The Nitrogen Cycle: Connections to the Neuse River Estuary

Transcription

1 1 The Nitrogen Cycle: Connections to the Neuse River Estuary Alexandria G. Hounshell Doctoral Student Department of Marine Sciences University of North Carolina-Chapel Hill Abstract: Using the Neuse River Estuary, North Carolina as a study site, students will discuss sources of nitrogen to estuaries and the harmful impacts of nutrient loading to these systems. Students will use data from the Neuse River Estuary to calculate both past and present nitrogen loading and discuss trends in nitrogen loading to the estuary. The lesson will cumulate in a class wide discussion of best practices for individuals, farmers, and municipalities to reduce nitrogen loading to the Neuse River estuary. Note: This lesson plan is aimed at students who already have an understanding of the types of nitrogen present in the environment and how the different forms are transformed and cycled through the environment. A Nitrogen Cycle Background Information sheet is provided on dropbox that discusses key points students should understand before the lesson. Learning Objectives: 1. Identify sources of nitrogen to an estuary and describe where these sources originate. 2. Explain the link between nitrogen loading and eutrophication within an estuary. 3. Calculate nitrogen loading to an estuary and discuss trends in nitrogen loading. 4. Synthesize key points of a primary scientific literature source. 5. Determine ways to reduce nitrogen loading to an estuary. 6. Communicate to stakeholders why nitrogen reduction is necessary for the health and sustainability of an estuary. Requirements: Appropriate grade level: High school, 9-12 th grade Approximate time: 2, 45 minute class periods, plus optional homework assignment(s) Group size: Any class size, with students arranged in pairs or groups of three. Setting: Indoors Resources: Students: Pen or pencil, calculator, Optional: in class computer access Educator: Powerpoint capabilities Documents: Nitrogen Cycle_Figures Worksheet 1* Lebo et al., 2011 Primary Literature Questions* * Key provided Case Study: The Neuse River Estuary 1. Ask students if they have ever been to the Neuse River or the Neuse River estuary (Nitrogen Cycle_Figures, Slide 2). Have they ever seen dead fish along the river or estuary? Tell students there have been seasonal fish kills along the banks of the Neuse River estuary. Today, students will learn one potential reason for these fish kills. See: (accessed: November 2, 2014) for news story related to the fish kills. These fish

2 2 kills are often yearly occurrences, typically during late summer and fall, and more recent examples may be found with a quick google search. 2. Introduce the Neuse River Estuary as a study site (Nitrogen Cycle_Figures, Slide 3): - Located in eastern North Carolina. The watershed extends from just northwest of Raleigh and flows towards the coast. The estuary begins about New Bern and extends to the Pamlico Sound. Question: Where are we located and do we fall within the Neuse River estuary watershed? Answer: Dependent on location. 3. Discuss sources of nitrogen to estuaries (Worksheet 1, Figure 1 or Nitrogen Cycle_Figures, Slide 4). The figure was originally designed for Puget Sound, Washington, but can be applied to systems closer to home. In recent years, the concentrations of these sources have increased, leading to increased loading of nitrogen to estuaries. Question: Can anybody think of estuaries in North Carolina (other than the Neuse River) that might be impacted by human, agricultural, and industrial sources of nitrogen? Possible answers: Pamlico Sound, Tar/Pamlico River, New River, Cape Fear River, etc. 4. Complete Part I of Worksheet 1. Divide students into pairs or groups of 3. The goal of this activity is to differentiate between natural and anthropogenic sources of nitrogen. Of the anthropogenic sources, have students identify what stakeholder would be responsible for these sources (individual, municipality, agriculture, or industrial). Discuss answers as a class. 5. Discuss important sources of nitrogen to the Neuse River estuary (Nitrogen Cycle_Figures, Slide 5). Show students the figure of land use in the Neuse River estuary. Question: Ask students to think about a list of sources of nitrogen to the estuary based on the landuse and the nitrogen sources they learned about above. Brainstorm a list on the board. Answer (Nitrogen Cycle_Figures, Slide 6): a. Agriculture fertilizer from crops b. Concentrated animal feeding operations (CAFO s) produce lots of animal waste high in nitrogen. In North Carolina, this is mainly from chicken and pigs. c. Urban run-off from Raleigh, Cary, Goldsboro, Kinston, New Bern d. Discharge from Wastewater treatment plants e. Atmospheric deposition 6. Discuss impacts of increased nitrogen loading due to population growth, urbanization, and agriculture (Nitrogen Cycle_Figures, Slide 7). - Most estuaries are nitrogen limited, such that, if nitrogen is added to these systems, there is an increase in phytoplankton biomass. - The increase in phytoplankton biomass leads to reduced light attenuation through the water column (phytoplankton bloom shades the underlying water column). Question: What impact would this have on the sea grasses growing on the bottom? Answer: The shading would reduce the growth of the bottom sea grasses as less light is available for photosynthesis. - As the phytoplankton bloom dies and sinks, bacteria re-mineralize the phytoplankton biomass, a process that uses oxygen. This generates hypoxia where oxygen levels in the water column are too low to support life.

