Impacts of Hydroelectric Dams on Aquatic Macroinvertebrate Oviposition Strategies: The Role of Desiccation

Previous studies quantifying the density, distribution and diversity of aquatic insects overwhelmingly focus on larval life stages. However, many aquatic insects exhibit selective oviposition behaviors, with a preference for emergent substrates along a river\u27s edge. The practice of hydropeaking creates an artificial intertidal zone that is absent from natural rivers and to which freshwater organisms are not adapted. We hypothesized that this novel disturbance could reduce the availability and temporal persistence of oviposition habitats resulting in egg mortality. To test this hypothesis, we quantified the oviposition behavior of four aquatic insects using a hierarchical field survey of habitat availability and utilization. We found that three out of four genera exhibited preferences for larger, emergent substrates located along the river edge, thus increasing the likelihood of desiccation during stage height fluctuations. When subject to experimental drying, we observed up to 93% egg mortality during desiccation lasting two hours or less, and 100% mortality when desiccation exceeded four hours. These paired field and experimental results suggest that hydropeaking could impart a population bottleneck on aquatic insects. This project is on-going and these writing do not reflect the final views of the authors

Empirical observations and numerical modelling of tides, channel morphology, and vegetative effects on accretion in a restored tidal marsh

Tidal marshes form at the confluence between estuarine and marine environments where tidal movement regulates their developmental processes. Here, we investigate how the interplay between tides, channel morphology, and vegetation affect sediment dynamics in a low energy tidal marsh at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island. Poplar Island is an active restoration site where fine‐grained material dredged from navigation channels in the upper Chesapeake Bay are being used to restore remote tidal marsh habitat toward the middle bay (Maryland, USA). Tidal currents were measured over multiple tidal cycles in the inlets and tidal creeks of one marsh at Poplar Island, Cell 1B, using Acoustic Doppler Current Profilers (ADCP) to estimate water fluxes throughout the marsh complex. Sediment fluxes were estimated using acoustic backscatter recorded by ADCPs and validated against total suspended solid measurements taken on site. A high‐resolution geomorphic survey was conducted to capture channel cross sections and tidal marsh morphology. We integrated simple numerical models built in Delft3d with empirical observations to identify which eco‐geomorphological factors influence sediment distribution in various channel configurations with differing vegetative characteristics. Channel morphology influences flood‐ebb dominance in marshes, where deep, narrow channels promote high tidal velocities and incision, increasing sediment suspension and reducing resilience in marshes at Poplar Island. Our numerical models suggest that accurately modelling plant phenology is vital for estimating sediment accretion rates. In‐situ observations indicate that Poplar Island marshes are experiencing erosion typical for many Chesapeake Bay islands. Peak periods of sediment suspension frequently coincide with the largest outflows of water during ebb tides resulting in large sediment deficits. Ebb dominance (net sediment export) in tidal marshes is likely amplified by sea‐level rise and may lower marsh resilience. We couple field observations with numerical models to understand how tidal marsh morphodynamics contribute to marsh resilience

Earthworm invasion : consequences and conservation implications for the endangered Garry Oak (Quercus garryana) and maritime meadow ecosystems

