Nutrient Trends in the Des Moines River Donna S. Lutz Des Moines River Water Quality Network

What is the Des Moines River Water Quality Network? Initiated in July 1967 as preimpoundment study for Saylorville Reservoir, expanded to Red Rock Reservoir in 1971 Long-term record, 36 years at many sites, total of 182 parameters, nearly 445,000 individual data records Currently 7 regular sampling sites, monitored 22 times per year for up to 50 parameters Data available through annual reports, paradox database, webpage (soon to be on Iowa STORET)

Des Moines River Basin Length 350 mi Width 50 mi Basin 12,884 sq mi about ¼ size of Iowa Saylorville Reservoir 24 mi valley/54 mi flood 5,520 acres/ 16,100 flood 1,100 ac-ft/yr sedimentation Red Rock Reservoir 18 mi valley/33 mi flood 15,250 acres/ 1,625,00 fl 4,470 ac-ft/yr sedimentation

Raccoon River Sub-basin North Raccoon/Middle Raccoon/South Raccoon Basin 3,411 sq mi

Routine Parameters Physical Physical temperature, flow/elevation temperature, flow/elevation turbidity, secchi disc depth, gas saturation turbidity, secchi disc depth, gas saturation Chemical Chemical dissolved oxygen, BOD, TOC, nutrients, suspended solids dissolved oxygen, BOD, TOC, nutrients, suspended solids metals, pesticides metals, pesticides Biological Biological chlorophyll pigments chlorophyll pigments bacteria bacteria

Long term Long term historical record historical record what is normal? what is normal? trend analysis trend analysis any improvement? any improvement? suspended solids suspended solids nutrient nutrient ammonia, nitrate, phosphate ammonia, nitrate, phosphate pesticides pesticides chlorophyll pigments chlorophyll pigments Important Programs Short term Short term bacteria at beaches bacteria at beaches safe to swim? safe to swim? pesticides in fish pesticides in fish safe to eat? safe to eat? total gas saturation total gas saturation safe for fish? safe for fish? overall monitoring overall monitoring why? what’s up? why? what’s up?

Significant Findings Non-point sources are the main contaminants ; Non-point sources are the main contaminants ; soil erosion and siltation primary resource problem soil erosion and siltation primary resource problem Ave. loading to Red Rock 5,400 metric tons/day Ave. loading to Red Rock 5,400 metric tons/day Point source loading has decreased Point source loading has decreased Improved wastewater treatment has significantly reduced ammonia loading Improved wastewater treatment has significantly reduced ammonia loading Nitrate levels increased until 1982, no current trend Nitrate levels increased until 1982, no current trend Total Phosphate levels have decreased slightly, but only by about 0.01 mg/year Total Phosphate levels have decreased slightly, but only by about 0.01 mg/year

Significant Findings (cont’d) Overall, water quality has significantly improved at most sites, according to water quality index values Overall, water quality has significantly improved at most sites, according to water quality index values Pesticide levels in fish are low, but may still be of concern Pesticide levels in fish are low, but may still be of concern Gas supersaturation-induced gas bubble trauma causes periodic fish kills below Red Rock Dam Gas supersaturation-induced gas bubble trauma causes periodic fish kills below Red Rock Dam

Nutrient Trends Total Nitrogen Total Nitrogen Nitrogen Forms Nitrogen Forms Nitrate Nitrate Ammonia Ammonia Nutrient criteria – total nitrogen (rivers) Nutrient criteria – total nitrogen (rivers) Total Phosphorus Total Phosphorus Orthophosphate Orthophosphate Nutrient criteria – total phosphorus (rivers) Nutrient criteria – total phosphorus (rivers) Phosphorus in sediment Phosphorus in sediment

Importance of River Flow Low Flow Low Flow Nutrients can decrease due to algal utilization Nutrients can decrease due to algal utilization However, nutrients may increase if there are point sources due to lack of dilution However, nutrients may increase if there are point sources due to lack of dilution High Flow High Flow Nutrients, especially nitrate and total phosphate may increase with storm events Nutrients, especially nitrate and total phosphate may increase with storm events Antecedent precipitation important Antecedent precipitation important

Algal Utilization of nutrients under low flow Temp C Flow cfs Chl a mg/m3 NH4 mg/l NO3 mg/l T PO4 mg/l O PO4 mg/l 7/22/ /5/ <0.03

Total N Organic N 14 Ammonia N 7 NO2+NO3 N Nitrogen Forms, % Above Saylorville Reservoir (St. 1) Below Saylorville Reservoir (St.5) Total N Organic N 16 Ammonia N 6 NO2+NO3 N

Total N Organic N 0.84 Ammonia N 0.40 NO2+NO3 N Nitrogen Forms, Concentration Above Saylorville Reservoir (St. 1) Below Saylorville Reservoir (St.5) Total N Organic N 0.89 Ammonia N 0.32 NO2+NO3 N

