Acadia National Park Flow Overview

Water moves through the water cycle in three ways: as an airborne gas, as moisture in the soil, and as a liquid.

As a gas, water exists as a colorless vapor in the air until it condenses in liquid form on the surfaces of airborne particles which, when heavy enough, fall to earth as precipitation (rain, snow, sleet, dew, etc.).

As soil moisture, water Flows largely unseen through particles of mineral and organic matter in the warmer months, or if the temperature falls below freezing, is locked in place as ice. If absorbed by root hairs, water enters plants from the soil, rises through stems and branches into leaves, where it supports food production and reenters the atmosphere through the process of evapotranspiration. Alternatively, utilizing cracks in bedrock or spaces between soil particles, water enters the water table to temporarily become stored as groundwater.

As a Flowing or standing liquid, water runs off or seeps from the land to collect in streams, ponds, wetlands and, ultimately, oceans, from whose surfaces it eventually evaporates, returning to the atmosphere as vapor, completing the cycle.

Only about 3% of earth's water is fresh, and most of that is locked in ice caps and glaciers. Of the small remainder, at any given time, there is about twice as much water in the soil as in the atmosphere, while streams and rivers contain less than one-tenth of that in the atmosphere.

Watersheds, as naturally-bounded geographical areas, are vital to the maintenance of almost every familiar form of life. They are land basins that receive precipitation, store it, and control its Flow downward toward the ocean. Watersheds are one of the primary ways the natural world organizes itself. All life on earth depends on water, and watersheds are systems for distributing water across time and space, making it available on a reliable enough basis for individual plants--and life dependent on those plants--to survive. Watersheds take water from large areas of higher ground on their peripheries and distribute it to ever smaller, concentric areas lower down, conveying a Flow of water, soil particles, and nutrients downward toward a central focus. Almost everything we take for granted on earth stems from the cyclical movement of water.

Marine Waters - Atlantic Ocean

Why are oceans salty? Over four billion years, the water cycle has been dissolving trace amounts of salts, including chlorine, sodium, sulfur, magnesium, calcium, and potassium from the crust of the Earth, delivering it to marine waters. The cumulative buildup of those small concentrations of salts now adds to a concentration of roughly 3.5 percent, which we label as salt because that's how it tastes to us. When the water cycle continues and moves into the air by evaporation from the surface of the ocean, the salts are left behind to increase in concentration.

There are other elements, too, in salt water. Particularly important are the mineral nutrients taken in by phytoplankton (from Greek planktos, wandering), the microscopic marine photosynthesizers that derive energy from sunlight and support the web of marine life. Phytoplankton convert dissolved carbon dioxide into the structural parts of their bodies, and into the organic molecules of life. We can't see them with the naked eye, but they are the miracle that brings the ocean to life.

Zooplankton, microscopic animals that graze on phytoplankton, are fed on by larger predators such as small fish and squid, which are fed on by larger fish with which we are more familiar because we sometimes find them on our dinner plates.

The average marine catch of the world's fisheries is currently about 87,000,000 metric tons (1 metric ton = 2,205 pounds). Roughly 25 percent of that catch--22,000,000 metric tons--is taken from the Atlantic Ocean.

In addition to its commercial fish, the North Atlantic contains a rich diversity of marine species, including 5 species of sea grasses, 13 species of corals, 432 species of mollusks (shellfish), 77 species of shrimps and lobsters, 87 species of sharks, 56 species of seabirds, and 48 species of marine mammals (whales, seals, dolphins, porpoises, and so on).

In the North Atlantic Ocean, prevailing winds blow in a clockwise motion out from the subtropical high, a semi-permanent high pressure belt located at 30 degrees latitude. Surface waters drift along with this whirl in the same direction, nudging waters from North America toward Europe. One thing leads to another, and pretty soon all that moving water begins to pile up. Pressure differences arise in the water column and soon, deep below, a slow reactive motion begins. This is the birth of the Atlantic's surface currents.

Perhaps the best known of these currents are the Gulf Stream and the Labrador Current. Both are part of an immense whirl of water in the Atlantic called a gyre. The Gulf Stream Flows northward along the East Coast of the United States, carrying quantities of warm water from the tropics to higher latitudes. Close to Cape Cod, the Gulf Stream veers away from shore and moves eastward, where it eventually slows and mixes with a much broader current called the North Atlantic Drift. In the far north, a smaller subpolar gyre shunts icy arctic water into the southward-moving Labrador Current. These two great currents collide close to the Grand Banks off the shore of Newfoundland, where intense fogs are often created by the contact of warm and cold waters.

Maine's coastal climate is influenced dramatically by the course of these two great Atlantic currents. Neither the Gulf Stream nor the Labrador Current Flows directly into the Gulf of Maine, which is separated from the greater Atlantic by a series of underwater banks and mountains. Occasionally, the Gulf Stream spills onto Georges Bank. When this happens, the sudden temperature rise and change in water chemistry results in massive die-offs of Gulf of Maine fish.

Climate

The story of Mount Desert Island's climate is told in much the same terms as its daily weather: temperature, relative humidity, precipitation, wind velocity and direction, barometric pressure, among other indicators. The major difference between climate and weather is the time span over which observations are made. Climate, then, is long-term weather, or, conversely, weather is climate here-and-now.

