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9-1-1999 Illinois River 1998 Nutrient and Suspended Sediment Loads at Bridge Marc A. Nelson University of Arkansas, Fayetteville

Thomas S. Soerens University of Arkansas, Fayetteville

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Recommended Citation Nelson, Marc A. and Soerens, Thomas S.. 1999. Illinois River 1998 Nutrient and Suspended Sediment Loads at Arkansas Highway 59 Bridge. Arkansas Water Resources Center, Fayetteville, AR. MSC 277. 17

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ILLINOIS RIVER 1998 NUTRIENT AND SUSPENDED SEDIMENT LOADS AT ARKANSASHIGHWAY 59 BRIDGE

Submitted to the Arkansas- ArkansasRvier Compact Commission

By Marc A. Nelson Ph.D. P.E. ArkansasWater Resources Center

Thomas S. SoerensPh.D., P.E. Department of Civil Engineering

Publication No. MSC-277

Arkansas Water Resources Center 112 Ozark Hall University of Arkansas Fayetteville, Arkansas 72701 ILLINOIS RIVER

1998 NUTRIENT AND SUSPENDED SEDIMENT LOADS

AT ARKANSAS HIGHWAY 59 BRIDGE

Submitted to the

Arkansas - Oklahoma Arkansas River Compact Commission

By

Marc A. Nelson Ph.D., P.E. Arkansas Water Resources Center

Thomas S. Soerens Ph.D., P.E. Department of Civil Engineering

University of Arkansas Fayetteville, Arkansas

September, 1999 SUMMARY

Results forIllinois River at AR59 forCalendar Year 1998.

Parameter Total Discharge Total Load Average Discharge Mean 3 3 (m /yr) (kg/yr) (m /s) Concentrations (mg/I) 588,000,000 18.6 N03-N 1,390,000 2.37 TKN 481,000 0.82 TP 232,000 0.39 TSS 72,600,000 123.5 Comparison between the loads anddischarge calculated for 1997 andthe loads and discharge calculated for 1998 indicate a significantincrease in 1998.

C ompanson b etween I 998 and 1997 Parameter 1997 1998 Percent Totals Totals Change

Discharge 458,460,000 (m") 588,000,000 (m') + 28 N03-N 1,020,000 (kg/yr) 1,390,000 (kg/yr) + 36 TKN 301,000 (kg/yr) 481,000 (kg/yr) + 60 TP 127,000 (kg/yr) 232,000 (kg/yr) + 83 TSS 18,400,000 (kg/yr) 72,600,000 (kg/yr) +394

Most of the increasefor the year can be attributed to a single storm that began on January 4, 1998. The river was above the trigger level forseventeen days. In that time, the followingdischarge andloads occurred.

Discharge and loads for January 4, 1998 Stonn. Parameter Stonn Values Percentage of 1998 Total

Discharge 150,739,967 (m�) 25.6% N03-N 351,920 (kg) 25.3% TKN 197,599 (kg) 41.1 % TP 100, 165 (kg) 43.2% TSS 37,263,085 (kg) 51.3 % The results for 1998 show that storms were the largest source of pollutant load duringthe year and that significantindividual storms can be a largepercentage of a year's total load. These significantstorms may or may not occur in a given year. Such storms can dramatically affectthe year's total loads and makes the prediction of trends very difficult, especially over short time periods. These results also reinforce the factthat storm events must be adequately sampled for accurate determination of pollutant loads. In addition, there must be a method to reasonably predict individual storm loads for 4'missed" storms. INTRODUCTION Automatic water samplers and a U.S. Geological Survey(USGS) gauging station were established in 1995 on the main stem of the Illinois River at the Arkansas Highway 59 Bridge. Since that time, continuous stage and discharge measurements and water quality sampling have been used to determine pollutant concentrations and loads in the Arkansas portion of the Illinois River. This report represents the results fromthe measurement and sampling for January 1, 1998 to December 31, 1998.

PREVIOUS RESULTS In the fall of 1995, a gauge was installed at the Highway 59 bridge by the USGS and the Arkansas Water Resource Center (AWRC) installed automatic sampling equipment. In September 1995, sampling was begun on the Illinois River. Grab samples were taken every week and storms were sampled using an automatic sampler set to take samples every 4 hours. During the period fromSeptember 13, 1995 to September 15, 1996 one hundred thirty seven grab samples and discrete storm samples were collected and analyzed. Table 1 summarizes the results fromthat study (Parker et al., 1997).

