The Portneuf River is a 124 miles (199.6 km) tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Snake River

Snake River

The Snake is a major river of the greater Pacific Northwest in the United States. At long, it is the largest tributary of the Columbia River, the largest North American river that empties into the Pacific Ocean...

 in southeastern Idaho

Idaho

Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. It drains a ranching and farming valley in the mountains southeast of the Snake River Plain

Snake River Plain

The Snake River Plain is a geologic feature located primarily within the state of Idaho in the United States of America. It stretches about westward from northwest of the state of Wyoming to the Idaho-Oregon border. The plain is a wide flat bow-shaped depression, and covers about a quarter of Idaho...

. The city of Pocatello

Pocatello, Idaho

Pocatello is the county seat and largest city of Bannock County, with a small portion on the Fort Hall Indian Reservation in neighboring Power County, in the southeastern part of the U.S. state of Idaho. It is the principal city of the Pocatello metropolitan area, which encompasses all of Bannock...

 sits along the river near its emergence from the mountains onto the Snake River Plain.

The river is part of the Columbia River Basin.

Course

The Portneuf River rises in western Caribou County

Caribou County, Idaho

Caribou County is a county located in the U.S. state of Idaho. As of the 2010 Census the county had a population of 6,963. The county seat and largest city is Soda Springs, followed by Grace and Bancroft.- History :...

, approximately 25 miles (40.2 km) east of Pocatello, along the eastern side of the Portneuf Range. It flows initially south, passing westward around the southern end of the range, and then turning north to flow between the Portneuf Range to the east and the Bannock Range to the west. It flows northwest through downtown Pocatello and enters the Snake at the southeast corner of American Falls Reservoir, approximately 10 miles (16.1 km) northwest of Pocatello.

Watershed and discharge

The Portneuf watershed drains 850290 acres (3,441 km²) in southeastern Idaho and is bounded by Malad Summit to the south, the Bannock Range to the west, the Portneuf Range to the southeast, and the Chesterfield Range to the northeast. Marsh Creek is the only major tributary to the Portneuf River. Other creeks in this watershed include Mink, Rapid, Garden,Hawkins, Birch, Dempsey, Pebble, Twentyfourmile, and Toponce creeks. The total area of the Chesterfield Reservoir is estimated at 1236 acres (500.2 ha).

The Portneuf River's drainage basin

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

 is approximately 1329 square mile in area.

Its mean annual discharge

Discharge (hydrology)

In hydrology, discharge is the volume rate of water flow, including any suspended solids , dissolved chemical species and/or biologic material , which is transported through a given cross-sectional area...

, as measured by USGS gauge 13075910 (Portneuf River at Tyhee

Tyhee, Idaho

Tyhee is a census-designated place in Bannock County, Idaho, United States. Its population was 1,123 as of the 2010 census....

), is 418 cuft/s, with a maximum daily recorded flow of 1730 cuft/s and a minimum of 32 cuft/s.

History

The Portneuf River was given its name sometime before 1821 by French Canadian

French Canadian

French Canadian or Francophone Canadian, , generally refers to the descendents of French colonists who arrived in New France in the 17th and 18th centuries...

 voyageurs

Voyageurs

The Voyageurs were the persons who engaged in the transportation of furs by canoe during the fur trade era. Voyageur is a French word which literally translates to "traveler"...

 working for the Montreal-based fur trading

Fur trade

The fur trade is a worldwide industry dealing in the acquisition and sale of animal fur. Since the establishment of world market for in the early modern period furs of boreal, polar and cold temperate mammalian animals have been the most valued...

 North West Company

North West Company

The North West Company was a fur trading business headquartered in Montreal from 1779 to 1821. It competed with increasing success against the Hudson's Bay Company in what was to become Western Canada...

.

The valley of the Portneuf provided the route of the Oregon Trail

Oregon Trail

The Oregon Trail is a historic east-west wagon route that connected the Missouri River to valleys in Oregon and locations in between.After 1840 steam-powered riverboats and steamboats traversing up and down the Ohio, Mississippi and Missouri rivers sped settlement and development in the flat...

 and California Trail

California Trail

The California Trail was an emigrant trail of about across the western half of the North American continent from Missouri River towns to what is now the state of California...

 in the middle 19th century. After the discovery of gold

Gold

Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

 in Montana and Idaho, it became a significant stage route for the transportation of people and goods. In 1877 the valley was used as the route of the Utah and Northern Railway

Utah and Northern Railway

The Utah and Northern Railway is a defunct railroad that was operated in the Utah Territory and later in the Idaho Territory and Montana Territory in the western United States during the 1870s and 1880s. It was the first railroad in Idaho and in Montana....

, the first railroad in Idaho.

Biogeochemistry of the Portneuf River watershed

The Portneuf River watershed is a heavily used and anthropogenically altered system. After a series of heavy floods in the early 1960s the Army Corps of Engineers designed and constructed a concrete channel to control flooding in 1965. The channelization followed the river's route and cut through the west side of Pocatello, and drastically altering the natural river processes. One common result of human activity is the loading of nutrients into the water system through both point and non-point sources. The river is subjected to use by four municipalities (Lava Hot Springs

Lava Hot Springs, Idaho

Lava Hot Springs is a city in Bannock County, Idaho, United States. It is part of the 'Pocatello, Idaho Metropolitan Statistical Area'. The population was 521 at the 2000 census...

, McCammon

McCammon, Idaho

McCammon is a city in Bannock County, Idaho, United States. It is part of the 'Pocatello, Idaho Metropolitan Statistical Area'. The population was 805 at the 2000 census.-Geography:McCammon is located at ....

, Inkom

Inkom, Idaho

Inkom is a city in Bannock County, Idaho, United States. It is part of the Pocatello, Idaho Metropolitan Statistical Area. The population was 738 at the 2000 census.-Geography:Inkom is located at ....

