Abstract

1. NUTRIENT CONCENTRATIONS AND TEMPORAL VARIATIONS: A STUDY OF PHOSPHATES AND NITRATES IN RAYSTOWN LAKE, PA Haley, Christopher J.1, Mutti, Laurence J.1 1Department of Geology at Juniata College Abstract Raystown Lake is a large (3360hm2) reservoir located in Huntingdon County, Pennsylvania. Despite being the largest in the state, it has received only modest attention with concern to its water quality since a post impoundment study written shortly after the reservoir’s completion in the mid-nineteen seventies. The intention of this study was to collect extensive nutrient data, specifically nitrate and phosphate (both total and reactive) values, from Raystown Lake to quantify seasonal variations in nutrient levels, and record nutrient concentrations both vertically and horizontally throughout the lake. Samples were collected in alternate weeks along horizontal and vertical profiles of the lake as well as from four major inputs. Colormetric methods were used to determine total phosphate, reactive phosphate, and nitrate values. The horizontal profile yielded a pattern showing a gradual decline of nitrates through mid summer until fall turnover. A departure from the anticipated pattern was a dramatic decrease in nitrates in early September. This decrease was also observed in the nitrates for the vertical profile, which showed a linear drop in nitrate concentrations at all depths from the start of the sampling in June. The nitrates from the vertical profile exhibited a pattern that gives reasonable resolution to the epilimnion, metalimnion, and hypolimnion layers within the lake while the total phosphates for this profile lacked any definable trends. Measurements from the two largest inputs to the lake, Trough Creek and the Raystown Branch of the Juniata River at an upstream sampling site (Saxton), show anticipated behaviors. Trough Creek, draining primarily heavily forested land, had lower initial and final total phosphate values while the Raystown Branch, reflecting predominately agricultural land, showed both high initial and final phosphate values. Analyses from these two sites showed a consistent and unnerving pattern of total phosphate at lower concentrations than reactive phosphate. This calls into question the accuracy of a commonly available technique for phosphate measurements in lakes. Introduction There are several aspects of Raystown Lake reservoir that make it an important site for nutrient study. The first of these is its relatively young age, having been completed and filled to its present level only 27 years ago. Its age makes it an interesting candidate for study because of the opportunity to observe the changing dynamics of the developing lake. This factor is also closely tied to another, the limited amount of research to date on the Lake. Aside from the post-impoundment survey conducted from 1976 to 1978, there has been no published information focusing directly on the lake. Unpublished reports, reflecting work performed by the Pennsylvania Department of Environmental Resources (1985-1987) and the Water Quality and Control Section of the U.S. Army Corps (1994-1998) represent samples collected typically only three times a year. The increasing amount of recreational use of Raystown Lake is a third factor, which raises the issue of water quality in the lake since increased activity often results in higher levels of pollutants. The increasing levels of pollutants will have some impact on the biological systems of the lake and measuring nutrient concentrations is one means of gauging the health of those systems. The agricultural activity within the watershed itself is yet another factor. With increased amounts of nutrients being incorporated into the lake from farm runoff, it may only be a question of time before this natural sink for many nutrients is exceeded. This study focused on nutrient measurement, nitrate and phosphate (reactive and total), for the water in Raystown Lake and it’s major inputs. The sites for collection as well as the methods for collection and analysis were adapted from earlier research performed on the lake by Smith (2001), an undergraduate at Juniata College, during the prior summer sampling season of 2000. At the start of this sampling season there were adjustments made to the project, including sampling of major stream inputs and a vertical column of the lake on alternating weeks. The hope was that by combining these two new features along with an extended sampling season for the horizontal profile a clearer picture of the lake’s nutrient patterns would emerge. Raystown Lake Raystown Lake is a man-made reservoir located in Huntingdon and Bedford Counties of south central Pennsylvania (Figure 3.1). The U.S. Army Corps of Engineers began construction on Raystown Dam in 1968 and completed the project in 1973 (Williams, 1978). The lake reached its current level in 1975. Hydroelectric generation capacity was installed in the dam and began operation in 1988. The reservoir is a multi-use facility with the triple objective of providing watershed management for the Juniata/Susquehanna River system, hydropower generation, and recreational activities including fishing, boating, and swimming. The watershed for the lake itself encompasses nearly 2490 km2 or 960 mi2 . Of this, only a small portion is used for commercial purposes, specifically the Seven Points and Raystown Resort marinas along with several state managed boat launch sites. A primarily forested buffer zone ranging in width from .25 miles to 1.5 miles surrounds the lake with both agricultural and forested areas on its perimeter. The strong majority of the lake’s watershed that can be characterized as agricultural is located at the upper-end of the lake where Raystown Branch enters (Smith 2001). The remainder of the lake’s watershed can generally be considered forested. The lake is of a long sinuous nature, winding back and forth nearly a dozen times along it’s 48km (30mi) stretch. It has a shoreline of about 190km (110mi), a water surface area of 3360hm2 (8300 acres), and a hydraulic residence time of approximately 230 days. Depth varies anywhere from 9 to 60 meters. Methods Sampling Four separate sampling runs were made during this sampling season. Sampling sites involved the ones initialized in prior research studies of the lake conducted by Juniata College students and faculty (Smith, 2001,Simpson, 1998). These sites were selected to reflect a more or less evenly spaced longitudinal profile of the lake as well as to roughly isolate the influence of each of the major tributary streams entering the lake. The principal sampling of this study defined a horizontal profile of Lake Raystown, which consisted of six sampling sites (R1, R8, R10, R20, R21, and R22) illustrated in Figure 3.1. These sites were monitored on alternate weeks from May until November 2001. Five samples were taken at a depth of two meters (epilimnion) from each site, using an alpha bottle, and were analyzed for total phosphate and nitrate. In August, the number of replicate samples was reduced to four because of a decrease in variation among total phosphate values. Figure 3.1 The second run of samples was also collected on alternate weeks from June until September. Four replicates were collected at Entriken Bridge, illustrated in Figure 3.1, at every 2 meters from 2 to 18 meters in a vertical profile. The samples collected were analyzed for total phosphate and nitrate. After September, a modified column was collected which took samples at 2, 9, and 15 meters, to maintain a general profile, so that the run could easily be incorporated into the first one. A third run was on a biweekly schedule through the months of June until November. These samples were collected at the two largest contributors to Raystown Lake, Trough Creek and the Raystown Branch, labeled in Figure 3.1. The four samples taken per site were analyzed for both total and reactive phosphates and nitrates. A fourth run had a much shorter duration than the first three, running on alternate weeks from July until August. Again four samples were collected at two strategic sites on the lake, at James Creek Boat Launch and Snyder’s Run, seen in Figure 3.1 and analyzed for total phosphates and nitrates. This run was seen as supplemental to the third run, representing smaller watershed draining inputs to the lake. Eventually the sampling was dropped as it yielded little new information about the lake. Because of this these data were not considered for the discussion in this paper. Laboratory Procedures To analyze for nitrate, the cadmium reduction method was implemented after which a spectrophotometric analysis was done. For total phosphates, a persulfate acid digestion was used followed by a spectrophotometric analysis designed to detect orthophosphate concentrations. Reactive phosphates underwent the same process less the persulfate digestion. The methods are outlined in the Hach DR/2000 Spectrophotometer Handbook (1989). One concern that arose late in the sampling scheme was that tungsten carbide boiling chips used during the persulfate acid digestion might have altered the levels of phosphate by adsorbing it to their surface. To test the validity of this concern, tests were performed to see whether the chips actually had an effect or not. When the tests were concluded it was determined that the chips did not render any measurable effect on the levels of phosphate observed, nor did it account for the variation seen between replicate samples. Data Analysis For all the values collected statistical analyses were conducted to determine outliers. Outliers were then disregarded in the final averages reported in this paper. While the cause of outlier values remains unknown, analysis performed on carefully prepared standards likewise included some outlier values, which clearly are invalid. Exclusion of the outliers from standard averages was well justified. The appearance of outlier values convinces us that replicate analyses of all samples are an essential component of a sampling routine using spectrophotometric methods and Hach reagents. Empirically determined error bars were included in every analysis done and included in this report to show the real variation that was seen in phosphate and nitrate values on the lake and in tributary samplings. Results Longitudinal Profile The nitrates for the horizontal sampling represented some of the most reliable information gathered for this run. Replicate analyses were tightly clustered with small standard deviations (averaging .05) as seen in Figure 4.1. Full data are reported in Appendix 1. The average for the season was .77 mg/L with a range between .28 and 1.16 mg/L. There is a consistent behavior between all of the sites for each of the samplings. In general, there was an increase (of about 0.12 mg/L) in the beginning of June followed by a return to prior concentrations, which then remained essentially constant from late June through August. In September, values dropped significantly (by .18 mg/L). Sites R10 and R22 undergo the most noticeable decrease. Then values begin to rise at the end of

