DOI: 10.5061/dryad.3d22k
title: Data from: Suburban watershed nitrogen retention: estimating the effectiveness of stormwater management structures

description: Excess nitrogen (N) is a primary driver of freshwater and coastal
 eutrophication globally, and urban stormwater is a rapidly growing source
 of N pollution. Stormwater best management practices (BMPs) are used
 widely to remove excess N from runoff in urban and suburban areas, and are
 expected to perform under a wide variety of environmental conditions. Yet
 the capacity of BMPs to retain excess N varies; and both the variation and
 the drivers thereof are largely unknown, hindering the ability of water
 resource managers to meet water quality targets in a cost-effective way.
 Here, we use structured expert judgment (SEJ), a performance-weighted
 method of expert elicitation, to quantify the uncertainty in BMP
 performance under a range of site-specific environmental conditions and to
 estimate the extent to which key environmental factors influence variation
 in BMP performance. We hypothesized that rain event frequency and
 magnitude, BMP type and size, and physiographic province would
 significantly influence the experts’ estimates of N retention by BMPs
 common to suburban Piedmont and Coastal Plain watersheds of the Chesapeake
 Bay region. Expert knowledge indicated wide uncertainty in BMP
 performance, with N removal efficiencies ranging from &lt;0% (BMP
 acting as a source of N during a rain event) to &gt;40%. Experts
 believed that the amount of rain was the primary identifiable source of
 variability in BMP efficiency, which is relevant given climate projections
 of more frequent heavy rain events in the mid-Atlantic. To assess the
 extent to which those projected changes might alter N export from suburban
 BMPs and watersheds, we combined downscaled estimates of rainfall with
 distributions of N loads for different-sized rain events derived from our
 elicitation. The model predicted higher and more variable N loads under a
 projected future climate regime, suggesting that current BMP regulations
 for reducing nutrients may be inadequate in the future.
description: Expert uncertainty
 estimates for all 60 questions in the SEJ protocol
 documentThis tab-delimited text
 file contains raw values provided by all 10 experts for all 60 questions
 in the structured expert judgment (SEJ) protocol document (Appendix S3).
 The six columns are defined as follows: “Expert” refers to the expert
 identification codes used in the article; “Qnum” refers to the number of
 each question in the SEJ protocol document (Appendix S3); “Qid” is a brief
 coded description of the key variables in each question (codes are
 arranged as watershed location – storm event number – site description –
 influent/effluent load – pre/post restoration condition; see Appendix S3
 for the full details of each question); “Percentile.05” is the 5th
 percentile of the probability distribution envisioned by each expert to
 describe the total nitrogen load for each question (units are kg total
 nitrogen); “Percentile.50” and “Percentile.95” refer to the 50th and 95th
 percentiles of the distribution, respectively (units are kg total
 nitrogen). Note that expert names are not associated with their estimates;
 the ordering of expert names in Appendix S2 is different than the ordering
 of their estimates in the data.Koch_SEJ_all_experts_TN_load_kg.txtRealizations for the 11 calibration variables in the SEJ protocol documentThis tab-delimited text file contains empirically measured values for the 11 calibration variables in the structured expert judgment (SEJ) protocol document (Appendix S3). The three columns are defined as follows: “Qnum” refers to the number of each question in the SEJ protocol document that corresponds to a calibration variable (Appendix S3); “Qid” is a brief coded description of the key variables in each question (codes are arranged as watershed location – storm event number – site description – influent/effluent load – pre/post restoration condition; see Appendix S3 for the full details of each question); “TN.load.kg” is the empirically measured total nitrogen load (units are kg total nitrogen).Koch_SEJ_calibration_variables_TN_load_kg.txt