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The Eastern Division is currently working on stream and lake aquatic habitat classifications.  The resulting habitat maps and datasets unite the disparate state classification systems into a single scheme for analysis of stream and lake processes, freshwater conservation, and climate change and scenario modeling.

Stream Classification


  • Northeast Habitat Guides: Simplified Aquatic Habitat Classification and Guide: This project simplified the original northeast aquatic habitat classification (original report and data here) to produce a  new user-friendly classification with simplified types, descriptions, pictures, distribution maps, and associated species and crosswalks (Website). 
  • Appalachian LCC Classification: Funded by the Appalachian LCC, this project will create a mapped stream classification linking parts of 17 states into a unified system (Expected December 2014; website).
  • Southeast Aquatic Resources Partnership Classification: This project created a stream classification database for 15 states in the southeast and lower central U.S. (SARP website, Report)



Basic stream classification methodology:

Within freshwater ecoregions, there are finer-scale patterns of stream channel, size, gradient, substrate, temperature, watershed physiography, and local zoogeographic sources that influence aquatic biological assemblages. These differences, along with variation in water temperature and tidal influence, create particular physical habitat templates for freshwater biota. The primary classification variables of size, gradient, geology, temperature, and tidal regime define a set of major stream and river habitat types. All five variables influence stream and river habitats; however, some were more important in structuring stream habitats versus riverine habitats. Tidal habitats were split by three size classes.

Stream size has been given the highest classification importance in many reach-scale stream classification systems because of its strong effect on determining aquatic biological assemblages at the reach scale. Although stream size is a primary classification variable, not all size classes have equal influence on stream composition. To highlight the predominant patterns in the stream biota the NE habitat guide focuses on four major differences in size: headwaters and creeks, small rivers, medium rivers, and large rivers.
Habitat Guide Size Classes Definition (sq.mi.) Definition (
Headwaters and Creeks Less than 38.6 Less than 100
Small Rivers 38.6 - 200 100 - 518
Medium Triburary Rivers 200 - 1000 518-2590
Large Rivers Greater than 1000 Greater than 2590

Stream gradient highly influences aquatic communities at the reach scale due to its influence on stream bed morphology, flow velocity, sediment transport/deposition, substrate and grain size. To highlight the predominant patterns in the stream and river biota the NE habitat guide uses three gradient classes for headwaters and creeks, and two gradient classes for rivers.

Geology and buffering capacity
Aquatic organisms need water pH to be within a certain range for optimal growth, reproduction, and survival. Most aquatic organisms prefer a pH of 6.5-8. Streams and lakes with calcium carbonate concentrations less than 2 mg/L and pH levels below five no longer support fish and many other forms of aquatic biota. Water chemistry parameters such as pH and acid neutralizing capacity (ANC) are strongly influenced by the minerals and ions that leech out of underlying bedrock and surficial material. To highlight the influence of buffering capacity on stream types, each stream and small river reach in the NE habitat guide was placed into one of three buffering capacity classes based on upstream watershed bedrock geology.

Stream temperature has been noted as a key stream classification variable as it sets the physiological limits where stream organisms can persist. Seasonal changes in water temperature often cue migration, influence growth rates of eggs and juveniles, and can affect the body size and therefore the fecundity of adults. To highlight the predominant effect of water temperature on structuring aquatic biological communities, streams and rivers in the NE habitat guide were placed into one of three temperature classes.

Tidal classes

Streams and rivers that connect directly to the ocean or to large tidal river estuaries are influenced by ocean tides. Their water level and flow fluctuates with the tides, and salinity can range from freshwater (0 to 0.5 ppt salinity), to brackish (0.5 to 18 ppt), to saline (18 to 30ppt or greater), depending on the extent of tidal influence along the length of the reach. In tidal rivers there is also a vertical salinity gradient, with a surface layer of fresh water (salinity less than 0.5 ppt) floating over a deeper layer of brackish water (salinity between 0.5 and 18.0ppt). Streams and river reaches with potential tidal influence in the NE habitat guide were placed into three size categories for the habitat guide. These groupings were based strongly on the distribution of anadromous fish, which vary in their preference for size of tidal river or stream.

Map of the 23 stream types from the Northeastern Aquatic Habitat Guide. Click for a larger image.

















