Phytoplankton community structure response to groundwater-borne nutrients in the Inland Bays, DE

We conducted a series of experiments, coupling seepage meters directly to phytoplankton enclosure experiments to determine the impacts of groundwater-borne nutrients on biomass and response in community structure of phytoplankton. To assess the impacts of groundwater-borne nutrients, we measured chlorophyll a concentrations as a proxy for overall biomass and used genetic sequencing techniques to characterize the phytoplankton community structure. Groundwater carried a high N load to the estuary with NO3- up to 295 µmol/L, and NH4 + up to 55 µmol/L. As a result treatment mesocosms had NO 3- concentrations up to 55.5 µmol/L and NH 4+ up to 4.0 µmol/L, while control mesocosms received filtered seawater, and were thus relatively low in nutrients (24.2 µmol/L NO3- and ∼2 µmol/L NH4 +). In June the highest chlorophyll a concentrations occurred after 3.5 days, with significant differences between control mesocosms (4.3±0.2 mg/L), groundwater amended mesocosms (7.0±0.6 mg/L), and mesocosms receiving groundwater across the sediment-water interface (10.9±0.2 mg/L). In August, biomass peaked after 3 days and showed larger variation across treatment groups with groundwater amended mesocosms reaching significantly higher values (36.6±2.0 mg/L) than mesocosms receiving groundwater across the sediment-water interface (18.7±4.8 mg/L), which showed significantly different values than both controls and phosphate amended mesocosms (11.9±0.7 and 9.9±0.2 mg/L respectively). Community gene sequence data showed that species assemblage was also impacted by availability of nutrients, with significant differences in community structure for mesocosms receiving nutrients vs control mesocosms in both June and August experiments. Several harmful algal species also proliferated in high nutrient treatments, including Cylindrotheca closterium, Karlodinium veneficum, Nitzschia ovalis, and Heterocapsa sp. Our study demonstrates the importance groundwater-borne nutrients play in structuring the phytoplankton community, and the potential impacts of nutrient loading through groundwater transport. More research is needed to further identify spatial and temporal differences in groundwater-borne nutrient discharge and response of phytoplankton community structure.

Grantor dc:publisher

University of Delaware

Year dc:date.issued

2016

Author dc:creator

• Torre, Daniel M.

DOI

https://doi.org/10.58088/qq3e-kr88

OAI identifier oai:identifier

oai:udspace.udel.edu:19716/21452