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• Phosphorus (P) enrichment eutrophication
• Algal Blooms
• NPDES Permit Point Sources
• Agriculture is a Nonpoint Source of P
Mary Ogdahl, GVSU - AWRI
A) Soil matrix flow: slowerB) Macropore flow: faster
C) TillageD) Crops Regime
(not to scale)
Land Use Area: 45% Agri33% Urban20% Natural
1-9: Tile Drains
10: Lake Macatawa
11: Lake Michigan
(Holland Sentinel)
• Drowned river mouth
• Hyper-eutrophic
• Lake TMDL for 72% TP reduction
• 1997: 125ppb Goal 50ppb
• 2015: 98 ppb
• 91% of P from nonpoint sources
Objectives
1) Conduct a tile drain effluent sampling survey of the Macatawa Watershed
SRP: soluble reactive phosphorus TP: total phosphorus
2) Investigate the seasonal changes in tile drain P
3) Use algal bioassays to measure the bioavailability of P found within the tile drains
Methods: Timeline
2015 2016
Mar Apr May Jun July Aug Sept Oct Nov Dec Jan Feb
Tile Drain Sampling x x x x x x x x x x x x
Bioassays x x x
Sampling Site
Collect Tile Drain Effluent
Bioassay 1Selenastrum
Bioassay 2Lake Mac Inoculum
Measure SRP and TP
Measure chlorophyll-a
Measure chlorophyll-a
Record DischargeRecord Land Management Factors
Determine Algal
Community
Lake Mac Algae Selenastrum
RPM = 175Light (PAR) + Temp: based on season
Low High Mean ± SE Median
SRP (ppb) <5 447 93 ± 11 64
TP (ppb) 10 560 136 ± 13 102
%SRP 0% 89% 60% ± 3% 69%
Tile drain phosphorus is highly bioavailable
Lake Macatawa: 98 ppb TP (2015 mean)
Lake Michigan: 1 – 7 ppb TP (Bioassay sample)
March 23, 2015 – February 23, 2016
Phosphorus Fraction Grouping Chi-
Square df p-value
SRPSite Location 59.834 8 <0.001
Time 3.4993 11 0.9823
TPSite Location 54.53 8 <0.001
Time 4.737 11 0.9432
%SRPSite Location 43.552 8 <0.001
Time 8.5723 11 0.6613
Results: Mean P Concentrations
%SRP
Macatawa Watershed with tile drain sampling sites.
Mean TP (ppb)
0 < 50
50 < 100
100 < 150
150 < 200
200 < 250
250 < 300
X2 = 59.834
p < 0.0001
N = 12
N/A
Phosphorus Fraction Grouping Chi-
Square df p-value
SRPSite Location 59.834 8 <0.001
Time 3.4993 11 0.9823
TPSite Location 54.53 8 <0.001
Time 4.737 11 0.9432
%SRPSite Location 43.552 8 <0.001
Time 8.5723 11 0.6613
Site Acres Drained Crops Winter Cover
Crops Fertilizer Tillage Dominant Soil Hydrologic Type
1 7 Variety No Fish emulsion for some crops No-tillage A/D
2 65 Corn/soybeans No Inorganic fertilizer at spring planting No-tillage C
3 80 Corn NoInorganic fertilizer at
spring planting; manure in fall
Disc-tilled at planting C
4 65 Corn NoInorganic fertilizer at
spring planting; manure in fall
Disc-tilled at planting A/D, B
5 22 Corn NoInorganic fertilizer at
spring planting; manure late summer
Disc-tilled at planting C
6 36 Corn No Inorganic fertilizer at spring planting No-tillage C
7 30 Soybeans No No P-containing fertilizers
Vertical tillage before
plantingB
8 50 Corn NoInorganic fertilizer at
spring planting, manure in fall
Disc-tilled at planting & fall
tillage sub-soiler
C
9 39 Corn Yes: radish, oats, crimson clover
Inorganic fertilizer at spring planting
Vertical till twice during
plantingC
Significant positive linear relationship
y = 0.002x + 0.020
R2 = 0.15
p < 0.05
Season Algae Inoculum Statistical Test Regression Equation Test Statistic p-value
SpringSelenastrum Linear
Regression y = 4217x + 316 R2adj = 0.478 0.0236
Lake Mac Phytoplankton
Spearman Correlation rho = -0.267 0.4933
SummerSelenastrum Linear
Regression y = 12335x + 232 R2adj = 0.289 0.1227
Lake Mac Phytoplankton
Linear Regression y = 132x + 9 R2
adj = -0.145 0.6446
FallSelenastrum Linear
Regression y = -1510x + 385 R2adj = -0.159 0.6060
Lake Mac Phytoplankton
Linear Regression y = 46x - 2 R2
adj = -0.202 0.7104
Lake Macatawa Phytoplankton
Microcystis
Tile drains are a source of bioavailable P to the watershed Above current Lake Macatawa P concentrations
Tile drain P concentrations vary temporally and spatially
Significant positive relationship between %SRP and acres drained
Unexpected response in bioassays
Change in Lake Macatawa algal community
TP Load 25% 35%
0.2 lb yr-1
(lowest) 85 11918.7 lb yr-1
(highest) 8,238 11,533
References Ogdahl, M., and Steinman, A. D. (2015). Project Clarity 2014
Annual Monitoring Report.
Walterhouse, M. (1999). Total Maximum Daily Load (TMDL) for Phosphorus in Lake Macatawa.
