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? 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 -Low flows in 2002 led to big algae blooms and development of a Cultural Eutrophication 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 Carrying Target Concentration Flow LOAD Capacity Target concentrations: Total Nitrogen = 0.42 mg/L, Total Phosphorus = 0.07 mg/L Calculated critical low flow: 88.79 cfs TMDL Calculation Total Maximum Critical Low Target Concentration Flow Daily Load 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 Water Min. Month Min. Month Year flow @ flow @ flows on the Animas Aztec (cfs) Fmtn (cfs) River 2018 <10 April <4 April “Critical low flow” defined in the 2017 90 Sept 80 Sept Animas nutrients TMDL as 88.79 cfs 2016 150 Jan 90 Oct, July Calculated using a 4Q3 regression 2015 40 Aug 50 Aug model- Minimum average four consecutive day flow (highlighted in 2014 120 Jan, Sept 100 Sept red) that occurs with a frequency of at least once every 3 years 2013 20 July 40-80, May, Assumed that 4Q3 flows will be critical 25 July periods for aquatic life 2012 40 Sept 82, Oct <60 Aug/Sep Flow data obtained from USGS gages 09364010 ANIMAS RIVER BELOW 2011 90 Jan 85 May AZTEC, NM 2010 25, July, 65 July 09364500 ANIMAS RIVER AT FARMINGTON, NM 60-80 Sept (flows estimated from graphs within 5 cfs) 2009 60 Aug 50 Aug-Sep
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
At what level does algae Nuisance level Chl-a become a “nuisance”? Mean Chl-a between State Line & Cedar Hill 2.94 ug/cm 2 Mean Chl-a Cedar Hill to Aztec 12.46 ug/cm 2 Mean Chl-a Aztec to Flora Vista 89.61 ug/cm 2 Mean Chl-a Flora Vista to Farmington 39.03 ug/cm 2 Nuisance benchmark 10 ug/cm 2
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 10% Margin of Point Safety Natural soil erosion Sources Wastewater Treatment Plants and (Permitted Background other NPDES permit holders Discharges) Sources Non-Point Wildlife Sources Stormwater Livestock Agricultural runoff Eroding streambanks and dirt roads
Conclusions and implications for future sampling and remediation projects • Excessive nutrients and • Algae blooms occur at flows algae blooms continue to be much higher than “critical low a problem on the Animas flow”, so they are likely to River continue as flows drop • Diurnal pH swings appear to • Depth of water may be a be driven by algal better predictor of blooms metabolism at a range of than flow alone – channel flows (100-500 cfs) when restoration (reducing not limited by other factors width/depth ratio) could help • Continuous flow, pH, and • Dissolved oxygen data is turbidity data help to needed to see if there is a risk predict/explain algal of fish kills during these growth. Thank you USGS! blooms
Conclusions and implications for future sampling and remediation projects • Nutrient and algae • N15 data supports dynamics are extremely hypothesis that reducing variable – need multi-year bacteria sources will also datasets for both to draw lessen nutrient pollution. specific conclusions. • Cost-effective to get • If algae sampling is started on landscape- prohibitively expensive, scale BMPs that reduce taking pictures of benthos nutrient runoff, especially while grabbing water via stormwater. samples will help tell the full story!
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
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