Thesis Proposal
Proposed Mechanisms Controlling Baseflow Phosphorous
Concentrations in Wadeable Streams in Wisconsin
Mark Breunig
Water Quality Modeling
College of Natural Resources, UWSP
Contents
Background ................................................................................................................................................... 5
Statewide Data .......................................................................................................................................... 6
Montello River Watershed Data ............................................................................................................... 6
Thesis Objectives........................................................................................................................................... 9
Proposed Methods...................................................................................................................................... 10
Objective 1 .............................................................................................................................................. 10
Objective 2 .............................................................................................................................................. 10
Field Methods for Stream Sediment Collection .................................................................................. 10
Laboratory Methods for Determining EPCo of the Stream Sediment ................................................. 10
Biotic Uptake Component ................................................................................................................... 11
Linking the EPC0 to the Landscape ...................................................................................................... 11
Works Cited ................................................................................................................................................. 12
Background
Phosphorous is of major concern to water quality managers in agricultural watersheds because it can
cause eutrophication in surface waters. Stream phosphorus concentrations are important to the stream
ecosystem and to the loading to downstream water bodies. Agricultural fertilizers and animal waste
contain phosphorus. This chemical has a tendency to absorb to soil particles, and is transported to
surface water primarily during runoff events. In cases of chronic over-application, it can be transported
independently of soil particles (USEPA 2007).
The Wisconsin DNR, in conjunction with the USGS, is currently working to develop total phosphorous
standards for Wisconsin streams. Based largely on their interpretation of the results of a recent study
by Dale Robertson of the USGS, median stream concentrations above 74 µg/L and median river
concentrations above 103 µg/L have a greater impact on the overall biotic integrity of a water body
(Robertson et al. 2006). Those levels can be compared to reference concentrations, representing the
natural condition of a water body, estimated to be between 30 and 40 µg/L. Using a different statistical
method, the United States Environmental Protection Agency (USEPA) estimated reference conditions in
the north central hardwood forest subecoregion, which spans across central Wisconsin, to be 29 µg/L
(Agency 2000).
Although efforts are underway to set stream standards in Wisconsin and elsewhere, there is still
controversy regarding the mechanisms that control stream phosphorous concentrations. Although
commonly ignored in water quality models, biotic and abiotic in-stream processing are important
mechanisms to consider (Froelich 1988; Haggard et al. 2007; McDaniel et al. 2009).
Statewide Data
The Robertson study, which considered over 200 sites
across Wisconsin, did not explain the specific mechanisms
that cause randomly sampled wadeable stream total
phosphorous concentrations to increase, but found
percent agriculture to be the best explanatory variable (R2
= 44%). While many basin characteristics were compared
to the phosphorous concentrations, it may be possible to
improve the percent of variation in median total
phosphorous
concentrations that can be
explained by one or more
spatially-based
variables.
Preliminary analysis has
been done on the data set
using different expressions
of flow distance (example images shown left and above), which have offered no noticeable improvement in
the regression. However, many possibilities to improve this technique or explore other spatial characteristics
exist.
Montello River Watershed Data
log10(B_medRPconc) = 1.029 + 1.899 Cultivated Crops
70
log median baseflow SRP
The Montello River Watershed Project,
which is just beginning the second of the
two years of the study, contains a data set
that may be useful in explaining the
mechanisms that influence median total
phosphorous concentrations. This project
consists of a much smaller scale than the
state-wide data set, which reduces the
variation attributed to geochemistry and
soils. An opportunity exists to explain the
mechanism behind the very strong percent
cultivated cropland – median phosphorous
concentration relationship observed in the
data set. Regressions comparing cultivated
cropland and log median baseflow total
and soluble reactive phosphorous (SRP)
concentrations at the 6 primary monitoring
sites are shown to the right.
KW02
60
KW03
50
UN01
40
WC02
30
TC01
20
WC01
adj R2 = 97%
p = 0.001
0.20
0.25
0.30
0.35
0.40
0.45
Cultivated Crops (proportion of total land use)
The Montello Dataset has a good distribution of phosphorous concentrations across sites. The effect of
total phosphorous on the biotic integrity of each stream site, according to the DNR proposed standards,
are shown below.
