Interactive Effects of Physical and Biogeochemical Feedback Processes in a Large Submersed Plant Bed
Submersed plants are sensitive to nutrient loading because excess algal growth creates light-limiting conditions. However, submersed plant beds can also modify nutrient cycling through feedback loops whereby algal growth is limited and plant growth is enhanced. Whereas most studies on the effect of submersed aquatic vegetation (SAV) beds on nutrient cycling concentrate on either biogeochemical or physical controlling mechanisms, we use a holistic approach that analyzes how these processes interact. We measured a suite of physical and biological processes in a large SAV bed and developed a simple, 1-dimensional reactive transport model to investigate the mechanisms underlying SAV bed effects on nutrient cycling. We observed lower water column concentrations of dissolved inorganic nitrogen and phosphorus (DIN and DIP) inside relative to outside the SAV bed during the summer. Sediment denitrification (mean N2-N flux in August = 46 μmol m−2 h−1) and plant nutrient assimilation (August rates =385 μmol N and 25 μmol P m−2 h−1) were mechanisms of nutrient removal. We also found that the physical structure of the bed decreased advection and tidal dispersion, resulting in increased water residence time that enhanced biologically mediated nutrient loss. These processes create conditions that enable SAV to outcompete other primary producers, as water column nutrient concentrations were low enough to limit algal growth and associated light attenuation, while sediment pore water concentrations were sufficient to satisfy SAV nutrient demand. These findings suggest that interactions between physical and biological feedback processes in SAV beds can play a key role in structuring shallow aquatic ecosystems.
KeywordsSubmersed aquatic vegetation Seagrass Feedbacks Biophysical Biogeochemical Interactions
We thank Laura Murray, Jonathan Garing, and Angela Cole for the help in collecting samples and Keith Williams and Bob Burkhardt from NorthBay Adventure for field support. WMK, JC, CG, and LS received support to carry out this research from Maryland Sea Grant under awards NA14OAR4170090 R/SV-2 and NA14OAR4170090 R/SD-1 from the National Oceanic and Atmospheric Administration, US Department of Commerce. CG was also supported by a postdoctoral fellowship from the National Socio-Environmental Synthesis Center (SESYNC) funded by the National Science Foundation (DBI-1052875). This paper is contribution no. 5343 of the University of Maryland Center for Environmental Science.
- Caffrey, J.M., M.C. Murrell, K.S. Amacker, J.W. Harper, S. Phipps, and M.S. Woodrey. 2014. Seasonal and inter-annual patterns in primary production, respiration, and net ecosystem metabolism in three estuaries in the northeast Gulf of Mexico. Estuaries and Coasts 37: 222–241. doi: 10.1007/s12237-013-9701-5.CrossRefGoogle Scholar
- Duarte, C. M. 1990. Seagrass nutrient content. Marine Ecology Progress Series 67:201–2017Google Scholar
- Gurbisz, C., W.M. Kemp, L.P. Sanford, and R.J. Orth. 2016. Mechanisms of storm-related loss and resilience in a large submersed plant bed. Estuaries and Coasts: 39. Estuaries and Coasts: 951–966. doi: 10.1007/s12237-016-0074-4.
- Havens, K.E., J. Hauxwell, A.C. Tyler, S. Thomas, K.J. McGlathery, J. Cebrian, I. Valiela, A.D. Steinman, and S.J. Hwang. 2001. Complex interactions between autotrophs in shallow marine and freshwater ecosystems: Implications for community responses to nutrient stress. Environmental Pollution 113: 95–107.CrossRefGoogle Scholar
- 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, E.D. Houde, D.G. Kimmel, W.D. Miller, R.I.E. Newell, M.R. Roman, E.M. Smith, and J.C. Stevenson. 2005. Eutrophication of Chesapeake Bay: Historical trends and ecological interactions. Marine Ecology Progress Series 303: 1–29. doi: 10.3354/meps303001.CrossRefGoogle Scholar
- Luhar, M., and H.M. Nepf. 2013. From the blade scale to the reach scale: A characterization of aquatic vegetative drag. Advances in Water Resources: 51. Elsevier Ltd: 305–316. doi: 10.1016/j.advwatres.2012.02.002.
