Utilizing field and modeling methodology, the effects of benthic micro-communities and physical transport mechanisms on sediment nutrient flux were investigated for two nearshore sediment types on Virginia’s Eastern Shore. Subtidal sandy mineral sediments were conducive to water transport and subsequently influenced by groundwater discharge to a greater degree than less permeable organic silt-clay sediments. Sediment ammonium and dissolved inorganic phosphorus (DIP) fluxes were strongly dependent on benthic aerobic respiration rates for silt-clay sediments as compared to sandy substrates. In situ studies indicated a significant decrease in ammonium and DIP fluxes as a result of nutrient uptake by benthic microalgal communities. The importance of advective solute transport mechanisms within nearshore sediments was demonstrated by a one-dimensional, steady-state model for a conservative substance. By incorporating dispersive and advective transport mechanisms, model predictability for chloride sediment flux was significantly improved as compared to a diffusion based model. Model results indicated that velocity associated transport of solutes, driven by elevated upland hydraulic heads, are significant and can dominate over diffusive flux in sandy sediment. In contrast, silt-clay sediment solute fluxes were dominated by dispersive processes. The importance of sedimentary nutrient flux in a shallow coastal embayment was demonstrated by short water column DIN and DIP turnover times with respect to sediment nutrient fluxes, by the significance of ammonium and DIP sediment nutrient fluxes with respect to phytoplankton nutrient assimilation demands, and by the relative importance of benthic respiration with respect to water column primary productivity. In order to evaluate water quality impacts of groundwater discharge on a larger scale, a surface, groundwater, and in situ groundwater discharge water quality survey was conducted in a shallow estuarine embayment. Sediment inorganic nitrogen fluxes were elevated adjacent to agricultural fields without benefit of a vegetative buffer. Nitrogen contributions from direct groundwater discharge and groundwater derived creek inputs appear to be of significant importance in terms of water quality and phytoplankton nitrogen assimilation demands. In summary, this study highlights the importance of nearshore sediments with regards to estuarine nutrient water quality and ecological processes. Neglecting groundwater discharge as a nutrient source and transport mechanism and potential biotic effects occurring at the sediment-water interface may lead to serious misinterpretation of data and error in water quality strategies. / Ph. D.

L’apport de sédiments fins au cours d’eau est un phénomène naturel mais qui sous les effets de l’anthropisation peut devenir excessif et conduire à perturber le fonctionnement de l’hydrosystème. Cet apport excessif provoque le colmatage du lit des rivières et peut perturber les échanges hydriques, les processus biogéochimiques et les communautés d’invertébrés benthiques et hyporhéiques. D’un point de vue méthodologique, la mesure de la conductivité hydraulique dans le substrat permet d’obtenir une image du niveau de colmatage de la zone hyporhéique et le pompage Bou Rouch permet d’étudier qualitativement la faune hyporhéique. D’un point de vue biologique, les effets du colmatage sont un peu plus importants pour l’hyporhéos que pour le benthos notamment au niveau de la richesse taxonomique, des assemblages faunistiques et des traits biologiques / Fine sediment input to the streambeds is a natural phenomenon but in addition to the effects of human impacts may become excessive and lead to disruption of the functioning of the hydrosystem. This excessive intake causes the clogging of river beds and can disrupt water exchange, biogeochemical processes and benthic and hyporheic invertebrate communities. From a methodological point of view, measurement of hydraulic conductivity in the substratum provides a realistic picture of the clogging level of the hyporheic zone and the Bou Rouch pump a good sampling for a qualitative study of the hyporheic fauna. From a biological point of view, the clogging effects on the hyporheos are higher compared to the benthos regarding taxonomic richness, changes in faunal assemblages and biological traits

