湖泊调查方法-水环境-英文授课ppt课件

1、Introduction to Lake Surveys Basic Water Quality AssessmentUnit 3 Module 8 Part B Field ProfilesObjectivesStudents will be able to:identify, utilize, calibrate and troubleshoot probes used for measuring temperature.identify, utilize, calibrate and troubleshoot probes used for measuring dissolved oxy

2、erpret information gathered by temperature and dissolved oxygen probes.identify examples of error from data gathered from field probes.identify, utilize, calibrate and troubleshoot probes used for measuring electrical conductivity (EC25).estimate total dissolved solid (TDS) concentrations in

3、lakesidentify, utilize, calibrate and troubleshoot probes used for measuring pH.explain how to effectively use a secchi disk to determine water erpret secchi disk data to evaluate water clarity trends in a lake.explain how to effectively use a transparency tube to determine water clarity.

4、identify, utilize, calibrate and troubleshoot probes used for measuring turbidity.relate the importance of light to lake profiles and chlorophyll production.Basic water quality assessmentThese slides focus on learning basic field techniques used by limnologists:Morphometry - estimating critical lake

5、 basin measurementsField profiles - physical and chemical parameters measured from top to bottom of the water columnSampling collecting water, sediments, and aquatic organismsInsert a wonderful image that captures the joy of measuring physical and chemical profilesPhysical and chemical profilesGoal:

6、Learn how to collect basic water quality data using common field instrumentationField profilesSensorsTemperatureDissolved oxygenpHSpecific conductivityTransparencySecchi, turbidityChlorophyll probesLight profilesProfiling guidelines/examples/helpful hintsPhysical and chemical field profilesPhysical

7、and chemical field profilesTopics covered:Definition - why its important (quick review)Units of measure - data reportingProbe types - calibration, storage, cleaningWhere and how often should profiles be measured?Troubleshooting and QA (what can go wrong and how to avoid or correct it) Field profiles

8、-temperatureTemperature importance and reportingTemperature regulates the rate of many biological and chemical processes within the lake.Units are degrees Celsius (oC) or Fahrenheit (oF)Reported to nearest 0.5 oCTemperature probesTypes of probesLiquid-in-glass: not very practical for lake temperatur

9、e profiles unless the lake is really shallow or your arms are really long. Absolutely NO mercury (Hg) thermometers, existing Hg thermometers should be turned in at your state water quality agency.Thermistor: based on measuring changes in electrical resistance of a semi-conductor with increasing temp

10、erature.Temperature probes Temp probeTemp probeonsetSome probe examples:Temperature probesTemperature is always measured concurrently with oxygen, pH, and conductivity because all of these parameters are temperature dependent.Most sensors have built-in temperature compensation.Temperature - calibrat

11、ionCalibrationCompare against a NIST-certified (National Institute of Standards and Technology) thermometer at 3 temperatures; 0, 25 and 40 oCThe thermometer should read within 0.2 oC of the NIST thermometer Typically you cannot adjust to calibrate but check the instrument manual. It is a good idea

12、to check it at 0oC in a slurry of ice-water and at room temperature if a calibrated (NIST) thermometer is not available.Temperature - calibrationCommon errorsTemperature is pretty fool-proof and thermistors generally last for 10 yrsTemperature - troubleshootingSymptomPossible cause and corrective ac

13、tionLiquid-in-glass thermometer doesnt read accuratelyliquid separatedThermistor doesnt read accuratelydirty sensorweak batteriesErratic thermistor readingsBad or dirty connection at meter or sensorBreak in the cablesWeak batteriesThermistor slow to stabilizeDirty sensorTemperature- field exampleExa

14、mple: Grindstone Lake- SummerTemp gradient sharpest from 5-6 metersConclusion: sample every meter to 10m to characterize the thermocline; then sample at 2 or even 5 m intervals to save time without losing much informationDOTDissolved oxygen (DO) DO importance and reportingOxygen is produced during p

15、hotosynthesis and consumed during respiration and decomposition. Generally 100% sat ?DO field measurements supersaturationDO field measurements supersaturationSupersaturation - possible causes:Photosynthesis High pressure injection below damsAir/Water equilibration (potential error)DO Field profiles

16、 supersaturationHeres the raw profile data from Medicine Lake DO field sensors cleaning & calibratinga month of periphytongrowthA nice clean Hydrolab sonde-beforeHydrolab calibrationYSI calibrationDO field sensors membrane installation1. Fill reservoir with saturated KCl solution then stretch a new