Table 1. Results from 1996 study period (Parker et al., 1997) Parameter Total Discharge Total Load Average Average (m3/yr) (kg/yr) Discharge Flow Weighted (m3/s) Concentrations (mg/I) 267,740,640 8.5 N03-N 550,000 2.0 NH3-N 8,530 0.031 TKN 201,000 0.74 TP 89,900 0.33 TSS 27,500,000 101 TOC 1,130,000 4.2

Sampling was discontinued on September 15, 1996 and no water quality samples were taken between September 15, 1996 and November 1, 1996. Stage and discharge was still recorded for this period, however, no loads were calculated. Water quality sampling was resumed on November 1, 1996. The samplingprotocol was changed to collection of grab samples every two weeks and flow-weighted storm composite samples. Between November 1, 1996 and December 31, 1996 a total of fourgrab samples and one storm composite sample were collected and analyzed. Stage and discharge were recorded.

During the period fromJanuary 1, 1997 to October 15, 1997, there were twenty-sixgrab samples and twenty-fivestorm composite samples collected and analyzed using the same protocol. During the period fromOctober 15, 1997 to December 31, 1997, the sampling protocol was changed to taking grab samples every two or three days and taking discrete storm samples every thirty or sixtyminutes. In thisperiod, there were twenty-fourgrab samples and one hundred and fortystorm discrete samples collected and analyzed. The

2 loads and mean concentrations for1997 calculated using these samples are summarized in Table 2.

Table 2. Results from 1997-studyperiod (Nelson and Soerens, 1998). Parameter Total Discharge Total Load Average Discharge Mean 3 (m3/yr) (kg/yr) (m /s) Concentrations 458,460,000 14.5 (mg/I) N03-N 1,020,000 2.24 TKN 301,000 0.66 TP 127,000 0.28 TSS 18,400,000 40.2

METHODS In the periods from January 1, 1998 to May 15, 1998 and November 1, 1998 to December 31, 1998, the Illinois River sampling was supplemented by sampling fromanother research project. This project, sponsored by the USGS Water Resource Institute Program, was titled "Investigation of Optimum Sample Interval for Determining Storm Water Pollutant Loads" by MarcNelson, Thomas Soerens and Jean Spooner. The sampling protocol forthat project consisted of taking grab samplesevery two days and discrete stormwater samples at thirty-minute intervals on the rising limb and sixty-minute intervalson the fallinglimb of stormhydrographs. Stormwater sampling was begun at a variable trigger level set to the currentstage plus ten percent and adjusted every two days. Afterthe firstthirty-six hours of each storm,sample times were increased to fromfour to twenty-fourhours until the stage fellbelow the initial trigger. All samples were collected within twenty-fourhours. All samples were analyzed fornitrate nitrogen (N03-N), ammonia nitrogen(NH4-N), total Kjeldahl nitrogen (TKN),total phosphorus (TP), ortho phosphate (0-P) and total suspended solids (TSS). A WRC Field Services personnel collected all samples and analyses were performedby the A WRC Water Quality Lab using standard fieldand laboratory quality assurance and quality control (QA/QC) procedures.

In the period from May 16, 1998 to October 31, 1998, the sampling protocol reverted to the collection of grab samples every two weeks and flow-weightedcomposite samples duringstorms. Storms were definedas all flowsabove a five-foottrigger level. Once stage had risen above the trigger,a USGS programmabledata logger began summing the volwneof water discharged. Once a determined amountof water had been discharged, the data logger sent a signal to an automatic water sampler that filledone of 24 one-liter bottles. The total was then reset to zero and discharge was again summed for the next sample. In this fashion up to 24 samples, each representing an equal volumeof storm water was collected. The volume of water represented by each individual sample was eight million cubic feet. Thesesamples were retrievedbefore all 24 bottles were filled,or within 48 hours afterbeing taken. The individual samples were composited into a flow­ weighted composite stormsample by combining equal volumes of each. Samples were taken as long as the stage remained above the trigger level. All samples were analyzed for nitrate-nitrogen(N03-N), total Kjeldahlnitrogen (TKN), total phosphorus(TP) and total suspended solids (TSS). A WRC Field Servicespersonnel collected all samples and

3 analyses performed by the A WRC Water Quality Lab using standard fieldand laboratory QA/QC procedures.

