Stream Reclamation Effectiveness Following Placer Mining

Figure 1. Probabilistic (teal) and targeted (white) sample points located in the Eastern Interior Field Office, AK. Probabilistic sample points are being used to assess RMP effectiveness for each of the three planning units (green polygons) and to quantify the range of potential natural conditions from which management objectives such as placer mining reclamation effectiveness can be compared. Blue lines represent major stream and river systems and red polygons, active placer mining claims.

BLM policy states that stream and river habitats altered by placer mining should be rehabilitated to provide a stable channel form with adequate vegetation to reduce erosion, dissipate stream energy, and promote the recovery of instream and riparian habitats (43 CFR 3809.420 and H-3809-1). As part of a larger effort in Alaska, the Eastern Interior Field Office is using the AIM-National Aquatic Monitoring Framework (AIM NAMF) to quantify stream reclamation effectiveness following placer mining. Specifically, they are following the AIM-NAMF to quantify the range of potential natural conditions for chemical, physical, and biological indicators, from which conditions at reclaimed sites can be compared (Figs. 1 and 2).

Initial results highlight the inadequacy of many stream reclamation efforts, with significant alterations to water quality, riparian, and instream habitat persisting post-reclamation (Fig. 2). Ongoing efforts are seeking to quantify how long it takes for different stream types to recover from placer mining, as well as the effectiveness of new, emerging reclamation techniques.

For a more detailed description of the project and how results were generated, please read more below.

Management objectives:

Read more...

Management objectives include reclaiming streams and associated fisheries and riparian habitat following placer mining.

Example BLM policy and guidance:

  • BLM Surface Management Handbook (H-3809-1): habitats altered by placer mining should be rehabilitated to provide a stable channel form with adequate vegetation to reduce erosion, dissipate stream energy, and promote the recovery of instream habitats.
  • Fortymile EIS ROD: streams are to be restored to a stable condition in order to provide for the recovery of the fish and wildlife habitat and reduction of non-point source erosion.

Indicators used to assess attainment of management objectives:

Read more...
  • Following guidance issued in IM AK-2015-002, the BLM AIM-NAMF core and contingent indicators (Table 1) for wadeable streams and rivers were used to assess water quality, channel form and stability, as well as the condition of instream and riparian habitats.
  • See Table 2 for specific monitoring objectives and the indicators used to assess individual objectives.

Aquatics_TreatmentEffectiveness_Indicators

Application of indicators to management objectives:

Read more...

Management objectives were defined in BLM Surface Management Handbook as well as the Fortymile EIS ROD (see Management Objective section).

Making condition determinations

For each of the indicators selected to quantify aspects of water quality, channel form and stability, and the condition of instream and riparian habitats, we established quantitative condition thresholds or benchmarks used to assess the attainment of management objectives (see “Developing monitoring objectives based on indicators“).

Specifically, observed indicator values (e.g., bank stability, etc.) at reclaimed stream reaches were compared to those values expected to naturally occur under minimal human influence (i.e., potential natural conditions). The difference between indicator values at reclaimed sites and the range of predicted natural conditions was used to make designations of functioning, functioning at risk, and not functioning. ‘Not functioning’ was defined as the 90th percentile for indicators that increase in response to disturbance (e.g., fine sediment) or the 10th percentile for indicators that decrease in response to disturbance (e.g., canopy cover, bank stability).

EasternInterior1

Figure 2. Example comparisons of observed channel form, instream and riparian habitat conditions for mined sites post-reclamation compared to the range of potential natural conditions across unmined (‘reference’) sites throughout the Forty Mile region in the Eastern Interior Field Office, AK. Indicator values for mined sites falling above the 90th percentile (floodplain connectivity) or below the 10th percentile (bank cover, bank stability, fish habitat complexity, riparian vegetative complexity) were categorized as not functioning and reclamation objectives were not achieved.

 

  • For example, in the Forty Mile region the 10th percentile of the potential natural conditions for bank cover was observed to be 38% or greater (Fig. 2). If bank cover at a reclaimed site was below 38%, we would conclude that significant departure existed, a stable stream channel had not been created, and the system is not functioning for bank cover.
  • The 90th and 10th percentiles are akin to selecting an alpha level of 0.10 (10% likelihood that the observed difference occurred by chance alone) and were selected to balance over (type I error) versus under protection (type II error).

Quantifying the range of potential natural conditions

We quantified potential natural conditions as the range of variability among regional reference conditions (i.e., 90th and 10th percentiles), using data from the ongoing effort of the EIFO to sample chemical, physical, and biological conditions at unaltered or reference stream reaches throughout the field office. To date, over 30 reference have been sampled and used to develop the range of potential natural conditions.

Developing monitoring objectives

Once the range of potential natural conditions was established for all indicators, we developed more explicit monitoring objectives specifying the indicator, condition threshold, allowable departure, and reporting unit. For example:

  • Determine whether bank stability and cover for the Franklin Creek mining claim is greater than 38%, the 10th percentile of regional reference conditions.
    • If bank stability is 38% or higher, on average, we could conclude that reclamation efforts had created a stable stream channel that is not likely to contribute significant sediment loading from local bank erosion following high flow events and that the system is ‘functioning’ or ‘functioning-at-risk’ for that indicator (e.g., Fig. 2).

The resulting monitoring objectives, AIM-NAMF indicators, and the methods used to evaluate the attainment of management objectives (i.e., condition thresholds and degree of allowable departure) are outlined in Table 2. We are in the process of determining for all computed indicators. ), and whether monitoring objectives were met are outlined in Table 2 for all computed indicators.

Aquatics_TreatmentEffectiveness2

Results and Management Implications:

Read more...

We assessed reclamation effectiveness across 14 reclaimed stream reaches, while the range of potential natural conditions was summarized across 30 unmined or reference reaches (Fig. 1).

  • Of the 14 evaluated indicators (Table 1), none were classified as ‘functioning’ across all 14 assessed reclamation reaches (e.g., Fig. 2 and Table 2).
  • Turbidity and bank stability had the highest frequency of ‘functioning’ ratings, while bank cover and riparian vegetative complexity were the indicators most frequently resulting in ‘non-functioning ratings’.
  • For the large majority of reclaimed reaches, a stable stream channel had not been created and the desired instream and riparian habitat conditions were not created and are unlikely to exist under current conditions.

Next Steps

Read more...

BLM Alaska is working with miners to implement new, innovative reclamation techniques to improve the effectiveness of reclamation efforts. These include actions such as:

  • Improve floodplain connectivity by reducing the height of the low bank and relocating stream segments away from the valley walls or constraining features.
  • Enhance bank cover and improve riparian habitat by transplanting willow clumps, installing brush mattresses on steep slopes, live staking, and seeding.
  • Constructing pool habitat and enhancing pool formation through the addition of large woody debris to the stream channel.

 

Comments are closed