Long-Term Trends of Nutrients and Phytoplankton in Chesapeake Bay
- 1.6k Downloads
Climate effects on hydrology impart high variability to water-quality properties, including nutrient loadings, concentrations, and phytoplankton biomass as chlorophyll-a (chl-a), in estuarine and coastal ecosystems. Resolving long-term trends of these properties requires that we distinguish climate effects from secular changes reflecting anthropogenic eutrophication. Here, we test the hypothesis that strong climatic contrasts leading to irregular dry and wet periods contribute significantly to interannual variability of mean annual values of water-quality properties using in situ data for Chesapeake Bay. Climate effects are quantified using annual freshwater discharge from the Susquehanna River together with a synoptic climatology for the Chesapeake Bay region based on predominant sea-level pressure patterns. Time series of water-quality properties are analyzed using historical (1945–1983) and recent (1984–2012) data for the bay adjusted for climate effects on hydrology. Contemporary monitoring by the Chesapeake Bay Program (CBP) provides data for a period since mid-1984 that is significantly impacted by anthropogenic eutrophication, while historical data back to 1945 serve as historical context for a period prior to severe impairments. The generalized additive model (GAM) and the generalized additive mixed model (GAMM) are developed for nutrient loadings and concentrations (total nitrogen—TN, nitrate + nitrate—NO2 + NO3) at the Susquehanna River and water-quality properties in the bay proper, including dissolved nutrients (NO2 + NO3, orthophosphate—PO4), chl-a, diffuse light attenuation coefficient (K D (PAR)), and chl-a/TN. Each statistical model consists of a sum of nonlinear functions to generate flow-adjusted time series and compute long-term trends accounting for climate effects on hydrology. We present results identifying successive periods of (1) eutrophication ca. 1945–1980 characterized by approximately doubled TN and NO2 + NO3 loadings, leading to increased chl-a and associated ecosystem impairments, and (2) modest decreases of TN and NO2 + NO3 loadings from 1981 to 2012, signaling a partial reversal of nutrient over-enrichment. Comparison of our findings with long-term trends of water-quality properties for a variety of estuarine and coastal ecosystems around the world reveals that trends for Chesapeake Bay are weaker than for other systems subject to strenuous management efforts, suggesting that more aggressive actions than those undertaken to date will be required to counter anthropogenic eutrophication of this valuable resource.
KeywordsEstuaries Chesapeake Bay Long-term trends Hydrology Eutrophication Water quality Phytoplankton Nutrients Chlorophyll
Our thanks to Dr. Jim Hagy of the EPA Gulf Breeze Laboratory for providing data from his Ph.D. Dissertation and to Dr. Bob Hirsch and his colleagues at the US Geological Survey for providing data on nutrient concentrations and loadings from the Nontidal Monitoring Program. Rich Batiuk and Gary Shenk of the EPA Chesapeake Bay Program provided point-source nutrient estimates and helpful comments on the manuscript. Detailed comments and suggestions by two anonymous reviewers significantly improved the manuscript. LWH was supported by the NSF Biological Oceanography Program and the NOAA Chesapeake Bay Program Office. HWP was supported by the NSF Biological Oceanography Program, the North Carolina Department of Environment and Natural Resources, ModMon and FerryMon Projects, and the Strategic Environmental Defense and Development Program (SERDP) of the Department of Defense.
- Anonymous. 2000. Directive 200/60/EC of the European parliament and of the council of 23 October 2000 establishing a framework for community action in the field of water policy. Official Journal L 327/1.Google Scholar
- Boicourt, W.C. 1992. Influence of circulation processes on dissolved oxygen in the Chesapeake Bay. In Oxygen dynamics in Chesapeake Bay: a synthesis of research, ed. D. Smith, M. Leffler, G. Mackiernan, 7–53. College Park: University of Maryland Sea Grant.Google Scholar
- Boynton, W.R., and W.M. Kemp. 2000. Influence of river flow and nutrient loads on selected ecosystem processes: a synthesis of Chesapeake Bay data. In Estuarine science, a synthetic approach to research and practice, ed. J.E. Hobbie, 269–298. Washington: Island.Google Scholar
- Bricker, S., B. Longstaff, W. Dennison, A. Jones, K. Boicourt, C. Wicks, and J. Woerner. 2007. Effects of nutrient enrichment in the Nation’s estuaries: a decade of change. NOAA Coastal Ocean Program Decision Analysis Series No. 26. National Centers for Coastal Ocean Science, Silver Spring, Maryland, USA. 328 p.Google Scholar
- Gallegos, C. L., P. J. Werdell, and C. R. McClain. 2011. Long-term changes in light scattering in Chesapeake Bay inferred from Secchi depth, light attenuation, and remote sensing measurements. Journal of Geophysical Research 116: C00H08, doi:10.1029/JC2011007160.Google Scholar
- Jassby, A.D., and J.E. Cloern. 2014. wq: some tools for exploring water quality monitoring data. R package version 0.4-1. http://cran.r-project.org/package=wq.
