TREATMENT SUMMARY. for. Phosphorus Inactivation in Long Pond. Brewster and Harwich, Massachusetts. The Towns of Brewster and Harwich, Massachusetts

Transcription

1 Prepared for: The Towns of Brewster and Harwich, Massachusetts TREATMENT SUMMARY for Phosphorus Inactivation in Long Pond Brewster and Harwich, Massachusetts Prepared by: February 9 Document No. 13-1C

2 TABLE OF CONTENTS Background...1 Target Dose... Treatment Protocol... Treatment Process Review... Treatment Monitoring... Pre- and Post-Treatment Chemistry...7 Pre- and Post-Treatment Biology...1 Future Monitoring... Conclusion... Appendix A: Water Quality Data... Appendix B: Plant and Mollusk Data...3 Appendix C: Phytoplankton Data...37 TABLES Table 1. Planned aluminum doses to Long Pond... Table. Summary of ph, conductivity, and alkalinity data for Long Pond...9 Table 3. Zooplankton of Long Pond...19 FIGURES Figure 1. Long Pond treatment areas...3 Figure. Individual treatment areas in Long Pond...5 Figure 3. Selected temperature-dissolved oxygen profiles for Long Pond.... Figure. Average phosphorus concentration in epilimnetic and hypolimnetic waters on Long Pond...1 Figure 5. Selected phosphorus profiles for Long Pond...13 Figure. Secchi disk transparency in Long Pond....1 Figure 7. Secchi disk transparency in Long Pond since Figure. Abundance of mussels at survey sites in Long Pond...17 Figure 9. Cover by rooted plants at survey sites in Long Pond Figure 1. Phytoplankton of Long Pond...1 AECOM P.O. Box 5, 11 Phelps Way, Willington, CT 79-5 T F

3 Background Long Pond in Brewster and Harwich, MA covers 7 acres with a mean depth of 9 ft and a maximum depth of about 7 ft. Precipitation and groundwater are the dominant sources of water, with a smaller amount of runoff from the very sandy watershed. Long Pond is a popular swimming, boating and fishing destination. It has two major town beach/boat launch facilities, one each in Brewster and Harwich, plus another less developed beach and boat launch area in Harwich. Both towns have actively sought to protect the desirable qualities of the pond. Erratic summer algal blooms and small fishkills raised concern and prompted further study. Investigations have revealed a lack of oxygen with hydrogen sulfide production and release of phosphorus from bottom sediments in >3 ft of water. Diffusion and upward mixing of deeper waters during storms may both contribute to effective internal loading, which is estimated to supply 5 kg/yr (5%) to the upper waters out of a total load of between and 51 kg/yr. The remaining load is attributed mainly to watershed sources (%) and precipitation (%). Available phosphorus within the sediment ranged from. to. g/m based on data for the upper cm of sediment. More recent data () collected by the Town of Brewster indicates a very similar range of.7 to.5 g/m. A summer release of. g/m with only 1% reaching the epilimnion could raise the phosphorus concentration by more than. mg/l and support algal blooms. Anoxia has been a feature of deep water in Long Pond for at least half a century, but excessive internal recycling of nutrients accumulated over many years seems to be a more recent phenomenon. It may have taken many decades for the internal load to reach the threshold where it could supply sufficient phosphorus to cause the observed blooms. The release of previously bound and sedimented P inputs back into the water column is cause for concern on several grounds: 1. Some algae may be able to access this increased nutrient level by moving between lower and upper water layers. Some of the P accumulated in the bottom waters does pass into surface waters during summer, fueling algal growth 3. Upon eventual mixing, more of that accumulated P becomes available to algae. The long detention time of Long Pond means that seasonal events such as P release from sediment may have longer term impacts 5. The release of P without a commensurate release of nitrogen will lower N:P ratios and favor cyanobacteria, the most troublesome of algae Remedial action aimed at that internal load was chosen to restore desirable conditions in Long Pond, and protective measures in the watershed are to be implemented to slow down the accumulation of phosphorus and internal loading in the future. Aluminum treatment was favored over aeration methods. The primary reason for the choice of alum over aeration was economics, as an appropriate aeration system would cost at least as much as an alum treatment, but also requires annual maintenance and operational costs not incurred with the alum treatment. At issue with aluminum treatments is the potential toxicity of reactive aluminum outside the ph range of - standard ph units. Use of unbuffered aluminum sulfate in poorly buffered waters such as those on Cape Cod can lower the ph and produce transient toxicity immediately during treatment. Likewise, overbuffering can raise the ph and also produce short-term toxicity. While there is always some risk of an adverse reaction in any such application, understanding of the key factors allows a treatment with minimal risk to non-target flora and fauna of Long Pond. Follow-up sediment testing, dose response evaluation, and fish bioassays allowed determination of the necessary and most advantageous dose of which aluminum compounds. Treatment was permitted under the Wetlands Protection Act and the applicator received a License to Apply Chemicals from the MA DEP. The treatment was planned for late summer and early fall of 7. Page 1

