We investigated the influence of multiple disturbances on ecosystem structure and function in a headwater stream adjacent to an abandoned arsenic mine using an upstream (reference) and downstream (mine-influenced) comparative reach approach. In this study, floods were addressed as a pulse disturbance, and the abandoned arsenic mine was characterized as a press disturbance. Chronically elevated levels of arsenic were specifically addressed as a ramp disturbance. Stream ecosystem structure and biogeochemical functioning were characterized monthly over a period from July to December 2004 by determining benthic organic matter standing stocks, ecosystem metabolism, and by using solute additions to examine differences in phosphorus uptake and hydrology over the monitoring period. Influences of the press disturbance were evident in the mine-influenced reach where arsenic concentrations (254 ± 39 µg/L) were >30 higher than in the reference reach (8 ± 1 µg/L). However, in almost all cases the presence of the abandoned arsenic mine appeared to exert little influence on reach-scale measures of ecosystem structure and function (e.g., organic matter standing crops, phosphorus uptake). Conversely, floods (i.e., pulse disturbances) influenced organic matter standing stocks and hydrologic interactions between the stream and transient storage zones in both study reaches. Interactions between press and pulse disturbances were evident in several cases and illustrated by phosphorus uptake responses. Phosphorus uptake was best predicted by coarse particulate organic matter standing stocks in the reference reach. However, in the reach exposed to the press disturbance (i.e., mine-influenced reach), both coarse particulate organic matter standing stocks and characteristics of the pulse disturbance regime (i.e., number of days post-flood) were significant predictors of phosphorus uptake. Within the mine-influenced reach, arsenic concentrations increased from 16–600 µg/L and were addressed as a ramp disturbance. Analysis of phosphorus uptake in the mine-influenced reach across a gradient of arsenic concentrations correlated with Michaelis-Menton models of enzyme kinetics in the presence of a competitive inhibitor. These results suggest that arsenic appears to competitively inhibit phosphorus uptake by microbial assemblages in the mine-influenced reach. Results from this study highlight the fact that ecotoxilogical studies at the ecosystem scale should consider not only contaminant influences, but rather place its implications within the extant disturbance regime generated from both natural and anthropogenic sources. / Master of Science

Streams and terrestrial ecosystems are linked through allochthonous organic matter inputs from streamside vegetation. This allochthonous material makes up the energy base for forested aquatic food webs. Therefore, removal of riparian vegetation associated with agricultural land use affects stream ecosystem structure and function. The objectives of this study were to measure and compare allochthonous input and leaf breakdown rates along a gradient of agricultural land use in southern Appalachian streams. Study streams were placed into the following land use categories: forest and light, moderate, and heavy agriculture. Several physical, chemical, and biological parameters also were measured including discharge, temperature, nutrient concentrations, macroinvertebrate abundance and density, periphyton biomass, and chlorophyll a concentration. In forested, light agricultural, and moderate agricultural streams, the quantity and quality of allochthonous input were not significantly different. However, the timing and composition of allochthonous materials were related to land use. Chlorophyll a and periphyton biomass did not vary among land use types. Leaf breakdown rates were significantly faster in light and moderate agricultural streams in comparison to forested and heavy agricultural streams. Slow breakdown rates in forested streams resulted from low nutrient concentration and cool stream temperature. The scarcity of shredding macroinvertebrates and sedimentation probably limited leaf breakdown in heavy agricultural streams. Though limited riparian vegetation along agricultural streams resulted in an energy supply equivalent to forested streams, agricultural land use may still have long term impacts on stream structure including nutrient concentrations, temperature, macroinvertebrate community, and sedimentation thus affecting stream ecosystem function. / Master of Science

Vane-type in-stream structures and step pool storm conveyance (SPSC) are more ecologically friendly alternatives to traditional stream channel stabilization and stormwater conveyance techniques. Vane-type structures have been widely accepted as elements of stream restoration projects and are regularly implemented in streams throughout the United States. However, these structures commonly experience partial or total failures of function or stability, often due either to improper installation or misapplication. This study undertook a thorough review of the available design guidance for the single-arm vane, j-hook vane, cross vane, and w-weir, which revealed that the existing guidance is composed of non-standardized recommendations largely based on practitioner experience and rules of thumb. Existing guidance was synthesized with current structure research and practitioner surveys to create factsheets for each of the four structures and the SPSC, with the intent of improving structure application and offering concise general guidance. This study also endeavored to improve the design of the SPSC by determining the most accurate of several common prediction methods for Manning's roughness coefficient n, used in SPSC design velocity calculations. This was done by using Rhodamine WT dye tracer experiments to determine n values during storm flows in two SPSC structures in Annapolis, MD, which were then compared to predicted n values. Values of Manning's n determined in the SPSCs at low flows (0.28-12) often exceeded the predicted n values (-0.17-3.9) by several orders of magnitude. Though the applicability of these results is limited, an increase in design n to 0.1-0.2 is still recommended. / Master of Science / Vane-type in-stream structures are stone or wood structures installed within a stream channel for purposes such as streambank stabilization or aquatic habitat creation. Step pool storm conveyance (SPSC) is a technique which converts an existing steep stream or gully into a step-pool channel. Both of these techniques are more ecologically friendly than many traditional stream channel stabilization or stormwater conveyance techniques such as riprap or concrete storm drains. Vane-type structures in particular have been widely accepted as elements of stream restoration projects and are regularly implemented in streams throughout the United States. However, these structures commonly experience partial or total failures, either through structural collapse or failure to function properly. This is often either because they were improperly installed or because they were installed at a stream site where they were inappropriate or unnecessary. A review of the available guidance for the design of these structures revealed that the existing guidance is composed of non-standardized and sometimes contradictory recommendations which are largely based on designer trial and error and rules of thumb, rather than on the results of scientific experiments or modeling. The goal of this study was to improve the success of vane-type in-stream structures and the SPSC by providing factsheets offering clear and concise general design guidelines and sound recommendations for structure application. Flow studies of two SPSC structures in Annapolis, MD were also conducted to improve the design of that structure by measuring its flow characteristics in the field.