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The structural arrangement of fibrous tissue is linked to the onset and progression of Alzheimer’s disease, heart disease, fibrosis, and cancer, yet its visualization remains challenging with conve...

Dielectric microcavities with quality factors (Q-factors) in the thousands to billions markedly enhance light–matter interactions, with applications spanning high-efficiency on-chip lasing, frequency comb generation and modulation and sensitive molecular detection. However, as the dimensions of dielectric cavities are reduced to subwavelength scales, their resonant modes begin to scatter light into many spatial channels. Such enhanced scattering is a powerful tool for light manipulation, but also leads to high radiative loss rates and commensurately low Q-factors, generally of order ten. Here, we describe and experimentally demonstrate a strategy for the generation of high Q-factor resonances in subwavelength-thick phase gradient metasurfaces. By including subtle structural perturbations in individual metasurface elements, resonances are created that weakly couple free-space light into otherwise bound and spatially localized modes. Our metasurface can achieve Q-factors >2,500 while beam steering light to particular directions. High-Q beam splitters are also demonstrated. With high-Q metasurfaces, the optical transfer function, near-field intensity and resonant line shape can all be rationally designed, providing a foundation for efficient, free-space-reconfigurable and nonlinear nanophotonics.

Metasurface lenses provide an ultrathin platform in which to focus light, but weak light-matter interactions limit their dynamic tunability. Here we design submicron-thick, ultrahigh quality factor (high-Q) metalenses that enable dynamic modulation of the focal length and intensity. Using full-field simulations, we show that quality factors exceeding 5000 can be generated by including subtle, periodic perturbations within the constituent Si nanoantennas. Such high-Q resonances enable lens modulation based on the nonlinear Kerr effect, with focal lengths varying from 4 to 6.5 μm and focal intensities decreasing by half as input intensity increases from 0.1 to 1 mW/μm2. We also show how multiple high-Q resonances can be embedded in the lens response through judicious placement of the perturbations. Our high-Q lens design, with quality factors 2 orders of magnitude higher than existing lens designs, provides a foundation for reconfigurable, multiplexed, and hyperspectral metasurface imaging platforms.

The light sources that power photonic networks are small and scalable, but they also require the incorporation of optical isolators that allow light to pass in one direction only, protecting the light source from damaging backreflections. Unfortunately, the size and complex integration of optical isolators makes small-scale and densely integrated photonic networks infeasible. Here, we overcome this limitation by designing a single device that operates both as a coherent light source and as its own optical isolator. Our design relies on high-quality-factor dielectric metasurfaces that exhibit intrinsic chirality. By carefully manipulating the geometry of the constituent silicon metaatoms, we design three-dimensionally chiral modes that act as optical spin-dependent filters. Using spin-polarized Raman scattering together with our chiral metacavity, we demonstrate Raman lasing in the forward direction, while the lasing action is suppressed by over an order of magnitude for reflected light. Our high-Q chiral metasurface design presents a new approach toward compactly isolating integrated light sources by directly tailoring the emission properties of the light source itself.

Phase gradient metasurfaces have revolutionized modern optical components by significantly reducing the path length of bulk optics while maintaining high performance. However, their geometric design makes dynamic modulation challenging, with devices facing a trade-off between the modulation range and efficiency. Here, we introduce Silicon-on-Lithium Niobate (LNO) high-Quality-factor (high-Q) metasurfaces for efficient electro-optic wavefront shaping and modulation. Periodic perturbations within Si metasurface elements allow incident light to be weakly coupled into guided modes, generating high-Q resonances that manifest in the far-field diffraction spectrum. The near field of each Si element spatially overlaps with the LNO substrate, enabling electrically tunable modulation of the resonant frequency. Using full-field simulations, we demonstrate near-infrared, dynamically tunable beamsteering, and beamsplitting metasurfaces. First, we demonstrate beamsteering metasurfaces whose +1st order diffracted intensity can be modulated from 70% to 7% absolute efficiency near the resonant frequency with applied electric fields of order V/μm. Next, we design a tunable beam splitter, switching between direct, 0th order transmission and beamsplitting with the application of 30 V across the metasurface. Our high-Q electro-optic metasurfaces provide a foundation for efficient, time-dependent transfer functions in subwavelength footprints.

We show theoretically and experimentally how high quality factor modes can be generated within dielectric metasurfaces, opening new possibilities for nonlinear freespace nanophotonics. We utilize these nonlinear metasurfaces for nanoscale nonreciprocity and neuromorphic nanophotonic networks.

We theoretically demonstrate a non-hermitian metamaterial exhibiting broadband and wide-angle nonreciprocity. The metamaterial consists of planar metal-dielectric layers with a Parity-Time (PT) symmetric distrubtion of loss and gain. With increasing loss and gain, the bandstructure and bandgap are strongly modified; further, the PT potential leads to distinct internal field distributions when illuminated from different sides. Including nonlinearities arising from natural loss and gain saturation leads to nonreciprocal transmission in the visible over a 50 nm wavelength and 60$^{\circ}$ degree angular range., Comment: 7 pages, 4 figures

Metasurfaces enable almost complete control of light through ultrathin, subwavelength surfaces by locally and abruptly altering the scattered phase. To date, however, all metasurfaces obey time-reversal symmetry, meaning that forward and backward traveling waves will trace identical paths when being reflected, refracted, or diffracted. Here, we use full-field calculations to design a passive metasurface for nonreciprocal transmission of both direct and anomalously refracted near-infrared light over nanoscale optical path lengths. The metasurface consists of a 100 nm-thick, periodically patterned Si slab. Owing to the high-quality-factor resonances of the metasurface and the inherent Kerr nonlinearities of Si, this structure acts as an optical diode for free-space optical signals. This structure also exhibits nonreciprocal anomalous refraction with appropriate patterning to form a phase gradient metasurface. Compared to existing schemes for breaking time-reversal symmetry, our platform enables subwavelength nonreciprocity for arbitrary free-space optical inputs and provides a straightforward path to experimental realization. The concept is also generalizable to other metasurface functions, providing a foundation for one-way lensing and holography.