3 3 Question: What impact would reduced oxygen have on fish and other organisms living in the water column? Answer: This could lead to fish kills, like those in the Neuse River estuary. - This process of large phytoplankton blooms leading to hypoxia and fish kills is a process called eutrophication. 7. How do we know nutrient concentrations have been changing? The Neuse River Estuary has been monitored for about 30 years. This results in a long term record of physical (temperature, salinity, turbidity), chemical (nutrients, including NH 4+, NO 3-, and TKN (Total Kjehldahl Nitrogen (TKN)) = measure of total nitrogen), and biological (chlorophyll-a, a proxy for phytoplankton) parameters. This allows scientists to look at long term trends to see how the estuary is changing due to changing environmental conditions (land use, climatic variations such as increased droughts or flood events). See: for more information. If students have access to computers in the classroom, this would be a good site for them to explore and learn about the parameters measured in the Neuse River Estuary and how the data are being used. 8. Calculate nitrogen loading to the estuary (Nitrogen Cycling_Figures, Slide 8). Start by explaining how to calculate nutrient loading to the estuary. a. First define nutrient loading: calculation of the mass of a nutrient (in this case nitrogen) over time to a given water body. This is a good way to monitor the change in nitrogen concentration being introduced to an estuary over time. b. This can be found by the equation (units= mass/time): Loading = Q f [NO 3 ] Where: Q f = discharge from the Neuse River to the estuary (found in this example as Flow averages for Streets Ferry Bridge) [NO 3- ] = average concentration of NO 3- -N at Streets Ferry Bridge Students will calculate N-loading for and at mid-flow levels (Worksheet 1, Tables 1 and 2 or Nitrogen Cycle_Figures, Slides 9 and 10). Students can either work in pairs to calculate both values or the class can walk through one calculation together (period from ) and then individually ( ). Students will be asked if this is the trend they expected based on what they know about N-sources and loading in recent years. See Worksheet 1 key for examples/answers. 9. As a class discuss why or why not this decrease in Nitrogen loading is expected. See Worksheet 1 key for answers. 10. Why did nitrogen loading decrease? (Nitrogen Cycle_Figures, Slide 11). In 1999 a Total Maximum Daily Load (TMDL) was introduced for the Neuse River Estuary. Meaning, reductions in NO 3 - and NH 4 + where mandated for the watershed, involving individuals, farmers, and municipalities. First: help orient students to the graph:

