EPSCoR Update 4/7/14
Work Completed to Date:
During September and October of 2013 sediment traps were designed, built, and tested. Four sediment traps were installed in Peck’s Pond in late November and monthly water sampling and testing was begun. A cold November resulted in an unusually early ice-in time for central Vermont and posed a sudden deadline for getting the sediment traps deployed. As a result, there was not enough time to implement plans to mark the position of the traps under the ice. The difficulty lay within finding a way to mark the position while also assuring that during ice-in and ice-out the marker would not be caught up in ice flow and disturb the traps. Thus, access to the sediment traps through the ice has not been possible. However, seasonal sediment trap data will be obtained as soon as ice-out occurs and will provide information on winter sedimentation composition and deposition. One set of sediment traps will be left in the pond for the duration of the year (until November, 2014).
Water sampling and testing has continued on a monthly basis at 5 sample sites: a deep-water pond site (6.75m water depth; samples taken at 0m and 6.00 m depth), a shallow-water pond site (3.00m depth), the northern wetland, the southern stream inflow, and the stream outflow. For the pond sites, in-situ measurements using the YSI multiprobe provided data on vertical changes in temperature, dissolved oxygen, conductivity, and pH. Stable and accurate pH readings were not always obtained because of very cold water and air conditions. A conversation with the technical support at YSI confirmed that the pH probe on our multiprobe works best at temperatures above 10°C.
Water samples were collected every month from late November to March from all 5 sites. Water samples from each site were put into two clean bottles, one for alkalinity and dissolved CO2 testing and a second for ICP analysis. Water samples were refrigerated and within 1-2 days the alkalinity and dissolved CO2 were measured. Phenolphthalein and total alkalinity were measured by titration using a HACH Basic Water Quality Kit. Samples taken for ICP analyses (major cation concentration) were filtered and stored in the refrigerator until enough samples were collected to warrant an ICP run.
ICP results show that calcium (58-93 ppm range) and sodium (25-170 ppm range) are the dominant cations at all sampling sites. Samples from the pond surface (both deep and shallow sites) show an increase in calcium and sodium as the winter progressed, while the other major rock-derived cations (Mg, Al, Si, Mn, K) do not show any definitive trend. The deep pond 6.00m samples show an increase in all rock-derived cations (Ca, Na, Mg, Al, Si, Mn, K) throughout the winter. The southern inflow, northern wetland, and outflow samples show a decline in concentrations of most rock-derived cations (Ca, Mg, Al, Si, and Mn) until February and then a slight increase in these cations in March. Sodium and potassium concentrations increase in the southern inflow and outflow samples but not in the northern wetland samples.
The in-situ conductivity measurements mirror the trends in rock-derived cation concentrations in the pond and northern wetland samples. At the southern inflow and outflow sites conductivity declines or stays the same initially then peaks in February. Dissolved CO2 generally increases in most of the samples between November and the months of January, February, and March. The shallow pond site consistently had the highest dissolved CO2, with peak concentrations in February. All samples had 0 phenolphthalein alkalinity, which indicates that total alkalinity is reflecting bicarbonate (HCO3) concentrations. Total alkalinity showed variable trends in all samples except for the deep pond 6.00m samples, which show an increase in alkalinity from 127 mg/L CaCO3 in November to 184 mg/L CaCO3 in March. The surface pond samples were the most variable in trend and range (120-334 mg/L CaCO3). Similar to the dissolved CO2 data, there is a peak in alkalinity in February in both surface pond samples. Alkalinity in the wetland and stream samples had a smaller range (120-170 mg/L CaCO3) but was just as variable in trend as the pond surface samples. Finally, the pond temperature, dissolved oxygen, and conductivity data from November show little variance with depth (more homogenous), while the January through March data display definitive trends between the surface and deep waters.
Discussion of Results:
The main findings from the winter water sampling and testing relate to the contribution of groundwater flow and its impact on water chemistry. Peck’s Pond has a strong groundwater component to its inflow. Variations in rock-derived cations (Ca, Mg, Si, Al, and Mn) indicate changes to the groundwater flow in and around the pond. The increase in these cations in the deep pond 6.00m samples suggests that groundwater flow continues at depth in the pond throughout the winter. In surface pond samples, only calcium increases, which reflects two things: 1) thermal stratification limits the exchange between surface and deep water and 2) a decrease in calcium utilization at the surface by organisms during the winter. The general decline in cations through the winter at the wetland and stream sites suggests a reduction of groundwater flow near the surface, as a result of freezing temperatures.