Plasmonics is a rapidly developing field at the boundary of physical optics and condensed matter physics. It studies phenomena induced by and associated with surface plasmons - elementary polar excitations bound to surfaces and interfaces of good nanostructured metals. This Roadmap is written collectively by prominent researchers in the field of plasmonics. It encompasses selected aspects of nanoplasmonics. Among them are fundamental aspects, such as quantum plasmonics based on the quantum-mechanical properties of both the underlying materials and the plasmons themselves (such as their quantum generator, spaser), plasmonics in novel materials, ultrafast (attosecond) nanoplasmonics, etc. Selected applications of nanoplasmonics are also reflected in this Roadmap, in particular, plasmonic waveguiding, practical applications of plasmonics enabled by novel materials, thermo-plasmonics, plasmonic-induced photochemistry and photo-catalysis. This Roadmap is a concise but authoritative overview of modern plasmonics. It will be of interest to a wide audience of both fundamental physicists and chemists, as well as applied scientists and engineers., J Schötz for financial support by the European Union via the ERC grant ATTOCO, by the DFG via SPP1840.

Control of the polarization state of light is essential for many technologies, but is often limited by weak light-matter interactions that necessitate long device path lengths or significantly reduce the signal intensity. Here, we investigate a nanoscale plasmonic aperture capable of modifying the polarization state of far-field transmitted light without loss in the probe signal. The aperture is a coaxial resonator consisting of a dielectric ring embedded within a metallic film; parity-time ($\mathcal{P}\mathcal{T}$) -symmetric inclusions of loss and gain within the dielectric ring enable polarization control. Since the coaxial aperture enables near-thresholdless $\mathcal{P}\mathcal{T}$ symmetry breaking, polarization control is achieved with realistic levels of loss and gain. Exploiting this sensitivity, we show that the aperture can function as a tunable waveplate, with the transmitted ellipticity of circularly polarized incident light changing continuously with the dissipation coefficient from $\ensuremath{\pi}$/2 to 0 (i.e., linear polarization). Rotation of linearly polarized light with unity efficiency is also possible, with a continuously tunable degree of rotation. This compact, low-threshold, and reconfigurable polarizer may enable next-generation, high-efficiency displays, routers, modulators, and metasurfaces.

Recently, there has been public concern that water quality in the nearshore of Southeast Lake Huron has been deteriorating, inferred partly from fouling of shoreline by algae. In 2010, fine-scale patterns in nutrient concentrations and other water quality features were examined to better understand the influence of the adjacent land on the nearshore environment in the region. Surveys at two areas of coastline were conducted over a seasonal cycle. Monitoring of water quality in tributaries to the study areas indicated that water of poor quality was periodically discharged to the lake as indicated by elevated levels of nutrients, fecal indicator bacteria, suspended solids and chloride. The extent of the nearshore that was directly influenced by land runoff was small, restricted to the shoreline fringe, relative to the broader nearshore. Pulse-like inputs of phosphorus from wave-induced erosional events and periods of precipitation-related runoff, both characterized by high levels of particle-bound phosphorus, contributed to highly dynamic and spatially variable levels of total phosphorus (TP), and proportions of TP in dissolved form, in the nearshore. The proportion of TP associated with particulate material was strongly correlated with lake depth. Phosphorus distributions in the nearshore indicate contrasting conditions with proximity to shoreline. Land runoff enriches nutrient levels along sections of the immediate shoreline, which contrasts sharply with the ultraoligotrophic conditions in the broader nearshore. The nearshore of Lake Huron arguably has always been highly sensitive to phosphorus pollution and it appears likely that the shoreline may be even more so today.

We conducted studies of algal fouling along the southeastern shore of Lake Huron to determine the kinds and spatial distribution of benthic algae, the spatial extent and timing of beach fouling, and the possible influences of biological changes to Lake Huron. There was no change in the physical texture of the substratum, but coverage by algal turf increased from 11% of sites in 1977 to nearly 90% in 2007. Shoreline surveys showed that Chara was most common on flat rocky substrata at depths of 0.15 to 0.20 m. Algae stranded on beaches consisted of 62% periphyton turf, 30% Chara and 8% Cladophora and were not evenly distributed; the largest accumulations were found where shoreline irregularities interrupted longshore flow. Quantities of stranded algae partially reflected the height and duration of waves directed onshore. Macroinvertebrate densities were not correlated with benthic algal abundance in 2010 and were lower with fewer large grazers than in 1980. Densities of Dreissena spp. increased with depth, and small tufts of Cladophora were found on larger individuals. The proliferation of algae in the nearshore zone of central eastern Lake Huron appears to be the result of several recent changes. Phosphorus management and filtering by dreissenid mussels have reduced phytoplankton abundance, improving the light regime. Changes in land use may have increased loadings of phosphorus through shallow groundwater and tributary streams. Dreissenids have also redirected nutrients to the lakebed, further enhancing benthic primary production, and predation by round goby has reduced the numbers of grazing benthic invertebrates.

Dreissenid mussels are notorious invasive organisms whose establishment is associated with large, ecosystem-scale changes to patterns of productivity in aquatic systems. We investigated how localized impacts of dreissenids affect the potential of littoral substrates to support primary and secondary production using in situ incubations and comparisons of natural mussel-colonized and mussel-free substrates in the littoral zone of a large, shallow lake. We compared dreissenid-colonized and dreissenid-free substrates in terms of nutrient balance, surface area, periphyton loads as well as benthic primary production and respiration rates. Dreissenid-colonized substrates acted as sources of dissolved nutrients to the water column, with mussel mass-specific rates of dissolved phosphorus and ammonia excretion averaging 7.2 ± 5.6 (mean ± SD), and 92.6 ± 64.7 μg/g mussel shell free dry mass/h, respectively. Mussel-colonized substrates also had higher surface area, and supported approximately double the amount of periphyton and organic matter loads compared to mussel-free substrates, as well as having higher rates of primary production and community respiration. We suggest that the localized effects of dreissenids can play an important role in changing whole-ecosystem production patterns, with the extent of dreissenid impacts strongly dependent on lake size and morphometry.

