As a result of a water chemistry survey at Whetstone Brook in western Massachusetts, during an acid mitigation study using a limestone doser, unusually high levels of aluminum were found in sediment pore waters with an overlying layer of limestone. Because of potential fish and biotic toxicity and the problems associated with commonly used speciation techniques for aluminum, a more comprehensive scheme was proposed including aluminum determination by optimized methods of GFAAS, cation exchange on a strong acid resin, and ultrafiltration at 0.5 kd, 1 kd, 3 kd and 10 kd MW cut-offs. The method of chemical extraction into MIBK following chelation by 8-HQ was also evaluated and all the experimental results were compared to a theoretical speciation using equilibrium calculations. No experimental conditions were found that could extract a consistent fraction with all the model organic ligands for the 8-HQ extraction procedure. Recoveries ranged from 10% to 200% of the organically bound aluminum relative to inorganic standards. Cation-exchangeable aluminum, complexed with malonate, oxalate, phthalate and salicylate, matched a theoretical speciation to within 5%. Theoretical and experimental results for citrate complexed aluminum differed by 24%. Ultrafiltrate experiments indicated that size fractionation may add more information about the aggregation of aluminum-organic monomers into higher MW oligomers and polymers. In all the synthetic systems studied there appears to be aggregation at lower MW values and the citrate, phthalate and salicylate complexes have fractions greater than 10 kd. Experiments with fulvic acid showed that approximately 80% of the aluminum complexed species were noncationic. Greater than 90% of the aluminum-fulvate was recovered in the MW range above 10 kd. Comparisons with stability constants in the literature showed that none of the available constants could predict the behavior of the citrate system and although constants were found that could predict the fulvate system, the majority could not.

Research was completed to determine factors affecting smolt production and overwinter mortality of Atlantic salmon (Salmo salar) stocked as fry in Vermont tributaries of the Connecticut River. Specific focuses included: (1) timing of smolt migration relative to environmental and physiological factors; (2) effect of ice formation on habitats selected and winter distribution of parr; (3) effect of maturation on parr growth and smolt recruitment; and (4) smolt production dynamics and recruitment modeling. Smolt migration timing and recruitment was determined using net weirs and counting fences and mark-recapture and winter habitat studies were completed by night snorkeling. Tributaries differed in the timing of smolt migration with the tributary warming earliest in the spring generally experiencing earlier smolt migration. Initiation and cessation of smolt migratory activity appeared to be linked to smolt physiological development. Peaks in river discharge increased smolt migratory activity after water temperature thresholds were surpassed, yet only while smolts maintained elevated gill Na$\sp+,$ K$\sp+$-ATPase activity. Ice formation caused significant changes in the physical stream environment, including a reduction in the abundance of habitats often selected by parr. Changes in the distribution of parr over the winter generally corresponded to changes in the distribution of high velocity habitats they rarely selected and low velocity habitats they often selected. Mature parr were abundant across and within tributaries. Percent mature in October/November was positively correlated with mean size the preceding June. Studies on individually marked parr showed that mature parr exhibited poorer June to October growth than immature parr resulting in large differences in fall size. Mature parr were recruited to smolt at a reduced frequency relative to immature parr and modeling analysis indicated that this difference resulted primarily from a one-third probability of smolting for mature parr rather than differences in fall to spring survival. Simulation modeling revealed that losses in potential smolt production attributable to parr maturation may be as high as 35% when maturation percentages reach the maximum of 45% observed in this study. It is concluded that smolt physiology, winter habitat, and parr maturation are primary factors affecting smolt production and overwinter mortality of Atlantic salmon stocked as fry.

<div> <p><a>Biotic interactions play key roles in determining invasive species’ establishment success in receiving ecosystems (Tilman 2004). The invasional meltdown hypothesis suggests that initial invaders can facilitate subsequent invasions through direct (e.g., commensalism, mutualism) and indirect (e.g., changes in habitat and energy flow) pathways (Simberloff & Holle 1999; Simberloff 2006). Such positive interactions among invaders can alter community-level processes, but little research on this has been done in aquatic-terrestrial landscapes. My dissertation explores the links between reciprocal facilitation of invasive species and ecosystem change in a desert river system in the southwest USA. </a></p> <p> Like most rivers in the southwestern United States, the San Juan River has been altered by hydrologic regulation and biological invasions that affect ecosystem function and act synergistically to induce substantial ecosystem change. Invasion of channel catfish (<i>Ictalurus punctatus</i>) has drastically altered the fish assemblage of the San Juan River, yet the impacts of riparian invasion by a fruit-bearing tree, Russian olive (<i>Elaeaganus agustifolia</i>) have largely been ignored. Channel catfish have been observed consuming Russian olive fruits, but the level of facilitation between species and corresponding impact on the ecosystem is unclear. </p> <p>Channel catfish may benefit directly from Russian olive invasion by feeding on fallen fruits and/or indirectly from habitat alteration and invertebrate prey production from Russian olive detritus. Additionally, channel catfish may facilitate germination, growth, and seed dispersal of Russian olive. Mutualism between these invaders could increase the fitness of each species, thereby facilitating invasion success. Plant-animal mutualism is the most common form of facilitation among invaders, but no studies, to our knowledge, have evaluated facilitation between invasive riparian plants and aquatic invaders and their combined impact on ecosystem function. My goal preparing this dissertation is to determine whether mutual facilitation between riparian and aquatic invasive species influences ecosystem change through biotic interactions. </p> <p>To test for mutual facilitation, I first determined the contribution of Russian olive fruits to channel catfish growth by evaluating seasonal diet composition across four sites and six time periods. I then used replicated growth experiments to determine assimilation rates of Russian olive fruits consumed by channel catfish. Using bioenergetics models, I then determined how Russian olive subsidies in San Juan River contribute to channel catfish biomass. To determine whether channel catfish benefit Russian olive reproduction, I compared germination rates of seeds consumed by channel catfish to seeds consumed by terrestrial mammals and control seeds that had not been eaten. </p> <p>Russian olive fruits were the most important diet item for channel catfish during the fall and spring, comprising up to 57 and 70% of stomach contents by mass, respectively, and were consumed throughout the year. Feeding trials revealed that Russian olive fruits contributed little to growth or lipid deposition, but they did provide metabolic energy allowing channel catfish fed exclusively Russian olive fruits to maintain weight. In addition, Russian olive trees received a reproductive benefit through increased germination success of seeds consumed by channel catfish over those transported by water. Using bioenergetic models, I showed that Russian olive fruits subsidized 46% of San Juan River channel catfish biomass, indicating that the subsidy from Russian olive fruits had a population-level impact. This dissertation thus establishes mutual facilitation by non-native species across ecosystem boundaries, a phenomenon that few studies heretofore have demonstrated in the ecology or invasion biology literature.</p> </div> <br>

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