The significance of climate is that it is a measure of the range of environmental conditions that living systems in a given region are used to or have grown to expect. Each species can survive within an envelope of variable conditions. If temperature, say, exceeds the upper or lower limit of that envelope, or stays at one extreme or the other too long, individuals become stressed and their survival is put at risk. Snowshoe hares and American bald eagles have means for adapting to Maine's year-round climate; armadillos and brown pelicans do not.

Habitats are closely related to climate. In the sense that they are the immediate surroundings in which plants and animals find the climates and other resources they need to survive, habitats are climates come to life. Watersheds are habitat regions in which water is the limiting resource. Aspects of climate affecting the amount of water in the soil during the growing season have a pronounced influence on a given watershed's productivity and well-being. Seasonal precipitation, humidity, and temperature largely determine a watershed's suitability as habitat for local plant and animal life.

Its year-round temperature moderated by the heat-holding capacity of the ocean, Mount Desert Island has a longer growing season than areas just a few miles inland. If spring arrives more slowly than some desire, fall lingers on, and on, and on. Water loss due to evaporation is lessened in summer by humid air blowing off the Gulf of Maine. And the overall amount of precipitation useful to plants, though highly variable year to year, is consistently ample for the support of such thirsty-rooted species as northern white cedar, tamarack, and black spruce. The town of Bar Harbor on Mount Desert Island receives comparatively more annual precipitation than most regions in the United States, 1.4 times as much as Chicago, for instance, 3.4 times as much as Denver, and 7.3 times as much as Phoenix.

Mark Twain knew it, and the data support it: variability is the name of the new England weather game. At Acadia National Park, though November immediately follows October, the range from lowest to highest amount of monthly precipitation from 1944 through 1993 was spanned in these two adjacent months. November 1983 with 14.57 inches being 182 times wetter than October 1947 with only 0.08 inches. Variability is evident year to year, January 1979 with 11.78 inches having 16 times as much precipitation as the same month a year later with 0.73 inches. The same story unfolds even within a single calendar year, June 1968 with 4.75 inches receiving 21.6 times as much rain as July of the same year with 0.22 inches.

The notion of a normal or expected amount of rainfall on Mount Desert Island is elusive at best. If we cite the 50-year average precipitation for January as 4.78 inches, we should not be surprised if some Januaries receive less than 2 inches while others receive more than 8 or 9 inches. The same pattern of variability is true for every month of the year.

Rather than gear our expectations to some fictitious norm, we would do better to think in terms of a range within which monthly or yearly precipitation is apt to fall. We will not be far off if we expect precipitation in January to be greater than the 0.53 inches that fell in January 1944, and less than the 11.78 inches of January 1979. Or to narrow the gap, to say that January precipitation will likely range somewhere between 3 and 6 inches (a range that includes roughly half the Januaries between 1944 and 1993.

Generalizing, mean monthly precipitation at Acadia ranges by a factor of 2, from 3 to 6 inches, climbing from minimum to maximum in three months (September through November) and declining more gradually over the next 9 months (December through August).

Annual precipitation of 37 inches deposits a million gallons of water on every acre of ground. Only 3 years between 1944 and 1993 have fallen just short of that level of precipitation on Mount Desert Island. Local watersheds typically receive between 1 and 1.7 million gallons of water per acre a year from all sources (rain, snow, sleet, fog, dew, etc.).

Climate statistics are based on records of past events. Two opposing trends seem to be wrestling to control Mount Desert Island's climate in the future. The first of these is the 100,000-year Milankovitch cycle governing alternating periods of glaciation (lasting 90,000 years) and interglacial warming periods (lasting 10,000 years). We are now on the cooling downside of the most recent warming period. The peak of the current interglacial interval occurred 10,000 years in the past. A resurgence of glaciation has been predicted to occur within the next few thousand years.

At the same time, the accumulation of carbon dioxide in the atmosphere has been on the increase from natural factors, accompanied by a global warming trend resulting from the buildup of carbon dioxide and other so-called greenhouse gases resulting from human activities on an ever-increasing scale. Glacial nurseries in the Alps, Himalayas, and Andes are ice-free for the first time in 10,000 years. Is the local climate on Mount Desert Island cooling or warming? It is changing, certainly. The answer will be told by hindsight from studies of records yet to come.

Freshwater Fish

The management and protection of native fish species and aquatic communities, while providing the recreational angler with a quality fishing experience, is the focus of the National Park Service's recreational fisheries program. The NPS together with the Maine Department of Inland Fisheries and Wildlife regulate and manage freshwater fishing in Acadia National Park.

The fish communities of ponds and brooks of Mount Desert Island, particularly those within the boundaries of Acadia National Park, have been influenced by humans for well over a century. Angling pressure has increased substantially, especially in the second half of the twentieth century. This has resulted in extensive stocking of fish species native to Mount Desert Island as well as non-native and exotic (e.g. brown trout) introductions.