Lake Simcoe, the largest lake in southern Ontario outside of the Laurentian Great Lakes, is affected by numerous stressors including eutrophication resulting from total phosphorus (TP) loading, climate change, and invasions of exotic species. We synthesized the long-term responses of Lake Simcoe to these stressors by assessing trends in water quality and biological composition over multiple trophic levels. Evidence for climate change included increasing thermal stability of the lake and changes in subfossil diatom communities over time. Although the deep water dissolved oxygen (O 2 ) minimum has increased significantly since TP load reductions, it is still below estimated historical values and the Lake Simcoe Protection Plan end-of-summer target level of 7 mg O 2 L −1 . Low deep water O 2 concentrations corresponded with a decline in coldwater fish abundance. Since 1980, some nutrient concentrations have decreased (spring TP) while others have increased (silica), but many show no obvious changes (ice-free TP, nitrate, ammonium). Increases in water clarity, combined with declines in chlorophyll a and phytoplankton biovolumes in Cook’s Bay, were temporally consistent with declines in TP loading and the lake-wide establishment of dreissenid mussels as a major component of the Lake Simcoe ecosystem. Using an investigative tool, we identified 2 periods when abrupt shifts potentially occurred in multiple parameters: 1986 and 1995–1997. Additional ecosystem level changes such as declines in zooplankton, declines in offshore benthic invertebrate abundance, and increased nearshore invertebrate abundance likely reflect the effects of invasive species. The interaction of these multiple stressors have significantly altered the Lake Simcoe ecosystem.

Establishment of dreissenid mussels in aquatic systems is often accompanied by major changes in the abundance, diversity, and community composition of benthic invertebrates. However, few studies have been published that address the effects of long-term dreissenid presence on the littoral benthos inhabiting hard substrata in lakes. We present the results of a depth-stratified, quantitative survey of littoral benthos conducted at 4 sites in 1993, just before dreissenid invasion, and in 2008, 14 y after the establishment of dreissenids in Lake Simcoe, Ontario. Average densities of nondreissenid invertebrates were 45× greater in 2008 than in 1993. Amphipods, isopods, chironomids and oligochaetes underwent the largest increases in absolute abundance. The taxonomic diversity of the benthic invertebrate community (α diversity) increased significantly. Community structure was more similar within and between depths and sites in 2008 than in 1993, a result implying lower β diversity of the postdreissenid li...

We examined latitudinal patterns of generic richness in stream insects across the Mackenzie River system in northern Canada. We focused on low- to mid-order tributaries flowing into the river and spanning ∼11° of latitude. Physical-habitat characteristics and water chemistry were examined as factors affecting diversity both at the local and regional scale. No overall latitudinal trend was found in richness, but trends were apparent at the order level. Local generic richness of Ephemeroptera and Plecoptera declined toward the north, Trichoptera generic richness was lowest in the middle of the latitudinal range, and Diptera generic richness increased with latitude. Most orders of aquatic insects followed the expected decline in richness with increasing latitude, but the family Chironomidae was an exception, probably because of their ability to tolerate subarctic environmental conditions and because of the relative absence of potential predation and competition from other invertebrates. Streams were ...

The effects of invasive organisms on an aquatic ecosystem will depend, in part, on the distribution and biomass of the invasive organisms in the system. Here we present the results of a lake-wide survey of the distribution of invasive dreissenid mussels ( Dreissena spp.) in Lake Simcoe, Ontario and discuss some of the factors that shape their distribution pattern in the lake. Dreissenid biomass averaged 27.2 g shell-free dry mass (SFDM)/m 2 in the main basin of Lake Simcoe and 12.4 g SFDM/m 2 in macrophyte-dominated Cook's Bay. We argue that water movement is an important determinant of dreissenid distribution, both through catastrophic disturbance in shallow water and through non-catastrophic effects on substrate distribution and possibly food supply rates. In areas of dense macrophyte growth, mussel abundance was shown to be associated with that of preferred macrophyte taxa, in particular with that of Ceratophyllum demersum . We used the results of our survey and the relationships between environmental variables and dreissenid biomass to estimate the total biomass of dreissenids in Lake Simcoe: 11,897 tonnes SFDM. This study contributes to the understanding of dreissenid ecology and provides a baseline for future studies of dreissenid distribution and impacts in Lake Simcoe.

One of the effects of the dreissenid invasion into the Laurentian Great Lakes appears to be a resurgence in the abundance of the nuisance alga Cladophora glomerata which experienced a marked decline following phosphorus abatement in the late 1970s and early 1980s. A subsidy of bioavailable phosphorus excreted by dreissenid mussels could be an important mechanism facilitating the growth of C. glomerata. To assess the importance of phosphorus released by mussels to C. glomerata growth in the nearshore, we conducted a survey of mussel distribution and abundance followed by in situ experiments designed to measure dreissenid phosphorus excretion rates. Average dreissenid mussel abundance in our study area was 3674 individuals/m2, with an average biomass of 52.2 g of shell free dry mass/m2. The mussels excreted bioavailable soluble reactive phosphorus at an average rate of 7.02 µg SRP/g shell free dry mass/hour, contributing about 11 t of soluble reactive phosphorus to our study area over the C. glomer...

The trophic roles of key Ponto-Caspian invaders (quagga mussels Dreissena bugensis, amphipods Echinogammarus ischnus and round goby Apollonia melanostomus) within the littoral food web of eastern Lake Erie were quantified using stable isotopes (δ13C, δ15N). A dual stable isotope parameter search with a mass balance component was used to assess the isotopic importance of quagga mussels and amphipods as dietary items to two size classes of round goby. The utility of the mass balance simulation was also evaluated as a tool to approximate isotopic contributions of feasible prey and identify gaps incurred by “missing” prey items not included in the sampling. The mass balance dietary simulation, confirmed by stomach content data, indicated that isotopically important prey to small round goby (

Heterotrophic bacteria growing without substrate limitation discriminate against the heavier stable isotopes of C and N, which is reflected in the isotopic signatures of consumers of bacteria. We measured bacteria and substrate isotopic separation (C and N) during glucose and ammonium uptake by three strains of bacteria ( Pseudomonas putida , Bacillus megaterium , and Enterobacter aerogenes ) grown in batch culture at 4 and 30 °C. Isotopic separation between bacteria and substrate was dependent on substrate availability. Higher discrimination against the heavier isotopes, and therefore more depleted δ13C and δ15N values of bacterial biomass, were observed during the exponential growth phase when the nutrient supply was in excess of the demand. We also compared the isotopic ratios of Chironomus tentans grown on aged macrophyte detritus and commercial fish food. Isotopic signatures of Chironomus larvae grown on fish food were within the ranges typical of one trophic step, whereas larvae grown on detritus were strongly depleted in13C, suggesting assimilation of bacteria that had grown on the C-rich detritus. Our results are consistent with the very few other studies of bacterial fractionation of nonlimiting nutrients and may also explain the frequent observation of unexpectedly depleted isotopic signatures in aquatic food web studies.