2. Figure 5.3 well as those observed by Smith. The difference in total phosphates may be accounted for by considering the age of the lake. When Williams’s measurements were being taken, Raystown had not yet even filled to its present level. This means there had been almost no time for a biological community to develop within the lake. Therefore, a fledging biological community could only tie up or cycle a small amount of phosphorus. The discrepancy between current phosphorus levels and those of the mid-nineteen seventies either must have been due to the allocation of phosphorus to another sink within the system or simply lower accumulation of this nutrient. With an array of possibilities open to a newly formed lake and no information collected in relation to potential sinks or phosphorus level inputs during this time, a definitive explanation cannot be determined. Williams alludes to the infancy of the lake concerning the biological community in his report, remarking several times of the scarcity of plankton and algae that prohibited substantial examination of some of the lake characteristics. Going into mid-July, phosphate values decreased rapidly (.55 mg L on average) followed by a more gradual decline in early August. In many temperate lakes, a similar decline is also seen in the algal communities, referred to as the initial summer stratification. This is when increasing temperatures, water column stability, and light availability cause a negative effect on the population (Blomqvist, 1994). This phase is also marked by low nutrient availability. As the biological community decreases in size, breakdown of the phosphorus within decaying members is slow. This organic particulate form of phosphorus is lost to a number of processes but most notably sedimentation of diatoms (Neale, 1991). William’s work with plankton, algal growth potential, and chlorophyll supports this interpretation (1978). From mid-August into early September, a rough plateau in phosphate concentrations developed (between .05 mg/L and .12 mg/L depending on the site). According to Wetzel (2001), this period of the season is still marked by many of the same factors listed above (2001). One of the most important changes however is the modest increase in nutrient availability created from the drastic decrease in populations of plankton and algae. This allow for a minor resurgence of these communities as well as the introduction of several more competitive ones. At the end of September another less severe drop was observed, reducing the average value to .05 mg/L. In offering an explanation for this decline, it would not seem imprudent to suggest that is was in fact due to decrease in nutrient availability initiated by the earlier resurgence of growth in the biological community. One other possibility that could coincide with the first would be a tendency for fauna and flora within the community to begin to more strictly conserve nutrients around this time for winter, a behavior noted for forests and other areas surrounding lakes (Gustafson, 2001, personal communication). Mid-October marked the end of the sampling and a notable increase in phosphates at all sites was seen (averaging .04 mg/L), with sites further uplake showing a larger increase proportionally. There is an established growth of algal and planktonic communities during this time due to moderate nutrient availability (Blomqvist, 1994). The source of these nutrients is from initial decomposition of plant material, primarily leaves, during this time of the year. Also, local farms are emptying their manure pits and spreading the contents onto their fields, presenting the opportunity for an incredible amount of nutrients to be introduced into the rivers. The larger increase in total phosphates uplake may be attributed to inputs from the Raystown Branch, which drains a sizeable amount of agricultural land and is suggested by the data shown in Figure 4.5. Spatially, behaviors of total phosphate in the horizontal profile exhibited loose similarities between sites. It was not atypical to find one or two from the six that differentiate themselves from the others following a pattern. There was never a single site that exhibited this behavior but rather each having a measurement or two that deviated from the norm at different periods of the season. Altogether, each of the sites followed the same general temporal variation through the season, thought the degree to which increases and decreases were adhered to was variable. There did exist, though, a fairly evident set of similarities between some sites that led to the division of the six sites into three categories. Sites R12 and R22 (uplake) have incredibly similar patterns for the temporal pattern throughout the season. In relation to the other sites, their values are typically lower excluding the last two samplings where their values fall into the range of those seen further downlake. The next grouping consists of sites (mid-lake) R21, R8 and R10. On average the values measured at these sites are the highest and also include the highest peak values and resurgent values of all the sites. The pattern between these three is fairly consistent, though not as precisely as between R12 and R22. The last site, R1, initially bears close resemblance to the second grouping but from mid-July to the end of the season it has much lower values than any of the three sites