Calendaryear pollutants loads and mean concentrations were calculated fromthe collected data. USGS stage and discharge data in 30-minute intervals was used to calculate 30-minute total volumes. Each volume was assigned a pollutant concentration. The pollutant concentrations were assigned by applying the results of grab samples betweenstorm triggerlevels and the results of stormwater samples above trigger levels. All concentrationdata were assigned to the time periods fromhalf way to the previous sample to half way to the subsequent sample except the firstand last of a storm or base flowperiod which were assigned to the start or end of the period. Thirty-minuteloads were calculated by multiplying 30-minute volumes by their assigned concentrations. The yearly loads were calculated by summing the thirty-minute loads during the calendar year. Yearly mean concentrations were calculated by dividing the yearlyload by the yearly volume.

RESULTS In the period fromJanuary 1, 1998 to December 31, 1998, there were 449 samples collected and analyzed. These results are summarized in Table 3 andFigure 1.

Table 3. Results for Illinois River at AR59 for Calendar Year 1998. Parameter Total Discharge Total Load Average Discharge Mean (m3/yr) (kg/yr) (m3/s) Concentrations (mg/I) 588,000,000 18.6 N03-N 1,390,000 2.37 TKN 481,000 0.82 TP 232,000 0.39 TSS 72,600,000 123.5

DISCUSSION

Comparison between the loads and discharge calculated for 1997 and the loads and discharge calculated for 1998 indicate a significant increase in 1998. The total discharge in 1998 was 28% higher than in 1997. The 1998 loads increased to an even greater extent.

Table 4. Comparison between 1997 and 1998. Parameter 1997 1998 Percent Total Load Total Load Change (kg/yr) (kg/yr) Discharge 458,460,000 (m.J/yr) 588,000,000 (m'/yr) + 28 N03-N 1,020,000 1,390,000 + 36 TKN 301,000 481,000 + 60 TP 127,000 232,000 + 83 TSS 18,400,000 72,600,000 +394

4 The differencesbetween the years can largely be attributed to the differencesin storm flows and storm flowconcentrations. Storm and base flows can be differentiated by definingstorm flowsas all discharges thatoccurred when the stage was above the five­ foottrigger level. Base flowvolumes forthe two years are essentially identical, 208 million cubic meters in 1997 and 209 million cubic meters in 1998. Concentrations measured during base flowsare also very similar (see figure2.). Storm flowvolumes increased from55 to 64% of the total volume. Since, with the exception of nitrate­ nitrogen, the concentrationsof the storm flowsincreased from 1997 to 1998, the percentages ofloads that occurred during storm flows increased substantially. Storm flow total phosphorus load increased from58 to 82% ofthe total. Storm flow total Kjeldahl nitrogen load increased from71 to 84% of the total. Storm flowtotal suspended solids load increased from77 to 94% ofthe total.

Most ofthe increase forthe year can be attributed to a single storm that began on January 4, 1998 (see Figure 3.). The river stage was above the trigger level forseventeen days. In that time, the followingdischarge andloads occurred.

Table 5. Discharge and loads for January 4, 1998 Stonn. Parameter StonnValues Percentage of 1998 Total

Discharge 150,739,967 (m�) 25.6% N03-N 351,920 (kg) 25.3% TKN 197,599 (kg) 41.1 % TP 100, 165 (kg) 43.2% TSS 37,263,085 (kg) 51.3 % The stage was above fifteenfeet for only twelve hours. In that time, 20% of the total yearly phosphorus load, nineteen percent ofthe total yearly TKNload and 26% ofthe total yearly suspended solids load occurred (see Figure 2).

The factthat such a large percentage of the year's total loads resulted froma single storm indicates the need for a means to estimate pollutant loads forstorms with missing concentration data. One method used to accomplish this is to develop a concentrationI discharge rating curve. Looking at the development of these rating curves fortotal phosphorus shows that they do not accurately predict the relationship even when segregated into threeflow regimes (see Figure 4). Even base flowvalues are not accurately predicted since they have a greater correlationwith time of year than with stage. Another technique being investigated using this data set is to develop a relationship between storm mean concentrationand peak stage (see Figure 5). The use of these or other techniques to predict loads for"missed" storms is critical foraccurate yearly load calculations

The year 1998 was not a particularlywet year.Looking at the yearly discharges at a site fivemiles down streamnear Watts Oklahoma, forwhich historic records are available, shows that the total discharge for 1998 was verynear the 33-year mean value of 577 million cubic meters (see Figure 6). Also plottedon figurefour is the trailing fiveyear moving average discharge that correspondsto the fiveyear moving average loads that the Arkansas-Oklahoma Arkansas River Compact Commission uses to determine trends in

5 phosphorus loads. This shows thecyclical nature of the yearly discharge fromthe Illinois River. A graph of calculated loads if available would probably exhibit the same cyclical nature with the peaks and valleys accentuated.