Biological invasions by non-native ‘ecosystem engineers’ can radically alter the ecological and socio-economic values of ecosystems in ways that may require decades to detect. The invasion of North American glacial refuges by non-native earthworms is a prominent but understudied example of a cryptic invasion by an ecosystem engineer. Non-native earthworms are known to reduce soil carbon, disrupt mycorrhizal networks, and homogenize plant communities in their role as seed predators, root foragers, and in nutrient cycling and redistribution. However, natural resource managers have struggled to discern the scale at which non-native earthworms influence plant species diversity across invaded biomes. With no effective methods to eradicate or control established earthworm populations, there is great need for preemptive strategies to identify high-value conservation areas at risk of invasion. Herein, I address two main questions with implications for forest management: 1) Can the influence of non-native earthworms on plant community assembly be reliably predicted using plant traits? 2) Can abiotic factors be used to identify and predict natural refuges from earthworms in heterogenous habitats? I found that the presence of earthworms contributed to the simplification of plant communities in experimental mesocosms and observational surveys of in-situ forest and meadow habitat. In general, earthworms were associated with plant communities dominated by species with large seeds and fibrous roots, whereas species with small seeds and taproots only persisted in multi-species mesocosms without earthworms. These findings suggest that earthworms shape community composition in the early stages of invasion by acting as ecological filters on morphological plant traits. Last, I constructed an ensemble species distribution model for non-native earthworms using data from 300 survey plots to identify the suite of environmental conditions needed to limit the dispersal and persistence of invading earthworms. This model showed that shallow and dry soils on steep terrain strongly limit the occurrence and abundance of non-native earthworms. My results show that earthworms reduce plant species richness in coastal forest and meadow habitats of southwest British Columbia and highlight the conservation value of shallow-soil habitats that limit earthworm distribution and persistence.Forestry, Faculty ofGraduat

Empirical observations and numerical modelling of tides, channel morphology, and vegetative effects on accretion in a restored tidal marsh

Tidal marshes form at the confluence between estuarine and marine environments where tidal movement regulates their developmental processes. Here, we investigate how the interplay between tides, channel morphology, and vegetation affect sediment dynamics in a low energy tidal marsh at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island. Poplar Island is an active restoration site where fine‐grained material dredged from navigation channels in the upper Chesapeake Bay are being used to restore remote tidal marsh habitat toward the middle bay (Maryland, USA). Tidal currents were measured over multiple tidal cycles in the inlets and tidal creeks of one marsh at Poplar Island, Cell 1B, using Acoustic Doppler Current Profilers (ADCP) to estimate water fluxes throughout the marsh complex. Sediment fluxes were estimated using acoustic backscatter recorded by ADCPs and validated against total suspended solid measurements taken on site. A high‐resolution geomorphic survey was conducted to capture channel cross sections and tidal marsh morphology. We integrated simple numerical models built in Delft3d with empirical observations to identify which eco‐geomorphological factors influence sediment distribution in various channel configurations with differing vegetative characteristics. Channel morphology influences flood‐ebb dominance in marshes, where deep, narrow channels promote high tidal velocities and incision, increasing sediment suspension and reducing resilience in marshes at Poplar Island. Our numerical models suggest that accurately modelling plant phenology is vital for estimating sediment accretion rates. In‐situ observations indicate that Poplar Island marshes are experiencing erosion typical for many Chesapeake Bay islands. Peak periods of sediment suspension frequently coincide with the largest outflows of water during ebb tides resulting in large sediment deficits. Ebb dominance (net sediment export) in tidal marshes is likely amplified by sea‐level rise and may lower marsh resilience. We couple field observations with numerical models to understand how tidal marsh morphodynamics contribute to marsh resilience

Rooting depth and xylem vulnerability are independent woody plant traits jointly selected by aridity, seasonality, and water table depth

Evolutionary radiations of woody taxa within arid environments were made possible by multiple trait innovations including deep roots and embolism-resistant xylem, but little is known about how these traits have coevolved across the phylogeny of woody plants or how they jointly influence the distribution of species. We synthesized global trait and vegetation plot datasets to examine how rooting depth and xylem vulnerability across 188 woody plant species interact with aridity, precipitation seasonality, and water table depth to influence species occurrence probabilities across all biomes. Xylem resistance to embolism and rooting depth are independent woody plant traits that do not exhibit an interspecific trade-off. Resistant xylem and deep roots increase occurrence probabilities in arid, seasonal climates over deep water tables. Resistant xylem and shallow roots increase occurrence probabilities in arid, nonseasonal climates over deep water tables. Vulnerable xylem and deep roots increase occurrence probabilities in arid, nonseasonal climates over shallow water tables. Lastly, vulnerable xylem and shallow roots increase occurrence probabilities in humid climates. Each combination of trait values optimizes occurrence probabilities in unique environmental conditions. Responses of deeply rooted vegetation may be buffered if evaporative demand changes faster than water table depth under climate change