Par Pond vegetation status Summer 1995 -- June survey descriptive summary

The water level of Par Pond was lowered approximately 20 feet in mid-1991 in order to protect downstream residents from possible dam failure suggested by subsidence on the downstream slope of the dam and to repair the dam. This lowering exposed both emergent and nonemergent macrophyte beds to drying conditions resulting in extensive losses. A survey of the shoreline aquatic plant communities in June 1995, three months after the refilling of Par Pond to approximately 200 feet above mean sea level, indicated that much of the original plant communities and the intermediate shoreline communities present on the exposed sediments have been lost. The extensive old-field and emergent marsh communities that were present on the exposed shoreline during the drawdown have been flooded and much of the pre-drawdown Par Pond aquatic plant communities have not had sufficient time for re-establishment. The shoreline does, however, have extensive beds of maidencane which extend from the shoreline margin to areas as deep as 2 and perhaps 3 meters. Scattered individual plants of lotus and watershield are common and may indicate likely directions of future wetland development in Par Pond. In addition, within isolated coves, which apparently received ground water seepage and/or stream surface flows during the period of the Par Pond draw down, extensive beds of waterlilies and spike rush are common. Invasion of willow and red maple occurred along the lake shoreline as well. Although not absent from this survey, evidence of the extensive redevelopment of the large cattail and eel grass beds was not observed in this first survey of Par Pond. Future surveys during the growing seasons of 1995, 1996, and 1997 along with the evaluation of satellite date to map the areal extent of the macrophyte beds of Par Pond are planned.


Introduction
Par Pond, a 2500-acre (1012-hectare) cooling water reservoir on the Savannah River Site (SRS), was created in 1958 by constructing an earthen dam across the upper reaches of the Lower Three Runs drainage system ( Figure 1) (Wilde andTilly 1985). Par Pond served as a recirculating, cooling water reservoir for R-Reactor until 1963 and for P-Reactor from 196 1 -1988. P-Reactor operated approximately 70% of the time prior to 1988. Nutrient-rich make-up water from the Savannah River was pumped into Par Pond to maihtain a constant water level. During the summer, the temperature of the water entering Par Pond from Pond C ranged from 72 to 108" F (22 to 42" C ) (Jones et al. 1979). Maximum shoreline water temperatures in the vi-. cinity of the hot dam ranged from 90 to 95" F (32 to 35" C) (Liu et al. 1978). The thermal effluent cooled rapidly as it dispersed primarily through the southern half of the reservoir (Ezra and Tinney 1985). The north and west arms of Par Pond had temperatures at, or only slightly above, typical lake temperatures for the region (Liu et al. 1978).
The water level of Par Pond remained relatively stable, fluctuating typically less than 0.5 foot (0.15 meter) during most years. Natural invasion of macrophytes in the lake and along the shoreline occurred over the 33-year history of the lake, until mid-199 1, when Par Pond was lowered from 200 feet (61 meters) above mean sea level (MSL) to 181 feet (55 meters) above MSL during a twomonth period. Lowering the water level was deemed necessary to protect downstream residents from possible dam failure suggested by subsidence on the downstream slope of the dam. Prior to lowering the water level in 1991, Par Pond was bordered by extensive beds of persistent and nonpersistent aquatic macrophytes. These beds often exceeded 66-13 1 feet (20-40 meters) in width (shoreline to deep water) and in several areas exceeded 328 feet (100 meters In 1987, 62 transects were established along the shoreline of Par Pond (Jensen et a]., 1991(Jensen et a]., , 1992a(Jensen et a]., , 1992b(Jensen et a]., , 1993Jensen and Mackey 1991;Narumalani 1993). The dominant aquatic macrophyte patterns were recorded each spring (April or May) and fall (September or October) from 1988 through June 199 1, just prior to the lowering of the Par Pond water level. In these previous studies, the major species present in both the persistent (emergent, i.e., cattails) and nonpersistent (floating-leafed, i.e., water lily, lotus [Nelumbo lutea]) macrophyte categories were recorded, along with the width of each bed along the transects and estimates of percent cover by species at each transect. Spring and fall SPOT satellite data also were collected and analyzed for the 1988-199 1 time period to provide estimates of area of coverage by major aquatic macrophyte category for the lake. These methods and data are summarized in the above-mentioned references.
Beginning occurring on about 65% of the exposed lake bed with approximately 35% still barren. Grasses, sedges, and rushes were the dominant forms with a mixture of old-field species, including dog-fen-ne1 (Eupatorium sp.) and loblolly pine (Pinus taeda) invasion, which became more evident after spring 1993. In isolated pockets within coves of Par Pond, sufficient groundwater seepage or inflow from small streams allowed remnants of the Par Pond macrophyte communities to survive (e.g., beds of water lilies in the cove south of the Par Pond pump house [ Figure 13) as evident in late April 1995 vertical aerial photography. In mid-October 1994, after dam repairs were complete, the U.S. Department of Energy initiated the refill of Par Pond and by mid-March 1995, Par Pond approached its former full pool level of approximately 200 feet (61 meters) above MSL ( Figure   2). The Par Pond water level has remained relatively constant since refill.