Nitrite +Nitrate N Ammonia oxidized to nitrate (bacterially mediated) Ammonia oxidized to nitrate (bacterially mediated) Nitrite, intermediate product, ( , max 0.68 mg/l, 99% of samples <0.20 mg/l) Nitrite, intermediate product, ( , max 0.68 mg/l, 99% of samples <0.20 mg/l) Sources Sources Fertilizers, oxidation or organic N, fixation of N 2, precipitation, sewage effluents Fertilizers, oxidation or organic N, fixation of N 2, precipitation, sewage effluents Losses Losses Leaching, assimilation living organisms, conversion to other forms Leaching, assimilation living organisms, conversion to other forms Soluble, easily leaches from soil Soluble, easily leaches from soil

Seasonality of Nitrate Concentrations SpringSummerFallWinter Raccoon River, monthly means unadjusted

Seasonality of Nitrate Concentrations SpringSummerFallWinter Raccoon River, monthly means flow adjusted

Seasonal Kendall Tau Trend Analysis, Significant Trends (95%) (from Monthly Mean Data, flow-adjusted) NO2+NO3 N

Nutrient Criteria T N in rivers 2.62 mg/l DMR Boone DMR Sayl Rac R Van Meter DMR DM DMR Runnells DMR Pella ave min max #months < n44 % Data from 5/

Stations a9 Water Year Mean Discharge (cfs) 3,1923,4282,0856,0647,6627,525 Suspended solids (1,000 kg/day) 1, ,3283,9325, Ammonia N (kg/day) 1,0841, ,2563,1563,669 Nitrate (kg/day) 66,00067,00046,000125,000145,000125,000 Total phosphate 6,7224,4228,35117,679–9,709 Transport of Nutrients and Effects of Reservoirs

Stream Flow Separation and Nitrate Nitrogen Hydrograph separation using USGS program HYSEP (Sloto and Crouse, 1996) Hydrograph separation using USGS program HYSEP (Sloto and Crouse, 1996) Regression analyses determined if annual Q vs P relationship changed over time Regression analyses determined if annual Q vs P relationship changed over time Regression analyses of annual P, Q, Qb, Qs, and Q% over time Regression analyses of annual P, Q, Qb, Qs, and Q% over time Nitrate data summarized into monthly means Nitrate data summarized into monthly means Regression and correlation of monthly mean nitrate to streamflow components Regression and correlation of monthly mean nitrate to streamflow components (Schilling and Lutz)

Results – Streamflow Changes

Streamflow Changes, cont. Annual precipitation also increased during period Annual precipitation also increased during period Regression residuals indicate change in rainfall-runoff relationship since 1916 (p<0.05) Regression residuals indicate change in rainfall-runoff relationship since 1916 (p<0.05) Thus, more precipitation is being routed into streamflow as baseflow in latter portion of 20 th century Thus, more precipitation is being routed into streamflow as baseflow in latter portion of 20 th century

Regression Models Relating Baseflow to Nitrate Qb provided best r 2 value (0.61) compared to Q (0.59), Qs (0.48) or Q% (0.27)

Historical Perspective What role might changing streamflow hydrology in the Raccoon River have had on nitrate concentrations? What role might changing streamflow hydrology in the Raccoon River have had on nitrate concentrations?

Ammonia N Sources Sources Biological degradation of organic matter Biological degradation of organic matter Point source - wastewater effluent Point source - wastewater effluent Nonpoint sources - fertilizer, feedlots Nonpoint sources - fertilizer, feedlots Importance Importance Oxidation of ammonia exerts an oxygen demand Oxidation of ammonia exerts an oxygen demand Unionized ammonia form toxic to aquatic life Unionized ammonia form toxic to aquatic life

Point Source Event 1977

Ammonia N DMR below DM

Unionized Ammonia DMR near Boone R River near Van Meter DMR below Des Moines DMR near Boone R River near Van Meter DMR below Des Moines Date No. months mean Min<0.001 Max %< %7%27%0%3%2%

Phosphorus Major sources Major sources Nonpoint - fertilizers associated with sediment Nonpoint - fertilizers associated with sediment Point – wastewater & food processing plant effluents Point – wastewater & food processing plant effluents Importance Importance Limiting nutrient (when N:P ratio >16:1) Limiting nutrient (when N:P ratio >16:1) Can be re-suspended or released from sediments Can be re-suspended or released from sediments

Seasonal Kendall Tau Trend Analysis, Significant Trends (95%) (from Monthly Mean Data, flow adjusted) Total Phosphate

Phosphorus DMR Boone DMR Sayl RR Van Meter DMR DM DMR Runnells DMR Pella O P ave min max T P ave min max % O P

Nutrient Criteria T P in rivers mg/l DMR Boone DMR Sayl Rac R Van Meter DMR DM DMR Runnells DMR Pella ave min max #months < n59 % Data from

Total Phosphorus Saylorville Reservoir Sediments aveDepth (cm) (cm) Water Content (%) Dry Bulk Density (g/cm 3 ) TP (mg/kg) Head Head Dam Dam Dam Cheney Reservoir, Kansas, USGS, Dam 647 mg/kg, Headwaters 477 mg/kg

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