Applying Nutrient Standards in Wadeable Streams in Montana

Vicki Watson, University of MontanaMichael Suplee, Montana DEQ

Presented at Nitrate in Montana Hydrologic Systems,

Helena, MTApril 23, 2014

Excess nutrients & nuisance algae –one of top 5 causes of impairment of Montana’s wadeable

streams

17% of MT impaired stream miles impaired by excess nutrients

Cladophora in Clark ForkRiver, 1980s

MT Numeric Nutrient CriteriaIn 2008, DEQ developed preliminary ecoregion-specific numeric criteria for nutrients and algae, based on regional stressor-response studies and reference-stream data for mountains and plains ecoregions (Level III)Harm to beneficial uses began around:• 90th percentile of reference in mountains• 75th percentile of reference in plains So criteria were set near these levels

How were the 2008 Criteria Derived?

• Based on nutrient concentrations where impact to these sensitive beneficial uses begins to occur – Fish and aquatic life – Recreation & aesthetics

• Impact-to-use thresholds determined using:– Stressor-response studies (e.g., TN vs. DO) – Public opinion surveys on nuisance algae levels

• Final criteria derived by:– Comparing impact threshold concentrations to

ecoregional reference data

<25 100(Summer mean)

>250 >500

50mg chlorophyll a per square meter

150(Summer max) 35g AFDW persquare meter

Stressor-response Studies vs. Reference-site Data

(in contrast to EPA’s suggestion of using the 25th percentile of all streams)

Level III Ecoregions & Stream reference sites (white)Cities (red dots)

MT’s Draft Level III Ecoregion Nutrient Criteria, 2008

In addition to N and P criteria, attached-algae criteria were suggested for western mountainous ecoregions.

Plains criteria set to maintain acceptable DO levels. Note seasonality. .

In 2012, MT nutrient criteria were refined, in light of:

additional stressor response studies additional reference site data Made it possible to look at

small scale level-IV ecoregions within some Level III ecoregions

Greater emphasis was placed on dose-response studies, and criteria were no longer linked to

specific percentiles in the reference distribution

N:P Ratios also ConsideredNuisance growths of Didymosphenia (rock snot) noted in low P streams withhigh N:P ratios (N:P 34:1)

Nuisance growths of Cladophora noted in high P streams with low N:P ratios

Didymo Distribution

U.S. EPA. Retrieved 2007-07-16.

Level III Ecoregions & Stream reference sites (white)Cities (red dots)

Level IV ecoregion within MiddleRockies: Absaroka-Gallatin Volcanic Mountains

Table 3-2. Descriptive Statistics for TN and TP concentrations in Reference Streams of the Absaroka-Gallatin Volcanic Mountains (17i) ecoregion.

Nutrient Concentration (µg/L) Conc. at given Percentile

NutrientNumber of

Reference SitesNumber of

Samples Min Max 25th

(Median)

50th 75th 90th

TN 4 13 7 181 52 80 100 163

TP 4 16 16 144 61 81 105 127

TN criteria 250 µg/L ( >100th percentile of reference) TP criteria: 105 µg/L (75th percentile of reference)N:P Ratio of Criteria: 2:1 N:P Ratio of Reference Sites: 1:1

Table 3-1. Descriptive Statistics for TN and TP concentrations in Reference Streams of the Middle Rockies ecoregion.

Nutrient Concentration (µg/L) Conc. at given Percentile

NutrientNumber of

Reference SitesNumber of

Samples Min Max 25th

(Median)

50th 75th 90th

TN 57 148 3 9580 55 95 141 220

TP 61 245 0.5 840 6 10 20 70

TN criteria 300 µg/L (93th percentile of reference)TP criteria: 30 µg/L (80th percentile of reference)N:P Ratio of Criteria: 10:1 N:P Ratio of Reference Sites: 11:1

Absaroka-Gallatin Volcanic Mountains (17i)

Middle Rockies (17)

Middle Rockies Stream Bloody Dick Creek

Absoroka-Gallatin Volcanic Mountain Streams

E. Rosebud Cr.

Gardner River

NW Glaciated Plains (gray), Mountain-to-plains transition zone level IV ecoregions (dark gray)

Table 3-6. Descriptive Statistics for TN and TP concentrations in Reference Streams of the Northwestern Glaciated Plains ecoregion.

Nutrient Concentration (µg/L) Conc. at given Percentile

NutrientNumber of

Reference SitesNumber of

Samples Min Max 25th

(Median)

50th 75th 90th

TN 17 52 55 3891 630 969 1398 1945

TP 18 59 10 638 28 60 111 184

Total Nitrogen: 1,300 µg/L (65th percentile)Total Phosphorus: 110 µg/L (75th percentile)N:P Ratio of Criteria: 12:1 N:P Ratio of Reference Sites 18:1

Table 3-7. Descriptive Statistics for TN and TP Concentrations in Transitional Level IV Ecoregions (42q, 42r) of the Northwestern Glaciated Plains. No data were available for 42l, 42n.