4 Target Dose The keys to a successful treatment include assessment of necessary dose and choice of chemicals to achieve that dose while maintaining a near-neutral ph during treatment. Review of the ENSR 1 report suggested that the actual dose necessary over most of the pond is on the order of 5 g/m. With the additional testing conducted, plus fish bioassays to determine the most advantageous ratio of aluminum compounds to achieve a desirable ph, re-evaluation of the dose calculation facilitates appropriate dose determination (Table 1). Table 1. Planned aluminum doses to Long Pond Lake Segment Long West Long Central Long East Total Mean Available Sediment P (mg/kg DW) Target Depth of Sediment to be Treated (cm)... Volume of Sediment to be Treated per m (m3)... Specific Gravity of Sediment Mass of Sediment to be Treated (kg/m)... Mass of P to be Treated (g/m) Target Area (ac) Target Area (m) Aluminum sulfate 11.1 lb/gal and.% aluminum (lb/gal)... Sodium aluminate 1.1 lb/gal and 1.3% aluminum (lb/gal) Stoich. Ratio (ratio of Al to P in treatment) Ratio of alum to aluminate during treatment (volumetric) 1.:1 1.:1 1.:1 Aluminum Load and Alum + Aluminate volumes Dose (kg/area) Dose (lb/area) Dose (gal specs above Dose (gal specs above Application (gal/ac) for alum 11 7 Application (gal/ac) for aluminate 1 15 Anticipated days of treatment in area The treatment areas are shown in Figure 1. The planned dose was therefore just under 7, gallons of aluminum sulfate and about 3,3 gallons of sodium aluminate. Adjustment of ratios in the field is expected, and nuances of delivery, loading, and application will usually cause some deviation, but application at a ratio near 1.:1 (for aluminum sulfate:sodium aluminate by volume) was planned. This ratio has been found to cause no toxicity to fish in the lab at the expected concentrations of aluminum at the time of treatment, using fish species present in Long Pond and actual Long Pond water for the testing. Ratios closer to :1 represent the theoretical balance point for ph in lakes with low buffering capacity (i.e., inability to maintain ph in response to acid inputs), but with a ph of. to.5 in Long Pond, and the potential for some variability during treatment, the lower ratio of aluminum sulfate to sodium aluminate (which will cause the ph to rise slightly) was found to be most protective. Page

5 Figure 1. Long Pond treatment areas. Page 3

6 Treatment Protocol The plan was to apply aluminum sulfate and sodium aluminate at a volumetric ratio of 1.:1 over areas 3 ft deep at a total dose of 1 (East Basin) to 15 (West Basin) to 3 (Central Basin) g/m. The two chemicals are released simultaneously from a motorized barge through nozzles on a boom lowered about 1 ft below the water surface. The motor that moves the barge also promotes mixing of the chemical and the lake water. A fine floc forms in the water, binding some phosphorus then, but settling to the bottom within hours and inactivating phosphorus in the surficial sediments as the main goal of the treatment. Aquatic Control Technology of Sutton, MA performed the treatment. The treatment area within Long Pond was divided into smaller target areas that could be treated in one to three days (Figure ), and the barge traversed a GPS-guided path to deliver as even a dose as possible. The barge had to be reloaded multiple times per target area, as it carries only about 1 gallons of aluminum sulfate and 5 gallons of sodium aluminate at a time. Target areas were treated non-sequentially to the extent possible, avoiding treatment of large contiguous areas on consecutive days. The main beach for the Town of Harwich was used as the staging area for chemical delivery and loading of the barge. The East Basin, having only 13 acres of target treatment area and being the shallowest with the lowest planned dose, was the first area treated. Evaluation of treatment impacts was conducted over several days following treatment before any other target area was treated. There was no fish mortality, no mussel mortality, and no unusual water quality variation as a result of the initial treatment, so treatment of other target areas commenced four days later and ran to completion, with interruptions as determined by weather, mechnical problems, weekends, or any other factor determined by the Orders of itions issued by both Harwich and Brewster under the Wetlands Protection Act. Treatment Process Review The final chemical amounts applied at Long Pond were 7,91 gallons of aluminum sulfate and 37,5 gallons of sodium aluminate, yielding a ratio of 1.:1. This input is very close to that expected based on Table 1. Doses per treatment area followed the guidance of 1 g/m for the East Basin, 15 g/m for the West Basin, and 3 g/m for the Central Basin. Application target areas treated on specific days are shown in Figure. The dates of treatment for each target area are shown. Some Central Basin areas are numbered as an aid to planning the treatment sequence to avoid treating contiguous areas on consecutive days. The East Basin was treated first, as planned, then portions of the West Basin and Central Basin were treated in alternating fashion until the West Basin was completed. Remaining treatment focused on the Central Basin, where the most aluminum was applied. Page

