From the June 2017 issue of GCM magazine:

How much do golf courses contribute to Gulf of Mexico hypoxia?

A reconnaissance study of nitrate and phosphorus concentrations at Iowa courses shows that golf facilities are not a major source of nutrients in groundwater and surface water resources in the state.


Figure 1. The golf courses selected for this study were located throughout Iowa.

Keith Schilling, Ph.D.

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eifg-75 This research was funded in part by GCSAA through the Environmental Institute for Golf.

Nonpoint source pollution from nitrogen and phosphorus contributes to nutrient enrichment in local streams and lakes and development of hypoxic (dead) zones in regional bodies of water, including the Gulf of Mexico. Prompted by the 2008 Gulf Hypoxia Action Plan, many Midwestern states, including Iowa, developed strategies to reduce nutrient loadings to the Gulf of Mexico from point and nonpoint sources. The Gulf Hypoxia Action Plan established a goal of at least a 45% reduction in total nitrogen and total phosphorus loads.

The nonpoint source portion of the Iowa Nutrient Reduction Strategy (INRS) focused exclusively on strategies to reduce nitrogen and phosphorus from agricultural lands — and rightly so, given that corn, soybeans and extended rotations account for more than 70% of Iowa’s land area. Unfortunately, news accounts, commodity interests and public perception often lump other potential nonpoint sources of nitrogen and phosphorus into the same category as agriculture despite their relative unimportance in terms of total land area occupied. One potential source often mentioned is nitrogen and phosphorus contributions from golf courses.


Figure 2. Monitoring well installation and soil logging at the East 18 course. Photos by Matthew Streeter, Iowa Geological Survey

Limited field-scale research suggests that concentrations of nutrients discharged from well-maintained turf at golf facilities are typically well below levels of major concern, but nutrient concentrations at Iowa golf courses have not been investigated despite the prominence of the INRS and the widespread public perception that golf courses are a major contributing source of nitrogen and phosphorus to local rivers. The objective of this study was to measure nitrogen and phosphorus concentrations in surface water and groundwater at a subset of Iowa golf courses to assess the risk posed by these facilities to contributing to nitrogen and phosphorus enrichment of Iowa rivers.

Study methods

Iowa is home to approximately 421 golf courses, with at least one course in each of the state’s 99 counties. We therefore used a stratified random design to select courses for water quality assessment. Six courses were selected for study, comprising an 18-hole course and a nine-hole course in each of three regions (western, central and eastern) in Iowa (Figure 1). Course sizes ranged from 49.4 to 81.5 acres (20 to 33 hectares) for nine-hole courses and 91.4 to 168 acres (37 to 68 hectares) for 18-hole courses. The East 18, East 9 and Central 18 courses were private country clubs located in medium-sized cities (10,000 to 60,000 population), whereas the Central 9, West 18 and West 9 courses were typical small-town golf courses (population <5,000) with a mix of private and public use.

At each course, three shallow monitoring wells were installed using a truck-mounted, hollow-stem drilling rig, one each on representative tee, fairway and rough locations (Figure 2). The golf course superintendents helped select well locations that could be accessed easily with a drilling rig with minimal course disruption. Soil samples were collected during drilling and analyzed for particle size and nutrients, and one well per course (fairway location) was instrumented with a transducer to measure hourly water table fluctuations (Figure 3). Monitoring wells were sampled eight times in 2015 and 2016, and analyzed in the field for temperature, specific conductance, pH and dissolved oxygen. Water samples were submitted to the State Hygienic Laboratory in Iowa City for analysis of nitrate-nitrogen (nitrate) and dissolved phosphorous.

Surface water samples were collected at four golf courses where open water was present. At East 18, a stream flows through the course, and upstream-downstream water samples were collected. At Central 9, a shallow pond is located on the course and is entirely surrounded by typical course features with no discernible inlet or outlet. At Central 18, an 8-inch (20.3-centimeter) tile from an adjacent agricultural field was sampled where it enters the course (Figure 4). The tile drains to a small pond, which then empties into a larger pond. Both the small and large ponds were sampled during this study. In the middle of the course at West 18, a small pond receives overland flow from the course and drainage from an urban area across the road. All surface water samples were analyzed in the field and laboratory with the same equipment and methods used for groundwater samples.


Figure 3. Monitoring wells were mounted flush to the ground surface at the courses for ease of management. At one well per course, a pressure transducer was installed to record hourly water level fluctuations.

Nutrient concentrations

Annual precipitation measured in the vicinity of the six courses averaged 43 inches (1,096 millimeters) in 2015 and 40 inches (1,012 millimeters) in 2016, amounts that are above the average for Iowa (which is about 34 inches, or 860 millimeters). The depth to the water table varied among the courses, ranging from an average of 18.7 feet (5.7 meters) at the West 18 course (the greatest depth) to less than 6.5 feet (2 meters) at the three courses with the shallowest depth. All the wells showed seasonal patterns of increasing in spring and early summer with precipitation inputs, and decreasing in midsummer through fall in response to evapotranspiration.