4 4 - SFB = Streets Ferry Bridge, which for this monitoring program, is defined as the start of the Neuse River Estuary. - TN = Total Nitrogen - Nitrogen is expressed as a percent difference from a baseline defined for the period from (+) percent indicates concentrations above the baseline and ( ) percent indicates concentrations below the baseline. The shaded area represents the 95% confidence interval for these calculations. - 3 types of nitrogen are plotted: TKN (measure of organic nitrogen + ammonium) NO 3- /NO 2 - (nitrate and nitrite) Total nitrogen (organic nitrogen + ammonium + nitrate + nitrite) - The baseline was the total maximum daily load (TMDL) calculated in the period. A 30% reduction from the baseline was mandated for the entire watershed (point out target line). Question: Has any form of nitrogen reached this target percent? Answer: No, nitrogen is still above the mandated level. Question: What does this mean for future reductions? Answer: More reductions are necessary to reach the mandated target. Question: Is there a type of nitrogen that has increased over time? Decreased? Answer: Yes, TKN has increased while nitrate/nitrite has decreased. This means that while nitrate/nitrite has decreased due to the introduction of TMDL s, the amount of organic nitrogen has increased. This has unknown consequences for the estuary (research is being conducted!). 11. Primary literature (optional in class or homework assignment): Either have all students read the Introduction for Lebo et al., 2011 (page 1-2 only) or divide the 4 paragraphs among students. The introduction summarizes the harmful effects of nutrient loading to estuaries, possible solutions to reduce nutrient loading (including the measures taken within the Neuse River Estuary), and why assessing nutrient loading to estuaries is difficult. A list of focus questions (and key) is attached (Primary Literature Questions). A copy of the primary reference is on dropbox (Lebo et al., 2011) and an annotated copy (Annotated Lebo et al., 2011). 12. Synthesis of information and class discussion: in pairs, have students brainstorm (and research if computers are available in the classroom) additional ways to reduce nitrogen loading to the estuary. Then, have a full class discussion about best practices for individuals, farmers, industry, and municipalities to reduce nitrogen to the Neuse River estuary (see Worksheet 1 for key). Final product and assessment: Have students generate a 1 page brochure for a single stakeholder (individual, farmer, industry, or municipality) explaining why nitrogen reduction is necessary for estuarine health and ways the stakeholder can reduce nitrogen to the estuary. NC Essential Science Standards: Bio.2.1.1; Bio.2.2.1; EEn Common Core Math Standards: OA6.1.2 Next Generation Science Standards: HS-LS27; HS-ESS3-6 Notes: Feel free to contact me (or have students contact me) via or twitter with any questions about the nitrogen cycle, nitrogen in estuaries, working in the marine sciences, graduate school, college, or any other questions you all come up with. I would also appreciate any and all feedback. I hope this is the first of many SciREN activities and am always looking to improve and expand my lesson plans!

5 5 Appendices: Worksheet 1, Worksheet 1 Key, Primary Literature Questions, Primary Literature Key, Nitrogen Cycle_Figures, Nitrogen Cycle Background Information Helpful references (with annotations): Harrison, J. (2014). The nitrogen cycle: Of microbes and men. Retrieved November 2, 2014, from - Overview of the processes in the nitrogen cycle and some information on anthropogenic sources of nitrogen to ecosystems. Honeycutt, J. (2014), Fish kill: Area of Neuse river banks covered in dead menhaden. Sun Journal. Retrieved November 2, 2014, from - Newspaper article reporting fish kills along the Neuse River estuary from October 16, Joyce, K. Nitrogen cycle. Retrieved November 2, 2014, from - Interactive and more detailed version of the marine nitrogen cycle. Good for students who want more detailed information. Lebo, M. E., Paerl, H. W., & Peierls, B. L. (2012). Evaluation of progress in achieving TMDL mandated nitrogen reductions in the Neuse river basin, North Carolina. Environmental Management, 49, Good source of primary literature on nitrogen loading to the Neuse River Estuary over time. Paper is available on the SciREN drop box as a resource. MODMON: The Neuse river estuary modeling and monitoring program. Retrieved November 2, 2014, from - Information on the Neuse River Monitoring program (MODMON). Good resource for becoming familiar with the monitoring program and the data the program produces. Washington State Department of Ecology. (2011). Sources and pathways of the nitrogen in Puget Sound. Retrieved November 2, 2014, from - Good website for an overview of the nitrogen cycle from how sources enter the estuary and from where. Designed for Puget Sound in Washington State but can be applied to the Neuse River. If the students have access to computers in the classroom, it may be helpful to have students explore the website when discussing sources of nitrogen to estuaries. Also a good resource for students when generating their brochure.