7 Figure. Individual treatment areas in Long Pond. Page 5

8 Deviations from the planned process included: 1. Treatment took a total of 17 days; the minimum expected number of days was 13, and equipment problems resulted in multiple partial days of treatment. Equipment problems included mainly failed pumps and barge motors. The treatment team was prepared to address these, but some possible treatment time was lost as a result.. Treatment could not be performed on 3 days due to high wind. Such delays were required by the Orders of itions and expected to occur during the treatment period at some point. 3. Treatment was not performed on one Monday (Columbus Day) due to a planned rowing regatta and the potential for interference and related safety issues.. Aluminum floc drifted into water shallower than 3 ft even with only low wind. As a result, treatment was shifted into water >35 ft deep in the Central Basin, although some limited drift into shallower areas still occurred. 5. The bathymetric map was not accurate in a few areas, resulting in adjustment in the area treated. The total area treated was roughly the same as planned and the total dose was very close to that expected. The barge operator watched depth closely and adjusted as needed.. Two continguous target areas in the Central Basin were treated on consecutive days at the end of the program. By that time, it was apparent that there was negligible risk of biological impacts from such treatment. Treatment Monitoring Alkalinity measurement during treatment revealed low buffering capacity nearly everywhere and nearly all the time, as expected for this waterbody. Alkalinity ranged from to 5 mg/l at all stations, treated or untreated, over the pre-treatment and treatment period, with very little variability observed. Treatment did not depress alkalinity except at perhaps at the most localized level; sampling right behind the barge as it applied the aluminum chemicals revealed ph values that suggested higher or lower alkalinities, but those alkalinities were not directly measured. The ph of Long Pond is known to range naturally from about. to., and measurements in untreated areas ranged from.1 to.5 during the treatment period. Measurements taken in accordance with the approved monitoring program, which included measurements three times per day in the target area, indicated that treated areas experienced ph values that ranged from.1 to 7.. Assessment of the water as the aluminum compounds were being applied (within 1 ft of the barge) on the first few days of treatment revealed ph values as low as 5. and as high as., but only 5 values out of 3 such measurements were <. or >7.. Thereafter, adjustments were made to keep the ph between. and 7.. Mixing behind the barge was substantial. Visual assessment of floc formation with the videocamera indicated that applied aluminum compounds were mixed over a depth of about ft upon application. This reduces the maximum aluminum concentration that could occur to about 5 mg/l, the upper bound of what is considered safe even with fluctuating ph. This may have been an important factor in the complete lack of fish mortality. Adding the maintenance of ph within the range of. to 7. minimizes the reactive aluminum concentration to non-toxic levels. The noise of the Page

9 barge tends to scare away fish, so exposure to higher aluminum doses at ph values outside the desirable range was minimal. There was concern that some fish, especially alewife, might perceive the floc as a food item, but this was not observed to occur despite extensive surveillance with an underwater videosystem. The immediate treatment area was assessed just prior to treatment, during treatment, and immediately after treatment for ph and alkalinity, and for impacts on fish and mollusks by visual observation. Observation included the surface by eye and the bottom by remote video camera, and extended to areas peripheral to and also downwind of the treatment area. One dead fish was observed on the first day of treatment, and was quite obviously dead prior to the start of treatment. Fish, including alewife, yellow perch, catfish, and bass, were observed in the treatment area with no ill effects. Most alewife, however, were observed around the edge of Long Pond, as would be expected at that time of year. After the one pre-treatment dead fish was observed, no dead fish were found at any time during treatment or shortly thereafter. No molluscan deaths appeared attributable to treatment. We observed dead bivalve mollusks ( mussels ) before treatment in many areas, as might be expected (shells do not deteriorate rapidly after death). Mollusks are generally found at water depths <5 ft in Long Pond, so overlap with treatment areas was intended to be minimal, but some drift of floc was observed. Mollusks were not buried in floc in any area, but mollusks were observed with enough floc around them to potentially induce temporary closure of shells, which was observed. Inspection of untreated areas revealed similar portions of close shells, however, so it was not clear that even that situation was a reaction to treatment. Pre- and Post-Treatment Chemistry Water column samples were collected on September 1, 7, prior to the start of any treatment. Samples were collected monthly for a year after treatment. Analysis focused on temperature, dissolved oxygen, ph, alkalinity, conductivity, total and dissolved phosphorus, and dissolved aluminum. Aluminum levels were negligible prior to treatment and returned to levels below the detection limit shortly after treatment (Appendix A). Ambient levels in late October and November were not higher than for pre-treatment samples. A reduced detection limit was applied after treatment, and dissolved aluminum was only detected in of 3 post-treatment samples, and then at low levels not of ecological or human health concern. In accordance with the Orders of itions, no further sampling for aluminum was required. erature and dissolved oxygen profiles were obtained on each sampling date (Appendix A) and indicated a typical seasonal pattern. The only direct pre-and post-treatment comparison possible is September 1, 7 vs. either August or September 3,, but there are differences due to date and weather; this is not as direct a comparison as would be preferred. There is no indication of any major improvement in deep water oxygen from these profiles (Figure 3) in 7 and. Page 7

10 Figure 3. Selected temperature-dissolved oxygen profiles for Long Pond. LP-1 (9/1/7) LP-1 (//) LP-1 (9/3/) Dissolved Oxygen Dissolved Oxygen Dissolved Oxygen LP- (9/1/7) LP- (//) LP- (9/3/) Dissolved Oxygen Dissolved Oxygen Dissolved Oxygen Page

