Report of significant findings--las Vegas Bay/ Boulder Basin investigations

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1 Publications (WR) Wate Resouces Repot of significant findings--las Vegas Bay/ Boulde Basin investigations James F. LaBounty Michael Hon Bueau of Reclamation Follow this and additional woks at: Pat of the Biochemisty Commons, Deset Ecology Commons, Envionmental Health and Potection Commons, Envionmental Indicatos and Impact Assessment Commons, Envionmental Micobiology and Micobial Ecology Commons, Envionmental Monitoing Commons, Fesh Wate Studies Commons, Natual Resouces and Consevation Commons, Natual Resouces Management and Policy Commons, and the Teestial and Aquatic Ecology Commons Repositoy Citation LaBounty, J. F., Hon, M., Bueau of Reclamation (1996). Repot of significant findings--las Vegas Bay/Boulde Basin investigations. Available at: This Technical Repot is bought to you fo fee and open access by the Wate Resouces at Digital It has been accepted fo inclusion in Publications (WR) by an authoized administato of Digital Fo moe infomation, please contact

2 TECHNICAL SERVICE CENTER Denve, Coloado Technical Memoandum No Repot of Significant Findings-Las Vegas Bay/ Boulde Basin Investigations Pepaed by James F. LaBounty and Michael Hon U.S. Depatment of the Inteio Bueau of Reclamation Apil 8, 1996!

3 *_* Repot of Significant Findings Las Vegas Bay/Boulde Basin Investigations Sampling Date Mach 26,1996 James F. LaBounty and Michael Hon Bueau of Reclamation Ecological Reseach and Investigations Goup P.O. Box Denve, Coloado (303) ; fax (303) INTRODUCTION This epot is a summay of findings fom the Mach 26, 1996, limnological field suvey of Boulde Basin, Lake Mead, Nevada. These data ae pesented to document and demonstate, in a clea manne, the influence of effluent flows fom Las Vegas Wash on the wate quality and aquatic ecology of the Basin. Even though this typifies the wate quality conditions, moe compehensive epots and publications ae in pepaation which will moe thooughly document the conditions fom 1990 though METHODOLOGY Field sampling was caied out between 0830 and 1500 beginning at the confluence of Las Vegas Wash and the Inne Las Vegas Bay. Ten (10) locations wee sampled, each in a simila manne. Locations of sampling stations ae in line fom the Wash-Bay confluence to a point midway between Saddle and Black Islands. In addition, sampling was done at a location midway between Sentinel Island and the base of Fotification Hill, and at the buoy line in font of Hoove Dam. Sampling stations ae labeled fom LV01, at Wash-Bay confluence, to LV17 at Hoove Dam.. A significant data collection point is LV14, which is the afoementioned sampling location between Saddle and Black Islands. The following data wee collected fom each location: > Pofile of the wate column including tempeatue, ph, dissolved oxygen concentation, specific conductance (conductivity), and tubidity. * Wate tanspaency using Secchi disc, and wate colo > Chloophyll concentation (an index of algae biomass) * Concentation of total inoganic plant nutients ammonia, nitate, and othophosphate * Abundance and kinds of algae * Abundance and kinds of zooplankton (micoscopic animal life) Analyses of wate samples fo nutient and chloophyll concentations wee done by the Lowe

