URI Watershed Watch Program Block Island Monitoring Results 1-6 May 7 Elizabeth Herron and Linda Green, URI Watershed Watch Summary: To date both the field monitoring and laboratory analyses indicate that Block Island s premier resource, the Great Salt Pond, is in good health. However, during the six years of monitoring increases in nutrients have been detected, and a number of tributary streams have high levels of both nutrients and bacteria, particularly following rain events. Tributary monitoring has shown a great deal of variability in water quality conditions, therefore is especially important to maintain. Continued monitoring of both Great Salt Pond and its tributary streams is essential in order to determine whether apparent nutrient increases are an actual trend in water quality, or due to natural variability in response to weather patterns and the degree of associated uses of this well-used and beloved ecosystem. Monitoring enables us to more accurately pinpoint if and when problems begin to develop, and how the ecosystem responds to changes in the watershed. Scientists recommend that ten years of monitoring is needed to fully assess the health of a water body. During that time there will be drought and deluge, warm and cool weather, maybe even a hurricane - a full span of natural conditions. With six years of data available for the Great Salt Pond and the original three tributary stream sites, overall water quality status as well as some trends are becoming discernable. Table: Block Island Watershed Watch Monitoring Site Information Great Salt Pond Locations (at 1 meter from the and 1. meter from the bottom, or mid-depth): mid-harbor @ Green can #5 Narragansett Inn cove Off Champlin's dock Trim's Pond Tributary Locations: BI Trib #1 Mill Tail Pond, Ocean Ave. culvert BI Trib # Bridgegate Square culvert - "colored side pipe" BI Trib #3 Cormorant Cove salt marsh culvert BI Trib #4 Beach Avenue (added in 3) BI Trib #5 Harris Pt (added in 3) BI Trib #6 Scott's (added in 4) Introduction: The 6 monitoring season was the sixth that dedicated volunteer water quality monitors from the Committee for the Great Salt Pond (CGSP) monitored four sites on the Great Salt Pond (GSP) and six tributary stream sites as a part of the URI Watershed Watch Program (URIWW) (see Table and Figure 1 for site information). These sites were selected by members of the Committee for the Great Salt Pond in 1
cooperation with URI Watershed Watch staff at a site visit in 1. Monitoring has been funded through the Block Island and Green Hill Pond National Decentralized Wastewater Demonstration Project. Three additional tributary streams were added in 3 and 4 in order to investigate additional potential inland pollution sources. Figure 1. Map showing CGSP Monitoring Sites URI Watershed Watch (URIWW) staff trained CGSP volunteers to conduct the water quality monitoring, and provided annual refreshers after the initial training. These water quality monitors were provided with all the necessary monitoring equipment and supplies as well as a written monitoring manual that detailed all the procedures. Their regular monitoring followed a schedule developed by URIWW designed to cover the period of peak activity on the island - from mid-june through mid-october each year.
Unfortunately late season storms that disrupted ferry service shortened the monitoring season in several years. The monitoring included biweekly on-site monitoring of water clarity, water temperature, dissolved oxygen content, salinity, and algae level. (Please see URIWW monitoring manuals and quality assurance project plans available on the website at http://www.uri.edu/ce/wq/ww/ for more specific information.) In 3 the CGSP purchased a multi-parameter field meter to measure dissolved oxygen, temperature and salinity, replacing the URIWW owned and maintained kits. However the basic field monitoring procedures (monitoring depth, time of day, etc.) were otherwise kept the same. The on-site monitoring data was submitted to URIWW on monitoring postcards. In addition to the bi-weekly on-site monitoring, once a month the volunteers also collected a suite of samples, packed them on ice in a cooler and