Eutrophication 2 Causes of Eutrophication Alice Newton University of Algarve.
Revisiting Eutrophication Data from the Animas River...Revisiting Eutrophication Data from the...
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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
Transcript of Revisiting Eutrophication Data from the Animas River...Revisiting Eutrophication Data from the...
Revisiting Eutrophication Data from the Animas River
What happens to stream algae during critical low flows?
Melissa MaySan Juan Soil & Water Conservation District
NM WRRI. Environmental Conditions of the Animas & San Juan Watersheds – Past Present and Future. June 21, 2018
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Presentation Notes
Today I’ll be building on what Jaclynn has presented, and doing a bit of a retrospective on eutrophication data collected on the Animas River over the past 15 years. I wanted to start by acknowledging the organizations who collected this data – San Juan Watershed Group, Mountain Studies Institute, NMED Surface Water Quality Bureau, Animas Watershed Partnership, and BUGS Consulting. I had to add the USGS logo on the front page here, because I am relying heavily on their stream gage data as well. If you aren’t visiting their website to look up discharge and Sonde data every day…
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
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What is eutrophication? In short, eutrophication is when a body of water becomes overly enriched with nutrients that induce excessive growth of algae and aquatic plants. These plants then die and begin to decompose, which reduces dissolved oxygen and in extreme cases can lead to fish kills and death of other aquatic species.
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
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As Jaclynn mentioned, this first became a concern during the drought and very low flows of 2002, where algae blooms were observed throughout the Animas. Follow up sampling was conducted in 2003, 2004, 2006, 2010, and 2014., leading to a multi-year dataset that included…
Total Maximum Daily Loads (TMDLs)
Carrying Capacity Calculation
Target Concentration Flow LOAD
Target ConcentrationCritical Low
FlowTotal Maximum
Daily Load
TMDL Calculation
Target concentrations: Total Nitrogen = 0.42 mg/L, Total Phosphorus = 0.07 mg/LCalculated critical low flow: 88.79 cfs
Carrying Capacity
TMDL = carrying capacity at the critical low flow
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Many of you may already be familiar with how Total Maximum Daily Loads are calculated, but the basic premise is to calculate the load of a pollutant the river can absorb in a given day and still meet it’s target water quality concentrations for that pollutant. Because dilution decreases with flow, the TMDL is calculated based on a “critical low flow” value which I’ll discuss more in a minute. While the river may be able to absorb greater loads when the flow is higher, the TMDL is designed to be protective at low flow, when the river is most vulnerable to negative impacts from pollutants. Measurements above the target concentration at flows greater than the critical low flow will be exceeding the TMDL by definition.
Target concentrations vs. Historical dataTotal Nitrogen = 0.42 mg/L Total Phosphorus = 0.07 mg/L
2008 BUGS Phase I Source ID and BMPs report
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This graph revisits some of the nutrient data Jaclynn presented, and just reiterates how frequently the target concentrations for total nitrogen and total phosphorus are exceeded. The left 2 bars in each graph are from the 2006 study, while the right 2 bars are from historical data.
10 years of Minimum flows on the Animas River
WaterYear
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
OctAug/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 yearsAssumed that 4Q3 flows will be critical periods for aquatic life
Flow data obtained from USGS gages09364010 ANIMAS RIVER BELOW AZTEC, NM09364500 ANIMAS RIVER AT FARMINGTON, NM(flows estimated from graphs within 5 cfs)
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So I mentioned that the “critical low flow” was a calculated as part of the TMDL development process. I won’t go into the exact details of how they determine the number, but it is defined as the “minimum four consecutive day flow” that occurs at least once in 3 years. The calculated critical low flow for the reach of the Animas from Aztec to the San Juan confluence is 88.79 cfs. I revisited flow data from the two USGS gages within this reach, and found that flows went below this 5 out of the past 10 years, with some years have flows below this threshold more than once. Interestingly, this year was the first for this to occur in April, and I wouldn’t be at all surprised if we reach it again later this summer.
TMDL: Target loads for nutrientsCultural EutrophicationAnimas 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
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Presentation Notes
We know our target concentrations, we know our critical low flow, so what is our target load in the TMDL? I did want to mention here that we aren’t leaving out the San Juan because it has low nutrients, but because the nutrient assessment methods used on the Animas are not applicable to large sand-bottomed channels like the San Juan. Because they can be limited by substrate, turbidity, and other factors, these rivers don’t respond in the same way to nutrients and thus can’t be judged by the same standards.
How did nitrogen and phosphorus loads compare to TMDL in 2014?
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So how are we doing? These graphs show variation in loads (concentration times flow) at sites on the Animas over 40 sampling dates in 2014. When you look at the graph on this scale, it looks like maybe there were a few peaks in loads that otherwise stayed fairly low and constant. Scale is everything though.
Loads of nitrogen and phosphorus frequently 10times greater than target loads
One period from mid-August to early September where loads appear to stay closer to the TMDL
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These are the same graphs, zoomed in to a scale that actually shows the target loads. On each graph, the bottom line is approximately at the TMDL, and the top line is 10 times the TMDL target load. The graphs are a little messy to look at, but the main takeaway is that not only are we not meeting our target loads for nutrient loading on the Animas, and most of the time we aren’t even in the ballpark. There is one period from mid-Aug to early September where loads do appear to stay closer to the TMDL.
