Poplar Hill - Effect of Saltwater Intrusion on Nutrient Release
Kate Tully, Associate Professor, Department of Plant Science and Landscape Architecture, UMD
Alison Schulenburg, Agroecology Research Scientist, University of Maryland
As sea levels continue to rise and high tide flooding events increase in frequency, researchers and farmers alike are looking for solutions to adapt to and mitigate the effects of saltwater intrusion (SWI). This phenomenon alters nutrient cycling and damages crop yields. Some landowners on the Lower Eastern Shore of Maryland respond to SWI by taking land out of agriculture. For example, they may 1) attempt to remediate salt-damaged soils (e.g., planting switchgrass, Panicum virgatum), 2) restore native marsh grasses (e.g., planting saltmarsh hay, Spartina patens), or 3) abandon fields altogether (e.g., allow for natural recruitment of weeds). This study focused on the survival of target species under saltwater-intruded conditions and the potential for these plants to survive and alter cation concentrations (e.g. calcium [Ca], magnesium [Mg], potassium [K], and sodium [Na]) in soil. This work also examined the ability of each of these land management practices to reduce phosphorus (P) levels in soils and porewater, with the overall goal to benefit both the farming community and water quality in the Chesapeake Bay. As SWI encroaches and soil Na concentrations increase in coastal landscapes, P. virgatum exceeded all other species in biomass production and remediated soil cations over time. S. patens removal of cations from soil was significant, but did not increase over time, suggesting the species is able to co-regulate cations. Furthermore, we found that both remediation and restoration practices are efficient at taking up soil P and reducing porewater P concentrations through biomass P uptake. Therefore, if harvested, implementing these strategies may ultimately decrease the amount of P available to runoff into the Chesapeake Bay. Remediating or restoring farm fields affected by SWI by planting S. patens or P. virgatum has benefits for the soil by decreasing Na and P levels and communities by protecting coastlines. Results from this work will help inform state-level coastal management policies and determine optimal strategies for climate resilience.
Figure 1. Plant leaf tissue cation concentrations at three saltwater-intruded field sites on the Lower Eastern Shore of Maryland from year 1 (baseline) to year 4. The x-axis is year and the y-axis is plant leaf tissue Na (A,B,C), Ca (D,E,F), K (G,H,I), and Mg (J,K,L) in milligrams per gram. Section was not significant, so 0-5 m and 15-20 m from the ditch were averaged together and separated by treatment which is represented by colors. S. patens is blue, P. virgatum is green, and weeds are purple. Statistical significance (p-value) is indicated by symbols ^ = p<0.05, * = p<0.01, ** = p<0.005, *** = p<0.001.
Figure 2. Conceptual diagram of saltmarsh hay (Spartina patens; A-C), switchgrass (Panicum virgatum; D-F), and weeds (Panicum dichotomiflorum and Digitaria sanguinalis; G-I) aboveground biomass P and respective belowground total and available P pools from three depths (0-10, 10-20, and 20-30 cm) in year 1 (baseline) compared to year 4 at three saltwater-intruded field sites on the Lower Eastern Shore of Maryland. The x-axis is phosphorus pools in kilograms per hectare and the y-axis is depth in centimeters. Mehlich-3 available P is the darker bars and total P is the lighter bars. Change in Mehlich-3 P from year 1 to year 4 is in the middle of the bars, and the change in total P from year 1 to year 4 is in the bottom right corner of the bars; positive numbers (+) indicate an increase in P pools and negative numbers (-) indicate a decrease in P pools.