6 6 Worksheet 1: Case Study The Neuse River Estuary: Name: Part I: First identify if each of the nitrogen sources to an estuary are from anthropogenic or natural processes. If the process is anthropogenic, then identify what stakeholder is responsible for the nitrogen source (farmer, individual, municipality, or industry). A stakeholder is a group or individual who has an impact on the estuary or whose livelihood is connected to the services provided by the estuary. Services include using the estuary as a drinking water source, recreational use, or as fishing grounds. Nitrogen Loading Figure 1: Image explaining the sources of nitrogen to an estuary ( Natural or anthropogenic source? Stakeholder Agricultural Sources: Natural Sources: Atmospheric Nitrogen: Oceanic Nitrogen: Wastewater treatment plans: Urban Sources: Marine Sediments: Septic Systems:

7 7 Part II: Nutrient Loading to the Neuse River: Calculate Nitrogen loading as NO 3- -N to the Neuse River estuary at mid-flow levels for the period of and at Streets Ferry (SFB) using the following two tables. Convert units to metric tons/yr and make sure answers are in correct significant figures. The following conversions may be useful: 1 m 3 = 1000 L 1 metric ton = 1,000,000 g Table 1: Flow values for several monitoring locations in the Neuse River and Neuse River Estuary (Lebo et al., 2011). Table 2: Average NO 3-N and TKN concentrations (mg/l) at Streets Ferry (SFB) (Lebo, el al., 2011).

8 Nitrogen Loading calculation: Nitrogen Loading calculation: 3. Is this the result you expected based on what you know about Nitrogen loading in recent years? Why or why not?

9 9 Part III: Brainstorm and research: List possible ways to reduce nitrogen for each stakeholder discussed (individual, farmer, municipality, industry): Part IV: Final Assessment: Generate a 1-page brochure for one of the stakeholders discussed above. Include what the stakeholder can due to reduce nitrogen inputs to the estuary and why nitrogen reduction is necessary for the health of the Neuse River Estuary. Helpful resources:

10 10 Primary Literature Questions: Lebo et al., 2011 Citation: Lebo, M. E., Paerl, H. W., & Peierls, B. L. (2012). Evaluation of progress in achieving TMDL mandated nitrogen reductions in the Neuse river basin, North Carolina. Environmental Management, 49, 253. Directions: Read the Introduction (page 1 and 2) of the Lebo et al., 2011 paper provided. The following questions are intended to help guide the reading. 1. What harmful effects of nutrient loading does the paper describe? 2. What solution do the authors propose to help reduce the harmful effects of nutrient loading to the Neuse River estuary? 3. What controls the delivery of nutrients to the estuary both overland and within the aquatic environment? 4. What makes assessing nutrient loading to an estuary difficult? 5. What strategies were used to control eutrophication within the Neuse River Estuary? 6. What source contributed the highest percent of nitrogen to the estuary? 7. What did the scientists and legislators propose to reduce nitrogen loading to the estuary? What stakeholders were involved and what were they required to do?

11 11 Worksheet 1: Case Study The Neuse River Estuary: Name: KEY Part I: First identify if each of the sources of nitrogen to an estuary are from anthropogenic or natural sources. If the process is anthropogenic, then identify what stakeholder is responsible for this nitrogen source (farmer, individual, municipality, or industry). A stakeholder is a group or individual who has an impact on the estuary or whose livelihood is connected to the services provided by the estuary. This includes the estuary as a drinking water source, recreation use, or as fishing grounds. Nitrogen Loading Image courtesy of: Natural or anthropogenic source? Stakeholder Agricultural Sources: Anthropogenic Farmer Natural Sources: Natural Atmospheric Nitrogen: Anthropogenic and Natural Individuals and Industry Oceanic Nitrogen: Natural; for Neuse this could be from the Pamlico Sound Wastewater treatment plans: Anthropogenic Municipalities Urban Sources: Anthropogenic Individuals and Municipalities Marine Sediments: Natural Septic Systems: Anthropogenic Individuals

12 12 Part II: Nutrient Loading to the Neuse River: Calculate Nitrogen loading as NO 3- -N to the Neuse River estuary at mid-flow levels for the period of and using the following two tables. Convert units to metric tons/yr and make sure answers are in correct significant figures. The following conversions may be useful: 1 m 3 = 1000 L 1 metric ton = 1,000,000 g Tables courtesy of Lebo, et al., Nitrogen Loading calculation: Units conversion: 0.82 mg L m3 mg m3 (76.8 ) = s L s

