Evaluating sediments as an ecosystem service in western Lake Erie through quantification of nitrogen cycling pathways

Lake Erie experiences annual cyanobacterial harmful algal blooms (HABs), comprised mostly of non-nitrogen-fixing Microcystis, due to excess nitrogen (N) and phosphorus (P) inputs (eutrophication). Lake Erie\u27s watershed is mostly agricultural, and fertilizers, manure, and drainage practices contribute to high nutrient loads. This study aimed to clarify the role of Lake Erie sediments in either exacerbating or mitigating conditions that fuel HABs via recycling and/or removal, respectively, of excess N and P. Sediment-water interface N dynamics were evaluated in low HAB (2016, dry) and high HAB (2017, wet spring and early summer) years. Intact sediment cores and overlying water were collected in the western basin of Lake Erie during the ice-free seasons in 2016 and 2017. Cores were incubated in a continuous-flow system with either no isotope addition (unamended control), a 15NO3- tracer, or a 15NH4+ tracer to help distinguish between N sinks (denitrification and anammox), N links (e.g., DNRA), and N sources (N2 fixation). Sediments were a net source of NH4+ (29.4 ± 7.41 μmol N m-2 hr-1) and ortho-phosphate (2.19 ± 0.52 μmol P m-2 hr-1) to the water column across all sampling sites and times. Net N2 fluxes reflected net N2 fixation (i.e., N2 influx) in spring 2016 and 2017, then switched to net denitrification (i.e., N2 efflux), the primary N removal mechanism, later in the season. On average, western basin sediments were a net N sink (-77.6 μmol N m-2 hr-1), suggesting that the sediments perform a valuable ecosystem service. Extrapolated to the entire western basin surface area, and considering Maumee and Detroit River discharges, western basin sediments can remove approximately 28.9 percent of the average annual total N load. However, denitrification rates were lower during the more severe bloom year (2017) than in 2016, suggesting that large blooms, similarly to high N loading, can inhibit the capacity of sediments to perform that ecosystem service. To mitigate HABs in eutrophic systems, such as Lake Erie, management efforts emphasizing reduction of non-point, agricultural sources of both N and P are necessary because high nutrient loads support larger, more toxic HABs, which limit the capacity of sediments to remove N via denitrificatio

Evaluating sediments as an ecosystem service in western Lake Erie through quantification of nitrogen cycling pathways

Lake Erie experiences annual cyanobacterial harmful algal blooms (HABs), comprised mostly of non-nitrogen-fixing Microcystis, due to excess nitrogen (N) and phosphorus (P) inputs (eutrophication). Lake Erie\u27s watershed is mostly agricultural, and fertilizers, manure, and drainage practices contribute to high nutrient loads. This study aimed to clarify the role of Lake Erie sediments in either exacerbating or mitigating conditions that fuel HABs via recycling and/or removal, respectively, of excess N and P. Sediment-water interface N dynamics were evaluated in low HAB (2016, dry) and high HAB (2017, wet spring and early summer) years. Intact sediment cores and overlying water were collected in the western basin of Lake Erie during the ice-free seasons in 2016 and 2017. Cores were incubated in a continuous-flow system with either no isotope addition (unamended control), a 15NO3- tracer, or a 15NH4+ tracer to help distinguish between N sinks (denitrification and anammox), N links (e.g., DNRA), and N sources (N2 fixation). Sediments were a net source of NH4+ (29.4 ± 7.41 μmol N m-2 hr-1) and ortho-phosphate (2.19 ± 0.52 μmol P m-2 hr-1) to the water column across all sampling sites and times. Net N2 fluxes reflected net N2 fixation (i.e., N2 influx) in spring 2016 and 2017, then switched to net denitrification (i.e., N2 efflux), the primary N removal mechanism, later in the season. On average, western basin sediments were a net N sink (-77.6 μmol N m-2 hr-1), suggesting that the sediments perform a valuable ecosystem service. Extrapolated to the entire western basin surface area, and considering Maumee and Detroit River discharges, western basin sediments can remove approximately 28.9 percent of the average annual total N load. However, denitrification rates were lower during the more severe bloom year (2017) than in 2016, suggesting that large blooms, similarly to high N loading, can inhibit the capacity of sediments to perform that ecosystem service. To mitigate HABs in eutrophic systems, such as Lake Erie, management efforts emphasizing reduction of non-point, agricultural sources of both N and P are necessary because high nutrient loads support larger, more toxic HABs, which limit the capacity of sediments to remove N via denitrificatio

The role of internal nitrogen loading in supporting non-N-fixing harmful cyanobacterial blooms in the water column of a large eutrophic lake

Western Lake Erie cyanobacterial harmful algal blooms (cyanoHABs) occur every summer as a result of anthropogenic nutrient loading. Although the physiological importance of nitrogen (N) in supporting bloom biomass and toxin production is established, the role of internal N recycling in the water column to support bloom maintenance is not as well understood. Over three field seasons (2015–2017), we collected water from western Lake Erie and employed bottle incubations with 15N-ammonium ((Formula presented.)) enrichments to determine (Formula presented.) regeneration and potential uptake rates in the water column. Potential (Formula presented.) uptake rates followed spatial and seasonal patterns, with greatest rates measured nearest the Maumee River inflow and during peak bloom months (August and September). Regeneration followed a similar spatial pattern but was greatest in early summer (June and July) and supported ~ 20–60% of potential (Formula presented.) demand during the height of the bloom. Basin-wide internal (Formula presented.) regeneration during the April–October period could supply (Formula presented.) at 60–200% of annual external N loading to the western basin. These results help explain how non-N-fixing cyanoHABs in Lake Erie and other large, eutrophic lakes continue producing biomass and N-rich toxins long after spring nutrient loads are exhausted or transported to other areas. Internal N loads are ultimately driven by external N loads; in low precipitation years, external nutrient loads result in smaller blooms, producing less substrate for subsequent internal N loads. Overall, these findings, along with others, confirm that both internal and external N loading must be considered when evaluating cyanoHAB management strategies

Glen Helen and Little Miami River Water Quality Fall 2015

Service Learning Intensive (SVI) - a teaching and learning pedagogy that engages faculty, students, and community members in a partnership to achieve academic learning objectives, meet community needs, promote civic responsibility, and reflect on the learning experience. More specifically, the objectives for this course are for students to: Apply environmental chemistry concepts learned in the classroom to the interpretation environmental analysis results Use Good Laboratory Practice (GLP) through the use of Standard Operating Procedures (SOPs) and EPA methods for the analysis of metals, anions, dissolved oxygen, pH, temperature, conductivity, ammonia, and turbidity Follow up on previous years’ results showing elevated E. coli and nitrates at some sites Present results to key stakeholders in the Village of Yellow Springs and Greene County Perform residential well sampling Complete periodic written reflections to tie classroom, laboratory, field, and community service experiences togethe