Loss and Restoration of Wild Celery (Vallisneria Americana) in the lower Hudson River

Edna Bailey Sussman Foundation Internship Report

December 2014

Lars Jonas Hamberg, MS Candidate

SUNY College of Environmental Science and Forestry

Background

The Hudson River in New York state has benefited from high abundance of the native submerged aquatic vegetation (SAV) V. americana (wild celery) improving dissolved oxygen levels in the river and providing habitat for aquatic life. Vallisneriaamericana, a native submerged aquatic species has made up the majority of the submerged aquatic vegetation (SAV) in the Hudson River, with all SAVs covering a total of 6% of the Hudson River and 18% of shallows in the river in the mid 1990’s (Nieder et al. 2004). V. americana is a dioecious, perennial, submerged aquatic freshwater plant, generally growing in thick beds in shallow waters. It has tape-like leaves that are submerged and rooted but can float on the surface.

The lower part of the Hudson River runs for 153 miles from Troy dam near Albany, NY to its outlet at New York City. The lower part of the Hudson River is a tidal estuary with 3-5 feet of tidal change twice daily. The lower Hudson is shallow for most part except for the shipping channel, creating conditions for large-scale growth of SAV. The river experienced a large scale loss (>90 %) of the plant in 2011 due to heavy rain events related to Hurricane Irene and Tropical Storm Lee. There has been little documented grow-back in 2012 and 2013 growing seasons. New York Department of Environmental Conservation (NY DEC) has outlined research on SAV restoration factors as one of the main research needs for restoration of the Hudson River (Miller 2013).

It is speculated that the 2011 loss may have been due to either scouring of the plants from bottom of the river, burial of plants and seed-beds from the increased amounts of sediment deposition or from lowered light conditions due to increased amount of suspended particles in water column (Daniel Miller and Stuart Findlay - personal communication). The hypothesis of burial of SAV in the Hudson River is based on the large amount of sediment washed into the river during the storm events. SAV rely on energy stored in reproductive structures (tubers) in the sediment to achieve enough stem and leaf growth to reach water with enough light for photosynthesis to take place.

SAV restoration, including for V. americana, has been conducted in multiple rivers in the United

States with multi-year projects ongoing by the Virginia Institute of Marine Sciences in Chesapeake Bay (Kenneth Moore - personal communication). One major factor of success has been herbivory protection, with experiments showing no regrowth of new seed-beds unless cages are set up to protect new seed-beds (Moore et al. 2010). With this in mind the lack of regrowth of SAV in the Hudson River in 2012 and 2013 may be hypothesised to be due to herbivory pressure on the few remaining plants. While a healthy ecosystem of SAV beds may have had enough growth to counter herbivory the SAV beds in the Hudson River that are already severely impacted by sediment burial may be experiencing increased herbivory pressure.

Proposed work

I proposed to work together with the Hudson River National Estuarine Research Reserve (HRNERR), a part of the National Estuarine Research Reserve program managed by NOAA and the New York Department of Environmental Conservation (NY-DEC), based at Norrie Point, NY. Together with these organisations and with the help of Cary Institute of Ecosystem Science (CIES) I proposed two experiments, one to test the ‘burial in sediment’ hypothesis both in greenhouse and river

Depth-in-sediment experiment

The ability for V. americana to re-sprout from asexually produced tubers will be tested in greenhouse as well as in the Hudson river by planting the tubers in different depths in sediment and observing for sprouting. Depths will be chosen based on the study by Rybicki and Carter (1986). Sediment will be taken from parts of the lower Hudson River that can be identified as having had V. americana growth earlier, samples from the sediment used will be defined. For the greenhouse experiment water will be taken from the lower Hudson River. The buried tubers will be observed for growth throughout the 2014 growing season and if possible measured.

Herbivory experiment

To test whether the lack of regrowth of V. americana could be due to herbivory pressure an exclusion experiment will be conducted in the lower Hudson River. A number of plots will be set up in the river with either a exclusionary cage, a control for the exclusionary cage or no structure at all. The exclusionary cage will prohibit larger herbivores from reaching the plants inside, the cage-control will control for factors unrelated to herbivory that the structure may impact such as flow or light conditions. Each plot will be planted with nursery-provided plant material and observed for growth and possible herbivory. If possible harvesting will be done at intervals to judge herbivory in the lab.

Work completed

For the depth in sediment experiment the greenhouse experiment was set up in the CIES greenhouses in Millbrook, NY. Four depths (5, 10, 20, 30 cm) were chosen and 10 tubers were planted for each depth and the pots were set in a large tub filled with water from the river. After two months no sprouting of any plants were observed. 15 tubers taken directly from the river and 15 from the nursery were planted at 2 cm depth as a ‘viability’ trial to test the viability of the nursery sourced tubers versus the tubers from the river.

The in-river part of the depth in sediment experiment was conducted outside Tivoli Bay, near Tivoli, NY. The wetland is part of HRNERR although our experiment was done in the mainstem of the river just outside the wetland (see map). 30 tubers sourced from the river were planted at 3 depths (2, 5 and 10 cm) in pots, the pots were then planted in clusters at our site, these were observed for sprouting mainly by feel (water being too turbid to observe visually). The pots were harvested at the end of the experiment and any plants were measured, dried and weighed.
For the herbivory experiment 12 plots of 4x4 feet were chosen with 4 exclusion cages (4x4x4 feet built from PVC pipe and chicken wire) and 4 cage controls (same as exclusion cages but with one side open) built from scratch and the 4 open plots marked with PVC pipe. The area was marked with buoys to warm boat-traffic. The cages were cleaned, maintained and repaired once a week during the summer, generally at low tide. 8 pots were planted in each plot with already sprouted V. americana. The pots were harvested in three subsequent harvests in end of July, end of August and mid-September. The harvested plants were measured, dried and weighed.

Preliminary results
In the depth in sediment study in the greenhouse the depth experiment yielded no results, there were no observations of sprouting. This may be due to 5 cm being too deep, or that the greenhouse temperature was too high. In the vitality experiment sprouting was observed both from nursery and river plants at about the same rate.

For the river experiment part four plants sprouted at 2 cm depth, 2 at 5 cm and none at 10 (see chart below.) This seems to indicate that burial by sediment is a possible reason for loss. As part of the work during the summer I also calculated the total amount of new sediment from the 2011 storm to 3 cm.

In the herbivory experiment no evidence of lowered mass (indicating herbivory pressure) was seen for the open and cage-control plots (see graph).

Future research

Data from the experiments will be used for my thesis and the results have been presented at a DEC hosted conference in October 2014. Further studies of the accumulated statistics will be done and the data will be used to create a dynamic model of the V. americana stock in the lower Hudson River and how it is impacted by storm events.

Acknowledgements

I would like to thank the Edna Bailey Sussman foundation as well as NY-DEC, HRNERR, CIES, and my advisors.

References

Rybicki, Nancy B., Dwilette G. McFarland, Henry A. Ruhl, Justin T. Reel, and John W. Barko. "Investigations of the availability and survival of submersed aquatic vegetation propagules in the tidal Potomac River." Estuaries 24, no. 3 (2001): 407-424.

Miller, Daniel E., 2013. Hudson River Estuary Habitat Restoration Plan. New York State Department of Environmental Conservation, Hudson River Estuary

Program.