Defining Biologically Relevant Thresholds for TN & TP in Coastal Bays Non-Tidal Streams

Transcription

1 Defining Biologically Relevant Thresholds for TN & TP in Coastal Bays Non-Tidal Streams Carol B. McCollough 1, Carol J. Cain 2 Roman Jesien 2 & Cathy Wazniak 1 1 MD-DNR RAS/TEA, 2 Maryland Coastal Bays Program Maryland Coastal Bays STAC January 6,

2 Stream TN & TP spring data collected by MCBP 53 stations Coastal Bays Report Card Non-Tidal Nutrient Indicators / Index monthly data collected by DNR 6 stations for consistency with MCBP use only data collected in April no data collected from Sinepuxent subwatershed at present Report Card uses multiple thresholds for each indicator 2

3 Identifying Stream Nutrient Thresholds What have others done? 3

4 Identifying Stream Nutrient Thresholds In 2009, MDE produced a Biological Stressor Identification Process Report Analysis is based primarily on the MBSS round 2 dataset ( ) Water chemistry, including TN & TP was included as stressors Threshold values were determined using 90 th percentile comparison among biological conditions (BIBI) for the Coastal Plain. Values indicating biological degradation were set by determining the presence of statistically significant differences between poor and fair BIBI, and between very poor and good BIBI. Only one threshold value, defining high nutrient condition, was derived in this process. TN: the Coastal Plain region did not show statistically significant differences between very poor and good sites a value of 3.0 mg/l TN was set (= ENR threshold for WWTP in MD) TP: Statistically significant difference found between very poor and good sites, none found between poor and fair sites 0.14 mg/l TP 4

5 Identifying Stream Nutrient Thresholds Problems: the MBSS Stressor ID provides only one threshold for each indicator, however the Report Card process has agreed to use multiple thresholds for indicators, to better demonstrate progress or decline. The MBSS Stressor ID did not identify a statistically significant threshold, based on biological criteria, for TN applicable to the Coastal Bays. 5

6 Identifying Stream Nutrient Thresholds a different approach use MBSS Eastern Shore freshwater stream data to determine threshold values use data from BIBI, TN, TP based on recommendation from STAC use data from sentinel sites to determine thresholds for high attainment scores 7 Eastern Shore stations, but none are in the Coastal Bays watershed 2 stations on Nassawango Creek are in Worcester County CORS-102-S-2010UT LOCR-102-S-2010 NASS-108-S-2010 NASS-302-S-2010 UPCK-113-S-2010UT UPCR-208-S-2010 WIRH-220-S-2010 Emory Creek Swan Creek Nassawango Creek Nassawango Creek Choptank River Cypress Branch Comelly Mill Branch 10-year increasing trend in TN values in Comelly Mill Branch skews results so this station was eliminated from threshold calculations non-sentinel sites for low attainment scores. 392 sites 6

7 Identifying Stream Nutrient Thresholds Separate Eastern Shore Coastal Plain stations into sentinel and non-sentinel sites. Calculate P5, P10, Q1, median, Q3, P90, P95 for each group, for each indicator nutrient regardless of BIBI score Method considers only whether a site is sentinel or nonsentinel to calculate potential nutrient thresholds. Assumption that sentinel sites will have better water quality, and therefore should define the upper range of thresholds, i.e. scores 4 and 5. The lower end of the threshold range would then be represented by non-sentinel sites. Method produces reasonable patterns of statistical values that are consistent with above assumptions, with minor exceptions. 7

8 attainment score 5 4 sentinel MIN P5 P10 Q1 MEDIAN Q3 P90 P95 MAX N MEAN TN_ TP_ attainment score non sentinel Min P5 P10 Q1 Median Q3 P90 P95 Max N Mean TN TP value in red decreases instead of increases as score worsens Attainment Score S- P5 S - P10 S - MEDIAN NS - Q1 NS - MEDIAN NS - Q3 NS - P90 NS - P95 TN_ TP_ value in orange is equidistant between score 2 and 4 Attainment Ranges TN_ TP_ P10 5 < < MEDIAN Q1 3 > > MEDIAN 2 > > Q3 1 > > P90 0 > >

9 Non-Tidal TN / TP Scores 2010 Coastal Bays Report Card 1) For each basin (segment), a median value is calculated from all April samples for the variables TN and TP. Those medians are assigned attainment scores. Attainment scores are averaged and multiplied by 20 to produce a Non-Tidal Index score (NTI). Basin N Median TN Median TP TN Attainment TP Attainment Non-Tidal Index Grade AB D CHINCO C IOW C NB D SMR D 2) For each basin (segment), each April sample value of TN and TP is assigned an attainment score. Scores for each variable are averaged. The average scores for each basin are averaged again and multiplied by 20 to produce a Non-Tidal Index score (NTI). Basin N Mean TN Attainment Mean TP Attainment Non-Tidal Index Grade AB D CHINCO C IOW C NB D SMR D 9

10 Alternate methods tested Identifying Stream Nutrient Thresholds 1) Use all Eastern Shore sites: Parse by BIBI scores converted to integer values calculate P5, P10, Q1, median, Q3, P90, P95 for TN & TP. rank by medians unexpected inverse relationships! high BIBI values were associated with high nutrient medians low BIBI values were associated with low nutrient medians interannual variability in BIBI? some station sampled only once in 10 years year effects? other? 10