shipped them via ferry to Point Judith. The sample schedule was set to ensure that samples were collected near low tide in order to better assess the impact of land based sources versus in-pond sources, while also making sure that the samples would reach the URIWW laboratory within acceptable hold times. URIWW staff picked up the water samples from Point Judith and delivered them to the URIWW Analytical Laboratory in URI s College of the Environment and Life Sciences in Kingston. These samples were analyzed for bacteria, ph, nitrogen, phosphorus, total suspended solids and chlorophyll according to standard URIWW laboratory procedures (please see Quality Assurance Project Plan: University of Rhode Island Watershed Watch Analytical Laboratory http://www.uri.edu/ce/wq/ww/publications/labsops.pdf for additional information). The analytical laboratory is Rhode Island Department of Health certified (#LAI94). Brief summaries and discussion of the results of the six years of water quality monitoring follow. Weather summary: Weather can significantly affect water quality, and can confound the assessment of water quality findings. This summary (figure ) is based on weather data from the URI Weather Station in Kingston, RI. Departures from normal were in relation to the average temperature and precipitation values over the past thirty years. Monthly temperature was above normal for the vast majority of months in the six monitoring seasons, particularly in August and September. Rainfall was more evenly distributed between above and below normal in this same time span. The 1 monitoring season was generally warmer than average, with about average rainfall during the monitoring season (that year July - October.) Droughts during much of the summers of, 4 and 5 brought long periods of sunny days and warmer than average temperatures, and potentially increased impacts from a better boating season. Annual precipitation was above average from 3 through 6 particularly in 5 and 6. In 6, distribution of precipitation was not as erratic (extended dry periods followed by unusually wet periods) as in previous years. In 4 the remnants of two hurricanes in September produced nearly six inches of rain over two weekends, ending a summer long drought. In 5 a wet winter preceded a record dry summer, which ended with week long rains including an October record setting rain event. More than 6 above normal rain in June 6, and more than 4 above normal in 6 contributed to the 9+ above normal rain for that year. These types of extreme weather patterns make assessment of the water quality data challenging, and argue for continued long- 3
term monitoring in order to help differentiate between true water quality trends and weather related impacts. Figure. Weather Summary (Kingston RI Weather Station) Inches 11 9 7 5 3 1-1 -3-5 Precipitation, Departure from Normal, 1-6 MAR APR MAY JUNE JULY AUG SEP OCT 1 3 4 5 6 Degrees F. 7 5 Temperature, Departure from Normal, 1-6 3 1-1 -3-5 MAR APR MAY JUNE JULY AUG SEP OCT 1 3 4 5 6 Great Salt Pond field monitoring summaries: Volunteers measured a number of key water quality indicators using field instruments and/or kits at four sites on the Great Salt Pond. These field measurements, which included temperature, dissolved oxygen, salinity and processing samples for chlorophyll, were typically done at either mid-depth at sites less than two meters, or at half a meter from the and within one meter from the bottom at sites er than two meters. With the exception of the Mid Harbor site (), which was the est, water clarity, or Secchi depth transparency was generally a measurement of bottom depth, with the Secchi disk usually visible on the bottom. These water quality indicators pointed to overall excellent water quality in the Great Salt Pond for all four sites (figures #3 and #4 show data from the est and shallowest sites.) Water clarity at Mid-Harbor () was excellent, with generally low algae levels. These both indicate low nutrient, or oligotrophic conditions. 4
