Water Chemistry. Water 101

Transcription

1 Water Chemistry Water 101

2 I. Introduction A. Water is not pure Many different kinds of chemicals dissolved in it Ions, organic chemicals, organic matter, particulate matter, and gases can all be in water Some are considered pollutants, others are natural components

3 II. Basic Water Quality Measurements DO dissolved oxygen ph Temperature Specific conductivity Turbidity

4 II. Basic Water Quality Measurements A. DO stands for dissolved oxygen. The amount of oxygen dissolved in the water Animals and protists require oxygen to live The amount of oxygen dissolved in water varies due to several factors

5 II. Basic Water Quality Measurements They include: 1. Water temperature More oxygen can be dissolved in cool water than in warm water. For example, at 20 o C (68 F) water can hold up to 9.2 mg/l, at 25 o C (77 F) water can only hold 8.4 mg/l

6 Graph showing Oxygen concentration dependence on temperature From:

7 II. Basic Water Quality Measurements 2. Biological activities that use oxygen (respiration, organic breakdown, etc.) Decomposition of organic material requires oxygen Decomposition tends to occur in the bottom sediments of aquatic systems

8 II. Basic Water Quality Measurements 3. Biological activities that produce oxygen (photosynthesis) Since sunlight is greatest at the surface, photosynthesis tends to add more oxygen to the upper layers 4. Physical activities that add oxygen (turbulent water) 0nce again, this tends to add oxygen to the upper surface of water

9 II. Basic Water Quality Measurements Dissolved Oxygen is usually measured in one of two ways 1. The first is a measure of the amount of oxygen per liter of water and is measured in the unit mg/l mg/l stands for milligrams per liter A DO of 10 mg/l means there are 10 milligrams of oxygen dissolved in 1 liter of water

10 II. Basic Water Quality Measurements 2. The second way to measure oxygen is called % saturation Saturation is the point at which water is holding all the oxygen it can hold % saturation compares the amount actually in the water with the amount at the point of saturation

11 II. Basic Water Quality Measurements Example: at 25 0 C water can hold 9.2 mg/l of oxygen at saturation Lets say you measure a stream at 25 0 C and the DO is 8.3 mg/l The % saturation would be calculated by taking 8.3 /9.2 which would equal 90% So the % saturation DO = 90%

12 II. Basic Water Quality Measurements It is actually possible to have a super saturated condition In waters that are highly oxygenated, there can be % saturation greater than 100%

13 II. Basic Water Quality Measurements A relationship seen in many aquatic ecosystems is the high amount of DO during the daylight hours and then a precipitous drop during the night. DO levels around 7 9 mg/l are considered optimal for fish A DO below 4 usually can not support fish.

14 II. Basic Water Quality Measurements B. Temperature Temperature varies during the day in aquatic ecosystems. Has a great affect on the DO in water Aquatic organisms have a particular tolerance range for temperature, some prefer cool waters, others can survive in fairly warm waters.

15 II. Basic Water Quality Measurements Cooling and Evaporation Water cools as it evaporates The physical process of water molecules changing from liquid to gas absorbs energy (heat) This cools the surface the water evaporates from

16 II. Basic Water Quality Measurements C. Specific conductivity This is a measure of the ability of the water to conduct an electrical current. It is actually a measure of the ion concentrations in the water high ion concentrations have a higher conductivity.

17 II. Basic Water Quality Measurements Water usually has several types of dissolved ions (salts) Common ions include calcium (Ca ++ ), magnesium (Mg ++ ), and bicarbonate (HCO 3- )

18 II. Basic Water Quality Measurements Other ions such as phosphates and nitrates are also a part of specific conductivity Important plant and algae nutrients Specific conductivity can give an estimate of the primary productivity of a water body

19 II. Basic Water Quality Measurements Other terms used in relation to dissolved ions Total dissolved solids (TDS) all organic and inorganic salts dissolved in the water High TDS means high specific conductivity Hardness relates to the amount of calcium and magnesium dissolved in the water

20 II. Basic Water Quality Measurements Salinity - measure of the total concentration of salts (mg per liter) dissolved in water

21 II. Basic Water Quality Measurements D. ph This is the measurement of the acidity or alkalinity of the river or stream Depends on a variety of factors, but especially the soil characteristics of the watershed Areas with high concentrations of calcium carbonate will tend to have a ph above neutral (7).