The loads calculated forthe year 1998 should be considered a very reliable estimate of the actual loads in the Illinois River in Arkansas. There were no gaps in the discharge data and all storm events were sampled. Most of the storm events were sampled using discrete samples taken at 30-minute intervals during rising flowand 60-minute intervals during fallingflow. The preliminary results of the research conducted during 1997 and 1998 at this site to determinean optimum sample interval indicate that on average, the loads calculated fromstorms that were sampled at 60-minute intervals or less are within 5% of the actual value.

A potential source of error in the use of automatic samplers to collect samples is that the sampler may take samples that are not representative of the cross-section. In an effort to determine the possible error, beginning in 1999, the USGS began taking samples that represent the entire cross-section at the same time the autosampler was taking samples. Preliminary results fromthose samples indicate that the auto samples may be underestimating concentrations during low flowand overestimating concentrations during high flow (see Figure 7). More measurements particularly at high flowsneed to be made to accurately characterize this relationship.

CONCLUSIONS

The results for 1998 show that storm flow carrieda large portion of nutrientand total suspended sediment loads during the year and that large individual storms can comprise a significantpercentage of a year's total load. These significantstorms may or may not occur in a given year and thus can dramatically affectthe year's total loads andmakes the prediction of trends verydifficult, especially over short time periods. These results also reinforcethe fact that storm events must be adequately sampled for accurate determination of pollutant loads. In addition, a method must be developed to reasonably predict individual storm loads for"missed" storms.

6 ILLINOIS RIVER HIGHWAY59 1998

25 2000

1800 i20 1600 1400

� 15 1200 - -STAGE I- -N03-N 1000 -T-P z0 enI 0 -TKN 10 I!? 0 800 -TSS g 600

5 en 400 200

0 0 Jan, Feb Mar Apr May Jun Jut Aug Sep Oct Nov Dec DATE

ILLINOIS RIVER HIGHWAY59 1997

25 2000

1800 20 1600 1z 1400 15 1200 _ -STAGE I- -N03-N 1(100 -T-P enI 0 -TKN 0 10 800 I!? -TSS g 600

5 en 400 200

0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec DATE

Figure 1. Stage and Measured Concentrations for 1998 and 1997. MEAN CONCENTRATIONS MEAN CONCENTRATIONS 1997 1998

250 250

200 200 i:" i � 1.50 �150 0 base 11.00 � I:i 1 DO

0 u u 0.50 0.50

0.00 0.00 T·P TI

PERCENTAGES OF LOADS FROM STORM FLOWS PERCENTAGESOF LOADS FROM STORM FLOWS (above5 feet) (above5 reet) 1997 1998 100%

9()'M, 100% l!O% 90% 70% 80% 70% 60% 6()'11, 50% 50% 40% 40% 30% 30% 20% 20% 10% 10% 0% 0% VOLUME NQ3.N TKN TSS VOLUME N03-N T.P TKN TSS T.P

PERCENTAGES OF LOADS PERCENTAGES OF LOADS above 15 feet above15 feet 1997 1998

100.00% 100.00% 90.00% 90.00% 80.00% ::: , ·1\4,1°" ... :4;w�· · 70.00% 60.00% 7:05%. . 3.01"· 60.00% 50.00% 50.00% 40.00% 40,00% 30.00% 30.00% 20.00% 20.00% 10.00% 1000% B ._. t!!:!:fi!!fl}, 0.00% VOLUME T.P TKN TSS 000%,i....;.VOLUME-==�- ==-.,...... :==....._.T·P �TKN= :::;..,;.;,;:...... ;.TSS

Figure 2. Comparisons between 1997 and 1998 IWNOIS RIVER HIGHWAY59 1998 TOTAL PHOSPHORUS

