Differences in nitrate uptakeamong benthic algal assemblages in a mountain stream

We evaluated how benthic algal assemblages that vary in composition, richness, and other diversity metrics remove NO 3 -N from the water column of a mountain stream. Ecological theory and empirical studies suggest that ecosystem process rates should increase as richness increases because of niche separation or activity of dominant taxa. Accordingly, we predicted that algal assemblages with highest richness would show the highest rates of NO 3 -N uptake. To test this prediction, we transplanted 225 rocks representing 3 patch types (green, yellow, and brown) that differed macroscopically in algal composition from a lake outflow stream to a lake inflow stream where an experimental release of 15 N-NO 3 was ongoing. We measured 15 N uptake in each patch type during the stable isotope release. Benthic algal richness varied from 28 genera in the green patch type and 26 genera in the yellow patch type to 22 genera in the brown patch type. Without accounting for differences in chlorophyll a content, NO 3 -N uptake (2.1–3.3 3 10 4 /d) was highest in the green patch type, lowest (0.3–0.6 3 10 4 /d) in the yellow patch type, and intermediate (1.2–1.5 3 10 4 /d) in the brown patch type. NO 3 -N uptake normalized to chlorophyll a increased in concert with algal richness in the 3 patch types. This result supports the hypothesis that increased assemblage diversity leads to higher rates of community processes. Aside from diversity differences per se, lower rates of NO 3 -N uptake in the brown patch type might be the consequence of differences in functional characteristics of the taxa present. Approximately 29% of algal biovolume in the brown patch type consisted of taxa capable of N 2 -fixation, a result that suggests that algae in this patch type might be capable of meeting N needs via N 2 -fixation rather than via removal from the water column

Organic Matter is a Mixture of Terrestrial, Autochthonous, and Wastewater Effluent in an Urban River

Terrestrially derived organic matter (OM) is known to dominate the OM pool in reference watersheds. Urban watersheds are known to receive large OM loads compared to reference watersheds, but the proportion of terrestrial, autochthonous, and anthropogenic (e.g., wastewater effluent) sources of OM in urban watersheds remains unknown. Organic matter was identified as a pollutant of concern in the Jordan River, an urban river in the Salt Lake Basin, U.S.A. Our objective was to identify autochthonous, terrestrial, and anthropogenic sources of three size-classes of OM to the Jordan River to inform OM reduction strategies within the watershed. Samples of coarse particulate OM (CPOM), fine particulate OM (FPOM), and dissolved OM (DOM) were analyzed for stable isotopes of carbon, nitrogen, and hydrogen. Stable isotope values of OM were used for Bayesian and graphical gradient-based mixing models to identify autochthonous, terrestrial, and anthropogenic sources. Fluorescent properties of DOM were also used to characterize the sources and composition of DOM. CPOM was primarily terrestrially derived with increased autochthonous inputs from macrophytes in warm months. FPOM was a mixture of terrestrial, autochthonous, and wastewater effluent throughout the year. DOM was primarily from wastewater effluent as well as DOM with isotope signatures unique to DOM from Utah Lake. Characterization of OM in urban rivers will help inform conceptual models of OM dynamics and load management in urban ecosystems

Nitrogen Partitioning and Transport Through a Subalpine Lake Measured with an Isotope Tracer

We used a stable isotope tracer to measure nitrogen (N) assimilation and transfer through Bull Trout Lake, a 0.3-km2 mountain lake in Idaho, specifically to explore the relative importance of pelagic and benthic producers. was added into the inflow stream above the lake during spring runoff and the resulting mass of tracer was measured within the various ecosystem compartments, including the outflow stream. Although a portion of the moved through the lake quickly due to a low hydraulic residence time during the addition, the tracer was also assimilated rapidly by seston in the water column and at a slower rate by benthic primary producers. By the end of the 10-d injection, 10% of the tracer had left via outflow, 21% was within seston, and 17% was in epiphytes and macrophytes. However, 70 d after the termination of the injection, only ∼ 1% of the tracer remained within seston, whereas 10% was within the benthic primary production compartment as N was recycled within the benthic zone. Quantitative transfer of 15N to invertebrate and fish consumers was low, but turnover in these compartments was slow. A conservative water mass tracer (bromide) indicated that the turnover rate for lake water was 1.8% d−1, whereas 15N turnover for the whole lake was only 0.7% d−1, demonstrating how lakes exert drag on nutrients as they move through the watershed. Due to uptake and storage of nutrients, Bull Trout Lake strongly influenced the timing and magnitude of nutrient export from its watershed

Dissimilatory nitrate reductionpathways in an oligotrophic aquatic ecosystem: spatial and temporal trends