Virtually all ponds have been influenced by stocking at some point during the century. Of 24 ponds, only 4 have not been stocked, and these are all under 16 acres in size. The first intentionally introduced species was smallmouth bass in 1891. Since that time, brook trout, rainbow trout, brown trout, Sunapee char, lake trout, landlocked salmon, alewives, rainbow smelt, largemouth bass, steelhead, sea-run Atlantic salmon, and various species of sticklebacks and cyprinids have all been stocked in waters within Acadia National Park. As a consequence of these community species alterations, 91% of the ponds that contain fish no longer contain their original species mix.

Historically, 30 species or subspecies of fishes (see list below) have been confirmed for waters within the Park, but only 14 of these are native to MDI. The most widespread of these native fishes are banded killifish and golden shiner, each found in 79% of the ponds, as well as in several brooks. Other widely distributed fish species within Park waters are brook trout (71% of ponds), pumpkinseed (67%), American eel (63%), white sucker (54%), and northern redbelly dace and rainbow smelt (each 50%).

As a general trend, there is less multi-species stocking in the 1990s compared to even two decades ago. Most recent stocking has been with salmonid fishes. Numbers stocked have declined, but the size of stocked fish is larger, to promote higher survival. Only Bear Brook Pond, Duck Pond, and Lakewood have presumably never been stocked. Thus, if natural fish communities are to be studied, these three small ponds probably reflect the original fish communities.

Since almost all waters within the Park are biologically altered from their original species mixture, most fish communities will never return to their original state, especially with high angler demands of salmonids from local residents and tourists. Stocking has been a tool for meeting this demand - to introduce new species of game fish or to supplement existing populations. Logical research directions for the future could address the biogeographical progression of community changes and the consequences of such species changes.

Groundwater

Groundwater on Mount Desert Island is stored in both surface deposits of porous soil and in fractured bedrock. The surface deposits are of glacial origin. They include unsorted glacial till, glacial stream deposits, end moraines, marine deposits, and glacial stream deltas. These groundwater storage sites are often in the vicinity of sand and gravel pits where the storage formation is mined for construction purposes. The water yield from wells drilled in such formations is low, often below 10 gallons per minute.

Water in bedrock resides in fractures, joints, and faults. Wells tapping these deeper groundwater storage areas produce about the same Flow of water, roughly 10 gallons per minute. Drawn by gravity, groundwater moves downward through fractured bedrock, but it also Flows sideways (laterally) for hundreds of miles, and can move upward by capillary action. The water table is groundwater's upper surface, which tends to lie parallel to the ground surface above it.

A layer of clay (pulverized rock) deposited by the last glacier often covers or caps other more porous deposits, creating perched reservoirs of groundwater unable to penetrate through the dense and impassable layer of clay. Most reliable supplies of groundwater on Mount Desert Island are tapped by wells driven into the fractured bedrock.

Groundwater on Mount Desert Island is characterized as soft and of generally good quality for domestic use. By rough estimate, half the residents of the Town of Bar Harbor, Maine, get their water from private wells tapping the local groundwater, while the other half uses water drawn from Eagle Lake supplied by the Bar Harbor Water Company.

The local granite can contain radon, which dissolves in the groundwater, and can be released into homes, particularly when the shower is turned on. This can release radioactive radon gas into poorly ventilated spaces, possibly reaching concentrations that are a potential risk to human health. When inhaled, radon can cause lung cancer.

Groundwater can be polluted by liquids poured or spilled on the ground filtering down through the soil into aquifers below. Since human taste buds can detect a single molecule of gasoline in a million molecules of water, one gallon of spilled gasoline can make a million gallons of groundwater unsuitable for drinking.

Marine Waters Gulf of Maine

On average, Maine's rivers pour about 250 billion gallons of fresh water into the Gulf of Maine every year. Add to that astounding volume sediments and nutrients from terrestrial runoff, whirl it into the Gulf's semi-enclosed basin, and you have a rich recipe for life. The crescent of underwater banks and mountains stretching from Cape Cod to Nova Scotia allows very little exchange between the waters of the Gulf and the Atlantic Ocean. As a result, Maine's coastal waters tend to be cooler, richer in sediments and nutrients, and more diluted by fresh water than the water beyond Georges and Brown banks.

The main entry into the Gulf of Maine is through the Northeast Channel, a deep underwater valley between Georges and Brown banks. Cold water from the North Atlantic enters the gulf by this means, then circulates counter-clockwise, requiring some three months to make one round of the gulf.

The gulf's resources are rich, but not inexhaustable. Phytoplankton (microscopic marine plants) supporting the food web depend on nutrients exported by watersheds mixing in the presence of sunlight with nutrients welling up from the deep. Those nutrients are available in limited supply, supporting limited populations of phytoplankton, in turn supporting limited populations of zooplankton (microscopic water-borne animals), invertebrates, sea mammals, and fish. Treating the Gulf as if it were an infinite source, we have mined it beyond its fisheries' capacity to regenerate. The only solution is for humans to back off for a time, and rethink the amount of fish they can take from the gulf. In one year, some 20,000 fishermen typically land some 530,000 metric tons (a metric ton is 2,205 pounds) of fifty-two different species of fish (including both fin fish and shellfish) from the Gulf of Maine. In 1993, Canada reported the crash of ground fisheries along its Atlantic coast. Continued declines seemed certain. In 1992, Newfoundland declared a total fishing moratorium.