Figure 3. Great Salt Pond #1 Mid-harbor Site Field Data Charts 4 Jul-1 Sep-1 Dec-1 Feb- May- Jul- Oct- Dec- Mar-3 May-3 Aug-3 Oct-3 Dec-3 Mar-4 May-4 Aug-4 Oct-4 Jan-5 Mar-5 Jun-5 Aug-5 Nov-5 Jan-6 Apr-6 Jun-6 Aug-6 Nov-6 Eutrophic - low water clarity Mesotrophic - Moderate water clarity SECCHI DEPTH - WATER CLARITY 6 Oligotrophic - Excellent water clarity 8 The Secchi disk has always been visible on the bottom. Depth (m) Apparent decline in water clarity was due to a switch to low-tide monitoring. ppb 1 8 Eutrophic - Elevated algae levels CHLOROPHYLL LEVELS 6 4 Mesotrophic - Moderate algae levels Oligotrophic - Low algae levels Jul-1 Sep-1 Dec-1 Feb- May- Jul- Oct- Dec- Mar-3 May-3 Aug-3 Oct-3 Dec-3 Mar-4 May-4 Aug-4 Oct-4 Jan-5 Mar-5 Jun-5 Aug-5 Nov-5 Jan-6 Apr-6 Jun-6 Aug-6 Nov-6 mg/l 1 DISSOLVED OXYGEN WITHIN 1 METER OF THE BOTTOM 8 6 4 Potentially stressful dissolved oxygen levels Potentially lethal dissolved oxygen levels Jul-1 Sep-1 Dec-1 Feb- May- Jul- Oct- Dec- Mar-3 May-3 Aug-3 Oct-3 Dec-3 Mar-4 May-4 Aug-4 Oct-4 Jan-5 Mar-5 Jun-5 Aug-5 Nov-5 Jan-6 Apr-6 Jun-6 Aug-6 Nov-6 Dissolved oxygen at all four sites remained high throughout all six seasons, an indicator of good tidal flushing as well as good overall water quality. Salinity measurements showed a slight fresh water influence at all the pond sites monitored. Salt water typically has 35 parts per thousand (ppt) salinity, fresh water has ppt. With the exception of 1, salinity typically ranged from 3 33 ppt salinity in the pond sites. The range during 1 was broader, with a 35 ppt maximum salinity value, and 5 ppt minimum value at Mid-Harbor (). Salinity values in 6 and 5 averaged approximately 9 ppt, reflecting the higher than average precipitation. This also suggests that ground water contribution to the pond was fairly stable throughout the monitoring season despite large fluctuations in rain, and therefore, stormwater runoff. 5
Figure 4. Great Salt Pond #4 Trim s Pond Site Field Data Charts ppb 14 CHLOROPHYLL LEVELS AT MID-DEPTH 1 Eutrophic - Elevated algae levels 1 8 6 Mesotrophic - Moderate algae levels 4 Oligotrophic - Low algae levels Jul-1 Sep-1 Dec-1 Feb- May- Jul- Oct- Dec- Mar-3 May-3 Aug-3 Oct-3 Dec-3 Mar-4 May-4 Aug-4 Oct-4 Jan-5 Mar-5 Jun-5 Aug-5 Nov-5 Jan-6 Apr-6 Jun-6 Aug-6 Nov-6 mg/l 1 DISSOLVED OXYGEN AT MID-DEPTH 8 6 4 Potentially stressful dissolved oxygen levels Potentially lethal dissolved oxygen levels 4 35 3 5 15 1 5 ppt Saltwater = 35 ppt Freshwater = ppt SALINITY AT MID-DEPTH Jul-1 Sep-1 Dec-1 Feb- May- Jul- Oct- Dec- Mar-3 May-3 Aug-3 Oct-3 Dec-3 Mar-4 May-4 Aug-4 Oct-4 Jan-5 Mar-5 Jun-5 Aug-5 Nov-5 Jan-6 Apr-6 Jun-6 Aug-6 Nov-6 Jul-1 Sep-1 Dec-1 Feb- May- Jul- Oct- Dec- Mar-3 May-3 Aug-3 Oct-3 Dec-3 Mar-4 May-4 Aug-4 Oct-4 Jan-5 Mar-5 Jun-5 Aug-5 Nov-5 Jan-6 Apr-6 Jun-6 Aug-6 Nov-6 Fecal coliform Bacteria Monitoring: Fecal coliform bacteria are an indicator of fecal contamination and potentially disease causing organisms. Both shellfishing and swimming standards for fecal coliforms in marine waters (14 colony forming units (cfu)/1 ml and 5 cfu/1 ml respectively) have been established in order to protect the public from exposure to unsafe levels of pathogens. 6
5 45 4 35 3 5 15 1 5 Figure 5. Annual Averages Fecal Coliform Bacteria at Great Salt Pond Sites cfu per 1 ml Great Salt Pond #1 (Middle of the harbor) Great Salt Pond Annual Average Fecal Coliform Values (June - Oct. Geomean) Swimming Standard = 5 fecal coliform f /1 l 1 3 4 5 6 1 Shellfish Standard = 14 fecal coliform f /1 l 6 17 14 1 8 4 1 55 68 6 Great Salt Pond # (Narragansett Inn Cove) 7 5 5 93 Great Salt Pond #3 (Champlin s) Yearly Maximum in Box 5 45 5 3 117 47 57 117 Great Salt Pond #4 (Trim s) Average fecal coliform values at the GSP sites typically were below the stringent 14 cfu/1 ml shellfishing standard the first three years of monitoring (figure 5). In the past three years counts above both shellfishing and the 5 cfu/1 ml swimming standards have become more frequent, at Champlin s () and Trim s Pond () and particularly at Narragansett Inn Cove (). All three sites exceeded both standards in at least four of the six monitoring seasons, with very high fecal coliform counts this past summer, 6 cfu/1ml on July 5, 6 at Narragansett Inn Cove (GSP#), 5 on July 19, and 63 on August 17. The July 5 sample far exceeded the previous maximum of 68 from the 9/1/5 