Acid rain: Rain containing acids that form when compounds - released into the atmosphere from the burning of fossil fuels, agricultural practices and other human activities -combine with water. Rain that has not been affected by these factors generally has a slightly acidic pH of ~ 5.6, while acid rain has a lower pH. For example, at the HBEF rain has a pH of ~ 4.2, over 10 times more acidic than the natural acidity of rainfall in the area. A tremendous amount of HBEF research has been conducted on acid rain and its effects on forests and aquatic ecosystems. Click here to learn more (you must have Adobe Acrobat Reader).
Acid deposition: Deposition that is acidic.
Acid precipitation: Precipitation that is acidic. Acid rain is a type of acid precipitation.
Acid-neutralizing capacity (ANC). A measure of the ability of water or soil to neutralize added acids, such as from acid deposition. Streams with higher ANC levels are affected less by acid rain than streams with lower ANC values.
Acidification: The process of becoming acidic. For example, as acid rain falls on a lake over the many years, the pH of the lake itself may drop (become more acidic); this process is called acidification.
Adsorption: The accumulation of gases, liquids, or solutes on the surface of a solid or liquid. At the HBEF scientists often examine how different compounds in the soil (e.g., nitrate) adsorb, or attach, to soil particles.
Allochthonous: Food material reaching an aquatic community in the form of organic detritus.
Ammonification: This is the process in which organic forms of nitrogen (e.g., nitrogen present in dead plant material compounds) are converted to ammonium (NH4+) by decomposers (bacteria).
Anion: Negatively charged ions such as nitrate (NO3-) or chloride (Cl-).
Anoxic: No oxygen present.
Autotroph: An organism that is capable of making and storing food using the sun (or another nonliving) energy sources. Plants are autotrophs because they use water, carbon dioxide, and the energy from the sun to make the complex sugars they use as food.
Average. A number that typifies a set of numbers of which it is a function; the usual or ordinary kind or quality. For example, since we have monitored precipitation at the HBEF for over 40 years, we can calculate how much precipitation falls on an "average," or normal year. However, rarely in any single year does the average amount of precipitation fall. That is, precipitation at the HBEF is variable, with annual precipitation levels frequently being much higher or lower than the calculated average, or normal year.
Bacteria: (Singular, bacterium). Extremely small, unicellular, prokaryotic microorganisms that multiply by cell division, occurring in spherical, rodlike, spiral, or curving shapes and found in virtually all environments; some types are important agents in the cycles of nitrogen, carbon, and other matter, while others cause diseases in humans and animals.
Base cation: Positively charged ions such as magnesium, sodium, potassium, and calcium that increase pH of water (make it less acidic) when released to solution through mineral weathering and exchange reactions.
Base-poor soils: Soils that have low levels of base cations such as magnesium, sodium, potassium, and calcium.
Biogeochemistry: The study of the relationship between the geochemistry of a region and the animal and plant life in that region.
Budgets: When developing budgets, scientists at the HBEF and other ecosystem sites measure fluxes and pools of water, nutrients (such as nitrogen, carbon, and calcium) and materials. Fluxes are inputs to and output from an ecosystem, and pools are quantities within an ecosystem.
Calcium (in terms of HB research): Acid rain has caused the leaching of calcium, a natural component of HBEF soils very important to plant growth, from forest soils over the past several decades. In 1999 an experiment started in which calcium was added to an entire watershed in an effort to restore soil calcium pools to pre-acid rain levels and study the corresponding ecosystem response. Click here for more information on this experiment.
Carbon Dynamics: Movement of carbon through an ecosystem.
Catchments: An area from which all the drainage water passes into one stream or other body of water.
Cation: Positively charged ions such as sodium (Na+) or ammonium (NH4+).
Cation Exchange Capacity (CEC): A measure of the number of sites on soil surfaces that can retain positively charged ions (cations) by electrostatic forces.
Chronosequence: A sequence of related variables (e.g., forest stands, soils) that differ from one another in certain properties primarily as a result of time. A set of stands of trees, in which one was recently clearcut, another had been cut 5 years ago, another 15 years ago, another 25 years ago is an example of a chronosequence.
Clearcut: To remove or cut all trees in a tract of timber at one time.
Conductivity: A measure of the transmission of heat, electricity or sound through something. For example, at the HBEF the electrical conductivity of water samples is often measured to determine ion concentration.