There are two possible outcomes: either we ask the Gulf of Maine to feed fewer mouths at a sustainable rate, or its fisheries will collapse and be able to feed none at all.

The greatest concentrations of life in the gulf occur in the summer during times when phytoplankton thrive, notably over Georges Bank where the water can be less than 9 feet deep in places. Such areas are among the most biologically productive regions anywhere on Earth.

Who lives in the Gulf of Maine? Bottom-dwelling species including corals, sponges, worms, and many others. Cod, haddock, and pollock are bottom dwelling fish species that feed on creatures on the gulf floor. Several species migrate into the gulf from the North Atlantic, including yellowfin and bluefin tuna, swordfish, dogfish, sharks, menhaden, squids, and great schools of herring. Species that mature in salt water but move into freshwater streams to reproduce include Atlantic salmon, Atlantic sturgeon, alewives, and striped bass.

A variety of marine mammals feed in the gulf during the summer months, including whales, dolphins and porpoises. The most common whales are humpback and finback whales, both baleen whales that gulp plankton by the mouthful. Smaller marine mammals include common dolphins, white-sided dolphins, and harbor porpoises. Harbor seals live in the gulf year-round, and the occasional hooded seal from more arctic waters explores its reaches.

A great many birds feed on fish in the surface waters of the Gulf of Maine, including several species of birds seldom seen on the mainland. Petrels, storm-petrels, shearwaters, northern gannets, auks, and puffins are a few of the birds that fish the Gulf of Maine. There are also the more familiar shoreside birds such as ducks, geese, gulls, terns, herons, cormorants, sandpipers, hawks, and many others.

The southern extent of the Gulf of Maine--from Cape Cod, Massachusetts, to Cape Elizabeth near Portland, Maine, is famous for its sandy beaches. The central region features the familiar rockbound coast where cobble beaches replace the sandy ones. In the northern reaches of the gulf, the Bay of Fundy funnels the tide into ever-narrowing bays that host the highest tides on Earth.

Ponds

Acadia National Park and Mount Desert Island are famous for their granite coastal hills, but between those hills lie valleys with streams and ponds equally deserving of fame.

Ponds are stream- or spring-fed lowlands or valleys where the water table (the level of water held in the soil) rises above the surface of the soil to form a body of relatively still water open to the air. In some places the word pond is reserved for shallow bodies of surface water and lake is used for deeper ones, but in Maine all surface waters are considered to be ponded and are referred to as ponds.

Just because water in ponds moves more slowly than it does in streams doesn't mean there's nothing happening in ponds. Changes in daily and seasonal temperatures of water near the surface of a pond sets up currents of Flowing water within the pond itself, promoting a corresponding Flow of nutrients. In both spring and fall, pond waters turn upside-down, bottom waters rising to the top, surface waters sinking to the bottom. The fall overturn is the result of falling temperatures that leave surface waters cooler than the depths, causing the warmer water on the bottom to rise to the top. In spring, equinoctial winds (winds near the equinox) stir up the surface waters of a pond, establishing currents that drive a second annual overturn.

Ponds are often full of plant and animal life, especially if their waters contain nitrogen (needed for plant growth) and phosphorus (needed for plant reproduction). Aquatic plants grow at various depths, some preferring the shallows near the edge of a pond, some thriving in moderate depths. Many free floating plants and algae benefit from the bright sunlight at the surface and the waterborne nutrients in the pond itself. Two examples of shallow ponds in Acadia National Park are the Tarn (in the valley between Dorr Mountain and Huguenot Head south of Bar Harbor) and Aunt Betty's Pond (north of Sargent Mountain). These two ponds are fast filling in with vegetation such as arrowhead, pond lily, and bayonnet grass and will be wetlands, not ponds at all, in the near future.

Acadia's deeper ponds have such clear water and low nutrient levels that they are relatively free of plant life. Eagle Lake is one such pond and is the water supply for the town of Bar Harbor, as Jordan Pond is for Seal Harbor, and Long Pond is for Southwest Harbor. Pond clarity is measured by dropping a weighted target (Secchi disk) overboard from a boat and lowering it until it can no longer be seen. Secchi depths for many of the ponds on Mount Desert Island are contained in the righthand column in the table of ponds below.

Only two ponds on Mount Desert Island are acidic, Sargent Mountain Pond and Duck Pond, which are about one acre in size with a pH of 5.0 or less. The acidity of Sargent Mountain Pond is thought to be caused by atmospheric deposition on a small, granitic watershed with little soil; the acidity of Duck Pond results from its being fed by a naturally acidic wetland. POND TROPHIC TYPES

OLIGOTROPHIC--Ponds lacking plant nutrients and plants, with high levels of dissolved oxygen (Eagle Lake and Jordan Pond) MESOTROPHIC--Ponds with moderate levels of nutrients, plants, and dissolved oxygen (Bubble Pond and Upper Hadlock Pond) EUTROPHIC--Ponds with abundant plant nutrients, algal blooms, with low levels of dissolved oxygen (The Tarn and Aunt Betty's Pond) DYSTROPHIC--Acidic ponds with high levels of vegetable matter from a small variety of plants (Duck Pond)

The following table contains readings that show variations with depth of water temperature and dissolved oxygen content in Eagle Lake on September 23, 1998. At a depth between 19 and 20 meters, the temperature abruptly falls several degrees and the dissolved oxygen drops and then trails off. Cooler waters and decaying organic matter on the bottom markedly decrease the amount of oxygen available to living organisms. Those bottom nutrients are carried upward at the spring and fall overturns, making food available to organisms in the upper levels where dissolved oxygen is more plentiful. Generally speaking, in ponds what goes down must come up.

