Coastal Acidification Monitoring in Long Island Sound
Understanding coastal acidification, as it varies from open ocean acidification, is crucial to identifying the unique problems occurring in coastal ecosystems such as Long Island Sound (LIS). The U.S. Geological Survey (USGS) is monitoring water quality parameters throughout LIS and its embayments to evaluate the status and trends of acidification processes in these waters. This project will inform the Long Island Sound Study on how to best manage the LIS to meet the goals of their Comprehensive Conservation and Management Plan and improve its ecological health.
Understanding Coastal Acidification
Coastal acidification is the decrease in pH in the fresh, salt, and brackish waters near the shoreline. While a decrease in pH in the open ocean is more directly influenced by an increase in atmospheric carbon dioxide, coastal acidification has a variety of possible causes, such as nutrient pollution from rivers and a higher amount of organic decomposition.
Coastal acidification is primarily driven by eutrophication (high amounts of nutrients entering a water body). Eutrophication can cause rapid algal growth, and at times algal blooms, which can result in subsequent rapid algal death leading to an increase in microbial respiration (utilizing oxygen) and an increased production of carbon dioxide. As carbon dioxide concentrations increase, pH goes down (becomes more acidic).
Coastal acidification can lead to:
- Reduced water quality limiting recreation and threatening fishing and aquaculture
- Decreasing shell growth and formation of bivalves, like clams and oysters
- Degraded habitat with low oxygen conditions not able to support animals and plants
Monitoring LIS Bottom Waters
The estuaries and embayments in southern New England and northern Long Island show the effects of eutrophication including algal blooms and low oxygen, particularly in bottom waters, which can indicate that acidification may be occurring. Therefore, this study is primarily focused on water-quality monitoring in near-bottom waters. Bottom waters are the most susceptible to coastal acidification because they are:
- Not often influenced by daily changes (such as tides)
- Less oxygenated due to water column stratification which limits mixing, preventing oxygen-rich surface waters from reaching the bottom
Data Collection
Monitoring sites were strategically selected to represent freshwater-quality contributions, and the water quality conditions in the near shore coastal environment of LIS’s:
- Rivers: Connecticut, Housatonic, Thames Rivers, Norwalk, Saugatuck, and Mystic Rivers
- Embayments: Oyster Bay and Flax Pond, NY
USGS is collecting baseline information to describe coastal water conditions, determine areas of concern, and document overall coastal acidification trends within LIS through the collection of continuous and discrete water quality data.
- Continuous: Real-time water quality data collection (water temperature, specific conductance, dissolved oxygen, pH, turbidity and chlorophyll)
- Discrete: Monthly samples of total alkalinity and acid neutralizing capacity (measure of buffering capacity), pH, and dissolved organic and inorganic carbon (measure of carbon species contributing to acidification)
Collection of continuous and discrete data can help isolate trends in acidification due to:
- Seasonality
- Daily changes
- Primary productivity
Social Relevance
By advancing our understanding of coastal acidification through these research efforts, we can better safeguard the ecological health of Long Island Sound and its invaluable marine resources.
Figure 1 – Location of monitoring stations across Long Island Sound.
Discrete water samples are collected according to the USGS National Field Manual at continuous monitoring stations and are processed immediately before in-house analysis or shipping to the USGS National Water Quality Laboratory (NWQL) or the USGS Reston Biogeochemical Processes in Groundwater Lab (RBPGL). Continuous data for water temperature, specific conductance, dissolved oxygen, pH, turbidity, and chlorophyll a can be found in Table 1.
Table 1. Data collection sites
| Station Number | Station Name |
| 411940071590300 | Mystic River at RAM Island Yacht Club, CT |
| 410502073236000 | Norwalk Harbor at the Cove Marina NR E Norwalk, CT |
| 410606073245700 | Norwalk River at Norwalk Aquarium nr S Norwalk, CT |
| 410724073221001 | Saugatuck River US Rt 136 Bridge, CT |
| 01127768 | Thames River at Groton, CT |
| 01194796 | Connecticut River at Old Lyme, CT |
| 01208837 | Housatonic River near Nells Island near Stratford, CT |
| 01303152 | West Harbor at Oyster Bay Nwr at Bayville NY |
| 01304057 | Flax Pond near Old Field, NY |
Figure 2. Continuous monitor servicing event at Saugatuck River US Rt 136 Bridge, CT (USGS Site ID 410724073221001).
Figure 3. Continuous water quality gaging station located at Flax Pond near Old Field, NY (USGS Site ID 01304057).
Figure 4. Discrete sampling at Thames River at Groton, CT (USGS Site ID 01127768).
Figure 5. Discrete sample collected at Connecticut River at Old Lyme, CT (USGS Site ID 01194796).
