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Our understanding of the effects of pharmaceuticals on key biogeochemical processes and biofilm assemblage composition in surface waters is limited despite the prevalence of ng/L to µg/L concentrations of these compounds. We examined the effects of 3 commonly-prescribed pharmaceuticals: ciprofloxacin (140 ng/L), diphenhydramine (300 ng/L), and fluoxetine (20 ng/L); both individually and as a mixture, on key ecosystem processes at environmentally-realistic concentrations. We used mesocosms to expose naturally-occurring biofilm communities and artificial benthic substrates to these pharmaceuticals and measured the effects of exposure on biofilm, seston, and sediment communities. Established biofilm functions were unaffected by pharmaceutical treatments. However, successional biofilms experienced 42 to 81% reductions in primary production and 59 to 83% reductions in community respiration. Denitrification in sediment communities was reduced by 41 to 73% in shaded conditions, but was not affected when left in ambient light. Diatom assemblage structure was unaffected by pharmaceuticals in successional biofilms, whereas the composition of established biofilm assemblages changed with exposure to treatments that contained ciprofloxacin, diphenhydramine, and all 3 pharmaceuticals. Our study adds to a growing body of evidence indicating that chronic exposure to sub-lethal concentrations of pharmaceuticals may substantially alter key ecosystem processes and communities. [ABSTRACT FROM AUTHOR]

1. Urbanisation severely affects stream hydrology, biotic integrity and water quality, but relatively little is known about effects on organic matter dynamics. Coarse particulate organic matter (CPOM) is a source of energy and nutrients in aquatic systems, and its availability has implications for ecosystem productivity and aquatic communities. In undisturbed environments, allochthonous inputs from riparian zones provide critical energy subsidies, but the extent to which this occurs in urbanised streams is poorly understood. 2. We investigated CPOM inputs, standing stocks, retention rates and retention mechanisms in urban and peri-urban streams in Melbourne, Australia. Six streams were chosen along a gradient of catchment urbanisation, with the presence of reach scale riparian canopy cover as a second factor. CPOM retention was assessed at baseflow via replicate releases of marked Eucalyptus leaves where the retention distance and mechanism were recorded. CPOM and small wood (>1 cm diameter) storage were measured via cores and direct counts, respectively, while lateral and horizontal CPOM inputs were assessed using riparian litter traps. Stream discharge, velocity, depth and width were also measured. 3. CPOM inputs were not correlated with urbanisation, but were significantly higher in 'closed' canopy reaches. Urbanisation and riparian cover altered CPOM retention mechanisms, but not retention distances. Urban streams showed greater retention by rocks; while in less urban streams, retention by small wood was considerably higher. CPOM and small wood storage were significantly lower in more urban streams, but we found only a weak effect of riparian cover. 4. These findings suggest that while riparian vegetation increases CPOM inputs and has modest/weak effects on storage, catchment scale urbanisation decreases organic matter availability. Using an organic matter budget approach, it appears likely that the increased frequency and magnitude of high flows associated with catchment urbanisation exerts an overriding influence on organic matter availability. 5. We conclude that to maintain both organic matter inputs and storage, the restoration and protection of streams in urban or rapidly urbanising environments relies on the management of both riparian vegetation and catchment hydrology. [ABSTRACT FROM AUTHOR]

1. Urbanisation and landuse changes threaten the ecological integrity of rivers and streams globally. A major challenge in such impacted environments is to develop functional indicators for use by waterway managers. We first reviewed cellulose decomposition potential (CDP) as one such indicator, and here present current understanding and highlight the knowledge gaps which hinder its widespread incorporation into programmes monitoring stream health. In a field study, we also evaluated two differing cellulose materials (Shirley soil burial test material and unbleached calico) and measurement techniques. 2. We also investigated the effects of urbanisation and riparian cover on CDP as a standardised indicator of ecosystem function. Cotton fabrics were deployed in paired open and closed reaches across six stream catchments varying in degree of urbanisation (in south-eastern Australia). After 7, 14 and 21 days materials were retrieved and their decomposition assessed in conjunction with a number of physicochemical variables. 3. We observed a strong positive relationship between the decomposition of Shirley and calico materials, thus indicating unbleached calico is an effective substitute for Shirley test cloth, which is no longer available. 4. Across sites, CDP was positively correlated with ammonium concentrations and also, to a lesser extent, with filterable reactive phosphorus and sediment silt and clay content/carbon availability. Despite these relationships, cellulose decomposition was not correlated with urbanisation or riparian cover. 5. Cellulose decomposition is a simple, rapid and sensitive functional indicator of water quality and associated anthropogenic landuse changes and is thus a valuable tool for monitoring stream health. [ABSTRACT FROM AUTHOR]