Rhithron Associates Inc.

Missoula, MT, United States

Rhithron Associates Inc.

Missoula, MT, United States
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Webb J.M.,Rhithron Associates Inc. | Burian S.K.,University of Connecticut
Check List | Year: 2017

New state records are provided for two recently described species of North American Acentrella Bengtsson, 1912. Acentrella nadineae McCafferty, Waltz & Webb, 2009 is newly reported from Connecticut, Massachusetts, and Minnesota, and A. rallatoma Burian & Myers, 2011 is reported from Minnesota. © 2017 Check List and Authors.

Andrus J.M.,Waterborne Environmental Inc. | Winter D.,Rhithron Associates Inc. | Winter D.,Algal Analysis LLC | Scanlan M.,MapTech Inc. | And 5 more authors.
Science of the Total Environment | Year: 2015

Potential effects of pesticides on stream algae occur alongside complex environmental influences; in situ studies examining these effects together are few, and have not typically controlled for collinearity of variables. We monitored the dynamics of periphyton, phytoplankton, and environmental factors including atrazine, and other water chemistry variables at 6 agricultural streams in the Midwest US from spring to summer of 2011 and 2012, and used variation partitioning of community models to determine the community inertia that is explained uniquely and/or jointly by atrazine and other environmental factors or groups of factors. Periphyton and phytoplankton assemblages were significantly structured by year, day of year, and site, and exhibited dynamic synchrony both between site-years and between periphyton and phytoplankton in the same site-year. The majority of inertia in the models (55.4% for periphyton, 68.4% for phytoplankton) was unexplained. The explained inertia in the models was predominantly shared (confounded) between variables and variable groups (13.3, 30.9%); the magnitude of inertia that was explained uniquely by variable groups (15.1, 18.3%) was of the order hydroclimate. >. chemistry. >. geography. >. atrazine for periphyton, and chemistry. >. hydroclimate. >. geography. >. atrazine for phytoplankton. The variables most influential to the assemblage structure included flow and velocity variables, and time since pulses above certain thresholds of nitrate. +. nitrite, total phosphorus, total suspended solids, and atrazine. Time since a ≥. 30. μg/L atrazine pulse uniquely explained more inertia than time since pulses. ≥. 10. μg/L or daily or historic atrazine concentrations; this result is consistent with studies concluding that the effects of atrazine on algae typically only occur at ≥. 30. μg/L and are recovered from. © 2014 Elsevier B.V.

Winter D.,University of Nebraska - Lincoln | Winter D.,Rhithron Associates Inc. | Sjunneskog C.,Florida State University | Harwood D.,University of Nebraska - Lincoln
Stratigraphy | Year: 2010

An extended lower to mid-Pliocene stratigraphic record of near-shore environmental variation in the southwestern Ross Sea, Antarctica is preserved in ANDRILL's McMurdo Ice Shelf Project AND-1B drillcore. A 94 meter-thick sequence of three diatomite and diatomaceous mudstone intervals represents the highest latitude record (78° S) of persistent open-marine conditions on the Antarctic continental shelf, in response to a protracted period of Pliocene warmth. This core provides new chronostratigraphic control for Antarctic paleoclimatic events, and describes a sequence of distinct diatom assemblages comprised of both extant and extinct species that are unknown on the Antarctic shelf today. Common taxa include those with modern distributions close to the Polar Frontal Zone (e.g. Shionodiscus tetraoestrupii, Stellarima stellaris, Thalassionema nitzschioides), suggesting marine temperatures in the southwestern Ross Sea warmer than at present. Representatives of the modern sea-ice assemblage (e.g. Fragilariopsis curta, Stellarima microtrias) and cold open-marine species associated with the retreating sea-ice front (e.g. Eucampia antarctica var. recta) are also present, but in much lower abundance than in the Ross Sea today as suggested by core top and surface sample data. The co-occurrence of species from these three distinct modern environments in Pliocene sediments, in close proximity to the continent, suggests that modern ecological zonal concepts cannot be applied directly in Pliocene paleoenvironmental analyses. Species present in the 4 m-thick lowest diatomite unit (~4.5 Ma) indicate a cold open marine environment, with the period of deposition likely comprising the length of one interglacial period. The middle diatomite unit (~4.1-4.3 Ma; 14m) records warmer and perhaps seasonally mixed conditions with often abundant Thalassionema nitzschioides and Shionodiscus tetraoestrupii and little evidence of sea-ice associated species. Documentation of changes in diatom assemblages through the upper 75m-thick diatomite interval (~3.3-3.6 Ma) offers the opportunity to resolve environmental limits of Pliocene diatom species that will serve as a guide to diatom-based paleoenvironmental interpretations for other Pliocene deposits. This upper unit records deposition during several glacial/interglacial cycles indicating an extended interval with open marine productivity during the mid-Pliocene. In addition, environmental associations for extinct species are inferred by their co-occurrence with extant taxa. Persistent intervals of pure diatomite suggest high productivity in an open-marine setting and minimal to no influence of sea ice. Commonly occurring species can be placed in five ecological categories; Neritic/Stratified, Warm, Cold/Sea Ice, Heavy/Wind Mixed and Mixed. Comparison of this long diatom-bearing interval with coeval Antarctic deposits presents a regional and continental picture of Pliocene warmth, suggesting East Antarctic Ice Sheet was smaller with sub-polar marginal conditions.