11 Measurements of ph, conductivity and alkalinity indicated no significant changes over time, but an increase in conductivity and alkalinity and a decrease in ph in deep water during stratification (Appendix A). A summary of all data (Table ) does not suggest any major ecological or human health issue from the variability observed, particularly since the lowest ph values and highest alkalinity and conductivity levels occur only in the deepest water at a time of low or no oxygen in that small water layer within Long Pond. The treatment does not appear to have changed water chemistry over space or time with regard to ph, alkalinity and conductivity. Table. Summary of ph, conductivity, and alkalinity data for Long Pond. LP-1 LP- ph (SU) uctivity (us/cm) Alkalinity ph (SU) uctivity (us/cm) Alkalinity Minimum Mean Maximum Total and dissolved phosphorus concentrations were the direct target of the treatment, with the intent to lower these to the point where algal blooms would not be supported. Total phosphorus (TP) values on the order of. mg/l will tend to support algal blooms, while concentrations <.1 mg/l rarely do. Prior to treatment, on September 1, 7, TP levels ranged from. to.3 mg/l in the upper waters (-1 m during stratification) at LP-1 and.15 to. mg/l over the same depth range at LP-; mean values were. mg/l at LP-1 and.3 mg/l at LP- (Figure, Appendix A). In the bottom waters (>13 m deep) the concentration at LP-1 averaged.133 mg/l and that at LP- was.1 mg/l, indication the accumulation of TP in those bottom waters. Dissolved phosphorus (DP) values mirrored TP levels, but as a subset of TP, were somewhat lower (Appendix A). The accumulation of P in deep waters during stratification is related to both settling organic matter and release from bottom sediments, and some portion moves upward into the water column, increasing the concentrations in less deep water. The alum treatment was intended to greatly reduce the releases from bottom sediment, thereby reducing the movement into overlying waters. Only 1 to % of the released P is expected to reach the upper waters during the growing season, but that is till a significant amount. Additionally, as the lake has a retention time on the order of years, the mixing of the remaining deep water P when stratification breaks down can affect productivity in following years. In October 7, less than a month after treatment, TP concentrations averaged. mg/l at both LP-1 and LP-, with stratification nearly gone for the year. This was as expected for an aluminum treatment, and experience with spring treatments in other lakes suggested that low P levels would be Page 9

12 maintained for months to come. However, fall treatments are less common, and winter monitoring data for aluminum treatments are very rare, so the pattern that arose after October 7 was unexpected. In essence, TP and DP increased gradually between October 7 and April, with TP reaching levels similar to those of the upper layer from September 7 in April and May (Figure, Appendix A). DP levels did not recover to pre-treatment levels, but did increase to more than half the pre-treatment concentration. Figure. Average phosphorus concentration in epilimnetic and hypolimnetic waters on Long Pond. (Note that the scale is different for total and dissolved forms) Average Total Phosphorus Levels at LP-1 Average Dissolved Phosphorus Levels at LP Epi mean Hypo mean.5.5. Epi mean Hypo mean.1.35 TP.. TP Sep- 7 Oct- 7 Nov- 7 Dec- 7 Jan- Feb- Mar- Apr- May- Jun- Jul- Aug- Sep-. Sep- 7 Oct- 7 Nov- 7 Dec- 7 Jan- Feb- Mar- Apr- May- Jun- Jul- Aug- Sep- Month Month Average Total Phosphorus Levels at LP- Average Dissolved Phosphorus Levels at LP-.1.1 Epi mean Hypo mean.3.5 Epi mean Hypo mean.. TP. TP Sep- 7 Oct- 7 Nov- 7 Dec- 7 Jan- Feb- Mar- Month Apr- May- Jun- Jul- Aug- Sep-. Sep- 7 Oct- 7 Nov- 7 Dec- 7 Jan- Feb- Mar- Month Apr- May- Jun- Jul- Aug- Sep- Page 1

13 At the lower phosphorus levels observed, which are near the detection limit for the method applied, fluctuations of.5 or even.1 mg/l are not especially meaningful, but it is quite apparent that P concentrations were substantially reduced at the time of treatment, but then increased again over the winter and spring. Explanations are difficult to substantiate, but several have been postulated: 1. Just over half the volume of the lake was treated, so it would not have been surprising to see a slight rise as the lake completely mixed. Yet the rise was much more gradual than the mixing and resulted in a concentration similar to the pre-treatment level for TP, which would not be possible without additional P inputs.. New phosphorus inputs from the watershed, atmosphere, or groundwater might have raised the P concentration over the winter. With the change of just half the volume from an average of about. mg/l to. mg/l, that is a reduction of 7 kg of P. The annual contribution from all external sources (precipitation, runoff and inseepage) is estimated at a maximum of kg. No external source can explain the rising concentration, which even if all inputs were converted into aqueous P, amounts to at least 31 kg. 3. Incoming alewife may have raised the P level. There does appear to be a spike in P in April and May, but most alewife activity is in May, and the earlier increases in P could not be accounted for in this manner. Additionally, alewife runs have reportedly not been so large as to bring that much P into the lake in recent years.. Release of sediment P from untreated areas could contribute to the P content of the pond. There is undoubtedly some available P in the untreated portion of the lake, which is about half the area. However, this half of the area is shallow and the bottom is almost all sand and cobble; stored P would be minimal and high oxygen levels would restrict release of iron-bound P. Some contribution is possible, but not nearly enough to achieve pre-treatment P levels. 5. There may have been a rebound effect in which unbound sediment P was released in response to low P concentrations in overlying water. This is a complex chemical effect not known to routinely occur, particularly since the sediment P is supposed to be bound by aluminum. However, the dose was based on loosely sorbed and iron-bound P, not any portion of the organic P, some of which might be available. This is a cutting edge topic of debate in the scientific literature, and coupled with a lack of data for overwinter P levels following aluminum treatments, there is considerable uncertainty here. If, however, there was a major release of P over the to 7 months following treatment from organic sources, this P apparently was gradually inactivated (either by aluminum or by conversion to truly unavailable organic matter), as lower P levels were encountered in summer of and no appreciable deep water accumulation was noted after July. None of these explanations is particularly satisfying, but the possible release of sediment P that had been organically bound might account for the observed effect, having raised P to about what it was before the treatment. The input of at least 317 kg is within the estimated annual net internal load of 5 kg. Contributions for all the other mechanisms listed above might exist, and together they could have raised the P concentration as observed. The bigger question revolves around whether or not this was a one time occurrence in response to treatment or an annual process. Page 11