collection. In contrast, the Mid-Harbor site () has never exceeded the swimming standard in the six years of monitoring. Even that site had its highest maximum to date in 6, above the shellfishing standard but still below the swimming standard. Tributary stream sites typically had much higher fecal coliform counts than the Great Salt Pond sites (figure 6a.) While freshwater fecal coliform standards for recreational contact such as swimming ( cfu/1 ml fecal coliform) are much higher than for salt water, the yearly averages for these sites exceeded even this higher standard with regularity. Since several of these tributaries discharge directly into the shellfishing waters of the Great Salt Pond, identifying the source(s) and taking action to correct problems in order to attain lower levels is an important goal. Ocean Ave (#1) and Bridgegate Square (#) have had the highest counts since the monitoring began, with values often in excess of thousands. Figure 6b shows the highest counts for each site for each monitoring season. The scale of that chart is nearly ten times higher than for the average counts and clearly illustrates the contribution of these streams. However, since there were no flow measurements made, the overall loading or impact from those sources may be different. It should be noted that during dry periods these sites have very low bacteria levels, with uniformly low values during the drought of. With no rain there was no overland flow or runoff bringing wastes into the streams. Low bacteria counts during dry weather also suggest that there were no direct discharges of waste water to the streams, such as from a pipe or a failed septic system. Overall the tributary site at Harris Point (#5) showed the least impact from bacterial contamination.
7 6 5 4 3 1 Figure 6a. Annual Average Fecal Coliform Bacteria Tributary Stream Sites cfu per 1 ml 8 Ocean Ave (#1) GSP Tributary Streams Annual Average Fecal Coliform (June - Oct. Geomean) Bridgegate Sqr (#) 1 3 4 5 6 Cormorant (#3) Beach Ave. (#4) Freshwater swimming standard () Harris Pt (#5) Scott s (#6) Figure 6b. Annual Maximum Fecal Coliform Bacteria Tributary Stream Sites cfu per 1 ml 6 5 4 3 GSP Tributary Stream Annual Maximum Fecal Coliform 1 3 4 5 6 Freshwater swimming Standard () 1 Ocean Ave (#1) Bridgegate Sqr (#) Cormorant (#3) Beach Ave. (#4) Harris Pt (#5) Scott s (#6) Nutrients: Total, Nitrate-, and Ammonium- Nitrogen. (BayWatchers II produced by the Coalition for Buzzard s Bay and available at http://www.savebuzzardsbay.org/pdf/baywatchers- pages3-34.pdf, provided the background information for this section.) Total nitrogen is widely used by scientists as an indicator of eutrophication or nutrient enrichment in marine waters. Levels below 35 ppb are characteristic of low nutrient waters, while values above 6-7 ppb indicate nitrogen enrichment. Using those values for comparison, Great Salt Pond water samples were in the low to moderate range for all years (figure 7.) However, that chart clearly shows increase in total nitrogen over these years, with the highest levels at Trim s Pond (GSP#4). Monitoring the Great Salt Pond for total nitrogen should definitely be continued. 6 total nitrogen levels have nearly tripled since monitoring began in 1. Total nitrogen is comprised of nitrate-n, ammonia-n and organic-n. Nitrate- and ammonia- account for about half the total nitrogen at each of the sites (data available upon request.) 8
ppb or ug/l 5 45 4 35 3 5 15 1 5 Figure 7. Annual Mean Total Nitrogen Great Salt Pond Sites Great Salt Pond Yearly Total Nitrogen Averages (June - Oct. average) 1 3 4 5 6 Moderate nutrient range Low nutrient range Monitoring tributary inlet streams is important for determining water quality impacts including nutrient loading. Nutrient loading is defined as the rate at which a substance such as N is added to a system. The measurement of loading includes multiplying the concentration of nutrient from a source by the volume of water from that source (see http://www.dnr.state.md.us/bay/monitoring/water/ for a discussion of the difference between concentration and loading.) Thus, while a particular tributary may have very high concentrations, if there is