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Prepared in cooperation with
New Hampshire Department of Environmental Services

Relation of Lake-Floor Characteristics to the Distribution of Variable Leaf Water-Milfoil in Moultonborough Bay, Lake Winnipesaukee, New Hampshire, 2005

By Denise M. Argue, Richard G. Kiah, Jane F. Denny, Jeffrey R. Deacon, William W. Danforth, Craig M. Johnston, and Amy P. Smagula

U.S. Geological Survey Scientific Investigations Report 2007–5125

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Abstract

Geophysical, water, and sediment surveys were done to characterize the effects of surficial geology, water and sediment chemistry, and surficial-sediment composition on the distribution of variable leaf water-milfoil in Moultonborough Bay, Lake Winnipesaukee, New Hampshire. Geophysical surveys were conducted in a 180-square-kilometer area, and water-quality and sediment samples were collected from 24 sites in the survey area during July 2005.

Swath-bathymetric data revealed that Moultonborough Bay ranged in depth from less than 1 meter (m) to about 15 m and contained three embayments. Seismic-reflection profiles revealed erosion of the underlying bedrock and subsequent deposition of glaciolacustrine and Holocene lacustrine sediments within the survey area. Sediment thickness ranged from 5 m along the shoreward margins to more than 15 m in the embayments. Data from sidescan sonar, surficial-sediment samples, bottom photographs, and video revealed three distinct lake-floor environments: rocky nearshore, mixed nearshore, and muddy basin. Rocky nearshore environments were found in shallow water (less than 5 m deep) and contained sediments ranging from coarse silt to very coarse sand. Mixed nearshore environments also were found in shallow water and contained sediments ranging from silt to coarse sand with different densities of aquatic vegetation. Muddy basin environments contained the finest-grained sediments, ranging from fine to medium silt, and were in the deepest waters of the bay.

Acoustic Ground Discrimination Systems (AGDS) survey data revealed that 86 percent of the littoral zone (the area along the margins of the bay and islands that extends from 0 to 4.3 m in water depth) contained submerged aquatic vegetation (SAV) in varying densities: approximately 36 percent contained SAV bottom cover of 25 percent or less, 43 percent contained SAV bottom cover of more than 25 and less than 75 percent, and approximately 7 percent contained SAV bottom cover of more than 75 percent. SAV included variable leaf water-milfoil, native milfoil, bassweed, pipewort, and other species, which were predominantly found near shoreward margins and at depths ranging from less than 1 to 4 m.

AGDS data were used in a Geographic Information System to generate an interpolated map that distinguished variable leaf water-milfoil from other SAV. Furthermore, these data were used to isolate areas susceptible to variable leaf water-milfoil growth. Approximately 21 percent of the littoral zone contained dense beds (more than 59 percent bottom cover) of variable leaf water-milfoil, and an additional 44 percent was determined to be susceptible to variable leaf water-milfoil infestation.

Depths differed significantly between sites with variable leaf water-milfoil and sites with other SAV (p = 0.04). Variable leaf water-milfoil was found at depths that ranged from 1 to 4 m, and other SAV had a depth range of 1 to 2 m. Although variable leaf water-milfoil was observed at greater depths than other SAV, it was not observed below the photic zone.

Analysis of constituent concentrations from the water column, interstitial pore water, and sediment showed little correlation with the presence of variable leaf water-milfoil, with two exceptions. Iron concentrations were significantly lower at variable leaf water-milfoil sites than at other sampling sites (p = 0.04). Similarly, the percentage of total organic carbon also was significantly lower at the variable leaf water-milfoil sites than at other sampling sites (p = 0.04).

Surficial-sediment-grain size had the greatest correlation to the presence of variable leaf water-milfoil. Variable leaf water-milfoil was predominantly growing in areas of coarse sand (median grain-size 0.62 millimeters). Surficial-sediment-grain size was also correlated with total ammonia plus organic nitrogen (Rho = 0.47; p = 0.02) and with total phosphorus (Rho = 0.44; p = 0.05) concentrations in interstitial pore-water samples.

Contents

Abstract

Introduction

Purpose and Scope

Previous Studies

Methods of Data Collection and Analysis

Geophysical Mapping of the Lake Floor

Acoustic Ground Discrimination System Survey

Water Column, Interstitial Pore Water, and Surficial-Sediment Sampling

Quality Assurance and Quality Control

Statistical Methods

Characterization of the Lake Environment

Lake Floor

Submerged Aquatic Vegetation

Water Quality of the Water Column and of Interstitial Pore Water

Chemical Characteristics of the Surficial Sediment on the Lake Floor

Characterization of the Distribution of Variable Leaf Water-Milfoil

Summary and Conclusions

References Cited

Appendix 1. Site Names, Locations, Water Depths, Textural Compositions, Median Surficial-Sediment Grain Sizes, Standard Deviations, Skewness, Kurtosis, and “Verbal Equivalents” (Shepard, 1954) for Sediment Samples Collected in Moultonborough Bay, Lake Winnipesaukee, New Hampshire, July 2005

Figures

1. Photograph showing variable leaf water-milfoil

2–3. Maps showing—

9–12. Maps showing—

15–19. Graphs showing—

Tables

1. Family, genus, species, and common name of the most common submerged aquatic plants in Moultonborough Bay, Lake Winnipesaukee, New Hampshire.
2. Lake-floor environments, sidescan-sonar backscatter patterns, descriptions, sediment textures, and water depths in Moultonborough Bay, Lake Winnipesaukee, New Hampshire.
3. Site numbers, site names, locations, water depths, selected field parameters, median surficial-sediment grain sizes, and percentages of vegetative bottom cover for sampling sites in Moultonborough Bay, Lake Winnipesaukee, New Hampshire.
4. Concentrations of potassium, dissolved nitrite plus nitrate, ammonium nitrogen, total ammonia plus organic nitrogen, total phosphorus, dissolved ortho-phosphorus, iron, and total organic carbon measured in water samples from sampling sites in Moultonborough Bay, Lake Winnipesaukee, New Hampshire.
5. pH (ratio); concentrations of potassium, total nitrate, total nitrite, ammonia plus ammonium, total ammonia plus organic nitrogen, phosphorus (strong acid digest), phosphorus (Olsen method), loosely sorbed phosphorus, iron-bound phosphorus, and iron; percent total organic carbon; and percent moisture measured in sediment samples from sampling sites in Moultonborough Bay, Lake Winnipesaukee, New Hampshire.
6. Percentage of the total sediment samples that were finer than the sieve diameter from sampling sites in Moultonborough Bay, Lake Winnipesaukee, New Hampshire.
7. Sediment composition of variable leaf water-milfoil and other-SAV sampling sites in Moultonborough Bay, Lake Winnipesaukee, New Hampshire.

Suggested Citation

Argue, D.M., Kiah, R.G., Denny, J.F., Deacon, J.R., Danforth, W.W., Johnston, C.M., and Smagula, A.P., 2007, Relation of lake-floor characteristics to the distribution of variable leaf water-milfoil in Moultonborough Bay, Lake Winnepesaukee, New Hampshire, 2005: U.S. Geological Survey Scientific-Investigations Report 2007–5125, 38 p.

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For further information, contact:

Director
U.S. Geological Survey
New Hampshire-Vermont Water Science Center
361 Commerce Way
Pembroke, NH 03275

dc_nh@usgs.gov

(603) 226-7807