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The article presents Microplastic accumulation in riverbed sediment via hyporheic exchange from headwaters to mainstems. Topics discussed include the identified mechanisms and time scales for small and lightweight microplastic accumulation in riverbed sediment reveal that these often-unaccounted components; and Long-term accumulation for all stream classifications averaged ~5% of microplastic inputs per river kilometer.

• Pathogens were quantified in the benthic sediment during low baseflow conditions. • We present a flow-dependent mobile-immobile particle tracking model for pathogens. • Longitudinal transport of pathogens during dynamic flow conditions simulated by model. • Benthic sediments are potential stores and sources of pathogens during storm events. • Transport into and out of benthic sediment regulates pathogen presence in the stream. The presence of bacteria and viruses in freshwater represents a global health risk. The substantial spatial and temporal variability of microbes leads to difficulties in quantifying the risks associated with their presence in freshwater. Fine particles, including bacteria and viruses are transported and accumulated into shallow streambed (i.e., benthic) sediment, delaying the downstream transmission during baseflow conditions but contributing to their resuspension and transport downstream during stormflow events. Direct measurements of pathogen accumulation in benthic sediments are rare. Until now, the dynamic role of benthic sediment as both a store and source of microbes, has not been quantified. In this study, we analyze microbial abundance in benthic sediment along a 1 km reach of an intermittent Mediterranean stream receiving inputs from the effluent of a wastewater treatment plant, a known point source of microbes in streams. We sampled benthic sediment during a summer drought when the wastewater effluent constituted 100 % of the stream flow, and thus, large accumulation and persistence of pathogens along the streambed was expected. We measured the abundance of total bacteria, Escherichia coli (as a fecal indicator) , and presence of enteric rotavirus (RoV) and norovirus (NoV). The abundance of E. coli , based on qPCR detection, was high (4.99∙102 gc /cm2) along the first 100 m downstream of the wastewater effluent input and in general decreased with distance from the source, with presence of RoV and NoV along the study reach. A particle tracking model was applied, that uses stream water velocity as an input, and accounts for microbial exchange into, immobilization, degradation, and resuspension out of benthic sediment during baseflow and stormflow. Rates of exchange into benthic sediment were 3 orders of magnitude higher during stormflow, but residence times were proportionately lower, resulting in increased longitudinal connectivity from up to downstream during stormflow. Model simulations demonstrated mechanistically how the rates of exchange into and out of the benthic sediment resulted in benthic sediment to act as a store during baseflow and a source during stormflow. [Display omitted] [ABSTRACT FROM AUTHOR]

A scoping review of the literature on parenting programmes that target the promotion of adolescent mental health was conducted to examine the quality of the studies and unique content of programmes for parents from ethnoculturally diverse communities. PsycINFO and Web of Science were searched in April, 2011 (for all publications prior to that date) and again in August, 2015 (for publications from April, 2011 to August, 2015) using specific keywords and inclusion criteria. A hand search was also conducted. Overall, 107 studies met inclusion criteria for final data extraction and included evaluations of interventions targeted at substance use, early/risky sexual activity and behavioural problems. Eighteen of the 107 studies described programmes targeting parents of adolescents from diverse ethnocultural communities; the quality of these 18 studies was assessed using a marginally modified version of the Downs and Black Checklist (Downs & Black 1998). Their average quality assessment score was 16 out of 28. In addition, two key themes reflected in successful interventions emerged: strengthening parent-adolescent relationship through communication, and importance of community engagement in designing and implementing the intervention. Findings indicate gaps in service delivery to parents of adolescents from ethnoculturally diverse communities; there are a limited number of studies on programmes targeting ethnoculturally diverse parents of adolescents, and the quality of studies that do exist is overall low. Given increasing diversity, more emphasis should be placed on developing and modifying programmes to meet the needs of ethnoculturally diverse communities. More rigorous, standardised efforts should be made to evaluate programmes that do exist. [ABSTRACT FROM AUTHOR]