22 II. Basic Water Quality Measurements In North Dakota, most river and streams are slightly alkaline and have a ph between 7.5 and 9 Values between 5 and 9 are considered safe for most aquatic life.

23 II. Basic Water Quality Measurements E. Turbidity This is the measurement of how clear the water is. The more suspended solids there are in the water column, the murkier it is Examples of suspended solids that can cause high turbidity are soil particles, algae, organic detritus, and sewage discharge.

24

25 II. Basic Water Quality Measurements Rivers in the North Dakota tend to have a fairly high turbidity because of a high amount of algae, or phytoplankton, in the water. Total Suspended Solids (TSS) measurement of the solids suspended in the water column

26 II. Basic Water Quality Measurements Do not confuse dissolved solids with suspended solids. Dissolved solids do not have a major impact on turbidity, You can have very clear water that has a high TDS and specific conductivity

27 III. Measuring Water Quality A. Probes electronic components for measuring certain parameters Probes are an expensive, but accurate ways of measuring water quality parameters Several companies make multiprobe sondes, a device that can measure many different parameters at once

28 III. Measuring Water Quality Multiprobe sondes take quick measurements and record them within the instrument You can later download them into a computer for analysis Multiprobes can also be used for long term monitoring This application is called data logging

29 III. Measuring Water Quality The probe is placed in a river and left for a designated period of time The probe will measure and record parameters at a set interval Most water resource professionals use multiprobes for measuring the water quality parameters discussed earlier

30 A Hydrolab multiprobe sonde

31 Moon Lake Vertical Profile, Depth meters ph DO% DO mg/l Temp C SpC µs/cm Turbidity NTU , , , , , , , , , , , , , , , ,072 na

32 0 Temperature Depth (M) 8 10 Temperature Temp in C

33 DO Depth (m) 8 DO Dissolved Oxygen mg/l

34 III. Nutrients A. Nutrients Phosphorus and nitrogen are considered the most important nutrients in aquatic system High nutrient loads can lead to eutrophication Phosphorus is considered to be the main limiting nutrient in fresh water bodies

35 Lake Winnipeg algal bloom

36 III. Nutrients The discovery that phosphorus was the liming nutrient in aquatic systems was fairly recent Most likely candidates were nitrogen, carbon dioxide, and phosphorus Chemical companies favored CO 2 as being the limiting nutrient because their products did not add it to water

37 III. Nutrients Several lines of evidence led to the idea of phosphorus being the main limiting nutrient in aquatic systems Carbon concentrations in Lake Erie have stayed the same the last 100 years Algae blooms have increased dramatically as phosphate levels increased

38 III. Nutrients Both CO 2 and nitrogen are more abundant in aquatic ecosystems and are readily available from the atmosphere In many lakes, comparison of PP and nutrient concentrations shows a strong correlation between PP and phosphorus In a whole lake manipulation it was shown that the addition of phosphorus caused extensive algae blooms

39

40

41 IV. Nutrient loads A. Excess nutrients are often considered detrimental to aquatic ecosystems They can lead to eutrophication of a water body They may be detrimental to certain species over long exposures

42 IV. Nutrient loads B. Presence of nutrients in the water are dependent on several factors 1. Urban discharges Studies show slightly higher levels of nutrients in the Red River above the Fargo Moorhead area Ammonia and Phosphorus were the two main nutrients

43 IV. Nutrient loads 2. Agricultural land use North Dakota is an agricultural state Fertilizers often end up in the water This runoff is an important part of the nutrient load of our rivers and streams

