Nutrient cycling in Salt Creek

Drew Tyre Author

07/19/2018 Added

24 Plays

Description

In this lab we examine how nutrient concentrations evolve as water in Salt Creek flows through Lincoln

Searchable Transcript

Search:

[00:00:04.660]So this week, we're getting ready
[00:00:05.890]to go out and look at water quality along Salt Creek,
[00:00:09.980]which is the big creek that runs
[00:00:11.290]right through the middle, the middle of Lincoln.
[00:00:16.690]Water quality's really quite important,
[00:00:19.940]and it's affected by all of the things
[00:00:22.840]that take place upstream of where you are.
[00:00:25.180]So one of the things that's sort of a truism
[00:00:27.150]in the water quality world
[00:00:28.400]is that everybody lives downstream from something.
[00:00:32.770]And so the things that happen up here in the mountains
[00:00:37.200]and across all these fields affect everyone
[00:00:39.710]who's living down here on the coastline.
[00:00:43.370]But people who are living in,
[00:00:46.330]there we go, getting better at this,
[00:00:47.830]people who are living in the middle of the watershed
[00:00:49.500]are still downstream from fields up here.
[00:00:53.010]So we all live downstream,
[00:00:54.600]we should all make care, then, about clean water.
[00:00:58.847]And one of the things about ecosystem ecology
[00:01:01.230]is that those streams, those rivers and wetlands
[00:01:05.740]are all ecosystems, and one of the things they provide are,
[00:01:10.290]the ecosystems services is regulating
[00:01:12.710]and cleaning up the pollution that we produce.
[00:01:16.110]And so part of what this lab is about
[00:01:17.830]is trying to get a handle
[00:01:19.470]on exactly how those ecosystems do that
[00:01:24.730]for at least one kind of pollutant,
[00:01:26.760]which is a very big problem in North America.
[00:01:31.210]Here's a map of the Salt Creek Watershed
[00:01:34.470]as it exists (grunts) there, right?
[00:01:39.420]So there's Lincoln, that's the confluence
[00:01:41.990]with Oak Creek right there.
[00:01:43.700]So this is the South Salt Creek Watershed,
[00:01:50.200]all the way down to the bottom corner
[00:01:52.410]of Lancaster County out here, all the way, oops, up here.
[00:01:58.540]This is all area that ends up draining
[00:02:00.430]down into this one spot in Lincoln.
[00:02:05.920]And so if we go just a little bit down Salt Creek
[00:02:10.160]to where it cuts across Pioneers Boulevard
[00:02:12.560]in southwest Lincoln, which is where we'll start,
[00:02:16.930]that's water that's pretty unaffected by urban runoff.
[00:02:20.070]That's rural runoff, there's still
[00:02:22.110]a lot of things going on there from rural runoff,
[00:02:24.380]but it isn't really impacted by the city yet.
[00:02:27.800]Whereas if we come out on this side of Salt Creek,
[00:02:30.900]downstream of the confluence from Oak Creek,
[00:02:33.890]we're gonna be getting a lot of effects of urban runoff,
[00:02:37.850]and in particular Lincoln's wastewater treatment plant
[00:02:40.860]is right about there, okay?
[00:02:42.680]So that'll become important in a little bit.
[00:02:48.020]One of the things that we end up putting
[00:02:50.430]in a lot of our water is nitrogen.
[00:02:54.380]It comes from lots of different places, plants,
[00:02:58.030]some kinds of plants fix nitrogen from the atmosphere.
[00:03:01.460]But a lot of what we put into our water
[00:03:04.160]comes from either wastewater treatment
[00:03:06.190]or from agricultural runoff.
[00:03:09.650]And so what we're interested in here
[00:03:11.980]is what's actually called the nitrogen cycle.
[00:03:13.980]Nitrogen moves through ecosystems in a variety of ways,
[00:03:17.710]and so our atmosphere is about 70% nitrogen,
[00:03:21.750]I think, something along those lines,
[00:03:25.420]and that's nitrogen gas, N2.
[00:03:28.490]So there's all sorts of bacteria, then,
[00:03:31.710]that help us out here.
[00:03:32.670]So nitrogen-fixing prokaryotes that are symbiotic
