Constructed Wetlands for Tile Drainage N Removal: 1. How they work; 2. How well they work; 3. How much they cost.

David A. Kovacic

(University of Illinois) Maria Lemke (The Nature Conservancy) Jeff Walk, Maria Lemke, Krista Kirkham & Ashley Maybanks

Suzy Friedman, Terry Noto, Karen Chapman

Jonathan Thayn

Kent Bohnhoff

Mackinaw Jackie Kraft River Drinking David Kovacic , Mike Wallace, Watersheds Miran Day Project

Jonathan Evers

Rick Twait

Goal is to move water to Modern Day the Gulf as fast as Tile Systems possible

Area in pink = 95 million acres

Contributes 90% of the nitrate- N flux to the Gulf 0.86 Million metric tons

80% of this nitrate-N flux (or 72% of the nitrate-N entering the Gulf) is a result of tile-drainage from the area in pink. Local Problems with Nitrate

•Methemoglobinemia (blue baby syndrome). EPA mcl=10 ppm for drinking water, Drinking water reservoirs.

•Eutrophication of surface waters Global Problem with Nitrate Hypoxia – The “Dead Zone” Before the discovery industrial fixation of N2 to NH4

N2

NO3 NO3 After the discovery industrial fixation of N2 to NH4

N2

NO3 NO3 ?

Vitousek et al. 1997 The Nitrogen Cascade Pop.

Food

N Fert.

W.Q.

There is an urgent need to implement management practices that reduce nitrate loading to surface waters while increasing production. Methods to remove Nitrate

• High tech engineering solutions – such as ion exchange and reverse osmosis are always available- the solutions are expensive and incur large annual costs. • In the Mid 90s I suggested a Green solution to the nitrate problem. – I proposed that constructed wetlands might

convert tile drainage water nitrate to N2 and reduce loading to streams through denitrification. - Less expensive than high tech From the N perspective one of Mother Nature’s most important free services

- Denitrification (NO3 → NO → N2O → N2) (Standard)

• conversion of NO3 - to gaseous forms (NO, N2O, N2) - one problem is that if the process is not complete NO (smog and

ozone former), N2O (300x the gwp of CO2) and #1 depeleter of ozone.

• if O2 is around they use it as an e- acceptor - • if anaerobic, they use NO3 as an e- acceptor • C and energy comes from organic matter provided by plants Anammox anaerobic ammonium oxidation + − (NH4 + NO2 → N2 + 2H2O)

• Biological process, nitrate and ammonium ions are converted directly into diatomic nitrogen and water.

• Bacteria that perform the anammox process belong to the bacterial phylum Plantomycetes What the wet prairie in Illinois looked like in the 1850s when the first settlers accessed to the region. Tile Drainage The major source of Nitrate to the Gulf

4-6 ft Soil surface deep Nitrate loading

Stream

Water penetrating tiles Drain tile spaces Water table Constructed Tile-Drainage Wetland Design

Natural soil bacteria Soil surface denitrify nitrate under anaerobic conditions in the wetland sediment Berm

Drain tile Plants required Stream to provide C for energy If the concept worked it would: Allow farmers to continue tile drainage and fertilizer use to maintain production, while reducing N loading to surface waters

N2 Denitrification Nitrate

Berm River Drain Tile Constructed Buffer Wetland To test the hypothesis 1. Created experimental (whole-ecosystem) wetlands

2. Tested the effectiveness of created wetland nitrate removal in several watersheds near Champaign, IL & Bloomington, IL

. Fig. 3 – Design of berms, inlet, and outlet flow structures, and in-line flow control structure (stoplog). A 0.9 m deep by 1.2 m wide trench was excavated the length of the berm to form a key to retard seepage below the berm. Soil was applied to the berm in 15-cm layers and compacted with a sheep’s foot roller until the required height was reached. The berm in W1 was2.4 m high, 3 m wide at the top and 19 m at the base, with a freeboard between the emergency spillway and the top of the berm of 0.6 m. The W2 berm was constructed 2.7 m high, 3 m wide at the top and 19 m at the base, with a freeboard between the top of the berm and the spillway of 0.4 m. The emergency spillways were 2.5 m wide. During construction of the berm, inlet and outlet pipes were installed as well as the in-line flow control structure. Berms to capture and allow the quantification of surface drainage were built above each wetland in a similar fashion to the main wetland berms described above using a water and sediment control basin (WASCOB) design (University of Illinois Extension Service, 2000). WASCOB berms were 1.8 m high, 3 m wide at the top and 12 m wide at the base and were similar to the berm depicted above. A tracked bulldozer with a pushing blade (Caterpillar Model D-8) was used to excavate and spread soil. The topsoil as well as the surrounding forest area provided a seed bank to revegetate the site.

