springs classification
TWELVE TYPES OF SPRINGS
Until recently, there has been no consistent and comprehensive classification system or common lexicon for springs. Springer and Stevens (2008) defined 12 spheres of discharge, describing their hydrogeology of occurrence, and the microhabitats and ecosystems they support. A few of the spheres of discharge had been previously recognized and used by hydrogeologists for over 80 years, but others had only recently been defined geomorphologically. Springer and Stevens provided a comparison of these spheres of discharge to classification systems for wetlands, groundwater dependent ecosystems, karst hydrogeology, running waters, and other systems. With a common lexicon for springs, hydrogeologists can offer more consistent guidance for springs ecosystem conservation, management, and restoration.
As additional comprehensive inventories of the physical, biological, and cultural characteristics are conducted and analyzed, it will eventually be possible to associate spheres of discharge with discrete vegetation and aquatic invertebrate assemblages, and better understand the habitat requirements of rare or unique springs species. Given the elevated productivity and biodiversity of springs, and their highly threatened status, identification of geomorphic similarities among spring types is essential for conservation of these important ecosystems.
Dichotomous Key
Stevens and Springer (2009) identified 12 springs types, then further refined them in 2021 in Ecological Applications along with a dichotomous key. See: Stevens, L.E., E.R. Schenk, and A.E. Springer. 2021. Springs ecosystem classification. Ecological Applications 31 : e2218. https://doi.org/10.1002/eap.2218.
Table 1. A dichotomous key to terrestrial springs types (Stevens et al. 2020). All springs can have more than one springs type, and all springs types can be perennial or ephemeral (i.e., secondarily hypocrene).
1 | Groundwater expression of flow is subterranean, emerging within a cave (a water passage, often through limestone or basalt), before emerging into the atmosphere or subaqueously into a surface pool or channel. Lentic (standing or slow-moving) and/or lotic (fast-moving) flow conditions can exist. | |
Groundwater expression of flow emerges or emerged in a subaerial setting (in direct contact with the atmosphere), including within a sandstone alcove or subaqueously (beneath a body of water), but not from within a cave. Lentic and/or lotic flow conditions can exist. | 2 | |
2 | Groundwater is not expressed at the time of visit (the springs ecosystem is not flowing; the soil may be dry or moist, but not saturated). | 3 |
Groundwater is expressed at the time of visit; saturation, seepage, and/or flow are actively expressed (water and/or saturated soil are evident); Lentic and/or lotic flow conditions can exist. | 5 | |
3 | Evidence of prehistoric groundwater presence and/or flow exists (e.g., paleotravertine, paleosols, fossil springs-dependent species, etc.), but no evidence of contemporary flow or aquatic, wetland, or riparian vegetation. | Paleospring |
Not as above. | 4 | |
4 | Soil is dry or moist but is not saturated by groundwater. Groundwater is expressed solely through wetland or obligate riparian vegetation. | |
Groundwater is expressed through saturated soil, or as standing or flowing water. Lentic and/or lotic flow conditions can exist. | 5 | |
5 | Groundwater is expressed, but discharge is primarily lentic (standing or slow-moving), and flow downstream from the springs ecosystem may be absent or very limited. | 6 |
Groundwater is expressed; discharge is primarily lotic (fast-moving) and flows actively within and/or downstream, away from the springs ecosystem. | 11 | |
6 | Groundwater is expressed as a patch of shallow standing water or saturated fine sediment or soil, usually strongly dominated by hydric soils and emergent herbaceous wetland vegetation, but sometimes can include woodland or forest vegetation (e.g., palm oases, swamp forests). The slope is usually low (<16°). These sites are colloquially called wet meadows or ciénegas and include some GDE fens. Lotic flow conditions prevail. | 7 |
Subaqueous flow creates an open, lentic body of water, typically more than a few square meters in area, not dominated by emergent wetland vegetation, and with or without outflow. | 8 | |
7 | A wet meadow with seepage emerging from the margin of an active surface flow-dominated channel or floodplain, and subject to regular flood scour by the stream channel into which it feeds. | Helocrene Spring; secondarily Rheocrene |
A wet meadow with seepage emerging outside and away from an active surface flow-dominated channel or floodplain, and not subject to regular flood scour by a stream. | ||
8 | The groundwater table surface is exposed as a pool with standing water, without a focused inflow source, and with no outflow. Lotic flow conditions exist. Many prairie pothole springs are classified as this springs type. | |
A pool is formed by one or more focused, usually subaqueous, inflow sources; generally with outflow, if not frozen. | 9 | |
9 | Springs source is surrounded by, and has contributed to the formation of, a mound composed of chemical precipitate, (e.g. travertine), ice, or organic matter. Both lentic and lotic flow conditions can occur. | 10 |
Springs source forms an open pool which is not surrounded by a springs-created mineral, ice, or organic mound; often with a focused outflow channel. Lentic flow conditions prevail, but lotic flow may occur in the outflow channel. | ||
10 | Springs source is surrounded by, and/or emerges from a mound composed of carbonate (including travertine) or other chemical precipitate. Both lentic and lotic flow conditions can occur. | Mound-form Spring (Carbonate) |
Springs source is surrounded by, and/or emerges from a mound composed of ice in an ice-dominated landscape. Flow may be seasonal, and both lentic and lotic flow conditions can occur. Also colloquially called pingos or aufweis springs. | Mound-form Spring(Ice) | |
Springs source is surrounded by, and/or emerges from a mound composed of organic matter, such as decomposing vegetation or peat. Lentic flow conditions generally prevail. Some GDE fens are classified as this springs type. | Mound-form Spring(Organic) | |
11 | Springs flow emerges explosively and periodically, either by geothermally-derived or gas-derived pressure. Lotic flow conditions generally prevail. This springs type includes geothermal geysers and “coke-bottle” (CO2 gas-driven geysers) | |
Springs flow emerges non-explosively, but by the action of gravity. | 12 |
12 | Artesian flow emerges from one or more focused points and rises 10 cm or more above ground level due to gravity-driven head pressure. After the flow falls to the ground, lentic or lotic flow conditions may prevail. Colloquially called artesian springs. | |
Springs flow may emerge from a focused point, but without substantial artesian rise above ground level. | 13 | |
13 | Springs flow emerges from a bedrock cliff and not within an established surface flow channel (although a surface flow channel may exist on top of the cliff, directly above the source). | 14 |
Not as above. | 15 | |
14 | Focused lotic flow emerges from a bedrock cliff and immediately cascades, usually as a madicolous sheet of whitewater flow, down the cliff face. | |
Flow emerges along a horizontal geologic contact, typically dripping along a seepage front and often creating a wet backwall. This springs type includes unvegetated or vegetated seepage patches on near-vertical or overhung bedrock walls. Both lentic and lotic flow conditions can occur. | ||
15 | Flow emerges from a surface flow-dominated channel bed. Upstream of the spring source, the channel may be a perennial stream or it may be dry. Lotic flow conditions generally prevail. These springs are subject to channel flood scour. | |
Flow emerges from a non-bedrock dominated slope that does not have a surface flow channel upslope of the springs source. Sources may emerge within an upland habitat or a floodplain, but not within the bed of a surface flow channel. In some cases, these springs may emerge from the base of a cliff, but not from the cliff itself. Lotic flow conditions generally prevail. | 16 | |
16 | Flow emerges from a 16-60° slope in an uplands habitat, not associated with a floodplain or channel that is subject to regular surface flow stream flood scouring. | |
Flow emerges from the bank or terrace of an active riparian channel or floodplain and the source is subject to regular flood scour by the stream into which it feeds. | Hillslope Spring; secondarily Rheocrene |