1000 250,000

900

800

700 - -DISCHARGE 600

500 -TOTAL

400 LOADPHOSPHORUS

200

100

0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec DATE

Figure 3. 1998 Discharge and Total Phosphorus load. BASER.ow WEf!lDN T.P T•P

o.9 0.11 o.a 0.6 o., 0.7 e o. o.e f 0.1!, I-0.!i � 0.4 � o,,t G.3 u o.2 0-l o., 0.t 0 0 e..oo 000 1D.OO 15.D0 20.(.!0 Jin Fm ,. tlltf .u Sap 01:l Oto !JfAGE (Ill�

RISINGSTORM FLOW IIJSll

2 f 2 1.5 I � � 1,5

0.5 0.5

0 0 • 0.00 5.00 10.D0 15.00 20.00 25.00 Jen Feb Pf1t May .i.. sep Oct Dee STi\GE[ftl DAT!!

FAlLINGSTORM FLOW FAlLING STORM FLOW T-P 3.5 3.5 3 3 2.5 2.5 2 I 2 � 1.5 I � 1.5

0.5 0.5 0 • 0.00 5.00 10.00 15.D0 20.00 25.00 Fell Pf1t May .u Or;t STAGE(I) sep DATE figUl"O It Dovalopm9nt of ratinq cu�e for total phosphorus. MEAN STORM CONCENTRATION Total Phosphorus vs. PEAK STAGE

1.00

0.20 +----=.;....;...---=-,------=------"-;.;..;.;_.;;.;__ 0.1 o ¥'����;µ;µ����2-+4F����LL_±:.sill..li§. 0.00 p���i4J�l...... d...Z:....,�±EL.l..Ili¥W£��4���i..ii.; 0 5 10 15 20 25 PEAK STAGE (ft)

Figure 5 Mean Storm Concentration vs. Peak Stage for Total Phosphorus. YEARLY TOTAL DISCHARGE ILUNOIS RIVER@ WATTS,OK

1.60E+09 ,. ,·, ...... '-·.:::: 1.40E+09 • 1.20E+09

ILi- 1.00E+09 CJ .. �'. �'.:'·'.·::??:� '.

� f,:,·v··

0 8.00E+08 ..

_, 6.00E+08

4.00E+08 2.00E+08 •• .. .;,:;.�::-�: '} ::-:.: 0.00E+00 �...;....;._....:....:.;.;,:.:.....;;.:._--,;;==-;;-.;�;..;;...... ,=�=r---;.;.;,;..;.:.--+==...:+-;;...... ;.:.:.:...;,:,;.;:...,:;...;;.._;.;..;,;_,;:;: 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 YEAR

Figure 6. Total discharge at Illinois river near Watts Oklahoma YEARLY TOTAL DISCHARGE ILUNOIS RIVER @WATTS, OK

1.60E+09

...- � 1.00E+09 n::

� 8.00E+08 -+-....;.;=;,::.:.;;.:,..;,...-___,..;;.;;.;_,....,..., ____ �-- --,,,,.,,..-"---r---.-;;..;.;..;.'---....,...-,,,.----

� 6.00E+08 +-:=::::=4.=�i;".:::.:::.:;;.:;;.:;;.:;;.:;;.:;;�.:;;.:;;,;;t:=-:::.==.:::.:::�.;:.:;;;;;.;;.:;;���=�t:.:::.:::.:::.:;;.:;;.:::.:::::::::�.::;.:;;�::;_;.-r..--a

O.0OE+O0 -+'--'·,:;,;.,_C" :�:·;:.;:;_· ' .;;__,�...;;...�.;...-���=��'--- ...... ""---T"...... ;...;.;;...... ,...... _ '----...i.....,===----"""'"""--'-'...... ; 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 YEAR

Figure 6. Total discharge at Illinois river near Watts Oklahoma YEARLY TOTAL DISCHARGE ILUNOIS RIVER@WATTS, OK

1.60E+09

1.40E+09 • - 1.20E+09 Ill 1.00E+09 • • five year • moving • 8.00E+08 • mean • ..J 6.00E+08 • •• •• 4.00E+08

2.00E+08 -1------__..:;.• •• • __•..:: •------0.00E+0O +-----.----.------..----,---..-----.----.-----,-----, 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 YEAR

Figure 6. Total discharge at Illinois river near watts Oklahoma ILUNOIS RIVER SAMPLE COMPARISON

1000 900 800 700 600 i • auto .§. 500 a usgs 400 300 200 100 0 0 2 4 6 8 10 12 14 STAC:IE(ftl

Figu:ce 7. Compa:cison between USGS cross section samples and auto samples.