mm) are assumed to contribute negligible AWSC to the overall profile given the physical inaccessibility of the majority of their internally stored water. AWSC estimates from the Saxton-Rawls equations were compared to results generated from application of Arya and Paris’s (1981) physicoempirical model to predict soil moisture characteristics from PSD data, which are known to be useful for coarse-textured mine-waste materials. For this comparison, we analysed data for a wide range of materials, representing a range of PSDs and gradations, and including the 12 study sites discussed further in Section 4. The comparison of the two methods indicates R2 values of 0.66 to 0.90, depending on assumed gradation, and indicates a tendency for the Saxton-Rawls methods to generate slightly lower estimated AWSC than the Arya-Paris methods. An example of a comparison for materials with an assumed uneven gradation favouring coarser particles is presented in Figure 1. The relatively good agreement between the two models was used to support continuation of use of the Saxton-Rawls methods, as these methods incorporate other useful factors such as organic-matter content, but we will continue to evaluate different approaches to estimating AWSC, and to investigate zones of poorer agreement between the Saxton-Rawls and Arya-Paris approaches.  Mine reclamation and surface water balances: ecohydrologic classification J. Straker, T. Baker, S.L. Barbour, M. O’Kane, S. Carey and D. Charest 6 Mine Closure 2015, Vancouver, Canada  Values derived from the above AWSC estimation methods are intended to represent a single material, and to be aggregated across a standard material profile or control section (typically 100 cm, but lesser sections could be used if stipulated). For instance, to estimate AWSC for a 50 cm soil cover placed on mining waste rock or tailings, one AWSC value is calculated for the cover material, another is calculated for the mine-waste material, and an aggregate AWSC is generated by summing the values. If multiple layers are present within the soil cover (or mine waste), then an AWSC value is calculated for each layer corresponding to depth and PSD data. For natural soils, calculation is based on horizon depths and characteristics. In the case of shallow soils over non-rooting-zone materials, the AWSC for the control section is based only on the depth of the soil material, and thus is reduced compared to a 1 m potential rooting zone. Although estimated AWSC values in mm water/cm material depth are based on continuous equations, their results can be summarised in a standard engineering ternary diagram as presented in Figure 1. (The values in Figure 1 assume well-graded materials. Some surficial and mine-waste materials deviate from this assumption; for instance, oil sands tailings from the McMurray formation in northeast Alberta, Canada, are predominantly fine sands, and research has indicated an AWSC for these materials of 1 mm/cm (Barbour et al., 2010), as opposed to the lower values shown in Figure 1 for these PSD positions.) Data are presented in this format to facilitate communication between mine planners/engineers (who often use USSC PSD classification systems) and reclamation specialists (who often use soil-science PSD or texture classification systems).  Ecosystem Reconstruction Mine Closure 2015, Vancouver, Canada 7  In the British Columbia BEC system, the topographic effect on energy is recognised through “warm” and “cool” site modifiers. These modifiers are applied to slope angles greater than 25% (14°), with warm aspects being southerly or westerly (135°–285°), and cool aspects being northerly to easterly (285°–135°; Resources Inventory Committee, 1998). The concepts behind this approach were adapted to the current classification system by using modelled solar radiation differences across latitudes, slopes and aspects to produce modifiers (additions or deductions) to the PSD-derived AWSC estimate. Short-wave radiation was calculated for different slopes, aspects and latitudes as the sum of the direct- and diffuse-beam components. The theoretical direct-beam component of solar radiation was determined after Garnier and Ohmura (1968, 1970). Diffuse clear-sky radiation was calculated after Iqbal (1983), assuming a standard atmosphere. These modelled values were then converted to additions or deductions to AWSC (in mm) by treating values above the median for each latitude band as deductions, and values below the median as additions. These modifiers are intended not to imply actual reductions or additions to AWSC on different slopes and aspects but as surrogate modifiers to AWSC based on increased or decreased evapotranspirative demand driven by varying energy regimes.  