Spatial variations in Chlorophyll a, C, N, and P in a Louisiana estuary from 1994 to 2016

• Published in: Hydrobiologia 2019-05, Vol.834 (1), p.131-144
• Main Authors: Turner, R. Eugene, Swenson, Erick M., Milan, Charles S., Lee, James M.
• Format: Article
• Language: English
• Subjects: Biomedical and Life Sciences; Brackishwater environment; Chlorophyll; Chlorophyll a; Cyanobacteria; Denitrification; Dilution; Ecology; Estuaries; Estuarine dynamics; Eutrophic environments; Eutrophic rivers; Eutrophication; Freshwater; Freshwater & Marine Ecology; Freshwater lakes; Inland water environment; Lakes; Life Sciences; Mineral nutrients; Nitrogen; Nitrogen fixation; Nutrients; Offshore; Organic nitrogen; Phosphorus; Phytoplankton; Primary Research Paper; Rivers; Salinity; Spatial variations; Uptake; Water; Water analysis; Water column; Water sampling; Watersheds; Zoology
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1007/s10750-019-3918-7

Intense sampling of an estuary can reveal relative spatial changes that are significant irrespective of whether or not the estuary is eutrophic, micro- or meso-tidal, disturbed, or restored. This ‘waterscape’ perspective is analogous to a landscape perspective. We collected monthly water samples in the Barataria Basin watershed from 1994 to 2016 at 37 stations along a 129 km transect from 1 km offshore to a freshwater stream. The average Chlorophyll a (Chl) concentration from 267 trips was supported from both nitrogen-fixing cyanobacteria in a freshwater lake and partially from nutrients in seaward sources. Estuarine salinity was correlated with the discharge of the nearby Mississippi River. The main form of N was as organic nitrogen, not inorganic forms that recycle quickly, making changes in inorganic nitrogen concentration an unreliable indicator of net denitrification or uptake. The total nitrogen (TN) and total phosphorus (TP) concentrations declined with dilution towards the coast, but not because of denitrification. The phytoplankton standing biomass reflected the TN:TP ratio in the water column and there was a significant rise in the variability of Chl concentration at 2–6 psu, which was otherwise unremarkably constant. These waterscape patterns and cautionary interpretations may be common to other estuaries.