A BIODEGRADABLE POT TECHNIQUE, AND EMERGY ANALYSIS TO IMPROVE RESTORATION OUTCOMES OF POTAMOGETON PERFOLIATUS L.

Abstract

Potamogeton perfoliatus (L.) (P. perfoliatus), is a species of submersed aquatic vegetation (SAV) in mesohaline Chesapeake Bay that provides important ecosystem services but has been in decline. Efforts to restore its populations have met with mixed success. While the challenges to healthy SAV growth such as inadequate light for photosynthesis, poor water quality, and site disturbance have been well documented, studies using microcosms have failed to specifically examine other factors such as propagule type and seed storage duration, source population, plant growth response to a fully characterized substrate, and planting techniques, for the duration of an entire simulated growing season. Also, no studies have conducted an environmental cost accounting to assess the sustainability of a given restoration approach. This research investigated the growth and reproductive responses of P. perfoliatus propagules to various substrates and planting techniques; and conducted an emergy analysis case study, a type of environmental cost accounting, to compare two restoration techniques. P. perfoliatus net primary productivity and reproductive potential was highest when grown in sediment cores taken from SAV beds (~1.0gDW/m2/day, 18% stems with inflorescences), with peat/oyster shell being the next most desirable substrate choice for propagation (~0.86 gDW/m2/day, 4% stems with inflorescences). Seeds grown in biodegradable pots grew no differently than seeds grown in control polyethylene pots, or seeds planted by hand onto the bare sediment surface of the microcosm, (although hand-planting required multiple attempts to keep buoyant, germinated seeds in place). Seeds grown from harvests four years apart also showed no differences in yield (~0.56 gDW/m2/day). Biodegradable pots lost on average 60 percent of their mass over 12 weeks, and degraded more in brackish vs. fresh SAV bed sediments in the field. Emergy analysis indicated that planting seed-filled biodegradable pots resulted in 97% more area (m2) SAV bed restored than hand transplanting sods, and was more ecologically sustainable. These results indicate that appropriate substrates for propagation and restoration sites, and the ability to securely place propagules in the sediment, may be critical to P. perfoliatus establishment and success, thereby enhancing SAV habitat in Chesapeake Bay.