Geology topics

David A. Lytle

Publications and source records attributed to David A. Lytle.

6 recordsLinked to original sources

USGS2026

Predicting reach-scale macroinvertebrate community changes due to declining flows in an aridland river

Understanding the connection between streamflow and macroinvertebrate community structure is critical for managing river ecosystems under scenarios of change caused by human activities and drought. Streamflow influences physical habitat characteristics, including depth, water velocity, and substrate composition, which structure macroinvertebrate communities. Although strong empirical evidence has linked macroinvertebrates to these variables, most studies are correlative, and predictive approaches that link altered streamflow to changes in habitat availability and community structure remain limited. To address this gap, we coupled benthic macroinvertebrate surveys with reach-scale, 2-dimensional hydraulic models to quantify changes in community structure in response to altered streamflows. We characterized macroinvertebrate communities and physical habitat conditions in riffle, run, and pool mesohabitats across 3 reaches of a free-flowing section of the Verde River (Arizona, USA) over 3 y and developed hydraulic models using overflight data, ground surveys, and streamflow monitoring. Macroinvertebrate communities differed among mesohabitats, with riffles supporting higher macroinvertebrate densities and pools exhibiting higher taxonomic richness. The 2-dimensional hydraulic models indicated that declining streamflows could reduce the area of suitable habitat in riffles and runs relative to pools, potentially shifting the distribution of mesohabitats and altering community composition. These changes may lead to declines in overall macroinvertebrate diversity and abundance under reduced flow conditions. By explicitly linking streamflow to habitat availability and community structure, this study demonstrates how integrating hydraulic modeling with biological surveys can improve predictions of ecological response to flow alteration. This framework provides a basis for flow management strategies aimed at maintaining habitat heterogeneity and supporting biodiversity in river networks.

Arizona↗

USGS2026

Modeling the temperature-mediated link between demography and biomass in ectotherms

Population models can forecast the effects of environmental change, disturbance, and management decisions on populations of interest. Most population models focus on abundance of individuals, but biomass may be a more relevant quantity at the community or ecosystem scale, especially when investigating interaction of multiple stressors and cross-ecosystem energy flows. We developed a stage-structured population model that integrates a temperature-mediated tradeoff between development rate and final body size of invertebrates, allowing projection of both population size and standing stock biomass in ecosystems that experience disturbances. We parameterized the model for four aquatic invertebrate life-history types spanning a range of lifespan and susceptibility to disturbance. We observed several emergent properties typical of invertebrate populations but not explicitly included in the model, including self-organization of cohort structure under seasonal environments, a tradeoff between lifespan duration and rate of post-disturbance population recovery, and chaotic population dynamics under high growth rates. Sensitivity analysis revealed that although elevated mean temperature increased population size, total population biomass remained unchanged or even decreased due to declining individual biomass, which has implications for ecosystem processes under a changing climate. The seasonal timing of disturbance showed a strong interaction with temperature regime, with summer versus winter pulse disturbances affecting biomass and abundance in characteristically different ways. Linking invertebrate abundance and biomass dynamics to abiotic drivers through this time-varying matrix population model reveals how life-history shapes aquatic invertebrate response to shifting seasons, temperatures, and disturbance, which is key to understanding the impacts of climate change on aquatic ecosystems.