Winter D.,Rhithron Associates Inc | Bahls L.,The Montana Diatom Collection
Phytotaxa | Year: 2013

A new species of Encyonema is described from the benthos of small mountain streams and rivers in western Montana and northern Wyoming. Previously this species had been identified incorrectly as E. hebridicum Grunow ex Cleve and Cymbella affinis Kützing or assigned the provisional name Encyonema sp. 1 MONTANA HAMSHER ANSP. Here we formally recognize this taxon as a new species, Encyonema hamsherae. © 2013 Magnolia Press.

Winter D.,University of Nebraska - Lincoln | Winter D.,Rhithron Associates Inc. | Sjunneskog C.,Louisiana State University | Scherer R.,Northern Illinois University | And 2 more authors.
Global and Planetary Change | Year: 2012

The ANDRILL AND-1B drillcore in southern Victoria Land Basin, Antarctica recovered an upper Miocene to early Pleistocene continental shelf stratigraphic section, including a spectacular Pliocene and Pleistocene sequence of alternating diamictite and diatom-rich sediments. This punctuated sequence reflects variation between glacial sediments deposited by ice advance over the site and open-marine diatom productivity and sedimentation. An early Pliocene age for the base of diatom-rich sediment is constrained through integrated diatom biostratigraphy and magnetostratigraphy. The presence of marine diatom Shionodiscus tetraoestrupii from the top of the core to 583.64. mbsf indicates the lowest diatom-bearing sediments are younger than 5. Ma. This drillcore provides important new chronostratigraphic control for paleoenvironmental changes also recorded in three drillcores from the western coast of the McMurdo Sound area, DVDP-10 and -11 in Taylor Valley and CIROS-2 from the seaward edge of Ferrar Fjord. The refined continental shelf biostratigraphy developed from AND-1B provides a framework for regional correlation to understand better the timing and character of large paleoenvironmental changes in the western Ross Sea that involve the history of the West Antarctic Ice Sheet (WAIS). Multivariate analysis, along with traditional biostratigraphic approaches, enables the correlation and comparison of coeval intervals in these drillcores. A composite stratigraphic sequence from these four cores suggests the early and mid-Pliocene Ross Sea experienced extended intervals of open-marine conditions with minimal sea-ice cover and high diatom production and sedimentation. This new information provides important constraints on Antarctic paleoclimate and ice sheet history during an important interval when global climate was warmer than today. The history preserved in these four drillcores will be an important tool to guide and test future ice sheet and climate models. © 2010 Elsevier B.V.

Andrus J.M.,Waterborne Environmental Inc. | Winter D.,Rhithron Associates Inc. | Scanlan M.,MapTech Inc. | Sullivan S.,Rhithron Associates Inc. | And 4 more authors.
Science of the Total Environment | Year: 2013