[00:03:36.720]with various plants can convert that into ammonia.
[00:03:43.420]And ammonia is a kind of nitrogen that plants can use,
[00:03:47.470]and so you get, this is a crude depiction
[00:03:51.480]of a soybean plant I think,
[00:03:53.375]so basically the plants are going to be taking up
[00:03:57.830]that ammonia and then using it for growth.
[00:04:00.144]They need, that's how they build proteins.
[00:04:02.850]Nitrogen is a critical component of protein,
[00:04:05.100]and so you get proteins in plants
[00:04:07.660]by them using up nitrogen either as ammonia
[00:04:11.450]or nitrate from the soil.
[00:04:15.510]Okay, so we got ammonia in our soil now from our,
[00:04:19.580]from either from fertilizer or from plants.
[00:04:22.770]Then there are another two groups of bacteria.
[00:04:25.910]The first group of bacteria
[00:04:27.400]converts ammonia into nitrite, NO2 minus,
[00:04:35.800]and nitrite is actually quite toxic
[00:04:38.880]to a lot of different kinds of species,
[00:04:41.340]but doesn't usually stay in this form very long.
[00:04:44.870]There's that second group of bacteria
[00:04:46.790]that then converts nitrite quite quickly to nitrate,
[00:04:50.660]so it adds, it oxidizes, this is an oxidation reaction,
[00:04:53.650]it's adding oxygen, and so it adds
[00:04:57.010]another oxygen atom to that.
[00:04:58.620]Nitrate is another kind of nitrogen that plants can use,
[00:05:02.950]and so then that can get taken up
[00:05:05.090]and converted into plant tissue.
[00:05:09.960]There's another couple of pathways involved here,
[00:05:13.000]there we go, final pathway from nitrate
[00:05:17.770]back to an atmospheric nitrogen is called denitrification.
[00:05:23.120]And again, it's a group of bacteria that do this,
[00:05:27.440]but these bacteria can only occur in the absence of oxygen.
[00:05:32.750]So if you've got anoxic soils
[00:05:35.460]at the bottom of a wetland like we found
[00:05:37.320]in the Saline Wetlands, that dark black mud,
[00:05:40.330]doesn't have a lot of oxygen in it.
[00:05:42.360]That's where you can get denitrifying bacteria
[00:05:46.390]that can convert nitrate back into nitrogen gas.
[00:05:51.890]And so plants, there's actually,
[00:05:55.160]where's that pathway, there we go,
[00:05:57.050]so organic matter from plants
[00:05:58.950]and actually from animals as well, okay,
[00:06:01.700]decomposes and contributes back
[00:06:04.370]to the availability of nitrate in the soil.
[00:06:09.450]So this is a cycle, so the soil, the nitrogen is starting,
[00:06:12.650]most of it's in the atmosphere.
[00:06:14.730]Through a variety of means it ends up
[00:06:16.420]in soil and also water, and then back in,
[00:06:20.820]then gets utilized by plants.
[00:06:23.460]Plants then get eaten by animals,
[00:06:25.330]and then in both cases those things can decompose,
[00:06:29.760]and the final step in that cycle
[00:06:32.640]is to go back to atmospheric nitrogen
[00:06:35.380]from our nitrate pool down here.
[00:06:41.900]So again, why would we care about this stuff?
[00:06:43.900]Well, we've got too much nitrate.
[00:06:46.550]This is a map of nitrate concentrations in groundwater.
[00:06:50.710]Nitrate is not as toxic as nitrite,
[00:06:54.900]which is good, but it is still toxic,
[00:06:58.260]so this particular groundwater map was made in 2002,
[00:07:02.830]and in some parts of Nebraska
[00:07:04.630]it's actually gotten a lot worse.
[00:07:06.690]You'll notice Nebraska's not in the darkest red of areas,
[00:07:10.650]but we're not in the light green, either.
[00:07:13.360]One of the reasons why we get nitrate ions
[00:07:15.730]in our groundwater is because we add ammonia fertilizer,
[00:07:20.770]or various kinds of nitrogen fertilizers
[00:07:23.550]to crops like corn and soybeans,
[00:07:26.100]and if that, if we put too much on,
[00:07:29.340]more than the plants can use,
[00:07:30.950]then a lot of that can leach into the groundwater.
[00:07:33.560]It can also run off and into the streams,