Mine reclamation and surface water balances: ecohydrologic classification J. Straker, T. Baker, S.L. Barbour, M. O’Kane, S. Carey and D. Charest 8 Mine Closure 2015, Vancouver, Canada An example of the described approach for 50° N latitude is presented in Table 2. Maximum and minimum values for modifiers at this latitude have been set at 30 mm, which reflects a shift of one entire SMR class (Section 3.5). Maxima and minima increase with increasing latitude and decrease to zero as latitude decreases to approximately 23.5° N or S. Energy class Class definition AWSC modifier Neutral Slopes <10°1 none, 0 Warm Slope >10°; aspects ~080-280°1 Calculated AWSC minus 1-30 mm2 Cool Slope >10°; aspects ~280°-080°1 Calculated AWSC plus 1-30 mm2  Note that specific classification depends on slope/aspect combination: some slopes greater than 10° have neutral aspects, and aspects may vary between warm and cool classifications depending on slope. Modifier values depend on specific slope and aspect, where the maximum value for warm slopes occurs at slope angles of 25° and aspects of 170–190°, and the maximum value for cool slopes occurs at slope angles of 35° and aspects of 350–010°. Adjusted AWSC values (PSD-based AWSC plus any applicable energy modifiers from Table 2) are used to determine SMR, as outlined in Table 3. This table uses the SMR classes of the BEC potential hygrotope, but replaces the relative ranking of various criteria with quantified ranges of adjusted AWSC. AWSC ranges for each SMR class are modified from the oil sands reclamation land capability classification system discussed above. The AWSC method for SMR determination applies only to upland (very xeric to mesic) SMRs, as wetter SMRs require input of seepage water or the presence of a water table within 100 cm of the soil surface, and are not dependent on soil storage. Thus, determination of SMRs wetter than mesic in this system is based on observations of shallow groundwater seepage and/or the presence of a water table within the top metre of surficial materials. Note that these moisture regimes are intended to reflect dominant soil-water conditions over a multi-year period, consistent with the BEC system hygrotope.                                                            1 Specific classification depends on slope/aspect combination – some slopes >10° have neutral aspects, and aspects may vary between warm and cool classifications depending on slope. 2 Modifier values depend on specific slope and aspect, where the maximum value for warm slopes occurs at slope angles of 25° and aspects of 170-190°, and maximum value for cool slopes occurs at slope angles of 35° and aspects of 350-010°. Ecosystem Reconstruction Mine Closure 2015, Vancouver, Canada 9 SMR  Primary water source Water-table depth  (cm below ground surface) Available water storage, surface 1 m (mm) Very Xeric (0) Precipitation and soil storage >100 <60 Xeric (1) Precipitation and soil storage >100 60-89 Subxeric (2) Precipitation and soil storage >100 90-119 Submesic (3) Precipitation and soil storage >100 120-149 Mesic (4) Precipitation and soil storage >100 >150 Subhygric (5) Precipitation and seepage >100 >150, seepage contributes to supply Hygric (6) Seepage 30-100 n/a Subhydric (7) Seepage or permanent water table 0-30 n/a Hydric (8) Permanent water table Water table permanently at or above soil surface n/a The methods discussed above were developed and tested at reclamation-monitoring sites at seven mining operations from 2012 to 2014: five steelmaking coal operations operated by Teck Resources Limited in south-eastern B.C. and west-central Alberta; at the Teck Highland Valley Copper Partnership’s Highland Valley Copper mine in south-central B.C.; and at Thompson Creek Metals’ Endako molybdenum mine in central B.C. The five Teck steelmaking coal mines are particularly relevant to testing, because in 2011 Teck commenced an integrated and multi‐disciplinary applied research and development program focused on managing water quality in mining‐affected watersheds. In 2012–13, this program included installation of soil and meteorological instrumentation and soils and vegetation assessments at 12 reclamation sites at these coal mines to provide data on reclamation conditions co‐located and concurrent with information on meteorological and soil‐moisture variables at each study site. This instrumented-site network and the data it provides supports increased understanding of how surface water balances and SMRs are affecting reclamation responses over time, and vice versa, as well as how reclamation approaches affect reconstructed landform water balances and watershed hydrology. PSD data from 65 mine-reclamation and non-mine reference sites were used to estimate AWSC values based on the methods described above. These values provide quantification of the potential hygrotope, as they indicate the capacity for soil water storage (and eventual release as evapotranspiration, interflow and/or net percolation), not actual storage. Actual storage is a product of the interaction between the potential Mine reclamation and surface water balances: ecohydrologic classification J. Straker, T. Baker, S.L. Barbour, M. O’Kane, S. Carey and D. Charest 10 Mine Closure 2015, Vancouver, Canada hygrotope and local climate, which delivers precipitation for storage and energy for evaporation and transpiration. To evaluate the relationship between potential (calculated) and actual hygrotope, VWC and matric-potential (φm) data collected from the instrumented study sites were analysed to derive mean growing-season available volumetric water contents (AWC) for each site. To do so, the VWC at PWP was calculated for each VWC sensor from interpolated plots of VWC against φm for each sensor pairing. In cases where VWC continued to decrease at matric potentials drier than PWP, the mean of the lowest 10 VWC measurements was used as an alternative VWC-at-PWP value in recognition of potential error in the paired sensor measurements. For sensors without sufficient data, VWC-at-PWP was assigned from neighbouring sensors in the same material type. Each sensor’s VWC-at-PWP value was then subtracted from each of its VWC measurements to calculate AWC (water content above PWP) for all sensors. To calculate mean AWC from all sensors over a profile depth, sensor AWC values