- Lyubchich, V., B.R. Gray, and Y.R. Gel. 2015. Multilevel random slope approach and nonparametric inference for river temperature, under haphazard sampling. In Approaches to Climate Science, ed. Machine Learning and Data Mining, 137–145. London: Springer International Publishing. doi: 10.1007/978-3-319-17220-0_13.Google Scholar
- Nixon, S.W., J.W. Ammerman, L.P. Atkinson, V.M. Berounsky, G. Billen, W.C. Boicourt, W.R. Boynton, T.M. Church, D.M. Ditoro, R. Elmgren, J.H. Garber, A.E. Giblin, R.A. Jahnke, N.J.P. Owens, M.E.Q. Pilson, and S.P. Seitzinger. 1996. The fate of nitrogen and phosphorus at the land-sea margin of the North Atlantic Ocean. Biogeochemistry 35: 141–180.CrossRefGoogle Scholar
- Odum, H. T. 1956. Primary production in flowing waters. Limnology and Oceanography 1:102–117Google Scholar
- Orth, R.J., M.R. Williams, S.R. Marion, D.J. Wilcox, T.J.B. Carruthers, K.A. Moore, W.M. Kemp, et al. 2010. Long-term trends in submersed aquatic vegetation (SAV) in Chesapeake Bay, USA, related to water quality. Estuaries and Coasts 33: 1144–1163. doi: 10.1007/s12237-010-9311-4.CrossRefGoogle Scholar
- Owens, M.S., and J.C. Cornwell. 2016. The benthic exchange of O2, N2, dissolved nutrients using small core incubations. Journal of Visualized Experiments (114): e54098. doi: 10.3791/54098.
- Parsons, T. R., Y. Maita, and C. M. Lalli. 1984. A manual of chemical and biological methods for seawater analysis. Pergamon Press Inc., Oxford, 173 pp.Google Scholar
- Risgaard-Petersen, N., and L.D.M. Ottosen. 2000. Nitrogen cycling in two temperate Zostera marina beds: Seasonal variation. Marine Ecology Progress Series 198: 93–107. doi: 10.3354/meps198093.
- Rybicki, N.B., H.L. Jenter, V. Carter, R.A. Baltzer, and M. Turtora. 1997. Observations of tidal flux between a submersed aquatic plant stand and the adjacent channel in the Potomac River near Washington, D.C. Limnology and Oceanography 42: 307–317. doi: 10.4319/lo.1997.42.2.0307.CrossRefGoogle Scholar
- Testa, J. M., D.C. Brady, D.M. Di Toro, W.R. Boynton, J.C. Cornwell, and W.M. Kemp. 2013. Sediment flux modeling: Simulating nitrogen, phosphorus, and silica cycles. Estuarine, Coastal and Shelf Science: 131. Elsevier Ltd: 245–263. doi: 10.1016/j.ecss.2013.06.014.
- Waycott, M., C.M. Duarte, T.J.B. Carruthers, R.J. Orth, W.C. Dennison, S. Olyarnik, A. Calladine, J.W. Fourqurean, K.L. Heck, A.R. Hughes, G.A. Kendrick, W.J. Kenworthy, F.T. Short, and S.L. Williams. 2009. Accelerating loss of seagrasses across the globe threatens coastal ecosystems. Proceedings of the National Academy of Sciences of the United States of America 106: 12377–12381. doi: 10.1073/pnas.0905620106.CrossRefGoogle Scholar
- Welsh, D.T., M. Bartoli, D. Nizzoli, G. Castaldelli, S.A. Riou, and P. Viaroli. 2000. Denitrification, nitrogen fixation, community primary productivity and inorganic-N and oxygen fluxes in an intertidal Zostera noltii meadow. Marine Ecology Progress Series 208: 65–77. doi: 10.3354/meps208065.CrossRefGoogle Scholar