14 Either way, the use of available P by algae results in incorporation into particles that sink, and some portion of the P becomes unavailable over time (refractory organic matter). Some of the P is released by decay, incorporated into new algae, which either sink or are eaten by zooplankton that eventually die, many consumed by fish; again some portion of the P becomes unavailable. Without replenishment from the sediment, where most reserves are now bound in aluminum or refractory organic compounds, the P level in Long Pond should decline to a level supported by new inputs. That level is much lower than the pre-treatment level, based on the nutrient budget work performed to date. Over the summer of the results of the aluminum treatment more closely approximated initial expectations (Figure 5, Appendix A). There was some apparent build-up of deep water P in July, after stratification in late June, although this was only observed at the deepest point at LP- and could be an anomaly. TP values averaged.1 mg/l in Long Pond, with values declining rather that increasing over the summer. The absence of internal releases of available sediment P during the summer is apparent in the data and led to improved clarity. Water clarity, while not the direct target of the treatment, was the real goal of the project. Data for each station are presented in Figure, while a comparison of post-treatment data with data from is provided in Figure 7. Data from the last ten years of volunteer monitoring indicated summer Secchi disk transparency (SDT) values lower than the desired ft visibility on occasion and average values <1 ft. The SDT just before treatment was just under 11 ft, at the clear end of the September range for the last decade. SDT increased slightly in October and at one of the two monitoring stations in November, then decreased over the winter. Spring values were not identical in the two main basins of the lake, such that SDT continued to decrease through April at LP-, but was slightly better in March and April in LP-1 than it had been over the winter; values were still <1 ft, however. In May, clarity increased in both basins and the increase continued through August. There was a slight depression of SDT in September, but SDT increased again by the start of October. Within the context of the larger data base from the last 1 years, water clarity has not been measured over the winter months, so there is no basis for comparison. The water was as clear as it had been in a decade in September, just before treatment, and remained near the clear end of the historic range through December. However, the clearest end of that range is only 1 to 1 feet, and much greater clarity would have been expected from a spring aluminum treatment if internal loading was the primary P source. We have no overwinter comparative data, and only one April value, which was close to what was observed in after treatment. The May SDT value was in the clearer half of the historic range, at an average of 13.3 ft, but is not especially clear. From June through the start of October, SDT values were the highest observed in over a decade. The peak occurred in August, with a value in excess of 19 ft, about what was expected of the treatment. There was a dip in September, just like in virtually all previous monitoring years, but SDT remained higher than previously observed and 3 ft higher than in 7 just before treatment. SDT rose again at the start of October, to about 1 ft, a time when mixing yielded extra P in most years and depressed clarity. Monitoring ceased at this point, the regulatory obligation having been met. Page 1

15 Figure 5. Selected phosphorus profiles for Long Pond. Long Pond LP-1 Total Phosphorus Levels Total Phosphorus Depth (m) 1 1 9/1/7 1/5/7 7/1/ // 9/3/ Long Pond LP- Total Phosphorus Levels Total Phosphorus Depth (m) 9/1/7 1/5/7 7/1/ // 9/3/ Page 13

16 Oct, Figure. Secchi disk transparency in Long Pond. Figure a. Long Pond Secchi Disk Transparencies LP-1 Figure b. Long Pond Secchi Disk Transparencies LP- Sept, 7 Oct, 7 Nov, 7 Dec, 7 Jan, Mar, April, May, June, July, Aug, Sept, Oct, Sept, 7 Oct, 7 Nov, 7 Dec, 7 Jan, Mar, April, May, June, July, Aug, Sept, Page 1 Depth (ft) Depth (ft)

17 Figure 7. Secchi disk transparency in Long Pond since 199. SDT Pre-treatment Average SDT vs. Post-treatment Mean and Range for 199- data 7 data data Month Jan J Feb J Mar J Apr J May J Jun J Jul J Aug J Sep J Oct J Nov J Dec J SDT (ft) Treatment (7) Page 15

