Influence from Hydrological Modification on Energy and Nutrient Transference in a Deltaic Food Web

Abstract

Alterations of hydrology are known to trigger changes in coastal ecosystems, such as the composition and abundances of local flora and fauna. It is less well known how these alterations lead to changes in nutrient and energy transfers in these systems. We used comparisons of stable isotope signatures (δ 13 C, δ 15 N, and δ 34 S) in the tissues of conspecific plants and animals collected on each side of the Mobile Bay Causeway to determine the extent to which the causeway may have altered energy and nutrient exchange between the Mobile-Tensaw Delta and upper Mobile Bay. While the δ 13 C signatures of most plants and animals varied irrespective of their location relative with causeway location, their δ 15 N and δ 34 S signatures were almost always more enriched south of the causeway, indicating significant alterations of trophic linkages within this estuarine food web. Dual isotope plots and mixing model analyses indicated that while terrestrial and floating plants were trophically important to consumers north of the causeway, submerged aquatic vegetation was more important to consumers south of the causeway. Although limited in spatial and temporal scale, our results preliminarily show that there are noteworthy differences in stable isotope signatures most likely due to the Mobile Bay Causeway altering energy and nutrient transference.

Oil carbon entered the coastal planktonic food web during the Deepwater Horizon oil spill

“…We employed δ 13 C as a tracer of oil-derived carbon incorporation into the lower marine food web across the middle and inner continental shelf. During June-August 2010, we followed two plankton size classes: the nominally 1 μm-0.2 mm 'small suspended particulate' and the >0.2-2 mm 'mesozooplankton' fractions, with the former considered likely food for the latter.…”

“…Since lipids are isotopically depleted and do not necessarily reflect time-integrated diet of organisms, variation in lipid content may introduce bias into stable isotope analyses. Established mathematical normalization techniques allow correction of δ 13 C values in lipid-rich samples, but preserve sample integrity for other analyses [7]. Here, bulk δ 13 C values in mesozooplankton were lipid-corrected according to [7], after comparison to C:N in mesozooplankton samples (figure 2(A).…”

“…Established mathematical normalization techniques allow correction of δ 13 C values in lipid-rich samples, but preserve sample integrity for other analyses [7]. Here, bulk δ 13 C values in mesozooplankton were lipid-corrected according to [7], after comparison to C:N in mesozooplankton samples (figure 2(A). Comparison of δ 13 C values to the C:N and relative C content (mg l −1 ) in suspended particulates indicated no correction was needed for the smaller fraction (figures 2(A) and (B)).…”

“…This sample was analyzed for δ 13 C at the University of Utah Stable Isotope Facility. Fresh Source Oil B (SOB) supplied by BP was collected on 22-23 May 2010, from the riser insertion tube on board the drill ship Enterprise.…”

“…To determine potential effects of freshwater discharge on δ 13 C, riverine discharge into Mobile Bay was estimated by adding daily discharge rates at two US Geological Survey gauging stations (http://waterdata.usgs.gov/usa/nwis/sw), the Coffeeville Dam on the Tombigbee River (#02469765) and the Claiborne Dam on the Alabama River (# 02429500). There is an estimated 5-10 d flow-dependent lag between readings at gauging stations and reference sites in Mobile Bay [9].…”