Aerial View of Constructed Wetland in S. Champaign Co. 3 years after initial construction no seeding

Wetlands Stop-log Inlet for Stop-log berm outlet stop-log Monitoring & Evaluation

• Monitor nitrate and dissolved phosphorus at inlets and outlets of experimental wetlands • N Removal = Inlet – Outlet budget • Flow x concentration used to determine budgets 1,733 kg N Nitrate - N

4,700 kg

Wetland Outlet

Tile Inlet Denitrification

2,544 kg Cumulative data from three wetlands over three years three over wetlands three from data Cumulative Subsequent Wetland Studies support our initial results

• Research with the city of Bloomington at Lake Bloomington • Research with The Nature Conservancy at the Franklin Demonstration Farm • The cumulative body of literature in the last 15 years indicates that wetlands can effectively reduce nitrate loading to rivers, lakes, and reservoirs. THIS LOOKS TOO GOOD Requires 5% of the effective drainage area to get 45% nitrate removal. Effective drainage.

Figure 4-2. Close up of 50m buffer zone around tile drains indicating effective drainage (area in yellow). To obtain 45% NO3 removal in Lake Bloomington Watershed

Must convert approximately 3.5% of the cropped area to wetlands, 1,484 acres out of 43,000 Once we were sure they worked to remove Nitrate we promoted wetlands as a solution to the nitrate problem Goal: To construct Tile-Drainage wetlands throughout the Lake Bloomington watershed.

To reduce nitrate loading to Lake Bloomington, the source of water for 80,000 people in Bloomington and Normal, IL.

A proof of concept study that proposes a more sustainable solution to pollution rather than a sole engineering solution BUT How do you actually implement such a solution?

To site wetlands in in the 43,000 acre watershed would require the creation of a major database that allowed us to work remotely Requirements of the database:

1. Provide unique naming 5. Determine land ownership system for all sub-basins 6. Determine existing in the watersheds wetlands, depressions 2. Determine surface 7. Determine areas of any drainage characteristics at basin or any plot of ground several levels 8. Provide information for the 3. Provide maximum location, sizing, and resolution of elevations construction of wetlands 4. Provide a tool to locate tile 9. Provide a database that can drainage systems and be adapted for use by all determine effective project workers drainage 36 Create a Lake Bloomington Database Using the following: 1. USGS maps 7. Google earth 2. Soil maps 8. Bing maps 3. Hydrology maps 9. Lidar data 4. USGS DEM data 10.Parcel data 5. Color infrared 11.Range and photography township maps 6. NRCS aerial 12.ArcGIS photography

Green Light Map

27 HUC 14 watersheds

The system was designed for use by the entire team, but the outreach team has used it most recently Tile Order/Tile Drainage Order confusion

Tiles

Tiles Tiles TilesTiles Tiles Tiles Tiles

1st order stream Tiles Semantics = 1st order stream

The majority of the drainage was invisible 41 Tile-Drainage Interception Wetlands

• Placed at the junctions of 1st, 2nd, 3rd order tiles

Tiles

Til TilesTiles e s Tiles 1st order stream Tiles Semantics = 1st order stream

Denitrification Denitrification

N2 N2

River NO3 First Order Tile Second Order Tile NO3 Tile Drainage NO3 Interception Tile Drainage Third Order Wetland Interception Tile Wetland 42 Recently completed 1. Lake Bloomington Watershed ArcGIS Online Database, - Protocols for BMP placement 2. Nitrogen Load Reduction Index - Effectiveness of BMPs and Cost Estimate