All of the sample sites showed high concentrations of sodium. The marked increase in February of sodium and potassium in the southern inflow and outflow reflects a surface water influx of de-icing road salts (NaCl, and KCl) . In addition, the southern inflow and outflow, which are closest to Rt. 64, showed the highest levels of sodium (30-170 ppm) of all the sites. Concentrations of sodium in the northern wetland, which is furthest from the highway were not as high and did not show the marked increase during February. The pond sites have the lowest levels of sodium (25-45ppm), which suggests that the wetlands surrounding the pond may provide somewhat of a buffer to sodium accumulation in the pond. Changes in sodium concentration in the pond and the northern wetland show the same trends as the other rock-derived cations and indicate that sodium in these two sites is sourced from the groundwater and not surface flow as in the southern sites. These results are significant because they show that surface water and groundwater in the Peck’s Pond basin have unnaturally high concentrations of sodium due to the accumulation of de-icing road salts. Previous water chemistry studies of streams and ponds in central Vermont done by Norwich University students, show sodium concentrations generally below 1ppm. The ecological impacts of accumulating road salts will be pursued in future studies of the Peck’s Pond basin.
Increases in dissolved CO2 between November and January-March are reflective of the increased gas saturation values of cold water. Relatively high dissolved CO2 concentrations in the shallow pond samples may also be explained by decreased photosynthesis but continued respiration and decomposition in the bottom sediment. The peak in dissolved CO2 and alkalinity in February in the surface pond samples was likely caused by a further decline in the utilization of inorganic carbon for photosynthesis resulting from cloudy conditions and deep snow pack. Alkalinity is higher in the pond samples as a result of the continuation of HCO3-rich groundwater flow into the lake through the winter and perhaps the further addition of inorganic carbon into the system through respiration and decomposition. Finally, vertical profiles of temperature, dissolved CO2, conductivity, and pH in the pond sites suggest that in November the lake was in a period of overturn and that from January to March it has been in a period of inverse thermal stratification.
The water chemistry data collected this winter has contributed to our understanding of the seasonal role of groundwater and surface flow into Peck’s Pond. As seen in the results, this impacts the water chemistry of Peck’s Pond and begins to addresses our initial research question concerning the relationship between temperature change, water chemistry, and sedimentation. However, there is still much to do. As soon as the ice is out on Peck’s Pond, the sediment traps will be retrieved from the deep and shallow water pond sites. Sediment trap samples will continue to be collected and analyzed monthly through to November, 2014. Water sampling and testing will also continue at all 5 sampling sites through November. The next few months are crucial to the project because we will begin to incorporate the sediment data and will cover a major seasonal change.
Summer research lead by senior researcher, Laurie Grigg, and student researcher, Roberto Armijo, will begin in mid-May following the end of the academic year. In addition to continuing with the monthly monitoring and testing of water and sediment samples, Laurie and Roberto will begin more in-depth data analysis. Calculations of the ionic activity product (IAP) of CaCO3 will be made and compared with the CaCO3 equilibrium constant as a measure of carbonate saturation in the lake. More time will be spent on graphing and statistical analysis of the changes observed in the data both through time and space (horizontal and vertical dimensions).
Roberto will be assisting with the monitoring project this spring and summer but will also begin a related study, investigating the primary productivity of the lake. A transect across the pond will be established and the following measures of primary productivity will be collected and analyzed:
1) Grab samples of the surface sediment to be analyzed for organic carbon, CaCO3, and macrofossils;
2) Secchi disk depths as a proxy for water clarity;
3) Water samples to be filtered and analyzed for phytoplankton;
4) A survey and identification of macrophytes.
Leslie Mathews from the Vermont Lakes and Ponds Management and Protection Program has made a tentative offer to analyze some samples from Peck’s Pond for chlorophyll-a, which is another measure of phytoplankton activity.
Interactions with Students:
Research support from a Norwich University work-study student throughout the 2013-2014 academic year. Several other students from NU contributed to field work as part of their course work in both a senior research course and oceanography.
At this point there are no significant impacts to the academic discipline. Although the discovery of accumulated road salts in Peck’s Pond and the surrounding wetlands could have some societal implications. On the one hand, the storage of salts in wetlands reduces its spread throughout the watershed but, it also has potentially harmful ecological impacts. The impacts of road salts on wetland ecology has not been adequately addressed in Vermont, which has many wetlands and a high use of road salt. This project highlights the need for a greater understanding of the role of wetlands in storing salts and of how wetland health can be balanced with winter road safety.
Collaborations and Partners:
Dr. Tara Kulkarini from Norwich University
Dr. Leslie Mathews, Vermont Lakes and Ponds Management and Protection Program.
We designed and built 4 sediment traps. Two of which will remain in Peck’s Pond, beyond the time-frame of this project as part of a longer-term monitoring of changes in annual sedimentation.
The discovery of high concentrations of sodium in Peck’s Pond and the surrounding wetlands has prompted a new set of research questions that will be explored with 5 seniors during the fall of 2014 for their senior research seminar. These students will examine the relationship between wetland water chemistry (both surface and groundwater) and vegetation composition and diversity. This latest branch of research questions was made possible by this Pilot Project.