Soil Quality Assessment in Urban

Gardens: Trace Metals and Phosphorus

Tolessa Deksissa, Yacov Assa & Sebhat Tefera

University of the District of Columbia

70th SWCS International Annual Conference. Greensboro, NC

July 26-29, 2015

World Population: Urban Share

www.newgeography.com

It is time to consider urban agriculture to address urban food security

Intro: Reason for Urban Gardening and Trend

All these four points are the reason for urban gardening in the

21st century.

Ornamental

Food Security

Food Safety

Climate Change

Intro: Urban Gardening

• Urban gardening can contribute to social,

health, economic and ecological benefit.

• Lack of knowledge about the quality of soil

used for gardening could pose a health

threat for consumers, gardeners and

environment.

• Excess addition of fertilizer or nutrients:

Nitrogen and Phosphorous can lead to

eutrophication of surface waters.

Intro: Effect of Excess Nutrient in Chesapeake

Bay Watershed

Sustainable DC Plan:

100% fishable and

swimmable by 2032

Does urban gardening help DC meet water quality standards?

Objective

• To assess the occurrence and extent of soil

contamination with trace metals in home and

community gardens in DC.

• To increase awareness of soil contamination in DC

urban gardens through free soil quality testing service.

• Educate DC residents in Sustainable Urban Gardening

Materials and Methods:

Sample Collection Sites

• 398 composite

samples:

• 142 community

• 257 home

Provided Free

Soil Quality

Testing Service

for DC Residents:

Nutrient and All

metals

Sample Analysis and Visualization

2. Data Visualization

or Geo-coding

1. Sample Analysis:

Inductive Couple

Plasma Mass

Spectrophotometer

Results: Copper

• Copper (Cu) - Higher

variability in home than

community gardens.

Both mean and median

concentrations of Cu is

higher home gardens.

Results: Arsenic

Arsenic (As) –

Higher variation in

home gardens,

similar mean

concentration, but

higher median

concentration in the

community gardens.

Results: Cadmium

Cadmium (Cd) –

Higher mean,

median and

variation in home

gardens than in

community

gardens.

Result: Lead

Lead (Pb) –

Higher mean,

median and

variation in

home gardens

than the

community

gardens.

Comparison of Community and Home

Gardens: Statistical Analysis

Metal T-test p value

Copper 0.0566

Chromium 0.1245

Arsenic 0.8808

Cadmium 0.00001

Lead 0.0000002

Home gardens are significantly higher than community

gardens in Cd and Pb

Results: Nutrient-Excessive Phosphate

• 83% gardens are

excessive in

phosphate

Result: Arsenic Level

EPA guidelines

As < 0.4 ppm

Conclusion Mean concentration of Arsenic is higher than the EPA

guidelines (0.4 ppm), which has potential risk to human

health.

Lead, Copper, Chromium and Cadmium levels are

below the EPA guidelines.

Home gardens have more contamination than

community gardens in Lead, Copper, Cadmium and

Chromium, but only Cadmium and Lead are statistically

significant.

Free soil testing service increased community awareness

about soil quality, soil amendment with compost,

excessive nutrient and nutrient management.

Farther Researches

Potential plant uptake of Arsenic and Lead is being

studied.

The application of urban gardening as a green

stormwater management strategy needs further

investigation.

Appropriate community education of soil amendment

and composting is needed.

Acknowledgement• NIFA/USDA funded the project

• Sample collection and analysis done by

graduate students:

• Harold Yapuwa, PSM

• Siaka Nuah, PSM

• Rahil Fofana, PSM

• Ulrich Bazemo, PSM

• Mulenga Chileshe, BS