Chemistry of Surface Waters: Distinguishing Fine-Scale Differences in Sea Grass Habitats of Chesapeake Bay

We tested the hypothesis that the physical and chemical processes acting in sea grass habitats of the lower Chesapeake Bay are spatially structured and that dissolved elemental chemistry of sea grass–habitat surface waters have their own unique identity. We sampled surface waters from July to September 2001 in five sea grass habitats of the lower bay: Potomac, Rappahannock, York, Island (Tangier-Bloodsworth), and Eastern Shore. Dissolved Mg, Mn, Sr, and Ba concentrations were measured by sector field inductively coupled plasma–mass spectrometry. As expected, Mg, Sr, and Ba exhibited conservative behavior, but Mn exhibited nonconservative behavior along the salinity gradient. Spatial differences in the chemistry of surface waters over sea grass habitats were fully resolvable independently of time. Moreover, classification accuracy of water samples was low in Rappahannock, moderate in Potomac and Eastern Shore, and high in the York and Island habitats. The chemistry of York was distinct because of the effects of physical mixing, whereas Island chemistry was unique, potentially because of the influence of Coriolis acceleration and river discharges from the Susquehanna River. The results of this study show that sites so close to one another in physical space maintain distinct chemical differences. Many studies have shown that coastal ecosystems, such as estuaries, are characterized by large-scale spatial and temporal variability in terms of water quality parameters such as temperature, salinity, turbidity, and elemental chemistry. Livingston (1984) argued that slight water quality changes due to pollution, which are outside of the evolutionary experience of organisms, can cause alterations of habitat structure, energy, and species composition of estuarine communities. Macfarlane and Booth (2001) believed that physical and chemical differences that occurred naturally in sediments were the most important determinants in species assemblages among sites in the estuarine reaches of the Hawkesbury River in Australia. Most aquatic ecologists have focused on identifying sources and sinks of contami1 To whom correspondence should be addressed. Present address: Southwest Fisheries Sciences Center, La Jolla Shores Drive, La Jolla, California 92037 ([email protected]).