4 Coloado Regional Wate and Soil Analytical Laboatoy. Laboatoy analysis of algae and zooplankton samples wee done, espectively, by contactos D. Ann St. Amand of St. Joseph, Michigan, and D. John Beave of Shake Heights, Ohio. Data wee plotted using softwae packages Quatto Po and Sufe. FINDINGS Figue 1 illustates the tend in wate claity o tanspaency at each of the ten sampling locations. Data ae plotted fom LV01 to LV17. Tanspaency pogessively inceased with distance fom the Wash-Bay confluence. Thee was a maked incease in claity (nealy double) fom LV10 to LV14. This diffeence was most likely due to the fact that a sping algal bloom was beginning to occu within Las Vegas Bay. Algal blooms commonly occu each Mach-Apil, usually eaching a peak in June. Of note is that tanspaency does not stabilize thoughout Boulde Basin, which indicates the influence of the Wash on the Basin. Choosing a sampling location which can be classified as untainted within the Basin may no longe be possible. On the othe hand, Secchi depths of 16 metes and geate fom LV12 to LV17 indicate this aea of the Basin to be unusually clea, and elatively low in biological poductivity. These obsevations, howeve, vay with season. Figue 2 is the pofile of physical-chemical data collected fom LV14, between Saddle and Black Islands on Mach 26, Data ae plotted fom suface to nea the bottom (115 metes deep). While themal statification (solid line) is pesent, highe specific conductance (dotted line) and tubidity (dash, double dot) just unde the epilimnion (top mixing laye of the lake) ae especially notable. These data indicate the pesence, between 24 and 65 metes below the suface, of a laye of wate highe in dissolved solids and almost thee times less tanspaent as wate above o below. This condition exists at all sampling locations fom the Wash-Bay confluence to this point (LV14), and can be taced to the Las Vegas Wash inflow. Based upon pevious yeas' data, this plume can be expected to be detectable thoughout the emainde of the yea, but at diffeent depths and to a geate o lesse intensity depending upon the degee of statification. The plume is thus quite pedictable both in natue and location. Each yea it is inceasingly extensive spatially and tempoally. As duing the sping seasons of othe yeas, the plume is not paticulaly notable at eithe LV15 o LV17. We do not sample in the middle of the Boulde Basin between Saddle and Sentinel Islands. Figues 3 and 4 ae plots of physical chemical data collected fom all ten sampling locations on Mach 26, These plots ae pesented as a "slice" of the lake, showing it in a vetical and hoizontal staightened plane fom the Wash-Bay confluence to Hoove Dam. Figue 3 includes tempeatue ( C), and dissolved oxygen (mg/l) and ph (units) concentations. Inflow (LV01) Saddle Island (LV14), and Hoove Dam (LV17) ae noted on each gaph. Note the appaent waming influence of the Las Vegas Wash inflow. This wam wate moves downsteam along the suface. Thee is nothing paticulaly notable egading eithe dissolved oxygen o ph 1

5 concentations. Howeve, as themal and density statification inceases, and the fequency of wind mixing deceases, dissolved oxygen concentation will dastically decease in bottom layes in the Inne Bay. This aea of the lake is highly eutophic, and the extent of this tophic status is expanding as the load of nutients continues to pou into the lake at an eve inceasing ate. Figue 4 includes plots of both specific conductance (us/cm), and tubidity (NTU's). As in figue 3, the plots extend fom Las Vegas Wash and Bay to Hoove Dam. These data demonstate clealy the souce of wate of high conductance and tubidity. Duing ealy sping the plume extends at least to the point between Saddle and Black Islands. Duing this season of the yea the plume simply "slides" along the bottom to a depth just below the epilimnion (uppe mixing zone of the wate column). On this date it was between 24 and 65 metes in depth (elevation=340 to 299 metes above mean sea level).this phenomenon is well documented duing all the yeas of ou study since The plume is pesent thoughout the yea, and moves in a faily pedictable manne. The geatest change since 1990 has been that its extent continues to incease, both tempoally and spatially. The stength of this dense plume of wate can be ealized when one consides that at this time of yea thee is ample oppotunity fo extensive mixing in the Inne Bay due to lack of stong themal stuctue, and the fequent occuence of stong winds. In fact, the aftenoon of Mach 25, until just befoe we began ou suvey, was an extemely windy peiod due to a stong weathe font passing though the aea. SIGNIFICANCE The data shown indicate a plume exists in Boulde Basin chaacteized by wate high in specific conductance and up to 300 pecent highe in tubidity than the suounding wate. The significance of this goes well beyond the fact that thee is a saltie laye in the lake. As evidence, figue 5 A plots total nitogen (as the sum of nitate and ammonia) fom samples collected at LV14 on Mach 26, 1996, fom the suface, 1 mete, 3 metes, and 33 metes (detemined in the field to be within the plume). Nitogen concentation at all sampling stations was highest within the plume (figue 5B). At each station the location of the plume was identified fom the pofile data, and wate samples wee collected. Figue 5B plots plume nitogen concentation going fom the confluence to Hoove Dam. These data demonstate that the souce of this nitogen is Las Vegas Wash (LV01), and that the concentations decease as the plume moves downsteam. Although tetiay teatment and numeous upgades at the wastewate teatment facilities on the Wash have esulted in obvious changes in the both wate chemisty of wate in the Bay, and in the esulting degee of biological poductivity, thee continues to be a loading effect. Fo example, about a yea ago teatment began to successfully educe ammonia dischage by convesion to nitate. Howeve, the total load of nitogen has emained nealy the same, o may be inceased due to inceasing dischage volume as population gows. The significance of this is that thee is a deceased loading of the toxic fom of nitogen, but the availability of nitogen fo use in biological poduction is just the same. Studies at othe locations have shown that with unoff fom pimaily uban aeas, both point

