Survey of Dissolved Oxygen in the Lamprey and Squamscott Rivers

Transcription

1 Summary Report Survey of Dissolved Oxygen in the Lamprey and Squamscott Rivers A final report to the United States Environmental Protection Agency, Office of Research and Development, Atlantic Ecology Division By Dr. Stephen Jones Jackson Estuarine Laboratory University of New Hampshire Durham, NH Submitted to Phil Trowbridge Watershed Management Bureau NH Department of Environmental Services Concord, NH July 27, 2005 This project was funded by a grant from the US Environmental Protection Agency under the National Coastal Assessment Program. Cooperative Agreement R

2 Introduction Both the Lamprey River (NHEST ) and the Squamscott River (NHEST ) are listed as Not Supporting for Aquatic Life Use Support because of low dissolved oxygen in the (b) report. The three lowest dissolved oxygen measurements from NCA survey were in the Squamscott River. Therefore, it was deemed important to accurately measure the spatial extent of low dissolved oxygen in these rivers. Extensive areas of low dissolved oxygen could indicate impacts to the aquatic life or the beginnings of eutrophication in the estuary. In contrast, localized pockets of low dissolved oxygen would indicate that the trend monitoring stations in the rivers are not representative of overall conditions. The EMAP study design is ideal for answering this question. Data from the GBNERR datasondes in 2003 indicated that late August was a likely time of year for low dissolved oxygen in the Lamprey and Squamscott rivers. Therefore, the goal of this project was to assess conditions in these rivers during late August. For comparison and context, assessments were also to be made in September. Methods The sampling sites for this study were located along transects in the Lamprey (Figure 1) and Squamscott (Figure 2) rivers. Field measurements were made on two days during the summer of 2004: August 11 and September 11. Both dates corresponded to tidal conditions where the tidal height was minimal and low tide occurred near sunrise. Two crews were deployed in separate boats, each to cover one of the rivers. The study areas for this project were the tidal portions of the Lamprey and Squamscott rivers. These areas are covered by hexagons 10-13, 15-19, 26-27, 36 in the NH NCA study design. The randomly selected sampling site locations were located in the field using a Garman GPS. Early morning at low tide was expected to be worst case for low dissolved oxygen. Therefore, for planning purposes, the targeted survey days where low tide in the Squamscott and Lamprey rivers coincided with early morning in August and September, Moreover, the weather prior to the chosen dates was also considered in choosing the exact sampling date. Basic hydrographic profile (water depth, sample depth) and water quality parameter (dissolved oxygen, temperature, salinity, ph) measurements were made with a YSI 6600 Datasonde and a YSI-85 Multi-parameter Field Probe. The YSI-6600 was lowered over the side of the boat at the surface depth (0.5 m) and while it was equilibrating the YSI-85 was lowered to the same depth to conduct a QC check. DO measurements made by the 6600 were recorded if the two probe DO readings agreed to within ±0.5 mg/l. All other measurements (ph, salinity, temperature) were also recorded. The 6600 was then lowered to a depth of 0.5 m above the bottom for sites with total water depths of > 1.5 m and allowed time to equilibrate, then measurements were made and recorded at that depth. The time on and off site were also recorded. All data were recorded on field sheets in the field. Field data were transcribed to electronic files in the laboratory and verified.