Graduation date: 2006 / Structure-forming invertebrates belong to a polyphyletic group of primarily sessile and sedentary megafauna that can significantly enhance the complexity of physical habitats. A number of these organisms, including cold-water corals and sponges, are known to be slow growing and vulnerable to physical disturbance. In addition, as filter feeders, these invertebrates can indicate areas of consistently favorable conditions for feeding and growth. This study provides the first quantitative analysis of structure-forming invertebrate communities in many areas along the continental margin of Oregon and Washington. Geological surveys during 1992-95, using the occupied submersible, Delta, sampled an extensive area in this region, primarily on and around rock outcrops. The videos from these surveys were analyzed to inventory and catalog sessile structure-forming invertebrates and to document their associations with geological habitat types. Detailed data on geological substrate, invertebrate diversity, abundance, and density were compiled and analyzed. It was found that geological substrate and depth were reliable indicators of suitable habitat for most species included in the study. Gorgonian corals tended to concentrate in high densities in depths between 200-250m, at the southern edges of submerged rocky banks, and where hard rocky substrate was covered with a thick layer of sediment. Because of recent fishery regulation changes, this information can be used as baseline data for future studies on the effectiveness of closed areas on the recovery of structure-forming invertebrates from disturbance, particularly bottom trawling.

A comparative study was made of environmental variables and the density, biomass, diversity, and species composition of macroinvertebrates in areas downstream from a dam with a hypolimnetic release (Hungry Horse Dam on the Flathead River) and a dam with a selective withdrawal system (Libby Dam on the Kootenai River). A major objective of this study was to examine the response of macroinvertebrate communities to defined environmental gradients in temperature, flow, substrate, and food-related variables (periphyton, particulate organic carbon in the seston). In addition, the effects of experimental manipulations in discharge on macroinvertebrate drift and stranding were assessed, and the effects of temperature on the growth rates and emergence of five species of insects were measured.

A wave energy park has been established on the Swedish west coast outside Lysekil and pioneer work about its interactions with the marine environment has been conducted. So far, little is known about the effects of offshore energy installations on the marine environment, and this thesis assists in minimizing environmental risks as well as in enhancing potential positive effects on the marine environment. The Lysekil research site is situated about two kilometres offshore and has been under development since 2005. During this time 26 “environmental devices”, without generators, consisting of a steel buoy attached via a wire to a foundation on 25 m depth have been placed out for ecological studies on macrofauna in surrounding sediments and on colonization of the foundations and the buoys. Sediment samples to examine macrofauna in the seabed have been taken during five seasons. Biomass, abundance and diversity of infauna in the test site were generally low, but higher than in a nearby control site. The species composition was typical for the area and depth. In addition to sediment analysis, the effect of wave power concrete foundations on the marine environment has been investigated by scuba diving. The surface orientation and its effect on colonization by sessile organisms was examined on the first five foundations, placed out in 2005, and observations of habitat use by fish and crustaceans were made. The results show a succession of colonization over time (three years of investigation) with a higher cover by sessile organisms on vertical surfaces. Mobile fauna abundance on and around the foundations was generally low. Three months after the deployment of the 21 new foundations in 2007, assemblages of mobile organisms were examined visually. Also here, mobile species exhibit a low density, but still higher than on surrounding soft bottoms. The edible crab used artificial holes in the foundations frequently. The foundations were placed in two different clusters, north and south, and the degree to which early recruits covered the foundations and the succession of epibenthic communities were documented during two years. Sessile organisms colonized the northern foundations more rapidly, producing a higher diversity which suggests that the placement of wave energy devices affects colonization patterns. Biofouling on buoys was examined and blue mussels, Mytilus edulis, dominated with a cover about 90%. Wave exposed buoys were particularly favoured by M. edulis which there had a higher biomass and larger shells compared to those on sheltered buoys. Biofouling on wave power buoys, independent whether these had a cylindrical or toroidal shape, was insufficient to markedly affect their energy production. Finally, the thesis incorporates a review describing wave power projects in general pointing out the need of future research on for instance no-take zones, marine bioacoustics and electromagnetic fields. The main conclusions are that large-scale renewable wave energy conversion will cause ecological impact primarily by adding new hard substrate to an area but not by harming organisms or decreasing biodiversity within wave power parks.

