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Dissertation Research

                 Figure 1 - Three hectare catchment, Hancock county Maine.

Figure 2 - Groundwater well placement.

Typical seep vegetation

Spotted Salamander (Ambystoma maculatum)
Dissertation Studies

I conducted my dissertation studies at the University of Maine in the Department of Plant, Soil, and Environmental Sciences in the Ecology and Environmental Sciences program.

My dissertation attempted to tackle a large question: How do forested headwater wetlands function in the landscape?

I tackled this question by incorporating what I had learned from my wetland delineation experience. Wetlands are delineated using a three parameter approach using hydrologic, soil, and vegetative indicators. The most important of the three are hydrologic factors. Without proper hydrololgy, wetlands will not exist in the landscape. When groundwater is close to the biologically active soil layers for a sufficient duration, it drives changes to soil processes. These changes only allow those plant species adapted to such conditions to thrive in these areas.

Wetland function is primarily concerned with wetland hydrology. In particular we are interested in its directionality, strength, and frequency in relation to where in the landscape the wetland is located (i.e., its geomorphic position). Changes in these factors will influence its effect on soil processes, available oxygen for respiration by soil organisms, and therefore influences the plant an animal communities within these systems.

I explored the functions of small headwater wetlands by investigating the extent to which seeps (these are small wetlands and are similar to springs) maintain stream hydrology and buffer stream chemistry, and how seeps contribute to local biodiversity through support of unique vegetation amphibian communities. The majority of this research was conducted in an eastern Maine headwater catchment (Fig 1, left).

The objectives of my research included:

1) Quantifying the relative importance of seeps in maintaining low stream-flow conditions and their relation to buffering stream chemistry (Figure 2).

2) The evaluation of seep biogeochemical distinctions from surrounding uplands.

3) Ecological community analysis of seeps and surrounding uplands through investigation of plant and amphibian community assemblages.

General Findings:

The results of this research indicate that headwater seepage wetlands are characterized by relatively concentrated groundwater discharge from shallow or local flow regimes. During summer low-flow, seeps were the primary source of surface water to the stream, contributing between 40% and 80% of stream water. Seeps significantly increased total cation concentration below seepage outflow. This component demonstrates that small wetlands can contribute to headwater stream processes and functions by serving as both recharge and discharge areas, increasing the duration and magnitude of stream discharge, and buffering stream chemistry particularly during low-flow conditions. 

Morley, T.R., A.S. Reeve, Aram J.K. Calhoun. (2011) The role of headwater wetlands in altering stream flow and chemistry in a Maine, USA catchment. Journal of the American Water Resources Association. doi:10.1111/j.1752-1688.2011.00519.x

Link: http://onlinelibrary.wiley.com/doi/10.1111/j.1752-1688.2010.00519.x/abstract

Herbaceous layer diversity measures were highest in hardwood seeps (as opposed to conifer wetlands and associated uplands) while containing highly variable species composition. This assessment provides further evidence that small, headwater wetlands support distinct vegetation communities within forested ecosystems and highlights the need for further refinement of vegetation classification schemes in Maine.

Morley, T.R. and Aram J.K. Calhoun. 2009. Vegetation characteristics of forested hillside seeps in eastern Maine, USA. The Journal of the Torrey Botanical Society. Vol. 136, Issue 4, pg(s) 520-531 doi: 10.3159/08-RA-073.1.


Amphibian community assessments highlighted the importance of seeps to supporting amphibian populations in terrestrial habitats. Headwater wetlands contained six to eleven species at varying distances from perennial waterbodies. Therefore, the presence of headwater wetlands increases the use of the terrestrial environment by amphibians. However, the preference of either habitat varied temporally among individual species and within life history stages of several species. 

Morley, T.R. and Aram J.K. Calhoun. (in revision) Seasonal Amphibian Activity in Headwater Wetlands in a New England Catchment.
This manuscript is in review at Herpetological Biology and Conservation.