Conservation Across Aquatic-Terrestrial Boundaries: Linking Continental-Scale Water Quality to Emergent Aquatic Insects and Declining Aerial Insectivorous Birds

Abstract

Larval aquatic insects are used to assess water quality, but less attention is paid to their adult, terrestrial life stage, which is an important food resource for declining aerial insectivorous birds. We used open-access water-quality, aquatic-invertebrate, and bird-survey data to study how impaired water quality can emanate from streams and lakes through changes in aquatic insect communities across the contiguous United States. Emergent insect relative abundance was highest across the West, in northern New England, and the Carolinas in streams, and highest near the Great Lakes, parts of the Southwest, and northern New England for lakes. Emergent insects declined with sedimentation, roads, and elevated ammonium concentrations in streams, but not lakes. The odds that a given taxon would be non-emergent increased by up to 2.0× as a function of pollution tolerance, underscoring the sensitivity of emergent aquatic insects to water-quality impairment. However, relationships between bird populations and emergent insects were generally weak for both streams and lakes. For streams, we observed the strongest positive relationships for a mixture of upland and riparian aerial insectivorous birds such as Western Wood-Pewee, Olive-sided Flycatcher, and Acadian Flycatcher and the strongest negative association for Purple Martin. Different avian insectivores responded to emergent insect abundances in lakes (e.g., Barn Swallow, Chimney Swift, Eastern Wood-Pewee, Common Nighthawk). In both streams and lakes, we observed stronger, but opposing, relationships between several aerial insectivores and the relative abundance of sensitive insect orders (E)phemeroptera, (P)lecoptera, and (T)richoptera (positive), and pollution tolerant individuals (negative). Overall, our findings indicate that emergent insects are negatively correlated with pollution tolerance, suggesting a large-scale loss of this nutritional subsidy to terrestrial environments from impaired aquatic ecosystems. While some bird populations tracked scarcities of emergent aquatic insects, especially EPT taxa, responses varied among species, suggesting that unique habitat and foraging behaviors likely complicated these relationships. Strengthening spatial and temporal concordance between emergent-insect and bird-survey data will improve our ability to interpret species-level responses over time. Thus, our analysis highlights the need for developing conservation and biomonitoring strategies that consider the cross-ecosystem effects of water quality declines for threatened insectivorous avifauna and other terrestrial wildlife.

Climate change shifts the timing of nutritional flux from aquatic insects

“…The relatively large body sizes of these aquatic insects also make them preferred food items for many species of birds. [58][59][60][61][62] Unfortunately, EPT taxa are especially sensitive to anthropogenic disturbances like increased agricultural intensification and urbanization. [63][64][65] As a consequence, EPT taxa are some of the first species to be lost from local food webs following disturbance and exposure to agricultural pesticides, 66 and their nutritional contributions to consumers cannot be readily offset by conservation of terrestrial systems alone (Figure 4).…”

Networked computing systems for bio-diversity and environmental preservation

“…In this context, the biosphere comprises terrestrial, underwater and avian habitats. However, the anthropogenic effect arising from pollution due to data centre cooling causes changes in aquatic and avian biodiversity 12 , 13 requires additional consideration.…”

Stream degradation affects aquatic resource subsidies to riparian ground-dwelling spiders

“…Lower EPA production at the base of the food chain is transferred to higher trophic levels (consumers), causing aquatic organisms including emergent insects to contain less EPA (Müller-Navarra et al, 2004;Taipale et al, 2016;Scharnweber et al, 2019). Second, the abundance of some stream invertebrates also can be reduced in degraded streams through negative impacts of high nutrient or fine sediment loads; e.g., aquatic invertebrates that emerge from the stream during their lifecycle seem to be particularly susceptible to environmental stressors (Manning and Sullivan, 2021). Consequently, the reduced biomass export via emerging insects will reduce EPA export to riparian zones.…”