Miran J. Day Cal Poly

David A. Kovacic Protocol used to evaluate placement of: TILE DRAINAGE TREATMENT WETLANDS. Several methods can be used to determine the location of wetlands. The first 2 involve: an evaluation based on the soil survey, and a way to determine basin suitability. a) Pond Reservoir Area Seepage • Not limited = zero or no value • Somewhat limited seepage = value greater than zero less than 1.0 • Very limited seepage = value is 1.0 b) Construction for “Embankments, dikes and levees” • Not Rated: No value for any of the factors (Depth to Saturated zone, thin layer, piping and seepage) • Somewhat limited: Values for any factor greater than zero but less than 1.0 • Very limited: Values for any factor is 1.0 (Bad for berm construction) c) Construction Material as a source of Sand • Not Rated • Fair • Poor d) Construction Material as a source of Gravel • Not Rated • Fair • Poor e) Soil Slope Average • 0 – 0.5% • 0.51% - 2.00% • 2.01% - 5.00% • 5.00% - Greater f) Hydric Soil • No Hydric Soil • Hydric Soil g) a) + b) + c) + d) + e) + f) + Sub-basins larger than 1acre Effective drainage of the LBW

Figure 4-3. 50 m buffer zone around tile-drains indicating effective drainage. Wetland depressions Nutrient removal wetlands Similar protocols were developed for other BMPs

• Annual cover crops • Perennial Cover Crops • Water table management • Riparian buffers • Grassed waterways • Bioreactors Nitrogen Load Reduction Index Excel Spreadsheet Calculator

The calculator uses available GIS information as input to an index that determines the effectiveness of Best Management Practices to reduce nitrogen loading from the LBW and estimates a potential cost. • Index to be used as a planning tool to maximize N load reduction through optimal siting of BMPs at the field scale. • A modification of the U. of Minnesota’s Watershed Nitrogen Planning Tool (NBMP) used at the HUC 8 level (Lazarus, W.F. et al. 2014). Nutrient Loss Reduction Strategy

Nitrogen Load Reduction Index (NLRI) The program we are establishing in the Lake Bloomington Watershed is specifically designed to construct wetlands and to site other management practices to reduce agricultural runoff.

Our goal is to provide a Conservation Blueprint for watershed management in the Midwest END “Global Rule” To obtain 45% Verhoven et al. 2006 NO3 removal Wetland nitrate removal data (U.S., Sweden, & Must convert China) suggests that a approximately ratio of 2-7% wetlands 3.5% of the to watershed area can cropped area to significantly improve wetlands or 1,484 water-quality. acres of the LB Requires 5% of the effective drainage area watershed

Effective drainage.

Figure 4-2. Close up of 50m buffer zone around tile drains indicating effective drainage (area in yellow). Nitrogen cycle - after Industrial Fixation 2018

Ammonia

NH3

Leaky Agricultural Nitrates Systems = NO - Losses to 3 Streams and Oceans

Water table management Riparian buffers Annual cover crops Perennial Cover Crops Grassed waterways Bioreactors

Nitrogen Load Reduction Index Spreadsheet Model to Determine the Effectiveness of Best Management Practices Used to Reduce Nitrogen Loading from Central Illinois Agriculture

D.A. Kovacic and M.J. Day. Tile Drainage Treatment Wetlands – Protocol used to evaluate placement of: TILE DRAINAGE TREATMENT WETLANDS. Several methods can be used to determine the location of wetlands. The first 2 involve: an evaluation based on the soil survey, and a way to determine basin suitability. I. Tile drainage lines are present. II. Soil water holding potential, related to factors including: a. Seepage b. Sand and Gravel content c. Clay content III. Slope is sufficient for gravity flow dynamics

IV. Soils are suitable for embankment construction Fig. 1 – Conceptual plan view of wetlands showing basins, tiles and location of instrumentation.

Nitrogen cycle - after Industrial Fixation 2018

Ammonia

NH3 N2 , NO, N2O Leaky Agricultural Systems = Losses to Nitrates Streams and - NO3 Oceans

Practice/scenario Nitrate-N reduction per acre (percent) Nitrate-N reduced (million lb) Nitrate-N reduction from baseline (percent) Cost ($/lb removed) Bioreactors on 50 percent of tile-drained land 40 56 13.6 1.38 Wetlands on 25 percent of tile-drained land 40 28 6.8 5.06 Buffers on all applicable crop land (reduction only for water that interacts with active area) 90 36 8.7 1.63 Perennial/energy crops equal to pasture/hay acreage from 1987 90 10 2.6 9.34 Perennial/energy crops on 10 percent of tile-drained land 90 25 6.1 3.18

Nutrient Loss Reduction Strategy

Nitrogen Load Reduction Index (NLRI)

Nitrogen cycle – before Industrial Fixation

Nitrogen cycle - after Industrial Fixation Haber process 1909

Ammonia

NH3

Goal: To construct Tile-Drainage wetlands throughout the Lake Bloomington watershed.