, and Pocatello) over its length. The dynamic geology of the region and the heavy use by the local populations have produced a unique set of chemical characteristics associated with both the biological processes and the interactions with the local geology.

Nitrates

Nutrient runoffs from intensive agriculture and ranching along the route of the river have noticeably increased the nitrate

Nitrate

The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...

 loads in the stream. This is only compounded by the addition of waste waters from the City of Pocatello’s wastewater

Wastewater

Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...

 treatment facility and the waste associated with the phosphate

Phosphate

A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...

 processing plant. This increased nutrient load supports an increased biomass

Biomass

Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

 within the system. The DEQ in collaboration with the Soil Conservation Commission and USDA are developing tools and practices designed specifically to alleviate the nitrogen issues associated with agriculture and its waste. Known as Best Management Practices (BMPs), these methodologies are designed and modified for varying situations, and have proven themselves effective through prior implementation projects.

Carbon exchange

The exchange of inorganic carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 between the solid earth and the atmosphere in the Portneuf watershed has produced deposits of CaCO2 throughout the system. Known as travertine

Travertine

Travertine is a form of limestone deposited by mineral springs, especially hot springs. Travertine often has a fibrous or concentric appearance and exists in white, tan, and cream-colored varieties. It is formed by a process of rapid precipitation of calcium carbonate, often at the mouth of a hot...

 and tufa

Tufa

Tufa is a variety of limestone, formed by the precipitation of carbonate minerals from ambient temperature water bodies. Geothermally heated hot-springs sometimes produce similar carbonate deposits known as travertine...

, these deposits are formed as a function of the dynamic groundwater and geology of the region. Tufa is known throughout the geologic collective as the soft and porous CaCO3 deposits associated with moving freshwater environments. Travertine is a related deposit separated by the fact that it is associated with thermal waters. Deposition of tufa is complex, involving processes of dissolution

Dissolution (chemistry)

Dissolution is the process by which a solid, liquid or gas forms a solution in a solvent. In solids this can be explained as the breakdown of the crystal lattice into individual ions, atoms or molecules and their transport into the solvent. For liquids and gases, the molecules must be compatible...

, saturation

Saturation (chemistry)

In chemistry, saturation has six different meanings, all based on reaching a maximum capacity...

, subsurface transport

Groundwater

Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

, emergence and precipitation

Precipitation (chemistry)

Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...

. Both versions of precipitated CaCO3 are present in the Portneuf watershed. Several very different but related processes control the precipitation of CaCO3 in natural aqueous systems. The chemical processes are driven by the chemical properties of the elements and molecules involved. The physical processes are driven by characteristics of the watershed system (gradient, flow, substrate, groundwater flow properties). The biotic processes are driven by the activities of living organisms.

Chemical processes

Calcium carbonate formations are associated with regions where meteoric waters become enriched with calcium carbonate by direct dissolution of CaCO3-rich rocks underground only to resurface and re-precipitate calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

. It is well known that the geology of the Portneuf watershed contains numerous large limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 and dolomite

Dolomite

Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....

 rock sequences that are mostly Paleozoic

Paleozoic

The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...

. Enrichment of CaCO3 in the meteoric waters is due to the addition of CO2 either through interaction with the atmosphere, or infiltrating through organic compound containing soil layers. This saturation of CO2 in the groundwater allows for the dissolution of carbonate rocks as it drives pH down. As the water reemerges it is exposed to the atmosphere and the concentration gradient of CO2 associated with it. As the enriched waters attempt to achieve equilibrium they precipitate calcite, through the reaction of Ca+2 + 2HCO− ⇔ CO2↑ + H2O+ CaCO3↓.The mountains surrounding the Portneuf are characterized by thick Paleozoic limestone deposits rich in carbonates, and many springs do emerge along the reach associated with Lava Hot Springs.

Physical processes

Another factor affecting the precipitation of tufa are the physical aspects of the river system. The gradient of the Portneuf through Lava Hot Springs is such that this reach is dominated by a series of riffles with some larger falls. This turbulence and increased surface area caused by aeration facilitates the out gassing of CO2, thus increasing the saturation of CaCO3 to the point of precipitation. This is a phenomenon noticed throughout the world as the development of waterfall tufa and is a relevant explanation for at least some formation through the region, especially through the town site of Lava Hot Springs. The figure below is a schematic representation of the stream gradient of the Portneuf from just below Chesterfield Reservoir and above American Falls Reservoir adapted from Minshall, 1973.

Biotic processes

The third recognized mechanism for tufa development is the active role played by the biota. Algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

 and moss

Moss

Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...

es, along with higher plants and some insects, often trap tiny particles within their sinuous roots, fronds, and shelter/feeding structures, acting as nucleation points for further precipitation. This may explain some of the deposition locations, but the biota plays a larger role as photosynthetic plants remove CO2 from the water, further concentrating the Ca2 CO3 and driving precipitation. The Portneuf through this reach is rich in plant life not only due to the nutrient accumulation as it travels through farmland but from the warm water inputs that protect the stream from the effects of the harsh cold of winter temperatures. This could be a mechanism for potentially increasing tufa formation through the reach. An interesting study completed in 1972 showed evidence that the development of tufa and travertine filled the interstices normally found on the rocky river. This had implications for some burrowing organisms as well as nutrient cycling.

Precipitation of tufa in the Portneuf drainage is produced through the combination of four complex mechanisms: dissolution of limestones by meteoric waters containing carbonic acids, degassing of CO2 at turbulent sites, the removal of CO2 by photosynthetic plants, and the trapping of particles of CaCO3 by the biota. The complex interactions between these different mechanisms may never be fully understood but offer insight into occurrence of formations.