Control: A treatment that reproduces all aspects of an experiment except the variable of interest. Most well-designed experiments have control and treatment groups. An experimental manipulation is applied to the treatment group, and nothing is done to the control group. For example, if you are interested in looking at how salt water affects the growth of corn seedlings, you would design an experiment with "control" corn seedlings and "treatment" corn seedlings. You would water the treatment seedlings with salty water, and the control seedlings with non-salty water. There should be no other differences between control and treatment groups - they both should have the same amount of sunlight, should receive the same quantity of water, should be exposed to the same temperature, and so forth. If, after your salt water experiment, there are differences in corn growth (for example, perhaps the corn with salt water grew less quickly), you can confidently explain that the differences were caused by the salt. If there were two different variables between the control and treatment groups (for example, salt water and different amounts of sunlight), you would not be able to tell what made the corn grow less quickly - the salt, or the lack of sun.
Demography: The study of the characteristics of populations, such as size, growth, density, distribution, and vital statistics.
Dendritic: Branched in a way that resembles trees or shrubs. For example, streams at the HBEF often have dendritic branching.
Denitrification: The process in which soil bacteria convert nitrate (and/or nitrite) to nitrogen-containing gases such as N2O and ultimately N2.
Deposition: The processes by which chemical constituents move from the atmosphere to the earth's surface. These processes include rain, fog, and clouds (wet deposition), as well as particle and gas deposition (dry deposition). The term, "acid deposition," includes acid rain and refers to all forms of wet and dry deposition that have a lower than normal pH.
Dissolved inorganic carbon (DIC): All inorganic carbon (e.g., carbon dioxide) dissolved in a given volume of water at a particular temperature and pressure.
Dissolved organic carbon: All organic carbon (e.g., compounds such as acids and sugars, leached from soils, excreted from roots, etc) dissolved in a given volume of water at a particular temperature and pressure. Streams at the HBEF that have high DOC values are often "tea-colored," or light to dark yellow-brown. The stream draining Watershed 9 is an example of such a stream.
Dissolved oxygen: Amount of oxygen gas dissolved in a given volume of water at a particular temperature and pressure.
Disturbance: A natural or human-induced disruption or alteration of an ecosystem. Forest fires, tornadoes, or rock slides are examples of natural disturbances; logging, acid rain, and road-building are examples of human disturbances.
Ecology: The study of the interactions of living organisms with one another and with their nonliving environment of matter and energy. An example of an ecological research question is, "How do weather, soil type, and topography affect the presence and growth of tree species?"
Ecosystem: A community of different species interacting with one another and with the chemical and physical factors making up the nonliving environment. An ecosystem can be small (for example, a pond), or very large (for example, a major river valley).
Evapotranspiration: The loss of water from a given area during a specified time by evaporation from the soil surface and by transpiration from plants.
Foliar: Relating to a leaf or leaves.
Food chain: Series of organisms, each eating or decomposing the preceding one. A simple example of a food chain is one in which a red-tailed hawk eats an eastern phoebe, which has eaten a great number of insects that lived in streams, which have all eaten stream algae.
Food web: Complex network of many interconnected food chains and feeding relationships.
Fungi: (Singular, fungus) Any of numerous eukaryotic organisms of the kingdom Fungi, which lack chlorophyll and vascular tissue and range in form from a single cell to a body mass of branched filamentous hyphae that often produce specialized fruiting bodies. The kingdom includes the yeasts, molds, and mushrooms.
Greenhouse Effect. Warming that results when solar radiation is trapped by the atmosphere, caused by the presence in the atmosphere of gases such as carbon dioxide, water vapor, and methane that allow incoming sunlight to pass through but absorb heat radiated back from the earth's surface. Many human activities cause levels of these gases to rise, resulting in an increase in the Earth's temperature.
Global Warming. An increase in the average temperature of the earth's atmosphere, especially a sustained increase sufficient to cause climatic change. Most scientists believe that a rise in carbon dioxide levels (caused by automobile, power plant, and other emissions) will lead to further global warming.
Herbicide: A chemical substance used to destroy or inhibit the growth of plants. At the HBEF an experiment was conducted in Watershed 2 where all the trees were cut down and herbicides were applied for three years to prevent the regrowth of any vegetation.
Herbivorous: Feeding on plants. For example, animals such as moose and snowshoe hares are herbivorous.
Heterogeneous: The state of being mixed in composition. For example, heterogeneous forests are comprised of many different species of trees.
Hydrograph: A chart or graph that depicts changes in water quantity over time. At the HBEF continuous streamflow is recorded on hydrographs attached to stream gauges at nine watersheds.
In-situ. Being in the original position. Many experiments are conducted in-situ, or in place in the field.
Inorganic compounds: Compounds not defined as organic. For example, water is inorganic.