6 souce and non-point souces comes a myiad of oganic, inoganic, and biological constituents which ae seldom sampled undestood. A few include oganochloides and oganophosphates used as pesticides past and pesent, by-poducts of chloine teatment, vial and bacteial pathogens, and othe detimental oganisms such as Cyptospoidium and Giadia. Fom ou point of view, and expeience in cases woldwide, thee ought to be some attention paid to the location of this plume elative to any stuctue which would delive wate fo domestic use. In addition, a igoous pogam to undestand the chemical and biological chaacteistics of the plume at vaious locations in the lake thoughout the yea should be undetaken and ongoing. A study published in the Mach 1, 1996, Annals of Intenal Medicine titled "Cyptospoidium: An outbeak associated with dinking wate despite state of-the-at wate teatment," by Goldstein et al. documents that 78 people wee diagnosed with Cyptospoidium infection in the Las Vegas aea in the fist quate of It states: "Ou epidemiologic data indicate that contaminated municipal dinking wate was the most likely vehicle of tansmission in this outbeak..." The poblem is that thee ae few o no guidelines developed to detect these health isks since thee is an absence of indicatos that can eliably pedict occuence of an outbeak if the teatment plant is opeating within existing fedeal and state standads. An extensive epot of findings fom suveys of the Boulde Basin done since 1990 is fothcoming. List of Figues Figue l.-secchi depth (wate tanspaency) eadings fom ten sampling stations of the Boulde Basin of Lake Mead, Mach 26, LV01 is loca ted at the confluence of Las Vegas Wash and the Inne Las Vegas Bay. LV14 is located Between Saddle and Black Islands. Location LV17 is just above Hoove Dam. Figue 2.-Pofile of physical/chemical data collected on Mach 26, 1996 at a site between Saddle and Black Islands of Boulde Basin of Lake Mead, (tempeatue = C, dissolved oxygen = mg/l, ph=ainits, conductivity =ns/cm, and tubidity^ntu's) ~ Figue 3.-Isopleths of tempeatue, dissolved oxygen, and ph, Mach 26, 1996 using data collected fom ten locations in a ten mile line fom the confluence of Las Vegas Wash to Hoove Dam. Figue 4.-Isopleths of conductivity and tubidity, Mach 26, 1996 using data collected fom ten locations in a line fom the confluence of Las Vegas Wash to Hoove Dam. Figue 5.-Plots of total nitogen concentation calculated fom ammonia and nitate. Samples _ wee collected Mach 26, A.-Gaph displays data fom suface to bottom at station LV14. B.-Gaph displays data fom samples collected in the plume detected in the wate columns at each of the sampling stations.