[00:07:36.320]and one of the videos that I've got
[00:07:38.530]that I link to, outside of this one,
[00:07:43.110]talks about the Gulf of Mexico dead zone down here,
[00:07:46.620]so a lot of this nitrate that is in this,
[00:07:50.300]where am I doing this, there we go,
[00:07:51.750]a lot of the nitrate that's in this,
[00:07:54.440]in the Mississippi, this whole red area here,
[00:07:57.220]all ends up in the Mississippi River,
[00:07:59.480]and all comes out down here into the Gulf of Mexico,
[00:08:01.770]and there's so much nitrate now in the Gulf of Mexico
[00:08:04.850]at the mouth of the Mississippi River,
[00:08:08.420]that algal blooms end up using up
[00:08:10.690]all the oxygen in the water,
[00:08:12.007]and the decomposition process of the algae
[00:08:14.320]uses up all of the oxygen in the water,
[00:08:16.500]and large parts of the Gulf of Mexico
[00:08:18.390]are essentially ecologically dead.
[00:08:20.890]These are some of the most productive fisheries
[00:08:22.660]in the country, and they're crippled
[00:08:25.640]by the fact that we put too much fertilizer on crops
[00:08:32.020]up here in this part of the country.
[00:08:34.100]So that's a problem, and it's getting worse.
[00:08:38.490]So I talked about the nitrogen cycle
[00:08:41.880]in the context of plants in soil,
[00:08:45.660]but the nitrogen cycle also operates
[00:08:47.700]in streams, and rivers and wetlands.
[00:08:50.730]One of the thing, lakes for that matter.
[00:08:53.090]One of the things that's a little different,
[00:08:54.470]so Salt Creek is a stream, right?
[00:08:56.020]One of the things that's different
[00:08:57.210]between a cornfield or a prairie and a stream
[00:09:01.450]is that the place where the nitrogen
[00:09:03.490]and the plants are is moving, okay?
[00:09:06.430]So the water is actually moving downstream.
[00:09:09.930]That makes things a little more challenging
[00:09:11.610]to figure out exactly what's going on.
[00:09:14.610]So we've got, if we divide our stream
[00:09:16.530]into different segments, so we've got benthos down here,
[00:09:20.640]that's the bottom of the stream.
[00:09:22.980]And then there are, there's water,
[00:09:26.110]and in the water compartment
[00:09:27.270]we've got sort of inorganic solutes,
[00:09:30.640]so that's our chemicals that are there,
[00:09:34.050]but they're nitrite and nitrate,
[00:09:37.420]and then you've got your plants and things,
[00:09:39.670]and carbon in those areas.
[00:09:43.150]And so these little circles down here
[00:09:45.980]are meant to represent the nitrogen cycle,
[00:09:48.870]and so that's happening mostly down in the benthos,
[00:09:51.600]in the soil, okay, just like it would be in a prairie,
[00:09:57.580]but the difference is, is that the plants
[00:09:59.260]that are using it aren't necessarily embedded
[00:10:01.160]in the benthos, they're up here in the water,
[00:10:03.050]and so they're moving downstream.
[00:10:05.850]And there lots, again lots of processes,
[00:10:07.720]so there's uptake of our mineral nitrogen,
[00:10:13.830]and then there's the mineralization process,
[00:10:16.360]the denitrification process is also taking place out here.
[00:10:19.580]But again, that only happens when we've got no oxygen.
[00:10:26.520]One of the things that this means
[00:10:28.210]is that the faster the water moves,
[00:10:31.310]the less time there is for some of these processes
[00:10:35.630]to take place over any given length of water.
[00:10:37.810]So if you're putting a lot of nitrate in in one spot,
[00:10:40.360]and then the river is moving very quickly, okay,
[00:10:43.090]it gets to the end, and it's had less time
[00:10:46.380]to process that nitrate input and get it converted
[00:10:52.330]into either plant biomass or into,
[00:10:55.660]back into the nitrogen gas.
[00:10:56.810]So stream flow rates actually make,
[00:10:59.360]play a big role here, too.
[00:11:02.650]Why does that matter for the Gulf of Mexico?
[00:11:04.530]It matters because our modifications