were mathematically weighted according to the relative depth interval represented by each sensor within the upper metre of soil. The reported AWC values are the means of all daily measurements made during the 2013 and 2014 growing seasons, defined as the period from April 1 to October 31 based on modelled PET for the study region. SMR was assigned for each of the 65 study sites using the PSD-based AWSC estimates with energy modifiers, as described above. For the Teck steelmaking coal mine research sites where AWC data are available, calculated AWSC values were evaluated using mean growing-season AWC (Figure 2). These data show support for the proposed classification system, with growing-season AWC significantly (p < 0.001) positively correlated with estimated AWSC (Figure 2); the derived linear relationship accounts for approximately 80% of variation in observed growing-season water contents. At least a portion of the unexplained variation is attributable to the various stages of vegetation development on the sites and the resulting differences in transpirative demand for soil water. It is anticipated that as these sites mature, fitting errors will be reduced. On average, very xeric sites have less than 45% of the plant-available water that subxeric sites have during the growing season. Research sites at Endako and Highland Valley Copper lack continuous measurement of soil water contents, and thus cannot be added to this database. However, reference sites in these studies provide some ability to evaluate system fit, as predicted SMR based on methods proposed in this paper can be related to potential hygrotopic classification using standard subjective keys and the presence of indicator plants. All reference sites studied to date are zonal site series with mesic SMR: the mean AWSC for these sites estimated with the proposed methods is 159 mm, which places them in the mesic SMR category according to the criteria presented in Table 3. It should be noted that there are currently no comparable methods for estimation of ecohydrologic behaviours and SMR at the sites used for methods testing. Estimation of soil water retention for design of revegetation programs is conducted using the expert knowledge of individual practitioners. The effects of surficial materials on surface water balances and underlying waste-material water balances are either not considered or modelled for specific conditions using standard engineering approaches, which generally do not provide information for other aspects of reclamation planning. Ecosystem Reconstruction Mine Closure 2015, Vancouver, Canada 11   This paper proposes a quantified and objective hygrotopic classification system broadly applicable to a range of ecosystems, including mine-waste-based landforms and mine-affected watersheds. Although the proposed classification system is initially based on potential hygrotope, the use of regional and local BECs allows its translation into actual hygrotopes based on regional and local climatic conditions. This translation from potential to actual hygrotope has been tested in two regions of western Canada on instrumented reclamation study sites. The initial results show promising relationships between predicted SMR using the proposed classification system and mean growing-season available water contents calculated from continuous measurement by in situ sensors, with increasing observed available water contents as SMRs predicted by the classification model progress from drier to wetter sites. In addition, the proposed classification system shows concordance with traditional ecosystem classification of non-mine reference sites where classification is based on indicator-plant presence and topographic/soil relationships. The potential management applications of the classification system include  Reclamation and revegetation planning: using methods discussed above, SMR can be estimated for existing or planned landforms and covers, and locally appropriate candidate vegetation species adapted to these hygrotopic positions can be selected for reclamation.  Assessment of pre- and post-development land capability: using estimated hygrotopic position and the BEC system or similar approaches allows comparison of anticipated post-closure ecosystems to pre-development inventories. These comparisons can then be used to evaluate the effects of mining on dependent values such as wildlife habitat, biodiversity or land productivity, Mine reclamation and surface water balances: ecohydrologic classification J. Straker, T. Baker, S.L. Barbour, M. O’Kane, S. Carey and D. Charest 12 Mine Closure 2015, Vancouver, Canada and can provide the basis for application for custodial transfer of reclaimed lands or assessment of such applications.  Quantification of the effects of surficial-materials management on landform surface water balances: when combined with information on local climatic conditions, the proposed classification system can be developed to provide relative estimates of surface-water-balance terms such as evapotranspiration and net percolation. Reclamation practitioners can use this information to understand the effects of cover placement for reclamation on movement of water through the surface layers of the reclaimed landscape.  This proposed classification system and empirical approach to its evaluation are evolving, and will continue to be updated and adapted as additional information is collected and as the classification system is refined. 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