To reduce nitrate loading to Lake Bloomington, the source of water for 80,000 people and Bloomington and Normal, IL.

A proof of concept study that proposes a more sustainable solution to pollution rather than a sole engineering solution To obtain 45% NO3 removal • Must convert approximately 3.45% of the cropped area to wetlands, or

• 1,484 acres of the 43,000 acre LB watershed

87 Must convert approx. 5% of cropland area to wetlands to get approx. 50% removal of nitrate “Man – despite his artistic pretensions, sophistication, and many accomplishments owes his very existence to a six inch layer of topsoil and the fact that it rains.” –

We forget that the water cycle and the life cycle are one. J. Cousteau AND WE CONTINUE TO MESS THINGS UP. D. Kovacic Area in Red is the major area contributing Nitrate-nitrogen to the Gulf of Mexico

The area in red excluding the lobe in Missouri covers 35,161,032 ha

5% of the artificially Of the red area 17,300,000 is drained artificially red area = drained, or 49% 865,000 ha Area in Pink is the major area contributing Nitrate- nitrogen to the Gulf of Mexico

43% 13% 34%

90% Nitrate from UMRB = MOM of this: uM = 43% Ohio = 34% Missouri = 13%

The average corn field in Illinois

Large yields require large amounts of N fertilizer Large yields require LARGE applications of NITROGEN FERTILIZER Bigger and Better

in Large yields require ILLINOIS large amounts of N fertilizer Nitrogen cycle Nitrogen cycle Nitrogen cycle

What the wet prairie in Illinois looked like in the 1850s when the railroad finally allowed access to the region.

Component Input to soil Loss from soil The Nitrogen Cycle Atmospheric nitrogen

Atmospheric Crop Industrial fixation fixation harvest (commercial fertilizers) and deposition

Animal Volatilization manures and biosolids Plant residues Runoff and Biological erosion fixation by legume plants Plant uptake Denitrification Organic nitrogen Nitrate - Ammonium (NO3) (NH+) 4 Leaching

to nitrites by certain micro-organisms present in foods and in the gastrointestinal tract. This has resulted in nitrite toxicity in infants fed vegetableswith a high nitrate level.No evidence currently exists implicating nitrite itself or nitrate as a carcinogen [24]. There are both experimental and epidemiologic studies that indicate possible chronic health effects associated with consumption of elevated levels of nitrate in drinking water, although results are inconsistent. Likewise, there are no good estimates of damage to health related to methaemoglobinemia owing to drinking water nitrate. Evidence is emerging for possible benefits of nitrate or nitrite as a potential pharmacological tool for cardiovascular health [18]. The available evidence supports a positive association between nitrite and nitrosamine intake and gastric cancer, between meat and processedmeat intake and gastric and oesophageal cancer, and between preserved fish, vegetable and smoked food intake and gastric cancer, but is not conclusive [25]. A diet high in red meat is associated with the formation of nitrosamines through the additives (sodium nitrite) that increase the red colour of the meat. The natural breakdownproducts of proteins can combine with nitrites to formcompounds such as nitrosamines. There are many different types of nitrosamines, most of which are known carcinogens in test animals. It is unknown at what levels, if any, nitrosamines are formed in humans after they eat cured meat products, or what constitutes a dangerous level in meat or in humans. (a) Aquatic ecosystems (i) Acidification Aquatic ecosystems with a low acid neutralizing capacity (primarily freshwater) can be acidified by atmospheric deposition of reactive N and S. With a sharp decline in sulfur emissions beginning in the mid-1980s, Nr has become the major component of acidic deposition in many areas of Europe and North America, and a growing problem in many developing countries. With persistent acidification, species composition at the base of the food chain is shifted, and often simplified, to favour acid-tolerant macrophytes and phytoplankton. Early life stages of fish and aquatic invertebrates can be especially sensitive to acidification, but direct and indirect impacts have been reported at all higher trophic levels, including zooplankton, benthic invertebrates, amphibians and birds [28,29]. (ii) Eutrophication Nutrient enrichment of freshwater and coastal ecosystems usually originates from surface sources such as fertilizer runoff, erosion of nutrient-rich sediments or sewage discharge. In oligotrophic ecosystems, biomass or diversity may increase with increasing nutrient load [30]. However, as levels of Nr and P increase, phytoplankton capable of efficiently assimilating these nutrients are increasingly favoured over species more limited by other factors (e.g. diatoms, requiring silica, or benthic primary producers, requiring light). Low-diversity algal or cyanobacterial blooms can result, leading to surface water hypoxia and the release of toxic compounds. This in turn impacts sensitive higher trophic level organisms, such as invertebrates and fish [27,31]. Sedimentation and decomposition of biomass from phytoplankton blooms can deplete oxygen in bottom waters and surface sediments, especially in ecosystems with low rates of water turnover [31]. This further shifts the benthic community towards fewer tolerant species. Changes in the benthic community alter nutrient cycling in the sediments and overlying water, feeding back to further alter the rest of the aquatic ecosystem ([32], and references therein). Coastal eutrophication has recently emerged as a global issue of serious concern, with a steady growth in the extent and persistence of eutrophic, hypoxic and anoxic coastal waters [31,33], and related incidences of toxic algal blooms Erisman et al. 2013

