The Stroud Preserve Reforested Riparian Buffer

Project Design

Nonpoint Source Control Strategy

A riparian forest buffer system was established in Morris Run (the treatment watershed) in April of 1992, in accordance with the specification published by the U.S.D.A. Forest Service (Welsch 1991, Publication NA-PR-07-91). Seedlings of Sugar Maple, Red Oak, Tulip Poplar, White Ash, Black Walnut, and Trembling Aspen were planted in a zone extending 23 meters (75 feet) from the stream bank on each side and upslope from its source. Prior to the planting, the buffer area consisted of mowed grass, some tilled area, and a narrow riparian strip (3-10 m) of hardwood trees and brush. Maintenance of the riparian buffer includes replacement of mortality (drought and deer damage), use of tree-tubes and wire tree protectors, and annual application of glyphosate around each tree.

Level lip spreader

The level-lip spreader in Zone 3 after construction in 1994. Reforested area (Zone 2) appears to the left of the spreader.

An additional 6 meters (minimum) beyond the reforested buffer is maintained as grassland, representing “Zone 3” of the Riparian Buffer specification. In accordance with this specification, the grassland zone was contoured in late May 1994 to form a level-lip spreader, designed by the NRCS. The purpose of the spreader is to intercept surface runoff, which is delivered to the buffer via grassed waterways, and to release the runoff to the forested buffer as dispersed sheet flow in order to minimize erosion within the buffer.

Other nonpoint source control measures applicable to both the treatment and control watersheds include contoured strips, waterways, and crop rotations in accordance with a soil conservation plan developed by the NRCS.

Water Quality Monitoring

The monitoring program is based on a paired watershed design. Although the riparian forest buffer was established in the first year of monitoring, the first several years (prior to rapid tree growth) serve as a calibration period to establish the pre-implementation comparison between the treatment and reference watersheds. To supplement the paired watershed design, nutrient and sediment retention by the riparian buffer are estimated by mass balance, using data from groundwater monitoring wells and overland flow collectors.

Parameters Measured

Biological Chemical and other Covariates
None Suspended solids (SS) Precipitation
  Volatile Solids Streamflow
  Dissolved nitrate+nitrite Groundwater level
  Dissolved ammonia Streamwater temperature
  Dissolved organic nitrogen, (discontinued 4/02) Basal area of woody vegetation within riparian zone
  Total phosphorus  
  Total dissolved phosphorus, (discontinued 4/02)  
  Dissolved orthophosphate  
  Dissolved organic carbon, (discontinued 4/02)  

Sampling Scheme

Streamwater samples are collected every 14 days throughout the year from all three streams. Discharge is continuously monitored at all three streams using v-notch weirs. Intensive sampling of streamwater during runoff events is conducted eight times annually from Morris Run and Mine Hill Run. Groundwater is sampled quarterly from 27 monitoring wells. Overland flow in Morris Run watershed is collected from four events annually.

Modifications Since Project Start

The monitoring program described above was implemented 1 April 1997, when the project was accepted for the National Monitoring Program. The monitoring program prior to 1 April 1997 differed from the current program in the following respects: Between January 1992 and 1 April 1997, regular grab samples from all three streams were taken for nitrate, dissolved ammonium, dissolved orthophosphate, conductivity, and pH, at a frequency of 18-24 times per year. Particulate phosphorus and total dissolved phosphorus were sampled regularly from October 1993 through September 1994. Dissolved organic nitrogen was not sampled regularly prior to April 1997. Sampling for suspended solids began in late 1993 for Morris Run and Half Way Run, and March 1995 in Mine Hill Run. Seven runoff events were sampled in Morris Run between November 1993 and June 1995 in Morris Run.

Beginning in March 1999, the target rate for sampling runoff during storm events (rainfall > 20 mm) was increased from four per year to eight per year, while the number of samples analyzed from each event was reduced from ten to four.

As of April 2002, monitoring intensity was reduced because tree growth and canopy closure has been slower than expected and further effects of reforestation may not be apparent until substantially more tree growth occurs. Monitoring continues at a level sufficient to detect an impact on baseflow water chemistry when it occurs. Intensive sampling of stormwater exports and overland flow, however, will be suspended until the riparian forest has matured sufficiently to expect measurable effects on these processes. It is anticipated that such maturation will require two to four years and that monitoring of stormflow and overland should resume at that time.

Also in April 2002, analyses for the following constituents were discontinued: dissolved organic carbon (DOC), total dissolved phosphorus (TDP), and dissolved organic nitrogen (DON). Ammonium analyses of groundwater samples were also discontinued, but ammonium analyses of surface water samples will continue.

In April 2005, sampling of stream water and overland flow during storms was reinstated in response to a rapid increase in tree growth that occurred between 2001 and 2005.  Five storm events were captured during 2005 including one overland flow event.

Basal area of trees in Zone 2 of the Morris Run Reforested Buffer

Progress To Date

Reforestation of the riparian area was initiated and completed in 1991 and the level-lip spreader was installed in 1994. Tree growth during the first seven years, 1992-1999, was lower than anticipated, attributable to both drought and deer-damage.

As of 1998 woody basal area within the reforested buffer was 0.15 m2 ha-1 or <1% of the expected (mature forest) basal area of 20-60 m ha-1.

Reforested buffer (Zone 2) in 2005.

Beginning in 1998, aggressive measures were instituted to assure vigorous forest development. These included annual herbicide (glyphosphate) treatment of each tree, installation of 5-foot plastic tree protectors (in place of 4-foot protectors) and wire mesh tree enclosures, application of deer repellants, and the planting of relatively mature trees to replace mortality, especially into critical remaining gaps.

Since 1999, tree growth has been rapid. Woody basal area increased to 0.65 m2 ha-1 in 2001 and 2.49 m2 ha-1 in 2005. Canopy closure by the 2005 growing season was 67%.