Burrowing mayflies (Hexagenia limbata and H. rigida) recolonized sediments of the western basin of Lake Erie in the 1990s following decades of pollution abatement. We predicted that Hexagenia would also disperse eastward or expand from existing localized populations and colonize large regions of the other basins. We sampled zoobenthos in parts of the western and central basins yearly from 1997–2005, along the north shore of the eastern basin in 2001–2002, and throughout the lake in 2004. In the island area of the western basin, Hexagenia was present at densities ≤ 1,278 nymphs/m2 and exhibited higher densities in odd years than even years. By contrast, Hexagenia became more widespread in the central basin from 1997-2000 at densities ≤ 48 nymphs/m2 but was mostly absent from 2001-2005. Nymphs were found along an eastern basin transect at densities≤ 382/m2 in 2001 and 2002. During the 2004 lake-wide survey, Hexagenia was found at 63 of 89 stations situated throughout the western basin (≤ 1,636 nymphs/m2, mean = 195 nymphs/m2, SE = 32, N = 89) but at only 7 of 112 central basin stations, all near the western edge of the basin (≤ 708 nymphs/m2), and was not found in the eastern basin. Hexagenia was found at 2 of 62 stations (≤ 91 nymphs/m2) in harbors, marinas, and tributaries along the south shore of the central basin in 2005. Oxygen depletion at the sediment-water interface and cool temperatures in the hypolimnion are probably the primary factors preventing successful establishment throughout much of the central basin. Hexagenia can be a useful indicator of lake quality where its distribution and abundance are limited by anthropogenic causes.

From 2001 through 2004, the densities of Dreissena bugensis and Amphipoda (Gammarus fasciatus and Echinogammarus ischnus) decreased by 94% and 85%, respectively, in the rocky northern nearshore (2–10 m depth) zone of eastern Lake Erie. Densities of Chironomidae and Oligochaeta did not change. The decline in D. bugensis was most evident for individuals with shell lengths in the 3 to 14 mm range. The mean (±SD, n) abundance of round gobies (Neogobius melanostomus) at 10-m depth increased from 6.5 (± 1.9, 12)/m2 in 2001 to 14(±1.0, 15/m2 in 2002. Analyses of stomach contents in 2001 and 2003, and stable isotopes of carbon in prey and muscle tissue in 2002, indicated that the diet of round gobies in 2001 was predominately dreissenids, but that chironomids and amphipods became more important as the abundance of appropriately sized mussels declined. Round gobies collected in 2003 contained more individual prey, but less total mass of prey than did gobies collected in 2001. Our observations suggest that round gobies probably became food-limited in eastern Lake Erie by 2002.

Dreissenid mussels have been exceptionally successful invaders in North American lakes and rivers, espe- cially in the lower Laurentian Great Lakes. As benthic filter feeders capable of attaching to hard substrates, the magni- tudes of their biomass and filtering activity in nearshore waters are without precedent. The dreissenid colonization has implications for the removal and fate of materials filtered from the water by the mussels and for the longer-term devel- opment of the nearshore benthic community and lake ecosystem. A conceptual model, the nearshore shunt, seeks to describe a fundamental redirection of nutrient and energy flow consequent to dreissenid establishment. The model ex- plains some emergent problems in the Great Lakes, such as reemergence of Cladophora in some coastal zones while offshore P concentrations remain low, and highlights areas in need of more research. The source of particulate nutrient inputs to dreissenids and the fate of materials exported from the benthic community are critical to understanding the role of dreissenids in the lakes and assessing the applicability of current models for managing nutrients and fisheries. The nearshore shunt would require even more stringent P management for lakes strongly impacted by dreissenids to maintain nearshore water quality. Resume : Les moules dreissenidees ont envahi avec un succes exceptionnel les lacs et rivieres d'Amerique du Nord, et en particulier les Grands Lacs inferieurs. Des animaux benthiques se nourrissant par filtration et capables de se fixer a des substrats durs, ils ont atteint des biomasses et des niveaux d'activite de filtration sans precedent dans les eaux cotieres. La colonisation des dreissenides a des consequences sur le retrait et le sort des materiaux filtres de l'eau par les moules, ainsi que sur le developpement a plus long terme de la communaute benthique pres du rivage et sur l'ecosysteme lacustre. Un modele conceptuel, la « deviation cotiere », cherche a decrire l'alteration fondamentale du cheminement des nutriments et du flux d'energie depuis l'etablissement des dreissenides. Le modele explique certains des problemes qui surgissent dans les Grands Lacs, comme la re-emergence de Cladophora dans certaines zones cotie- res, bien que les concentrations de phosphore au large restent faibles et il identifie des domaines qui necessitent des recherches supplementaires. Une connaissance des sources des apports de particules nutritives pour les dreissenides et du sort des materiaux exportes de la communaute benthique est essentielle pour comprendre le role des dreissenides dans les lacs et pour evaluer l'applicabilite des modeles courants de gestion des nutriments et des peches. La « devia- tion cotiere » exigerait une gestion encore plus rigoureuse du phosphore dans les lacs fortement affectes par les dreis- senides afin de maintenir la qualite de l'eau pres du rivage.

