Looking into Earth's eye:
A watershed view of clear lakes

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by John A. Downing

In the mid-1800s, Henry David Thoreau moved away from urban New England and spent two years immersed in the daily observation of nature. He felt that Walden Pond was the focus of the landscape, reflecting the qualities of the surrounding terrain. When I returned to my native Iowa in 1995, Thoreau's observations assumed new meaning.

In the years since Thoreau retreated to nature, Iowa's landscapes were transformed from prairies and savanna with woodland-fringed watercourses to some of the most agriculturally productive and disturbed landscapes on the planet (read more about major changes in the Iowa landscape).

Today, Iowa struggles with poor water quality, official labels of impaired waters and the stigma of contributing to water quality problems as far away as the Gulf of Mexico. Thoreau's perceived connection between landscapes and lakes is underscored by modern data-and our own eyes. The changes in Iowa's landscape are reflected in Iowa's waters.

Watersheds and Water quality
A watershed is all the land that drains into a river, lake or other water body-so every lake is downhill from 100% of its watershed.

The watersheds of Iowa lakes average about 35 times the size of the lake. Some lakes-such as Cold Spring, Little Wall and the Iowa Great Lakes-have small watersheds relative to their areas, while others have watersheds more than 100 times the lake area. In other words, one acre of lake can receive run-off and nutrients from a land area between 1 and 200 acres. Because of land disturbance, fertilizer run-off, and soil loss in agricultural and urban environments, lakes with high ratios of watershed area to lake area have the poorest water quality.

For every ten gallons of rain that falls on the land, about three gallons run off and head directly to the lake. The bigger the rainfall, the higher the concentration of contaminants in run-off. The faster this water moves, the more nutrient, soil and other materials leave with it-and the water moves fastest when there are no wetlands or other storage reservoirs to slow it down.

Even water that sinks into the soil often ends up in the lake. Although soil can filter impurities from water, Bill Simpkins of Iowa State University's Geology department has found that the groundwater around Clear Lake now has much more nutrient than normal-a pattern we'd expect to find in other Iowa watersheds as well.

The linkages between watersheds and water quality are so tight that measurements of water quality correctly predict the kinds of land use in watersheds. The most important indicators of water quality revolve around nutrient concentrations, particularly nitrogen (N) and phosphorus (P). Kelly Poole of the Iowa Department of Transportation has found that measuring the ratios of N and P that end up in lakes allows one to predict the amount of animal versus row-crop agriculture in watersheds. Livestock manures are generally rich in P, while row crop fertilizers can be pure N. Urban watersheds can have even tighter linkage because hard surfaces lead to greater runoff.

The good news is that most water quality problems occurring in lakes appear to originate in very small parts of watersheds. For example, near Rock Creek Lake, we found that between 60-80% of the nutrients and erosion came from 5-7% of the watershed. This means that "surgical remediation," performed on the most run-off prone lands, can solve some water quality problems without major changes in overall land use. Likewise, because strings of adjacent, erodible parcels of land can allow nutrient-laden water to move quickly across watersheds, re-engineering watersheds to slow water flow may also reduce water quality problems.

Human values, nature's values
When I ask students how they sense good water quality, they are about evenly divided between appearance and odor. Most people like clear, blue water; a fresh scent; and a clean, healthy-looking shore. Few like bright green or brown turbid water with a fishy odor. More formal surveys show people want lakes that are (in order) free from dangerous bacteria and toxins, clear, odor-free, diverse in wildlife habitat and good for fishing.

A Clear Lake middle schooler summed it up well when asked what changes we should make in Iowa lakes. "Get rid of the ugly algae! It feels gross when it gets under your suit." She was right. Cyanobacteria (the misnamed "bluegreen algae" that plagues Iowa's most nutrient-laden lakes) can contain skin and nerve toxins.

People value good water quality so much that some of Iowa's most valuable "land" is water. Lakes like Clear Lake generate revenues of tens of thousands of dollars per acre each year. Cathy Kling and Joe Herriges of ISU's Economics Department have found that both residents and visitors are willing to invest much more for water quality improvement. Lake-use typically doubles with improved water quality, making lake and watershed restoration a very cost-effective investment. When Lake Ahquabi and its watershed were restored, the Iowa Department of Natural Resources (DNR) saw recreational use rebound to unprecedented levels.