Invertebrate: An animal without a backbone. Butterflies are invertebrates.
Ion: An atom or a compound with a net (positive or negative) electrical charge.
Isotope: One of multiple forms of an element that has a different number of neutrons than other atoms of that element. Some elements have isotopes that are unstable or radioactive, while others have "stable isotopes." Stable isotopes are not radioactive, and do not decay over time. For example, most nitrogen atoms have 14 neutrons, while a very small percentage of naturally-occurring nitrogen atoms have 15 neutrons. These 15N atoms are referred to as stable isotopes. It is possible to use special equipment to determine how much of a stable isotope is present in something. For example, scientists can take a leaf sample and determine how much of the nitrogen present in the leaf has 14 neutrons and how much has 15 neutrons. Because stable isotopes do not break down, and because scientists can measure exact quantities present in samples, it is possible to use stable isotopes as tracers.
Labile: Readily undergoing change or breakdown. The term labile is often used to describe compounds (such as carbon or nitrogen) that are available to easily move through soils.
Limnology: The scientific study of the life and phenomena of fresh water, especially lakes, ponds, and streams.
Litterfall: Leaves, twigs, and other plant material that falls to the ground.
Long-Term Ecological Research (LTER) network. A National Science Foundation program consisting of 24 sites across the nation that focuses on long-term ecological research. Click here to visit the LTER network's webpage.
Lysimeter: Devices that are placed in the ground to collect soil water. There are two types of lysimeters in use at the HBEF: tension, and zero-tension. Zero-tension lysimeters collect soil water that is naturally (i.e., only gravity is influencing) percolating downward through soils. Tension lysimeters have a vacuum (similar to what roots might exert on soils) applied to them and gently "suck" soil water through a porous material. Zero-tension lysimeters are designed to capture soil water that might otherwise make its way into groundwater or lower soil horizons, while tension lysimeters are designed to capture soil water that roots might take up. Click here to see a soil pit containing lysimeters.
Microbial ecology: The branch of ecology that deals with the study of the interactions of living microorganisms with one another and with their nonliving environment of matter and energy.
Mineral soil: Soil that consists of less than 30% organic matter and is mostly derived from rock. At the HBEF, mineral soil is generally located under a thick (2-20 cm) organic soil horizon.
Mineralization: The process in which organic compounds (e.g., dead plant or animal material) are converted to inorganic compounds (e.g., nitrate, carbon dioxide).
Model: A quantitative representation of the relationships among the entities in a system, often used to make predictions about the system. For example, scientists at the HBEF have developed models to predict how future pollution levels may affect stream acidity. The model predicts that as sulfate emissions drop, stream acidity will drop.
Mycelium: The root-like network of filaments (hyphae) making up the nonreproductive part of the body of a fungus.
Mycorrhizae: The symbiotic association of the mycelium of a fungus with the roots of certain plants.
Neotropics: The biogeographic region of the New World that stretches southward from the Tropic of Cancer and includes southern Mexico, Central and South America, and the West Indies. At the HBEF scientists study many neotropical migratory birds. These birds live in the HBEF for a few summer months (~ May - September) and make the very long flight to the Neotropics for the winter.
Net Primary Production: Accumulation of total biomass over a given period of time. Gross primary production includes plant respiration.
Nitrification: Nitrification is the process in which ammonium is converted to nitrite and then nitrate. This process naturally occurs in the environment, where it is carried out by specialized bacteria.
Nitrogen Dynamics: Movement of nitrogen through an ecosystem.
Nitrogen Fixation: The process by which nitrogen gas (N2), a form of nitrogen that is readily available in the atmosphere but that cannot be used by plants, is converted to ammonium (NH4+), a form of nitrogen that can be used by plants. Nitrogen fixation is accomplished naturally by bacteria and by lightning, and by humans in industrial processes such as the production of fertilizer.
Nitrogen Mineralization: This is the process in which organic forms of nitrogen (e.g., proteins in dead plant material) are converted by microbes to inorganic forms of nitrogen (e.g. ammonium and nitrate).
Nitrogen Saturation: Occurs when nitrogen inputs saturate the retention capacity of a forest ecosystem. That is, as more and more nitrogen is deposited on forests (due to increases in nitrogen emissions and corresponding increases in deposition), eventually forests will no longer be able to absorb all the nitrogen. This could lead to increased nitrate leaching (which could pollute streams, lakes and drinking water), soil acidification, and maybe even forest health problems.
Oligotrophic: Term applied to a body of water low in nutrients and in productivity. Mirror Lake is oligotrophic.
Oxic: Oxygen present.
