Date of Award

12-2002

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Laurie J. Osher

Second Committee Member

Hilary A. Neckles

Third Committee Member

Les Watling

Abstract

Coastal ecosystems worldwide face increased nutrient enrichment from shoreline and watershed development and atmospheric pollution. To gain an understanding of the effects of nitrogen loading on the natural faunal community of Ruppia maritima beds in Northeast Creek estuary (Acadia National Park, Maine, USA), we (1) assessed the response of the faunal community to increased nitrogen loading using an in situ enrichment experiment during the summer growing season of 2001 (Chapter I), and (2) completed a description of the natural macroinvertebrate community in the estuary in 2001 with qualitative (May-July) and quantitative (August-October) monthly sample collections (Chapter 2). This study formed part of a larger study by the U.S. Geological Survey of the relationship between increased nutrient enrichment and ecosystem integrity in the estuary. Faunal community response to increased nitrogen loading was characterized by (1) assessing quantitative shifts in macroinvertebrate community composition and (2) identifying changes in food web structure using stable C and N isotope ratios of producers and consumers. Salinity in the estuary indicated that the system was dominated by freshwater inputs in the spring and became increasingly more marine throughout the summer (reaching 30% in the fall). Euryhaline freshwater fauna dominated Northeast Creek estuary throughout 2001. The most common invertebrates were non-biting midge larvae (Chironomidae: Dicrotendipes, Cricotopus and Chironomus), damselfly larvae (Coenagrionidae: Enallagma), gastropods and ostracods. Less common invertebrates included oligochaetes, water boatmen (Corixidae: Trichocorixa), water mites (Acari), and amphipods (Gammaridae: Gammarus). Brackish water fish, Fundulus heteroclitus, were also common in the estuary. Total macroinvertebrate densities were 31100 m-2 in August, 23200 m-2 in September and 27700 m-2 in October. Freshwater insects composed between 50 and 80% of the macroinvertebrate community in the estuary during this time period. The estuary was characterized by low taxa richness, diversity and evenness. Experimental nutrient additions resulted in significantly lower densities of herbivorous chironomids and predatory damselflies and higher densities of deposit feeding oligochaetes. Both R. maritima and epiphytic algae were more enriched in 15N under higher N conditions possibly due to increased denitrification. R. maritima was more depleted in 13C with loading while epiphytic material showed the opposite trend, indicating shifts in metabolic activity with increased loading. Mixing models showed a dependence of grazing chironomids on epiphytic algae under both natural and enriched conditions. Chironomus was dependent on allochthonous sources of detritus under natural conditions but under enriched conditions exhibited a shift to autochthonous sources of detritus. Predatory Enallagma was found to be largely dependent on grazing chironomids for prey although under the highest loading conditions this link may be broken. Experimental nutrient loading altered the composition and structure of the natural community in this estuary. This study 'provides a baseline on faunal community composition and community response to nitrogen loading in NEC estuary for use in developing predictive tools for watershed-based planning and monitoring.

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