44 IV. Nutrient loads 3. The geology of the area Area with a shallow ground water aquifer may lead to faster leeching of nutrients into the ground water May have higher pesticide and nitrate levels since they are able to infiltrate faster

45 IV. Nutrient loads C. TMDL - Total Maximum Daily Load TMDL is the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards These standards are usually set by states or tribes

46 V. Measuring Nutrients A. Multiprobe sondes Several sonde manufacturers have developed probes for to measure directly or indirectly nutrients in the water Ex. - Nitrates, ammonium, chlorophyll, cyanobacteria, BOD, etc. Expensive and fairly high maintenance

47 V. Measuring Nutrients B. Chemistry Kits Kits that use chemical reactions that result in a color change Hach and LaMotte are best known for making kits used in educational settings for Nitrates and Phosphates Not accurate or precise enough for regulatory purposes

48 V. Measuring Nutrients C. Chemical analysis For nutrients and many other substances, such as heavy metals and pesticides, analysis is best done by a chemistry lab Water is collected and then shipped to the lab There are certified labs that can do this analysis

49 Condition s 8:00 AM Mostly cloudy Date Time Latitude Longitude 7/19/201 6 Max Depth (ft.) Water Temp LMG16-04 Adobe Wall Creek Sp. Cond. ph %DO DO Comments Little to no flow. Heavily vegetated (submergent). Mucky bottom Time Collected Analyte Result Units Result Comment 8:00 Na (ICP) 652 mg/l 8:00 Mg (ICP) 70.5 mg/l 8:00 K (ICP) 9.4 mg/l 8:00 Ca (ICP) 34 mg/l 8:00 Mn (ICP) mg/l 8:00 Fe (ICP) mg/l 8:00 Cl 15.1 mg/l 8:00 ph :00 CO3 93 mg/l 8:00 HCO3 100 mg/l 8:00 OH < 1 mg/l 8:00 Alk. Total 236 mg/l 8:00 Cond 3370 umhos/cm 8:00 Temp (C) 12 Deg C 8:00 Delivery H 78 hrs 8:00 SO mg/l 8:00 Hardness 375 mg/l 8:00 Cation Sum me/l 8:00 Anion Sum me/l 8:00 Difference me/l 8:00 % Diff % 8:00 Na % 78.5 % 8:00 SAR :00 TDS (C) 2430 mg/l 8:00 Rerun Ion Ion Balance OK Ion Balance OK 8:00 C/A v Cond Cat/An/Cond OK Cat/An/Cond OK 8:00 Blank Chk No Blank Check No Blank Check 8:00 XI-Dig-H2O Prepared 8:00 ICP inst Completed

50 VI. Heavy Metals A. Heavy metals include a variety of elements such as Cadmium, Chromium, Mercury, Selenium, Zinc, and Arsenic They can be found in the sediment of rivers and streams Most of the levels measured in North Dakota are due to natural sources

51 VI. Heavy Metals One exception to this may be Mercury It is often released into the atmosphere by industrial processes, waste incineration, and coal burning Some large game fish taken in the Red River Basin have had higher than 1 ppm of mercury in their tissues This is the US Food and Drug standard

52 VI. Other Chemicals of concern A. Pesticides Since North Dakota is dependent on agriculture, herbicides can be found at detectable levels in the our waters However, none exceeded standards for drinking water The most common detected herbicide is atrazine

53 VI. Other Chemicals of concern B. Polychlorinated Biphenyls PCBs Industrial compounds that have been banned in the US because of their toxicity and persistence in the environment Commonly found in low concentrations in fish samples taken from the basin Concentrations were some of the lowest in the NAWQA study, however

54 VI. Other Chemicals of concern C. Polycyclic aromatic hydrocarbons PAHs PAHs can occur naturally, but are also released by the burning of fossil fuels D. Volatile organic compounds VOCs These include industrial solvents and petroleum products