The document discusses how constructed wetlands can help address coastal pollution by reducing excess nutrients from stormwater runoff and wastewater. Constructed wetlands use shallow and deep cells to effectively remove nitrogen, phosphorus, and pathogens below regulatory limits. They also improve dissolved oxygen levels and reduce organic carbon. Well-designed constructed wetlands generate community support as amenities and produce revenue from harvesting wetland plants for renewable energy like ethanol. This dual role of improving water quality while creating assets ensures the long-term sustainability of constructed wetlands in protecting coastal resources.

1. Turning problems into assets:
protecting coastal resources with
constructed wetlands
Prof. Ron Carroll
Assoc. Dean
Director-Science, River Basin Center
Odum School of Ecology
University of Georgia-Athens

2. Principal Collaborators
• Laurie Fowler: international water law and policy, UGA
• Prof. David Gattie: Environmental Engineering, UGA
• Dr. Dianne Sanzone: Research Head, Energy and
Environment, Batelle Labs
• Prof. Manuel Spinola: Ecologist, National Univ. of Costa
Rica
•Prof. William Tolner: Environmental Engineering, UGA

3. Problem Statement
The coastal zone is at the receiving end
of excess nitrogen and phosphorus
causing fish kills and human health risk
from…
• blooms of toxic algae
• dead zones due to depleted oxygen

4. The sources of these excess nutrients are
storm water run off, sewage and septic
systems, irrigation with fertilizers, all of
which also contaminate the coastal zone
with
• pathogens
• pesticides
• other toxic chemicals

5. Due to high
nitrogen and
phosphorus
…in wastewater from
sewage, septic
systems, livestock , and
fertilizer run off with
irrigation

6. “Dead zones” shown in red are a worldwide problem,
especially along densely populated coastal zones

8. Coastal pollution from these non-point
sources will likely get worse in the U.S.
because more than half the nation’s
population lives in coastal counties and these
counties generally experience the highest
growth rates.

9. We need a better solution…..
According to the American Society of Civil
Engineers (2009) our wastewater
treatment systems should receive a grade
no better than D-.
“Many systems have reached the end of
their useful design lives. Older systems are
plagued by chronic overflows during major
rainstorms ….and are bringing about the
discharge of raw sewage into U.S. surface
waters.”

10. To be successful the “solution”
must be…
• broadly effective at meeting
water quality standards
• affordable and cost-effective
to build and manage
• resilient to environmental
change

11. To be successful the “solution”
must be…
• adaptable to new conditions
• scalable to meet demands
from growing populations
• accepted by the community
Continued

12. Constructed treatment
wetlands meet these
conditions

13. How they work: the surface flow design
Shallow zone Deep pools

15. Constructed wetlands with alternating
shallow aerobic and deep anaerobic cells
and sized properly….
• reduce N and P below TMDL standards for
swimmable streams
• increase dissolved oxygen and greatly
decrease organic carbon
• eliminate pathogenic bacteria and viruses

16. Constructed wetlands are often seen as a
community asset
For example, the constructed wetlands of Clayton
County, Georgia are listed among the top five birding
spots in the mid-Atlantic

17. Attractive flowering
plants can be used to
increase the aesthetics
of the wetland

18. Overview of Panhandle Treatment Wetlands
in Jonesboro GA. Our principal research site.

19. Panhandle wetlands consist of two
sequences of 8 treatment cells and
one sequence of 6 cells. Each cell is
about 15m wide by 30m long and
divided into two deep pool areas,
separated by a shallow area with
dense cattails.
The design allows a comparison of
treatment effectiveness along a
transect.

20. Jenny Pahl at first treatment cell. Complete coverage by
duckweed indicates high nitrogen levels…but no
mosquitoes

21. Duckweed benefits
• accumulates heavy metals
• stores nitrogen (as protein)
• fast growth (doubling time in days)
• metabolites strongly inhibit mosquito
larval development

22. Note the very large number of baby duckweed
waiting for new space.

23. By cell 3 or 4 nitrate nitrogen, ammonia N
and phosphorus are at or below TMDL
limits for swimmable streams

24. N-fixing Azolla (red) in bottom pond
indicates low levels of effluent nitrogen

25. Pathogenic, disease causing, bacteria and viruses are
eliminated when the flow rate through the wetland is
greater than three days. Generally, flow rates are much
longer in constructed wetlands.
Pseudomonas auruginosa,
a human respiratory
pathogen sometimes found
In wetlands.