Lake Classification


 Northeast Lake Classification: This project developed a mapped classification of lakes and ponds for 13 states in the northeastern United States.  Key classification variables include trophic state, light penetration zone, presence of coldwater habitats, and alkalinity class. The project also developed related condition information such as the impoundment status and type of associated dams, impervious surfaces and basic measures of human alteration to landcover around the waterbody. Expected delivery October 2014. 




Basic Lake Classification Attributes and Ecological Significance

Trophic Status
Lakes are often classified by their trophic state, which is often defined by chlorophyll, total phosphorus, and Secchi transparency. The  concentrations of these variables can be a surrogate for actually measuring algal biomass.  This classification scheme used chlorophyll-a concentrations to define trophic class, as that is the predominant type of chlorophyll found in green plants and algae, based on recommendations from the National Lake Assessment at the Steering Committee for this project.  The four trophic classes used in this classification system are:
1. Oligotrophic, which are nutrient-poor and clear lakes,
2. Mesotrophic, which fall somewhere in between Oligotropihic and Eutrophic,
3. Eutrophic, which are nutrient-rich and have high rates of primary production,
4. Hypereutrophic, which are very high nutrient lakes  often resulting from an excess of human activity .
Buffering Capacity
Alkalinity and acid neutralizing capacity (ANC) are measures of how well compounds like bicarbonate ions can buffer lake waters from acidity.  The higher a lake’s alkalinity or ANC, the greater its resistance to acidification.  Lake acidification disrupts the life cycles of fish and other aquatic organisms and intensifies the mobilization and bioaccumulation of toxic mercury compounds in the food web.  Most aquatic organisms need water pH to be within 6.5-8 for optimal growth, reproduction, and survival. Lakes with alkalinity concentrations less than 2 mg/L and pH levels below 5 no longer support fish and many other forms of aquatic biota.  Fish that can tolerate some acid conditions include yellow perch, brown bullhead, and brook trout; however brook trout will not spawn if waters are too acidic.  Alternatively, acid intolerant fish of the northeast include the blacknose dace and creek chub, which cannot tolerate pH below 6.0-5.5.  The northeast lake classification recognizes three classes of buffering capacity: low, medium, and high, based on alkalinity values.
A lake’s temperature and concentration of dissolved oxygen influence what types of fish can live and reproduce in that lake. The northeast lake classification recognizes four types of lakes based on the presence of cold to warm available habitats. These include lakes with 1) very cold, 2) cold, 3 cold-cool, and only 4) warm habitats .
Lake-Pond split
For this study, the split between lakes and ponds was defined based on the degree of light penetration, using maximum depth as a proxy for this  zone. Because thresholds in light penetration are not independent of trophic state, we classified the pond depth threshold as follows: Oligotrophic less than 30ft, mesotrophic  less than 20ft, and eutrophic less than 10ft .





Class Definition Direct Measures Used
Trophic Class

National Lake Assessment breaks in Chlorophyll-a.

 1. Oligotrophic: <= 2 ug/l,

2. Mesotrophic >2 -7 ug/l,

3. Eutrophic >7-30 ug/l, and

4. Hypereutrophic >30 ug/l. <="2"/>

Chlorophyll a (July-Aug)
Alkalinity Class

1. Low Alkalinity <12.5 mg/L

2. Medium Alkalinity >=12.5 & < 50 mg/L

3. High Alkalinity >=50 mg/L

Temperature Class

Presence of greater than 1 meter of following habitat throughout the summer (use July/August profile if available)

1. VERY COLD: <12.8C and >=5 mg/l DO or indicator fish = lake trout reproduction

2. COLD: 12.8C<=18C, >=5 mg/l DO or indicator fish = wild brook trout reproduction

3. COLD-COOL: >18<=21C, >=4 mg/l DO : or indicator fish = holdover or reproduction of brown trout, kokanee, smelt

4. WARM >21C

temperature-dissolved oxygen depth profiles, indicator fish reproduction
Lake or Pond Class

1. Ponds

2. Lakes

Ponds have light penetration to the bottom. Because thresholds in light penetration are not independent of trophic state, we classified the pond depth threshold as follows: oligotrophic<30ft, mesotrophic <20ft, and eutrophic <10ft .

maximum depth, trophic state
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