So how should we make that investment? As noted above, attempting to improve water quality without landscape change is a wasted gesture. Don Bonneau of the Iowa DNR says that there is little point in fixing a lake until you fix the watershed. Everything we learn about Iowa lakes shows this to be true.

Restoring watersheds for water quality: a Clear Lake example
The remediation project undertaken by the Clear Lake community is a good model for many other Iowa lakes. Once funding is in place, this will be the largest lake and watershed restoration undertaken in the state.

Clear Lake's water quality has declined over the last century (read about major changes) due to increased phosphorus and nutrient loads from the watershed. Decreased water clarity has reduced the diversity and abundance of aquatic vegetation while allowing carp to exacerbate water quality problems by digging up sediment and destroying wetland habitat.

The key in this and other Iowa watersheds is to target the parts of the watersheds that will make the greatest difference to water quality-then take specific steps to decrease nutrient concentrations on the land, slow water transport across watersheds and alleviate erosion.

Reduce nutrient load: Unchecked erosion, improper sewage disposal (animal or human), overzealous fertilizer applications and other poor watershed practices can overload lakes with nutrients. Excessive nutrients cause eutrophication, an overproduction of plant life. Eutrophication can give lakes uncontrolled algae blooms; rotten-egg, fishy or ammonia smells; and silty bottoms-while decreasing their water clarity, biological stability, fish habitat and production of high quality sportfish.

Reduce phosphorus applications: Antonio Mallarino of ISU's Agronomy department has found that soils frequently have more phosphorus than plants need, so farmers and homeowners can save money and the environment by avoiding over-applying phosphorus fertilizer. As other research has shown, proper fertilization reduces phosphorus runoff, which reduces eutrophication.

Make water walk, not run: Restoring and constructing wetlands along key tributaries can slow water long enough for nutrients to be absorbed. Any unneeded tile lines can be converted back to slower streams and wetlands, which can slow water transport and decrease watershed nutrient losses.

Reduce erosion: Planting permanent vegetation on the most erodible parcels, maintaining drainage-ways and grass waterways, installing buffer strips and protecting waterways from human and livestock damage can all reduce erosion-and that reduces sediment. When sediments are stopped, we also stop harmful nutrients.

Don't forget urban watersheds: Check and reroute storm drains, septic systems and sewers. Keep streets clean and protect watersheds from construction erosion.

Improve ecosystem balance: Carp in the Ventura Marsh, a protective tributary of Clear Lake, became too abundant, stirring up sediments, destroying wetland vegetation and allowing nutrients to get into the lake. Within weeks of carp reduction, the wetland began to hold much of the sediment and phosphorus it received, developing a healthy wetland plant community and improving the lake water quality.

In Clear Lake, the improvement in water quality from relatively inexpensive watershed restoration projects will be substantial and disproportionate to their cost. Thanks to hard work by dedicated citizens, some improvements have already occurred-though more remains to be done.

Toward cleaner lakes
Cleaning up the lake itself makes sense only after watershed restoration has been successful. Attempts to decrease the impact of accumulated problems will not succeed until the problems cease to accumulate. After the watershed has been restored, the lake manager's toolbox offers many means of deepening, restoring and improving the function of lake ecosystems.

Once Iowans make appropriate watershed corrections, we can expect to see some improvement in water quality in three to five years-though the full effect of restoration may not be seen for decades. Unfortunately, it has taken us over a century of landscape change to bring our lakes to their current quality and it may take us decades to get back-but all the more reason to get started now!

As Thoreau looked into his Walden Pond and contemplated the depth of his own nature, we can look to our lakes to gauge our own commitment to water quality. Instead of being daunted by the average water clarity of Iowa lakes (now only 2.6 feet), we can look to improved watersheds that are reflected in the lakes they sustain.

The black lines show how the landscape of Iowa has been altered by human activities over the past 150 years-particularly by three major transitions:

1) conversion of more than 90% of the land to farmland (1850-1930),
2) drainage and tiling of more than 90% of the wetlands (1900-1960), and
3) four-fold intensification of agricultural yields through fertilization, increased mechanization and pesticide use (1940 to present).

Increased soil erosion, more volatile hydrology, and increased non-point pollution are a legacy of these watershed changes.

The red line shows the steady decline in the clarity of Clear Lake that has been correlated with changes in the Iowa landscape. Clarity in the late 1800s allowed aquatic plants to grow to depths of 18 feet. Today, water clarity is 1-3 feet, depending on the weather and season.

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Released 10/24/03

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