Elevated nitrate (NO3−) concentrations can cause eutrophication, which may lead to harmful algal blooms, loss of habitat and reduction in biodiversity. Denitrification, a dissimilatory process that removes NO3− mainly as dinitrogen gas (N2), is believed to be the dominant NO3− removal pathway in aquatic ecosystems. Evidence suggests that a less well-studied process, dissimilatory nitrate reduction to ammonium (DNRA), which retains nitrogen (N) in the system, may also be important under favorable conditions. Using stable isotope tracers in sealed microcosms, we measured the potential for NO3− losses due to DNRA and denitrification in an oligotrophic freshwater ecosystem. We took sediment and water samples at runoff and baseflow, across several ecotypes. Our objective was to quantify the relative importance of DNRA compared to denitrification with changes in ecotype and season. Potential denitrification rates ranged from 0 to 0.14 ± 0.03 µgN gAFDM−1 d−1. ­Potential DNRA rates ranged from 0 to 0.0051 ± 0.0008 µgN gAFDM−1 d−1. Denitrification losses peaked at the inflow stream ecotype at 96.2% of total dissimilatory NO3− removal, whereas losses due to DNRA peaked in the lake ecotype at 34.4%. When averaged over the entire system, denitrification peaked at baseflow (31.2%), while DNRA peaked at runoff (2.9%). Although NO3− transformations due to denitrification were higher than DNRA in all ecotype and temporal comparisons, our results suggest that DNRA is also important under favorable conditions

Towards More Realistic Estimates of DOM Decay in Streams: Incubation Methods, Light, and Non-Additive Effects

Dissolved organic matter (DOM) is the largest pool of organic matter in aquatic ecosystems and is a primary substrate for microbial respiration in streams. However, understanding the controls on DOM processing by microbes remains limited, and DOM decay rates remain largely unconstrained. Many DOM decay rates are quantified with bioassays in dark bottles, which may underestimate DOM decay in streams because these bioassays do not include a benthic zone and do not account for abiotic factors of DOM loss, such as photodegradation and volatilization. We measured decay of labile and semi-labile DOM over 3 d in experimental streams and bottle bioassays. Incubations included 3 types of labile DOM (algal, light-degraded soil, and light-degraded plant leachates) and 2 types of semi-labile DOM (plant and soil leachates). We also quantified decay rates when labile and semi-labile DOM were mixed to test for non-additive effects, or priming, of semi-labile DOM by labile DOM. We converted dissolved organic carbon (DOC) decay rates to half-lives and uptake velocities and compared these metrics to previous studies that quantified DOC loss in bioassays or real streams. Percent DOC lost over time, or biodegradable DOC, was greater in experimental streams than in bioassays. DOC decay rates and uptake velocities did not differ between bioassays and experimental streams but were lower than in real streams. Mixing of labile and semi-labile DOM resulted in both positive and negative non-additive effects. Consistent non-additive effects were difficult to quantify because decay rates were not constant over the course of each incubation, as shown by faster decay rates calculated over the first 6 h of incubation compared to \u3e70 h. Decay rates of leachates from natural substrates (e.g., algae and soil) incubated over short periods of time (hours–days) are needed for models that aim to quantify organic matter transformation in aquatic ecosystems with short residence times, such as rivers and streams

Adolescent decision making about participation in a hypothetical HIV vaccine trial

Purpose The purpose of this study was to examine the process of adolescent decision-making about participation in an HIV vaccine clinical trial, comparing it to adult models of informed consent with attention to developmental differences. Methods As part of a larger study of preventive misconception in adolescent HIV vaccine trials, we interviewed 33 male and female 16–19-year-olds who have sex with men. Participants underwent a simulated HIV vaccine trial consent process, and then completed a semistructured interview about their decision making process when deciding whether or not to enroll in and HIV vaccine trial. An ethnographic content analysis approach was utilized. Results Twelve concepts related to adolescents' decision-making about participation in an HIV vaccine trial were identified and mapped onto Appelbaum and Grisso's four components of decision making capacity including understanding of vaccines and how they work, the purpose of the study, trial procedures, and perceived trial risks and benefits, an appreciation of their own situation, the discussion and weighing of risks and benefits, discussing the need to consult with others about participation, motivations for participation, and their choice to participate. Conclusion The results of this study suggest that most adolescents at high risk for HIV demonstrate the key abilities needed to make meaningful decisions about HIV vaccine clinical trial participation

Are rivers just bigstreams? Using a pulse method to measure nitrogen demand in a large river

Given recent focus on large rivers as conduits for excess nutrients to coastal zones, their role in processing and retaining nutrients has been overlooked and understudied. Empirical measurements of nutrient uptake in large rivers are lacking, despite a substantial body of knowledge on nutrient transport and removal in smaller streams. Researchers interested in nutrient transport by rivers (discharge \u3e10000 L/s) are left to extrapolate riverine nutrient demand using a modeling framework or a mass balance approach. To begin to fill this knowledge gap, we present data using a pulse method to measure inorganic nitrogen. (N) transport and removal in the Upper Snake River, Wyoming, USA (seventh order, discharge 12000 L/s). We found that the Upper Snake had surprisingly high biotic demand relative to smaller streams in the same river network for both ammonium (NH4+) and nitrate (NO3-). Placed in the context of a meta-analysis of previously published nutrient uptake studies, these data suggest that large rivers may have similar biotic demand for N as smaller tributaries. We also found that demand for different forms of inorganic N (NH4+ vs. NO3-) scaled differently with stream size. Data from rivers like the Upper Snake and larger are essential for effective water quality management at the scale of river networks. Empirical measurements of solute dynamics in large rivers are needed to understand the role of whole river networks (as opposed to stream reaches) in patterns of nutrient export at regional and continental scales