Understanding coastal acidification, as it varies from open ocean acidification, is crucial to identifying the unique problems occurring in coastal ecosystems such as Long Island Sound (LIS). The U.S. Geological Survey (USGS) is monitoring water quality parameters throughout LIS and its embayments to evaluate the status and trends of acidification processes in these waters. This project will inform the Long Island Sound Study on how to best manage the LIS to meet the goals of their Comprehensive Conservation and Management Plan and improve its ecological health.
Understanding Coastal Acidification
Coastal acidification is the decrease in pH in the fresh, salt, and brackish waters near the shoreline. While a decrease in pH in the open ocean is more directly influenced by an increase in atmospheric carbon dioxide, coastal acidification has a variety of possible causes, such as nutrient pollution from rivers and a higher amount of organic decomposition.
Coastal acidification is primarily driven by eutrophication (high amounts of nutrients entering a water body). Eutrophication can cause rapid algal growth, and at times algal blooms, which can result in subsequent rapid algal death leading to an increase in microbial respiration (utilizing oxygen) and an increased production of carbon dioxide. As carbon dioxide concentrations increase, pH goes down (becomes more acidic).
Coastal acidification can lead to:
- Reduced water quality limiting recreation and threatening fishing and aquaculture
- Decreasing shell growth and formation of bivalves, like clams and oysters
- Degraded habitat with low oxygen conditions not able to support animals and plants
Monitoring LIS Bottom Waters
The estuaries and embayments in southern New England and northern Long Island show the effects of eutrophication including algal blooms and low oxygen, particularly in bottom waters, which can indicate that acidification may be occurring. Therefore, this study is primarily focused on water-quality monitoring in near-bottom waters. Bottom waters are the most susceptible to coastal acidification because they are:
- Not often influenced by daily changes (such as tides)
- Less oxygenated due to water column stratification which limits mixing, preventing oxygen-rich surface waters from reaching the bottom
Data Collection
Monitoring sites were strategically selected to represent freshwater-quality contributions, and the water quality conditions in the near shore coastal environment of LIS’s:
- Rivers: Connecticut, Housatonic, Thames Rivers, Norwalk, Saugatuck, and Mystic Rivers
- Embayments: Oyster Bay and Flax Pond, NY
USGS is collecting baseline information to describe coastal water conditions, determine areas of concern, and document overall coastal acidification trends within LIS through the collection of continuous and discrete water quality data.
- Continuous: Real-time water quality data collection (water temperature, specific conductance, dissolved oxygen, pH, turbidity and chlorophyll)
- Discrete: Monthly samples of total alkalinity and acid neutralizing capacity (measure of buffering capacity), pH, and dissolved organic and inorganic carbon (measure of carbon species contributing to acidification)
Collection of continuous and discrete data can help isolate trends in acidification due to:
- Seasonality
- Daily changes
- Primary productivity
Social Relevance
By advancing our understanding of coastal acidification through these research efforts, we can better safeguard the ecological health of Long Island Sound and its invaluable marine resources.
Figure 1 – Location of monitoring stations across Long Island Sound.
Discrete water samples are collected according to the USGS National Field Manual at continuous monitoring stations and are processed immediately before in-house analysis or shipping to the USGS National Water Quality Laboratory (NWQL) or the USGS Reston Biogeochemical Processes in Groundwater Lab (RBPGL). Continuous data for water temperature, specific conductance, dissolved oxygen, pH, turbidity, and chlorophyll a can be found in Table 1.
Table 1. Data collection sites
| Station Number | Station Name |
| 411940071590300 | Mystic River at RAM Island Yacht Club, CT |
| 410502073236000 | Norwalk Harbor at the Cove Marina NR E Norwalk, CT |
| 410606073245700 | Norwalk River at Norwalk Aquarium nr S Norwalk, CT |
| 410724073221001 | Saugatuck River US Rt 136 Bridge, CT |
| 01127768 | Thames River at Groton, CT |
| 01194796 | Connecticut River at Old Lyme, CT |
| 01208837 | Housatonic River near Nells Island near Stratford, CT |
| 01303152 | West Harbor at Oyster Bay Nwr at Bayville NY |
| 01304057 | Flax Pond near Old Field, NY |
Figure 2. Continuous monitor servicing event at Saugatuck River US Rt 136 Bridge, CT (USGS Site ID 410724073221001).
Figure 3. Continuous water quality gaging station located at Flax Pond near Old Field, NY (USGS Site ID 01304057).
Figure 4. Discrete sampling at Thames River at Groton, CT (USGS Site ID 01127768).
Figure 5. Discrete sample collected at Connecticut River at Old Lyme, CT (USGS Site ID 01194796).