3 Results and Discussion The selected and actual sample locations (Table 1) were all well within the accepted ±120 ft tolerance (U.S. EPA 2001). The time required to sample at all sites ranged from 1:02 to 1:03 h in the Lamprey River and from 1:51 to 2:05 h in the Squamscott River (Tables 2 & 3). There was marked stratification in the Lamprey River on August 11, based on the salinities of bottom and surface waters, especially further up the river below the tidal dam at LMP 1 (Table 2). The lowest DO concentration was 5.3 mg/l, equivalent to 73% saturation in bottom water at LMP 1; the surface water concentration art the same site was 7.9 mg/l. All other DO concentrations were higher, ranging from 6.4 to 7.9 mg/l, with % saturation values ranging from 85.3 to 95.1 %. In the Squamscott River on the same day, the water was well mixed with little evidence of stratification (Table 2). The lowest DO concentration, 5.7 mg/l, was recorded in bottom water at SQM 1. All other concentrations ranged from 5.8 to 7.9 mg/l, with saturation values for all samples ranging from 75.2 to 99.2%. Much less stratification in the Lamprey River was observed on September 11, 2004 (Table 3). The lowest DO concentration was 6.7 mg/l, equivalent to 82.4% saturation in bottom water at LMP 3; the surface water concentration at the same site was 9.3 mg/l. All other DO concentrations were higher, ranging from 7.3 to 9.6 mg/l, with % saturation values ranging from 88.5 to %. In the Squamscott River on the same day, the water was well mixed with little evidence of stratification and low salinity (0.1 to 2.4 ppt) throughout the river (Table 3). The lowest DO concentration, 9.4 mg/l, was recorded in bottom water at SQM 2. All other concentrations ranged from 9.5 to 11.9 mg/l, with saturation values for all samples ranging from to 126.6%. The higher DO concentration observed during September were expected because of lower water temperatures. Comparison of the transect data to water quality data recorded by the GBNERR/SWMP datasondes in both rivers is useful to help determine if the timing of the transect measurements were coincident with conditions for the lowest DO concentrations on the two sample dates. Data for the sondes was available from NOAA (2004). The sondes are located nearest to LMP-2A in the Lamprey River (Figure 1) and downstream from SQM-1A in the Squamscott River (Figure 2). Data from the Lamprey River datasonde on 8/11/04 showed DO concentrations ranged from mg/l from 6:30-7:00 AM (Table 4), the times bracketing the sampling time (6:42 AM) at LMP-2A where the DO concentration was 7.9 mg/l (Table 2). The lowest DO concentration recorded at the sonde that day was 6.6 mg/l and 89.4 % saturation at 5:00 AM, an hour after the lowest depth was recorded. Thus, the timing of the sampling for this study was ~2 h later than the time when the lowest DO concentrations occurred. Data from the Squamscott River datasonde on 8/11/04 showed DO concentrations ranged from mg/l from 5:30-6:00 AM (Table 4), the times bracketing the sampling time (5:57 AM) at SQM-1A where the DO concentration was mg/l between 0.5 and 1.5 m below the surface (Table 3). The lowest DO concentration recorded at the sonde that day was 5.7 mg/l and 74.6 % saturation at 4:00 AM, the same time the lowest depth and salinity were recorded. Thus, the timing of the sampling for

4 this study was again ~2 h later than the time when the lowest DO concentrations occurred. On 9/11/04, data from the Lamprey River datasonde showed DO concentrations ranged from mg/l from 7:00-7:30 AM (Table 4), the times bracketing the sampling time (7:21 AM) at LMP-2A where the DO concentration was 9.3 mg/l (Table 2). The lowest DO concentration at the sonde that day was after the sampling time. Thus, the timing of the sampling for this study was ~2 h later than the time when the lowest DO concentrations occurred. The wide differences between DO concentrations suggest the datasonde could have been out of calibration for DO, but the sonde did show that the sample time for this study occurred ~2 h after the lowest depth was recorded (5:30 AM). In the Squamscott River the sonde showed DO concentration was 7.6 mg/l from 6:00-6:30 AM (Table 4) while the concentration at SQM-1 was mg/l between m below the surface (Table 3). The differences between DO concentrations suggest the datasonde could have been out of calibration for DO, but the sonde did show that the sample time for this study occurred ~2 h after the lowest depth was recorded (4:30 AM). Conclusions and Recommendations The field studies conducted in this showed no signs of widespread or even localized areas with dissolved oxygen problems in either the Lamprey or the Squamscott rivers. The timing of the sampling could have missed the critical times during the summer of However, the summertime temperatures during 2004 were not as hot as it can be in Seacoast New Hampshire and the weather was often overcast, both conditions that could decrease the impact of natural processes that may induce depressed DO levels. In a related study, the general conclusions were similar in that the lowest DO concentrations occurred in high salinity bottom waters under stratified conditions in the Lamprey River (Pennock 2004). Direct comparisons between sonde data and the results from this study were expected to be somewhat different because the sondes are located at different depths and locations compared to this study sites, and calibrations occurred prior to the study sample dates, depending on deployment dates. However, the datasonde data were useful to determine when the lowest DO concentration occurred on the study sample dates. The timing for lowest DO conditions was expected to occur just prior to sunrise. However, based on the datasonde data for the two sample dates, these conditions appeared to occur at the time of the lowest depth and salinity, in both cases before sunrise. More in depth analysis of the Squamscott River datasonde data from 2004 showed the times when the lowest DO concentrations were recorded were consistently more frequent during July and August spring tides and began 2-5 h prior to low tide (data not shown). These events all had DO concentrations <5.0 mg/l, which is much lower than observed in this study and at a level of ecological concern. The results of this study and the sonde data will help to focus future efforts to characterize DO conditions in these rivers.

