# Effects of Invasive Watermilfoil on Primary Production in Littoral Zones of North-Temperate Lakes
## Materials and Methods  
### Study Area  
This field study was conducted July-September 2017 in littoral zones of 6 lakes in the Upper Peninsula and northern Lower Peninsula of Michigan (Figure 2). Waterbodies with IWM were selected based on personal observation and Michigan Invasive Species Investigation Network (MISIN) database records [34]. Additionally, waterbodies with management programs for macrophytes and IWM using herbicides were avoided unless treatments were limited in scope, and at a distance we judged would not affect our study. This was determined by checking the Michigan Department of Environment, Great Lakes and Energy's MiWaters database [35] and personal communication with aquatic managers. In the largest waterbodies (Lake St. Helen, Sturgeon Sloughs of Portage Lake, and Ishington Bay of Lake Huron) some treatments occurred, but treatment locations were not hydroologically connected to our study areas (e.g., between embayments with limited water exchange, in adjacent slough areas > 1.5 km from the selected study plots). Selected waterbodies were oligotrophic to mesotrophic and ranged in size from small inland lakes to connected waterways of the Laurentian Great Lakes (Table 1). Torch Lake was the largest and deepest lake sampled (area = 11.0 km\({}^{2}\), mean depth 15 m), and is connected to the Keweenaw Waterway, which bisects the Keweenaw Peninsula of the Upper Peninsula and is connected to Lake Superior. Sturgeon Sloughs of Portage Lake is a complex of littoral habitat adjacent to the Sturgeon River delta also on the Keweenaw Waterway. An open bay in the Sturgeon Sloughs of Portage Lake (area of bay = 1.0 km\({}^{2}\), mean depth 2 m) was used as a study area. Iron Lake (area = 1.6 km\({}^{2}\), mean depth 6 m) is an inland lake in southwest Upper Peninsula and 1/10 th the size of Torch Lake. Islington Bay of Lake Huron is an oligotrophic, shallow enclosed bay (area = 1.6 km\({}^{2}\), mean depth 2 m) in the Les Cheneaux Islands region of northern Lake Huron. Horseshoe Lake is oligotrophic and the smallest inland lake included in this study (area = 0.15 km\({}^{2}\), mean depth 3 m), located in central Lower Peninsula. Lake St. Helen is a large inland lake (area = 9.7 km\({}^{2}\), mean depth 2 m) in central Lower Peninsula with a high percentage of littoral habitat. A paired-plot design was used within each waterbody to investigate the hypothesized effects of IWM on littoral zone primary producers. Circular 500-m\({}^{2}\) plots were located in macrophyte stands based on visual presence of IWM (+IWM) and paired with a nearby plot with similar macrophyte \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Waterbody** & **Area** (**km2)1** & **Maximum** **Depth (m)1** & **Mean** **Depth (m)1** & **Plot** **Type2** & **Coordinates** **(Latitude, Longitude)** & **Plot** **Depth (m)** \\ \hline Horseshoe Lake & 0.15 & 11 & 3 & \(-\)IWM & 44.415065, & 1.6 \\  & & & & \(+\)IWM & 44.417395, & 2.1 \\  & & & & & \(-\)84.281130 & & \\ \hline Lake St. Helen & 9.70 & 8 & 2 & \(-\)IWM & 44.370373, & 1.4 \\  & & & & \(+\)IWM & 44.369626, & 1.7 \\  & & & & \(-\)84.499011 & & \\ \hline Islington Bay of & 1.61 & 4 & 2 & \(-\)IWM & 45.977832, & 2.5 \\ Lake Huron3 & & & & \(+\)IWM & 45.973228, & 2.6 \\  & & & & \(-\)84.353715 & & \\ \hline Sturgeon Sloughs of & & & & \(-\)IWM & 47.032063, & 1.3 \\ Portage Lake 3 & 0.96 & 9 & 2 & \(-\)IWM & 47.031971, & 1.2 \\  & & & & \(+\)IWM & 47.031971, & 1.2 \\  & & & & \(-\)88.485941 & & \\ \hline Iron Lake & 1.60 & 17 & 6 & \(-\)IWM & 46.149005, & 1.5 \\  & & & & \(+\)IWM & 46.151059, & 2.4 \\  & & & & & \(-\)88.644730 & 2.4 \\ \hline Torch Lake & 11.00 & 37 & 15 & \(-\)IWM & 47.133131, & 2.2 \\  & & & & & \(-\)88.457900 & \\  & & & & & \(-\)88.45841 & \\ \hline \hline \end{tabular} 1
[FOOTNOTE:1]Footnote 1: footnotetext: Physical descriptions of lakes were determined from measuring and visually interpreting bathymetric lake maps (Navionics [36; 37], except for Torch Lake, which were from [38]). 2  
\end{table}