Figure 1. Distribution of Nr deposition classes and exceedance of deposition levels in the period 2000–2030 on Protected Areas (PAs) under the Convention on

Biological Diversity [41]. Red PAs show an exceedance of 10 kg N ha21 yr21 and deposition in 2030 higher than 2000. Orange PAs show a current exceedance, but deposition in 2030 lower than 2000. Yellow PAs might be under threat in the near future since Nr deposition exceeds 5 kg N ha21 yr21, but is increasing over the period 2000–2030.

Gulf of Mexico 'dead zone' is the largest ever measured | National ... www.noaa.gov/media-release/gulf-of-mexico-dead-zone-is-largest-ever- measured August 2, 2017 ... Gulf of Mexico dead zone in July 2017 ... 5,806 square miles, three times larger than the Gulf Hypoxia Task Force target of 1,900 square miles. Modern Day Tile Systems

Goal is to move water to Modern Day the Gulf as fast as Tile Systems possible

Area in pink = 95 million acres

Contributes 90% of the nitrate- N flux to the Gulf 0.86 Million metric tons

80% of this nitrate-N flux (or 72% of the nitrate-N entering the Gulf) is a result of tile-drainage from the area in pink. Area in Pink is the major area contributing Nitrate- nitrogen to the Gulf of Mexico

Pink area = 28.6 million ha = 70.7 million acres Engineering Approach • Concentrate polluted water in one central location and treat – focus on point source pollution cost high: – Ion exchange = 3 million dollars for Blooming., IL Excluding annual maint., chemicals, brine disposal – Reverse osmosis = 8 million dollars for plant construction, – 1 million $ for annual operation EcologicalEcological Engineering ApproachApproach • Focuses on non-point source pollution less expensive Techniques that use natural processes for source reduction – Reduce N fertilizer application – Apply techniques that use natural processes for source reduction to eliminate pollutants before they enter surface waters: – Riparian buffer strips – CreatedCreated wetlandswetlands – plants provide bacteria with carbohydrates

– bacteria reduce N2 to NH3, which can be used by plants

• Nitrogen fixation is most important in low-N environments, early in primary succession Ammonification – oxidation of carbon in amino acids, freeing ammonia

– carried out by all organisms when recycling proteins – important in decomposition

Mineralization vs immobilization • gross mineralization – total amount of N released via mineralization by microbes

• immobilization – uptake of inorganic NH4 + or NO3 - by microbes

• net mineralization – the net accumulation of inorganic N in the soil solution over a given time interval

– this is what’s available to plants net mineralization = gross mineralization – immobilization Critical C:N ratio • C:N requirements of microbes and substrate define whether they will immobilize N – (recall decomp lecture, see also Box 9.1 in text) • high C:N substrates lead to immobilization (microbes remove additional N from the soil to decompose substrate) • low C:N substrates lead to mineralization (microbes secrete excess N into soil) • rule of thumb, 25:1 + − NH4 + NO2 → N2 + 2H2O.

