THE CHALLENGE OF NUTRIENT CONTROL IN LARGE SCALE WATERSHEDS: EFFORTS IN THE U.S.

Transcription

1 THE CHALLENGE OF NUTRIENT CONTROL IN LARGE SCALE WATERSHEDS: EFFORTS IN THE U.S. NAE Convocation of the Professional Engineering Societies David Dzombak Carnegie Mellon University May 16, 2011

2 OUTLINE Nutrients and water quality Hypoxia in coastal waters Chesapeake Bay Northern Gulf of Mexico The Clean Water Act Agriculture and water quality Summary

3 NUTRIENTS AND WATER QUALITY Primary production (algae) in natural waters 106 CO NO 3- + HPO H H + C 106 H 263 O 110 N 16 P O 2 Biochemical oxygen demand bacteria biomass + O 2 CO 2 + H 2 O light

4 HYPOXIA: OXYGEN DEPLETION Dissolved oxygen important to ensure the ecological health of a receiving water Solubility of oxygen is low ( 10 mg/l at 20C) Low dissolved oxygen levels (< 4.0 mg/l) are toxic to many types of fish and other aquatic organisms

5 SOURCES OF NUTRIENT DISCHARGES Source:

6 HYPOXIA IN COASTAL WATERS Global problem N loadings are the most significant driver (NRC, 2000) Production and application of N-fertilizers for agriculture has greatly increased in last 50 yrs In U.S., 6x increased N fluxes to coastal waters relative to natural loadings (Howarth et al 2002) NAE Grand Challenge for Engineering: Manage the N cycle (

7 MANAGING NUTRIENT INPUTS: A GLOBAL CHALLENGE

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9 CHESAPEAKE BAY PROGRAM Chesapeake Bay Agreement: 1983 Multi-state partnership with EPA on bay restoration (PA, MD, VA, WV, NY, DE, DC) Focused on reducing nutrient and sediment loadings; restoring bay grasses, fish, blue crabs and other aquatic life Basin-wide, coordinated monitoring, modeling and action programs

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12 HYPOXIC ZONES IN NORTHERN GULF OF MEXICO HYPOXIA, 2010 Source: Rabalais et al. (2010)

13 Total Nitrogen Delivered Incremental Yield HUC 8 Scale (818 basins) Delivered TN Incremental Yields (kg/km2) to the Gulf Nitrogen SPARROW Model Output for 2002 Source: Robertson (2009)

14 Phosphorus Yield (kg/km 2 ) Total Phosphorus Delivered Incremental Yield 2002

15 NRC STUDIES OF MR WATER QUALITY Committee on the Clean Water Act Implementation Across the Mississippi River Basin ( ) Committee on the Mississippi River and the Clean Water Act: Scientific, Modeling, and Technical Aspects of Nutrient Pollutant Load Allocation and Implementation (2008) Committee on the Mississippi River and the Clean Water Act ( )

16 NRC MR STUDY SPONSORS McKnight Foundation Minneapolis, Minnesota US Environmental Protection Agency Office of Water

17 CHARACTERISTICS OF THE MR SYSTEM Basin covers nearly 50% of continental US Extensive modification of the basin (land cover and land use) and of the river over past 200 years Construction of river control structures (levees, dams) and wetland loss influence water discharge and quality UMR is much smaller river than LMR, different recreational and commercial value.

18 AVG MR WATER DISCHARGE (km 3 /yr) Source: Meade (1995)

19 MR WATER QUALITY PROBLEMS At the scale of the entire river, nutrients and sediment are two primary water quality problems Nutrient and sediment inputs derive mostly from nonpoint sources, and mostly from agriculture Sediment: excess sediment loads in UMR, sediment deprivation in LMR

20 MR NUTRIENT INPUTS Source: Goolsby (2000)

21 THE CLEAN WATER ACT Cornerstone of surface water quality protection in US; 39 years old Contains variety of reg and non-reg tools Technology-based standards for point-source discharges CWA has been effective in addressing point sources of water pollutants CWA addresses nonpoint source pollution only in a limited manner

22 THE CLEAN WATER ACT Primary mechanism for nonpoint source control: total max daily load (TMDL) process to establish loads that will achieve water quality standards CWA requires states or EPA to establish water quality standards and develop TMDLs for water bodies that do not meet standards For water quality standards and TMDLs to be effectively implemented in interstate waters like the MR, essential that interstate pollutant loadings be fully considered

23 TMDLs FOR MISSISSIPPI RIVER NRC recommendations: EPA should develop water quality criteria for nutrients in the MR and north Gulf of Mexico. EPA should ensure that states establish standards (designated uses and water quality criteria) and TMDLs to protect these waters from excessive nutrient pollution. EPA should develop a federal TMDL or its equivalent, using a process similar to that developed for the Chesapeake Bay.

24 State or regional nutrient caps to reduce nutrient flow to Gulf Numerical Nutrient criteria

25 LIMITATIONS OF THE CWA CWA cannot be the sole legal vehicle used to achieve water quality objectives for the MR Weak nonpoint source control provisions Most agriculture discharges exempted

26 AGRICULTURE AND MR WATER QUALITY NRC recommendations Important that USDA conservation programs be aggressively targeted at areas of high sediment and nutrient input EPA and USDA should strengthen their cooperative activities For example, EPA can help USDA identify land that should receive priority attention for USDA conservation programs

27 AGRICULTURE AND WATER QUALITY Reduction in nutrient loadings from agriculture, crucial for improving MR water quality USDA has important role through its land and water conservation programs (CRP, EQIP, CSP) USDA MR Basin Healthy Watersheds Initiative (MRBI)

28 SUMMARY Excess nutrient (N,P) loadings to coastal waters are a global problem Nonpoint sources primarily agriculture Key impact: low dissolved oxygen (hypoxia) Large watersheds and major discharges are affected, e.g., Ches Bay and MR/Gulf of Mexico Clean Water Act limited authority with respect to nonpoint sources TMDL provisions being tested USDA MRBI

29 Questions?

30 SPARROW Modeling Approach - Relates water quality measurements at monitoring stations to watershed attributes - Incorporates in-stream decay of nutrients Sources D Land-to-water transport S Instream transport Monitored load Source: Robertson, 2009

31 USGS SPARROW Model Load at a specific site F i * N S n 1 Flux from Within the Watershed S n, i D n n D S R Z ; θ T Z, Z ; θ, θ i D Sources Land-to-Water Delivery Calibration Coefficients SPARROW: SPAtially Referenced Regressions On Watershed attributes i i S R Transport/Decay Flux from Upstream Watersheds j J i F j it Z S i, Z R i ; θ Transport Calibration of National model based on 425 sites with coinciding loads and GIS information S, θ R Source: Robertson (2009)

32 TMDLs for Mississippi River State EPA- Approved TMDLs Pollutants Addressed % of Miss River in State covered by TMDLs Minnesota 3 Mercury, PCBs, Nutrients Not available Wisconsin 0 0 Iowa 0 0 Illinois 0 0 Missouri 1 PCBs, Chlordane 100 Kentucky 0 0 Tennessee 0 0 Arkansas 0 0 Mississippi 0 0 Louisiana 0 0