Soil carbon distribution and quality in a montane rangeland forest mosaic in northern Utah

Relatively little is known about soil organic carbon (SOC) dynamics in montane ecosystems of the semi-arid western U.S. or the stability of current SOC pools under future climate change scenarios. We measured the distribution and quality of SOC in a mosaic of rangeland-forest vegetation types that occurs under similar climatic conditions on non-calcareous soils at Utah State University’s T.W. Daniel Experimental Forest in northern Utah: the forest types were aspen [Populus tremuloides] and conifer (mixture of fir [Abies lasiocarpa] and spruce [Picea engelmannii]); the rangeland types were sagebrush steppe [Artemisia tridentata], grass-forb meadow, and a meadow-conifer ecotone. Total SOC was calculated from OC concentrations, estimates of bulk density by texture and rock-free soil volume in five pedons. The SOC quality was expressed in terms of leaching potential and decomposability. Amount and aromaticity of water-soluble organic carbon (DOC) was determined by water extraction and specific ultra violet absorbance at 254 nm (SUVA) of leached DOC. Decomposability of SOC and DOC was derived from laboratory incubation of soil samples and water extracts, respectively. Although there was little difference in total SOC between soils sampled under different vegetation types, vertical distribution, and quality of SOC appeared to be influenced by vegetation. Forest soils had a distinct O horizon and higher SOC concentration in near-surface mineral horizons that declined sharply with depth. Rangeland soils lacked O horizons and SOC concentration declined more gradually. Quality of SOC under rangelands was more uniform with depth and SOC was less soluble and less decomposable (i.e., more stable) than under forests. However, DOC in grass-forb meadow soils was less aromatic and more bioavailable, likely promoting C retention through cycling. The SOC in forest soils was notably more leachable and decomposable, especially near the soil surface, with stability increasing with soil depth. Across the entire dataset, there was a weak inverse relationship between the decomposability and the aromaticity of DOC. Our data indicate that despite similar SOC pools, vegetation type may affect SOC retention capacity under future climate projections by influencing potential SOC losses via leaching and decomposition

Metabolism, Gas Exchange, and Carbon Spiraling in Rivers

Ecosystem metabolism, that is, gross primary productivity (GPP) and ecosystem respiration (ER), controls organic carbon (OC) cycling in stream and river networks and is expected to vary predictably with network position. However, estimates of metabolism in small streams outnumber those from rivers such that there are limited empirical data comparing metabolism across a range of stream and river sizes. We measured metabolism in 14 rivers (discharge range 14–84 m3 s−1) in the Western and Midwestern United States (US). We estimated GPP, ER, and gas exchange rates using a Lagrangian, 2-station oxygen model solved in a Bayesian framework. GPP ranged from 0.6–22 g O2 m−2 d−1 and ER tracked GPP, suggesting that autotrophic production supports much of riverine ER in summer. Net ecosystem production, the balance between GPP and ER was 0 or greater in 4 rivers showing autotrophy on that day. River velocity and slope predicted gas exchange estimates from these 14 rivers in agreement with empirical models. Carbon turnover lengths (that is, the distance traveled before OC is mineralized to CO2) ranged from 38 to 1190 km, with the longest turnover lengths in high-sediment, arid-land rivers. We also compared estimated turnover lengths with the relative length of the river segment between major tributaries or lakes; the mean ratio of carbon turnover length to river length was 1.6, demonstrating that rivers can mineralize much of the OC load along their length at baseflow. Carbon mineralization velocities ranged from 0.05 to 0.81 m d−1, and were not different than measurements from small streams. Given high GPP relative to ER, combined with generally short OC spiraling lengths, rivers can be highly reactive with regard to OC cycling. © 2015, Springer Science+Business Media New York

Risk of SARS-CoV-2 transmission from humans to bats : an Australian assessment

SARS-CoV-2, the cause of COVID-19, infected over 100 million people globally by February 2021. Reverse zoonotic transmission of SARS-CoV-2 from humans to other species has been documented in pet cats and dogs, big cats and gorillas in zoos, and farmed mink. As SARS-CoV-2 is closely related to known bat viruses, assessment of the potential risk of transmission of the virus from humans to bats, and its subsequent impacts on conservation and public health, is warranted. A qualitative risk assessment was conducted by a multi-disciplinary group to assess this risk in bats in the Australian context, with the aim of informing risk management strategies for human activities involving interactions with bats. The overall risk of SARS-CoV-2 establishing in an Australian bat population was assessed to be Low, however with a High level of uncertainty. The outcome of the assessment indicates that, for the Australian situation where the prevalence of COVID-19 in humans is very low, it is reasonable for research and rehabilitation of bats to continue, provided additional biosecurity measures are applied. Risk assessment is challenging for an emerging disease where information is lacking and the situation is changing rapidly; assessments should be revised if human prevalence or other important factors change significantly. The framework developed here, based on established animal disease risk assessment approaches adapted to assess reverse zoonotic transmission, has potential application to a range of wildlife species and situations