18 Pre- and Post-Treatment Biology A survey of mussel density was conducted in August prior to treatment and one year after treatment, with mussels quantified as absent, trace (1 per viewing field), sparse (- per field), moderate (5-1 per field) or dense (>1 per field). No dense populations were found, based on survey areas of about 1 m. The results indicated no significant change in mollusk abundance or distribution (Figure, Appendix B) between August of 7 and August of, based on observations at 11 locations. Rooted plants were monitored at the same time and locations as mussels, in August of 7 and. Eight species of vascular plants were observed, plus green and blue-green algal mats and the macroalga Nitella. Based on five cover categories (absent, 1=1-5%, =-5%, 3=51-75%, and =7-1%), there was no apparent difference between the pre- and post-treatment cover data (Figure 9, Appendix B). The same species were encountered each year, with Najas flexilis, Nitella flexilis, and Potamogeton pusillus var. tenuissimus most frequent. Phytoplankton were of definite interest in this evaluation, being the algae that most influence water clarity in Long Pond. In the 199s and early in this decade, blooms of cyanophytes (blue-green algae, or more properly cyanobacteria) greatly depressed water clarity in Long Pond. The results of monitoring and focused investigation determined that the key process was internal phosphorus loading, especially during dry weather. Wet weather tended to force iron-rich groundwater into the pond, which inactivated available P and limited its abundance. Hence the relatively wetter summers since 3 have fostered fewer blooms and higher water clarity. The treatment sought not so much to reduce algal abundance as to shift it away from cyanobacteria, which thrive at higher P levels. Phytoplankton in September, prior to the treatment, was dominated by cyanobacteria in terms of numbers of cells, and those cells are small, imparting more turbidity (and lowering clarity more) than larger cells at the same mass. After treatment cyanobacteria were much reduced, and while they regained dominance the following summer, the biomass was lower (Figure 1). Cell count approached 7,/mL in September 7, but exceeded 1, cells/ml only once after that, barely, in August, when cyanobacteria were again dominant. However, there was a shift in types of cyanobacteria, with only one of four previously common types observed after treatment. In terms of biomass, the September 7 samples were a fairly even mix of cyanobacteria, diatoms, golden algae and dinoflagellates, at 15 ug/l, a moderate value (Figure 1). Severe blooms often exceed 1, ug/l, while great clarity is associated with values <5 ug/l. Cyanobacteria were never again a significant fraction of the phytoplankton biomass. This is not surprising for winter or spring samples, which are often dominated by diatoms and golden algae as observed in Long Pond, and those algae are considered valuable parts of the food web. Yet the lack of significant cyanobacterial biomass in summer suggests that the treatment lowered the P concentration sufficiently to achieve control over algal biomass in general and specifically over cyanobacteria. Page 1

19 Figure. Abundance of mussels at survey sites in Long Pond. Pre- (August 7) and Post- (August ) Treatment Mussel Survey Results 1 Number of Sites with Listed Density 1 1 Moderate mussels Sparse mussels Trace mussels No mussels 7 Date Figure 9. Cover by rooted plants at survey sites in Long Pond. Pre- (August 7) and Post- (August ) Treatment Plant Survey Results Number of Sites with Listed Cover Rating Date Cover = Cover = 3 Cover = Cover = 1 No Plants Page 17

20 Figure 1. Phytoplankton of Long Pond. Figure 1A. Long Pond Phytoplankton Density 3 Density (Cells/mL) PYRRHOPHYTA EUGLENOPHYTA CYANOPHYTA CHRYSOPHYTA CHLOROPHYTA BACILLARIOPHYTA Sep- 7 Oct- 7 Nov- 7 Dec- 7 Jan- Feb- Mar- Apr- May- Jun- Jul- Aug- Sep- Date Figure 1B. Long Pond Phytoplankton Biomass 5 Biomass (ug/l) PYRRHOPHYTA EUGLENOPHYTA CYANOPHYTA CHRYSOPHYTA CHLOROPHYTA BACILLARIOPHYTA Sep- 7 Oct- 7 Nov- 7 Dec- 7 Jan- Feb- Mar- Apr- May- Jun- Jul- Aug- Sep- Date Page 1

21 Biomass values were still moderate, but included mainly species of algae that are consumed in the food web more readily than cyanobacteria and impart less turbidity to the water. These results represent only one year of information, but indicate very favorable results of the treatment if they continue; clarity has been improved, but desirable algae have not been eliminated or even substantially depressed. Zooplantkon are also of substantial interest, as they consume algae and are an intermediate link in the food web. However, Long Pond hosts an annual run of sea-run alewife and has a potentially large population of juvenile alewife for the summer (or longer if the water level is too low for them to exit at the outlet). Alewife can minimize zooplankton populations by their density and feeding mode, which involves filtering the water column and straining out particles larger than about.3 mm. Ponds dominated by alewife have few large zooplankton, and often few zooplankton at all. Long Pond exhibits a classic alewife-impacted zooplankton population both before and after the treatment (Table 3). Biomass <1 ug/l provides limited grazing; Long Pond zooplankton average < ug/l. Mean size <.5 mm indicates few large grazers that can control algal density; Long Pond zooplankton average <. mm in length. A variety of types are present, none is particularly dominant, but none are abundant. In essence, there is no phytoplankton control by zooplankton, so algal biomass will be as large as nutrient levels allow. Controlling P is essential to preventing algal blooms in Long Pond. Table 3. Zooplankton of Long Pond LP-1 LP- LP-1 LP- SUMMARY STATISTICS 9/1/7 9/1/7 // // DENSITY (#/L) PROTOZOA.... ROTIFERA COPEPODA.... CLACERA OTHER ZOOPLANKTON.... TOTAL ZOOPLANKTON BIOMASS (ug/l) PROTOZOA.... ROTIFERA COPEPODA..5.. CLACERA OTHER ZOOPLANKTON.... TOTAL ZOOPLANKTON TAXONOMIC RICHNESS PROTOZOA ROTIFERA 3 COPEPODA 3 3 CLACERA 3 OTHER ZOOPLANKTON TOTAL ZOOPLANKTON S-W DIVERSITY INDEX EVENNESS INDEX MEAN LENGTH (mm): ALL FORMS MEAN LENGTH: CRUSTACEANS Page 19

