Click for classification map.
The Eastern Division is currently working on four aquatic habitat classifications. The resulting habitat maps and datasets unite the disparate state classification systems into a single scheme for analysis of stream processes, freshwater conservation, and climate change and scenario modeling.
- Northeastern Habitat Classification: This project created a single mapped stream classification linking 13 state classifications into a unified system (Report and data available on RCN grants page).
- 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)
- Northeast Habitat Guides: Simplified Aquatic Habitat Classification: This project simplified the original northeast habitat classification to produce a user-friendly document with simplified types, descriptions, pictures, distribution maps, and associated species and crosswalks (Website).
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
|Headwaters and Creeks
||Less than 38.6
||Less than 100|
||38.6 - 200
||100 - 518|
|Medium Triburary Rivers
||200 - 1000
||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.
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.
Geology and buffering capacity
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.
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 in the northeastern United States. Click for a larger image.