Streams

Streams as habitats for plants and animals are directly affected by the watersheds in which they lie. Locales within streams or ponds having certain characteristics (substrates, banks, vegetation) are embedded within watersheds that determine streamFlow, stream chemistry, stream temperatures, sediment loads, and so on, which govern biological activity in the stream.

The community of life in a stream varies with its position along the length of the stream from steep, shaded, rushing headwaters to flat, sunny, slow-moving meanders low in the watershed. A stream can be seen as a continuum of life dependent on a continuum of physical features. Headwater (generally shaded) stream habitats are strongly influenced by surrounding watershed vegetation. Lower down, as stream size increases and shading decreases, a decrease in terrestrial organic input (such as leaves falling from trees) is balanced by greater instream food production and distribution. Populations of stream invertebrates shift with stream size and food production, and fish species follow the presence of their preferred insect foods, whether collectors, shredders, grazers, or collectors. Headwater streams depend on their watersheds for input of nutrients and organic matter that are not produced in the streams themselves. In that sense, a stream cannot be considered apart from the watershed that maintains it as a biological system. Small stream habitats, then, are largely determined by the vegetation, soils, climate, and topography of the watersheds in which they rise.

A stream is an expression of the watershed that is its source. In headwaters, dissolved nutrients feed aquatic and terrestrial algae and plants, which in turn feed everything else. Life in shaded headwater streams often relies more on plant matter fallen from stream side vegetation than on dissolved nutrients and aquatic vegetation itself. In one section of a stream, for example, black fly larvae feed on bacteria-enriched detritus, and trout feed on the larvae. Lower down the stream, aquatic algae, mosses, phytoplankton, and rooted plants assume greater importance in sustaining stream life. Here, perhaps, invertebrates and zooplankton feed on aquatic vegetation, and are in turn eaten by, say, alewives, which are eaten by pickerel, herons, kingfishers, ospreys, and people.

The streams of Mount Desert Island and Acadia National Park generally drain the granite ridges of the island to surrounding salt water. They tend to be only a few miles long with steep initial drops and few tributaries. The two largest streams, Otter Creek and Northeast Creek, have peak discharges of 30,000 liters per minute or above. Recent water chemistry information for streams in Acadia: 1999 and 2000 .

Senator George Mitchell Center for Environmental and Watershed Research For stream Flow conditions in Maine and other states, see Water Resources of Maine . STREAMS WITHIN ACADIA NATIONAL PARK and where they Flow Bubble Pond Brook Bubble Pond to Eagle Lake Chasm Brook north slope of Sargent Mountain to Gilmore Meadow Duck Pond Brook Duck Pond to Long Pond Great Brook north slope of Mansell Mountain to Long Pond Heath Brook to Marshall Brook and Bass Harbor Marsh Hodgdon Brook to east side of Hodgdon Pond Hunters Brook valley south of Bubble Pond to Hunters Beach Lurvey Spring Brook to Echo Lake Man O' War Brook $#149; south slope of Acadia Mountain to Somes Sound Seal Cove Brook Seal Pond to Seal Cove Steward Brook western slope of Western Mountain to Seal Cove Pond STREAMS PARTLY OUTSIDE ACADIA NATIONAL PARK and where they Flow Bear Brook Beaver Dam Pond to Frenchman Bay Breakneck Brook Breakneck Ponds to Hulls Cove Buttermilk Brook to Bass Harbor Marsh Canon (Canyon) Brook east slope of Cadillac Mountain to Otter Creek Cromwell Brook the Tarn and Great Meadow to Cromwell Harbor Duck Brook Eagle Lake to Frenchman Bay Halfway Brook to Mitchell Cove Jordan Stream Jordan Pond to (Little) Long Pond Kebo Brook the Notch to Cromwell Brook Kitteredge Brook Long Heath to Babson Brook Little Harbor Brook the Amphitheater to Eastern Way Marshall Brook south slope of Western Mountain to Bass Harbor Marsh N. S. branch of Hadlock Brook west slope of Sargent Mtn. to Somes Sound Northeast Creek Fresh Meadow Marsh to Eastern Bay Old Mill Brook to Northeast Creek Otter Creek to Otter Cove Reservoir Brook the Reservoir to Marshall Brook Richardson Brook Aunt Betty's Pond to Somes Sound Sargent Brook northwest slope of Sargent Mountain to Somes Sound Stanley Brook to Seal Harbor

Terrain

Terrain--the lay of the land--interacts with precipitation in determining the pattern of Flow of water through a watershed. Where that terrain is largely impervious bedrock, as is found on the granite hills of Mount Desert Island, Maine, water seeks the most direct route of descent along the surface. Where the ground is porous with layers of organic and mineral matter, water Flows among the particles in the soil, picking up nutrients and carrying them with it in its descent. The elevation, slope, and physical composition of the local terrain influence the amount of nutrients in water Flowing through it, and determine the types of vegetation and animate life that water can support in the local watershed.

