| Code | Description |
| Lacustrine | Includes wetland and deepwater habitats with all of the following characteristics: (1) situated in a topographic depression or a dammed river channel; (2) lacking trees, shrubs, persistent emergents, emergent mosses or lichens with greater
than 30% areal coverage; and (3) total area exceeds 8 hectares
(20 acres). Similar wetland and deepwater habitats totaling less
than 8 hectares are also included if an active wave-formed or
bedrock shoreline feature makes up all or part of the boundary,
or if the deepest part of the basin exceeds 2 m (6.6 feet) at
low water. Lacustrine waters may be tidal or nontidal, but
ocean-derived salinity is always less than 0.5 ppt. |
| Lacustrine, limnetic | All deepwater habitats within the Lacustrine System. Many small Lacustrine systems have no Limnetic Subsystem. |
| Lacustrine, littoral | All wetland habitats in the Lacustrine System. Extends from the shoreward boundary of the system to a depth of 2 m (6.6 feet) below low water or to the maximum extent of nonpersistent emergents, if these grow at depths greater than 2 m. |
| Palustrine | Includes all nontidal wetlands dominated by trees, shrubs, persistent emergents, emergent mosses or lichens, and all such wetlands that occur in tidal areas where salinity due to ocean-derived salts is below 0.5 ppt. It also includes wetlands lacking such vegetation, but with all of the following 4 characteristics: 1) area < 8 hectare (20 acres); 2) active
wave-formed or bedrock shoreline features lacking; 3) water
depth in the deepest part of basin less than 2m at low water;
and 4) salinity due to ocean-derived salts < 0.5 ppt. |
| Riverine | Includes all wetlands and deepwater habitats contained within a channel, with two exceptions: (1) wetlands dominated by trees,
shrubs, persistant emergents, emergent mosses, or lichens, and
(2) habitats with water containing ocean-derived salts in excess
of 0.5 ppt. A channel is "an open conduit either naturally or
artificially created which periodically or continuously contains
moving water, or which forms a connecting link between two
bodies of standing water" (Langbein and Iseri 1960:5). |
| Riverine, tidal | The gradient is low and water velocity fluctuates under tidal influence. The streambed is mainly mud with occasional patches
of sand. Oxygen deficits may sometimes occur and the fauna is
similar to that in the Lower Perennial Subsystem. The floodplain
is typically well developed. |
| Riverine, lower perennial | The gradient is low and water velocity is slow. There is no tidal influence, and some water flows throughout the year. The
substrate consists mainly of sand and mud. Oxygen deficits may
sometimes occur, the fauna is composed mostly of species that
reach their maximum abundance in still water, and true
planktonic organisms are common. The gradient is lower than that
of the Upper Perennial Subsystem and the floodplain is
well-developed. |
| Riverine, upper perennial | The gradient is high and velocity of the water fast. There is no tidal influence and some water flows throughout the year. The substrate consists of rock, cobbles, or gravel with occasiona patches of sand. The natural dissolved oxygen concentration is normally near saturation. The fauna is characteristic of running water, and there are few or no planktonic forms. The gradient is high compared with that of the Lower Perennial Subsystem, and
there is very little floodplain development. |
| Riverine, intermittent | The channel contains nontidal flowing water for only part of the year. When the water is not flowing, it may remain in isolated pools or surface water may be absent. |
| Riverine, unknown perennial | See R2 and R3 for information. |
| Upland | |