Annual energy budgets of dominant benthic macro-invertebrates were examined during November 1973 to October 1974 from the benthos of a small pond ecosystem in north-central Texas. Estimates of annual secondary production (Hynes and Coleman 1968) were Procladius s. (Diptera, Chironimidae), 2.4 g m^-2 y^-1 (13 kcal m^-2 y^-1 ); Tendipes decorus (Diptera, Chironomidae), 6.0 g m^-2 y^-1 (40 kcal m^-2 y^-1 ); Brachycercus sp. (Ephemeroptera, Caenidae), 1.9 g m^-2 y^-1 (11 kcal m^-2 y^-1). Energy metabolism was measured in the laboratory at six seasonally encountered temperatures (5, 10, 15, 20, 25, and 30 C) on an acclimatization basis, and then extrapolated to the field. Estimates of annual energy metabolism are Procladius sp., 5.0 kcal m^-2 y^-1 ; Tendipes decorus, 17.2 kcal m^-2 y^-1 ; Brachycercus sp. 40.0 kcal m^-2 y^-1.

Les objectifs étaient 1) l'évaluation des interactions existant entre le sédiment et le compartiment benthique; 2) le suivi des processus de restauration d'une communauté benthique ayant subi l'immersion de 6.10^6m3 de déblais de dragages. La texture sédimentaire, la qualité alimentaire de la matière organique et les paramètres faunistiques ont été mesurés dans 3 sites des parages de l'embouchure du Rhône (1 témoin, 1 sous l'influence du fleuve et 1 dans la zone d'immersion). Les phases de la restauration de la communauté ont été suivies et les facteurs ayant influencé la communauté benthique ont été mis en évidence. Ce travail a permis de préconiser aux gestionnaires des adaptations pour optimiser les prochaines campagnes de dragages et d'améliorer la connaissance des interactions entre le compartiment "macrofaune benthique" et les sédiments qui l'abrite, en montrant l'influence, non seulement de la quantité de la matière organique, mais aussi de sa qualité.

Experiments on the colonization of artificial substrates by stream benthos were conducted in upper Chingmei Stream, Taiwan. The artificial substrates were colonized by stream benthos for periods of 3, 6 12, 21, 30 and 42 days.The two experiments were designed for different purposes. Experiment I from December 15, 1990 to January 29, 1991 investigated the colonization patterns of stream benthos at two sites: a polluted site caused by coal mining activities (Site 1) and a recovery site further downstream of the polluted site (Site 2). Experiment II from March 14, 1991 to April 28, 1991 tested the effect of two different sizes of substrate (cobble and gravel) on the colonization patterns of stream benthos at Site 2. In Experiment I, the total number of individuals and taxa were significantly affected by exposure period of experimental substrates and sites which indicate the occurrence of succession and the detrimental effect of coal mining activities on the benthic community. At Site 1, only Caenis sp., Euphaea sp. and Chironomidae occurred on all sampling dates and were abundant. The other taxa may just continue to drift away from the site. The chironomid larvae were most abundant. They accounted for over 90% of the colonizing individuals from day 12 to day 42. At Site 2, Baetis spA and Chironomidae were most abundant. They accounted for over 80% during the experiment, except on day 21. The relative abundance shifted from Baetis sp.A to Chironomidae with an increase in colonization time. Association analysis was performed on the abundance of taxa pairs within the same functional feeding group at Site 2. The results suggest that filter-feeders and predators have concordant colonization patterns. The relationship between taxa and abundance at the two sites also was tested by lognormal distribution to determine the degree of equilibrium of the community. In Experiment II, the substratum types influenced only the total number of individuals colonizing baskets. The gravel substrate provides more surface area for stream benthos and supports more individuals. Baetis sp.A and chironomid larvae were abundant; they accounted for over 84% of the individuals from day 6 to 42 on both gravel and cobble. The chironomid larvae comprised 36% of the fauna on the gravel substrate and 35 - 79% of the fauna on the cobble substrate. The results of association analysis on the abundance of taxa pairs within the same functional feeding group showed that there were more taxa pairs with significant associations on cobble than on gravel. The negatively significant associations also occurred more on the cobble substrate. This indicates that biological interactions may be important in determining the development of community on the cobble substrate. Disturbance caused by floods influenced the colonization patterns, especially on the gravel substrate. It reset the artificial substrates back to earlier conditions. This study only suggests that competition may occur in the subtropical Taiwanese stream and further experimentation is needed to demonstrate whether competition occurs. / Graduation date: 1992