Ecological Modelling↗

USGS2022

Population connectivity of aquatic insects in a dam-regulated, desert river

Humans have exaggerated natural habitat fragmentation, negatively impacting species dispersal and reducing population connectivity. Habitat fragmentation can be especially detrimental in freshwater populations, whose dispersal is already constrained by the river network structure. Aquatic insects, for instance, are generally limited to two primary modes of dispersal: downstream drift in the aquatic juvenile life stages and flight during the terrestrial winged adult stage. Yet the impacts of large hydropower dams can make rivers uninhabitable for incoming (drifting) juvenile insects, with remaining refugia found only in tributaries. The ability of adult aquatic insects to traverse such river stretches in search of suitable tributary habitat likely depends on factors such as species-specific dispersal ability and distance between tributaries. To explore the intersection of natural and human-induced habitat fragmentation on aquatic insect dispersal ability, we quantified population genetics of three taxa with varying dispersal abilities, a caddisfly (Hydropsychidae, Hydropsyche oslari ), a mayfly (Baetidae: Fallceon quilleri ), and a water strider (Veliidae: Rhagovelia distincta ), throughout tributaries of the Colorado River in the Grand Canyon, Arizona, USA. Using 2bRAD reduced genome sequencing and landscape genetics analyses, we revealed a strong pattern of isolation by distance among mayfly populations. This contrasts with caddisfly and water strider populations, which were largely panmictic. Analysis of thousands of informative single nucleotide polymorphisms showed that realized dispersal ability may not be accurately predicted by species traits for these widespread species. Principal components analysis revealed a strong division between caddisfly populations upstream and downstream of Havasu Creek (279 km through the 390 km study reach), suggesting that the geography of the Grand Canyon imposes a dispersal barrier for this species. Our use of genetic tools in the Grand Canyon to understand population structure has enabled us to elucidate dispersal barriers for aquatic insects. Ultimately, these data may be useful in informing effective conservation management plans for understudied organisms of conservation interest.

River Research and Applications↗

USGS2021

Hydropeaking intensity and dam proximity limit aquatic invertebrate diversity in the Colorado River Basin

River biodiversity is threatened globally by hydropower dams, and there is a need to understand how dam management favors certain species while filtering out others. We examined aquatic invertebrate communities within the tailwaters 0–24 km downstream of seven large hydropower dams in the Colorado River Basin of the western United States. We quantified aquatic invertebrate dominance, richness, abundance, and biomass at multiple locations within individual tailwaters and across the basin and identified biological community responses associated with dam operations and distance from dam. We found that each tailwater was dominated by 3–7 invertebrate taxa, accounting for 95% of total abundance. Half of these dominant taxa were non-insect, non-flying species and thus were unavailable to terrestrial consumers. Consistent with previous studies, aquatic insects and sensitive taxa were negatively associated with hydropeaking intensity (magnitude of daily flow fluctuations associated with hydropower generation), which limits the composition and potentially the quality of the invertebrate food base. While total invertebrate abundance and biomass did not change with increasing distance downstream from dams, insect and sensitive taxa richness, abundance, and biomass all increased, suggesting that impacts of hydropeaking are most acute immediately downstream of dams. Our results demonstrate that tailwaters experiencing hydropeaking support high abundances of aquatic invertebrate, but the diversity of these communities is low.

Arizona, California, Colorado, Nevada, New Mexico,↗

USGS2014

Are large-scale flow experiments informing the science and management of freshwater ecosystems?

Greater scientific knowledge, changing societal values, and legislative mandates have emphasized the importance of implementing large-scale flow experiments (FEs) downstream of dams. We provide the first global assessment of FEs to evaluate their success in advancing science and informing management decisions. Systematic review of 113 FEs across 20 countries revealed that clear articulation of experimental objectives, while not universally practiced, was crucial for achieving management outcomes and changing dam-operating policies. Furthermore, changes to dam operations were three times less likely when FEs were conducted primarily for scientific purposes. Despite the recognized importance of riverine flow regimes, four-fifths of FEs involved only discrete flow events. Over three-quarters of FEs documented both abiotic and biotic outcomes, but only one-third examined multiple taxonomic responses, thus limiting how FE results can inform holistic dam management. Future FEs will present new opportunities to advance scientifically credible water policies.

Frontiers in Ecology and the Environment↗

USGS2011

Large-scale flow experiments for managing river systems

Experimental manipulations of streamflow have been used globally in recent decades to mitigate the impacts of dam operations on river systems. Rivers are challenging subjects for experimentation, because they are open systems that cannot be isolated from their social context. We identify principles to address the challenges of conducting effective large-scale flow experiments. Flow experiments have both scientific and social value when they help to resolve specific questions about the ecological action of flow with a clear nexus to water policies and decisions. Water managers must integrate new information into operating policies for large-scale experiments to be effective. Modeling and monitoring can be integrated with experiments to analyze long-term ecological responses. Experimental design should include spatially extensive observations and well-defined, repeated treatments. Large-scale flow manipulations are only a part of dam operations that affect river systems. Scientists can ensure that experimental manipulations continue to be a valuable approach for the scientifically based management of river systems.

BioScience↗