within that grouping. An explanation for the behaviors in these groups could not readily be identified but consideration was given to the fact that it did bear some resemblance to the grouping of characteristic within Thornton’s model for reservoirs (1990). The vertical column for total phosphates yielded no discernable pattern either with depth or time. The reason it was included in this report was to show that a sampling had been taken and that no pattern was established. One observation that might have given rise to the erratic behavior is the geomorphology of the lake at the site, representing the narrowest and one of the more shallow areas (outside of the riverine setting) of the lake. It is believed this area may have lent itself to increased mixing from the amount of boat traffic as well as water flow through this bottlenecked part of the lake. Another point of reflection was the movement of the sampling bottle up and down it’s vertical path (which occurred fourteen times during the course of single column sampling) may have disturbed already subtle differences in phosphate concentrations. These conditions alone were not considered the explanation for the erratic behavior of the total phosphates but rather as possible contributors to it. Erratic behavior in phosphates vertically at this site is not mirrored by similarly erratic nitrate concentrations. Measurements of phosphate levels from inputs to the lake also at first seemed to have had no definition. Further investigation after collection revealed though that the time of day may have a significant effect on the amount of phosphorus present in the water. Hatch has observed that discharge in many streams fluctuates according to the time of day and that levels of both dissolved and particulate phosphorus are affected by this, in some cases by almost half an order of magnitude (1999). Combining this with seasonal discharge fluctuation and intermittent storm events, a very ragged pattern might be expected from an every other week sampling of the inputs. In retrospect, a more frequent schedule of sampling including set times for collection as well as additional samplings after storm events would have provided a more useful data set for the study. Other factors that have a substantial role in the levels and variations of phosphates measured from the inputs are topography, vegetative cover, land use, and parental materials from which soils are derived within the watershed (Wetzel, 2001). Of these, land use is one of the most influential and whose relationship is easily recognizable. Earlier description of the make up of the watershed for the Raystown Branch and Trough Creek in the nitrates section of this paper detailed land use of the first as being predominately agricultural while the latter is primarily forested. Many authors have suggested a relationship between land use and phosphorus runoff observing a general increase in nutrient levels with the introduction of land management practices that included the use of fertilizers (e.g. Jordan and Weller, 1996). The difference in average total phosfinphates (.03 mg/L) between the Raystown Branch and Trough Creek, at .14 mg/L and .11 mg/L respectively, seems to be in agreement with this generalization. A serious issue was raised when, midway through the sampling season, reactive phosphate levels for the inputs were measured at higher levels than those for total phosphates. Sample collection and processing was checked for problems that could account for this discrepancy. None were found. We were forced to conclude that an inherent flaw in the standard processing of samples (Hach) for testing of total phosphates produced the discrepancy. This assertion certainly brings into question the absolute accuracy of any phosphate values obtained during the course of this study. It is also our belief, though, that this discrepancy is a matter of precision rather than pattern. While measurements taken may not reflect the true values, any systematic errors should affect all analyses similarly, leaving intact the pattern of rise and fall in levels upon which our conclusions are based. Summary/Conclusions Extensive measurements of nitrates, reactive phosphates, and total phosphates were taken to determine spatial and temporal patterns in Raystown Lake. Longitudinal and vertical profiles of nitrates and total phosphates were established along with sampling of nitrates, reactive phosphates, and total phosphates for two inputs into the reservoir. The longitudinal profile for nitrates demonstrated a gradual decline in values through the summer until fall turnover. The vertical profile for nitrates gave fair resolution to the epilimnion, metalimnion, and hypolimnion zones of the reservoir. Recognizable behaviors in seasonal and spatial variation were established from total phosphate sampling horizontally along the lake though no definable pattern was rendered from the vertical profile of total phosphates. Sampling of inputs yielded levels of nitrates and total phosphates reflective of their respective watershed characteristics. Reactive phosphates for both stream inputs at times showed higher levels than total phosphates for the same samples, which raises concern about the accuracy of our method of analysis. These findings indicate that Raytown Lake has spatial and temporal variation patterns that are comparable to lakes that share similar climatic, limnologic, and geomorphic characteristics. 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