- Kemp, W.M., W.R. Boynton, J.E. Adolf, D.F. Boesch, W.C. Boicourt, G. Brush, J.C. Cornwell, T.R. Fisher, P.M. Glibert, J.D. Hagy, L.W. Harding Jr., E.D. Houde, D.G. Kimmel, W.D. Miller, R.I.E. Newell, M.R. Roman, R.M. Smith, and J.C. Stevenson. 2005. Eutrophication of Chesapeake Bay: historical trends and ecological interactions. Marine Ecology Progress Series 303: 1–29.CrossRefGoogle Scholar
- Langland, M.J., P.L. Lietman, P.L., and S.A. Hoffman. 1995. Synthesis of nutrient and sediment data for watersheds within the Chesapeake Bay drainage basin. U.S. Geological Survey Water-Resources Investigations Report 95-4233, 121 p.Google Scholar
- Langland, M., J. Blomquist, D. Moyer, and K. Hyer. 2012. Nutrient and suspended-sediment trends, loads, and yields and development of an indicator of streamwater quality at nontidal sites in the Chesapeake Bay watershed, 1985–2010. U.S. Geological Survey Scientific Investigations Report 2012-5093, 26 p.Google Scholar
- Malone T.C. 1992. Effects of water column processes on dissolved oxygen: nutrients, phytoplankton and zooplankton. In Oxygen dynamics in Chesapeake Bay: a synthesis of research, ed. D. Smith, M. Leffler, and G. Mackiernan, 61–112. College Park: University of Maryland Sea Grant.Google Scholar
- Moyer, D.L., RM. Hirsch, and K.E. Hyer. 2012. Comparison of two regression-based approaches for determining nutrient and sediment fluxes and trends in the Chesapeake Bay watershed. U.S. Geological Survey Scientific Investigations Report 2012–5244, 118 p. (http://pubs.usgs.gov/sir/2012/5244/).
- Mozetić, P., C. Solidoro, G. Cossarini, G. Socal, R. Precali, J. France, F. Bianchi, C. De Vittor, N. Smodlaka, and S. Fonda Umani. 2010. Recent trends towards oligotrophication of the Northern Adriatic: evidence from chlorophyll a time series. Estuaries and Coasts 33: 362–375.CrossRefGoogle Scholar
- Paerl, H.W., J.D. Bales, L.W. Ausley, C.P. Buzzelli, L.B. Crowder, L.A. Eby, J.M. Fear, M. Go, B.L. Peierls, T.L. Richardson, and J.S. Ramus. 2001. Ecosystem impacts of three sequential hurricanes (Dennis, Floyd, and Irene) on the United States’ largest lagoonal estuary, Pamlico Sound, NC. Proceedings of the National Academy of Sciences 98: 5655–5660.CrossRefGoogle Scholar
- Paerl, H.W., L.M. Valdes, A.R. Joyner, B.L. Peierls, C.P. Buzzelli, M.F. Piehler, S.R. Riggs, R.R. Christian, J.S. Ramus, E.J. Clesceri, L.A. Eby, L.W. Crowder, and R.A. Luettich. 2006b. Ecological response to hurricane events in the Pamlico Sound System, NC and implications for assessment and management in a regime of increased frequency. Estuaries and Coasts 29: 1033–1045.CrossRefGoogle Scholar
- Paerl, H.W., K.L. Rossignol, N.S. Hall, B.L. Peierls, and M.S. Wetz. 2010. Phytoplankton community indicators of short- and long-term ecological change in the anthropogenically and climatically impacted Neuse River Estuary, North Carolina, USA. Estuaries and Coasts 33: 485–497.CrossRefGoogle Scholar
- Paerl, H.W., S.N. Hall, B.L. Peierls, K.L. Rossignol, and A.R. Joyner. 2013. Hydrologic variability and its control of phytoplankton community structure and function in two shallow, coastal, lagoonal ecosystems: the Neuse and New River estuaries, North Carolina, USA. Estuaries and Coasts. doi: 10.1007/s12237-013-9686-0.Google Scholar
- Riemann, B., J. Carstensen, K. Dahl, H. Fossing, J.W. Hansen, H.H. Jakobsen, A.B. Josefson, D. Krause-Jensen, S. Markager, P.A. Stæhr, K. Timmermann, J. Windolf, and J.H. Andersen. 2015. Recovery of Danish coastal ecosystems after reductions in nutrient loading: a holistic approach. Estuaries and Coasts. doi: 10.1007/s12237-015-9980-0.Google Scholar
- Trenberth, K. E., Jones, P. D., Ambenje, P., Bojariu, R., Easterling, D., Klein, T. A., Parker, D., Rahimzadeh, F., Renwick, J. A., Rusticucci, M., Soden, B., and Zhai, P. 2007. Observations: surface and atmospheric climate change. In Climate change 2007: the physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, ed. S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller, 235–336. Cambridge and New York: Cambridge University Press.Google Scholar
- U.S. Environmental Protection Agency. 1987. 1987 Chesapeake Bay agreement. U.S. Environmental Protection Agency, Chesapeake Bay Program Office, Annapolis, Maryland.Google Scholar
- U.S. Environmental Protection Agency. 2003. Ambient water quality criteria for dissolved oxygen, water clarity and chlorophyll a for Chesapeake Bay and its tidal tributaries. EPA 903-R-03-002. U.S. Environmental Protection Agency, Region 3, Chesapeake Bay Program Office, Annapolis, Maryland, USA.Google Scholar
- U.S. Environmental Protection Agency. 2010. Chesapeake Bay phase 5.3 community watershed model. EPA 903S10002 - CBP/TRS-303-10. U.S. Environmental Protection Agency, Chesapeake Bay Program Office, Annapolis, Maryland, USA.Google Scholar
- Valdes-Weaver, L.M., M.F. Piehler, J.L. Pinckney, K.E. Howe, K. Rossignol, and H.W. Paerl. 2006. Long-term temporal and spatial trends in phytoplankton biomass and class-level taxonomic composition in the hydrologically variable Neuse–Pamlico estuarine continuum, North Carolina, U.S.A. Limnology and Oceanography 51: 1410–1420.CrossRefGoogle Scholar
- Wood, S.N. 2006a. Generalized additive models (an introduction with R), 392. Boca Raton: Chapman & Hall/CRC.Google Scholar
- Yarnal, B. 1993. Synoptic climatology in environmental analysis. London: Belhaven Press.Google Scholar