The purpose of TAC Updates and “Thoughts from the Coastal Scientist” is to summarize information (facts and data) from meetings and to articulate other questions, concepts, and connections that the TAC is considering. The information is intended only to help advance TAC discussions and is NOT intended to be used by an individual or group as final or conclusive statements. All information presented through this TAC page during the State of Our Estuaries report development is considered preliminary until it is published by PREP in December 2017.
THOUGHTS & NOTES FROM THE COASTAL SCIENTIST:
The Technical Advisory Committee had its fourth meeting on March 28th 2017 to solicit input for the development of the 2017 PREP Data Report and 2018 State of Our Estuaries (SOOE) Report. This fourth meeting was focused on nutrient loading, nutrient concentration, dissolved oxygen, phytoplankton, and suspended sediment concentrations.
We also talked about the upcoming TAC calendar. The next TAC meetings are scheduled for May 9th and May 10th. These will be the final TAC meetings before our first draft of the 2017 Data Report and the 2018 State of the Estuaries Report. Please stay tuned to this newsletter and the PREP e-mail list for more information on this process.
Below, is an executive summary followed by a more detailed summary of our discussions from March 28th. These Coastal Scientist Thoughts and detailed notes are also available through the TAC mailing list and the TAC website. If you’re not on that list or aren’t sure if you are please contact Kalle Matso.
Executive Summary: March 28th Technical Advisory Meeting discussed the following:
- Nutrient loading (2012 – 2016)
- Nutrient concentrations (2012 – 2015; 2016 data will be added before July, 2017)
- Dissolved Oxygen, phytoplankton, and suspended sediment concentrations (all 2012 – 2015)
Preliminary Results (from TAC discussion, based on available data)
Compared with the 2009 through 2011 period, nutrient loading from wastewater treatment facilities was reduced by 25%. (Looking at reductions on an annual basis would show a greater reduction still, since most of the upgrades took place in the latter half of the 2012 through 2016 period.) This is due, in part, to reductions in nitrogen effluent concentrations made by the Cities of Rochester and Dover. Also, Durham has reconfigured its treatment plant as a pilot to achieve additional nitrogen removal. Finally, it should be noted that Portsmouth, Newington, Exeter and Newmarket are in the process of upgrading their treatment plants.
Reductions were also seen in the non-point source component of nutrient loading.
Nutrient concentrations—especially dissolved inorganic nitrogen (DIN) and total nitrogen—were also discussed. At five of the eight stations, there were no statistically significant long-term trends in the data. At the Lamprey River Station, there was an increasing trend in Total Nitrogen. At both the Oyster River and NH-0057A (Upper Piscataqua) station, there were decreasing trends in DIN.
Based on preliminary analysis of the data presented on March 28th, the dissolved oxygen story remains mostly unchanged from the 2009 and 2012 State of Our Estuaries reports. In the Great Bay and coastal waters, there are no dissolved oxygen issues to speak of. Further up the tributaries, dissolved oxygen levels can drop below desired thresholds, but there are many possible reasons for these incidents, and we cannot currently determine the causes.
Phytoplankton levels show no increasing or decreasing trends and, overall, annual averages remain below 10 ug/L.
Suspended sediment levels vary, depending on the station. Five of the sampling stations showed no trend and three stations showed statistically significant trends. At Adam’s Point, there was an increasing trend; this is based on very low numbers at the beginning of the data set in the 1970s. Since 1989, there is no increasing trend in the data. At the Lamprey River station, there was an increasing trend. Finally, at the NH-0057A site in the Upper Piscataqua River, there was a decreasing trend.
Discussion (from the perspective of the PREP Coastal Scientist)
Regarding the reduction in non-point source nutrient loading, potential factors in this reduction may include region-wide efforts to better manage stormwater as well as lower amounts of precipitation during the period from 2012 to 2016.
When discussing phytoplankton and sediments, it’s important to understand that these two light-attenuation components are additive and should be thought of together and not independent of each other.
Phytoplankton and sediments data represent annual averages from grab samples taken roughly once a month and can vary significantly in between these sampling events. This variability does have an impact on biological resources; therefore, caution must be exercised in the interpretation of these data. The need for additional stations in different parts of the estuary is going to be addressed going forward so that we have a more accurate picture of the system.
What do these numbers mean for oysters*, a biological resource in the Great Bay Estuary? Although annual averages for phytoplankton are low, evidence from other estuaries indicates that these levels are not limiting oyster health. The same goes for suspended sediment concentrations; levels are likely not high enough to stress oysters. Sedimentation, the process of sediment settling on the bottom, is a different though related issue from suspended sediments. There are concerns that sedimentation is stressing oyster reefs in the Great Bay Estuary, and experts agree that a sediment transport model would clarify this issue.
Finally, what do these numbers mean for eelgrass*, which experts agree has been struggling since the late 1990’s? Unfortunately, we still lack the data to definitively say whether changing any of these single parameters will impact eelgrass. It’s possible that further decreasing any of these parameters could help eelgrass, but we don’t know. That even goes for phytoplankton, which is surprising to most people, who assume that phytoplankton levels are so low that they’re not an issue. However, work by Jud Kenworthy, a member of the Technical Advisory Committee, has shown that in certain conditions, the light needs of eelgrass can increase which lowers the thresholds for light attenuating components, such as phytoplankton and sediments. (That’s why PREP will continue to urge that we further reduce non-point source pollution, which carries many potential stressors to the estuary.)Other light attenuation components include: CDOM, which is difficult to reduce through management actions; epiphytes (algae and other organisms growing on eelgrass leaves); and seaweed, in particular, drift seaweed, as opposed to attached seaweed.
*Oysters and eelgrass integrate conditions continuously and so annual averages must be used with care.
