Revisiting Eutrophication Data from the Animas River What happens - - PowerPoint PPT Presentation

Revisiting Eutrophication Data from the Animas River

What happens to stream algae during critical low flows?

Melissa May San Juan Soil & Water Conservation District NM WRRI. Environmental Conditions of the Animas & San Juan Watersheds – Past Present and Future. June 21, 2018

What is Eutrophication?

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Nutrients “fertilize” the river Algal Blooms Die off & Decomposition Reduced Dissolved Oxygen Death of fish & aquatic species

Nitrogen & Phosphorus

2002 Animas algal blooms spur further study

Cultural Eutrophication

• Low flows in 2002 led to big algae blooms and development of a

workgroup to investigate further.

• Sampling occurred for multiple parameters throughout 2003-2004;

Animas from San Juan to Estes Arroyo listed for nutrient impairment

• Synoptic studies in 2006, 2010
• 2014 concurrent nutrient/

bacteria sampling

• Multi-year dataset includes:

– Chlorophyll-a – Ash free dry mass – Total nitrogen/phosphorus – Dissolved oxygen – Nitrogen isotopes – Nutrient limitation growth assay

Total Maximum Daily Loads (TMDLs)

Carrying Capacity Calculation Target Concentration Flow

LOAD

Target Concentration Critical Low Flow

Total Maximum Daily Load

TMDL Calculation

Target concentrations: Total Nitrogen = 0.42 mg/L, Total Phosphorus = 0.07 mg/L Calculated critical low flow: 88.79 cfs Carrying Capacity

TMDL = carrying capacity at the critical low flow

Target concentrations vs. Historical data

Total Nitrogen = 0.42 mg/L Total Phosphorus = 0.07 mg/L

2008 BUGS Phase I Source ID and BMPs report

10 years of Minimum flows on the Animas River

Water Year Min. flow @ Aztec (cfs) Month Min. flow @ Fmtn (cfs) Month 2018 <10 April <4 April 2017 90 Sept 80 Sept 2016 150 Jan 90 Oct, July 2015 40 Aug 50 Aug 2014 120 Jan, Sept 100 Sept 2013 20 July 40-80, 25 May, July 2012 40 Sept 82, <60 Oct Aug/Sep 2011 90 Jan 85 May 2010 25, 60-80 July, Sept 65 July 2009 60 Aug 50 Aug-Sep

“Critical low flow” defined in the Animas nutrients TMDL as 88.79 cfs Calculated using a 4Q3 regression model- Minimum average four consecutive day flow (highlighted in red) that occurs with a frequency of at least once every 3 years Assumed that 4Q3 flows will be critical periods for aquatic life Flow data obtained from USGS gages 09364010 ANIMAS RIVER BELOW AZTEC, NM 09364500 ANIMAS RIVER AT FARMINGTON, NM

(flows estimated from graphs within 5 cfs)

TMDL: Target loads for nutrients

Cultural Eutrophication Animas San Juan to Estes Arroyo

• TN = 201 lbs/day
• TP= 33.5 lbs/day

Animas Estes Arroyo to SUIT

• TP= 46.6 lbs/day
• Target load at state line = 88.4 lbs/day

(measured load 415.5 lbs/day in TMDL study)

Note: Currently no nutrient assessment protocols approved for San Juan River (large, sand-bottomed channel)

NMED staff collecting algae samples on San Juan River 10/9/14

How did nitrogen and phosphorus loads compare to TMDL in 2014?

3 4 5

Loads of nitrogen and phosphorus frequently 10 times greater than target loads

One period from mid-August to early September where loads appear to stay closer to the TMDL

8/ 18/ 2014 9/ 02/ 2014

Do water column nutrients show the whole picture?

 Concentrations of inorganic

nutrients can be misleading

 Determined by a balance between

uptake and remineralization, which act so rapidly that pool size can be misleading (Dodds 2003)  Total N and Total P are

snapshots in time

 Water column nutrients affect

algal growth, but algae metabolism also affects the water column  In very productive systems,

nutrients may be undetectable in water column because they are metabolized so quickly

Algal metabolism influences water column

Photosynthesis during the day removes acidic CO2, raising the pH; respiration at night adds CO2 which lowers it again. Dissolved oxygen data would complete this picture of algal metabolism.

Algal metabolism influences water column, and vice versa

When not limited by light, flow, or nutrients, algal photosynthesis drives diurnal pH swings in the water column. As flow and turbidity increase (less light, more scour), diurnal cycle slows down. As algae decompose, pH will drop.

June 13, 2018 June 18, 2018

Nuisance level Chl-a

Mean Chl-a Cedar Hill to Aztec 12.46 ug/cm2 Mean Chl-a Aztec to Flora Vista 89.61 ug/cm2 Mean Chl-a Flora Vista to Farmington 39.03 ug/cm2 Mean Chl-a between State Line & Cedar Hill 2.94 ug/cm2

Nuisance benchmark 10 ug/cm2

At what level does algae become a “nuisance”?

Nuisance level Chl-a

N15 isotopes

Higher delta-N15 signifies N inputs from human and animal wastes

Where is the nutrient load coming from?

2014 Nitrogen Loads

Increasing Total Nitrogen

Mounting body of evidence for stormwater as main pathway

• Studies of inflows have never led to a “smoking gun”
• Highest nutrient loads/concentrations measured after storm events;

positively correlated with turbidity and E.coli

• TKN makes up majority of TN (not NO3 which travels in groundwater)
• Still big ??? on how nutrients cycle through benthic algae and sediments

Pollutant Sources

Livestock Eroding streambanks and dirt roads Agricultural runoff Stormwater Wastewater Treatment Plants and

• ther NPDES permit holders

Wildlife Natural soil erosion

Non-Point Sources Point Sources

(Permitted Discharges)

Background Sources

10% Margin of Safety

Conclusions and implications for future sampling and remediation projects

• Excessive nutrients and

algae blooms continue to be a problem on the Animas River

• Diurnal pH swings appear to

be driven by algal metabolism at a range of flows (100-500 cfs) when not limited by other factors

• Continuous flow, pH, and

turbidity data help to predict/explain algal

• growth. Thank you USGS!
• Algae blooms occur at flows

much higher than “critical low flow”, so they are likely to continue as flows drop

• Depth of water may be a

better predictor of blooms than flow alone – channel restoration (reducing width/depth ratio) could help

• Dissolved oxygen data is

needed to see if there is a risk

• f fish kills during these

blooms

Conclusions and implications for future sampling and remediation projects

• Nutrient and algae

dynamics are extremely variable – need multi-year datasets for both to draw specific conclusions.

• If algae sampling is

prohibitively expensive, taking pictures of benthos while grabbing water samples will help tell the full story!

• N15 data supports

hypothesis that reducing bacteria sources will also lessen nutrient pollution.

• Cost-effective to get

started on landscape- scale BMPs that reduce nutrient runoff, especially via stormwater.

THANK YOU!

Melissa May melissa.may@sanjuanswcd.com 505-334-3090 x 5 San Juan Soil & Water Conservation District 1427 W. Aztec Blvd. Ste. 1 Aztec, NM 87410

Measured loads vs. TMDL vs. Carrying Capacity

2006 Nitrogen Loads

Nuisance level Chl-a

N15 isotopes