Gretchen Rollwagen-Bollens

Environmental influence on cyanobacteria abundance and microcystin toxin production in a shallow temperate lake.

The increasing frequency of harmful cyanobacterial blooms in freshwater systems is a commonly recognized problem due to detrimental effects on water quality. Vancouver Lake, a shallow, tidally influenced lake in the flood plain of the Columbia River within the city of Vancouver, WA, USA, has experienced numerous summertime cyanobacterial blooms, dominated by Aphanizomenon sp. and Anabaena sp. Cyanobacteria abundance and toxin (microcystin) levels have been monitored in this popular urban lake for several years; however, no previous studies have identified which cyanobacteria species produce toxins, nor analyzed how changes in environmental variables contribute to the fluctuations in toxic cyanobacteria populations. We used a suite of molecular techniques to analyze water samples from Vancouver Lake over two summer bloom cycles (2009 and 2010). Both intracellular and extracellular microcystin concentrations were measured using an ELISA kit. Intracellular microcystin concentrations exceeded WHO guidelines for recreational waters several times throughout the sampling period. PCR results demonstrated that Microcystis sp. was the sole microcystin-producing cyanobacteria species present in Vancouver Lake, although Microcystis sp. was rarely detected in microscopical counts. qPCR results indicated that the majority of the Microcystis sp. population contained the toxin-producing gene (mcyE), although Microcystis sp. abundance rarely exceeded 1 percent of overall cyanobacteria abundance. Non-metric multidimensional scaling (NMDS) revealed that PO4-P was the main environmental variable influencing the abundance of toxic and non-toxic cyanobacteria, as well as intracellular microcystin concentrations. Our study underscores the importance of using molecular genetic techniques, in addition to traditional microscopy, to assess the importance of less conspicuous species in the dynamics of harmful algal blooms.

Feeding dynamics of the copepod Diacyclops thomasi before, during and following filamentous cyanobacteria blooms in a large, shallow temperate lake

Cyanobacteria blooms are an increasing problem in temperate freshwater lakes, leading to reduced water quality and in some cases harmful effects from toxic cyanobacteria species. To better understand the role of zooplankton in modulating cyanobacteria blooms, from 2008 to 2010 we measured water quality and plankton abundance, and measured feeding rates and prey selectivity of the copepod Diacyclops thomasi before, during and following summertime cyanobacteria blooms in a shallow, eutrophic lake (Vancouver Lake, Washington, USA). We used a combined field and experimental approach to specifically test the hypothesis that copepod grazing was a significant factor in establishing the timing of cyanobacteria bloom initiation and eventual decline in Vancouver Lake. There was a consistent annual succession of zooplankton taxa, with cyclopoid copepods (D. thomasi) dominant in spring, followed by small cladocerans (Eubosmina sp.). Before each cyanobacteria bloom, large cladocerans (Daphnia retrocurva, Daphnia laevis) peaked in abundance but quickly disappeared, followed by brief increases in rotifers. During the cyanobacteria blooms, D. thomasi was again dominant, with small cladocerans abundant in autumn. Before the cyanobacteria blooms, D. thomasi substantially consumed ciliates and dinoflagellates (up to 100% of prey biomass per day), which likely allowed diatoms to flourish. A shift in copepod grazing toward diatoms before the blooms may have then helped to facilitate the rapid increase in cyanobacteria. Copepod grazing impact was the highest during the cyanobacteria blooms both years, but focused on non-cyanobacteria prey; copepod grazing was minimal as the cyanobacteria blooms waned. We conclude that cyclopoid copepods may have an indirect role (via trophic cascades) in modulating cyanobacteria bloom initiation, but do not directly contribute to cyanobacteria bloom decline.

The influence of water quality variables on cyanobacterial blooms and phytoplankton community composition in a shallow temperate lake

Cyanobacterial blooms and their detrimental effects on water quality have become a worldwide problem. Vancouver Lake, a tidally influenced shallow temperate freshwater lake in Washington state, U.S.A., exhibits annual summer cyanobacterial blooms that are of concern to local resource managers. Our objectives were to describe changes in phytoplankton community composition in Vancouver Lake over seasonal, annual, and interannual time scales, and to identify strong water quality predictors of phytoplankton community structure, with an emphasis on cyanobacterial blooms, from 2007 through 2010. Cluster analysis, indicator species analysis, and non-metric multidimensional scaling were used to identify significantly different phytoplankton community groupings and to determine which environmental factors influenced community changes. From 2007 through 2009, depletion of NO3–N followed by elevated PO4–P concentration was associated with increased biomass and duration of each cyanobacterial bloom. Time-lag analysis suggested that NO3–N availability contributed to interannual changes within the summer phytoplankton community. Specifically, in summer 2010, a distinct cyanobacteria community was not present, potentially due to increased NO3–N and decreased PO4–P and NH4–N availability. Our study provides a comprehensive assessment of species-level responses to water quality variables in a shallow non-stratifying temperate lake, contributes to a better understanding of phytoplankton dynamics, and may aid in predicting and managing cyanobacterial blooms.