The principal BEDROCK FORMATIONS on Mount Desert Island include: GRANITE , plutons formed during the collision of tectonic plates nearly 400 million years ago, formed by intrusions of quartz, feldspar, hornblende, and other minerals into the country rock. ELLSWORTH SCHIST , the oldest rock exposed on Mount Desert Island (seen, for example, at Thompson Island), a gray layered rock laid down as mud on the sea floor over 500 million years ago, then heated during the collision of tectonic plates and altered to its current form. BAR HARBOR FORMATION , another sedamentary rock formation, originally laid down as silt and sand under the sea, then transformed by heat and pressure into the rocks we see today along the Shore Path in Bar Harbor. GABRO-DIORITE, rich in iron, magnesium, and calcium, gabbro and diorite are two different rocks often associated together. Older than granite, gabbro-diorite formations intruded into the country rock as granite did later. This rock can be seen along Route 3 west of Salsbury Cove and on Great Head in Acadia National Park. CRANBERRY ISLAND SERIES , originating in volcanic eruptions that deposited light gray and blue-gray layers of debris that settled on the sea floor. SHATTER ZONE , a mixture of older rock in a matrix of granite, seen on Otter Head or at the eastern end of Sand Beach in Acadia National Park. DIABASE DIKES , fine-grained black rock forced upward through fractures in older formations. Diabase, basalt, and gabbro are similar in composition but formed differently, basalt erupting onto the surface, diabase cooling underground, and gabbros lying deeper still. Many of the hiking trails in Acadia National Park cross diabase dikes that are only a few inches to many feet wide. Dikes are particularly prominent in the granite at Schoodic Point.

The terrain of Mount Desert Island features a range of coastal hills running from east-northeast to west-southwest, a range cut by valleys running north-northwest to south-southeast. The striking ridges and valleys of Mount Desert Island have been largely shaped by four primary forces: vulcanism, glaciation, erosion, and deposition.

Vulcanism here refers to the Flow of minerals from deep in the earth toward the surface (whether they break the surface or not), as happened in the geologic forerunner of the state of Maine some 350 million years ago as the result of heat generated by friction between colliding tectonic plates. Some of that Flow erupted into the atmosphere, spewing new rock into the landscape of the period, but much of it cooled in plutons (subterranean formations of slow-cooling rock) composed of large crystals of quartz, feldspar, mica, and hornblende--a combination which today we call granite, the principal bedrock of the Bar Harbor Hills (and of the valleys between them).

Glaciation is the scouring action of glaciers pressing on and sliding across the landscape. Wave after glacial wave has traversed the land region we call Maine, propelled by the outward Flow of ice from its center far to the north, alternately retreating during warmer interglacial periods when melting exceeded the rate of buildup at the core, only to resurge when the climate cooled, grinding away the hardest rock beneath mile-thick sheets of ice trundling across the land. The tempo at which ice sheets alternately advance and retreat is governed by the 100,000-year Milankovitch cycle affecting differences in seasonal temperatures. The alternation of enduring periods featuring hot summers and cold winters, or cool summers and mild winters, brings about the motion of ice sheets during a glacial age. We live on the cooling edge of an interglacial period, in the aftermath of the Laurentian glaciation, the one we know most about because it is closest to us. Human civilization has blossomed in the brief warm period between the last and coming waves of ice. We credit the coming of that last glacier with the sculpting of the Bar Harbor Hills, but there could easily have been more than thirty glacial advances since granite welled up from plutonic regions, each doing its bit to shape the land we know today as Mount Desert Island.

Erosion is the abrading away of earth's crust by currents of air, ice, or water (whether fresh or salt). Winds, marine waters, glaciers, and streams strip layer after layer of earth from its substrate of bedrock, which, once exposed, breaks up and is sloughed away as well, successively exposing deeper and deeper levels of geological structure. The terrain detailed on modern topographic maps is only temporary; it, too, will crumble and turn to sand. The watershed basins of Mount Desert Island are no accident; they are products of 350 million years of painstaking erosion which has chiseled and polished the landscape of today, flake-by-flake, grain-by-grain. Water is the medium by which watersheds live and die. It brings them forth, sustains them, and carries them away. Wherever we look, we see a landscape seemingly fixed forever, but actually it is Flowing with the forces of creation and destruction, change and time.

Erosion often gets a bad press as the relentless weathering-away of the world we know, but without erosion there would be scant life on Earth. Mountains need to crumble into grains of mineral soil in order to provide enough surface area for water to dissolve calcium, potassium, phosphorus, sulfur, and trace amounts of other minerals it then transports to living systems which require them for health and growth. Water is not the only substance Flowing through a watershed. Rock (from boulders down to clay), minerals, soils, and nutrients, too, seek the lowest level they can in sloping terrain. Watershed soils are distributed along a gradient from talus at the base of cliffs to fine organic soils in alluvial bottoms and wetlands lower down. Glaciers coursing at intervals through the land hasten the process, grinding and depositing a range of mineral soils as they advance and retreat. But given the vagaries of climate almost everywhere, big rocks are ground into little rocks by wind, ice, and water acting persistently over time, creating a variety of substrates and microclimates favored by diverse vegetation. Somewhere in that range between clay and boulders, particles present enough surface area to hold water by adhesion while also providing tunnels giving access to air, creating ideal habitat for root hairs that need nutrients, water, and air. Soil not only holds water, but an equable temperature as well, smoothing out abrupt shifts in day and nighttime temperatures, insulating delicate roots against extremes of heat and cold. If cliffs did not break off and resolve into boulders and gravel, watersheds would host mainly lichens on the surface, and know nothing of rooted plants drinking water, breathing air, consuming nutrients underground.

