Nitrogen cycling in seagrass meadows

A large-scale seagrass seeding project at the Virginia Coast Reserve Long-Term Ecological Research Site has lead to the establishment of over 25 square kilometers of restored seagrass meadow since 2001. A primary focus of my dissertation was to measure how this shift from a bare, unvegetated state to a mature seagrass meadow affected nitrogen cycling. To achieve this goal, I measured a suite of nitrogen transformations in the meadow, including denitrification, fixation, burial, and assimilation, to construct a nitrogen budget for the restored meadow. I also made analogous measurements in unvegetated sediments, in order to compare the seagrass meadow budget to a bare sediment budget. My data show that on an annual scale, the seagrass meadow is a net sink for reactive nitrogen, due in part to high rates of nitrogen burial in the sediments. In comparison, the bare sediment is a net source of nitrogen to the surrounding waters. The restored meadow thus acts as an important filter for nitrogen inputs to the coastal bays.

I have presented portions of this work at the CERF 2015, CERF 2017, and ASLO 2017 meetings. A comparison of denitrification and DNRA in the restored seagrass meadow and unvegetated sediments is published in Marine Ecology Progress Series here. A full comparison of the seagrass and bare sediment nitrogen processes is published in Limnology and Oceanography here.

Conceptual diagram of nitrogen (N) cycle processes measured in the restored seagrass meadow.

Image of the restored seagrass meadow at the Virginia Coast Reserve