Environmental identity, pro-environmental behaviors, and civic engagement of volunteer stewards in Portland area parks

We conducted surveys of adults participating in municipally sponsored volunteer events in the Portland, OR metropolitan area in order to understand the range of attitudes and behaviors associated with volunteer work. We sampled 172 individuals in 18 events from February to June 2012. Principal components and factor analyses of survey responses identified three groups based on annual frequency of participation in stewardship events: first-time volunteers, mid-level volunteers (3–10 events per year), and frequent volunteers (>10 events per year). Our analyses revealed three main factors that explained the variation in survey response for the three volunteer groups: environmental identity, private pro-environmental behavior, and civic engagement. All three factors were positively correlated with frequency of participation in stewardship events, with the most frequent volunteers indicating the highest degree of attention to environmental issues, environmental identity, and self-reported pro-environmental behaviors. Frequent volunteers were more likely to feel personally attached to their local environment, believe that their efforts help solve environmental problems, and enjoy being part of community efforts. These results suggest that stewardship activities provide opportunities for volunteers to interact with others while working collectively toward restoring and maintaining parks, which may contribute to more resilient communities.

Interactive effects of phosphorus and zooplankton grazing on cyanobacterial blooms in a shallow temperate lake

Cyanobacterial blooms are becoming increasingly common worldwide. These blooms can be moderated by grazing and/or nutrient availability, but the interactive effects of these processes are not well understood. We examined the interactive effects of phosphate and copepods on growth of phytoplankton (algae and cyanobacteria) in a shallow temperate lake. Field sampling of nutrient and chlorophyll a concentrations was conducted weekly from May through October, 2013. Five two-factorial experiments, spanning pre-, mid-, and post-bloom periods, were conducted with unfiltered lake water incubated with amended copepods, phosphate, or both. Changes in chlorophyll a concentration were used to calculate net phytoplankton biomass growth rates, and cell counts were performed on selected experiments to calculate growth rates of six microplanktonic taxonomic groups. Field data revealed cyanobacterial bloom development in July and decline in September. Experimental results indicated that phytoplankton growth increased with added phosphate pre-bloom, and decreased with added copepod grazers post-bloom, but that a more complex interactive (phosphorus x copepods) effect was observed immediately prior to and during peak bloom times. More specifically, the addition of phosphate and copepods enhanced ciliate growth pre-bloom, while selective grazing by copepods reduced dinoflagellate growth mid-bloom, possibly enhancing cyanobacterial growth and bloom duration via trophic cascade effects.

A genetic reconstruction of the invasion of the calanoid copepod Pseudodiaptomus inopinus across the North American Pacific Coast

The rate of aquatic invasions by planktonic organisms has increased considerably in recent decades. In order to effectively direct funding and resources to control the spread of such invasions, a methodological framework for identifying high-risk transport vectors, as well as ruling out vectors of lesser concern will be necessary. A number of estuarine ecosystems on the North American Pacific Northwest coast have experienced a series of high impact planktonic invasions that have slowly unfolded across the region in recent decades, most notably, that of the planktonic copepod crustacean Pseudodiaptomus inopinus. Although introduction of P. inopinus to the United States almost certainly occurred through the discharge of ballast water from commercial vessels originating in Asia (the species’ native range), the mechanisms and patterns of subsequent spread remain unknown. In order to elucidate the migration events shaping this invasion, we sampled the genomes of copepods from seven invasive and two native populations using restriction-site associated DNA sequencing. This genetic data was evaluated against spatially-explicit genetic simulation models to evaluate competing scenarios of invasion spread. Our results indicate that invasive populations of P. inopinus exhibit a geographically unstructured genetic composition, likely arising from infrequent and large migration events. This pattern of genetic patchiness was unexpected given the linear geographic structure of the sampled populations, and strongly contrasts with the clear invasion corridors observed in many aquatic systems.

Veligers of the invasive Asian clam Corbicula fluminea in the Columbia River Basin: Broadscale distribution, abundance, and ecological associations

ABSTRACT Hassett W, Bollens SM, Counihan TD, Rollwagen-Bollens G, Zimmerman J, Katz S, Emerson J. 2017. Veligers of the invasive Asian clam Corbicula fluminea in the Columbia River Basin: broadscale distribution, abundance, and ecological associations. Lake Reserv Manage. 00:00–00. The invasive Asian clam Corbicula fluminea was introduced to North America in the 1930s and now inhabits most regions of the conterminous United States; however, the distribution and ecology of C. fluminea in the Columbia River Basin is poorly understood. During 2013 and 2014, 5 Columbia-Snake River reservoirs were sampled monthly from May through September, along with 23 additional lakes and reservoirs sampled once each summer. Associations among C. fluminea veligers, other components of the plankton, and environmental variables were analyzed using non-metric multidimensional scaling and canonical correspondence analysis. Corbicula fluminea veligers were found in high abundances in all mainstem Columbia-Snake River reservoirs, with an annual mean abundance of 71.2 individuals per cubic meter (inds./m3). Only 3 of 23 lakes and (non-mainstem) reservoirs contained C. fluminea, with abundances considerably lower (maximum = 21.2 inds./m3) than in the mainstem reservoirs. A diatom-dominated community preceded the spawning of C. fluminea in early summer at all sites. Corbicula fluminea veligers characterized the plankton community in late summer and were associated with cyanobacteria and high water temperatures. A third community, characterized by cyanobacteria, was apparent in non-mainstem sites in July and August. Our analyses describe the relationship of C. fluminea to the plankton community and environment, which contributes to our understanding of the possible effects of C. fluminea infestations and which waterbodies in the Columbia River Basin are at risk for infestation. Understanding the effects and environmental determinants of invasive mollusks will be increasingly important in the future with the possible arrival of zebra (Dreissena polymorpha) or quagga (D. bugensis) mussels to the region.