Transcript Document

Bioavailability of Dissolved Organic Nitrogen Originating from Natural Sources and
Wastewater Effluent in the Truckee River
N. Bertrando*, R. G. Qualls*, M. Brisbin**, M.
*Univ. of Nevada, **City of Sparks,
In processing the wastewater generated by the Reno-Sparks metropolitan
area, the Truckee Meadows Water Reclamation Facility (TMWRF) uses
an advanced Tertiary treatment system which employs bacteria to convert
inorganic N and P to less available Organic forms (i.e DON and DOP)
such that most of the N discharged into the river is DON. However, the
current regulations only consider the Total Maximum Daily Load
(TMDL) of all types on N combined.
Objective
In order to assess the affects that TMWRF effluent will have on the N
balance of the Truckee River, our study examines the spatial and seasonal
variations in bioavailability of Dissolved Organic Nitrogen originating
from natural sources and wastewater effluent. This effort will help us to
understand the nutrient loads in the Truckee River and how the urban
corridor of the Reno-Sparks metropolitan area influences these loads. In
particular, we have monitored in-stream nutrient limitation of periphyton
growth and microbial mineralization of natural and effluent DON.
Chl a (ug/sq cm)
Spring 2008 Periphyton Growth
Control
9.00
Nitrogen
8.00
Phosphorous
7.00
Nitro + Phos
Amino Acids
6.00
5.00
4.00
3.00
2.00
1.00
1
Castano*
Of Nevada Undergraduate Researchers
Methods
DON Biodegradation Summer 2007
Bioassays:
1000.00
Since the variety of constituents in DON have not been thoroughly
identified and may vary based on source, the primary method for
determining bioavailability is through bioassays. These bioassays
provide an estimate of the fraction of DON that is biologically
available. Samples of water were collected from above and below the
Reno-Sparks metropolitan area, from an urban runoff site (the North
Truckee Drain), and from the TMWRF effluent spout. These samples
were then inoculated with a mixture of local soil microbes and
exposed to a solar simulator UV light for 4 hours per day. Samples
taken on days 0, 3, 7, 14, and 67 were analyzed for Total N (TN),
Total Dissolved N (TDN), (NO3+NO2)-N, and NH4-N. From these
measurements, the DON was calculated:
Upstream
900.00
Downstream
800.00
Effluent
700.00
[DON] ug/L
Nitrogen is an element of concern to the quality of water in the
Truckee River. The supplies of either nitrogen (N) or phosphorus (P) are
the elements that are most likely to limit the production of algae in
freshwater streams, rivers, and lakes. High concentrations of available
nitrogen or phosphorus can stimulate excessive algal growth, which in
turn can lead to die off, decay, and anaerobic conditions. While
inorganic forms of N (NO3, NH4) are considered 100% bioavailable,
Dissolved Organic Nitrogen (DON) has many components varying
degrees of bioavailability. These DON compounds range from small
compounds such as urea and amino acids to large humic acid
compounds, with the specific makeup DON in a water sample being
dependent upon its specific source.
K.L. Dean*, & L.
Urban Runoff
600.00
y = 806.64e -0.0067x
R2 = 0.874
500.00
400.00
y = 482.48e -0.0053x
R2 = 0.9013
300.00
y = 289.43e -0.0069x
R2 = 0.8939
200.00
100.00
y = 158.31e -0.0074x
R2 = 0.8339
0.00
0
10
20
30
40
50
60
70
80
Time (days)
DON = TDN – ((NO3+NO2)-N + NH4-N)
DON Biodegradation Fall 2007
These tests were repeated seasonally for two consecutive years.
900.00
Upstream
Nutrient Limitation Studies:
800.00
Since the affects of N inputs to the river are dependent upon the needs
of the organisms which live there, we tested the nutrient limitation of
periphyton growth in the river using Nutrient Diffusing Substrates
(NDS) to create locally enriched zones of N, P, N+P, and Amino
Acids. These NDS were places in riffle zones of the river for 11 days
then collected and analyzed for chlorophyll a as a measure of
biomass. The sampling locations were the same sites where we
collected water samples with one addition at the E. McCarran Bridge
just upstream from TMWRF and the North Truckee Drain.
700.00
Downstream
Effluent
Urban Outfall
[DON] ug/L
Introduction
1Univ.
1
Springer* ,
600.00
y = 723.72e -0.0031x
R2 = 0.7704
500.00
400.00
300.00
200.00
100.00
0.00
0
10
20
30
40
50
60
70
80
Time (days)
Results and Discussion
The results of the bioassays varied between season and between
samples. A significant fraction (23-48%) of the wastewater
effluent DON was mineralized in every trial while DON from the
upstream sample was mineralized during the summer sampling
(43%) but not during other seasons (<5%).
The DON
mineralization was most variable in the urban runoff sample (370%). It is also important to note the magnitude of [DON] was
consistent at each site throughout the year, with the wastewater
effluent being much higher than any other sample (~ 800 ug/L-N
vs. <500 ug/L). For all samples where DON was degraded, the
fate was primarily NH4 (ammonia) with some becoming
particulate N.
Figure 2. Biodegradation of DON in water sampled
from three locations on the Truckee River and from
TMWRF effluent.
Confluence of North Truckee
Drain and the Truckee River.
TMWRF in background.
Upstream of the RenoSparks metropolitan
area, near Mogul
0.00
Upstream
McCarran Bridge
Urban Outfall
Downstream
Site
Summer 2008 Periphyton Growth
Control
12.00
Nitrogen
Phosphorous
Chl a (ug/sq. cm)
10.00
Nitro + Phos
8.00
The nutrient limitation studies demonstrated both seasonal and
spatial variability as well. All locations on the Truckee River
were consistently N+P limited, but the urban runoff did not
exhibit nutrient limitation. Limitation by N alone was apparent
only at the McCarran Bridge and showed a borderline effect
downstream from the TMWRF discharge point.
Downstream of TMWRF,
Train Bridge near
Lockwood, Truckee River
Katie Dean installing
stakes for securing NDS
assemblies in the river.
Amino Acids
6.00
4.00
2.00
0.00
Upstream
McCarran Bridge
Urban Outfall
Downstream
Site
Figure 1. Tests of nutrient limitation to periphyton
growth, measured as chlorophyll a (ug/cm2), on
NDS at four locations in the Truckee River system.
These results suggest that wastewater DON has a higher
bioavailability than naturally derived DON and that
bioavailability of natural DON may experience a seasonal cycle
with increased DON bioavailability during the summer months
(the growing season). However, no more than 50% of the
wastewater DON was mineralized in any trial. Since the site
downstream from the TMWRF experienced borderline N
limitation during the spring and summer, the bioavailability of
wastewater DON may play an important role in the nutrient
dynamics in the Truckee River.
Acknowledgements: Field work and lab analyses
were assisted by Greg Wilson and the TMWRF
Staff.