8/18/2014 9/02/2014
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This is what the rocks looked like during that supposed low-nutrient period though.
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
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So the question then becomes, do water column nutrients show the whole picture for eutrophication? I would say that the answer to that is a clear no, and a lot of data in the literature supports that.
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.
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Continuous nutrient data or complicated bioassays would be needed to get an accurate picture of how algae respond to pulses in nutrient enrichment. We can however use the USGS pH gauges to get a picture of another way algal metabolism can affect the water column. I took the background picture shown here off the bridge in Aztec last Wednesday evening, and you can see there is a thoroughly green mat of algae covering nearly the whole streambed. As these algae photosynthesize during the day, acidic CO2 is taken out of the water column, raising the pH. At night, respiration adds CO2 which lowers it again.
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.
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This graph shows even more USGS data from the past week, with the star in the same place last Wednesday, and showing pH in blue, discharge in red, and turbidity in green. On Saturday the 16th is when the rains from Tropical Storm Bud hit, And you can see the flow and turbidity start to increase, which corresponds to a dampening in the diurnal pH swing.
June 13, 2018 June 18, 2018
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And here are the pictures that correspond to those differences in turbidity. I’ll be curious to see whether the mat of algae from last week will be totally scoured away by the storm event, or if it will persist after the water clears.
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 benchmark10 ug/cm2
At what level does algae become a “nuisance”?
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Presentation Notes
Now I’ve been talking about algae as if it’s all bad, which is unfair, so I’ll introduce the “nuisance” benchmark at which point it can start to negatively affect benthic habitat and having the other detrimental effects previously discussed. In the 2006 sampling, mean chlorophyll levels reached nuisance from Cedar Hill all the way to the San Juan confluence, with the worst blooms visible between Aztec and Flora Vista
Nuisance level Chl-a
N15 isotopes
Higher delta-N15 signifies N inputs from
human and animal wastes
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Presentation Notes
Isotopes are forms of an element that differ in number of neutrons but have the same number of protons and electrons. This gives the isotope a different atomic mass. For example, most often N has an atomic mass of 14, but the heavy isotope is 15 due to an extra neutron. Ratios of 15N/14N are reported as delta 15-N. Delta 15N increases with trophic level, so an increase in delta 15N usually signifies an increasing source of N from human and animal wastes. Synthetic fertilizers have a low delta 15N though, and can mimic “natural” sources
Where is the nutrient load coming from?2014 Nitrogen Loads
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Now, in studying nutrient loading to the Animas, we have really wanted to point to specific inflows as the big culprits that are responsible for the majority of the nutrient load. Unfortunately for our original hypotheses, we did not find this pattern in either 2006 or 2014. In both synoptic samplings, the nutrient loads from inflows shown in yellow did not account for the loads observed in the mainstem of the river, shown in blue. This means that the nutrients are getting into the river some other way.
Incr
easin
g To
tal N
itrog
en
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 other NPDES permit holders
Wildlife
Natural soil erosion
Non-Point Sources
Point Sources(Permitted Discharges)Background
Sources
10% Margin of
Safety
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Presentation Notes
Probable non-point plant nutrient sources include: Urban and suburban fertilizer runoff Fertilizer and manure runoff from agricultural and rangeland Manure management practices and improper manure disposal Failing septic systems Sediment from road networks and gas and oil well disturbance (soils in the area have high levels of phosphorus) Groundwater inflow from high density septic system areas Loss of river’s assimilative capacity Disconnected with floodplain Lack of riparian vegetation
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 of 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
San Juan Soil & Water Conservation District
1427 W. Aztec Blvd. Ste. 1Aztec, NM 87410
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Measured loads vs. TMDL vs. Carrying Capacity
2006 Nitrogen Loads
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So, when the Animas Watershed Partnership and San Juan Watershed Group were getting started, they set out to identify sources of nutrient pollution in the landscape. They designed a study to float down the river and measure every inflow, and quantify the loads of nitrogen and phosphorus entering the Animas. This graph was the result of one of those sampling efforts. The dark bars are the nitrogen loads that were measured in the mainstem of the Animas. The short gray bars are the cumulative loads of nitrogen as you move downstream. Now, if the majority of the nutrient loading was coming from point sources that discharge all the time, you would expect the gray bars to add up to the black bars, and for the black bars to steadily increase as you move downstream. That is not what was found. Instead, the loads measured in the river are extremely variable, and are much higher than what was measured in the inflows. These results were fairly hard to interpret into management decisions, so a similar study was repeated in 2014 when we were revising the watershed plan for the NM stretch of the Animas.
Nuisance level Chl-a
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Presentation Notes
2008 BUGS Phase I Source ID and BMPs report, MSI AWP Narrative Description and Interpretation of Chl-a
N15 isotopes
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Presentation Notes
Isotopes are forms of an element that differ in number of neutrons but have the same number of protons and electrons. This gives the isotope a different atomic mass. For example, most often N has an atomic mass of 14, but the heavy isotope is 15 due to an extra neutron. Ratios of 15N/14N are reported as delta 15-N. An increase in delta 15N usually signifies an increasing anthropogenic source of N (human and animal wastes). Synthetic fertilizers have a low delta 15N though, and can mimic “natural” sources