Results indicate that, with the exception of one well located at the West 18 course, groundwater nitrate concentrations were very low (Figure 5). Eight of the 18 wells did not have detectable nitrate (<1 milligram/liter), and nine wells contained nitrate ranging from 1 to 5 milligrams/liter. Because the golf courses were selected using a stratified random design, we can generalize the results to other Iowa golf courses. Based on an average of all wells at the six courses, the overall mean nitrate concentration in Iowa golf courses was 2.2 milligrams/liter.

At the West 18 course, a single well in the fairway had a mean nitrate concentration of nearly 15 milligrams/liter, which was something of an anomaly. The soils measured at that location were not different from the other two well locations at the course, and the other two wells had average nitrate concentrations of 1.3 and 4.7 milligrams/liter. Furthermore, the current nitrogen application rate for the fairway was not particularly high. We hypothesize that the high nitrate concentrations may have been due to historical management practices at the club or nitrogen storage in the soil profile. The West 18 course is in the region of Iowa underlain by thick silt (loess) deposits, and the unsaturated soil zone is nearly 20 feet (6 meters) thick at this location. An estimated decade-long delay may be expected between changes in turf management operations implemented at the land surface and changes in groundwater quality.


Figure 4. Location of tile, surface water and groundwater monitoring well samples collected at Central 18 and East 18 golf courses as shown in a 2015 aerial photograph from the Iowa Department of Natural Resources, Geographic Information Systems Library. Images courtesy of NRGIS Library

Groundwater-dissolved phosphorus concentrations varied among courses and well positions. They ranged from 0.05 to 0.22 milligram/liter and averaged 0.13 milligram/liter (Figure 5). These groundwater phosphorus concentrations are very similar to concentrations measured in a variety of settings across Iowa.

Nutrient loading rates

To estimate the nutrient loading rates, the average annual nitrogen and phosphorus concentrations at the six courses were multiplied by their respective annual groundwater recharge measurements developed from the continuous water table measurements. Annual nitrate yields ranged from 0.89 to 8.6 pounds/acre (0.1 to 9.7 kilograms/hectare) among the six courses, and among all courses and both years, nitrate yields averaged approximately 2.7 pounds/acre (3 kilograms/hectare). Compared with annual nitrogen fertilizer rates, results indicate that nitrate yield represented approximately 6% to 8% of applied nitrogen at the East 18, East 9 and West 18 courses, and less than 0.2% of the applied nitrogen at the West 9, Central 18 and Central 9 courses. 

Annual phosphorus yields ranged from 0.08 to 0.46 pound/acre (0.09 to 0.52 kilogram/hectare) among the six courses and averaged approximately 0.23 pound/acre (0.26 kilogram/hectare) for all courses. Only one golf course (West 9) applied any phosphorus fertilizer. It was applied to the tee, and the phosphorus yield represented approximately 1.8% of the applied phosphorus.

Comparisons to watershed and state conditions

To put the annual nitrate loading rates in perspective, annual nitrate yields measured at the golf courses were compared with nitrate yields measured in their respective watersheds. The golf course nitrate yields were approximately 10% of the annual watershed yield for 2015 and 2016 (Table 1). This suggests that, compared with the rest of the land areas in their respective watersheds, golf courses are contributing less nitrate per hectare to their receiving rivers.

The average golf course nitrate concentrations were also compared with those measured in shallow private drinking water wells (wells less than 30 feet [9 meters] deep) located within a 20-mile (32-kilometer) radius of each course (Table 2). The results for private drinking water wells were gathered from an Iowa Department of Natural Resources database. Results indicated that nitrate concentrations in groundwater beneath golf courses were lower than those measured in nearby private drinking water wells.


Figure 5. Average groundwater nutrient concentrations were measured at tee, fairway and rough locations at the six Iowa golf courses.

Lastly, the contribution of golf courses to statewide Iowa nitrate loads was estimated by comparing the total amount of nitrate lost from golf courses with the estimated annual loads reported in the Iowa Nutrient Reduction Strategy (5). Iowa has 421 golf courses: 273 nine-hole courses with average course areas of 69 acres (28 hectares), and 148 18-hole courses with average course areas of 138.4 acres (56 hectares) (personal communication, Iowa Golf Course Superintendents Association). Assuming an average golf course yield of 2.9 pounds/acre (3.3 kilograms/hectare), the total annual nitrate lost from Iowa courses is approximately 115,908 pounds (52,575 kilograms). The annual nitrate load exported from Iowa was estimated to be 614,000,000 pounds (278,505,715 kilograms) (5), meaning golf courses were estimated to contribute approximately 0.019% of the total nitrate load exported from Iowa.

