Do Watershed and In-Stream Liming Accelerate Recovery of Macroinvertebrate Communities in Acidified Tributaries to an Adirondack Lake?
Scott George1, Barry P. Baldigo2, Gregory B. Lawrence3 and Randall L. Fuller4
Liming techniques are being explored as tools to accelerate the recovery of aquatic biota from decades of acid deposition in many regions. The preservation or restoration of native sportfish populations has typically been the impetus for liming programs, and as such, less attention has been given to its effects on other biological assemblages such as macroinvertebrates. Furthermore, the effects of various lime application strategies such as in-stream and watershed applications are not well understood. In 2012, a program was initiated using in-stream and aerial (whole-watershed) liming to improve water quality and Brook Trout (Salvelinus fontinalis) recruitment in three acidified tributaries of a high-elevation Adirondack lake in New York. Concurrently, macroinvertebrates were sampled annually between 2013 and 2016 at 3 treated sites and 3 untreated reference sites to assess the effects of each liming technique on this community. Despite increases in pH and acid neutralizing capacity and decreases in inorganic aluminum in all three limed streams, neither liming technique improved the condition of macroinvertebrate communities. The watershed application caused a brief decrease in the density of macroinvertebrates and increase in the proportion of sensitive taxa. These changes were driven primarily by a one-year 71 percent reduction of the acid-tolerant Leuctra stoneflies and likely represent an initial chemistry shock from the lime application rather than a recovery response. The in-stream applications appeared to reduce the density of macroinvertebrates, particularly in one stream where undissolved lime coated the natural substrate. The close proximity of our study sites to the in-stream application points (50 and 1230 m) may partly explain these negative effects. Our results are consistent with those from prior studies which indicate that in-stream liming often fails to restore macroinvertebrate communities to a pre-acidification condition, especially at distances within 1.5 km downstream of the lime application point. The inability of either liming technique to improve the condition of macroinvertebrate communities may be partly explained by the persistence of acidic episodes in all three streams. This suggests that in order to be effective, liming programs should attempt to eliminate even temporary episodes of unsuitable water chemistry rather than just meeting minimal criteria most of the time. Because watershed liming produced a more stable water chemistry regime than in-stream liming, this technique may have greater future potential to eliminate toxic episodes and accelerate the recovery of acid-impacted macroinvertebrate communities.
1U.S. Geological Survey, sgeorge@usgs.gov 2U.S. Geological Survey, bbaldigo@usgs.gov 3U.S. Geological Survey, glawrenc@usgs.gov 4Colgate University, rfuller@colgate.edu