but getting better
Here’s Why:
Dissolved oxygen levels remain poor in the Estuary but are getting better. Strengthening water quality protections will be crucial to restoring dissolved oxygen levels to sustain the health of the Delaware River watershed’s ecosystems and communities into the future.
What do bubbling streams and lush aquatic vegetation have in common?
They both contribute to an essential life-supporting element in our waters – dissolved oxygen (DO). Just as humans need oxygen to breathe, so do the countless creatures that inhabit our waters’ aquatic environments, from fish to invertebrates. Dissolved oxygen is essential for marine life, entering rivers and oceans from the atmosphere and through photosynthesis via aquatic vegetation. However, disrupting the balance of oxygen in the water can pose a risk to these ecosystems. Despite challenges, significant progress has been made since the 1960s, partly due to ongoing monitoring and control of harmful nutrient discharge (like excess carbon and nitrogen). Many areas historically low on dissolved oxygen now meet the necessary standards to support life. Fish such as shad and striped bass are rebounding, but there are still areas struggling with low oxygen levels during the summer, underscoring the need to continue working on the health of our waters. This section explores the factors that alter the amount of dissolved oxygen levels and how to improve them.
The health of these water systems hangs in a delicate balance, with oxygen levels depending on species and their life stages. Human activities, such as overuse and improper use of fertilizers and discharge of partially treated sewage, can disrupt this balance, leading to excess nutrients like organic materials and ammonia nitrogen in the water. While balanced levels of phosphorus and nitrogen are essential to water health, too many of these nutrients can tip the scales and be harmful. During rainfall, nutrient-laden runoff enters the water and can trigger an explosive growth of algae, called an algal bloom. When these algal blooms exhaust their nutrient supply, they die en masse. Their decomposition consumes a significant amount of oxygen in the water. This leads to a sharp drop in dissolved oxygen levels, creating a hostile environment where fish and other aquatic organisms struggle to breathe and may die.
The Delaware River Watershed has historically had low oxygen levels during warmer months, disrupting the harmony of life especially in urban portions of the tidal Delaware River (i.e., Philadelphia, – Camden, New Jersey, and – Wilmington, Delaware, areas) and displacing the species that once thrived here. Efforts are ongoing to improve oxygen levels and reintroduce sensitive species to our waters. Most zones now meet the necessary standards to support life, and fish species like shad and striped bass are returning. Yet, areas remain where oxygen levels fall short, highlighting a need for continued efforts.
The story of dissolved oxygen in the Delaware River Watershed is one of resilience, recovery, and ongoing restoration. There have been encouraging signs of progress, but the journey isn’t over and challenges remain. Work continues for monitoring waterways and pushing for pollution reduction efforts to maintain and improve water quality. The health of waterways doesn’t just affect the fish and other wildlife. It’s indicative of the planet’s health for future generations.
Help prevent nutrient-rich runoff from entering our waterways by making changes on your property by:
The Delaware River Basin Commission is exploring whether dissolved oxygen criteria require revisions to protect fish reproduction.
The Philadelphia Water Department developed the Delaware Estuary Water Quality Improvement Partnership with other large regional municipal utilities to share strategic utility planning and technology evaluations in response to potential changes in water quality criteria that could impact acceptable levels of dissolved oxygen in local waterways and establish a foundation for communication and data sharing among municipal wastewater treatment facilities.
Long-term initiatives, like Philadelphia’s Green Cities Clean Waters program, aim to address potential threats to dissolved oxygen levels by reducing stormwater runoff inputs into combined sewer overflows (CSO). These antiquated systems have connected stormwater runoff and sewer lines. When flooding occurs, sewage mixes with the stormwater and overflows into our river. Initiatives like these help counteract human-generated stressors on our water bodies and work to improve water quality.
How does monitoring dissolved oxygen levels connect to the strategies and goals outlined in the Delaware Estuary Program’s Comprehensive Conservation and Management Plan (CCMP)?
CCMP STRATEGY W1.5: Conduct research and monitoring on nutrient impacts in the Delaware Estuary for biological and ecological endpoints
This dissolved oxygen indicator status report is based on research compiled in the 2022 Technical Report for the Delaware Estuary and Basin (2022 TREB). Please refer to this document for more information.