very little flow from that source, its overall load or contribution, may be very minimal. Since the flow of these tributary sites has not been measured, it is impossible to accurately assess the actual nutrient loads to the Great Salt Pond. However the results to date can help target areas for additional investigation and monitoring. Total nitrogen values in the inlet streams were generally at least twice as high as the pond sites (figure 8). All sites except for Scott s (#6) have moved from the low N to the moderate N range. Ocean Ave (#1) and Cormorant (3) have shown the greatest increase since monitoring began. The previous 3 maximum was passed in 6 at all sites except Cormorant Cove (#3). It should be noted that total nitrogen levels in these Block Island tributary streams were within the range of other tributaries monitored as a part of URIWW. However, Bridgegate Square (#), and Beach Ave (#4) have been consistently higher, with N levels more similar to urban rivers and streams. In light of the impact that additional nitrogen loads could have on the pond, continued monitoring of these tributary inlet streams is strongly recommended. 9
Figure 8. Annual Mean Total Nitrogen Tributary Sites ppb or ug/l 16 14 Tributary Inlet StreamsYearly Total Nitrogen Averages (June - Oct. average) 1 3 4 5 6 1 1 8 6 Nutrient enriched range (above 6-7 ppb) 4 Ocean Ave (#1) Bridgegate Sqr (#) Cormorant (#3) Beach Ave. (#4) Harris Pt (#5) Scott s (#6) Nitrate-nitrogen is a soluble form of nitrogen, readily taken up and used by algae and submerged vegetation, especially during the summer growing season. Nitrate-nitrogen levels were very low, below the detectable range for most of the sampling events in most years for the pond sites (figure 9.) As with total nitrogen, nitrate-nitrogen levels in the tributaries inlet streams were also higher than in the pond at Ocean Ave. (#1) and Bridgegate Sq (#), with measurable levels all years (figure 1.) These levels were within the range of other URIWW monitored tributaries, with Bridgegate Sq. similar to urban tributary streams. It should be noted that all levels were well below the 1 ppb (1 ppm) nitrate-nitrogen levels that the US Geological Survey considers an indication of some type of groundwater contamination. Figure 9. Annual Mean Nitrate-Nitrogen Great Salt Pond Sites ppb or ug/l 3 Great Salt Pond Yearly Average Nitrate-Nitrogen (June - Oct. Average) 1 3 4 5 6 1 analytical limit of detection 1
Figure 1. Annual Mean Nitrate-Nitrogen Tributary Sites ppb or ug/l 1 8 6 Tributary Stream Yearly Average Nitrate-Nitrogen (June - Oct. Average) USGS criteria for an indication of groundwater contamination 1 3 4 5 6 4 Ocean Ave (#1) Bridgegate Sqr (#) Cormorant (#3) Beach Ave. (#4) Harris Pt (#5) Scott s (#6) Ammonium-nitrogen is the other soluble form of nitrogen that the URI Watershed Watch program analyzes for. It is also readily used by algae, thereby indirectly contributing to biological oxygen demand or BOD, which can reduce dissolved oxygen concentration in water. The acceptable level for ammonia-n depends on ph, salinity and temperature in salt water, and on temperature, ph and life stage (of critical organisms) in freshwater, (see http://www.dem.ri.gov/pubs/regs/regs/water/hq6.pdf for specifics.) For the Great Salt Pond it is 411 ppb and for the tributary inlet streams it is 1 ppb. Average values for each year and at each monitoring site in the pond were considerably below that critical level (Figure 11). While ammonium-nitrogen levels were low, a very slight trend of increasing values has been noted, and bears continued watching. Figure 11. Annual Mean Ammonium-Nitrogen Great Salt Pond Sites ppb or ug/l 4 35 3 5 15 1 5 Great Salt Pond Annual Ammonium Nitrogen (June - Oct. Mean) Critical chronic ammonium-nitrogen level for GSP 411 ppb 1 3 4 5 6 11