Phenology: Study of the timing of biological activity over the course of a year, particularly in relation to climate. For example, scientists at the HBEF have maintained long-term yearly records of tree phenology, recording when trees "leaf out" in the spring and lose their leaves in the fall.
Photosynthesis: The process in green plants and certain other organisms by which carbohydrates are synthesized from carbon dioxide and water using light as an energy source. Most forms of photosynthesis release oxygen as a byproduct.
Phytosociology: The branch of ecology that deals with the characteristics, classification, relationships, and distribution of plant communities.
Population dynamics: The study of factors affecting the variability of populations of plants and animals over time and space.
Rain gauge: A device used to quantitatively measure rainfall. Weekly rainfall is measured at the ~30 rain gauges throughout the HBEF. Click here to see a rain gauge.
Reference. Similar to "control," referring to a treatment that reproduces many of the aspects of an experimental design, while excluding the variable of interest. Whereas in an experiment using a true control, the treatment and control differ only in terms of the variable of interest (see the salt water example under "control," above), a reference and a treatment are designed to be as similar as possible, but may have several differences. For example, at the HBEF, Watershed 3 (and Watershed 6 as well) serves as a "reference" to the "experimental" watersheds. That is, when Watershed 2 was logged, scientists compared what happened after the logging in Watershed 2 to what happened in Watershed 3. Presumably, any difference between the two could be attributed to the logging effects. However, Watershed 3 cannot be referred to as a "control," because it was not exactly the same as Watershed 2 before the experiment. It is often impossible to have true controls in field experiments (it is impossible to find two absolutely identical watersheds), so references are often the best option.
Regeneration: Regrowth of destroyed parts. Forest regeneration is the process of regrowth after a large disturbance (e.g., by a hurricane or logging operation).
Reproductive success: The number of progeny born, or surviving progeny produced by an organism. An animal that has few offspring relative to other animals in its population has low reproductive success, while an animal that has many offspring has a higher reproductive success. Studies of birds and bird populations at the HBEF often examine factors affecting reproductive success.
Residence time: The ratio of the size of a compartment to the flux through it, expressed in units of time; thus, the average time spent by energy of a substance in the compartment. For example, scientists are often interested in the residence time of certain nutrients in a lake. The lake is the compartment, and the nutrient is the substance. Residence time is a measure of how long this nutrient (e.g. after it arrives via a stream, or deposition, etc.) stays in the lake before being removed (e.g., by the outflow stream).
Riparian zones: Thin strips and patches of land and vegetation that border streams.
Roots (fine): The underground component of plants, responsible for anchoring plants and providing them with water and nutrients. Fine roots, the subject of many research projects at the HBEF, are the very small ephemeral roots (less than 1 mm in diameter) that are largely responsible for providing plants with water and nutrients.
Sandy Loam Texture: A classification used to describe soil texture. A sandy loam is a soil containing much sand but which has enough silt and/or clay to make it somewhat coherent. The individual sand grains can readily be seen and felt. Soils in the HBEF are generally of a sandy loam texture.
Silviculture: The care and cultivation of forest trees; forestry.
Soil horizons: Soils are generally composed of many different layers, or horizons lying on top of one another. A variety of biological (e.g., decomposition), chemical (e.g. rain/soil interactions), and physical (e.g., weathering) processes form these horizons. In the HBEF, soils often consist of an organic horizon containing dead plant material in various stages of decay at the surface, with mineral (non-organic) soil horizons underneath it. The O (organic) horizon is closest to the surface, with mineral horizons such as A, E, B, and C lying underneath the O horizon and above bedrock. Click here to see a typical HBEF soil profile.
Spodosols: Spodosols are soils characterized by an accumulation of aluminum, iron, and organic matter. These soils are often present in cool, moist environments, and represent the soils most commonly found at the HBEF.
Stochastic: A random variable, or referring to patterns resulting from random effects.
Stream gauge: A device used to measure streamflow volume over time. At the HBEF there are nine watersheds that have stream gauges and "weirs." These weirs are permanent concrete structures that consist of a large stilling basin with a v-notch at one end. By constantly measuring how high the stream is at is passes over this v-notch, and entering this height into a known formula, researchers can determine streamflow volume. Click here to see a picture of the weir at the base of Watershed 1.
Subsample. A small portion of an homogenous sample. For example, scientists interested in historical qualities of precipitation may take a 100 mL subsample of an archived 1 L precipitation sample. See Introduction Page 7 for more information about the HBEF Archive.