Benthic invertebrates were collected from nine sites in the wave-zone along the Ontario shore of Lake Huron and western Georgian Bay in 1974, and again in 2003. The most substantial differences were declines in the formerly dominant Hydropsychidae (Trichoptera) and several species of Ephemeroptera, and increases in the relative abundance of Amphipoda, Chironomidae, Gastropoda and Tubificidae. The exotic species Dreissena polymorpha, D. bugensis, and Echinogammarus ischnus were found at most sites but accounted for < 4% of the animals collected. Total diversity increased from 136 taxa in 1974, to 154 taxa in 2003. The decrease in relative abundance of hydropsychid caddisflies may be a result of interactions with dreissenid mussels. The causes of other changes in the fauna are unclear, but could signal the existence of hitherto unrecognized stresses in Lake Huron.

An airlift was used to collect 170 quantitative samples of benthic macroinvertebrates from the rocky nearshore zone of islands in southern Lake Malawi from August 1998 to Febuary 1999. Total invertebrate densities were very low (< 6,000 ind/m2), and were dominated by Ostracoda, Hydracarina, and Chironomidae. Most of the insects were lotic forms, including hydropsychid caddisflies, heptageneid mayflies, and dryopoid beetles. Sampling sites differed in degree of exposure to wave-action, substratum texture, depth (1.5 to 5 m), and abundance of fish, and the density and diversity of the benthic fauna varied significantly with each of these factors. Both numbers of taxa and densities of invertebrates were greater at exposed than sheltered sites, and decreased with increasing depth. Gravel substratum harbored more taxa and higher densities of macroinvertebrates than did cobble or bedrock. The only seasonal change observed was a decrease in the abundance of animals during the rainy season at a sheltered site where sediment was deposited from a large river. There was a weak inverse relationship between the densities of fish and larger invertebrates on cobble and bedrock substrata. Bedrock surfaces covered by fish-exclusion cages supported five-fold more invertebrates than open surfaces after 2 months. Overall, the benthic fauna of rocky shores in southern Lake Malawi is a taxonomically rich community similar in composition and diversity to those reported from other Great Lakes worldwide. Continuous, intense fish predation appears to be responsible for low invertebrate densities and probably influences invertebrate species diversity.

In order to assess the trophic role of Diporeia in Colpoys Bay, amphipods were collected from depths of 30 and 50 m using an Ekman grab or a dredge. These were used to estimate the production dynamics, seasonal feeding patterns and lipid content. Stable isotope signatures of carbon and nitrogen were used to determine the sources of energy actually assimilated. Mean annual density of Diporeia was 1.7 times greater, and production was 2.7 times greater, at 50 m than at 30 m. Animals at both depths fed more or less continuously from April through November, but gut fullness was greatest in spring. Isotopic analyses suggested that, whereas Diporeia preferentially consumes freshly deposited diatoms when they are available, most of their carbon is derived from bacteria. The importance of littoral diatoms appeared to increase with proximity to shallow water.

We assessed the impact of bleached kraft pulp mill effluent on benthic invertebrate community structure in the shallow (1 m) nearshore waters of Jackfish Bay, Lake Superior. Duplicate benthic samples were collected from 0.5 m2 quadrats at twenty-three stations along two shorelines of Jackfish Bay up to 1800 m from the point of effluent discharge, and from a reference station located within the Jackfish Bay study area. Detrended correspondence analysis (DCA) revealed a gradient of stations on both shorelines which was strongly correlated with distance from effluent outfall and hence exposure to the effluent plume. Within this gradient were two distinct clusters of stations. The first cluster contained all but one station on both shores 90%) by tubificids (Limnodrilus hoffmeisteri, Tubifex tubifex, T. ignotus and Spirosperma ferox) and the naidid Chaetogaster diaphanus. The second cluster contained all stations on both shores >300 m from the outfall; community structure at these stations was generally comparable to that at the reference site and was characterized by several species of Chironomidae, C. diaphanus and Nais barbata, and low numbers of several insect taxa. The results of this study show that benthic community structure in nearshore environments can be significantly impacted by pulp mill effluent and should be considered in monitoring assessments. At Jackfish Bay, such impacts appear to be restricted primarily to within the first 500 m of effluent discharge.

There is veiy little information about the wildlife utilization of Stormwater detention ponds although such ponds often self-seed into wetland habitats. To inventory wildlife utilizing Stormwater ponds, a study was performed in 1997 and 1998 of 15 Stormwater ponds and one natural wetland varying in age from 3 to 22 years in the Guelph and the Greater Toronto Area (GTA) in Ontario, Canada. Seven of the Stormwater ponds were primarily open water with the aquatic vegetation accounting for less than 50% of the surface area. However, 90% of the surface area of four ponds was covered in aquatic vegetation. The surface area of those ponds covered with vegetation was positively correlated with total organic carbon and copper concentrations in sediment Invertebrate populations in the Stormwater ponds were often dominated by a single taxon. The most abundant benthic animals were tubificid worms or chironomidae. The number of taxa in sweep-net samples ranged from 4 to 25 and correlated positively with the age of the pond and total organic carbon in sediment The number of taxa in the benthos correlated negatively with oil and grease concentrations in sediment The range in number of amphibian species was one to seven in Guelph and zero to four in the GTA. In total, 40 species of birds were observed in the GTA ponds and 71 species were observed in the Guelph ponds during April to November 1997. A mean of 1.6 to 1.7 bird species was observed per survey at Stormwater ponds in Guelph and the GTA. The number of species of amphibians and birds did not correlate with water quality, sedimentology, contaminant concentration, percentage of surface area of the pond covered with plants, or any benthic community parameter measured. Four species of reptiles and eight species of mammals were noted at or adjacent to the Stormwater ponds and six species of fish were found in the ponds. We concluded that wildlife made use of the ponds, but species richness at almost all sites was low to moderate indicating that the ponds did not provide high quality habitat for wildlife