17、membrane on to the probe2. Stretch the O-ring on avoiding touching the top of the membrane with your fingers3. Trim off the excess membrane. Invert the probe and check for air bubbles.4. If bubbles or wrinkles are present, guess what? You get to do it all over again ! Note if you get really good you

18、 can use this two-handed, no knees technique DO field sensors membrane installationDO field measurements helpful tipsReplace the membrane at least monthly.Change the membrane the day before you need it and let it sit “on in a bucket of water overnight to stabilize (called “polarization).DO field mea

19、surements helpful tips Avoid prolonged periods in anoxic, high H2S water most manuals state that this can poison the sensor although some of us have never experienced this.This is very important for continuously deployed data logging sensors. Dont “park it in anoxic zones for extended periods.If in

20、doubt, check the sensor in surface water it should rise within a few minutes from zero to 80% saturation.If your multi-sensor probe is equipped with a stirrer or circulator make sure it is turned on.DO field measurements helpful tipsEquilibration time is critical - it takes longer, the steeper the O

21、2 gradient. It may take 5 minutes at the oxycline (where it drops abruptly to near zero).Make sure the line is taut and vertical ! The data is worthless if you report the wrong depth because of trigonometry. DO field measurements helpful tips Never leave your DO meter sitting outside, uncovered for

22、3 years. It voids the warranty.Lower the cable + probe into the water, not the meter box, even if the cable is too short to reach bottom.DO field measurements error exampleShagawa lake, May 2002 : DO profiles “seemed funky during this period.Heres the table of data for May 11, see how the DO values

23、are up and down with depth but temp and EC are uniform?DO field measurements error exampleTo the right is an example of the color mapper and line plot set for DO data from Shagawa Lake.DO field measurements error exampleHeres the QA/QC manual profile that we trust from May 7, 2002. DO field measurem

24、ents error exampleThe WOW DxT tool doesnt really help much unless you look carefully at those low DO vertical bars on 5/10 and 5/11 from 9-14 m depth. Are they real?Specific electrical conductivity = EC25EC25 - importanceCheap, easy way to characterize the total dissolved salt concentration of a wat

25、er sample.For tracing water masses and defining mixing zones.Groundwater plumesStream flowing into another stream or into a lake or reservoirFor characterizing density stratified layers in a lake.Lots of data examples from WOW lakesPrinciple of measurementA small voltage is applied between 2 paralle

26、l metal rod shaped electrodes, usually 1 cm apart. Measured current flow is proportional to the dissolved ion content of the water.If the sensor is temperature compensated to 25oC, EC is called “specific EC (EC25)EC25 units and reportingEC25 unitsWhat in the world are MicroSiemens per centimeter (S/

27、cm)?Units for EC and EC25 are mS/cm or S/cm 25oC. The WOW site reports it as EC 25oC (in S/cm).Usually report to 2 or 3 significant figures (to + 1-5 S/cm).YSI 33-field conductivity meter (with metered, weighted cable).thermistorEC 25 probe visuals1 cmEC 25 probes EC 25 probesHydrolab (Surveyor II)

28、Temperature probeConductivitybridgeYSI 6820Conductivity and temperature probeKCl is the typical standardStandard concentrations should approximate field valuesDry solid KCl at 105oC for 1 hr, cool, then weighDilute volumetrically to 1L with lab grade deionized water ( 4 readings (i.e. at least month

29、ly from Jun-Sep) for 8 -10 yrs for statistically significant trend (20% change) at the 10% level of confidence. Means there is a 10 % chance of identifying a trend that doesnt exist.Monthly Secci trendsSignificant Secchi trendsYoyo secchi/program_areas/environmental/teach/smprimer/secchi/secchi.html

30、Secchi long-term trends- Lake TahoeVisibility has decreased by over 35 feet in the last 40 years.Secchi depth is directly related to the amount of suspended matter, both organic (largely algal growth) and inorganic. /research/response.html/tahoe/trg_update_apr_99/west/reno/gallery.htmlLake Tahoe eut

31、rophication storyData courtesy of C.R. Goldman and J.E. Reuter, Tahoe Research Group, U. of California-Davis, /tahoetv/ /tahoe/trg_update_sept_98The million $ versionThe thousand $ versionTahoe Secchi - modelsTahoe Secchi modelsField replication secchidissolved O2 / temperatureflowin situ/./pictures

32、/ secchi/pages/015.html Water clarity transparency tubesWater clarity transparency tubesUsed in streams, ponds, wetlands, and some coastal zonesAnalogous to Secchi depth in lakes: a measure of the dissolved and particulate material in the waterWater clarity transparency tubesUseful for shallow water