22 Future Monitoring These results have indicated very favorable results of the treatment for the summer following treatment. There is no reason to believe that adverse impacts from the treatment on fish, invertebrates or plants would occur beyond the timeframe of this project, but the level and longevity of the improved phosphorus level, phytoplankton composition, and water clarity should be tracked. Also, some improvement in deep water oxygen levels remains to be seen. To that end, the following recommendations are offered: 1. Sample LP-1 and LP- monthly from April into October, with a sample collected at the surface and near the bottom for total and dissolved phosphorus.. At each station in each month, obtain a surface sample of phytoplankton for analysis and measure Secchi disk transparency. 3. At each station in each month, generate a temperature dissolved oxygen profile.. Convene the interested parties in each town to further a watershed management plan to protect the investment made in Long Pond through the treatment. There is an active volunteer monitoring group that could most likely handle the field portion of this program. AECOM would be happy to assist in any way, but it is most cost-effective to have the volunteer monitors conduct this program. Some professional assistance may be needed to develop the watershed management plan, and this was required in the Orders of itions for the project, but there are people in both towns who comprehend the need and have an understanding of the available techniques. Conclusion The treatment of Long Pond with aluminum compounds for the inactivation of phosphorus was successfully conducted in September and October of 7. Approximately 37 acres were treated with aluminum sulfate (7,91 gallons) and sodium aluminate (37,5 gallons) on 17 days over a day period. The ratio of alum to aluminate was 1.:1, close to the targeted ratio. Doses were approximately 1 g/m in the East Basin, 15 g/m in the West Basin, and 3 g/m in the Central Basin, as planned. Alkalinity was low but largely unaffected by treatment. The ph was maintained between. and 7. in all compliance samples, although additional samples collected to reveal the instantaneous extremes near the application point did yield a few values outside that range. No mortality of fish or mollusks was observed, despite extensive monitoring. Post-treatment assessment of water quality at multiple depths at two stations revealed a distinct decline in both total and dissolved phosphorus and no aluminum levels above pre-treatment values for two months after treatment. Beginning in November 7, phosphorus levels began to rise and water clarity declined. Late winter and spring phosphorus levels were similar to pre-treatment levels and spring water clarity was within the historic range observed in the pond, suggesting no distinct benefit from the treatment. Multiple possible explanations exist, but none is completely consistent with all data, and there is a minimal Page

23 track record for fall treatments and winter monitoring, so we have little context within which to evaluate this treatment for that time period. Several mechanisms may have combined to limit winterspring control of phosphorus and improved clarity. However, beginning in May and progressing through August, water clarity increased dramatically, exceeding all measured values for the last decade. There was a decrease in clarity in September, consistent with historic trends, but an increase at the start of October, after which monitoring ceased. Water clarity during summer was the highest observed in over a decade. Biologically, the treatment has had no measurable negative impact on any valued biota. Plant and mollusk communities are very similar between August 7 and August, and no dead fish were found during treatment, despite extensive surveys. There was no appreciable change in zooplankton, but this community is minimal in Long Pond as a consequence of abundant alewife. The change in phytoplankton is very encouraging; cyanobacteria that were responsible for past blooms were abundant in September 7, but have been minimal in biomass since then. Other algal groups more useful in the food web and less likely to cause problem blooms remain at moderate abundance. The treatment appears to have properly targeted problem algae without disrupting the food web. However, these conclusions are based on only one year of post-treatment data. Continued intensive monitoring does not appear necessary, but sampling of the two stations at the is warranted on a monthly basis beginning in April and running to October, with a focus on phosphorus, clarity, oxygen and phytoplankton. Page 1

24 Appendix A: Water Quality Data Page

25 Table A.1. Dissolved aluminum at LP-1. LP-1 values Aluminum Depth (m) 9/1/7 1/5/7 11/15/7 <.5.1 <.1 <.5 <.1 <.1 <.5 <.1 <.1 <.5 <.1 <.1 <.5 <.1 <.1 1 <.5 <.1 <.1 1 <.5 <.1 <.1 1 <.5 <.1 <.1 1 <.5.11 <.1 1 <.5 <.1 <.1 Duplicate None None <.1 Depth of Dup.(m) N/A N/A Table A.. Dissolved aluminum at LP-. LP- values Aluminum Depth (m) 9/1/7 1/5/7 11/15/7 <.5 <.1 <.1 <.5 <.1 <.1 <.5 <.1 <.1 <.5.11 <.1 <.5 <.1 <.1 1 <.5 <.1 <.1 1 <.5 <.1 <.1 1 <.5 <.1 <.1 Duplicate None <.1 None Depth of Dup.(m) N/A N/A Page 3

