Many ecosystems are losing biodiversity, raising concern for the services they provide. However, the extent of loss is uncertain, especially for insects that use freshwater during their life. Further study is needed to assess freshwater insect abundances and diversity. In Central Appalachian streams, macroinvertebrate diversity declines in response to mining-induced salinization and resulting changes to ecosystem processes remain largely unknown, such as how the availability and movement of macroinvertebrate biomass is altered in stream food webs. However, taxa observed are dependent upon sampling effort that could bias diversity-process interpretation. Taxon sampling curves can be used to estimate sampling effort that maximizes the probability of complete community characterization. We sampled six streams in the Central Appalachian region for benthic macroinvertebrates and explored the number of samples needed to capture taxonomic richness in salinized streams. Sampling effort did not differ between reference and salinized streams, though more uneven distributions of macroinvertebrates in salinized streams seemed to necessitate greater sampling effort relative to reference streams. We also used taxon and trait-based sampling curves to expand our understanding of biodiversity and functional responses to environmental change. Because macroinvertebrate biomass and emergence can assess the movement and changes in organic material and energy in response to a salinization gradient, we added them as additional metrics. Macroinvertebrates may have varied responses to a stressor dependent upon life stage, suggesting that assessments relying only on immatures may not fully characterize the effects of salinization. We sampled benthic macroinvertebrate biomass and emergent insect biomass from six streams in the Central Appalachian region to be representative of a salinization gradient. We predicted benthic biomass would either decrease, be maintained by greater density and biomass of salt-tolerant taxa, or increase from a salt subsidy effect, while emergent biomass would decrease disproportionately relative to benthic biomass due to late instar and pupae succumbing to stress. Our results suggest that total benthic macroinvertebrate biomass is maintained along a salinization gradient despite the loss of salt-sensitive mayflies due to compensation by salt-tolerant taxa that experience a subsidizing effect. Emergent biomass was variable among streams with peak emergence occurring in spring, with no apparent negative response to increasing conductivity. The present study can help to further develop metrics of stream ecosystem processes in response to a disturbance gradient. / Master of Science in Life Sciences / Freshwater salinization is a growing, global concern. Pollution and accelerated weathering of rock, caused by human activities, introduce salts to streams and other freshwaters. Surface coal mining is a common land use in the Central Appalachian region and increases leaching of sulfate and other major ions that increase stream salinity, leading to losses of aquatic insect species. Aquatic insects are important to stream processes, such as providing food to other animals, and they can serve as the bioassessments when impacts are suspected. For example, the impacts of salinization on streams are not fully understood despite bioassessments. We sampled aquatic insects from six Appalachian streams with varying levels of salinity. We estimated the sampling effort needed to characterize aquatic larval insect communities in streams with low salinity compared to streams with high salinity. We found that about six samples captured 80 percent of estimated total taxa and that insect communities with greater unevenness required more sampling effort. Such comparisons will allow us to make more informed decisions when sampling aquatic insects and assessing the effects of salts on streams. We also estimated insect biomass in streams using two life stages, larvae and adults, to determine if these life stages would respond differently to salinization. As we expected, total larval biomass slightly increased as the concentration of salt increased, but mayfly biomass decreased. Mayflies are an important and diverse group of insects in Appalachian streams and decreases in their biomass can have consequences for insect communities and stream food webs. Even though emergent insect biomass was found to represent only a small proportion of the larval biomass observed in streams, they represent critical food for terrestrial animals. Estimates of benthic and emergent biomass could be considered to refine bioassessments that support future management and policy regarding surface mining and the rising issue of freshwater salinization.

Although it is well documented how introduced species can negatively affect native species, we only poorly understand how they may alter ecosystem functions. We investigated how an invasive fish affected the flux of aquatic insects to terrestrial food webs using mesocosms in a desert spring ecosystem. We compared aquatic insect emergence between alternative community states with monocultures and polycultures of two native species of fish, least chub (Iotichthys phlegethontis) and Utah chub (Gila atraria) plus, introduced western mosquitofish (Gambusia affinis). We tested three hypotheses: (1) aquatic insect biomass will be greater than terrestrial insect biomass and thus, constitute a vital source of energy for terrestrial consumers (2) invasive mosquitofish will negatively impact the biomass of emerging aquatic insects, and (3) terrestrial consumers will negatively respond to decreased emerging aquatic insect biomass. Aquatic insects represented 79% of the flying insect community, and treatments with mosquitofish significantly reduced emergent aquatic insect biomass by 60% relative to the control without mosquitofish. Behavioral traits of invasive species are important, because mosquitofish most heavily affected insects that emerged during the day. Also, spiders that build horizontal webs were negatively correlated with decreasing aquatic insect biomass. Invasive mosquitofish can achieve very dense populations because of their high intrinsic rate of population increase, which can significantly disrupt the flow of energy between aquatic and terrestrial ecosystems, thereby reducing the energy available for terrestrial consumers.

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