PADEP has recently developed a wadeable freestone acidification assessment method. One biological metrics used for assessments of acidified surface waters is the Acid Tolerance Index (ATI), which relies on Acid Tolerance Values (ATVs) developed for 112 macroinvertebrate taxa. These ATVs represent organism acid tolerance on a 0 (sensitive to acidification) to 10 (tolerant of acidification) scale. ATVs were generated using unconstrained correspondence analysis (CA).
WVDEP and VADEQ have developed their own attributes of macroinvertebrate acid tolerance. This is a comparison of the attributes between states.
Tetra Tech (2020) developed general and single stressor-specific tolerance values (TVs) for WVDEP. Tetra Tech used PCA to develop a stressor gradient based on a pH sample associated with each macroinvertebrate sample. Acid deposition TVs resulted from this exercise and represented tolerance on a 0-10 scale, matching the schema of PADEP. WVDEP’s acid deposition TVs were developed for WVSCI (family-level) and GLIMPSS (genus level) taxonomic units. Genus level comparisons were used for this exercise.
Tetra Tech (2019) developed Biological Condition Gradient (BCG) tolerance attributes for macroinvertebrate and fish in the mid-Atlantic (beyond VA boundaries) for VADEQ. BCG attributes were coded 2 - 5, with 2 and 3 representing senstive taxa, 4 moderately tolerant, and 5 representing tolerant taxa. Similar to WVDEP, BCG attributes were generated for general stress and single stressors. One of the single stressors included in the VADEQ study was pH (acidity and alkalinity). The resulting BCG attribute for pH (acidity) was used in comparisons.
WVDEP has acid deposition TVs for 130 genus-level (or higher) taxa, while PADEP has ATVs for 112 taxa. Of these there are 71 matching taxa.
There is a positive, significant correlation (Spearman and Pearson r > 0.4; P < 0.001) between the TVs from these agencies for the 71 taxa where attributes are available. The plot below shows the relationship, with a 1:1 slope line that would result from perfect agreement. The plot is interactive; hovering over points will display information about each taxa and state TVs. Taxa in the upper left quadrant have PADEP ATVs suggesting higher acid tolerance than WVDEP, and vice-versa for the lower right quadrant.
VADEQ has acidity BCG attributes for 208 genus-level (or higher) taxa, while PADEP has ATVs for 112 taxa. Of these there are 93 matching taxa.
There is a significant, positive correlation (Spearman and Pearson r > 0.49; P < 0.001) between the BCG and TVs from these agencies for the 93 taxa where attributes are available. The plot below shows the relationship. A 1:1 relationship is not expected due to the different scales used (BCG 2-5 vs. ATV 0-10). A LOESS smoother is overlaid. The plot requires a bit more interpretation due to the different scales. The plot is interactive; hovering over points will display information about each taxa and state BCG/TVs. There are no sensitive taxa (BCG 2) with a ATV >3. There are only two BCG 3 taxa (Optioservus and Caenis) that have an ATV >3. However there are moderately tolerant taxa (BCG 4) with ATVs ranging from the minimum of 0 (Taeniopterygidae and Cinygmula) to the maximum of 10 (Peltoperla and Wormaldia). BCG 5 (tolerant) taxa have ATVs ranging from 2 (Ceratopogonidae) to 9 (Ostrocerca and Leuctra).
The next boxplot shows taxa within each VADEQ acidity BCG class by their optimum conditions, represented by the 50th percentile of capture probability from the General Additive Model (GAM) output (Tetra Tech 2019). Median optimum pH for each taxa decreases with increasing BCG class.
The final PADEP - VADEQ comparison is a boxplot showing the optimum pH for each taxa (50th percentile of capture probabilty) generated by Tetra Tech (2019), broken out along the horizontal axis by PA ATV. Optimum pH for each taxa decreases with increasing ATV, similar to the pattern shown in the VADEQ BCG plot shown above, with the exception of taxa with an ATV of 7 (Optioservus and Paracapnia).
There is significant correlation in acid tolerance attributes between PA, WV, and VA. Regional differences in taxa sensitivity/tolerance could be responsible for divergences - or possibly because of different analytical approaches taken to derive tolerance values - or both.
The majority of points in the WV/PA comparison are below the 1:1 line, meaning WV acid tolerances are higher than PA (e.g. Ameletus - PA = 6, WV = 8).
VADEQ followed a BCG approach which resulted in a different scale (2-5) compared to PA ATVs (0-10). However, correlation between the taxa that shared attributes was significant. A potentially more useful comparison of optimum pH for all shared taxa also resulted in visual agreement.
Plot interactivity allows for identification of taxa with disparate acidity tolerances between states. These taxa deserve additional attention in future efforts.