Riparian Buffer Strip

Denitrification Nitrate Stream

Aquiclude

“Hydraulic connectivity between roots and stream” RiparianRiparian BufferBuffer StripStrip 50 ft forest buffer reduced subsurface (Osborne & Kovacic, 1993) flow concentration by 90%

150 ft grass buffer reduced subsurface flow concentration Nitrate Denitrification by 80%

Stream

Aquiclude

““HydraulicHydraulic connectivityconnectivity betweenbetween rootsroots andand streamstream”” Riparian Buffer Strip

Nitrate

Stream

Drain tile

Aquiclude “Drain tile short-circuits the buffer strip” Results of buffer strip study (Osborne and Kovacic)

• 50 ft Forest buffer reduced subsurface water nitrate concentration by 90% before it reached the stream (peak concentration 4 ppm)

• 150 ft Grass buffer reduced subsurface water nitrate concentration by 80% before it reached the stream (peak concentration 8 ppm)

(As compared to the non-buffer strip area peak concentration 40 ppm) Constructed Wetland Design

150’ 50’

4’ River Drain Tile Constructed Berm Margin Wetland Constructed Wetland Function

N2 Denitrification Nitrate

150‘ 50’ River Drain Tile 4’ Constructed Berm Margin Wetland Allow farmers to continue tile drainage and fertilizer use to maintain production while reducing N loading to surface waters If the concept worked it would: Allow farmers to continue tile drainage and fertilizer use to maintain production, while reducing N loading to surface waters

N2 Denitrification Nitrate Berm

River Drain Tile Constructed Buffer Wetland Problems with Nitrate-Nitrogen ▪ Methemoglobinemia (blue baby syndrome). - EPA mcl=10 ppm for drinking water ▪ Eutrophication of surface waters -Nutrient enrichment causes rapid algal growth, algae die are decomposed by bacteria, decomposition reduces oxygen levels and aquatic organisms suffocate N Removal = Inlet – Outlet budget Flow x concentration used to determine budgets

Inlet Outlet Monitoring & Evaluation

• Monitor nitrate and dissolved phosphorus at inlets and outlets of experimental wetlands • Paired watershed experimental design – compare water quality in treatment subwatersheds with reference subwatersheds

Fig. 2 – Conceptual design of experimental wetlands. (a) Modification of design from Osborne and Kovacic (1993) with water and sediment control basin (WASCOB) added. Stop-log tile flow control Surface Wetland berm runoff WASCOB inlet outlet Stop-log Inlet for Stop-log berm outlet stop-log • To site wetlands in in the 43,000 acre watershed would require the creation of a major database that allowed us to work remotely Lake Bloomington Constructed Wetland Design

Fig. 2 – Conceptual design of experimental wetlands. (a) Modification of design from Osborne and Kovacic (1993) with water and sediment control basin (WASCOB) added. Wetland A 3000000 Tile Inlet

2000000

1000000

0 3000000 Wetland Outlet

Daily Volume (L)

2000000

1000000

0 10/1/94 4/1/95 10/1/95 4/1/96 10/1/96 4/1/97 10/1/97 Wetland A

80 Tile Inlet

60

) 40

-1

20

0 80 Wetland Outlet

60

Daily Total N (kg N d Daily Total

40

20

0 10/1/94 4/1/95 10/1/95 4/1/96 10/1/96 4/1/97 10/1/97 Requirements of the database 1. Provide unique naming 5. Determine land ownership system for all sub-basins 6. Determine existing in the watersheds wetlands, depressions 2. Determine surface 7. Determine areas of any drainage characteristics basin or any plot of at several tiers ground 3. Provide maximum 8. Provide information for resolution of elevations the location, sizing, and 4. Provide a tool to locate construction of wetlands tile drainage systems 9. Provide a database that and determine effective can be adapted for use by drainage all project workers Green Light Map

27 tier 2 or HUC 14 watersheds

The system was designed for use by the entire team, but the outreach team has used it most recently Area Part of Tier 2

Tier 3 boundary • Nitrogen (N) – essential for proteins, DNA/RNA – 78% of the atmosphere

– atmospheric form (N2) can’t be used by plants – often the limiting resource for plants, especially in oceans, deserts

• Nitrogen fixation – conversion of N2 to NH3 (ammonia) by bacteria or lightning • Nitrogen-fixing bacteria assimilate N2 and transform it into NH3 – some N fixation occurs in free-living soil bacteria – most in roots of nitrogen-fixing plants

• Legumes – plants in the pea family (Fabaceae) – have root nodules inhabited by nitrogen- fixing Rhizobium bacteria Microbial Microbial transformation transformation Plant Uptake in AIR NO AIR, Anaerobic

Nitrification Denitrification in soil in sediment