La séquence sédimentaire de la carotte COR0503-CL05-37PC, prélevée dans le chenal Laurentien au centre du Golfe du Saint-Laurent (48°20'N - 61°29'W, à 408 m de profondeur), a fait l'objet de plusieurs analyses géochimiques et micropaléontologiques dans le but de reconstruire les variations de la productivité pélagique et des conditions du milieu benthique dans le golfe du Saint-Laurent pendant les derniers millénaires. Les analyses géochimiques (Corg et Corg/N) et isotopiques(δ13Corg et δ15N) montrent des variations importantes de flux de matière organique, notamment une augmentation du taux de carbone organique, depuis environ 2300 ans cal. BP, que l'on estime être liée à l'augmentation de l'apport en matière organique d'origine marine. Les kystes des dinoflagellés permettent également de reconstruire une augmentation de la productivité biogénique dans les eaux de surface. Par ailleurs, plusieurs changements ont été enregistrés dans les assemblages de foraminifères benthiques calcaires. Ces changements se manifestent essentiellement par l'augmentation de l'abondance relative, vers 2000 ans cal. BP, de Brizalina subaenariensis, Globobulimina auriculata et Bulimina exilis, des espèces tolérant de faibles taux d'oxygène et des flux de carbone organique élevés. La variation de l'abondance de Nonionellina labradorica indique des changements dans l'apport des eaux du Courant du Labrador. En outre, les analyses isotopiques (δ18O) sur les tests de foraminifères benthiques Bulimina marginata, montrent des variations de la température et/ou de l'origine des eaux profondes qui sont indépendantes de la variation de la productivité pélagique et de l'augmentation de l'apport en matière organique. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Golfe du Saint-Laurent, hypoxie, dinokystes, productivité, foraminifères benthiques, géochimie, isotopes stables, Holocène.

Headwater streams typically have no fish, owing to steep gradients and impassible barriers; therefore, scientific research and protection measures have been focused on fish bearing streams. The Scientific Panel for Sustainable Forest Practices in Clayoquot Sound (CSP) developed a channel classification system which is pertinent to all streams, fishless and fish bearing alike, and upon which management prescriptions in Clayoquot Sound, Vancouver Island, British Columbia are based (CSP, 1995). The CSP classification delineates channels according to four physical criteria: bed material, gradient, entrenchment, and width. The current study was undertaken to determine the efficacy with which the CSP classification system delineates small, steep streams, on the basis of channel geomorphic units within them, and to examine the benthic macroinvertebrate habitat capability of these geomorphic units. Falls, bedrock cascades, boulder cascades, rapids, chutes, riffles, glides, and pools were described according to their bed slope and dominant channel-material type and organization. In addition, the area of each geomorphic unit was measured. Seventeen streams were grouped into four CSP channel classes which were compared with respect to the mean relative proportion of class area in geomorphic units. Stratified random benthic samples were extracted from geomorphic units in order to investigate and to compare their habitat capability. "Alluvial channels" in the study exhibited only weak, very infrequent fluvial transport; therefore, they were termed semi-alluvial. In general, high gradient geomorphic units (i.e. bedrock and boulder cascades) were dominant in steep, largely non-alluvial channels. Lower gradient units (i.e. riffles and rapids) were common in semi-alluvial streams with more mild slopes. Accordingly, channel classes with opposing bed material and gradient designations exhibited notable differences with respect to relative proportions of geomorphic units while width and entrenchment designations exerted little influence on channel organization. Ultimately, only two of the four CSP classification criteria effectively systematized channels on the basis of channel geomorphic units within them. Abundance of benthic macroinvertebrates was greatest in riffles (≈100 individuals per two minute kick sample), followed by rapids (≈80 individuals/sample), pools (≈70 individuals/sample), boulder cascades (≈60 individuals/sample), chutes (≈50 individuals/sample), and lowest in bedrock cascades (≈25 individuals/sample). In addition, abundance of invertebrates in channels with ephemeral flow regimes was considerably lower compared to channels with seasonal or perennial flow regimes. Ordination of macroinvertebrate taxa showed that community structure of bedrock cascades and chutes were similar but different from other habitats. Similarly, the benthic macroinvertebrate community structure of channels with ephemeral flow regimes was very distinct.