Herbaceous seepage marsh (S3)
Herbaceous seepage marsh communities occur in a variety of settings where minerotrophic groundwater discharge is prominent. They are often found near upland borders of various wetland types, in headwater positions, along stream drainages (including the interface of a drainage with a larger marsh), or in other areas where groundwater discharge is prominent. They tend to be larger than forest seeps and usually have little tree canopy (except along their borders). While technically a marsh, these communities are intermediate between fens and marshes, both floristically and environmentally. They contain a mixture of graminoids, forbs, and ferns including indicators of seepage and minerotrophic conditions. Some examples also have a moderate cover of alder and may be successional to alder wooded fen.
Soils consist of shallow peat or fibric muck organic layers over silt or silty muck. Mosses may be abundant but Sphagnum is generally absent. Lake sedge seepage marsh is a similar community that is dominated by lake sedge (Carex lacustris). Soils tend to be shallow fibric peats or mucks over silty muck, silt, or silty sands. In four examples, pHs range from 5.5 to 6.3, indicating subacid to circumneutral conditions.
Characteristic Vegetation: Dominant species indicative of seepage or minerotrophic conditions include sensitive fern (Onoclea sensibilis; high frequency among known examples), lake sedge (Carex lacustris), spotted Joe-pye-weed (Eupatorium maculatum), royal fern (Osmunda regalis), marsh fern (Thelypteris palustris var. pubescens), skunk cabbage (Symplocarpus foetidus), swamp saxifrage (Saxifraga pensylvanica), and rough sedge (Carex scabrata).
Other minerotrophic indicators are usually present in lower abundance and may include Robbins’ ragwort (Senecio robbinsii), water pennywort (Hydrocotyle americana), golden saxifrage (Chrysosplenium americanum), awl sedge (Carex stipata), delicate sedge (Carex leptalea), leek-green drooping sedge (Carex prasina), spotted touch-me-not (Impatiens capensis), field mint (Mentha arvensis), poison sumac (Toxicodendron vernix), white turtlehead (Chelone glabra), swamp candles (Lysimachia terrestris), and water horsetail (Equisetum fluviatile).
Other occasionally abundant species indicative of at least weakly minerotrophic conditions may include bluejoint (Calamagrostis canadensis), field horsetail (Equisetum arvense), purple-stemmed aster (Symphyotrichum puniceum), marsh cinquefoil (Comarum palustris), meadowsweet (Spiraea alba), and wire sedge (Carex lasiocarpa). In general, mosses may be abundant in this meadow-like wetland, and include include Mnium spp. and Philonotis
Good examples of this community occur at College Woods (
Herbaceous seepage marshes sometimes occur as part of larger emergent marsh - shrub swamp systems.
Herbaceous seepage marsh at Great Bay National Wildlife Refuge (photo by Ben Kimball)
Herbaceous seepage marsh at UNH's College Woods
(photo by Ben Kimball)