Stream hydraulics control flux into and out of slow-moving water transient storage (WTS) zones and, thus, hydrologic retention in stream channels. In-stream nutrient uptake is thought to depend on hydrologic retention, so stream hydraulics could influence the extent to which in-stream nutrient biogeochemistry affects nutrient export downstream. Our goals were to: 1) characterize WTS with an emphasis on water residence time and 2) evaluate its influence on nutrient uptake. We analyzed data from 2 y of monthly solute-tracer injections with accompanying nutrient-uptake estimates in 2 hydrogeomorphically different streams. We fit the conservative tracer breakthrough curves to 2 hydrodynamic models: the one-dimensional transport with inflow and storage (OTIS) and the stochastic mobile-immobile model (SMIM), which allows for a wide distribution of water residence times. The 2 streams differed hydraulically, especially in water residence-time distributions in WTS zones. SMIM parameters depended less on discharge than did OTIS parameters, indicating that SMIM may be influenced more by local features of channel morphology than by hydrologic conditions. NH4+ uptake differed between streams, was correlated with all SMIM hydraulic parameters, and was weakly correlated with only 1 OTIS parameter. Based on SMIM correlations, the parameters related to the exchange of free-flowing water with water storage zones and the in-stream retention times explained 43 and 41%, respectively, of the variation in NH4+ uptake in the streams. Soluble reactive P (SRP) uptake was similar between streams and was not correlated with hydraulic parameters. These results indicate that hydraulics and residence time of water can be important regulators of WTS zones and nutrient uptake in headwater streams, but other environmental factors must be considered for complete understanding of in-stream nutrient processing capacity. [ABSTRACT FROM AUTHOR]

Long-term survival of pathogenic microorganisms in streams enables long-distance disease transmission. In order to manage water-borne diseases more effectively we need to better predict how microbes behave in freshwater systems, particularly how they are transported downstream in rivers. Microbes continuously immobilize and resuspend during downstream transport owing to a variety of processes including gravitational settling, attachment to in-stream structures such as submerged macrophytes, and hyporheic exchange and filtration within underlying sediments. We developed a stochastic model to describe these microbial transport and retention processes in rivers that also accounts for microbial inactivation. We used the model to assess the transport, retention, and inactivation of Escherichia coli in a small stream and the underlying streambed sediments as measured from multitracer injection experiments. The results demonstrate that the combination of laboratory experiments on sediment cores, stream reach-scale tracer experiments, and multiscale stochastic modeling improves assessment of microbial transport in streams. This study (1) demonstrates new observations of microbial dynamics in streams with improved data quality than prior studies, (2) advances a stochastic modeling framework to include microbial inactivation processes that we observed to be important in these streams, and (3) synthesizes new and existing data to evaluate seasonal dynamics. [ABSTRACT FROM AUTHOR]

In streams and rivers, the benthic and hyporheic regions harbor the microbes that process many stream-borne constituents, including O2, nutrients, C, and contaminants. The full distribution of transport time scales in these highly reactive regions must be understood because solute delivery and extended storage in these metabolically active zones control the opportunity for biogeochemical processing. The most commonly used transport models cannot capture these effects. We present a stochastic model for conservative and reactive solute transport in rivers based on continuous-time random-walk theory, which is capable of distinguishing and capturing processes not described by classical approaches. The model includes surface and subsurface storage zones with arbitrary residence-time distributions. We used this model to evaluate the effects of sorption and biological uptake on downstream solute transport. Linear or mildly nonlinear sorption in storage delays downstream transport without changing the fundamental shape of the breakthrough curves (BTCs). Highly nonlinear sorption isotherms can induce power-law tailing in stream BTCs. Model simulations show that sorption of commonly used solute tracers is not sufficient to explain the power-law tailing that has been observed in field tracer-injection studies, and instead, such tailing most probably reflects broad distributions of hyporheic exchange time scales. First-order biological uptake causes an exponential decline in instream tracer concentrations at the time scale of the uptake kinetics, thereby tempering power-law BTCs. The model can be used to calculate reach-scale reaction-rate coefficients in surface and subsurface storage from observed BTCs of co-injected conservative and reactive solutes, providing new capability to determine reaction-rate coefficients in storage zones with broad residence-time distributions. [ABSTRACT FROM AUTHOR]