Oxygen Trends in Coeur d Alene Lake and Potential Impacts on Contaminant Metals

Transcription

1 Oxygen Trends in Ceur d Alene Lake and Ptential Impacts n Cntaminant Metals Craig Cper, Ph.D. Idah Department f Envirnmental Quality Limnlgist, Ceur d Alene Lake Management Our Gem Sympsium Ceur d Alene, ID March, 2016

2 Envirnmental Challenge 1. Histric mining cntributed ver 75 millin metric tns f metal cntaminated sediments int lake Arsenic, cadmium, lead, zinc Have damaged lake health Still entering lake tday Legacy pses a cntinuing threat 2. Beautiful and desirable lake sustains a vibrant cmmunity 3. Human activities in the regin can imprve r degrade water quality

3 Scientific Backgrund Metals Want t trap metals in sediments by maintaining an O 2 cap in the lake s bttm waters O 2 Zinc O 2 O 2 Cadmium Lead Cd Zn Pb Lake Sediments

4 Scientific Backgrund Oxygen Keep metals in sediments with an O 2 cap in bttm waters O 2 cntrlled by mixing, temperature, and O 2 demand Lakes stratify Islates hyplimnin Planktn (+ O 2 ) Traps fixed mass f O 2 in the hyplimnin Bacteria (- O 2 )

5 Seasnal Oxygen Dynamics O2 (mg/l) DOmg (mg/m3/day) Jan 30 Jan 14 Feb Winter 29 Feb 15 Mar 30 Mar 14 Apr 29 Apr Spring 14 May 29 May 13 Jun 28 Jun 13 Jul Mnths f the Year 28 Jul Summer Average O 2 ver all depths (site C1) 12 Aug 27 Aug 11 Sep 26 Sep 11 Oct Fall 26 Oct 10 Nv 25 Nv 10 Dec Average hyplimnin (site C1) O2 (mg/l) DOmg (mg/m3/day) Apr 29 Apr 14 May 29 May 13 Jun 28 Jun 13 Jul Summer seasn (Jul Oct) 28 Jul Mnths f the Year 12 Aug 27 Aug 11 Sep 26 Sep 11 Oct 26 Oct 10 Nv

6 Cre Mnitring Lcatins Nrthern Pl C1, Tubbs Hill Central Pl C4, University Pint Suthern Pl C5, Chippy/Blue Pint Envirnment C1, C4 are cld, deep C5 is warmer, and shallwer

7 Summer O 2 clse t sediments, C1 Data cllected by IDEQ, USGS back t early 1990 s Apparent trend f decreasing July - Octber hyplimnetic O 2 Trend significant t 95% cnfidence (P = 0.017, < 0.05) Trend Slpe ~ (-0.04) mg/l per year

8 Disslved O 2 Overall July Octber Hyplimnin, C1 Time Trend 9 Seasnal Regressin: y = x ; R = ; p = Residuals Regressin: y = x ; R = ; p = Seasnal Regressin Residuals Regressin 8 7 DOmg (mg/m3/day) Trend significant t 95% cnfidence (P = 0.004, < 0.05) Trend Slpe ~ (-0.04) mg/m3 per day Years

9 C1 Tubbs Hill, Oxygen Demand in Hyplimnin June Octber Apparent increase, but nt significant t 95% cnfidence May be significant at a lwer cnfidence level slpe = 0.21 average ~20 Trend nt significant t 95% cnfidence (P = 0.13, > 0.05)

10 Summer O 2 clse t sediments, C4 Data cllected by IDEQ, USGS back t early 1990 s Apparent trend f decreasing July - Octber hyplimnetic O 2 Trend significant t 95% cnfidence (P = 0.024, < 0.05) Trend Slpe ~ (-0.03) mg/l per year

11 Disslved O 2 Overall July Octber Hyplimnin, C4 Time Trend 9 Seasnal Regressin: y = x ; R = ; p = Residuals Regressin: y = x ; R = ; p = Seasnal Regressin Residuals Regressin 8 7 DOmg (mg/m3/day) Trend nt significant t 95% cnfidence (P = 0.08, > 0.05) Trend is significant t 90% cnfidence (P < 0.10) Trend Slpe ~ (-0.02) mg/m3 per day Years

12 C4 University Pint O 2 Demand in Hyplimnin, June Octber Apparent increase is significant t 95% cnfidence slpe = 0.26 average ~20 Trend is significant t 95% cnfidence (P = 0.02, < 0.05)

13 Summer O 2 clse t sediments, C5 Data cllected by Tribe, USGS back t 2004 N recent trend, n significant change relative t

14 Disslved O 2 Overall July Octber Hyplimnin, C5 Time Trend 11 Seasnal Regressin: y = x ; R = ; p = Residuals Regressin: y = x ; R = ; p = Seasnal Regressin Residuals Regressin DOmg (mg/m3/day) N apparent trend (P = 0.88) Years

