Jeffrey D. Muehlbauer

Short-term responses of decomposers to flow restoration in Fossil Creek, Arizona, USA

Dam decommissioning projects, although numerous, rarely include complete sets of data before and after restoration for evaluating the ecological consequences of such projects. In this study, we used a before-after control-impact (BACI) design to assess changes in leaf litter decomposition and associated macroinvertebrate and fungal decomposers following dam decommissioning in Fossil Creek, Arizona, USA. Leaf litterbags were deployed in a relatively pristine site above the dam and a highly disturbed site below the dam where over 95% of the flow was previously diverted for hydropower generation. Leaf litter decomposition was significantly slower below the dam both measurement years (pre- and post-restoration) with no site-year interaction, indicating that decomposition in this stream section was not affected by increased flow. In contrast, both macroinvertebrates and fungi differed significantly above and below the dam prior to restoration but were similar post-restoration, supporting the concept that decomposer communities can quickly rebound following reintroduction of full flow. Our results indicate that some aquatic ecosystem variables can return to a more natural state following ecological restoration activities such as water flow restoration.

Response of stream macroinvertebrates in flow refugia and high-scour areas to a series of floods: a reciprocal replacement study

Abstract Disturbances from flooding are a dominant feature of the habitat template in streams. Frequent floods created by recreational releases (1–2 d between releases/floods) from Abanakee Dam in the Adirondack Mountains, USA, result in a static mosaic of scoured patches in areas of high shear stress (low diatom densities) and mats of algae in areas of low shear stress (refugia); this pattern is different from the shifting mosaic of patches more typical of streams recovering from floods. Predictable, recreational release floods and similar bed size particle distributions in this stream enabled us to use a reciprocal replacement experiment to examine macroinvertebrate community responses in high scour and flow refugia areas without the confounding variable of different substrata. Trays of substrata were embedded in both high shear stress (HSS) and low shear stress (LSS) areas. Half of the trays from each area were then reciprocally exchanged while resident trays remained in their original positions. After 2, 6, and 12 releases, 20 trays for each of 4 treatments were sampled. Lower macroinvertebrate densities in the LSS area reflected an absence or loss of filter-feeders that require higher current velocities than were present between releases, and this absence probably was responsible for the lower species diversity in the LSS area. The net-spinning caddisfly, Macrostemum, dominated the HSS area because its retreat design protects the fine-meshed net from high velocities. The filter-feeding mayfly, Isonychia, thrived in the HSS area because it could seek refuge during releases and could benefit from the potentially higher particle delivery in the higher flow velocities between releases. Ordinations showed that community composition shifted quickly (2–12 d) in trays moved from the LSS area to the HSS area because of the rapid colonization by filter-feeders in the HSS area. However, trays from the HSS area moved to the LSS area were slower (>21 d) to change to the LSS community composition. We suggest that hydrologic conditions strongly influenced macroinvertebrate composition with filter-feeders dominating where shear stresses scoured periphyton. However, in LSS areas where periphyton was abundant, the community was dominated by collector-gatherers and scrapers. Also, HSS substrata transferred to the LSS areas were slow to be colonized by gatherers and scrapers probably because periphyton had not yet developed on the HSS rocks.

Knickpoint effects on macroinvertebrates, sediment, and discharge in urban and forested streams: urbanization outweighs microscale habitat heterogeneity

Abstract.  Knickpoints are dynamic geomorphic formations in the longitudinal stream profile that have long been a subject of interest for geomorphologists, but have been largely unstudied in stream ecology. We measured discharge, bed sediment, and macroinvertebrate communities around knickpoints in forested and urban catchments. Knickpoints introduced microscale heterogeneity in discharge. This heterogeneity may be important in providing refugia for benthic biota during low-flow conditions, depending on the condition of the bed sediment below the knickpoint, which was highly variable. In addition, knickpoints supported a unique filterer-dominated community of macroinvertebrates not found elsewhere in the stream reach. The knickpoint itself also may maintain a higher overall density of macroinvertebrates in comparison to other habitats in the stream reach, but this prediction was only weakly supported. Instead, the largest differences in macroinvertebrate community metrics were consistently between urban and forested knickpoints. Decreases in density, species richness, and diversity from forested to urban knickpoints greatly outweighed any longitudinal differences in the macroinvertebrate community within individual knickpoint sites. Thus, we conclude that knickpoints may serve as hotspots of biodiversity and provide substantial habitat heterogeneity over a small area, but the valley-scale influence of catchment land use far outweighs the effect of these microscale geomorphic features in influencing benthic communities.