In this study, we assessed the impact of bleachedkraft pulp mill effluent (BKME) on the distributionand composition of benthic communities at JackfishBay, Lake Superior. Sediment samples were collectedfrom 44 stations from which several environmentalvariables (extractable organic chlorine [EOCl],metals, organic carbon, particle size, secchi depth,and water depth) and benthic community compositionwere determined. Relationships between environmentalvariables and benthic community structure wereassessed using canonical correspondence analysis(CCA). CCA revealed two distinct biological gradientsat Jackfish Bay, the first associated with degradedbottom sediments and nutrient enrichment and thesecond associated with water depth. Both gradientsrevealed three distinct regions at Jackfish Bay: 1) anarea of highly degraded sediments, located 300–1200 mbelow the outfall, 2) a small, mesotrophic (nutrientenriched) area adjacent to this zone, and 3) remainingareas of Jackfish Bay, including the internalreference sites in Tunnel Bay. Sediments in theimpaired region contained high concentrations oforganic matter (7–21% as loss on ignition [LOI]) andEOCl (up to 5200 mg/kg dw); together these variablesaccounted for 73% of the variation associated withthe first canonical axis of the CCA. This region wasdominated by the oligochaetes Tubifex tubifexand Limnodrilus hoffmeisteri (64–100% of thebenthic community). Sediments in the second regionwere characterized by an abundant and diverse benthiccommunity comprised of benthic harpacticoids,Chironomidae, and oligochaetes. Stations outside ofthese two regions were characterized by a benthiccommunity similar in composition to that expected foroligotrophic Lake Superior waters, including Diporiea sp., Stylodrilus heringianus, Mysis relicta, Sphaerium, Pisidium and benthicharpacticoids. Based on a Monte Carlo significancetest, benthic community structure was significantly(p = 0.01) related to the environmental variablescomprising the first axis of the CCA. Water depth wasthe most important explanatory variable associatedwith the second axis of the CCA; both taxa richnessand abundance declined significantly with increasingdepth. The comprehensive approach employed in thisstudy clearly delineated the occurrence and degree ofimpact on the benthic environment and may be useful infuture risk assessments of sites affected byanthropogenic activity.

Summary 1. The relationship between fish and benthic invertebrate communities in wadeable streams in southern Ontario, Canada, was examined using three independent and spatially distinct data sets. 2. Associations between fish and benthos were always significant when benthos were identified to family and often at the level of phylum. Identification to genus improved the strength of the fish–benthos association in one case. In contrast, identification to species did not improve the strength of the fish–benthos association. Associations between benthos and fish were weaker for one study utilizing a ‘rapid’ bio-assessment protocol involving field sorting and identification, and a second study which utilized winter benthic collections. 3. In two surveys, stream temperatures were important to the distributions of both fish and benthos, while in a third survey, fish and benthos were primarily influenced by stream size. In all three studies, fish and benthos were associated with similar suites of environmental variables, suggesting that the fish–benthos associations in these streams was driven by corresponding environmental tolerances. 4. Although there was significant variation in the strength of the fish–benthos association which could be attributed to differences in sampling methodologies, the findings from the present study confirm that stream fish and benthos are significantly associated. Therefore, surveys of benthos can be used to make inferences on the condition of fish community composition.

Periphyton was allowed to grow on glass plates suspended in the water column of a small stream under two conditions of light and water velocity, over two seasons, to assess the influence of the thickness of benthic boundary layers on stable isotope fractionation. Isotopic signatures for both carbon and nitrogen in samples of periphyton varied with light intensity and season, but not with current velocity. In summer, periphyton grown under low-light conditions had depleted 13C and 15N values relative to periphyton grown under high light. In autumn, isotopic signatures were generally more depleted than in summer, but did not vary systematically with light intensity or water velocity. These results suggest that isotopic fractionation in periphyton was more strongly influenced by the intensity of metabolic activity than by variations in the thickness of the benthic boundary layer.

From January 1964 through January 1966, Dr. F.P. Ide and colleagues at the University of Toronto Great Lakes Institute (GLI) collected benthic macroinvertebrates from up to 63 stations during each of 16 cruises on Lake Ontario. This intensive survey was conducted at a time of rapidly increasing anthropogenic impact. Total invertebrate abundance decreased with increasing depth; this distribution was bimodal on the northern side of the lake, with peaks at ca. 35 and 80 m. Oligochaeta were more abundant along the southern than on the northern side of the lake, except in Humber Bay. The amphipodDiporeia was rarely collected at most stations near the mouth of the Niagara River. Chironomidae were most abundant in the Kingston Basin but were common throughout the lake at depths less than 50 m. Sphaeriidae were confined to water

Samples of benthic invertebrates from four pairs of streams in southwestern Ontario collected monthly from May through August 1991, and once during the subsequent autumn and winter, demonstrated that conservation tillage practices have a remedial effect on the water quality of adjacent streams as indicated by biotic, rather than physical or chemical, parameters. One stream of each pair drained a basin under conventional tillage (CONV, mainly mouldboard ploughing), the other primarily under conservation tillage (CONS). The paired drainage basins were otherwise similar to one another in type of crops grown, as well as size, topography, soils and hydrology. CONS streams yielded a greater variety of Insecta but fewer taxa of Mollusca, Annelida and Crustacea than did samples from CONV streams. Both kick-net and Surber samples from CONS streams yielded significantly more taxa, more kinds of Ephemeroptera, Plecoptera and Trichoptera, and lower Hilsenhoff Biotic Index scores than did samples from CONV streams. Kick samples from CONS streams were significantly more similar to expected reference communities in overall taxonomic composition. Surber samples from CONS streams contained significantly larger numbers of invertebrates. The relatively greater abundances of infaunal species, especially Tubificidae and Chironomini, in CONV streams suggest greater accumulation of fine sediment particles. Conditions during low flow appear to have the greatest influence on the composition of benthic invertebrate communities. The results of the study indicate that conservation tillage practices have a beneficial effect on the quality of surface waters.