We will continue to hone in on what these data—and other data—mean for eelgrass at the next TAC meetings, which are taking place on May 9th and 10th.
A More Detailed Summary of the March 28th Meeting
- Michelle Shattuck presented on nutrient loading.
- Not all the data is in but Michelle has been working very hard to incorporate 2016 data. Regarding wastewater treatment facilities, the data she has analyzed represents 92% of the Total Nitrogen (TN) and Dissolved Inorganic Nitrogen (DIN) from all the wastewater treatment facilities.
- Based on preliminary estimates, the period 2012 through 2016 average TN loading from waste water treatment facilities is down 25% from the previous period (2009 through 2011), from 360.5 tons/year to 269.7 tons/year. DIN loading from wastewater treatment facilities is down 19%, from 284.1 tons/year to 230.8 tons/year.
- A significant portion of this reduction comes from the efforts of Rochester, which decreased its TN and DIN loading by 59% and 56%, respectively. Dover decreased its TN and DIN load by 27% and 10%, respectively.
- The significance of these reductions is underemphasized by averaging the results over the five-year period, since most of the reductions took place in the last two or three years. The State of Our Estuaries report will break the changes down by year so that people can see the dramatic reductions that have taken place recently.
- It is notable that the communities of Newmarket, Newington, Exeter and Portsmouth are due to finish waste water treatment facility upgrades in the next two years, so further reductions are scheduled.
- Preliminary assessments of non-point source nutrient loading from the main watersheds (including the Bellamy, Cocheco, Exeter, Great Works, Lamprey, Oyster, Salmon Falls and Winnicut) show similar reductions.
- Based on preliminary estimates, the period 2012 through 2016 average TN watershed loading from is down 30% from the previous period (2009 through 2011), from 830.3 tons/year to 582.5 tons/year. DIN loading from watersheds is down 27%, from 358.9 tons/year to 263.7 tons/year.
Discussion (from the perspective of the PREP Coastal Scientist)
- Note that these numbers will change in the final analysis as the influence of upstream waste water treatment facilities is backed out of the assessment.
- As has been shown in previous years, precipitation has a significant impact on watershed nutrient loading, with increases seen in years with high precipitation. Overall, the last five years have been dry.
- It continues to be debated whether these loading levels are conducive to the goal of increasing eelgrass habitat in the Great Bay Estuary.
- Therefore, using these numbers to understand/determine appropriate levels of nutrient loading is impossible without additional information.
- Few statistically significant trends were seen in TN and DIN concentrations. Exceptions included:
- An increasing trend for TN at the Lamprey River Station.
- A decreasing trend for DIN at the Oyster River Station.
- A decreasing trend for DIN at the NH-0057A Station, located in the Upper Piscataqua River.
Discussion (from perspective of PREP Coastal Scientist)
- Nutrient concentrations tell us what is in the water column at a specific point in time after microbes and plants have taken up the nutrients. Therefore, these data tell only a portion of the nutrient cycling story, especially since it doesn’t capture what is being stored and cycled in the sediments or delivered by loadings.
- DO levels in the bays, on the coast and the mouths of the rivers continue to consistently meet common thresholds (e.g., 5 mg/L for concentration and 75% for percent saturation) of oxygen required for the health of fish and invertebrates.
- Higher up in the tributaries, dissolved oxygen levels sometimes drop below these thresholds.
Discussion (from perspective of PREP Coastal Scientist)
- Temporary drops can be caused by many different factors. It is possible that these low DO events are stressing fish and/or invertebrates on and in the sediments.
- Phytoplankton levels, measured as chlorophyll-a in the water column, remain below 10 ug/L. The highest levels were measured at the Chapman’s Landing station in the Squamscott River, but even those levels have averaged less than 10 ug/L for the last three years.
- There were no statistically significant trends.
Suspended Sediment Concentrations
- Suspended sediment levels vary depending on the station. The highest total suspended sediments (TSS) levels were in the Squamscott River at the Chapman’s Landing station (35 mg/L) and Squamscott River station (29.7 mg/L); the third highest levels were in the Oyster River station (22.1 mg/L).
- There were three statistically significant trends. First, at Adam’s Point, there was an increasing trend; based on very low numbers at the beginning of the data set in the 70s. Since 1989, there is no trend in the data. In the last period, the average TSS level was 18 mg/L.
- At the Lamprey River station, there was an increasing trend with the last four years on record measuring above all the proceeding years, for an average of 13.3 mg/L.
- Finally, at the NH-0057A site in the Upper Piscataqua River, there was a decreasing trend, with the last four years being much less than proceeding years, with an average of 3.3 mg/L.
Phytoplankton & Suspended Sediments Discussion: (from perspective of PREP Coastal Scientist)
*** In the discussion of phytoplankton and sediments below, it’s important to understand that these two light-attenuation components are additive and should be thought of together and not independent of each other.
Also, the data below represent annual averages from grab samples taken roughly once a month. Phytoplankton and suspended sediments can vary significantly in between these sampling events, and this variability does have an impact on biological resources; therefore, caution must be exercised in the interpretation of these data.
Do current phytoplankton levels present a problem for eelgrass? Generally speaking, these are low levels and shouldn’t normally present a problem. However, studies have shown that, in some circumstances, phytoplankton levels and suspended sediment levels must be much lower than normal to compensate for other stressors (e.g., high temperatures, poor sediment quality). In other words, eelgrass light needs are not constant; they increase in impaired conditions.
Do suspended sediments levels present a problem for eelgrass? As was noted with phytoplankton, more data is required to answer that question. A related and important question concerns the sources of the sediments. The Great Bay Estuary needs a sediment transport model so that we can understand how much of the sediments are simply being resuspended by wind and storm events versus new sediment coming in from the tributaries.