Eric Lund Kyle Bales Carol Lowenberg Deanne C. Drake 2021 <p>The Long Term Resource Monitoring (LTRM) element of the Upper Mississippi River Restoration program employs a harvest method for sampling submersed aquatic vegetation (SAV) whereby a rake is dragged ~1.5 m over the substrate and plant materials are retrieved.&nbsp; “Plant density” (PD) scores indicate SAV abundance and are based on the amount of plant material collected on the teeth of the rake.&nbsp; Standard PD scores are ordered, whole numbers from 0 (no SAV on the rake) to 5 (80-100% of rake teeth full) and are assigned at each subsite for all species combined and for each individual species.&nbsp;</p><p>In LTRM monitoring between 1998 and 2018, ~73% of non-zero, all-species-combined PD scores were 1s, and ~89% of individual SAV species were 1s.&nbsp; The preponderance of PD = 1 scores along with the wide range of fresh mass represented by PD = 1 (quantified in Drake and Lund 2020) limits inference about SAV abundance from LTRM monitoring data.&nbsp;</p><p>Field personnel noted that small plant fragments comprised a substantial fraction of PD = 1 observations and proposed a modification of the existing LTRM methods where PD = 1 was subdivided to include “trace” scores to represent such small fragments.&nbsp; Trace was defined as PD = 0.08, indicating a maximum of 1 of 13 gaps in the sampling rake filled to the level of an original PD = 1.&nbsp; Amounts of plant material greater than PD = 0.08 and up to the original score of 1 were defined PD = +1.&nbsp; This study used field data collected in 2018 (scoring and fresh weights of scored plant materials) from 136 vegetated sites in Pools 4, 8 and 13 to evaluate the proposed subdivision and to examine among-pool differences in PD data.&nbsp; In the study data, 33% of all-species-combined observations and 69% of species (grouped by morphology) that would previously have received a score of 1 were classified as PD = 0.08.&nbsp; PD scores of 0.08, +1, and 2-3 represented statistically distinct amounts of fresh mass in rake samples.&nbsp; There were systematic differences in the mass of SAV reflected by PD score based on plant morphology and species composition.&nbsp; The mean fresh mass of plant materials assigned a given PD score varied among the three pools, suggesting bias attributable to personnel.&nbsp; To reduce this bias in future data collection efforts, the field crews incorporated a calibration of plant density scores in annual field training.&nbsp; The results presented here describe how including a trace PD score in LTRM data collection improves the description of SAV abundance and consequently estimates of biomass from those PD scores.&nbsp; LTRM vegetation crews have recorded trace scores in annual sampling since 2019 as extra information (i.e. which does not change the LTRM data stream as 0.08 and +1 scores can still be combined for PD=1).&nbsp; Trace data are not currently available to outside users through the LTRM data browser but are available from vegetation component personnel upon request.&nbsp;</p> application/pdf en U.S. Army Corps of Engineers, Upper Mississippi River Restoration Program Evaluation of a “trace” plant density score in LTRM vegetation monitoring reports