Deposition of the end products of erosion in sorted or mixed layers of clay, sand, gravel, cobbles, and boulders puts the finishing touches on the landscape roughed-out by vulcanism, glaciation, and erosion. The hills of Mount Desert Island stand today largely as they were shaped by the most recent glacier, but the valleys between them contain an assortment of deposits left by glacial streams, retreating glaciers, and ocean waves. Glacial till (unsorted glacial debris compacted by the weight of the glacier) and glacio-marine sediments are common in low-lying areas of the park where they frequently serve as the stony treadway of many miles of hiking trails. Balance Rock on South Bubble in Acadia National Park is a fine example of a glacial erratic boulder transported by the last ice sheet.

WATERSHED SOILS

Properties of Mount Desert Island soils have great significance for the functioning of local watersheds. Steep slopes and shallow depths to bedrock reduce water infiltration and increase stormwater runoff. Soils not only govern the storage and movement of water, but contribute minerals, dissolved organic carbon, and other materials to ground and surface waters through natural decomposition and weathering.

On granite ridges the predominant soil classification on Mount Desert Island is a complex made up of Schoodic, rock-outcrop, and Lyman soils. This soil complex is derived from tills bearing granite and schist components.

The Schoodic, rock-outcrop, and Lyman soil complex includes extensive areas of exposed bedrock where soils are absent, along with areas where soils exist as thin deposits of gravely sandy loam less than 15 cm deep (Schoodic soils) and areas where soils form a black and reddish sandy loam less than 50 cm deep (Lyman soils). This soil complex is described as excessively well drained, with slopes that range from 0 to 100 percent for bare rock, and from 0 to 80 percent in areas with soil. On steep slopes these soils are usually droughty (prone to drought). Lyman and Schoodic soils are spodosols--acidic forest soils characterized by an accumulation of iron, aluminum, and organic matter.

Precipitation drains so rapidly through these mountainous Lyman soils that it has little time to dissolve minerals of subsequent value to vegetation at lower elevations. Lyman soils are considered low productivity soils from a forestry perspective.

Valley soils on Mount Desert Island are typically part of the Hermon-Monadnock-Dixfield complex derived from granite and gneiss tills.

They range from excessively to moderately well drained with slopes up to 60 percent. Below elevations of approximately 40 m, these soils are often underlain by glaciomarine silts and clays of the Presumpscot formation. These and similar soils are found, for example, on the western shores of Jordan Pond and Eagle Lake, and in the Kebo Mountain--Sieur de Monts Spring area.

Wetland soils found in such places as Bass Harbor Marsh, Great Meadow, and Fresh Meadow Marsh along Northeast Creek have a low mineral (rock) and high organic (vegetable) content. These often mucky (containing highly decomposed vegetable matter) lowland soils are characteristically wet for large portions of the growing season, and are generally known as hydric soils.

The Soil Conservation Service (SCS) (1987) defines a hydric soil as a soil that is saturated, flooded, or ponded long enough during the growing season to develop anaerobic (i.e., oxygen depleted) conditions in the upper part. Hydric soils develop under conditions wet enough to support the growth and regeneration of hydrophytic (water loving) vegetation.

Wetlands

Freshwater wetlands provide good examples of watershed areas having a strong interaction with other parts of a larger watershed system. The Environmental Protection Agency lists the following freshwater wetland benefits.

FRESHWATER WETLANDS: greatly influence the water quality of an adjacent stream by removing pollutants such as sediments, nutrients, and both organic and inorganic matter detain floodwaters, thereby reducing Flow velocity, erosion, and flood peaks in downstream areas provide habitat for wildlife such as waterfowl, mammals, and unique vegetation contribute to the aquatic food chain by providing detritus (decaying organic matter) to species living in adjoining waters prevent excessive water temperatures during summer months which could be lethal to invertebrates or fish The freshwater wetlands of Acadia National Park and Mount Desert Island are living communities that are still in the process of formation. In a hundred years, many of them will look different than they do today. The Tarn and Aunt Betty's Pond, for instance, are filling in and emergent wetland plants such as arrowhead, bayonet grass, and pickerelweed make the two ponds look like green meadows in late summer. These wetlands got their start after the last glacier receded some 12,000 years ago, leaving deposits of sand, clay, and till that in many places blocked or reduced the free Flow of runoff and streams. As the climate warmed, plants repopulated the region, and within 2,000 years, a succession of forest trees was reintroduced, including birch, white pine, hemlock, and by the time European settlers appeared on the scene, the prevalent spruce-fir forest we see around us today. Forested wetlands are one type of freshwater wetland. In Acadia, the dominant species include Northern white cedar, red spruce, and black spruce, together with subordinate species such as larch, red maple, quaking aspen, and white birch. Shrubs include serviceberry, winterberry, speckled alder, green alder, highbush blueberry, wild raisin, meadowsweet, mountain holly, sheep laurel, blueberry, sweetgale, black huckleberry, Labrador tea, and leatherleaf. Ground cover species include skunk cabbage, bunchberry, Canada mayFlower, starFlower, twinFlower, goldthread, swamp dewberry, creeping snowberry, large-leaved cranberry, three-seeded sedge, cinnamon fern, and sphagnum moss. Reflecting their need for water during the growing season, certain species of plants serve as indicators to the availability of water in the freshwater wetlands in which they thrive.

