Chesapeake Bay Nitrogen Assessments

Transcription

1 Chesapeake Bay Nitrogen Assessments May 20, 2010 Workshop on Nitrogen Assessment Science in the USA Thomas E. Jordan

2 Chesapeake Bay Watershed Area=167,000 km 2 Spans 6 states + DC 6 physiographic provinces 58% forest 22% agricultural 9% developed land

3 Susquehanna Chesapeake Bay Balt. Largest estuary in the US 322 km long X 48 km wide 11,601 km 2 Shallow (ave. depth 14m) Shorelines in MD and VA Many sub-estuaries DC

4 Nitrogen loads to Chesapeake Bay from the Susquehanna River doubled during the 1960s and 1970s (Hagy et al. 2004).

5 Increasing nitrogen loads contributed to eutrophication causing: Deep water hypoxic dead zone Shallow water hypoxia Demise of submerged aquatic vegetation Declines in oyster and blue crab fisheries?

6 N Red is dead. Chesapeake Bay Program Monitoring Data

7 Deep water hypoxia Forms below pychnocline More severe if more river flow Volume of hypoxic water increased from (Hagy et al. 2004) 1950 (10 9 m 3 ) 2001 (10 9 m 3 ) Anoxic Hypoxic (DO<2mg/L)

8 Dissolved Oxygen (g m -3 ) Diel Hypoxia in Shallow Water Corsica River Day of Year 2005 Data from Maryland Department of Natural Resources Shallow Water Monitoring Program

9 Demise of Submerged Aquatic Vegetation (Orth and Moore 1983, Moore et al. 2004) Greatest decline: SAV area: Before decline = 840 km 2 In 2004 = 360 km 2 Shading by phytoplankton, periphyton, and suspended sediment Waterfowl dependent on SAV decline Possible effects on blue crab habitat

10 Chesapeake Bay Program Monitoring Funded by EPA and states (esp. MD & VA) Started in 1983 Focus on effects of nutrient loading E.g., see:

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12 Anthropogenic Nitrogen Exchanges Via Agriculture Fertilizer N Fixation by Crops Via Atmosphere Nitrate Deposition Ammonia Volatilization And Deposition ?? N Fluxes: kg ha -1 yr -1 (Castro et al. 2003) Chesapeake Watershed Via Trade Food Feed 13.5 Riverine N Discharge

13 Annual Flow-Weighted Mean Nitrate Concentrations 18 (Jordan, Weller, and Correll, 1997a,b,c and unpublished data) Conestoga R. Lancaster Co. PA 10 North of Balt Central PA 2 E. and W. Shores Percentage of Cropland

14 N sources to Bay (Castro et al. 2003) Agriculture 51% Atmospheric Deposition 25% Sewage 15% Forest 7% Urban Non-Point Source 1%

15 Actions Clean Water Act 1972 Chesapeake Bay Agreements: 1983, 1987, 2000 $ 6 billion spent over 25 years (Washington Post, 5/12/10)

16 Management in the Estuary SAV restoration Bivalve (esp. oyster) restoration

17 Management: Developed Lands Sewage infrastructure Biological N removal for sewage or septic Storm water management Critical areas laws

18 Management: Agricultural Lands Riparian buffer and wetland restoration Conservation reserve lands Nutrient management plans Increase livestock N assimilation efficiency Manure management Cover crops Minimum tillage

19 Nitrate ( mol L -1 ) Flow-weighted annual mean nitrate concentration in the Susquehanna River at Conowingo Dam Based on data from USGS:

20 Obstacles to reducing N loads Population increase million 1970-now Voluntary participation for agriculture Privacy of agriculture e.g. secret wetlands and censored chickens Economies of concentrating livestock Growing corn for ethanol biofuel Lag time for seeing mitigation effects Effects of management practices not known

21 Wetlands Restored in Agricultural Watersheds: Percentage of Inflowing N Removed Annually (Jordan 2009) Wetland Area (% of watershed)

22 SERC Riparian Buffer Transect Studies Peterjohn & Correll Ecology 65: Buffer removes most of the N load. Bohlke et al Journal of Environmental Quality 36: Buffer removes little N.

23 Statistical models suggest that N removal by riparian buffers differs among physiographic provinces. Coastal Plain buffers on average remove most of the N received from uphill croplands. Piedmont buffers remove about one third of the N received from uphill croplands. Appalachian buffer N removal is not statistically significant. (Weller et al. in review Ecological Applications)

24 N knowledge gaps Denitrification at large spatial scales Gaseous ammonia transport Agricultural activities Effectiveness of N mitigation practices

25 Hope? Obama issues executive order for Bay cleanup (May 2009). EPA settles suit by the Chesapeake Bay Foundation by setting enforceable goals and pollution caps (May 2010). Pending legislation to give EPA authority to punish states for not complying.

26 References: Castro, M.S., C.T. Driscoll, T.E. Jordan, W.G. Reay, W.R. Boynton Sources of nitrogen to estuaries in the United States. Estuaries 26: Hagy, J. D., W. R. Boynton, C. W. Keefe, and K. V. Wood Hypoxia in Chesapeake Bay, : Long-term change in relation to nutrient loading and river flow. Estuaries 27: Jordan, T. E Wetland restoration and wetland creation best management practices. Pages in Developing best management practice definitions and effectiveness estimates for nitrogen, phosphorus, and sediment in the Chesapeake Bay watershed, Report to the Chesapeake Bay Program by T. Simpson and S. Weammert. Jordan, T. E., D. L. Correll, and D. E. Weller. 1997a. Relating nutrient discharges from watersheds to land use and stream flow variability. Water Resources Research 33: Jordan, T. E., D. L. Correll, and D. E. Weller. 1997b. Effects of agriculture on discharges of nutrients from Coastal Plain watersheds of Chesapeake Bay. Journal of Environmental Quality 26: Jordan, T. E., D. L. Correll, and D. E. Weller. 1997c. Nonpoint source discharges of nutrients from Piedmont watersheds of Chesapeake Bay. Journal of the American Water Resources Association 33: Moore, K. A., D. J. Wilcox, and B Anderson Historical analysis of submerged aquatic vegetation (SAV) in the Potomac River and analysis of Bay-wide SAV data to establish a new acreage goal. Report prepared for the Chesapeake Bay Program (CB ). Orth, R. J. and K. A. Moore Chesapeake Bay: An unprecedented decline in submerged aquatic vegetation. Science 222:51-53.