Acid rain alters freshwater pH and ion composition, preventing organisms from performing essential bodily functions causing mortality. Macroinvertebrate communities in acidified streams are characterized by species loss in response to physiological stress and altered food quality resulting from the degradation of microbial (e.g., fungi on leaves) communities. Although freshwater acidification in the U.S. is lessening following reduced industrial emissions, little is known about macroinvertebrate recovery. Often, biotic recovery is assessed by looking at changes to what taxa and how many individuals are present in the community (e.g., richness, density). While providing a metric for change, changes in "who" is there (i.e., richness) doesn't necessarily tell us changes in "what" they are doing (i.e., function). The relationship between diversity and function requires linking a "who" to their "what" with direct measurements or as indicated by their traits. Traits are attributes of an organism that aggregate biological, morphological, and behavioral information and may relate to their success in a particular environment. For example, taxa that cannot survive with stream drying (not desiccation resistant) may only be found in streams with permanent water. Trait-based taxonomic metrics could bridge "who" and "what" and expand the impact of stream recovery assessments. My objective was to assess trends over time in water chemistry and macroinvertebrate taxonomic and trait richness and density following reduced industrial emissions. To do so, I studied two long-term data sets from Shenandoah National Park to assess trends in water chemistry and macroinvertebrate taxa and trait composition over a 30-year period to identify taxa and traits that are sensitive to acidification. I also measured how much biomass macroinvertebrates produced in a year (i.e., secondary production) in two streams (1 acidified; 1 not acidified) to determine taxa and traits that are functionally sensitive to acidification. I used these structural and functional measures of sensitivity to determine if changes in trait richness or density predict changes in the function of that trait (e.g., secondary production).
Changes over time show that streams have some recovery from acid rain with increasing stream pH and a greater number of taxa and traits present in the community. Changes in taxa were greater than changes in traits over time. While this result was expected as multiple taxa make up each trait category, it may also suggest minimal or delayed functional recovery over time. Still, macroinvertebrate secondary production indicated that function did differ with differences in acidification. Therefore, observed small changes in traits over time mirror prior studies that found other variables, such as competition for food or space, delay or inhibit macroinvertebrates from returning to the recovering streams. Additionally, there were similarities between traits changing over time and the secondary production of traits that differed between more and less acidified streams. Taxa characterized by long life spans and large body size (e.g., semivoltine, long adult life, slow seasonal development) appeared to be the most sensitive to changes in acidification. These findings suggest that some compositional attributes, like taxonomic or trait richness, may predict functional changes measured as secondary production while others, such as density, do not. / Master of Science in Life Sciences / Acid rain causes the acidification of freshwater stream water observed as decreased stream pH and decreased ability of watershed soils to neutralize or "soak up" acidic inputs before they enter the stream. These changes in stream water chemistry inhibit the ability of aquatic animals to perform essential bodily functions resulting in mortality. The total number of aquatic insect taxa and total number of individuals in the community have been found to decrease in response to acidification. Although freshwater acidification is lessening following reduced industrial emissions, little is known about if and how aquatic insects can recover. Often, aquatic insect recovery is assessed through looking at changes to what taxa and how many individuals are present in the community. While providing a metric for change, changes in "who" is there (i.e., richness) doesn't necessarily tell us changes in "what" they are doing (i.e., function). The relationship between diversity and function requires linking a "who" to their "what". This is often done by assessing changes in the taxa present but also looking at how the composition of traits associated with those taxa also change. Traits or taxa-specific characteristics aggregate biological, morphological, and behavioral information and may relate to their ability to live in a given environment. For example, taxa that rely on filtering and consuming fine particles may only be found in faster flowing streams where they function to remove fine particulates. Trait-based assessments could link "who" and "what" to expand our understanding of how stream ecosystems change with a stressor. My objective was to assess recovery of streams in Shenandoah National Park following reduced industrial emissions. To do so, I studied two long-term (1987-2017) data sets from to assess trends in water chemistry and macroinvertebrate taxa and traits. This enabled me to determine "who" is changing in these streams over time. I also measured how much insect biomass s produced in a year (i.e., secondary production) in two streams (1 more acidic; 1 less acidic) to determine what taxa and traits alter "what" (e.g., secondary production) they are doing.
I found that long-term trends indicate some recovery from acid rain with improving water quality and an increased number of insect taxa and traits present in the community over time. Changes in insect taxa were greater than changes in their traits suggesting that stream acidification did not greatly alter "what" the insects are doing greatly to begin with or that recovery may be delayed. In contrast, my secondary production study showed that "what" macroinvertebrates are doing does differ in more or less acidic streams. Therefore, our observed minimal changes in traits over time suggest that other variables, such as competition for food or space, delay or inhibit macroinvertebrates from returning to the recovering streams. Additionally, there were similarities between traits changing over time and traits that were different in the more or less acidic streams. Taxa characterized by long life spans and large body size (e.g., semivoltine, long adult life, slow seasonal development) appeared to be the most affected by differences or changes in stream water acidity. These findings suggest that changes in "who" can predict changes in "what" to some degree though static metrics of abundance do not always reflect the function of the taxa or community.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/104173 |
| Date | 14 July 2021 |
| Creators | McIntyre, Kelly Christine |
| Contributors | Entomology, Entrekin, Sally A., Schuerch, Roger, Brown, Bryan L., Snyder, Craig D., Mims, Meryl C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Coverage | Virginia |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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