Based on the ph and temperature values commonly seen in the GSP tributaries during the monitoring season, chronic ammonium-nitrogen values in the range of 16 to 53 ppb or higher would be a concern to salmonid species at various life stages. During the past six monitoring seasons average values were quite low, and 1% or less than the values of critical concern (figure 1.) In addition, ammonium-nitrogen levels in the tributaries have not shown any clear overall trends, either increasing or decreasing. ppb or ug/l 1 9 8 7 6 5 4 3 1 Figure 1. Annual Mean Ammonium-Nitrogen Tributary Sites Ocean Ave (#1) Tributary Annual Ammonium Nitrogen (June - Oct. Mean) Critical chronic ammonium-nitrogen level for GSP tributaries > 1 ppb 1 3 4 5 6 Bridgegate Sqr (#) Cormorant (#3) Beach Ave. (#4) Harris Pt (#5) Scott s (#6) Phosphorus. In most estuaries such as the Great Salt Pond, nitrogen is the primary nutrient that controls algal & plant growth. However like nitrogen, phosphorus is also essential for life, and thus in salt water environments phosphorus levels must be considered in relationship to nitrogen levels. In estuaries the recommended level of total phosphorus is 1 to 1 ppb with 1 to 1 ppb of total nitrogen (a 1:1 ratio of nitrogen to phosphorus). Under these conditions, most phosphorus-caused algal blooms may be avoided. (Please see http://www.water.ncsu.edu/watershedss/info/phos.html for more information.) Like nitrogen, phosphorus also occurs in the total form which includes phosphorus bound in particulate (organic and inorganic) matter and soluble or dissolved forms which are readily used by algae. 1
ppb or ug/l 8 7 6 5 4 3 1 Figure 13. Annual Mean Total Phosphorus Great Salt Pond Sites Great Salt Pond Annual Total Phosphorus (June - Oct. Averages) 1 3 4 5 6 Approximate Maximum recommended TP (=1% of TN) Total phosphorus levels in the Great Salt Pond have been in the -4 ppb range (figure 13) and do not show the increases seen with total nitrogen. They were mostly in the dissolved form (data not shown), indicating that it was being absorbed and used by microscopic algae and aquatic plants. Overall total phosphorus is close to 1% of overall average total nitrogen, indicating that has the potential to help cause algae blooms. Figure 14. Annual Mean Total Phosphorus Tributary Sites ppb or ug/l 16 14 1 1 8 6 4 Ocean Ave (#1) Tributary Streams Annual Total Phosphorus (June - Oct. Averages) 1 3 4 5 6 Bridgegate Sq (#) Cormorant (#3) Recommended Maximum TP for streams Beach Ave. (#4) Harris Pt (#5) Scott s (#6) For freshwater streams, a maximum concentration of 5 ppb total phosphorus is the advised limit for protection of downstream resources. Concentrations below 5 ppb were generally found in the tributary sites (figure 14.) In 6 Cormorant Cove (#3) had an extraordinarily high total phosphorus value of 74 ppb. This elevated that year s average to well above the advisory limit, the only time this happened during the six 13
years of monitoring at that site, although annual values have been close to the 5 ppb recommended maximum. Bridgegate Square (#), Harris Point (#5) and Scott s (#6), have all had water samples from multiple dates that exceeded 5 ppb. The regularity with which these sites have exceeded the recommended total phosphorus maximum in particular warrant continued monitoring of phosphorus. However the discussion of concentration versus loading in the section on total nitrogen also applies here. Acknowledgements: Volunteer water quality monitoring would not be possible without the dedication of outstanding volunteers such as Carl Kaufman, Kyra Riggie, Henry DuPont, Corrie Heinz, Pat and Shirley Howe. These individuals have devoted a great deal of time on the water collecting a many, many water samples and in their kitchens running tests and diligently processing samples for later URIWW lab analysis. We are indeed indebted to them for providing the information that has gone into this assessment. We also thank the Committee for the Great Salt Pond for helping to oversee the BI monitoring component of the Demonstration Project, and the technical committee that helped to identify areas of concern. We are most heartened by the cooperation and collaboration among various monitoring programs on Block Island that has continued partially as a result of this project. Finally, we thank Lorraine Joubert, Galen Howard McGovern and Bill Healy who have managed this project and enabled us to a get a clearer picture of the status of Block Island s greatest resource the Great Salt Pond and its watershed. 14