5 References National Oceanic and Atmospheric Administration, Office of Ocean and Coastal Resource Management, National Estuarine Research Reserve System-wide Monitoring Program. (NOAA) Centralized Data Management Office, Baruch Marine Field Lab, University of South Carolina Pennock, J. and P. Trowbridge UNH Study of Dissolved Oxygen in the Lamprey River Quality Assurance Project Plan. NH Estuaries Project, Portsmouth, NH. U.S. EPA Environmental Monitoring and assessment Program (EMAP): National Coastal assessment Quality Assurance Project Plan United Stated Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Gulf Ecology Division, Gulf Breeze, FL. EPA/620/R-01/002.

6 Figure 1. Sampling sites in the Lamprey River.

7 Figure 2. Sampling sites in the Squamscott River.

8 Table 1. Selected and actual sampling locations in the Lamprey and Squamscott rivers: 2004 Sample Randomly selected Actual 8/11/04 Actual 9/11/04 sites Latitude Longitude Latitude Longitude Latitude Longitude Lamprey River LMP1 A 43º º º º º º LMP2 A 43º º º º º º LMP3 A 43º º º º º º LMP4 A 43º º º º º º LMP5 A 43º º º º º º LMP6 A 43º º º º º º LMP7 A 43º º º º º º LMP8 A 43º º º º º º LMP9 A 43º º º º º º LMP10 A 43º º º º º º Squamscott River SQM1 A 43º º º º º º SQM2 A 43º º º º º º SQM3 A 43º º º º º º SQM4 A 43º º º º º º SQM5 A 43º º º º º º SQM6 A 43º º º º º º SQM7 A 43º º º º º º SQM8 A 43º º º º º º SQM9 A 43º º º º º º SQM10 A 43º º º º º º SQM11 A 43º º º º º º SQM12 A 42º º º º º º SQM13 A 42º º º º º º SQM14 A 42º º º º º º SQM15 A 42º º º º º º

9 Table 2. Water quality measurements in the Lamprey and Squamscott rivers: 8/11/04. 8/11/04 Time on Depth Surf./Bot. Dissolved Oxygen Temperature Salinity ph station (m) Depth (m) (mg/l) (% saturation) ( C) (ppt) Lamprey River LMP1 A 6: LMP2 A 6: LMP3 A 6: LMP4 A 6: LMP5 A 6: LMP6 A 6: LMP7 A 6: LMP8 A 6: LMP9 A 6: LMP10 A 5: Squamscott River SQM1 A 5: SQM2 A 6: SQM3 A 6: SQM4 A 6: SQM5 A 6: SQM6 A 6: SQM7 A 6: SQM8 A 7: SQM9 A 7: SQM10 A 7: SQM11 A 7: SQM12 A 7: SQM13 A 7: SQM14 A 7: SQM15 A 8:

10 Table 3. Water quality measurements in the Lamprey and Squamscott rivers: 9/11/04. 9/11/04 Time on Depth Surf./Bot. Dissolved Oxygen Temperature Salinity ph station (m) Depth (m) (mg/l) (% sat) ( C) (ppt) Lamprey River LMP1 A 7: LMP2 A 7: LMP3 A 7: LMP4 A 7: LMP5 A 6: LMP6 A 6: LMP7 A 6: LMP8 A 6: LMP9 A 6: LMP10 A 6: Squamscott River SQM1 A 6: SQM2 A 6: SQM3 A 6: SQM4 A 6: SQM5 A 6: SQM6 A 7: SQM7 A 7: SQM8 A 7: SQM9 A 7: SQM10 A 7: SQM11 A 7: SQM12 A 7: SQM13 A 7: SQM14 A 8: SQM15 A 8:

11 Table 4. Water quality data from GBNERR/SWMP datasondes in the Lamprey and Squamscott rivers during the sampling times for this study Time Temp SpCond Sal DO % DO_mgl Depth ph Turb 8/11/04 Lamprey River 2:30: :00: :30: :00: :30: :00: :30: :00: :30: :00: Squamscott River 3:00: :30: :00: :30: :00: :30: :00: :30: :00: :30: :00: :30: /11/04 Lamprey River 4:30: :00: :30: :00: :30: :00: :30: :00: Squamscott River 4:00: :30: :00: :30: :00: :30: :00: :30: :00: :30: