ERDC/TN APCRP-EA-15

April 2007

Contribution of Potamogeton crispus

Decay to the Phosphorus Budget of

McGinnis Lake, Wisconsin

by William F. James, Amy Dechamps, Nancy Turyk, and Paul McGinley

PURPOSE: This research evaluated the potential contribution of Potamogeton crispus (curly-leaf 

pondweed) senescence to the phosphorus budget of a small Wisconsin seepage lake. 

BACKGROUND: Internal phosphorus loading (i.e., recycling of phosphorus stored in the sediment 

of lakes) represents an important source of nutrients for phytoplankton growth that needs to be 

considered in lake management plans that address phosphorus control. Phosphorus can be recycled 

from sediments via eH (i.e., oxidation-reduction) and pH reactions (Mortimer 1971, James et al. 

1996), movement of groundwater through phosphorus-rich sediment (Brock et al. 1982), sediment 

phosphorus resuspension and boating activity (James and Barko 1994, James et al. 2003), and plant 

decomposition (Carpenter 1980). McGinnis Lake (Adams County, Wisconsin) is a small (13 ha) 

glacial seepage lake that currently exhibits mesoeutrophic conditions (total P = ~ 0.025 mg L-1; 

chlorophyll = 8-13 μg L-1). However, there is concern that internal phosphorus inputs by 

groundwater and by bottom sediment during periods of hypolimnetic anoxia may be contributing to 

algal blooms in the system. In addition, the nuisance macrophyte, Potamogeton crispus, occupies 

most shallow regions in the lake. The life cycle of this species is unusual because dieback occurs in 

mid-summer. Root uptake of phosphorus from the sediments by this plant, incorporation as tissue 

phosphorus, and senescence in mid- to late June can result in substantial recycling of phosphorus 

into the water column for phytoplankton uptake and growth during the middle of the growing season 

(James et al. 2003). In addition, metabolic activities (i.e., photosynthesis and respiration) of 

macrophyte communities can result in substantial diel variations in eH and pH that can indirectly 

enhance phosphorus flux from sediments, exacerbating internal phosphorus recycling to the water 

column. The objectives of this study were to quantify important phosphorus flux pathways in 

McGinnis Lake and to identify phosphorus control management activities that can reduce these 

inputs to the lake. 

METHODS 

Study Site. McGinnis Lake has two basins (lobes) connected by a narrow channel (Figure 1). The 

North lobe has an area of ~ 4.6 ha and a maximum depth of 8.5 m. The South lobe has a much larger 

surface area (8.5 ha) and is shallow; maximum depth is ~ 3 m. No defined watershed tributary inflow 

to the lake exists and the hydrology of the system is dominated by groundwater seepage. The 

outflow is located in the South lobe and consists of a surface withdrawal structure. The lake is 

surrounded by permanent and seasonal residential homes that use septic systems. 
Report Documentation Page Form Approved

OMB No. 0704-0188

Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and

maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information,

including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington

VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it

does not display a currently valid OMB control number.

1. REPORT DATE

APR 2007

2. REPORT TYPE

N/A

3. DATES COVERED

 - 

4. TITLE AND SUBTITLE

Contribution of Potamogeton crispusDecay to the Phosphorus Budget

ofMcGinnis Lake, Wisconsin

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S) 5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

U.S. Army Engineer Research and Development Center Geotechnical and

Structures Laboratory 3909 Halls Ferry Road Vicksburg, MS 39180-6199

8. PERFORMING ORGANIZATION

REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S)

11. SPONSOR/MONITOR’S REPORT 

NUMBER(S)

12. DISTRIBUTION/AVAILABILITY STATEMENT

Approved for public release, distribution unlimited

13. SUPPLEMENTARY NOTES

The original document contains color images.

14. ABSTRACT

15. SUBJECT TERMS

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 

ABSTRACT

SAR

18. NUMBER

OF PAGES

19

19a. NAME OF

RESPONSIBLE PERSON

a. REPORT

unclassified

b. ABSTRACT

unclassified

c. THIS PAGE

unclassified

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std Z39-18 
ERDC/TN APCRP-EA-15 

April 2007 

Figure 1. Map of McGinnis Lake showing sampling stations. 

Hydrology. Water discharge from the lake through the outlet (Figure 1) was monitored continuously in 2002 using an ISCO 4150 area-velocity meter. Daily precipitation over the lake surface was 

measured at a station located next to the lake’s outflow. Relative lake level was measured at 2-day 

intervals. Groundwater flow into McGinnis Lake was measured by the University of Wisconsin – 

Stevens Point1 using mini-piezometer methodology. Forty sampling stations were established 

around the lake for measurement of groundwater upwelling and downwelling. Groundwater samples 

collected from the mini-piezometers were analyzed for soluble reactive phosphorus. 

 

Routine Water Quality Monitoring. The University of Wisconsin – Stevens Point conducted a 

water quality monitoring study on McGinnis Lake at biweekly intervals between May and 

September 2002 (Figure 1). Sampling stations were established in the deep basin of the North lobe 

and in the approximate center of the South lobe for water sampling purposes. In situ measurements 

of temperature, dissolved oxygen, conductivity, and pH were collected at 2-ft depth intervals 

between the surface and bottom at each station. Secchi disk transparency was measured using an 

alternating black and white 10-cm disk. Water samples for chemical analyses were collected 0.6 m 

below the lake surface, in the metalimnion, at the top of the hypolimnion, and immediately above the 

sediment surface in the North lobe. A composited water sample representing the entire water column 

was collected in the South lobe using an integrated sampler. Water samples were transported to the 

University of Wisconsin – Stevens Point in coolers on ice for analysis of the following variables 

(i.e., those used in this study) using standard analytical and automated techniques (American Public 

1

 Personal Communication. 2003. A. DeChamps, N. Turyk, and P. McGinley, University of Wisconsin – Stevens 

Point. 

2
ERDC/TN APCRP-EA-15 

April 2007 

Health Association (APHA) 1998; Lachat Instruments, Hach Company, Lachat Division, Loveland, 

Colorado): total phosphorus, soluble reactive phosphorus, and chlorophyll. Samples for total phosphorus were digested with potassium persulfate before colorimetric analysis (Lachat Method 

10-115-01-1-B). A portion of the water sample was filtered through a 0.45-μm filter before determination of soluble reactive phosphorus. Chlorophyll was extracted using 90 percent acetone (APHA 

1998). The trophic state index of McGinnis Lake was calculated using equations developed by 

Carlson (1977) and Lillie et al. (1993). 

Internal Sources of Phosphorus to the Lake. 

Phosphorus Release from Sediments. Triplicate cores were collected at seven stations distributed 

throughout the lake at differing depths (Figure 1). For each station, one sediment core was analyzed 

for phosphorus release under oxic conditions at pH ~8, another core for phosphorus release under 

oxic conditions at pH ~ 9, and a final core for phosphorus release under anoxic conditions. 

A Wildco KB Sediment Core Sampler (Wildco Wildlife Supply Co.), equipped with an acrylic core 

liner (6.5-cm ID and 50-cm length), was used to collect sediment. The core liners, containing both 

sediment and overlying water, were immediately sealed using stoppers and stored in a protective box 

until analysis. Additional lake water was collected for incubation with the collected sediment. 

In the laboratory, sediment cores were carefully drained of overlying water and the upper 10 cm of 

sediment was transferred intact to a smaller acrylic core liner (6.5-cm dia and 20-cm ht) using a core 

remover tool. Lake water was filtered through a glass fiber filter (Gelman A-E), and 300 mL was 

siphoned onto the sediment contained in the small acrylic core liner without causing sediment resuspension. Sediment incubation systems consisted of the upper 10 cm of sediment and filtered overlying water contained in acrylic core liners that were sealed with rubber stoppers. The sediment 

incubation systems were placed in a darkened environmental chamber and incubated at a constant 

temperature (20 °C). The incubation temperature was set to a standard temperature for all stations 

for comparative purposes. 

The oxidation-reduction environment in each system was controlled by gently bubbling either air 

(oxic) or nitrogen (anoxic) through an air stone placed just above the sediment surface. Higher pH 

was adjusted by bubbling core systems with carbon dioxide-free air. Bubbling action ensured complete mixing of the water column but did not disrupt the sediment. Control systems, containing only 

lake water, were incubated under the same redox and pH conditions. 

Water samples for soluble reactive phosphorus (SRP) were collected daily from the center of each 

sediment incubation system using an acid-washed syringe and filtered through a 0.45-μm membrane 

syringe filter (Nalge). The water volume removed from each system during sampling was replaced 

with filtered lake water preadjusted to the proper oxidation-reduction condition. SRP was determined colorimetrically using the ascorbic acid method (APHA 1998). Rates of phosphorus release 

from the sediment (mg m-2 d-1) were calculated as the linear change in concentration (corrected for 

dilution effects) in the overlying water divided by time and the area of the incubation core liner. 

A station was established in the South lobe of the lake for determination of diel and seasonal variations in dissolved oxygen and pH in macrophyte beds that might impact rates of phosphorus release 

from sediments (Figure 1). YSI 6000 in situ water quality monitors (YSI Incorporated, Yellow 

3
ERDC/TN APCRP-EA-15 

April 2007 

Springs, Ohio) were deployed 0.25 m above the sediment and measurements were collected at 4-hr 

intervals between May and September. Deployed monitors were exchanged every two weeks with 

new, calibrated monitors. Both before and after deployment, the monitors were pre- and postcalibrated using Winkler titrations and pH buffers (APHA 1998). Before each deployment, the 

monitors and probes were cleaned and dissolved oxygen probes were serviced with new membranes. 

Potamogeton crispus decomposition. The University of Wisconsin – Stevens Point conducted a survey to determine P. crispus biomass near the time of macrophyte scenescence in early June of 2002 

using quadrat sampling techniques. Three transects were established randomly in the North lobe and 

six transects were established randomly in the South lobe, perpendicular to the shoreline (Figure 1). 

For sampling purposes, each transect was demarcated with a rope extending from the shoreline to 

the 6-ft depth. Each transect was stratified with respect to depth using the 0- to 3-ft and 3- to 6-ft 

depth contours. One sampling location was established within the 0- to 3-ft depth contour and two 

sampling locations were established in the 3- to 6-ft depth contour. This sampling stratification 

scheme weighted the larger area encompassed by the 3- to 6-ft depth contour by ~ 2x. Stations were 

located by estimating the total distance between the two contours, then using a random number to 

determine the percent distance along the transect to sample. 

The quadrat sampler measured 0.5 m x 0.5 m and consisted of an enclosure ~ 6 ft tall. The sampler 

was lowered to the lake bottom to trap a known sediment surface area containing a macrophyte community. A rake was used to remove plant material from the sampler. On the boat, the cut material 

was gently rinsed to remove sediment and periphytin and sorted to determine P. crispus biomass 

only (other macrophytes were removed from the sample). P. crispus samples were rinsed in a dilute 

(0.5 M) hydrochloric acid solution to remove calcium-carbonate and then weighed for fresh mass. 

Rinsed samples were brought back to the laboratory and dried at 40 o

C to a constant weight for 

determination of an FW:DW conversion factor and percent tissue phosphorus. Tissue phosphorus 

analyses were performed by the University of Wisconsin – Stevens Point. Lake-wide mass, and mass 

of P. crispus in the North and South lobes of McGinnis Lake were estimated by weighting average 

biomass and phosphorus content with respect to area in each lobe. For the North lobe, P. crispus

growth was assumed to be confined to the 2-m depth or less. For the South lobe, the entire area was 

used to estimate average P. crispus biomass. P. crispus decomposition, loss of tissue phosphorus, 

and internal phosphorus loading from this source were modeled using exponential decay equations 

developed by James et al. (2003) for P. crispus decomposition in Half Moon Lake, Wisconsin. 

Phosphorus Loading Reduction Modeling. The water quality model Bathtub was used to 

assess current water quality conditions and the probable response of important water quality indicators (i.e., phosphorus, chlorophyll, Secchi transparency) to a reduction in phosphorus inputs to the 

lake (Walker 1996). The model used two lake compartments in order to assess lake responses to 

phosphorus loading reductions in the North and South lobes. The averaging period for the model 

was May through September. 

RESULTS AND DISCUSSION 

Phosphorus Sources to the Lake. Modest increases in discharge flow from McGinnis Lake 

were associated with several precipitation events that occurred during the summer period (Figure 2). 

Discharge flows were highest in May through June during a period of frequent precipitation and 

lower in July through September as a result of drier conditions. Relative lake elevation exhibited 

4
ERDC/TN APCRP-EA-15 

April 2007 

very minor peaks which coincided with precipitation events. Lakewide groundwater flow was estimated as the approximate base flow in the discharge from the lake (Figure 2). Groundwater flow was 

assumed constant during the study period. The summer hydrological balance indicated that groundwater and precipitation accounted for all of the water income to the lake (Table 1). Overland runoff 

was not measured directly during the study period. However, the hydrological balance indicated that 

this component was negligible to the water budget (Table 1). 

Figure 2. Seasonal variations in mean daily discharge flow, relative pool elevation, daily precipitation and 

groundwater base flow between May and September 2002. 

Table 1 

Mean Summer (May – September, 2002) Inflows and Discharges in McGinnis Lake 

Hydrologic Variable Flow (cms) Percent 

Change in Pool -0.00013 

Precipitation 0.00584 22.8 

Groundwater 0.01940 75.8 

Inflows 

Overland Runoff 0.00035 1.4 

Discharges 0.02572 

cms = cubic meters per second. 

Overland runoff was estimated indirectly by mass balance. However, water losses from McGinnis Lake via groundwater 

downwelling and evaporation were not included in the hydrological budget and estimation of overland runoff. 

5
ERDC/TN APCRP-EA-15 

April 2007 

Discrete groundwater flows, measured by the University of Wisconsin – Stevens Point using minipiezometers, were greatest in the North lobe of McGinnis Lake and much lower in the South lobe 

(Figure 3). There was an inverse relationship between soluble reactive phosphorus concentration in 

the groundwater and groundwater flow velocity (Figure 3). Thus, higher groundwater flow velocities 

were associated with lower concentrations of soluble reactive phosphorus in the groundwater. The 

average groundwater soluble reactive phosphorus concentration entering the lake, weighted with 

respect to flow velocity, was 0.021 mg L-1. 

Figure 3. Relationship between mini-piezometer flow velocity and soluble 

reactive phosphorus (P) concentration for McGinnis Lake. 

The South lobe exhibited greater P. crispus biomass than the North lobe during the June survey 

(Table 2). However, P. crispus biomass was generally low throughout the lake. Leaching (defined as 

cellular autolysis) and decomposition (defined as fragmentation and bacterial breakdown) of 

P. crispus and flux of phosphorus to the water column were modeled using equations developed 

from another study (James et al. 2003). Leaching of phosphorus from plant tissue dominated breakdown during the early stages of senescence (Figure 4). The model suggested that nearly complete 

breakdown of senescing P. crispus occurred within 30 days. Overall, ~ 6.8 kg of phosphorus in 

P. crispus biomass was potentially available for breakdown and release into the water column (primarily the South lobe) during senescence in the summer. 

6
ERDC/TN APCRP-EA-15 

April 2007 

Table 2 

Estimates of P. crispus Phosphorus (P) Content Near the Time of 

Peak Biomass (June) in the North and South Lobes of McGinnis 

Lake 

Location Biomass (g m-2) P Content (mg m-2) P Content (%) 

North Lobe 3.27 5.47 1.67 

South Lobe 25.03 48.82 1.95 

Lakewide 17.37 33.56 1.93 

Areal estimates were weighted with respect to the entire area of each lobe or the entire lake. 

Figure 4. Loss of phosphorus via leaching (i.e., cellular autolysis) and 

breakdown (i.e., fragmentation and microbial metabolism) for 

Potamogeton crispus near the time of senescence in June. 

Rates of phosphorus release from sediments in McGinnis Lake were regulated primarily by anoxic 

(i.e., no dissolved oxygen in the water due to bacterial respiratory demand), reducing conditions. 

Fluxes of phosphorus from the sediments were not detected under oxic conditions or at high pH. 

There was a linear relationship between rates of phosphorus release from the sediments under anoxic 

conditions and depth below the lake surface (Figure 5). This depth-related pattern is typical for lakes 

and due to the seasonal erosion of fined-grained phosphorus-rich sediments from shallow regions of 

the lake and settling to deeper accumulation zones during periods of turnover (James et al. 2000). 

Anoxic rates of phosphorus release from sediments in the deep basin of the North lobe were very 

high at > 5 mg m-2 d-1, suggesting that sediments in this region were phosphorus-rich. When 

weighted with respect to depth, the overall rate of phosphorus release from sediments in the North 

7
ERDC/TN APCRP-EA-15 

April 2007 

lobe was 3.5 mg m-2 d-1, which was indicative of eutrophic sediments. Anoxic rates were lower at 

~ 2.7 mg m-2 d-1 for sediments collected in the shallow South lobe of the lake. However, this mean 

value was still within the range of rates found for eutrophic lakes. 

Figure 5. Variations in laboratory rates of internal phosphorus (P) loading under 

anoxic conditions as a function of collection depth in the North lobe of 

McGinnis Lake. 

Water Quality Patterns. The North lobe of McGinnis Lake exhibited strong thermal stratification 

during the summer period (Figure 6). Between the end of May and August, the epilimnion was confined to the upper 2 m depth of the lobe. Associated with thermal stratification was the development 

of anoxic conditions in the hypolimnion. Anoxia extended from the bottom to near the 3-m depth 

within the metalimnion between the end of May and September. 

8
ERDC/TN APCRP-EA-15 

April 2007 

Figure 6. Contour plot of seasonal variations in (upper) temperature and (lower) dissolved oxygen in the 

North lobe of McGinnis Lake. Temperature contours are °C and dissolved oxygen contours are 

mg L-1. Gray shaded areas represent dissolved oxygen concentrations < 2 mg L-1. Black areas 

represent dissolved oxygen concentrations near zero. 

9
ERDC/TN APCRP-EA-15 

April 2007 

In situ patterns of pH in the South lobe were high (> 10) during May, coincident with the seasonal 

growth period of P. crispus (Figure 7). Values declined and fluctuated near 9 in late June through 

early July. They declined to < 9 in late July through early August, and increased to about 9 in late 

August. Diel fluctuations in pH were caused by net photosynthetic activities during the day that 

cause increases in pH and net respiratory activities at night that cause declines in pH. Although high 

pH induced by macrophyte photosynthesis can indirectly enhance phosphorus release from sediment 

through ligand exchange (James et al. 1996), phosphorus release from sediments in McGinnis Lake, 

measured in the laboratory, were not found to be susceptible to high pH and ligand exchange 

processes. Thus, pH was not a factor in internal P loading from the sediments. 

Figure 7. Diel and seasonal variations in in situ pH measured in the South lobe 

of McGinnis Lake between May and September 2002. 

Dissolved oxygen concentrations in the South lobe were high in May, coincident with high pH and 

the occurrence of P. crispus growth (Figure 8). Concentrations declined in early June and 

approached anoxia at night on several days. Similar to pH patterns, dissolved oxygen fluctuated on a 

diel basis as a result of photosynthetic (i.e., increased concentration) and respiratory (i.e., decreased 

concentration) metabolic processes. Seasonal declines in dissolved oxygen and the occurrence of 

anoxic conditions at night on several occasions in June may have been attributed to the development 

of peak P. crispus biomass and the onset of its senescence. In July through September, dissolved 

oxygen concentrations exhibited a bimodal seasonal pattern. They exhibited a peak in July and 

September and a period of depressed concentrations in late July through early August. During the 

latter period, dissolved oxygen concentrations approached anoxic conditions on four nights. Internal 

P loading from sediments likely occurred in the South lobe of the lake under conditions of nighttime 

anoxia. 

10
ERDC/TN APCRP-EA-15 

April 2007 

Figure 8. Diel and seasonal variations in in situ dissolved oxygen measured in the South lobe of 

McGinnis Lake between May and September 2002. 

Coincident with stratification and hypolimnetic anoxia in the North lobe was the buildup of high 

concentrations of total phosphorus in the bottom waters, suggesting the occurrence of internal P 

loading via release from profundal sediment under anoxic conditions (Figure 9). Total phosphorus 

concentrations were much lower in the surface waters of the North lobe. In the South lobe, total 

phosphorus was also low (i.e., < 0.05 mg L-1). Chlorophyll concentrations were < 20 μg L-1 in the 

surface waters of the North lobe during the summer (Figure 9). The South lobe exhibited a concentration peak in early July which may have been associated with P. crispus decomposition and uptake 

of phosphorus leached from plant tissue for growth. However, bottom-dwelling filamentous algae 

were present at the time of sampling and may have contaminated the sample, biasing it toward a 

higher concentration than was actually present in the water column. During other sampling dates in 

the summer, the chlorophyll concentration was < 20 μg L-1 in the South lobe. 

Mean summer concentrations of total phosphorus, chlorophyll, Secchi transparency, and trophic 

state indicators (TSI) for the surface waters of the North and South lobes of McGinnis Lake are 

shown in Table 3. Overall, mean concentrations of chlorophyll and total phosphorus were low in 

both lobes. The TSI values for these variables between 40 and 60 indicated only moderately 

eutrophic conditions in the lake. Mean Secchi transparency was between 1.1 m and 1.6 m. 

11
ERDC/TN APCRP-EA-15 

April 2007 

Figure 9. Seasonal variations in total phosphorus and chlorophyll at various depths in the North lobe and 

integrated over the entire water column in the South lobe of McGinnis Lake. 

Table 3 

Estimates of the Carlson and Wisconsin State Trophic Index (TSI) Values for the North 

and South Lobes of McGinnis Lake During the Summer (May-September) 20021

Carlson TSI Wisconsin TSI 

Location SD (m) Chla (μg L-1) TP (mg L-1) TSISD TSICHLA TSITP TSISD TSICHLA TSITP

North lobe 1.6 8.00 0.023 53.4 50.5 52.4 53.2 51.0 49.4 

South lobe 1.1 12.76 0.029 58.7 54.1 54.2 58.6 55.5 52.7 

1

 Concentrations of chlorophyll (Chla), total phosphorus (TP), and Secchi transparency (SD) represent epilimnetic means over the

summer period. 

Phosphorus Budgetary Analysis. The above observations were used to construct a phosphorus 

budget for the lake (Table 4). Inputs to the lake included phosphorus from direct precipitation over 

the lake (Pprecipitation), groundwater (Pgroundwater), P. crispus decomposition during the summer 

(Pplant decomposition), and phosphorus release from sediments and movement into the water column 

(Psediment). The measured output from the lake was phosphorus discharge from the outlet structure 

(Pdischarge). Phosphorus discharge from the lake via groundwater downwelling was assumed to be 

12
ERDC/TN APCRP-EA-15 

April 2007 

negligible. Using a mass balance approach, sedimentation of particulate phosphorus (Pdeposition) in the 

lake was calculated as: 

Δ= + + + − + PP P P P P P lake precipitation groundwater plant decomposition sediment deposition discharge ( ) ( ) (1) 

where ∆Plake is the change in phosphorus mass in the water column. All fluxes were normalized with 

respect to a 153-day summer period (i.e., May through September) and the surface area of the North 

lobe, the South lobe, or the entire lake. For instance, P. crispus phosphorus fluxes to the lake via 

decomposition occurred over a 30-day period between late June and July. However, during the other 

123 days of the summer period (i.e., May through September), phosphorus fluxes from this source 

were assumed to be zero. Thus, the overall phosphorus flux from this source was adjusted to account 

for periods of zero flux as well as flux via decomposition during the May through September 

averaging period. 

Table 4 

Sources and Sinks of Phosphorus (P) to the Epilimnion of McGinnis Lake During the 

Summer (May-September) Period 2002 

Flux 

North lobe rate 

(mg m-2 d-1) 

South lobe rate 

(mg m-2 d-1) 

Lake-wide rate 

(mg m-2 d-1) 

Lake-wide mass 

(kg) 

Precipitation 0.11 0.11 0.11 2.2 

Groundwater 0.59 0.08 0.26 5.3 

Plant decomposition 0.05 0.50 0.34 6.8 

Bottom sediment 0.161 0.08 0.11 3.6 

P inputs 

Overland runoff 0 0 0 0 

P output Discharge 0.62 12.5 

1 Represents P flux to the epilimnion. 

For the South lobe, Psediment was assumed to be zero during periods when dissolved oxygen was 

≥ 1 mg L-1 and ~ 2.7 mg m-2 d-1 when dissolved oxygen conditions in the lobe were < 1 mg L-1, 

based on an analysis of in situ dissolved oxygen patterns in the lobe (Figure 8). Anoxia occurred in 

the South lobe ~ 3 percent of the time during the summer period. For the North lobe, an attempt was 

made to estimate the vertical flux of phosphorus from the hypolimnion into the surface waters during 

the summer, as not all phosphorus originating from the bottom sediments will be transported 

vertically into the surface waters for uptake by algae in a stratified system. Observations of phosphorus concentrations in the surface waters and bottom waters during the summer period (Figure 10) 

and information on fluxes of phosphorus from other sources (i.e., the phosphorus mass balance 

Equation 1) applied to the North lobe of McGinnis Lake were used to compute an upward phosphorus flux of ~ 0.16 mg m-2 d-1 from the hypolimnion into the epilimnion during the summer. 

The dominant phosphorus input to the North lobe was from groundwater (59 percent), which 

reflected groundwater flow patterns to this region of the lake (Table 4). Even though phosphorus 

flux from bottom sediments was high in the North lobe and anoxic conditions occurred in the hypolimnion during most of the summer period, only about 5 percent of this phosphorus was estimated to 

be transported into the surface waters for potential uptake by algae. Thus, Psediment represented about 

13
ERDC/TN APCRP-EA-15 

April 2007 

16 percent of the overall phosphorus inputs to the North lobe. Phosphorus fluxes via Pplant decomposition

accounted for < 15 percent of the total phosphorus input to the lake because P. crispus biomass was 

very low in this region. Pprecipitation only accounted for ~ 11 percent of the phosphorus budget of the 

North lobe. 

Figure 10. Seasonal variations in phosphorus (P) mass in the epilimnion (i.e., upper 2 m) and the metahypolimnion (i.e., water column below the epilimnion) between May and September 2002. The 

horizontal gray bar represents the period used to calculate net upward P flux to the epilimnion. 

In the South lobe, Pplant decomposition was the dominant phosphorus input (67 percent; Table 4). Psediment

accounted for ~17 percent and Pprecipitation accounted for < 10 percent of the total phosphorus input to 

the South lobe. Pgroundwater inputs were low in the South lobe compared to the North lobe and 

accounted for only 6 percent of the total phosphorus input to this region of the lake. 

Overall, individual phosphorus fluxes to the lake were low relative to internal phosphorus loading 

estimates determined in some other eutrophic lakes in Wisconsin (James and Barko 1993; James 

et al. 2000, 2003). However, multiple internal phosphorus sources to each lobe in the summer could 

contribute to algal blooms. When summed, total internal phosphorus fluxes were ~ 1 mg m-2 d-1, 

which is moderate compared to eutrophic lakes. 

14
ERDC/TN APCRP-EA-15 

April 2007 

Bathtub Modeling. To evaluate phosphorus loading and water quality response to McGinnis 

Lake, it was assumed that phosphorus sources from P. crispus decomposition and bottom sediment 

phosphorus release under anoxic conditions could be managed using various techniques (Table 5). 

P. crispus decomposition can be controlled by harvesting biomass before the onset of senescence 

(James et al. 2003) or by controlling its growth and uptake of sediment phosphorus by pre-emptive 

management in the fall or spring. Aluminum sulfate, a chemical floc that irreversibly binds sediment 

phosphorus and removes it from recycling pathways (Cooke et al. 1993), has been used to control 

phosphorus release from bottom sediments in many eutrophic lakes exhibiting high internal P loading. This management technique might be applicable for control of sediment phosphorus fluxes in 

McGinnis Lake, particularly the North lobe. 

Table 5 

Practical Phosphorus Management Techniques for Various 

Phosphorus Sources to McGinnis Lake1

Phosphorus Source Practical Management Techniques 

Precipitation None 

Groundwater None 

P. crispus decomposition Harvesting, Pre-emption 

Bottom sediment Alum salts 

Overland runoff BMPs 

1

 BMP = Best Management Practices. 

Relative to current conditions, the Bathtub model suggested that total phosphorus, chlorophyll, and 

Secchi transparency would not improve appreciably in response to a 100-percent reduction in phosphorus loading from bottom sediments, plant decomposition flux, or a 100-percent reduction in both 

fluxes (Figure 11). This model response was not surprising because water quality conditions in the 

surface waters of this lobe are within the mesoeutrophic range and phosphorus inputs to this region 

from these sources were low. Reductions in groundwater phosphorus inputs, which represented the 

greatest phosphorus load to the North lobe, would have resulted in improvement over current conditions. However, control of groundwater phosphorus to the lake is probably not feasible. 

The model suggested that total phosphorus and chlorophyll concentration could be reduced in the 

South lobe by 36 percent and 48 percent, respectively, via a 100-percent reduction in P. crispus

decomposition (Figure 11). Control of sediment phosphorus flux in this region, either separately or 

in combination with control of P. crispus decomposition, did not result in further appreciable 

improvement. Overall, it appeared that control of P. crispus decomposition in the summer represented the most effective phosphorus control management option for improvement of water quality 

over current conditions in the lake. 

The model response of algal bloom concentration and frequency during the summer is shown in 

Figure 12. Model output indicated that bloom concentration and frequency (percent of time in the 

summer) were moderate in the lake under current conditions during 2002. As with other water 

quality indicators, model reductions in bloom frequency and concentration appeared to be greatest 

when P. crispus decomposition was reduced by 100 percent. Control of sediment phosphorus flux 

did not appear to affect algal bloom concentration and frequency. The model also suggested that 

15
ERDC/TN APCRP-EA-15 

April 2007 

improvements in algal bloom concentration and frequency via control of P. crispus decomposition 

would be greatest for the South lobe of the lake, where P. crispus is found in greatest densities. 

Figure 11. Bathtub model response of total phosphorus, chlorophyll, and 

Secchi transparency to current phosphorus loading conditions and 

to control of phosphorus loading from sediments, from plant 

decomposition, and from both sources. 

16
ERDC/TN APCRP-EA-15 

April 2007 

Figure 12. Bathtub model response of bloom frequency (y-axis) and 

chlorophyll concentrations (x-axis) to current phosphorus 

loading conditions and to control of phosphorus loading from 

sediments, from plant decomposition, and from both 

sources. 

17
ERDC/TN APCRP-EA-15 

April 2007 

CONCLUSIONS: Although McGinnis Lake receives multiple internal phosphorus sources during 

the summer, measured fluxes to the lake were modest and its trophic state index fell within the 

mesoeutrophic range. Internal phosphorus sources from groundwater and P. crispus decomposition 

represented the greatest phosphorus inputs to the lake. Although internal P loading from anoxic profundal sediments was high in the North lobe of the lake, we suggest that only a small portion of this 

phosphorus was transported vertically to the surface waters for uptake by algae. Thermal stratification in the summer most likely restricted upward flux of phosphorus to the epilimnion (Stefan and 

Hanson 1981). 

Model results suggested that removal of P. crispus biomass prior to its senescence in the summer 

could reduce the occurrence and intensity of algal blooms. Control of P. crispus biomass can be 

achieved by harvesting as much as possible before mid-June or by attempting to control its growth in 

the spring or fall. In contrast, the current results suggest that control of sediment phosphorus fluxes 

is not necessary at this time. 

It also appeared that overland runoff from the watershed and export to the lake was very minor to 

negligible during the summer period. In many lakes, this source represents an important phosphorus 

input that can regulate algal growth and result in overfertilization. BMP’s (Best Management 

Practices) and shoreline conservation practices need to be continued in order to prevent watershed 

fluxes from becoming a problem. 

ACKNOWLEDGMENTS: The authors gratefully acknowledge Adams County, The State of Wisconsin, and the U.S. Army Engineer District, St. Paul for providing additional funding for this 

research; the University of Wisconsin – Stevens Point Environmental Task Force Laboratory for 

field sampling and analyses of water samples; T. Brunner, M. Daniels, H. Eakin, K. Johnson, 

L. Pommier, and M. Weiss of the Eau Galle Aquatic Ecology Laboratory for installation and monitoring of gauges on McGinnis Lake outflow and the determination of phosphorus release from the 

sediments; and D. Soballe and J. Skogerboe for review and improvements to this note. We also 

thank J. Rous, resident of McGinnis Lake and President of the lake association, for collecting rainfall and lake level information during the study period. 

POINTS OF CONTACT: This technical note was written by Mr. William F. James of the Eau 

Galle Aquatic Ecology Laboratory (EGAEL) of the Environmental Processes and Effects Division 

(EPED) of the Engineer Research and Development Center (ERDC) and Amy Dechamps, Nancy 

Turyk, and Paul McGinley of the University of Wisconsin at Stevens Point, Wisconsin, Department 

of Natural Resources, Stevens Point, Wisconsin. For additional information, contact the manager of 

the Aquatic Plant Control Research Program, Mr. Robert C. Gunkel (601-634-3722, Robert.C. 

Gunkel@erdc.usace.army.mil). 

This technical note should be cited as follows: 

James, W. F., A. DeChamps, N. Turyk, and P. McGinley. 2007. Importance of Potamogeton crispus decay to the phosphorus budget of McGinnis Lake, Wisconsin.

APCRP Technical Notes Collection. ERDC/TN APCRP-EA-15. Vicksburg, MS: 

U.S. Army Engineer Research and Development Center. www.wes.army.mil/el/aqua. 

18
ERDC/TN APCRP-EA-15 

April 2007 

REFERENCES: 

American Public Health Association (APHA). 1998. Standard methods for the examination of water and wastewater. 

20th ed. American Public Health Association, American Water Works Association, Water Environment Federation. 

Brock, T. D., D. R. Lee, and D. Winek. 1982. Groundwater seepage as a nutrient source to a drainage lake, Lake 

Mendota, Wisconsin. Water Research 16: 1253-1255. 

Carlson, R. E. 1977. A trophic state index for lakes. Limnology and Oceanography 22:361-36. 

Carpenter, S. R. 1980. Enrichment of Lake Wingra, Wisconsin by submerged macrophyte decay. Ecology 61: 1145-

1155. 

Cooke, G. D., E. B. Welch, S. A. Peterson, and P. R. Newroth. 1993. Restoration and management of lakes and reservoirs. 2nd edition. CRC Press, Lewis Publishers. 

James, W. F., and J. W. Barko. 1993. Analysis of summer phosphorus fluxes within the pelagic zone of Eau Galle 

Reservoir, Wisconsin. Lake and Reservoir Management 8: 61-71. 

James, W. F., and J. W. Barko. 1994. Macrophyte influences on sediment resuspension and export in a shallow 

impoundment. Lake and Reservoir Management 10: 95-102. 

James, W. F., J. W. Barko, and S. J. Field. 1996. Phosphorus mobilization from littoral sediments of an inlet region in 

Lake Delavan, Wisconsin. Archiv für Hydrobiologie 138: 245-257. 

James, W. F., J. W. Barko, H. L. Eakin, and D. R. Helsel. 2000. Distribution of sediment phosphorus pools and fluxes in 

relation to alum treatment. Journal of the American Water Works Association 36: 647-656. 

James, W. F., J. W. Barko, H. L. Eakin, and P. W. Sorge. 2003. Phosphorus budget and management strategies for an 

urban Wisconsin lake. Lake and Reservoir Management 18: 149-163. 

Lillie, R. A., S. Graham, and P. Rasmussen. 1993. Trophic state index equations and regional predictive equations for 

Wisconsin Lakes. Research Management Findings, No. 35. Madison, WI: Bureau of Research, Wisconsin 

Department of Natural Resources. 

Mortimer, C. H. 1971. Chemical exchanges between sediments and water in the Great Lakes - speculations on probable 

regulatory mechanisms. Limnology and Oceanography 16: 387-404. 

Stefan, H. G., and M. J. Hanson. 1981. Phosphorus recycling in five shallow lakes. ASCE Journal of Environmental 

Engineering 107: 713-730. 

Walker, W. W. 1996. Simplified procedures for eutrophication assessment and prediction: User manual. Instruction 

Report W-96-2. Vicksburg, MS: U.S. Army Engineer Waterways Experiment Station. 

NOTE: The contents of this technical note are not to be used for advertising, publication 

or promotional purposes. Citation of trade names does not constitute an official 

endorsement or approval of the use of such products.

19