130
120
117
110
median TP (µg/L)
100
91
90
80
70
60
90
effected
70
minimally effected
58
least impacted
50
40
30
40
natural conditions
KW02
KW03
TC01
UN01
WC01
WC02
SITE
It is hypothesized that a metric known as the stream sediment equilibrium phosphorous concentration
(EPC0), controls baseflow phosphorous concentrations. When EPC0 is greater than the stream SRP,
sediments are a potential phosphorous source to the stream. When EPC0 is less than the stream SRP, it
is suggested that stream sediments will sorb phosphorous from the water column (McDaniel et al. 2009).
A time series of baseflow total phosphorous concentrations during the 2008 monitoring season is shown
on the next page. These data show an interesting temporal pattern. The highest values were observed
after the major flood and early June, which steadily decreased until the end of the sampling season in
November. It appears that phosphorous release rates from streambed sediments deposited in the flood
were higher directly after the event; the release rate decreased over time as the stream sediment and
water approached equilibrium. Seasonality may have also influenced this trend, as biologic activity is
higher in the summer. Sites on Klawitter Creek, KW02 and KW03, also had higher concentrations in
early spring, which decreased until the flood in early June. Phosphorous enriched sediments were
deposited into the stream during spring runoff, and release rates decreased until the next major input in
June. Samples representing winter baseflow concentration were collected 2/22/08, which were
significantly lower at KW02 and KW03 than the spring baseflow concentrations. This suggests that the
groundwater discharging into Klawitter Creek did not have elevated total phosphorous concentrations.
4/1/2008 7/1/2008 10/1/2008
300
KW02
KW03
MR01
TC01
UN01
WC01
150
TP (µg/L)
0
300
150
300
SITE
KW02
KW03
MR01
TC01
UN01
WC01
WC02
0
WC02
4/1/2008 7/1/2008 10/1/2008
150
0
4/1/2008 7/1/2008 10/1/2008
DateTime15
This data set will also include phosphorous index (PI) estimates calculated by Snap-Plus nutrient
management software, which have potential benefits over generalized spatial datasets. This study
represent a pioneering effort in the application of the PI to stream monitoring data at the watershed
scale.
Thesis Objectives
1. Determine whether the statewide cropland vs median total phosphorous regression can be
improved by incorporating a more spatially-based explanatory variable.
2. Explain the mechanism that causes baseflow phosphorous concentrations in the Montello River
Watershed to steadily decline after major runoff events
a. Use the EPC0 as evidence behind the mechanism controlling baseflow total
phosphorous concentrations in the Montello River Watershed.
b. Provide some estimate of the relative contribution of biotic uptake to this process.
c. Link the EPC0 to landscape characteristics. This could involve applying the spatiallybased metric derived in objective 1, or it could be completely independent of this.
The results of this study will increase our understanding of the factors that control stream phosphorous
concentrations. This information could be used to more effectively manage the landscape to achieve
desired total phosphorous concentrations, and establish standards for streams. It also could be used to
develop a predictive model, offering great benefit to the scientific community and others.
Proposed Methods
Objective 1
Continue testing different models and terms with the statewide data set. This will be supplemented by
python script and/or visual basic to automate and streamline this process, allowing for more iterations
than would be possible manually. The success of these models will be assessed using standard
regression statistics, involving the use of the general linear model, best subsets, and multiple linear
regression.
Objective 2
Preliminary field and laboratory work has been done to refine the methods proposed below.