Effect of tributary and braided confluences on aquatic macroinvertebrate communities and geomorphology in an alpine river watershed

River-channel confluences create habitat heterogeneity by introducing multiple zones of hydraulic flow and increase macroinvertebrate densities and diversity via the input of coarse sediment, allochthonous detritus, and nutrients. Current understanding of confluence effects on stream community structure and function is based mostly on research conducted at medium-to-large tributary confluences where nutrient and detrital loads are typically high. Confluences of headwater streams and in streams without the input of these materials are understudied. In this study, we sampled macroinvertebrate communities and measured sediment and flow conditions upstream, within, and downstream of confluences. Our sampling included braided confluences, which lack allochthonous detritus and coarse sediment sources, and headwater-stream confluences. Braided confluences had lower macroinvertebrate densities and richness compared to up- and downstream reaches, whereas headwater-stream confluences had a negligible effect on confluence communities. Our results indicate that confluences are not always areas of increased species richness and density for macroinvertebrates. Rather, severe shear stress conditions created by confluence hydraulics can reduce benthic community density and richness relative to adjacent stream locations, especially when tributary inputs of allochthonous food sources to the confluence are low. In addition, we found that all confluences that we studied created small step changes in community composition. Thus, braided rivers may create new habitat patches every time a channel divides or joins, promoting habitat heterogeneity on a broader scale.

Linking Stoichiometric Homeostasis of Microorganisms with Soil Phosphorus Dynamics in Wetlands Subjected to Microcosm Warming

Soil biogeochemical processes and the ecological stability of wetland ecosystems under global warming scenarios have gained increasing attention worldwide. Changes in the capacity of microorganisms to maintain stoichiometric homeostasis, or relatively stable internal concentrations of elements, may serve as an indicator of alterations to soil biogeochemical processes and their associated ecological feedbacks. In this study, an outdoor computerized microcosm was set up to simulate a warmed (+5°C) climate scenario, using novel, minute-scale temperature manipulation technology. The principle of stoichiometric homeostasis was adopted to illustrate phosphorus (P) biogeochemical cycling coupled with carbon (C) dynamics within the soil-microorganism complex. We hypothesized that enhancing the flux of P from soil to water under warming scenarios is tightly coupled with a decrease in homeostatic regulation ability in wetland ecosystems. Results indicate that experimental warming impaired the ability of stoichiometric homeostasis (H) to regulate biogeochemical processes, enhancing the ecological role of wetland soil as an ecological source for both P and C. The potential P flux from soil to water ranged from 0.11 to 34.51 mg m−2 d−1 in the control and 0.07 to 61.26 mg m−2 d−1 in the warmed treatment. The synergistic function of C-P acquisition is an important mechanism underlying C∶P stoichiometric balance for soil microorganisms under warming. For both treatment groups, strongly significant (p<0.001) relationships fitting a negative allometric power model with a fractional exponent were found between n-HC∶P (the specialized homeostatic regulation ability as a ratio of soil highly labile organic carbon to dissolved reactive phosphorus in porewater) and potential P flux. Although many factors may affect soil P dynamics, the n-HC∶P term fundamentally reflects the stoichiometric balance or interactions between the energy landscape (i.e., C) and flow of resources (e.g., N and P), and can be a useful ecological tool for assessing potential P flux in ecosystems.

Building a better sticky trap: description of an easy-to-use trap and pole mount for quantifying the abundance of adult aquatic insects

Abstract: Insect emergence is a fundamental process in freshwaters. It is a critical life-history stage for aquatic insects and provides an important prey resource for terrestrial and aquatic consumers. Sticky traps are increasingly being used to sample these insects. The most common design consists of an acetate sheet coated with a nondrying adhesive that is attached to a wire frame or cylinder. These traps must be prepared at the deployment site, a process that can be time consuming and difficult given the vagaries of field conditions. Our goals were to develop a sturdy, low-cost sticky trap that could be prepared in advance, rapidly deployed and recovered in the field, and used to estimate the flight direction of insects. We used 150-mm Petri dishes with lids. The dishes can be coated cleanly and consistently with Tangle-Trap® adhesive. Deploying traps is simple and requires only a pole set near the body of water being sampled. Four dishes can be attached to the pole using Velcro and aligned in 4 different directions to enable quantification of insect flight direction. After sampling, Petri dishes can be taped closed, packed in boxes, and stored indefinitely. Petri traps are comparable in price to standard acetate sheet traps at ∼US

Phenology of the adult angel lichen moth ( Cisthene angelus ) in Grand Canyon, USA

0.50/directional deployment, but they require more space for storage than acetate sheet traps. However, a major benefit of Petri traps is that field deployment times are those of acetate traps. Our study demonstrated that large Petri dishes are an ideal platform for sampling postemergent adult aquatic insects, particularly when the study design involves estimating flight direction and when rapid deployment and recovery of traps is critical.

How wide is a stream? Spatial extent of the potential “stream signature” in terrestrial food webs using meta‐analysis

Abstract We investigated the phenology of adult angel lichen moths (Cisthene angelus) along a 364-km long segment of the Colorado River in Grand Canyon, Arizona, USA, using a unique data set of 2,437 light-trap samples collected by citizen scientists. We found that adults of C. angelus were bivoltine from 2012 to 2014. We quantified plasticity in wing lengths and sex ratios among the two generations and across a 545-m elevation gradient. We found that abundance, but not wing length, increased at lower elevations and that the two generations differed in size and sex distributions. Our results shed light on the life history and morphology of a common, but poorly known, species of moth endemic to the southwestern United States and Mexico.