26. Cañas wetland project
A developing country feasibility
study

27. Cañas, Costa Rica, Project Teams
University of Georgia
• Two ecology faculty plus students
• Two environmental engineering faculty plus students
• Two environmental design faculty plus students
EARTH university, Costa Rica
• Two environmental sciences faculty plus students
National University of Costa Rica
• Two conservation ecologists plus students

29. Cañas, Costa Rica, is a small town
representative of other towns in
the seasonally dry Pacific side of
Central America.
Like all towns in this region, waste
water is poorly treated, if at all.

30. The Cañas River runs
through the town and
empties its polluted waters
into the head of the Gulf of
Nicoya, a major domestic
and export fisheries
resource.

31. We have initiated a feasibility study of low
cost options for cleaning and reusing Cañas
waste water while producing value-added
market assets.
These assets include
• Methane from anaerobic waste stabilization
ponds
• Biomass stock for renewable energy (ethanol or
methane) from constructed wetlands.

32. Waste stabilization (or oxidation) lagoons are the only sewage treatment facilities

33. Drainage ditch empties into the Cañas River

34. Circle encompasses area for constructed wetland. Cañas river is to the right.

35. Downstream tilapia farm.
Nutrient rich effluent also contains male hormone ( synthetic
androgen).

36. The large amount of biomass
produced in constructed wetlands
is a source of renewable energy.
Cattails and ethanol

37. Cattails play an important functional role
in contributing to restoration of water
quality by taking up N and P and
providing surface area for microbial
degradation of organic carbon and
destruction of pathogens.
But, because their growth is so prolific,
they must be periodically cut or burned
to maintain flow and prevent stagnant
areas that would breed mosquitoes.

38. We propose harvesting cattails to
meet management objectives and,
importantly, to produce significant
revenue.
To accomplish this, the wetlands
must be designed to allow harvesting
without disrupting their function.

40. Parallel wetlands allow one to be drained and
harvested while the other continues to function.

41. Our constructed wetland design for the Sewanee Utility District on the
Cumberland Plateau, Tennessee. Similar parallel wetlands would be
designed for the Cañas project.

42. To get a sense of the revenue potential
from harvesting cattails and fermenting
them into ethanol, we can make a
comparison to average ethanol yields
from Iowa corn.

43. Ethanol from Iowa corn
100 acres yields 32,364 gal.*
* Must add fertilizer, pesticides and
fossil fuel

44. Ethanol from southeastern cattails in
constructed wetlands….
100 acres yields approximately 102,287
gal., three times the yield of Iowa corn.*
* Without fertilizer, pesticides or fossil fuel

45. At $2.40 per gallon (20ll market price), 100
acres of constructed wetland cattails in the
southeastern U.S.
produces $245,487 gross revenue.

46. THE TAKE HOME MESSAGES…..
WITH THE RIGHT DESIGN AND MANAGEMENT,
CONSTRUCTED WETLANDS….
• ARE BROADLY EFFECTIVE AT REMOVING EXCESS
NUTRIENTS, AS MUCH AS HALF TON OF NITROGEN
• AND DESTROYING PATHOGENS, PHARMACEUTICALS, AND
MANY TOXIC CHEMICALS
• RESTORE OXYGEN AND REDUCE ORGANIC MATTER IN THE
TREATED WASTE WATER
• DO NOT CREATE MOSQUITO PROBLEMS

47. • ARE SEEN AS AN AMMENITY BY THE COMMUNITY
• ARE RELATIVELY AFFORDABLE AND EASY TO MANAGE
• CAN PRODUCE SIGNIFICANT REVENUE FROM
ETHANOL AND SOMETIMES FROM METHANE
Constructed wetlands (con’t)

48. THROUGH THEIR EFFECTIVE
IMPROVEMENT OF WATER QUALITY,
CONSTRUCTED WETLANDS CAN PROVIDE
SIGNIFICANT PROTECTION OF COASTAL
WATERS.
THE STRONG ASSETS THAT ARE GENERATED
THROUGH COMMUNITY SUPPORT AND
BIOMASS RENEWABLE ENERGY HELP
ENSURE THE LONG TERM VIABILITY OF THE
WETLANDS AND THEIR PROTECTIVE ROLE.