Nutrient Concentration (µg/L) Conc. at given Percentile

NutrientNumber of

Reference SitesNumber of

Samples Min Max 25th

(Median)

50th 75th 90th

TN 5 20 24 2830 115 253 515 704

TP 5 17 1 380 9 20 78 246

Total Nitrogen: 560 µg/L (80th percentile)Total Phosphorus: 80 µg/L (75th percentile)N:P Ratio of criteria: 7:1 N:P Ratio of Reference Sites: 7:1

Northwestern Glaciated Plains (42)

Mountain-to-plains transition zone (various)

Northwestern Glaciated Plains Streams

Battle Cr.

Porcupine Cr.

Transitional Stream

Clear Creek,Flowing down From the Bear PawMountainson to the Glaciated Plains

Northwestern Great Plains(gray), Wyoming Basin (light gray). Mountain-to-plains transition zone level IV ecoregions (dark gray)

Table 3-9. Descriptive Statistics for TN and TP concentrations in Reference Streams of the Northwestern Great Plains ecoregion.

Nutrient Concentration (µg/L) Conc. at given Percentile

NutrientNumber of

Reference SitesNumber of

Samples Min Max 25th

(Median)

50th 75th 90th

TN 30 100 50 9900 482 792 1389 3141

TP 32 112 1 9911 36 73 137 519

Total Nitrogen: 1,300 µg/L (68th percentile)Total Phosphorus: 150 µg/L (77th percentile)N:P Ratio of Criteria: 9:1 N:P Ratio of Reference Sites 13:1

Table 3-11. Descriptive Statistics for TN and TP Concentrations in Transitional Level IV Ecoregions (43s, 43t, 43u) of the Northwestern Great Plains. No data were available for 43o, 43v.

Nutrient Concentration (µg/L) Conc. at given Percentile

NutrientNumber of

Reference SitesNumber of

Samples Min Max 25th

(Median)

50th 75th 90th

TN 12 40 50 753 78 112 174 224

TP 12 40 3 108 6 10 22 34

Total Nitrogen: 440 µg/L (98th percentile) Total Phosphorus: 33 µg/L (87th percentile)N:P Ratio of criteria: 13:1 N:P Ratio of Reference Sites: 13:1

Northwestern Great Plains (43)

Mountain-to-plains transition zone (various)

NorthwesternGreat Plains Streams

Box Elder Cr.

O’Fallon Cr.

Transitional Zone Stream – Elk Creek

Most Streams Already Meet the Criteria

Based on probabilistic stream survey:

• About 70-80% of stream miles statewide currently meet the TP criteria

• About 85-90% of stream miles statewide currently meet the TN criteria

Reach Specific Criteria

used where naturally elevated nutrients (e.g., due to geology) from

a level IV ecoregion affect reaches downstream in another ecoregion.

Acceptable downstream concentrations are estimated from

relative contribution of sources in the two ecoregions.

1. Criteria are not “no sample shall exceed”

2. EPA recommends 10-25% exceedence rate for most types of criteria (303(d) listing guidance)

3. A 9-year dataset on MT’s Clark Fork River shows• Sites with consistent nuisance algae – 54% of N and P samples exceed criteria• Sites without nuisance algae – only 6% of N and P samples exceed criteria• 25% exceedence appears to be a threshold. Above that, nuisance algae very likely.

Recommend: 20% allowable exceedence rate

Allowable Exceedence Rate for Criteria

MT draft numeric nutrient standards were out for public comment until April 1st. See Circular DEQ-12A

Recent hearing before MT BER

Application of Proposed Nutrient Standards

Examples: discharge from existing permitted source where:

A. Discharge is directly to stream, stream is on the 303(d) list for nutrientsB. Discharge is directly to stream, stream is not on the 303(d) list for nutrientsand

C. Discharge of effluent is to groundwater with hydrologic connection to surface water (if no connection, only groundwater standards apply)

A. Stream is on the 303(d) list for nutrients• Stream already exceeds nutrient standards so

standards are to be met at end-of-pipe (July-Oct)– If cost prohibitive/technologically infeasible,

permittee can apply for a variance:• > 1 MGD: 1 mg TP/L, 10 mg TN/L• < 1 MGD: 2 mg TP/L, 15 mg TN/L• Lagoons: Maintain performance/monitor

• Variance applies for up to 20 years, but stricter treatment requirements over that period are likely

• Other, case-specific variances also available

B. Stream is not on the 303(d) list for nutrients

• Dilution in mixing zone based on stream’s ambient nutrient concentrations and the seasonal 14Q5 flow from July to Oct – Seasonal 14Q5 flow = lowest average 14

consecutive day low-flow (July-Oct) occurring once every 5 years, on average– Nutrient standards met end-of-mixing zone

• Variance can be requested if calculated limit is still cost prohibitive

C. Discharge to groundwater with hydrologic link to surface water

• Discharge permit written to meet surface water nutrient standards at the 14Q5 flow, after mixing– Volume of discharge and post-mixed groundwater

concentration are mixed in with 14Q5 flow – Monitoring occurs end-of-pipe even though

discharge is to groundwater– Likely to be written for year-round application

• Nutrient variance can be requested (if limits are still cost prohibitive) because nutrient surface-water standards are being applied

Thanks. Questions?

vicki.watson@umontana.edu(406) 243-5153

msuplee@mt.gov(406) 444-0831