[00:11:07.770]on the Mississippi and the Missouri River
[00:11:09.850]have changed those systems
[00:11:11.570]so the water moves much faster than it used to.
[00:11:16.290]All right, but we're gonna be in Salt Creek.
[00:11:17.870]Oh yeah, then another, here's the trend over time,
[00:11:21.750]so starting back in 1980,
[00:11:24.010]coming up to about 2011 here for this particular draft.
[00:11:30.730]This is the concentration of nitrate as nitrogen,
[00:11:35.050]milligrams per liter of nitrogen,
[00:11:37.590]over that same timeframe for a station
[00:11:40.720]just in the Missouri River just south of Nebraska.
[00:11:44.730]And what you can see is the trend is increasing, okay,
[00:11:47.180]so we're getting more and more nitrogen in the river,
[00:11:49.687]and that means more and more getting to the Gulf of Mexico,
[00:11:52.530]and that means a bigger problem.
[00:11:56.450]So what can we do about these sorts of things?
[00:11:58.610]So what we're gonna do is we're gonna visit,
[00:12:01.672]this is the site sort of outside of,
[00:12:04.150]just outside of Lincoln at Pioneers Park.
[00:12:07.330]There's the wastewater treatment plant,
[00:12:09.820]which actually adds quite a lot of ammonia to the river,
[00:12:15.280]okay, which is the start of that cycle.
[00:12:17.390]So ammonia gets converted to nitrite, and then to nitrate.
[00:12:21.000]This ammonia is the byproduct
[00:12:22.650]of all the decomposition of all the waste that we,
[00:12:25.070]the people who live in Lincoln, produce.
[00:12:28.050]And so what we're gonna do is we're gonna,
[00:12:29.960]I'm gonna get you guys to predict
[00:12:31.550]what's gonna happen, what do you expect to happen
[00:12:33.380]to the nitrogen content of Salt Creek
[00:12:35.540]as we go from upstream, past the wastewater treatment plant,
[00:12:39.220]and then to sites downstream.
[00:12:43.460]So each lab section's gonna split up into two teams,
[00:12:46.220]and each van will visit two sites,
[00:12:49.530]not that way, this way,
[00:12:50.670]two sites along Salt Creek.
[00:12:53.220]Each team will collect duplicate water samples
[00:12:55.580]at each of those sites, as well as blanks, distilled water.
[00:12:59.810]And you'll record data and observations
[00:13:05.346]on stream conditions.
[00:13:07.810]Why are we gonna collect blanks and duplicate water samples?
[00:13:10.480]Well, when we get back to the lab the following week,
[00:13:14.190]we'll break into smaller groups.
[00:13:15.500]Each group will analyze samples
[00:13:16.950]for nitrate, ammonia and phosphorous,
[00:13:18.810]but what we'll do is we're gonna double blind,
[00:13:20.600]we're gonna blind those samples,
[00:13:21.960]so the individuals doing the sampling
[00:13:25.180]will be from the opposite team,
[00:13:26.930]and they won't know which bottle has distilled water in it
[00:13:29.870]and which bottle has sample water in it.
[00:13:32.140]And this way we'll be able to get some quality control
[00:13:35.680]and measure how accurate are we.
[00:13:38.830]Are we actually measuring something real?
[00:13:43.050]So what are our learning objectives here?
[00:13:44.550]We're gonna be predicting changes
[00:13:45.940]in nitrogen species, that's what we call ammonia,
[00:13:48.370]nitrite, nitrate, along a rural-urban gradient.
[00:13:52.880]You're gonna be using colorimetric methods,
[00:13:55.130]so we've got a meter where you're gonna be adding
[00:13:57.280]chemicals to the water, it changes color
[00:13:59.820]depending on how much nitrogen is present, or phosphorous.
[00:14:04.480]And you're gonna quantify those water quality metrics
[00:14:07.490]using those meters.
[00:14:09.370]We're gonna estimate error rates
[00:14:10.640]using our blind samples and controls.

The screen size you are trying to search captions on is too small!

You can always jump over to MediaHub and check it out there.

Comments

0 Comments

Nutrient cycling in Salt Creek

Description

Searchable Transcript

Comments icon comment

Related Channels

Comments