11 2) Use all Eastern Shore sites: Identifying Stream Nutrient Thresholds Group by sentinel and non-sentinel site type calculate mean, median, maximum BIBI rank for each site. group by integer value truncated BIBI score BIBI score rounded to nearest integer calculate P5 P10 Q1, median Q3 P90 P95 for TN & TP for each group rank by TN & TP median and P90 values Unexpected inverse relationships occurred in all 6 methods, mainly for TN (5) at non-sentinel sites. high BIBI values were associated with high nutrient medians low BIBI values were associated with low nutrient medians No pattern was found for TP at non-sentinel sites for 5 of 6 methods. Many potential patterns have missing values for one or more BIBI ranks, and frequently have low values out of pattern for the lowest BIBI rank scored CONCLUSION: Parsing the data by site type does not eliminate the problems associated with defining thresholds based on BIBI ranks. 11

12 Identifying Stream Nutrient Thresholds Future: Would it be more appropriate to develop thresholds based on Coastal Bays watershed stream conditions, rather than Eastern Shore Coastal Plain MBSS sites, none of which are located in the Coastal Bays watershed? 12

13 Here s the rub. The Maryland Coastal Bays Program is not comfortable using MBSS Sentinel Site data as the basis of the Stream Index because 1. Nutrient and physical data indicate that some Coastal Bays streams are healthy. (Low N, low P, low Chlor, sufficient DO) 2. Nearly every stream in the Coastal Bays watershed consistently ranks as poor in the FIBI and BIBI. Is this because the FIBI, BIBI and combined indices are not sensitive to black water streams? Our coastal streams are flat, sandy, often tannic, slow moving, tidally influenced, have short reaches, small catchements and smaller refugia for biota.

14 Management implications The Coastal Bays are not considered as MDE/DNR Priority Watershed, or as a Stronghold Watershed 1. MCBP is often excluded from the competition for targeted resources to protect and restore the Coastal Bays. (in addition to not being in the Chesapeake watershed). Ex. Land preservation activities are targeted to Stronghold watersheds 2. As BMPs are applied to the landscape, the improvements to water quality and biota will be difficult to measure without blackwater criteria & indices. This may open the door to opponents of restoration (i.e., is the expense and effort of BMPs worthwhile?)

15 Alternatives? Work with MBSS to discern blackwater criteria/indices, and Investigate potential reference sites based upon local stream sampling ( ) ~50 streams sampled each April for chemistry & physical parameter. Limited biota information.

16 Identifying Potential Reference Streams / Sites Potential reference sites chosen by percentile distributions EPA Nutrient Criteria Technical Guidance Manual, Rivers & Streams (2000)

17 Distribution of chlor. a, TN & TP determined All STREAM data over time ( ) CHLOR TN_mgL TP_mgL MIN MAX MEDIAN AVERAGE STD DEV BIN 5 PCT PCT PCT PCT PCT count

18 Identifying Potential Reference Streams Median parameter values by stream calculated & compared to the 25 th PCT of all stream data Streams with 6 year median concentrations at or below the 25 th PCT of all Coastal Bays Streams for MULTIPLE parameters: Hancock Creek Icehouse Branch* Purnell Bay UT * Scarboro Creek * Tanhouse Creek * * Streamwaders sample collected in 2011 The chemistry and physical data indicate that some streams appear to have minimal anthropogenic impact. green = <0.26 green = <0.011 green = <1.08 green = <0.035 green = <1.65 overall 25th PCT Stream medians DIN DIP TN TP Chlor Assateague NPS housing Bassett Creek Big Mill Pond Crippen Branch Cropper rep site Drum Creek Hancock Creek Holland Creek UT Hudson Branch Icehouse Branch Jake Gut Kitts Branch Little Mill Creek -Tier Montego Bay Pond Newport Creek Paw Paw Creek Payne Ditch Pikes Creek UT # Pikes Creek UT # Poplartown Branch Porter Creek Powell Creek Purnell Bay trib Riley Creek Robins Creek Rowley Creek Roy Creek Sand Branch Scarboro EAVaughn Scarboro Rt Scarboro Creek trib (P.Lndg) Swan Gut VA Tanhouse Creek Turville Creek

19 Reference site TN Cumulative Bin Frequency % % % % % % More % Reference site TP Cumulative Bin Frequency % % % % % % More % Reference site data is consistently lower than the bottom 25PCT of all streams ~80% < 1.07 mg/l (25 PCT of all data) ~76% mg/l (25 PCT of all data) All streams 25 PCT (n = 294) TN = 1.07 mg/l TP = mg/l

20 Why doesn t the chemistry match the biota? Coastal Bays data nutrient distributions are very similar to the proposed Sentinel Site/Report Card threshold criteria. How can we use MBSS data at the local level to secure the resources need to preserve and restore the watershed? Management perspective: Obtain resources to preserve & protect high quality areas Management perspective: Obtain resources to restore impaired waters along with pre & post monitoring

21 Next steps Wait for Streamwader 2011 results (20 sites) Will the results provide further weight of evidence to support the nutrient criteria at the proposed reference sites? Freshwater fish Delmarva Ches. Bay Families Coastal Bays Species R. Jesien Conduct a pilot with MBSS to determine Narrowed indices of blackwater/coastal biota? Coastal Bays stream assemblages at reference sites? Why is there an inverse relationship between chemistry and biota? Biota crash due to eutrophication? Agree on final reference ranges for TN, TP, etc., to be used for the Coastal Bays Report Card

22 Questions? 22