33、 or fast moving streams bodies where a Secchi would still be visible on the bottomforestry-suppliers/Water clarity transparency tubesBest for clearwater bodies of water (not stained with dissolved organic compounds from bogs) but not too clear waterIt is a good measure of turbidity and suspended sed

34、iment (TSS)Used in many volunteer stream monitoring programs How does Turbidity relate to TSS ? A general rule of thumb:1 mgTSS/L 1.0 - 1.5 NTUs of turbidityBUT Turbidity scattering depends on particle size so this is only a rough approximationWater clarity transparency tubesWater clarity transparen

35、cy tubes Turbidity measures the scattering effect suspended particles have on light inorganics like clay and silt organic material, both fine and colored plankton and other microscopic organismsEven small amounts of wave action can erode exposed lakeshore sediments, in this case a minepit lake from

36、northeastern Minnesota. Guess the mineral mined here.Water clarity turbidityTurbidityField turbidity measurements are made with turbidimeters (bench meter for discrete samples)Submersible turbidity sensors (Note - USGS currently considers this a qualitative method) Turbidimeters - Nephelometric opti

37、cs nephelometric turbidity estimated by the scattering effect suspended particles have on light detector is at 90o from the light source/eagles/turbidity.htmTurbidityTurbidity units and reportingNephelometric Turbidity Units (NTU)standards are formazin or other certified materialJTUs are from an “ol

38、der technology in which a candle flame was viewed through a tube of water1 NTU = 1 JTU (Jackson Turbidity Unit)Turbidity formazin unitsFormazin is most commonly the standard for turbidity Turbidity clay exampleHeres a sample containing clay particles with corresponding NTUsBench and portable instrum

39、ents and kits vs YSI wiping turbidityYSI 6820 with unwiped turbidityHydrolabTurbidity meters and probesSubmersible TurbidimetersTurbidity - methodsComparability of different methods:With the proliferation of automated in situ turbidity sensors there is concern about the comparability of measurements

40、 taken using very different optical geometries, light sources and light sensors. The US Geological Survey and US Environmental Protection Agency are currently (August 2002) developing testing procedures for a field comparison of a number of instruments produced by different manufacturers. Turbidity

41、- calibrationTurbidity free water = zero (0 NTU) standard USGS recommends filtering either sample water or deionized water through a 0.2 um or smaller filter to remove particlesWOW uses deionized water that is degassed by sparging (bubbling) with helium to minimize air bubbles that give false turbid

42、ity readingsTurbidity standardsStandards range depends on anticipated sample values:Lakes - typically 0-20 NTUStreams and wetlands - 0-20, 0-50 or 0-100 NTU 2 non-zero standards typically adequate (response is linear)Turbidity - standardsTypes of standards Formazin particles (either from a “recipe o

43、r purchase a certified, concentrated stock solution (usually 4000 NTU)other materials - polystyreneneed to worry about storage limits - primary stock of 400 NTUs lasts 1 month when refrigerated. Dilute working standards from intermediate stock solution daily.Prepare daily2 to 20 NTUHach CompanyPrepa

44、re weeklyAll dilutionsEPAPrepare dailyAll dilutionsStandard MethodsPrepare monthly20 to 40 NTUSuggested holding timesConcentrationsSourceTurbidity standards Light Light importance in aquatic systemsPrimary production (PPr; photosynthesis)Euphotic (photic) zone = layer where there is a positive net d

45、aily PPrfrom surface to depth where irradiance 0.5-1% of surface lightstratum of net O2 production & CO2 -fixation during the dayAphotic zone = bottom of photic zone to lake bottomtoo little light for photosynthesisLight importance in aquatic systemsPlant germination (macrophytes) Navigation, predat

46、ion, breeding behavior, prey refugiaHeat (see Module 3 and WOW Lake Ecology Primer) Light profiles radiometry The semi-log plot of Light vs depth will linearize exponential attenuationLn I(z) = -nz + Ln I(0) BAlight vs depth plot I(z) = I(0) * e-kz BALight profiles attenuationLight definitionsIo = t

47、he irradiance at the water surfaceIz = the irradiance at any depth zZ sd = Secchi depthEuphotic zone = layer where there is a positive net daily primary productivityAphotic zone = bottom of photic zone to lake bottomI(z) = I(0) * e-kz orLn I(z) = -nz + Ln I(0) Light reference charts intl-light/handbook/physicsclassroom/physicsclassroom/light at Z