1. Benthic invertebrates were surveyed in 213 headwater streams in southern Ontario to test the utility of Percent Model Affinity (PMA) for assessing the relative impact of agriculture on invertebrate communities. Qualitative samples were collected from reference (= forested, sixty-nine samples) and agricultural (195 samples) streams between May 1990 and August 1993. The percentage composition of samples from reference streams was averaged by season and type of substratum, and the most homogeneous groupings were used as expected communities for the calculation of PMA. 2. The lower confidence limit about the mean PMA for each expected community was calculated as for a one-tailed t-test comparing a single observation with the mean of a sample. Samples from agricultural streams whose PMA scores were outside these confidence limits were judged to indicate significant impact. 3. The sensitivity of PMA to differences in land use increased with taxonomic resolution: 40% of agricultural sites were significantly different from reference communities at the ordinal level, 79.5% were significantly different at the lowest practical taxonomic level. Most of the increase in discrimination between reference and agricultural sites was due to Chironomidae. Identification to species, rather than genus, yielded only a small increase in discrimination between reference and agricultural sites, largely because of taxonomic difficulties and because most members of several diverse genera were very similar in their distributions. 4. All of the samples from streams which drained orchards and vinyards (n = 7) were significantly different from the expected communities, as were 89% of those from streams draining corn (n = 94). A larger percentage of streams draining hay (78%, n = 26) were impacted than were streams bordered by pasture (66%, n = 51), but the average magnitude of impact was greater in pasture streams. Only six of eleven samples from streams draining tobacco indicated significant impact. 5. The effect of land use adjacent to the sampling site was greatest early in the growing season. Comparison of natural channels and ditches draining agricultural land suggests that channelization and subsurface tile drainage eliminate most of the benefits of riparian buffer strips and magnify the effects of farming practices on the benthic fauna.

The composition of algae, invertebrates and fish communities, and specific characteristics of fish populations, are widely used as tools for monitoring the condition of aquatic resources. The power of these tools would be much greater if there were defendable decision criteria and interpretation methods that allow one to speculate on the specific cause of impacts. Without defendable decision criteria, assessments of impact can be made only in relative terms, and can be questioned. In addition, determining that a site is impacted is of little value unless we can simultaneously determine the root cause of the impact. We have developed both generic decision criteria for ecosystem descriptors considered worth protection (such as fish communities), and more specific decision criteria for surveys of benthic invertebrates in southern Ontario streams based on the protection of fish communities. We have also developed frameworks that utilize algal, benthic and fish communities, and demonstrated the use of fish pop...

Field experiments were used to assess the importance of intraspecific and interspecific competition in two grazing caddisflies, Neophylax fuscus Banks (Uenoidae) and Pycnopsyche guttifer (Walker) (Limnephilidae) and to examine the effect of larval density on the biomass of their algal food. Chlorophyll a was unaffected by manipulations of the density of either caddisfly species, although indicators of algal "quality" (the ratios of chlorophyll a to ash-free dry weight or to pheophytin a) displayed weak but significantly positive relationships with the dry weight of P. guttifer and N. fuscus, respectively. This suggests that grazing may remove older or overstory algae and thereby prevent senescence of the algal assemblage. Both active larvae and diapausing prepupae of N. fuscus were affected strongly by densities of conspecifics, exhibiting increases in weight only in treatments at 33% of natural density; this suggests a release from intraspecific competition. Survivorship of N. fuscus larvae and prepupae ...

Lake Temiskaming, a rift valley lake on the Ontario-Quebec border, exhibits a permanent gradient of turbidity due to tributary streams which cut through clay deposits to the north of the lake. Concentrations of total phosphorus (TP) also decreased from north to south, with values suggesting mesotrophic conditions. Concentrations of chlorophyll a were characteristic of oligotrophic lakes and showed little relationship to either turbidity or TP. Large numbers of Tubificidae were found at our northernmost sampling station at a depth of 50 m, probably reflecting the localized impact of allochthonous organic matter introduced by a tributary stream. Numerical abundance of the benthic fauna was much lower and did not vary significantly among the six more southerly 50 m stations, but biomass declined from north to south as Heterotrissocladius oliveri relaced Pontoporeia hoyi. Numerical abundance did not differ significantly among stations at depths of 10 m, but biomass decreased from north to south reflecting the distributions of the largest species, Hexagenia sp. and P. hoyi. Intensive sampling on two transects showed that maximum numbers of invertebrates occurred in the profundal zone. While these results are consistent with the correlation between TP and zoobenthic biomass reported by other investigators, size selective predation by fish may also be important in controlling the distribution of benthic invertebrates in Lake Temiskaming.

Proc. 8th Environmental Monitoring and Assessment Program (EMAP) Symposium, Washington, DC. April 2007

A lake-wide benthic survey of Lake Erie during summer 2002 indicated that Dreissena bugensis is the dominant dreissenid in Lake Erie, especially in the east basin where this species was found at every station but no Dreissena polymorpha were collected. Mean (±SD) densities of dreissenid mussels were comparable between the west (601 ± 2,110/m 2 ;n = 49) and central (635 ± 1,293/m 2 ; n = 41) basins, but were much greater in the east basin (9,480 ± 11,173/m 2 ; n = 17). The greater variability in mussel density among stations and replicate samples in the central and west basins than in the east basin is attributable to the preponderance of fine-grained substrata in the nearshore, higher episodic rates of sediment deposition, and periodic hypoxia in bottom waters. Although there was little change in lake-wide mean dreissenid densities between 1992 and 2002 (declining from ca. 2,636 individuals/m 2 to 2,025 individuals/m 2 ), basin-averaged shell-free dry tissue mass increased by almost four-fold from ca. 6.8 ± 15.6 g /m 2 to 24.7 ± 71.3 g/m 2 in the same interval. Up to 90% of this biomass is in the eastern basin. Other changes in 2002 include the virtual absence of mussels in the 3 to 12 mm size range, probably because of predation by round gobies, and an increase in the average size of mature mussels. The substantial changes observed between 1992 and 2002 suggest that dreissenid populations in Lake Erie were still changing rapidly in abundance and biomass, as well as species composition. The results of this survey suggest that a direct link between Dreissena spp. and hypolimnetic hypoxia in the central basin is unlikely.