Field Methods for Stream Sediment Collection
Stream sediment samples will be collected from the 6 primary monitoring sites in the Montello River
Watershed every 2 weeks, in synchronization with the water quality samples that are already being
collected. Sample collection will terminate in late summer. Seven sub-samples extending from the
downstream portion of the monitoring site to 100 feet upstream will be collected at equally spaced
intervals. Sub-sample collection will not be biased by the ease of sample collection. In the case of large
rocks, sediment will be sampled immediately upstream of the obstruction. The samples will be
homogenized in a shallow plastic mixing bucket, and sieved (< 4mm). The wet sediment will be placed in
a 500 mL polypropylene (PP) or high density polyethylene (HDPE) bottle, placed immediately on ice, and
transported back to the laboratory.
Laboratory Methods for Determining EPCo of the Stream Sediment
Phosphorous sorption isotherms will be performed on the samples, in order to determine the EPC0 of
each sample. All samples will be run as 3 replicates. The sorption isotherms will be performed by
analyzing 5 subsamples – each representing the pseudo-equilibrium concentration (EPC) of each spiked
stream water solution (0, 0.5, 1.0, 2.0, 5.0 mg/L TP added to filtered stream water). Stream water will
be filtered with a 0.45 micron filter upon arrival at the laboratory. Each EPC subsample will contain
roughly 6 mg of wet sediment. The wet sediment will be re-homogenized prior to distributing it into
each respective EPC tube. Each EPC subsample will be mixed with a rotating drum mixer for 24 hours to
approximate the pseudo equilibrium concentration. The EPC subsamples will then be centrifuged for 30
minutes. Most of the water will be removed with a pipette, and filtered through a 0.45 micron filter.
Special attention will be used to not removed any sediment from the tube with the pipette. The
remaining wet sediment will be emptied into a tin, which will be air dried (25 ⁰C) and then oven dried
(100 ⁰C). The filtered EPC subsample water will be analyzed using a Ocean Optics spectrophotometer,
using the ascorbic acid colormetric technique. This spectrophotometer has a precise but narrow range
(about 0.000 to 0.250 mg/L), which will necessitate careful dilution of the spiked EPC subsamples. For
each batch of sediment EPC samples, there will be an accompanying series of subsamples that contain
the phosphorus spikes and stream water only. These concentrations will be needed to properly
calculate the EPC0 of the samples. On the top of the next page is an example of how the sorption
isotherm is used to calculate the EPC0 of each stream sediment sample (note: the dependent variable
will be mg of P removed per kg of dry sediment for the actual samples).
In an attempt to more accurately define the EPC0, solutions of equal ionic strength to the stream water,
but 0 mg/L of P will be used to plot a regression point below the EPC0 (which would be an assessment of
the P released from the sediment)
Biotic Uptake Component
This part of the study needs further revision. Possible ideas include in-situ experiments during hot
summer days to estimate biotic uptake using some sort of tracer and a known added phosphorous
concentration.
Linking the EPC0 to the Landscape
This will involve similar regression statistic techniques as mention in the methods for objective 1, only
using the Montello River Watershed data set rather than the state-wide data set.
Works Cited
Agency, U. S. E. P. (2000). Ambient Water Quality Criteria Recommendations. O. o. S. a. T. Office of
Water, Health and Ecological Criteria Division. Washington, D.C., U.S. Environmental Protection
Agency: 92.
Froelich, P. N. (1988). "Kinetic Control of Dissolved Phosphate in Natural Rivers and Estuaries: A Primer
on the Phosphate Buffer Mechanism." Limnology and Oceanography 33(4): 649-668.
Haggard, B. E., D. R. Smith, et al. (2007). "Variations in Stream Water and Sediment Phosphorus among
Select Ozark Catchments."
McDaniel, M. D., M. B. David, et al. (2009). "Relationships between Benthic Sediments and Water
Column Phosphorous in Illionois Streams." Journal of Environmental Management 38: 607-617.
Robertson, D. M., D. J. Graczyk, et al. (2006). "Nutrient Concentrations and Their Relationships to the
Biotic Integrity of Wadeable Streams in Wisconsin." USGS Professional Paper(PP 1722).
USEPA. (2007, 9/11/2007). "Phosphorus." Retrieved Nov 11, 2008, from
http://www.epa.gov/oecaagct/ag101/impactphosphorus.html.