Retention Basins and Rain Gardens

1. Retention Basins and Rain Gardens A Possible Solution to Nutrient Pollution in Natural Waters?

2. Population Growth & Urbanization • Impervious surfaces lead to excessive storm water • Because of urbanization hydrology is changed

3. Water Quality Decline • Influx of pollutants • Nitrogen (N2) and phosphorous (P) • Excessive quantities can cause eutrophication • ↑ in algae • ↓ dissolved O2 levels • Leads to widespread fish kills

4. Water Quality Decline N Concentrations in Bay Streams, 1987-1997 • Key problem is nutrient pollution, particularly nitrogen (N) pollution • About ½ half of N load to Barnegat Bay comes from surface runoff (Kennish et al. 2007) • Removing nutrients from surface water before it enters the Bay is cost effective way to improve Bay health Source: Hunchak-Kariouk and Nicholson, 2001

5. Nitrogen Cycle – a Key Player • N2 makes up over 75% of air • Contained in Amino Acids, proteins & nucleic acids of living things • Comes in various forms • Only ammonium (NH4+) & nitrate(NO3-) are useable by plants & algae

6. Nitrogen Cycle – a Key Player • Nitrogen-fixation • anaerobic bacteria convert atmospheric into NH4+ & NO3- • Vital part of Nitrogen Cycle • Made of several parts • Nitrification • Denitrification • Ammonification http://www.google.com/imgres?q=nitrogen+cycle&hl=en&gbv=2&biw=1024&bih=566&tbm=isch&tbnid=Oer5J0d51BtSrM:&imgrefurl=http://www.h2ou.com/h2nitrogencycle.htm&docid=cnNVBqgcmbsX0M&imgurl=http://www.h2ou.com/h2images/NitrogenCycle-lgr-F.jpg&w=697&h=605&ei=qZKzT9DaBNCN6QHmobiQCQ&zoom=1

7. http://www.google.com/imgres?q=nitrogen+fixation&hl=en&biw=1024&bih=566&gbv=2&tbm=isch&tbnid=cl6dCdYpP-4HkM:&imgrefurl=http://landscapeforlife.org/give_back/3c.php&docid=KXqSzFlwUhex0M&imgurl=http://landscapeforlife.org/images/nitrogencycle.jpg&w=880&h=687&ei=qpGzT8b4C8Gbgwfk89T_Bg&zoom=1http://www.google.com/imgres?q=nitrogen+fixation&hl=en&biw=1024&bih=566&gbv=2&tbm=isch&tbnid=cl6dCdYpP-4HkM:&imgrefurl=http://landscapeforlife.org/give_back/3c.php&docid=KXqSzFlwUhex0M&imgurl=http://landscapeforlife.org/images/nitrogencycle.jpg&w=880&h=687&ei=qpGzT8b4C8Gbgwfk89T_Bg&zoom=1

8. You tube Video on Nitrogen Cycle • Nitrogen Cycle Description

9. NO3 CONCENTRATION (AS N), MG/L 1994/95 LAND USE/ LAND COVER, % INCREASING URBAN LAND Rationale • Human development increases impervious cover in watersheds • Traditional rain gardens collect storm water from impervious areas and infiltrate it through soil, slowing delivery to rivers and bays, but don’t reliably remove nutrients, esp. Nitrogen Source: Hunchak-Kariouk and Nicholson, 2001

10. Nutrient Pollution Standards • US Federal Government changed standards in 2007 • Resulted in a call to lower nutrient pollution from industry, commercial, and residential areas • ↓ non-point pollutants • ↓ N2 and P

11. Rationale • 2008 National Estuarine Eutrophication Assessment suggests Barnegat Bay is in pretty bad shape • Problems are expected to worsen over time

12. Solution: Keep nutrients out of waterways • Limit amounts of N-& P- containing nutrients making their way into aquatic ecosystems • In turn, algal blooms would decrease • Also slow flow and possibly divert storm water away from rivers and streams • Reduce downstream flooding

13. Prior Studies • Many studies have investigated ways to reduce nutrient pollution in waters of East Coast of United States e.g. • Charles River in Boston • North Carolina • Aimed at decreasing excessive nitrogen and phosphorous in bodies of water

14. Bioretention hydrology & nutrient Removal in North Carolina • Bioretentions built in proximity to Shopping Center with proper filtration can allow in upwards of 40% of nitrogen & phosphorous removal • Water outflow also reduced, especially in warmer seasons

15. Stormwater ponds & biofilters in Charles River, Boston MA • Reduction of phosphorous from nearby industries into bodies of water can be achieved • Up to 65% removal with the use of detention pond and filter system

16. Traditional “Infiltration Style” Rain Garden • Designed to slow water flow • Absorbs excess water flow from nearby impervious surfaces • Flood reduction by in increased absorbency • Decreases soil erosion

17. Traditional “Infiltration Style” Rain Garden • Unreliable at nutrient removal • Maximum phosphorus and nitrogen removal is between 30 – 40% • Inadequate at reducing the amount of nutrients making its way into bodies of water • Water generally flows vertically through traditional style rain garden

18. Current Studies • Univ. of New Hampshire Stormwater Center is a leader in study of methods for nutrient removal • Their proposed solution uses horizontal filtration of water through a “Gravel Rain Garden” • Dense plantings at surface means lots of plants to take up nutrients through their root system • More important, though, is the anaerobic environment created in crushed stone that lies beneath. • Allows for denitrification

19. Nitrogen-Removing Rain Gardens • Create extensive saturated zone designed to maintain anoxic conditions to promote denitrification through use of impervious liner • Longer retention of water, increases nitrogen removal efficiency • Base of gravel to provide high surface area for microbial activity • Top with soil and plant with typical rain garden plants

20. Disadvantages • More expensive • New technology so not yet commonly constructed • Replacement of vegetation every three years to ensure nitrogen removal capabilities are optimized

21. Advantages • Existing ponds and detention basins can be turned into subsurface gravel rain gardens • Works well in cold climates • Much superior and more reliable nutrient removal than obtained with traditional “infiltration style” rain gardens

22. Questions?