Total Dissolved Solids (TDS) Fact Sheet
Definition: The
total amount of minerals, organic matter, and nutrients that are
dissolved, (not merely suspended) in the water. They are the particles
that you can't see in the water.
| Dissolved
Substances within Water Considered TDS |
| Substance |
Natural
Source |
Substance |
Natural
Source |
| Calcium
(Ca+2) |
sed./meta.
rock |
Bicarbonate
(HCO-) |
sed./meta.
Rock |
| Magnesium
(Mg+2) |
sed./ign.
rock |
Sulfate
SO4-2 |
sed./ign.
Rock |
| Sodium
(Na+) |
sed./ign.
rock |
Chlorine
(Cl-) |
all
rocks, sea spray |
| Potassium
(K+) |
sed./ign.
rock |
Silica
(Si+4) |
all
rocks |
| Hydrogen
(H+) |
sed./ign.
rock |
Nitrogen
(N2) |
N2
fixation, runoff |
| Phosphorus
(PO4-3) |
sed
rocks, runoff |
Iron,
copper, aluminum |
sed.
Rock, runoff |
Background:
- Total dissolved solids help regulate the process of osmosis,
(water flow in and out of an organism's cells)
- Majority of dissolved material in water is from weathering
rocks & soil erosion
- Groundwater, (wells, springs, etc.), is high in TDS
- Typically, the greater the land area of a watershed, the higher
the TDS
Environmental Impacts:
- Each land region has specific,
normal TDS levels. Changes can affect stream life and can indicate
a disruption in the watershed
- Higher TDS values can correspond to low flow periods, when
waterway is dominated by groundwater inputs
- More runoff increases the TDS concentration because of more
soil erosion, ( the dissolved particles are carried into the
soil).
- Road salt runoff can increase TDS to over 1000 mg/L. Which
is toxic to life
- Industrial boiler water inputs can increase TDS
- Abnormally high or low dissolved solids disturb osmotic balance
of native species, (like putting freshwater species in saltwater!)
Water Quality:
- For drinking water, 500 mg/L is the limit
- For aquatic life, a monthly average of 500 mg/L and a max
of 750 mg/L
- Each component that makes up TDS has water quality limits
also.
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