26 Table A.3. Long Pond Water Quality Profiles- Pre Treatment Monitoring LP-1 LP- 9/1/7 9/1/7 Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Table A.. Long Pond Water Quality Profiles- Post Treatment Monitoring LP-1 LP- 1/5/7 1/5/7 Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Table A.5. Long Pond Water Quality Profiles- Post Treatment Monitoring LP-1 LP- 11/15/7 11/15/7 Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Page

27 Table A.. Long Pond Water Quality Profiles- Post Treatment Monitoring LP-1 LP- 1/13/7 1/13/7 Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Table A.7. Long Pond Water Quality Profiles- Post Treatment Monitoring LP-1 LP- 1/3/ 1/3/ Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Table A.. Long Pond Water Quality Profiles- Post Treatment Monitoring LP-1 LP- 3/11/ 3/11/ Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Page 5

28 Table A.9. Long Pond Water Quality Profiles- Post Treatment Monitoring LP-1 LP- /15/ /15/ Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Table A.1. Long Pond Water Quality Profiles- Post Treatment Monitoring LP-1 LP- 5/1/ 5/1/ Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Table A.11. Long Pond Water Quality Profiles- Post Treatment Monitoring LP-1 LP- /1/ /1/ Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Page

29 Table A.1. Long Pond Water Quality Profiles- Post Treatment Monitoring LP-1 LP- 7/1/ 7/1/ Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Table A.13. Long Pond Water Quality Profiles- Post Treatment Monitoring LP-1 LP- /// // Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Table A.1. Long Pond Water Quality Profiles- Post Treatment Monitoring LP-1 LP- 9/3/ 9/3/ Depth (m) ph (SU) (us/cm) Alk Depth (m) ph (SU) (us/cm) Alk Page 7

30 Figure A.1. T- Profiles LP-1 (9/1/7) LP-1 (1/5/7) LP-1 (11/15/7) Dissolved Oxygen Dissolved Oxygen Dissolved Oxygen LP- (9/1/7) LP- (1/5/7) LP- (11/15/7) Dissolved Oxygen Dissolved Oxygen Dissolved Oxygen Page

31 Figure A.. T- Profiles LP-1 (1/13/7) LP-1 (1/3/) LP-1 (3/11/) Dissolved Oxygen Dissolved Oxygen Dissolved Oxygen LP- (1/13/7) LP- (1/3/) LP- (3/11/) Dissolved Oxygen Dissolved Oxygen Dissolved Oxygen Page 9

32 Figure A.3. T- Profiles LP-1 (/15/) LP-1 (5/1/) LP-1 (/1/) Dissolved Oxygen Dissolved Oxygen Dissolved Oxygen LP- (/15/) LP- (5/1/) LP- (/1/) Dissolved Oxygen Dissolved Oxygen Dissolved Oxygen Page 3

33 Figure A.. T- Profiles LP-1 (7/1/) LP-1 (//) LP-1 (9/3/) Dissolved Oxygen Dissolved Oxygen Dissolved Oxygen LP- (7/1/) LP- (//) LP- (9/3/) Dissolved Oxygen Dissolved Oxygen Dissolved Oxygen Page 31

34 Table A.15. Long Pond Total Phosphorus Levels at LP-1 Depth (m) 9/1/7 1/5/7 11/15/7 1/13/7 1/3/ 3/11/ /15/ 5/1/ /1/ 7/1/ // 9/3/ Duplicate None None.. None None None.3 None None None None Depth of Dup.(m) N/A N/A N/A N/A N/A 1 N/A N/A N/A N/A Table A.1. Long Pond Dissolved Phosphorus Levels at LP-1 Depth (m) 9/1/7 1/5/7 11/15/7 1/13/7 1/3/ 3/11/ /15/ 5/1/ /1/ 7/1/ // 9/3/ < Duplicate None None.5. None None None.13 None None None None Depth of Dup.(m) N/A N/A N/A N/A N/A 1 N/A N/A N/A N/A Page 3

35 Table A.17. Long Pond Total Phosphorus Levels at LP- Depth (m) 9/1/7 1/5/7 11/15/7 1/13/7 1/3/ 3/11/ /15/ 5/1/ /1/ 7/1/ // 9/3/ Duplicate None.3 None None None..1 None None Depth of Dup.(m) N/A N/A N/A N/A N/A N/A Blank(Distilled) None None None None None None Blank (DI water) None None None None None None None.7 None None None None Table A.1. Long Pond Dissolved Phosphorus Levels at LP- Depth (m) 9/1/7 1/5/7 11/15/7 1/13/7 1/3/ 3/11/ /15/ 5/1/ /1/ 7/1/ // 9/3/ Duplicate None.3 None None.9.9. None.7.13 None None Depth of Dup.(m) N/A N/A N/A N/A N/A N/A Blank(Distilled) None None None None None.5 Blank (DI water) None None None None None None None.11 None None None None Page 33

36 Appendix B: Plant and Mollusk Data Plant Cover or Biovolume None 1 1-5% -5% % 7-1% Plant Species Bg Ec Ea Fg Ld Nf Ni Ppt Prob Sg Va Blue-green algal mats Elodea canadensis Eleocharis acicularis Filamentous green algae Lobelia dortmanna Najas flexilis Nitella sp Potamogeton pusillus var. tenuissimus Potamogeton robbinsii Sagitaria graminea Vallisneria americana Sediment S C G M Mussels N T S M D Sand Cobble Gravel Muck None 1/field -/field 5-1/field >1/field Page 3