Indicator Species in Acadia's Freshwater Wetlands

Permanently Flooded Wetlands--white water lily, spatterdock, pondweeds, floating heart Semipermanently Flooded Wetlands--burreeds, bayonet rush, pickerelweed, common arrowhead, common pipewort Seasonally Flooded Wetlands--cattail, tussock sedge, marsh fern, mountain holly, wild raisin, red maple Wetlands with Seasonally Saturated Soils--pitcher plant, white beakrush, leatherleaf, sphagnum moss Freshwater wetlands provide habitat for three groups of plants and wildlife: (1) upland species that can tolerate wetland conditions including white pine, white-tailed deer, garter snakes, as well as frog and salamander species that breed in flooded wetlands in spring; (2) aquatic species including mummichogs, snapping turtles, otters, and water striders that can survive in wetland pools; and (3) species that live predominantly in wetlands including cattails, muskrat, beaver, and pickerel frogs. Learn more about Acadia's water resource program .

Sea - Air Exchange

The zone of contact where the lower surface of the atmosphere interacts with the upper surface of the ocean may seem to be of negligible thickness. Yet the exchange between these two bodies--one gaseous, one liquid--is crucial to the formation of ocean currents, winds, weather, and other earthshaking events. And when it comes to storm formation, this is where torrents meets the waves.

Most of the energy input driving atmospheric circulation comes from contact with earth's surface. The ocean's heat-storage capacity is much greater than that of either land or air. Given that the specific heat capacity (the ability to absorb or lose heat without changing temperature) of water is more than four times that of air, and considering that only the 70 m deep top layer of the ocean can be mixed, this top layer of the ocean alone can store about thirty times more heat than the entire atmosphere can.

What does that mean? For the same increase or decrease in energy, the atmosphere's temperature change will be thirty times greater than the ocean's. This explains the "moderating effect" of the ocean on nearby land. In the summertime, seaside towns are almost always cooler and breezier than non-coastal areas. The ocean's ability to store heat also keeps seaside areas warmer in winter so that snowfall is often less and temperatures generally milder than conditions inland. Watch out for sea squalls and fog, though! When the ocean and atmosphere are at markedly different temperatures, storms or heavy fog can be spawned in the air-sea contact zone. Winds, storms, fog, rain, and clouds are all results of the dramatic interaction between the air, sea, and the sun's energy.

What is exchanged in the boundary layer where air and oceans meet? The atmosphere is the source of carbon dioxide and oxygen dissolved in marine waters. Too, nitrogen, and iron enter saltwater from the air, as do windblown dust and a variety of air pollutants contributed by human activities. The exchange of carbon dioxide between air and ocean is crucial in regulating Earth's climate and temperature.

What does the atmosphere receive from the world ocean? Water vapor, for sure. Which affects the temperature and humidity of the lower atmosphere. It now appears that marine life affects emissions of di-methyl sulfide, which oxidizes to produce condensation nuclei around which water droplets can form.

Concentration differences between substances in air and water affect the air-sea exchange, as do winds, currents, and turbulence in both fluids (yes, air is a fluid). The exchange of gases and energy at the interface between air and saltwater is extremely complex and little understood. One thing is clear: the exchange is a crucial regulator of the water cycle and has a powerful impact everywhere on Earth.

Like so many life processes, we don't understand very well how air and saltwater interact, but we do know the interaction is essential to maintaining the integrity of planetary life.

Air Quality Factors

Since 1979, Acadia National Park has had an air quality monitoring program that is designed to document current conditions and determine long-term trends. Although spectacular vistas are still common in Acadia, pollutants from upwind sources contaminate park air and degrade visibility. Monitoring data show that visibility conditions at the park have improved slightly from 1988 through 1998, but are still less than half what they should be at "natural background" levels.

Summer ozone levels occasionally exceed federal health standards. The highest ozone concentration reported in Maine was measured at Acadia (Isle au Haut) on June 15, 1988. Ozone concentrations below the federal health standard have been shown to damage sensitive park vegetation. The effects of atmospheric deposition are another major concern at the park. Acid precipitation (rain, snow, and fog) can be a major influence on lake and stream chemistry, cause nutrient enrichment in estuaries, and affect sensitive vegetation. Recent studies discovered high concentrations of mercury in several freshwater fish species sampled in park lakes.

The major source of mercury in lakes appears to be deposition from the atmosphere, and it then concentrates in the food chain. Consumption of mercury-contaminated fish can be harmful to humans as well as to other wildlife.