The last biennial report included a section that discussed the Illinois NLRS Science Team. It outlined a formal evaluation procedure to adopt new conservation practices and update practice performance numbers, which can also be found at go.illinois.edu/NLRS. One of the science team’s duties is to perform these evaluations for proposed additions to the practices listed in the strategy’s first science assessment. When proposals are received, this formal procedure is enacted. Note: Updates to the proposal process are described in chapter 8 of the 2021 Illinois NLRS Biennial Report.
In December 2020, stakeholder organizations submitted two proposals: one for saturated buffers and another recommending several practices, including grade stabilization, blind inlets, terraces, and water and sediment control basins. First, the NLRS Steering Committee evaluated the proposals for completeness. They determined that both proposals contained the requested information and forwarded them to the Illinois NLRS Science Team for full consideration. Table 3.10 is a summary of the team’s decisions made during a series of virtual meetings held January through March 2021.
Additional details from the science team’s discussions by practice area follow.
Table 3.10. Summary of NLRS Science Team proposed practice decisions
Practice | Decision | Efficiency Number | Cost |
Saturated buffers | Include as an NLRS practice | 40% nitrate-N loss reduction; 0% P loss reduction | $10/ac/yr* |
Grade stabilization | Insufficient information | - | - |
Blind inlets | Insufficient information | - | - |
Terraces | Include as an NLRS practice | 40% P loss reduction in non-tiled fields; 0% nitrate-N loss reduction | $40/ac/yr |
WASCOBs | Insufficient information | - | - |
*Annual operation and maintenance would be less than a bioreactor, so assumed a $2.50 annual operation and maintenance cost. The following formula was used:
Equivalent Annual Cost = NPV × r 1 / (1÷r)-n
Saturated Buffers
The science team decided that saturated buffers should be included in the list of NLRS practices due to the number of studies submitted, their geographic relevance, and the quality of the work. They decided on a nitrate-N loss reduction efficiency value of 40%, which was the median value of the 27 site-years
selected for inclusion in the science team’s assessment. No phosphorus loss reductions were associated with saturated buffers. The proposal included a cost estimate for this practice of $10/treated acre/year, factoring in installation costs, expected practice life, and the drainage area treated. These data were converted into
an equivalent annual cost by multiplying the installation cost by a 6% discount factor, then dividing by (1- (1+6%)^(-life)). Similar to bioreactors, an assumed annual operation and maintenance cost was added. Little information was available to draw from, though the science team expected that operation and maintenance for saturated buffers would be half of the $5/treated acre/year assumed for bioreactors.
Grade Stabilization
Insufficient information about this practice precluded inclusion at this time.
Blind Inlets
Due to a lack of studies that determine removal efficiency, the team decided not to add blind inlets to the list of NLRS practices. However, looking forward, the team expects to see future studies that will provide this information about blind inlets and encourages resubmission when these studies become available.
Terraces
Because terraces are an established practice that has been used in Illinois for many years, the team decided to include it. The literature has little existing information on terrace phosphorus dynamics; however, the team felt it unlikely that any forthcoming new research would refine nutrient loss reduction efficiencies. Therefore, the following efficiency numbers were decided: 40% P loss reduction in non-tiled fields; 0% N loss reduction. These estimates were based on the lowest reported phosphorus loss reduction in the proposal.
Concern regarding total and dissolved phosphorus dynamics, especially when terraces are drained, led the science team to select a conservatively low estimate. A cost estimate of $40/treated acre/year was assumed based on the presented annualized installation costs (rounded to the nearest $10), as well as reported installation, and operations and maintenance costs presented by Yang, et al. (2010), which were inflated to 2021 dollars and rounded.
Yang, Q., Zhao, Z., Benoy, G., Chow, T. L., Rees, H. W., Bourque, C. P. A., & Meng, F. R. (2010). A watershed-scale assessment of cost-effectiveness of sediment abatement with flow diversion terraces. Journal of environmental quality, 39(1), 220-227.
Water and Sediment Control Basins
The science team discussed, but ultimately decided not to include WASCOBs at this time, due to a lack of studies. However, studies are currently underway. They encourage collaboration among NLRS partners and resubmission after more studies are published.
