Benthic filter feeders (BFF) can reduce phytoplankton concentration (abundance) thereby controlling eutrophication in several ecosystems, including rivers. However, experiments suggest warming can alter the relationship between BFF grazing rate and the growth rate of (heterotrophic) planktonic prey. To investigate how eutrophication control by grazers is altered with temperature under the influence of other important abiotic (water depth, and speed, light, and turbidity) and biotic factors (initial phytoplankton concentration [hereafter: Pin value], BFF density and spatial BFF distribution), we developed a spatially-explicit computer simulation model. This model simulates the dynamics of a phytoplankton population traveling through a simplified river channel while being grazed by BFF. Our model includes the thermal responses of BFF grazing and phytoplankton growth. The results show that BFF grazing can qualitatively alter and, in some circumstances, even reverse the response of phytoplankton to warming. Moreover, the response of grazer-controlled phytoplankton to warming, water depth and Pin value is non-linear and phytoplankton can increase steeply with slight changes within some ranges of these variables. In addition, these variables can interact causing their combined effects on eutrophication to differ from what is expected considering their isolated effects. Generally, the effect of most variables, including temperature, Pin value and BFF density and spatial distribution, is larger at shallow waters. Moreover, our study shows that phytoplankton control can be substantially improved by heterogeneous BFF distributions where the BFF are located at the extremes of the river either upstream or downstream instead of homogenously distributed along the whole river. However, warming can cause a switch between these two optimal distributions or even can cause differences among the spatial distributions to disappear. In general, the homogeneous BFF distribution can be used as conservative estimate of eutrophication control. In conclusion, this work shows that trophic control can qualitatively alter the response of eutrophication to warming, supporting previous studies suggesting that the prediction of global warming effects requires considering not only the thermal responses of organisms but also their trophic interactions. In addition to these biotic variables, this thesis reveals that considering the interactions between abiotic and biotic variables and including their spatial distribution are important for eutrophication control. Especially, the detection of thresholds in the response of grazer-controlled phytoplankton to temperature, water depth, Pin value, and spatial BFF distribution indicates that one should be careful with predictions because of potential abrupt changes. Although further studies are needed to make specific recommendations for water quality management, our work provides preliminary suggestions on the conditions where grazers or Pin reductions can be more efficient to control eutrophication.

Metallic nanoparticles (MetNPs) with unique nanoscale properties, including novel optical behavior and superparamagnetism, are continually being developed for biomedical and industrial applications. In certain biomedical applications where extended blood half-lives are required, MetNPs are surface-functionalized using polymers, proteins, and other stabilizing agents to facilitate their resistance to salt-induced aggregation. Given their colloidal stability in high ionic-strength matrices, functionalized MetNPs are anticipated to be persistent aquatic contaminants. Despite their potential environmental significance, the persistence of surface- functionalized MetNPs as individually-stabilized nanoparticles in aquatic environments is largely unknown. Further, few studies have investigated the fundamental factors that influence MetNP uptake and fate/transport processes in ecologically susceptible aquatic biota, such as filter- feeding bivalves, which ingest and accumulate a broad range of dissolved- and particulate-phase contaminants. The present study describes a comprehensive approach to prepare and rigorously characterize MetNP test suspensions to facilitate fundamental examinations of nanoparticle uptake and fate/transport processes in freshwater and marine bivalves. We demonstrate the importance of accurately characterizing test suspensions in order to better understand MetNP persistence as individually-stabilized nanoparticles within aquatic test media, and define an optical-activity metric suitable for quantifying and comparing the persistence of variable MetNP formulations as National Nanotechnology Initiative (NNI) definable nanoscale materials. We also show that individually-stabilized MetNPs of variable elemental composition, particle diameter, and surface coating are accessible to bivalves in both freshwater and marine environments. Clearance rates for MetNPs are positively related to the diameter and initial concentration of MetNP suspensions. The observed size-dependence of particle filtration rates facilitates ‘size-selective biopurification' of particle suspensions with nanoscale resolution, and may have applicability in future sustainable nanomanufacturing processes. Filtered MetNPs are retained for extended periods post-exposure primarily within the bivalve digestive tract and digestive gland, but migration to other organ systems was not observed. Clusters of MetNPs were recovered in concentrated form from excreted feces, suggesting that biotransformation and biodeposition processes will play an important role in transferring MetNPs from the water column to benthic environments. / Ph. D.