On the basis of a review of current literature, France (1995) questioned the utility of stable isotope analysis (SIA) in describing food webs and understanding the effects of human perturbation in lotic ecosystems. His three main conclusions were (i) “autotrophic pathways within forested headwaters are much more important to lotic food webs than would be suggested by their particulate inputs alone,” (ii) “the great variability in attached algal δC may often preclude use of SIA for identifying carbon pathways in stream ecosystems,” and (iii) “the utility of carbon SIA in understanding anthropogenic alterations to the carbon budget of streams is presently minimal.” The first of these conclusions may well be correct, but points ii and iii appear to be based on a fundamental misunderstanding of the use of SIA. We have examined the same reports considered by France, as well as the wider literature concerning SIA, and feel that SIA can be a powerful technique for deciphering food webs and identifying impacts of alterations in land use. France’s attempt “to search for general patterns that transcend individual studies” by pooling δC data on carbon sources and animal consumers from freshwaters throughout the world is fundamentally flawed. While allochthonous organic matter is remarkably uniform in its isotopic signature, δC values of aquatic plants are widely recognized to be extremely variable between sites (Deines 1980; Osmond et al. 1981; Boutton 1991). It would be very surprising if there were any consistent pattern of C depletion or enrichment in the δC values of aquatic algae on a global scale. The fact that allochthonous δC values (≈–28‰) fall within the global range of reported autochthonous δC values (–46 to –22‰) in no way invalidates SIA as a means of assessing the importance of the two potential sources of energy. Rather, it means that such evaluations must be site specific (Rosenfeld and Roff 1992), and they are easily interpreted only when the potential carbon sources are isotopically distinct (Bunn et al. 1989). Since France bases his conclusions on pooled data, and not on site-specific algal and leaf litter δC values, no conclusions regarding the utility of SIA and the carbon dependencies of stream animals are possible. In addition, France fails to mention the importance of trophic fractionation in the interpretation of faunal δC values. Animals are usually enriched by ≈+1‰ relative to their diets (DeNiro and Epstein 1978), so that primary consumers are expected to be enriched by ≈+1‰, secondary consumers by ≈+2‰, and top predators by ≈+3‰ compared with their primary food sources (Rau et al. 1983). If one does not consider the trophic position of the organisms that are analyzed (France apparently expected the δC values of invertebrates and fish to be exactly the same as that of the primary carbon sources), no statement can be accurately made as to which animals are outside (or inside) the range of allochthonous dependence. There are similar problems with France’s critique of SIA in understanding anthropogenic alterations to the carbon flow of streams. After pooling data on “similar” species from forested and open sites, he found that (i) faunal δC could increase, decrease, or remain unchanged, and (ii) in almost 80% of the cases there was little or no change in faunal δC with landscape modification. The only surprising aspect of this is France’s expectation of consistent decreases in faunal δC values as evidence of increased utilization of autochthonous carbon following riparian deforestation. We agree that there have been too few analyses of autochthonous carbon sources, but it is precisely the “confounding by environmental co-determinants” that disallows France’s direct comparison between the δC values of similar species at forested and open sites: “although there is strong temptation to compare absolute

In this study, we assessed the acute and chronic toxicity of sediments contaminated by bleached kraft pulp mill effluent (BKME). Sediments were collected in August 1991 and 1992, and May 1993 from eight stations exposed directly to the effluent and from four reference sites. Acute toxicity was determined for five macroinvertebrates (Hyalella azteca, Daphnia magna, Chironomus riparius, Hexagenia spp., and Tubifex tubifex) using pore water, elutriate, and bulk sediment exposures. Chronic toxicity was assessed using C. tentans and H. azteca (growth and survival) and D. magna and T. tubifex (reproduction) in bulk sediment exposures. Mortality declined with decreasing proximity to the outfall; acute toxicity (>20% mortality after 48 h) was observed at the two stations closest to the outfall (300 and 400 m). At 300 m, pore water was consistently more toxic than elutriate or bulk sediment phases, resulting in 100% mortality for all invertebrates except T. tubifex (23%). Elutriate exposures were toxic to C. riparius (88%), D. magna (54%), and Hexagenia (47%), but not H. azteca. Bulk sediments were toxic to Hexagenia (100%) and D. magna (88%), but not to C. riparius or H. azteca. In chronic tests, mortality in H. azteca and T. tubifex was highest at 300 and 400 m, indicating that toxicity observed in the short-term aqueous exposures adequately predicted long-term toxicity in bulk sediments. In both acute and chronic tests, mortality was significantly correlated with the concentration of extractable organic chlorines (EOCl) in the sediment, with LC50 values ranging from 4500 to 5500 mg EOCl/kg organic carbon. Growth of C. tentans larvae was depressed at 300 and 400 m in August 91 but enhanced in May 93 relative to the reference sites. Growth of H. azteca also declined near the outfall in August 91 sediments and was approximately one half that observed in 92/93 sediments; however, growth did not differ among stations in 92 or 93. Reproductive output in D. magna (neonates) and T. tubifex (cocoons) was highest at 300 and 400 m. In T. tubifex, the number of hatched young was lowest at these stations. This study provides evidence that toxicity may occur in sediments exposed to BKME, and emphasizes the need to incorporate sediment toxicity bioassessment as part of efforts directed toward remedial action in the pulp and paper industry.

Benthic macroinvertebrate communities consisting mainly of Amphipoda, Trichoptera and Chironomidae develop in the 0-2 m zone along the Canadian shore of Lake Erie's central basin during summer, but are eliminated by storm and ice scouring in fall and spring. Most species probably overwinter offshore and re-enter the wave-zone by drifting via lake currents. Overwintering refuges were not found for three of the dominant wave-zone species—Hydropsyche recurvata, H. guttata and Polypedilum illinoense.

During studies of the environmental effects of oil sands development in northeastern Alberta in 1976–1977, 36 species of Ephemeroptera and 21 of Plecoptera were collected using various techniques. Individuals of 18 mayflies and 17 stoneflies were taken in numbers sufficient to determine their basic life histories and habitat preferences. Among the mayflies, 8 (possibly 10) species exhibited fast seasonal development, 8 slow seasonal, and 2 non‐seasonal. Among the Plecoptera, these patterns were exhibited by 5, 7 and 5 species, respectively. Nymphs of most fast seasonal mayflies developed in pools and silty backwaters, often in association with aquatic macrophytes. Slow seasonal mayflies and most stoneflies were found in riffles, or on bedrock and debris in the Athabasca River. The fauna included a mixture of Eastern, northern and cordilleran species. Eastern species probably reached the Athabasca River drainage via glacial Lake Agassiz.

Recent U.S. textile and apparel imports were examined at a detailed product level to assess factors explaining the level of non-tariff trade barriers (NTBs). Determinants of NTBs at the micro level were consistent with prior studies utilizing more aggregated data. Import penetration, per unit import cost, import quantity change, import value, and product type were significant variables in explaining the variability of import controls.