Numerous studies characterizing the potential effects of atrazine on algal assemblages have been conducted using micro- or mesocosms; however, few evaluations focused on in situ lotic algal communities, potentially confounding risk assessment conclusions. This exploratory study, conducted at several sites in the midwestern United States where atrazine is commonly used, presents in situ observations of native algal communities relative to atrazine exposure and other parameters. Planktonic and periphytic algae from three streams in three Midwestern states, having historically differing atrazine levels, were sampled over a 16-week period in 2011 encompassing atrazine applications and the summer algal growth period at each site. Changes in abundance, diversity, and composition of algal communities were placed in the context of hydrological, climatic, and water quality parameters (including components sometimes present in agricultural runoff) also collected during the study. Diatoms dominated communities at each of the three sites and periphyton was much more abundant than phytoplankton. As expected, significant variations in algal community and environmental parameters were observed between sites. However, correspondence analysis plots revealed that patterns of temporal variation in algal communities at each site and in periphyton or phytoplankton were dominated by seasonal environmental gradients. Significant concordance in these seasonal patterns was detected among sites and between phytoplankton and periphyton communities (via procrustes Protest analysis), suggesting synchronicity of algal communities across a regional scale. While atrazine concentrations generally exhibited seasonal trends at the study watersheds; no effects on algal abundance, diversity or assemblage structure were observed as a result of atrazine pulses. This lack of response may be due to exposure events of insufficient concentration or duration (consistent with previously reported results) or the composition of the algal assemblages present. This was in contrast to the effects of elevated flow events, which were associated with significant changes in periphyton abundance, diversity and assemblage. © 2013 Elsevier B.V.

Labiobaetis sonajuventus n.sp. is described from nymphs collected in a tributary of the Okanogan River in north-central Washington, USA. The new species is distinguished from North American congeners by the well-developed keel between the bases of the antennae, the concave lateral margin of labial palp segment 2, the apically expanded submarginal setae on the labrum, and its western Nearctic distribution. Copyright © 2013 Magnolia Press.

Shackleton M.E.,La Trobe University | Webb J.M.,Rhithron Associates Inc.
Zootaxa | Year: 2015

The caddisfly genus Caenota Mosely 1953 (in Mosely & Kimmins 1953) currently contains 5 species known from eastern Australia. Caenota is distinguished from other Calocidae genera by having adult males with greatly expanded maxillary palpi and a large membranous process associated with the antennal scape. Of the 5 described species, the larvae of only 1 is known. Here, we describe 2 new species, Caenota cudonis sp. nov. and C. equustagna sp. nov., from adult, larval, and pupal material. Also, we describe for the first time the larva of C. nemorosa Neboiss. These descriptions increase the number of Caenota species to 7 and the number of associated and described larvae to 4. This paper also provides descriptions of features associated with the adult head capsule of all described species of Caenota. Each of the known species is considered, with illustrations and re-descriptions of these features given. Copyright © 2015 Magnolia Press.

Sullivan S.P.,Rhithron Associates Inc
Check List | Year: 2011

Two males and a female of Zaitzevia posthonia Brown 2001 were collected from a shallow riffle in a swift, second-order stream west of the continental divide near Lincoln, Montana. This new record confirms the presence of the species in the state, and extends the range of the species 267 km northeast of the nearest previously known record. © 2011 Check List and Authors.

PubMed | La Trobe University, North East Water, Rhithron Associates Inc. and CSIRO
Type: Journal Article | Journal: Environmental monitoring and assessment | Year: 2016

Bayesian networks (BNs), or causal Bayesian networks, have become quite popular in ecological risk assessment and natural resource management because of their utility as a communication and decision-support tool. Since their development in the field of artificial intelligence in the 1980s, however, Bayesian networks have evolved and merged with structural equation modelling (SEM). Unlike BNs, which are constrained to encode causal knowledge in conditional probability tables, SEMs encode this knowledge in structural equations, which is thought to be a more natural language for expressing causal information. This merger has clarified the causal content of SEMs and generalised the method such that it can now be performed using standard statistical techniques. As it was with BNs, the utility of this new generation of SEM in ecological risk assessment will need to be demonstrated with examples to foster an understanding and acceptance of the method. Here, we applied SEM to the risk assessment of a wastewater discharge to a stream, with a particular focus on the process of translating a causal diagram (conceptual model) into a statistical model which might then be used in the decision-making and evaluation stages of the risk assessment. The process of building and testing a spatial causal model is demonstrated using data from a spatial sampling design, and the implications of the resulting model are discussed in terms of the risk assessment. It is argued that a spatiotemporal causal model would have greater external validity than the spatial model, enabling broader generalisations to be made regarding the impact of a discharge, and greater value as a tool for evaluating the effects of potential treatment plant upgrades. Suggestions are made on how the causal model could be augmented to include temporal as well as spatial information, including suggestions for appropriate statistical models and analyses.

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