Ripple Trough wetlands occur in the valleys in the Meadow and Beaver Lakes Area. These uniquely arranged hills and valleys were apparently created by the waves formed during a huge glacial outburst flood. The features have also been called ribbed moraine, specifically Rogen. Rogen are formed by deformation of till beneath a glacier.

Many ripple troughs support lakes, the largest of which is 230 acre Seymour Lake. Ripple trough lakes are of relatively uniform depth; all of them are about 20 feet deep. Lakes are defined as areas of standing water greater than 20 acres (and deeper than six feet). Lakes are mapped separately from wetlands.

Ripple Trough Ecosystem wetlands are peatlands. They often support a bisecting stream. Because the adjacent glacial sediments are coarse-grained cobbles and gravels which allow rapid groundwater transmission, ripple trough peatlands are fens, at least toward the east. They should receive ample shallow groundwater discharge near the surface. Accordingly, they usually show higher pH and specific conductance values (table 1.).

However, Ripple Trough peatlands segregate into both bogs and fens. Eastward, where precipitation barely exceeds evapotranspiration, fens dominate. Westward, Ripple Trough peatlands support bogs atop fen peat. Bogs have lower pH (less than about 4.2) and specific conductance (less than about 50 µS at 25°C) and lack fen indicator plant taxa. In the Matanuska-Susitna Valley, bogs are often forested by black spruce (Picea mariana), with a dense shrubby leatherleaf (Chamaedaphne calyculata) and/or Labrador tea (Ledum palustre ssp. decumbens) understory. Many burned in the 1996 Miller's Reach Fire.

Bogs result because precipitation is in ample excess of evapotranspiration. This climatic condition allows certain sphagnum moss species, especially S. papillosum and S. fuscum to thrive. When thick enough, these mosses can hold a mound of precipitation-derived shallow groundwater above groundwater discharging from beneath. The condition of a mound of meteoric groundwater above shallow groundwater discharge results in a zone within the peat profile where head reversals occur. In this zone, the meteoric water from the sphagnum mound sometimes recharges to below, while at other times groundwater discharges to it. Wet conditions favor recharge from above and dry conditions favor discharge from below. Water chemistry in the zone varies accordingly.

Explanation:

Peat depth is a minimum, because some sites had thicker peat deposits than the length of the auger used (usually 493 cm).

Water table depth is a one time measurement. At sites with seasonally variable water tables this measurement reflects both the conditions that year, and the time of year.

Redox features with low n and deep depths typically indicate deeper peat deposits, which mask redox indicators.

pH and specific conductance measured in surface water or a shallow pit with a YSI 63 meter calibrated each sample.

Plant Prevalence Index calculated based on Alaska indicator status downloaded from the USDA PLANTS database, which may use different values than the 1988 list.

Explanation:

Soils from 1998 Soil Survey of the Matanuska-SusitnaValley Area, Alaska, available online, follow the link in the table heading.

Plant communities based on Kenai Peninsula wetland mapping and soil survey, or other published accounts, especially Viereck, et.al., 1992.

Ripple Trough Ecosystem Wetland Map Components:

RT1: Ponds in Troughs.

RT2: Trough peatlands with water table near the surface most of the growing season. Often dominated by sedges and/or buckbean.

RT3: Troughs with deeper water table, often dominated by shrubs especially sweetgale and dwarf birch.

RT4: Forested Troughs, deeper, seasonally fluctuating water table, some are bogs.

Map Units currently in use: RT1, RT1-3, RT1-4, RT12, RT1d, RT2, RT2-4, RT23, RT24, RT3, RT32, RT32d, RT34, RT34d, RT3d, RT4, RT43, RT43d, RT4d

Contact: This e-mail address is being protected from spambots. You need JavaScript enabled to view it Kenai Watershed Forum PO Box 15301 Fritz Creek, AK 99603 907-235-2218

2 April, 2009