What Causes Iron and Manganese in Surface Water?
- zach9517
- Mar 12
- 1 min read
Understanding Metal Release in Lakes and Drinking Water Reservoirs
Iron and manganese are naturally occurring metals commonly found in lakes, reservoirs, and other surface water sources used for municipal drinking water supplies. While small amounts are normal, elevated concentrations can create significant challenges for drinking water treatment plants.
High levels of iron and manganese can cause:
Discolored water
Metallic taste
Black or brown staining
Increased chemical demand during treatment
Filter clogging in water treatment systems
Understanding why iron and manganese appear in surface water is the first step toward effectively managing these problems.
Natural Sources of Iron and Manganese in Lakes
Iron and manganese are naturally present in many soils and rock formations. As rainwater moves through a watershed, these metals can dissolve and enter lakes and reservoirs.
Common natural sources include:
Weathering of rocks and minerals
Soil runoff during storms
Organic matter decomposition
Groundwater inflows containing dissolved metals
In many reservoirs, these metals accumulate in bottom sediments over time.
Under certain conditions, those sediments can begin releasing metals into the water column.
Oxygen Depletion in Deep Water
One of the most common causes of iron and manganese release in lakes is low dissolved oxygen near the lake bottom.
During warm months, lakes often develop thermal stratification, which separates surface water from deeper water layers.
The lake forms three distinct zones:
Epilimnion – warm, oxygen-rich surface water
Metalimnion – middle transition layer
Hypolimnion – cold bottom water
Because the bottom layer becomes isolated from atmospheric oxygen, dissolved oxygen levels gradually decline.
When oxygen levels drop too low, sediments begin releasing iron and manganese into the surrounding water.
Sediment Release of Metals
Lake sediments naturally contain iron and manganese compounds. Under oxygen-rich conditions, these metals remain bound within the sediment.
However, when oxygen becomes depleted:
Iron and manganese are chemically reduced
Metals dissolve into the surrounding water
Concentrations increase in deep reservoir zones
This process is known as internal loading.
Once metals dissolve into the water column, they can migrate toward drinking water intakes.
Seasonal Lake Turnover
Seasonal turnover can also introduce iron and manganese into surface waters.
In many reservoirs, turnover occurs during:
Fall cooling
Spring warming
As temperature differences disappear, the lake mixes from top to bottom.
When this happens:
metal-rich bottom water mixes throughout the reservoir
iron and manganese concentrations increase in raw water supplies
Water treatment plants often experience sudden spikes in manganese during these periods.
Watershed Runoff and Storm Events
Stormwater runoff can also contribute to elevated iron and manganese levels.
Heavy rainfall may wash soil particles and organic material into lakes and reservoirs. These materials often contain trace metals.
Runoff can introduce:
iron-rich soil particles
dissolved manganese
organic compounds that influence metal chemistry
Watersheds with clay soils or mining history are especially susceptible to these inputs.
Groundwater Contributions
In some reservoirs, groundwater inflows can also introduce iron and manganese.
Groundwater often contains lower oxygen levels than surface water. Under these conditions, metals dissolve from underground mineral deposits.
When groundwater enters lakes or reservoirs, it may bring dissolved metals with it.
How Iron and Manganese Affect Drinking Water Treatment
Elevated iron and manganese create several challenges for drinking water treatment facilities.
Common treatment problems include:
Water Discoloration
Manganese can cause black or dark brown water, while iron often produces reddish or orange staining.
Increased Chemical Demand
Water plants may need additional oxidants such as chlorine or potassium permanganate to remove dissolved metals.
Filter Fouling
Iron and manganese particles can accumulate in filters, reducing filtration efficiency.
Taste and Odor Problems
High metal concentrations can cause metallic taste and aesthetic issues in finished water.
Managing Iron and Manganese in Reservoirs
Many drinking water utilities address metal problems by improving oxygen conditions in their reservoirs.
Maintaining dissolved oxygen near the lake bottom prevents sediments from releasing iron and manganese.
One of the most effective tools for this is deep water aeration.
Deep water aeration systems deliver oxygen directly to deeper reservoir layers, preventing oxygen depletion and stabilizing water quality.
These systems can significantly reduce metal concentrations entering drinking water intakes.
A municipal reservoir aeration project in Waldron, Arkansas demonstrated dramatic reductions in manganese levels after aeration was installed near the drinking water intake.
Signs a Reservoir May Have Iron or Manganese Problems
Water utilities may suspect elevated metals in reservoirs if they observe:
Dark or discolored raw water
Seasonal manganese spikes
Increased oxidant demand
Poor filter performance
Taste or staining complaints
Monitoring dissolved oxygen and metal concentrations throughout the reservoir can help identify the underlying cause.
Improving Reservoir Water Quality
Managing iron and manganese in surface water sources requires a combination of monitoring, watershed management, and reservoir treatment strategies.
In many systems, maintaining adequate dissolved oxygen in deeper waters can dramatically improve raw water quality.
Aeration technologies are commonly used to stabilize reservoirs and prevent metal release from sediments.
Learn More About Reservoir Aeration
Advanced Treatment Technologies designs aeration systems that improve dissolved oxygen levels in lakes and drinking water reservoirs.
These systems help utilities:
Reduce iron and manganese levels
Improve dissolved oxygen profiles
Stabilize raw water quality
Reduce treatment costs
Learn more about reservoir aeration solutions here:
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