15 Disslved Oxygen Demand in Hyplimnin June Octber, C5 N significant trend Average ~40 slpe = Trend is nt significant t 95% cnfidence (P = 0.38, > 0.05)

16 Interim Summary Oxygen Evidence that O 2 in the July Octber hyplimnin has decreased since the 1990 s in the nrthern lake (sites C1, C4). Near-bttm and verall hyplimnin O 2 demand in the hyplimnin may als have increased in nrthern lake. Higher O 2 demand leads t lwer O 2 levels Variability in the dataset, but statistics shw that the trend is real. Much f the variability arises frm the hydrgraph (water cycle) Different trends in the suthern lake (site C5) O 2 demand in suthern lake ~2x higher O 2 in nrthern lake trending away frm desired levels

17 Oxygen, Metals, and Nutrients Primary Objective f the 2009 Lake Management Plan T prtect and imprve lake water quality by limiting basin-wide nutrient inputs that impair lake water quality cnditins, which in turn influence the slubility f mining-related metals cntaminatin cntained in lake sediments. Nutrients reducing nutrients reduces lake metablism Lake Metablism lwer lake metablism leads t higher O 2 levels Higher O 2 Levels Keep metals trapped in the sediments. Uncertainty ver the details f this prcess

18 Anxic Micrcsm in CDA Lake Shallw basin in NW crner f CdA Lake, adjacent t Blackwell Isl. Marina Bttm waters islated frm main lake, experiences seasnal anxia and hypxia Natural labratry t investigate relatinships between O 2 and metals cycling in CDA Lake m depth, cmparable t C5 in suthern lake Hydrlab Depth (m) /1/2013 Disslved O2 at Cugar-2 ( ) 10/1/2013 1/1/2014 4/1/2014 7/1/ /1/2014 1/1/2015 4/1/2015 7/1/ /1/2015 Disslved O2 (mg/l) < > 12.00

19 O 2 Impacts n Metals are Cmplicated

20 Interim Summary Sediment Metals Metals in the lake are influenced by changes in hyplimnetic O 2 Metals are released frm sediments at lw O 2 levels Subsequent effects are cmplicated. Extent f change varies with metal, depth, and time Metals can be released befre O 2 levels reach 0 mg/l Begin t see effects when near-sediment O 2 drps belw 2 4 mg/l Multiple influences. Likely mix f physical, chemical, and bilgical

21 Putting it All Tgether Metals and Oxygen lw O 2 releases metals frm sediments But what happens next is cmplicated Oxygen in Hyplimnin declined since 1990 s in nrthern lake Changes are subtle, impacted by variability, statistically real Next Step evaluate significance, causes, and implicatins Hw imprtant is the xygen signal? What are the causes? What are the implicatins fr metals management?

22 Factrs That Impact O 2 Oxygen in water is cntrlled by 4 things Temperature Mixing Carbn Sediment O 2 demand Carbn impacted by Lake prductivity Nutrients River lading CDA River at Harrisn 2008 high water event All impacted by climate, hydrlgy, weather, land-use, and the lake s eclgic structure

23 Lake Management Prgram Team Laura Laumatia Website: Phne: (Laura) (Jamie) Sctt Fields Jamie Brunner Bb Witherw Michael Gerge Craig Cper Ben Scfield Dale Chess

24 Extra Slides

25 Uncertainty in Hw O 2 Impacts Metals 2005 Natinal Academies study, Superfund and Mining Megasites Lessns frm the Ceur d Alene River Basin The large uncertainties in the present understanding f the mechanism f release f metals and nutrients frm Lake Ceur d Alene sediments and their transprt and fate after release will limit develpment f an effective lake management plan (pg 405) Kuwabara et. al. (2003), Envirnmental Management (v. 32, #3) Results frm deplyments f an in-situ flux chamber indicated that benthic fluxes f disslved Zn and rthphsphate were cmparable in magnitude t riverine inputs (abstract f paper, pp ) Ceur d Alene Press, 15-Nvember 2015 all scientists dn t necessarily agree that anxic cnditins will cause the metals t leach int the lake water. (frnt page article)

26 Cugar-2, Near Bttm, 2015 Cmpare Anxic site (Cugar-2) with Hypxic site (CG-9)

27 Cugar-2, Near Bttm, 2015

28 Site CG-9, Near Bttm, 2015

29 Scientific Backgrund Oxygen Keep metals in sediments with an O 2 cap in bttm waters O 2 cntrlled by mixing, temperature, and O 2 demand Lakes stratify Islates hyplimnin Planktn (+ O 2 ) Traps fixed mass f O 2 in the hyplimnin Bacteria (- O 2 )