Urban Landscape Irrigation with Recycled Wastewater: Water Quality and Salinity Issues Yaling Qian Colorado State University

Water Reuse In dry and highly populated metropolitan areas, where water is a limited natural resource, water reuse is a viable means of coping with potable water shortages. In dry and highly populated metropolitan areas, where water is a limited natural resource, water reuse is a viable means of coping with potable water shortages. Without doubt, water reuse for landscape irrigation will increase in the future. Without doubt, water reuse for landscape irrigation will increase in the future.

Benefits of Recycle Water Irrigation Water conservation; Water conservation; Always available; Always available; Water reclamation; Water reclamation; Nutrient recycling. Nutrient recycling.

Water Source for Golf Courses in Colorado - In 2000 Using recycled wastewater for landscape irrigation in Colorado started in the 1960’s to irrigate golf courses.

Water Source for Golf Course in Colorado: In 2002 Water reuse practice has increased dramatically recently.

Successful Recycled Wastewater Reuse Cases Olympic Club Castle Pine International

Challenges Sodicity and salinity problems; Sodicity and salinity problems; Residential use of water typically adds about mg/L of dissolved salts. Those salts have relatively high Na content that remain after wastewater treatment. Nutrient issues; Nutrient issues; Groundwater quality. Groundwater quality.

ParameterUnitValue Salt load Total dissolved salts (TDS) ppm or mg/L lb/100 gal Electrical conductivity (EC) dS/m or mmho/cm 0.84 Sodium ppm or mg/L 99 Calcium 61 Magnesium 15 Sodium adsorption ratio 3.1 Adjusted SAR 5.0 Bicarbonate ppm or mg/L 112 Chloride 95 BoronNitrogen Phosphorus 0.8 Water Quality

Effects of salinity on landscape plants Physiological drought: Physiological drought: P lants cannot take up enough water due to salts.

Turf Injury Salinity caution levels in irrigation water: Salinity caution levels in irrigation water: EC > 0.75 mmho/cm or TDS > 500 ppm.

Turf Injury Salinity problems are functions of: soil type, soil type, management, management, shallow water table will reduce leaching and introduce salts to the root zone, shallow water table will reduce leaching and introduce salts to the root zone, salinity of irrigation water. salinity of irrigation water. Susceptible sites for salt accumulation: Shallow water table, High clay content, Poorly drained sites, Compacted sites.

To reduce salt accumulation in the soil Improve irrigation uniformity; Improve drainage; Leach and flush periodically.

ParameterRWW Total dissolved salts (ppm) 514 Conductivity (dS/m) 0.84 Sodium (ppm) 99 Calcium (ppm) 61 Magnesium (ppm) 15 Sodium adsorption ratio (SAR) 3.1 Water Quality Sodium absorption ratio (SAR) Sodium absorption ratio (SAR) [Na] [Na] SAR = [Ca]+[Mg]/2

Sodium Effect on Soil Structure Sodium Problems

Sodium permeability hazard: Sodium permeability hazard: High SAR (> 12) can induce soil structure deterioration, including soil sealing, crusting, and reduced water penetration.  For fine textured soil and heavy traffic areas, irrigation water SAR as low as 6-9 can cause problems.

Sodium Management I. Chemical amendments of water and soil Water Treatments Calcium nitrate; Calcium nitrate; Gypsum (calcium sulfate); Gypsum (calcium sulfate); Calcium chloride; Calcium chloride; Soil Treatments Lime + sulfuric acid injection; Lime + sulfuric acid injection; Gypsum Gypsum Calcium nitrate Calcium nitrate Calcium chloride Calcium chloride

ParameterRWW Total dissolved salts (ppm) 614 Conductivity (dS/m) 0.84 Sodium (ppm) 99 Calcium (ppm) 61 Magnesium (ppm) 15 Sodium adsorption ratio 3.1 Adjusted SAR 5.0 Bicarbonate (ppm) 112 Water Quality Adjusted SAR: Adjusted by considering bicarbonate, carbonate, and the water’s total salinity, in addition to water’s calcium, magnesium, and sodium content.

Bicarbonate and Adjusted SAR Bicarbonate can combine with Ca ++ and Mg ++ to precipitate them out and increase the water SAR; Bicarbonate can also raise water pH to undesirable levels; If recycled wastewater has high bicarbonate (> 120 mg/L), it is recommended that SAR be adjusted to consider bicarbonate content in the water - SAR adj.

To reduce bicarbonate in irrigation water Acidification of irrigation water (to 6.5 –7.0 pH) is effective in converting bicarbonate to CO 2 and H 2 O. Acidification of irrigation water (to 6.5 –7.0 pH) is effective in converting bicarbonate to CO 2 and H 2 O.

ParameterRWW Total dissolved salts (ppm) 614 Conductivity (dS/m) 0.84 Sodium (ppm) 99 Calcium (ppm) 61 Magnesium (ppm) 15 Sodium adsorption ratio 3.1 Adjusted SAR 5.0 Bicarbonate (ppm) 112 Chloride (ppm) 95 Sodium (ppm) 99 Boron (ppm) 0.23 Water Quality

Specific ion toxicities/problems Trees are more sensitive to salts especially sodium and chloride are sprayed directly onto plant leaves through irrigation water. Trees are more sensitive to salts especially sodium and chloride are sprayed directly onto plant leaves through irrigation water. If irrigation water is applied to roots rather than leaves, plant tolerance level to Cl and Na will increase. If irrigation water is applied to roots rather than leaves, plant tolerance level to Cl and Na will increase. B is usually absorbed by roots. B is usually absorbed by roots.