Surface water quality

Surface water samples were collected at four golf course sites based on availability, and generalizing across the monitored sites is difficult. At one location (West 18), groundwater nitrate and phosphorus concentrations were higher in shallow groundwater than in a golf course pond, but at three other courses, groundwater nitrate concentrations were the same or lower than those of surface water streams or ponds. Conditions at the Central 18 course were unique in that golf course groundwater could be compared with tile water draining an adjacent row crop field. In this case, tile water had nitrate concentrations of 13.1 milligrams/liter, whereas golf course groundwater had nitrate values below 1 milligram/liter. Considering that both sites have the same soils and were monitored during the same climate regime, differences in subsurface water concentration can only be due to differences in land use and fertilizer management. At the Central 18 location, nitrate in drainage water from the row crop field was more than 13 times higher than it was in groundwater beneath the golf course.


Table 1. Comparison of golf course nitrate-nitrogen loading rates to watershed yields. River yields estimated by multiplying daily river discharge at a U.S. Geological Survey gaging station located at the basin outlet by daily nitrate-nitrogen concentrations estimated using linear interpolation of Iowa Department of Natural Resources ambient water data collected at co-located sites (

At the East 18, the course may be diluting nitrate concentrations in a small stream that meanders through the course. Average concentrations decreased approximately 2.2 milligrams/liter from upstream to downstream locations (10.2 to 8 milligrams/liter), and baseflow containing low nitrate concentrations from the course (1.5 milligrams/liter) may be contributing to lower downstream concentration levels. However, without more intensive monitoring of surface water volumes and concentrations (4), the data on surface water quality from the Iowa golf courses is not sufficiently robust to make definitive conclusions about golf course effects on surface water resources.


Study results indicate that golf courses in Iowa are not a major source of nutrients for groundwater and surface water resources. Nitrate concentrations were not detected above 1 milligram/liter at three of the six courses monitored in this study, and the overall mean nitrate-nitrogen concentration in Iowa golf courses was 2.2 milligrams/liter. Nitrate yields averaged 3.3 kilograms/hectare at the six courses, which represents approximately one-tenth of the yield produced by the watershed that contains the course, and 0.019% of the total nitrate load exported from Iowa. No correlation was observed among fertilizer application rates, soil nitrogen and groundwater nitrate concentrations. Nitrate loading rates represented approximately 0.1% to 8% of the nitrogen fertilizer applied. Groundwater phosphorus concentrations averaged 0.13 milligram/liter, which was similar to concentrations measured in a variety of settings across Iowa. 


Table 2. Comparison of nitrate concentrations (milligrams/liter) measured at Iowa golf courses to private wells located within 20 miles of the course. n = the number of wells tested.

Because only one course (West 9) applied phosphorus fertilizer (tee areas only), we could not assess the influence of current management practices on phosphorus concentrations and loading rates. Phosphorus concentrations in golf course groundwater are higher than proposed nutrient criteria for streams in the ecoregion, but these criteria are routinely exceeded in shallow groundwater in Iowa (2,6). 

Results from the Iowa golf course study are consistent with national assessments that indicate groundwater nutrient concentrations beneath golf course facilities are typically well below levels of concern (1,3). This study fills an important gap by providing information from Midwestern facilities that were notably missing from national assessments. Overall, the study results should prove useful in addressing public concerns about nutrient contributions from golf courses in Midwestern states where nutrient reduction strategies are being pursued.


Funding for this study was provided by GCSAA, the Iowa GCSA, the Iowa Golf Association and the Iowa Turfgrass Institute. Jeff Wendell, Randy Robinson, Chauncey Berry and the Iowa water quality committee members provided outstanding leadership and assistance with the project. The author is extremely grateful to the golf course superintendents at the six courses for their willingness to participate in the study.

Literature cited

  1. Baris, R.D., S.Z. Cohen, N.L. Barnes, J. Lam and Q. Ma. 2010. Quantitative analysis of over 20 years of golf course monitoring studies. Environmental Toxicology and Chemistry 29(6):1224-1236.
  2. Burkart, M.R., W.W. Simpkins, A.J. Morrow and J.M. Gannon. 2004. Occurrence of total dissolved phosphorus in unconsolidated aquifers and aquitards in Iowa. Journal of the American Water Resources Association 40(3):827-834. doi:10.1111/j.1752-1688.2004.tb04461.x
  3. Cohen, S., A. Svrjcek, T. Durborrow and N.L. Barnes. 1999. Water quality impacts by golf courses. Journal of Environmental Quality 28:798-809. doi:10.2134/jeq1999.00472425002800030010x
  4. King, K.W., J.C. Balogh, K.L. Hughes and R.D. Harmel. 2007. Nutrient load generated by storm event runoff from a golf course watershed. Journal of Environmental Quality 36(4):1021-1030. doi:10.2134/jeq2006.0387
  5. Iowa Nutrient Reduction Strategy (INRS). 2013. Available at Accessed March 30, 2017.
  6. Schilling, K.E., M.T. Streeter, D. Quade and M. Skopec. 2016. Groundwater loading of nitrate-nitrogen and phosphorus to an Iowa Great Lake. Journal of Great Lakes Research 42(3):588-598.

Keith Schilling is a research scientist for the Iowa Geological Survey, University of Iowa, Iowa City.