13 mg m 3 L s x 1000 L 1 m 3 x 60 s 1 min metric ton 3 = 2. 0x10 year 60 min 24 hr x x 1 hr 1 d x 365 d 1 yr x 1 g 1 metric ton x 1000 mg 1,000,000 g Nitrogen Loading calculation: Units conversion: mg m 3 L s 0.59 mg L x 1000 L 1 m 3 x 60 s 1 min metric ton 3 = 1. 4x10 year m3 mg m3 (76.8 ) = s L s 60 min 24 hr x x 1 hr 1 d x 365 d 1 yr x 1 g 1 metric ton x 1000 mg 1,000,000 g 3. Is this the result you expected based on what you know about Nitrogen loading in recent years? Why or why not? No, this is not expected. Based on what we ve learned, nitrogen loading has increased in recent years, but these calculations indicate there has been a decrease in nitrogen for the Neuse River. Part IV: Brainstorm and research: List possible ways to reduce nitrogen for each stakeholder discussed (individual, farmer, municipality, industry): Individual: reduce (or eliminate) use of fertilizer (fertilizer contains NO 3 - and NH 4 + that can be washed form lawns to waterways). Farmer: reduce use of fertilizer (see above). Control or reuse animal waste (animal waste is a reactive form of organic nitrogen). This is an important issue for the Neuse River where there has been drastic growth in concentrated animal operations in recent years. Municipality: can enact stricter regulations on nitrogen released from sewage treatment plants (releases potentially reactive forms of nitrogen; necessary to enact stricter regulations before sewage wastewater can be released to the environment). Reduce use of fertilizer at parks and county lawns. Increase the amount of permeable surfaces in towns (this allows water to percolate through the soil where microbes can convert reactive nitrogen into unreactive forms in the process of denitrification). Industry: enact stricter regulations on wastewater released from industry sources. This can be beneficial for with respect to nitrogen and other nutrients/pollutants. Part V: Final Assessment: Generate a 1-page brochure for one of the stakeholders discussed above. Include what the stakeholder can due to reduce nitrogen inputs to the estuary and why nitrogen reduction is necessary for the health of the Neuse River Estuary. Helpful resources:

14 14 Primary Literature Questions: Lebo et al., 2011 Citation: Lebo, M. E., Paerl, H. W., & Peierls, B. L. (2012). Evaluation of progress in achieving TMDL mandated nitrogen reductions in the Neuse river basin, North Carolina. Environmental Management, 49, 253. Directions: Read the Introduction (page 1 and 2) of the Lebo et al., 2011 paper provided. The following questions are intended to help guide the reading. 1. What harmful effects of nutrient loading does the paper describe? Paragraph 1: lower productivity at all trophic levels, pervasive algal blooms including toxic species, bottom water hypoxia and anoxia, fish kills, and habitat loss. 2. What solution do the authors propose to help reduce the harmful effect on nutrient loading to the Neuse River estuary? Paragraph 1: Nitrogen and phosphorus loading to the estuary must be reduced (phosphorus is another macronutrient phytoplankton need to fix biomass). 3. What controls the delivery of nutrients to the estuary both overland and within the aquatic environment? Paragraph 2: Landscape controls include: amount, timing, and composition of fertilizer; location and extent of land use change; magnitude and location of rainfall; and storm water controls. And in stream controls: sedimentation and re-suspension; biological uptake; and denitrificaiton. 4. What makes assessing nutrient loading to an estuary difficult? Paragraph 2: Climatic variability, including droughts, hurricanes, and flood events, make assessing nutrient loading difficult. 5. What strategies were used to control eutrophication with in the Neuse River Estuary? Paragraph 3: First legislators enacted a Phosphorus detergent ban in addition to reductions in phosphorous point sources. This led to a reduction in freshwater algal blooms in the lower river/upper estuary, but did not reduce algal blooms and eutrophication in the lower estuary. Legislators later enacted a 30% reduction in nitrogen loading to the estuary. 6. What source contributed the highest percent of nitrogen loading to the estuary? Paragraph 4: Cropland contributed 67% of the nitrogen loading to the estuary. 7. How did the scientists and legislators propose to reduce nitrogen loading to the estuary? What stakeholders were involved and what were they required to do? Paragraph 4: Municipalities and counties were required to develop storm-water management plans to reduce nitrogen loading; agriculture was required to reduce 30% of its nitrogen loading through best management practices; atmospheric deposition was assumed to decrease due to the Clean Water Act that introduced legislation to reduce reactive nitrogen forms in the atmosphere; and protection of riparian buffers in the watershed were mandated to reduce nitrogen loading from forested areas.