Use low angle nozzle to reduce leaf ion toxicity on trees and shrubs. Use low angle nozzle to reduce leaf ion toxicity on trees and shrubs.

Declines of conifer trees have been observed under prolonged use of RWW

Mineral Concentration in Ponderosa Pine Needles Parameters Surface Water Irrigation Recycled Water Irrigation Firing (0-100%) 3.17****33.58 B35.69***50.27 K Na237****2750 K/Na9.7****0.8 Cl *, ***, **** Significant at P  0.05,  0.001, and  respectively.

Pine needle burn and Na + in the needles

ParameterRWW Total dissolved salts (ppm) 614 Conductivity (dS/m) 0.84 Sodium (ppm) 99 Calcium (ppm) 61 Magnesium (ppm) 15 Sodium adsorption ratio 3.1 Adjusted SAR 5.0 Bicarbonate (ppm) 112 Chloride (ppm) 95 Boron (ppm) Nitrogen (ppm) Phosphorus (ppm) 0.8 Water Quality

Nutrients in Irrigation Pond Test recycled wastewater on regular basis, and calculate N and P input via irrigation. These amounts of N and P should be deducted from the fertilization program. Increased nutrient content will increase algae population in irrigation ponds, which will result in secondary problems, such as decreased clarity and aesthetic appearance. Some algal metabolites are toxic. Increased nutrient content will increase algae population in irrigation ponds, which will result in secondary problems, such as decreased clarity and aesthetic appearance. Some algal metabolites are toxic. Irrigation pond maintenance level will increase, needing additional aeration and chemical modification. Irrigation pond maintenance level will increase, needing additional aeration and chemical modification.

To make water reuse a success: Support water reuse; Support water reuse; Recognize that reused water and fresh water are not of equal value and quality; Recognize that reused water and fresh water are not of equal value and quality; Yes, we can manage aesthetic appealing landscapes, but hidden costs exist. Yes, we can manage aesthetic appealing landscapes, but hidden costs exist.

What should be done to manage landscapes receiving recycled wastewater? Irrigation Regularly monitor water quality. More vigorous aeration in irrigation pond; Improve irrigation uniformity; Irrigate based on ET with additional periodic leaching and flushing; Improve drainage; Conversion to low angle nozzles to reduce leaf damage of trees.

What should be done to manage landscapes receiving recycled wastewater? Compaction control More intensive cultivation programs (deep aeration and water injection) to maintain oxygen diffusion and water movement; More vigorous traffic control.

What should be done to manage landscapes receiving recycled wastewater? Fertilization and Amendments Reduce N and P fertilization; Fertilize to alleviate nutrient imbalance; Additional chemical amendments to displace Na; Add to soil Add to water Leaching to remove excess Na after soil amendment treatment;

What should be done to manage landscapes receiving recycled wastewater? Plant Selection Replace with more salt tolerant species and cultivars.

Deciduous Woody Plants Salinity Tolerance PearCottonwood Siberian Elm Green Ash Red Maple Amur Maple Littleleaf Linden High Low

Cool Season Turfgrasses Alkaligrass Creeping bentgrass Tall fescue Fine fescues Perennial ryegrass Kentucky bluegrass High Low

Related Research at CSU

Management Options for Mitigating Sodium Stress in Effluent Irrigated Turfgrass Systems Research Project at CSU Sponsored by the City of Westminster, Denver Water, Plum Creek Water Authority, and Castle Pine Golf Club

Treatments: TreatmentGypsum Calcium chlorideHumate Mycorrhizae (VAM) Humate + Gypsum VAM + GypsumControl Application Rate 50 lb/ 1000 ft 2 1qt/ 1000 ft 2 15 lb/ 1000 ft lb/1000 ft No amendment

Preliminary Findings Soil texture is playing a dominant role; Soil texture is playing a dominant role; Mycorrhizae treatment did not help to reduce sodium problems and improve turf quality, but enhanced soil redox status; Mycorrhizae treatment did not help to reduce sodium problems and improve turf quality, but enhanced soil redox status; Gypsum (CaSO 4 ) treatment enhanced leaching of Na, but did not improve turfgrass quality; Gypsum (CaSO 4 ) treatment enhanced leaching of Na, but did not improve turfgrass quality; Calcium chloride treatment helped to reduce Na accumulation and increased turf quality in both greenhouse and field studies. Calcium chloride treatment helped to reduce Na accumulation and increased turf quality in both greenhouse and field studies.

Warren et al. (2005)

Development and Selection of Salt Tolerant Plants Sponsored by US Golf Association

New saltgrass nursery at Colorado State Univ. that contains accessions and progenies

Four acres of saltgrass plots at CSU (containing 250 accessions and progenies.)

Selecting Conifers Trees For Landscapes With Recycled Wastewater Irrigation Sponsored by Denver Water