Hydropeaking is important to meet peak demand of electricity on the Swedish powergrid. The rapid changes in discharge may affect the ecology of streams and rivers negatively downstream of hydropeaking powerplants. In this study, the composition of five functional feeding groups (FFG) was investigated in the families Ephemeroptera, Plecoptera and Trichoptera (EPT) in samples collections by Hester-Dendy-sampler in 27 locations in streams and rivers with and without hydropeaking. The groups shredders, grazers, gatherers, filter feeders and predators were identified for each toxon. I expected that the flow regime downstream of a hydropeaking powerplant would affect the composition of FFG compared to non-hydropeaking streams and rivers, except for the group predators. No significant differenses in FFG between the streams and rivers with and without hydropeaking was found. These results indicate that effects from hydropeaking on FFG is not general and that spatially-explicit investigations may be needed to shed light on the effects of hydropeaking. / För att reglera effektbehovet på det svenska elnätet är korttidsregleringen från vattenkraftverk en viktig faktor. Dessa snabba förändringar i flödesregimen medför dock en påverkan på ekologin i vattendraget. I den här studien undersöktes sammansättningen av fem olika funktionella födosöksgrupper (FFG) hos Ephemeroptera, Plecoptera och Trichoptera (EPT) från insamling av evertebrater med Hester-Dendy-provtagare i 27 lokaler i vattendrag med och utan korttidsreglering. Identifiering av grupperna shredders, grazers, gatherers, filter feeders och predators gjordes för varje taxon. Jag förväntade mig att flödesregimen som förekommer nedströms korttidsreglerade vattenkraftverk skulle påverka sammansättningen av FFG i jämförelse med ett icke korttidsreglerat vattendrag, förutom för gruppen predators. Data visade att det inte fanns någon signifikant skillnad hos FFG mellan vattendragen med vs. utan korttidsreglering. Detta visar att påverkan på FFG av korttidsreglering inte är generell och att platsspecifika undersökningar kan behövas för att belysa regleringens effekter.

Noble metal nanoparticles such as gold and silver are of interest because of the unique electro-optical properties (e.g., localized surface plasmon resonance [LSPR]) that originate from the collective behavior of their surface electrons. These nanoparticles are commonly developed and used for biomedical and industrial application. A recent report has predicted that the global market for gold nanoparticles will be over 12.7 tons by year 2020. However, these surface-functionalized nanoparticles can be potential environmental persistent contaminants post-use due to their high colloidal stability in the aquatic systems. Despite, the environmental risks associated with these nanoparticles, just a few studies have investigated the effect of nanofeature factors such as size and shape on the overall fate/transport and organismal uptake of these nanomaterials in the aquatic matrices. This study presents a comprehensive approach to evaluate the colloidal stability, fate/transport, and organismal uptake of these nanoparticles while factoring in the size and shape related properties. We demonstrate the importance and effect of anisotropicity of a gold nanoparticle on the colloidal behavior and interaction with ecologically susceptible aquatic biota. We also show how readily available characterization techniques can be utilized to monitor and assess the fate/transport of this class of nanoparticles. We further describe and investigate the relationship between the aspect ratio (AR) of these elongated gold nanoparticles with clearance mechanisms and rates from the aquatic suspension columns including aggregation, deposition, and biopurification. We illustrate how a fresh water filter-feeder bivalve, Corbicula fluminea, can be used as a model organism to study the size and shape-selective biofiltration and nanotoxicity of elongated gold nanoparticles. The results suggest that biofiltration by C. fluminea increases with an increase in the size and AR of gold nanoparticle. We develop a simple nanotoxicity assay to investigate the short-term exposure nanotoxicity of gold nanoparticles to C. fluminea. The toxicity results indicate that for the tested concentration and exposure period that gold nanoparticles were not acutely toxic (i.e., not lethal). However, gold nanoparticles significantly inhibited the activities of some antioxidant enzymes in gill and digestive gland tissues. These inhibitions could directly affect the resistance of these organisms to a secondary stressor (temperature, pathogens, hypoxia etc.) and threaten organismal health. / Ph. D.