7 Figue l.-secchi depth (wate tanspaency) eadings fom ten sampling stations of the Boulde Basin of Lake Mead, Mach 26, LV01 is located at the confluence of Las Vegas Wash and the Inne Las Vegas Bay. LV14 is located Between Saddle and Black Islands. Location LV17 is just above Hoove Dan. i -

8 I! I Secchi Depth (Wate Tanspaency) Mach 26, E 12 Q) 0 Q LV01 LV02 LV03 LV05 LV08 LV10 LV12 LV14 LV15 LV17 >»Downsteam>»

9 Figue 2.-Pofile of physical/chemical data collected on Mach 26, 1996 at a site between Saddle and Black Islands of Boulde Basin of Lake Mead, (tempeatue = C, dissolved oxygen = mg/l, ph=units, conductivity =us/cm, and tubidity=ntu's)

10 PofileLVI 4, Mach c o. (U Q Tubidity - ph Tempeatue Oxygen Conductivity Tempeatue ( C) Specific Conductance (Conductivity) (as/cm) 7 8 Dissolved Oxygen (mg/l) i PH Tubidity (NTU) 3

11 Figue 3.-Isopleths of tempeatue, dissolved oxygen, and ph, Mach 26, 1996 using data collected fom ten locations in a ten mile line fom the confluence of Las Vegas Wash to Hoove Dam.

12 Tempeatue ( C) Mach Inflow Gov't Wash Saddle Island Hoove Dam Dissolved Oxygen (mg/l) 0.00-k ' H f o> Q -moon Inflow Gov't Wash Saddle Island Hoove Dam ~ Inflow Gov't Wash Saddle Island Hoove Dam Distance fom Inflow (miles)

13 Figue 4.-Isopleths of conductivity and tubidity, Mach 26, 1996 using data collected fom ten locations in a line fom the confluence of Las Vegas Wash to Hoove Dam. 8

14 .>- Specific Conductance (Conductivity) (us/cm) Mach CX.& Inflow Gov't Wash Saddle Island Hoove Dam Tubidity (NTU) tl 0> Inflow Gov't Wash Saddle Island Hoove Dam Distance fom Inflow (miles)

15 Figue 5.-Plots of total nitogen concentation calculated fom ammonia and nitate. Samples wee collected Mach 26, A.-Gaph displays data fom suface to bottom at station LV14. B.-Gaph displays data fom samples collected in the plume detected in the wate columns at each of the sampling stations. f

16 I H z O af O CO CD Concentation (mg/l) U) Si Depth (m) C*> zg.? s Po g ^ e 3 F* oco O a CD

17 PEER REVIEW DOCUMENTATION PROJECT AND DOCUMENT INFORMATION Poject Name Las Vegas Wash Effluent WOID LC089 Document Repot of Significant Findings--Las Vegas Bav/Boulde Basin Investigations Document Date Mach 26, 1996 Date Tansmitted to Client Apil Team Leade James F. LaBountv and Michael Hon Leadeship Team Membe John C. Lease (Pee Reviewe of Pee Review/QA Plan) Pee Reviewe Rick Roline Document Autho(s)/Peoae(s) James F. LaBountv and Michael Hon Pee Reviewe James Satois REVIEW REQUIREMENT Pat A: Document Does Not Requie Pee Review Explain Pat B: Document Requies Pee Review: SCOPE OF PEER REVIEW Pee Review esticted to the following Items/Section(s): Reviewe: REVIEW CERTIFICATION Pee Reviewe - I have eviewed the assigned Items/Section(s) noted fo the above document and believe them to be in accodance with the poject equiements, standads of the pofession, and Reclamation policy. _ y ^ >~^ Reviewe^ "fca-gg-^-tf"^*'*'*-*!:7^g-t-^-«-we,review Date: ~ / a" I 7»s' Signatue / /./- ;-&- s s Reviewe^ ~7Q?~~\. - _ ±e^j*4<*/~ M^ Review Date: ^~\"/& Signatue I Pepae - I have discussed the above document and eview equiements with the Pee Reviewe and believe that this eview is completed, and that the P document will me~fet the equiements_q-e the poject. I V\ 1 7^7-^Vl " /". /) Q Team Membe: XX^^1^T. 6--f «^K^, ^ Date: ^>^)/v»x Q ;"