H. Nutrients

Drivers & Stressors Condition of the bay human connections

H. Nutrients

Nutrient Pollution Puts Bay Water Quality at Risk Jerry Monkman, Ecophotography.com

Community Efforts to Protect Water Quality and the Bay’s Natural
Resilience Have Prevented Widespread Impacts

why it matters

Nutrients like nitrogen and phosphorus are essential to all Recent data provide Several nutrient sources of potential
life, but high levels in aquatic ecosystems can sometimes good estimates of importance to Casco Bay are not
fertilize excessive growth of phytoplankton and other algae. atmospheric, waste- well characterized because of lack of
The consequences can be profound: harmful algae blooms, water, and tributary recent, reliable data, notably:
low dissolved oxygen, disappearance of eelgrass and kelp, loads, but the size • combined sewer overflow (CSO),
loss of marine habitat, declines in marine harvests, coastal of the runoff compo- • direct runoff from urban areas, and
acidification, even fish kills. While phosphorus is often the nent is not as well • septic systems.
nutrient of primary concern in Maine lakes, nitrogen is more understood.
likely to be a primary concern in Casco Bay.
Data from the 1990s and early 2000s indicated that Casco
Nutrients entering Casco Bay come predominately from Bay's overall nitrogen load was low compared to most
three sources: wastewater treatment facilities, direct other large estuaries in the northeastern U.S. However,
atmospheric deposition, and runoff (including stormwater, the nitrogen loading is concentrated near Portland, raising
combined sewer overflows, and river discharges). local concerns.

500 status & trends 500
442 MT 400
Documented Nitro5g0e0 n Loads from Three Sources
400
424 MT
*
400
300 Total Nitrogen
(Metric Tons per Year)Capisic300 Freeport 300 Ammonium
200 Royal 200 Falmouth Nitrate
Total NitrogenPresumpscot100Yarmouth 200
100 (Metric Tons per Year)OtherSouth Portland 135 MT
Portland
Total Nitrogen 100
(Metric Tons per Year)

000

Tributaries Wastewater Atmospheric Deposition

Estimated nitrogen loads from rivers and streams Compared to tributaries, direct wastewater Direct atmospheric deposition of nitrogen is a
entering the Bay are about 440 metric tons per discharges of nitrogen to Casco Bay are slightly relatively small, and declining, share of nitrogen
year. About two thirds of that nitrogen enters the lower, on the order of 425 metric tons per year. entering the Bay. “Atmospheric deposition”
Bay from the Royal and Presumpscot Rivers. Trib- Well over three quarters of those discharges transfers airborne pollutants, including ammo-
utaries carry nitrogen from all upstream sources, occur in Portland and South Portland. nium and nitrate, to the surface of Casco Bay,
including agriculture, runoff, and wastewater. via rainfall and dust.

*Total Nitrogen (TN) includes the sum of nitrogen from ammonium (NH4+), nitrate (NO3-), nitrite (NO2-), and organic nitrogen in water. Source: University of Maine, Maine Department
of Environmental Protection (DEP), and National Atmospheric Deposition Program. CBEP estimates of annual loads based on most recent available data.

19 casco BAY estuary partnership

▶ Controlling nitrogen delivery in runoff from urban areas can be difficult. Most stormwater control structures are more ▶ Over the last five years, understanding of nitrogen in Casco Bay has improved thanks to focused efforts by Maine’s ▶ Atmospheric deposition of nitrogen has been declining for several decades, likely as a result of adoption of emission ▶ Portland Water District updated the aeration system at the East End Wastewater Treatment Facility in 2016 and 2017. Nitrogen Deposition (kg/ha) Long-Term Decline in Atmospheric Deposition of Nitrogen Outer Bay 2015-20S1a9mSpalme pLloecsabtiyonLocation Total NiDtrEoPgae2n0nd15RF-O2e0Cg1B9ulDaarltya Exceeds Water Quality Thresholds condition of the bay
effective at trapping phosphorus than nitrogen. “Green infrastructure,” which relies on living organisms for nitrogen Department of Environmental Protection, the University of Maine, Friends of Casco Bay, and Casco Bay Estuary control technologies on power plants and automobiles; improved automobile fuel efficiency; and reduced reliance on Summer discharges of nitrogen to the Bay have dropped by nearly three quarters.
control, can be more effective than traditional structures, but adoption has been slow. Partnership. More research is needed to characterize terrestrial sources, understand how water movement affects coal for electrical generation. Further reductions in nitrogen deposition are likely with increasing adoption of electric 5 0.5 1.0 0.32
nutrients in the Bay, and learn how recycling of nutrients from the Bay’s sediments affects water quality. vehicles and reduction in fossil fuel use. 4 0.45
3 TotaTloNtailtNroitgroegnen(m(mgg/l/)l)

2000 Maine DEP thresholds

2005 Elevated nitrogen levels have been observed regularly in portions of Casco Bay, especially
in the tidal estuaries of the Royal, Presumpscot and Fore Rivers. Above left: Data collected
2010 Avg Rate 2015-2019 from 2015 through 2019 by Friends of Casco Bay and Maine Department of Environmental Harraseeket Royal River Estuary
2.52 kg/ha Protection show that levels above DEP’s advisory thresholds (0.32 mg/l TN to protect eelgrass; Inner Bay
0.45 mg/l TN to reduce risk of low dissolved oxygen) occurred in most areas. Above right: New Meadows
2015 Typical nitrogen concentrations are higher in Casco Bay’s restricted bays and tidal tributaries Presumpscot Estuary
than in the Bay’s open waters, where tidal currents facilitate waters mixing. Fore River

successes & challenges The rate of atmospheric deposition #*)" !(*# Median Total Nitrogen (mg/l)
of nitrogen at a DEP monitoring (! !( (!*#")*#!()")"(!#* (! 0.18–0.30
station in Freeport, Maine is (! 0.31–0.45
declining. Total atmospheric loads !( ")"))" !( 0.46–0.60
to Casco Bay have dropped ")!()")"")!( !( 0.61–0.75
roughly a third in recent decades,
mirroring regional trends. In recent (!")!("))"!((!)"")
years (2015 through 2019), the
annual rate of atmospheric nitrogen !(
deposition at the monitoring station
in Freeport has been about 2.5 kg !( (! *# Both!( Friends of Casco Bay") Maine DEP Data Source:
nitrogen per hectare. The elevated (!
level in 2012 was caused by an
unknown, but apparently short-
2020 term, local source.

!(

Long-term data on total nitrogen show declines at Total Nitrogen (mg/l) Nitrogen Decreasing Over Time
three of five locations that have been monitored
regularly by Friends of Casco Bay for more than ten 0.25 0.75 0.75 0.75 0.75 BBrrooaadd SSoouunndd
years. Downward trends at the other sites are not 0.50 0.50 0.50 0.50
strong enough to distinguish clearly from seasonal, 0.25 0.25 0.25 0.75
year to year, and other sources of variation.
Collecting nutrient data in Casco Bay. 2010 0.50
(Photo: CBEP)
STATE OF casco BAY 20 2015 SMCC Pier FFoorrtt GGoorrggeess QQuuaahhoogg BBaayy CCllaappbbooaarrdd IIssllaanndd 0.25

SMCC Pier

2020 H. Nutrients