Succession: Process in which communities of plant and animal species in a particular area are replaced over time by a series of different and usually more complex communities. There are two types of succession: primary and secondary. Primary succession occurs in a bare area that has never been occupied by a community of organisms (for example, on a newly-cooled lava flow, or newly-risen oceanic island), and secondary succession occurs in an area in which natural vegetation has been removed or destroyed but the soil has not been destroyed (for example, after forest logging). Scientists at the HBEF have conducted a great deal of research focusing on secondary succession after different logging practices.
Symbiosis: A close, prolonged association between two or more different organisms of different species that may, but does not necessarily, benefit each member. The relationship between nitrogen-fixing bacteria and roots of legumes is an example of a symbiotic relationship. The bacteria live in the roots of these legumes, and convert atmospheric nitrogen gas (not useful to plants) to nitrate, a plant nutrient. The bacteria benefit by having a good habitat in which to live, and the plants benefit by using the produced nitrate. Many other types of roots have symbiotic relationships with certain kinds of fungi.
Temperate: Characterized by moderate temperatures, weather, or climate; neither hot nor cold. The HBEF is situated in a northern temperate forest - it is neither in the colder northern Canadian or hot southern US or South American forests.
Temporal: Of, relating to, or limited by time. Research is often conducted to look at "temporal patterns," or those patterns that occur and change over time. A "temporal scale" refers to a scale of time (e.g., a scale of many years or months).
Throughfall: Rain that falls through and can be collected under the tree canopy of a forest. Throughfall interacts with leaves and materials present on leaves (e.g., dust, plant secretions, insect droppings, etc.) and therefore can be chemically very different from rain that falls directly to the surface.
Till (glacial): A deposit of sediment formed under a glacier and left in place after the glacier's departure, consisting of an unlayered mixture of, silt, sand, and gravel ranging widely in size and shape. The soils in the HBEF have been formed from and lie on till left from glaciers that retreated ~10,000 years ago.
Tracer: An identifiable substance, such as a dye, a radioactive isotope, or an inert chemical (i.e. bromide), that is introduced into a biological system and can be followed through the course of a process, providing information on the pattern of events in the process or on the redistribution of the parts or elements involved; this can also be referred to as a "label." At the HBEF a great deal of research has used tracers. For example, in a current study where calcium has been applied to an entire watershed, a tracer is being used to determine exactly where the calcium goes - how much is washed out by the stream, how much trees take up and where in these trees the calcium goes (leaves, bark, etc), and how much herbaceous plants, such as ferns, take up.
Transpiration: Process in which water is absorbed by the root systems of a plant, moves up through the plant, passes through pores (stomata) in leaves, and then evaporates into the atmosphere as water vapor.
Treatment: In an experiment, the group to which an experimental manipulation has been applied; paired with a control group. See control for an example.
Tree core: A small-diameter cylindrical sample removed from a tree trunk - from its surface all the way to its center - that does no permanent damage to the tree. It is possible to count the number of tree rings in cores, providing accurate estimates of tree age and growth patterns.
Variability. The quality of being likely to change or vary over time; lack of uniformity. There are two types of variability: temporal and spatial. Consider the amount of precipitation HBEF receives annually: in some years the Valley receives more precipitation than the "average year", and in some years it receives less. This is an example of temporal variability. Spatial variability refers to how different areas in the HBEF may receive different amounts of precipitation in the same period of time (for example, one day or one year).
Water yield: Amount of water leaving a watershed, as measured at the weir. Given in units of height per area (e.g, mm water per square meter).
Watershed: The drainage area of a stream, river, or other body of water. There are nine gauged watersheds in the HBEF, ranging in size from 11 to 76 hectares, and researchers have conducted experiments on many of them. Because these watersheds are similar to each other, researchers can experiment with one entire watershed (for example, by cutting all the trees down in the "treatment" watershed), leave another one alone ( the "reference" watershed), and then compare them. If, in following years, the treatment watershed is very different from the reference watershed, scientists will learn how cutting down trees affects entire forests. This type of experiment is referred to as a "paired watershed" experiment. More information about watersheds can be found on Page 8 of the Introduction Tour.
Weir: See "Stream Gauge."
Whole-tree harvesting: A form of logging in which entire trees, including branches and crowns, are removed from a site. An experimental whole tree harvest was conducted on Watershed 5.
(CaSiO3): A mineral containing calcium silicate. In 1999 a new experiment
was started at the HBEF in which scientists are looking at how an addition
of calcium affects a watershed that has had its calcium soil pools depleted by
acid rain over several decades. Calcium was applied to the watershed in the form
of pelletized Wollastonite.
For more information on this experiment, click
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