Methods
Of the 62 transects along the Par Pond shoreline in June 199 1,48 were relocated in March 1995. Descriptive notes on the vegetation patterns at each transect were taken in June 1995 to indicate the condition of any standing vegetation following refill and initial regrowth of macrophyte communities. Also, photographs of each transect were taken in June 1995. The species present were recorded along with a nominal estimate of percentage cover for any species appearing to occupy more than a "trace" (less than 0.1% of the water surface) (Phillips 1959;Mueller-Dombois and Ellenberg 1974). Two zones (an inner and outer zone) were characterized on this initial survey. Both zones started at the transect marker used in 1988-199 1 surveys to mark the boundary between the persistent emergent aquatic beds (i.e., primarily cattails, spike-rush [Eleocharis sp.]) and the nonpersistent floating-leafed macrophytes beds (i.e., water lilies and lotus). The inner zone extended from the transect shoreward and the outer zone extended from the transect to deeper water. Water depth at the transect marker averaged approximately 3.3 feet (1 meter) in previous surveys (Jensen et al. 1991(Jensen et al. , 1992a(Jensen et al. , 1992b(Jensen et al. , 1993Jensen and Mackey 1991;Narumalani 1993).
Baseline, vertical, aerial 9-by-9-inch format, falsecolor infrared photographs of Par Pond were taken in April 1995 from an altitude of 10, OOO feet. These photographs were used as a general reference during the Par Pond surveys, even though little emer-

Results
Since the refilling of Par Pond, most of the oldfield species that had invaded much of the exposed shoreline are dead or dying. For example, numerous dead or stressed loblolly pine were observed in both the outer and inner transect zones (Figure  3; scientific names of all plants are presented in Appendix A). Dead dog-fennel (Eupatorium sp.), broom sedge (Andrupugon virginicus), poke berry (Phytulacca umericunu), briars (Rubus spp.), and other terrestrial plants were observed at the transects. The most common woody species along the Par Pond shoreline before the refill were newly invaded willow (Sulix spp.) and fed maple (Acer rubrum). Extensive maidencane (Punicum hemitumon) beds were observed along the shoreline in both the inner and outer zones. The maidencane had undergone extensive stem elon-gation (Kirkman and Sharitz 1993) in areas of deeper water (1.6 feet, more than 0.5 meter) and was the most common emergent macrophyte in Par Pond during the June 1995 survey. Figure 3 summarizes an estimate of percent Occurrence (number of transects in which a species occurred divided by the total number of transects), and Figure  4 summarizes an estimate of percent cover at the transects for the most common species observed at the transects.

Discussion and Conclusions
The shoreline aquatic vegetation of Par Pond is undergoing rapid redevelopment which is likely to continue. The exact composition of the final community types are speculative at this point. The water chemistry of Par Pond is now likely to be more similar to that of Pond B, which receives only groundwater and runoff, than it was during P-Reactor operations when Savannah River water was routinely pumped to Par Pond. watershield are likely to become more common, and cattails less common, than in the past.
Furthermore, the water level of Par Pond may be allowed to fluctuate naturally as much as 3 to 7 feet (1 to 2 meters). Plants inhabiting areas with changing water levels are subject to a wide range of environmental conditions ranging from near drought to total inundation. Although many wetlands species can survive such fluctuating hydrologic regimes, species tolerances to the hydrologic extremes will determine future community dominance patterns.
Documentation of the relative performances and adaptive strategies of dominant plant species under different hydrological regimes is necessary to develop predictive models of community patterns in freshwater bodies. For example, Kirkman and Sharitz (1993), on studies of maidencane in Carolina bays at SRS, noted that this species survived inundation to 4 feet (1.2 meters) via stem elongation and had percentage cover estimates as high as 30% of this species in water depths to approximately 6 feet (1.7 meters) (Kirkman and Sharitz 1993). Maidencane flower production also was observed under flooding conditions in the same study.
The refilling of Par Pond during spring 1995 apparently did not exceed the rates of stem growth and elongation following the emergence of maidencane in 1995 along much of the formerly exposed Par Pond shoreline. Kirkman and Sharitz (1 993) postulate that increased dominance by maidencane occurs during periods of deep inun-dation during the growing season. Elongation of stems as a result of inundation during the growing season and prior to deepening winter water enables this species to survive greater depths of flooding in winter. However, if the dead stems of maidencane are lost due to wave action during the winter, then areas of maidencane in deep water would not persist. Maidencane, with its dense root system as well as its ability to tolerate more acidic, lower-nutrient water and to adjust to changes in water level, may prove to be a future dominant species of the Par Pond shoreline. If Savannah River water is no longer pumped to Par Pond, the reservoir is likely to become less nutrient-rich and more acidic, similar to lakes whose major source of input is groundwater. However, wave action in deeper, more open water areas of Par Pond may inhibit continued survival and growth of maidencane, especially if the overwintering stem biomass is lost and subject to flooding (Kirkman and Sharitz 1993). Relative drought tolerances infer that maidencane probably would become more prominent in the plant community during natural drawdown or cycling of Par Pond lake levels (Kirkman and Sharitz 1993).
Remnants of the past Par Pond macrophyte communities still exist in portions of the north arm, the west arm, and in isolated coves that received drainage during the four years of the drawdown and may continue to persist for years to come, as do the-large water lily and lotus beds in the northern protected coves of Pond B. Two to three years of surveys should provide good evidence of the likely direction the Par Pond communities will take in their development. Polygonum sp.