Hicklin Lake Floating Islands Installation and Water Quality Investigation: final report for WDOE Grant G1300120

March 2017

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Hicklin Lake Floating Islands Installation and Water Quality Investigation: final report for WDOE Grant G1300120

Prepared for: Freshwater Algae Control Program Washington Department of Ecology

Submitted by: Timothy Clark and Chris Knutson King County Water and Land Resources Division Department of Natural Resources and Parks

Hicklin Lake Floating Islands Final Report for WDOE Grant G1300120

Acknowledgements Thanks to the White Center community for their enthusiastic support for this project, to all who helped with installation in July 2013, and in particular to Sally Abella (retired) and Rachael Gravon, who collected water quality samples, assisted with island maintenance, and provided thorough review of this document. Thanks also to the King County Environmental Laboratory for chemical analyses.

Citation King County. 2017. Hicklin Lake Floating Islands Installation and Water Quality Investigation: final report for WDOE Grant G1300120. Prepared by Timothy Clark and Chris Knutson, Water and Land Resources Division. Seattle, Washington.

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Table of Contents

Executive Summary...... v 1.0 Introduction ...... 1 1.1 Project Background Information ...... 1 1.2 History and Geography of the Watershed ...... 1 1.3 Historic Water Quality and Contaminants of Concern ...... 4 1.4 Floating Islands ...... 5 2.0 Floating Island Installation and Maintenance ...... 6 2.1 Island Design ...... 6 2.2 Island Installation ...... 6 2.3 Island Maintenance ...... 10 3.0 Sampling and Analysis Methods ...... 12 3.1 Sampling Locations ...... 12 3.2 Sampling Methods ...... 13 3.3 Analytical Methods ...... 16 3.4 Data Analysis Methods ...... 17 4.0 Water Quality Results ...... 21 4.1 Physical Parameters ...... 21 4.1.1 Lake Level ...... 21 4.1.2 Water Temperature ...... 22 4.1.3 Dissolved Oxygen ...... 23 4.1.4 Conductance ...... 24 4.1.5 pH ...... 25 4.2 Nutrients ...... 26 4.3 Chlorophyll a ...... 30 4.4 Secchi Transparency ...... 33 4.5 Trophic State Indices ...... 33 4.6 Cyanotoxins ...... 34 4.7 Metals ...... 35 4.8 Fecal Coliform...... 41 4.9 Biofilm Monitoring ...... 41

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5.0 Discussion ...... 44 6.0 References ...... 46

Figures

Figure 1. Map of Hicklin Lake watershed and stormwater flows to lake...... 3 Figure 2. Biomatrix Water floating island design, media column weight, and dynamic media columns (source: Biomatrix Water)...... 6 Figure 3. Team that installed floating islands: YouthSource, UW students, WCC, and King County staff and contractors...... 7 Figure 4. Construction of the islands was completed on shore...... 8 Figure 5. Holes were cut in the jute/plastic mesh and plants were installed in coir fiber...... 9 Figure 6. Towing the floating islands into place...... 9 Figure 7. Floating islands installed in Hicklin Lake in July 2013...... 10 Figure 8. King County staff maintaining floating islands...... 11 Figure 9. Location of installed floating islands (in pink) and stations (dots) set up for the water quality monitoring component of the project...... 12 Figure 10. King County staff extracting biofilm from dynamic media column recovered from beneath floating island...... 14 Figure 11. Sampling frequency at Hicklin Lake sites from May 2013 to October 2015. A745C in green and A745D in blue...... 15 Figure 12. Sampling frequency for the A745 site in central Hicklin Lake from 1997 to 2015...... 16 Figure 13. Hicklin Lake bathymetry and surrounding surface elevation (ft) releative to sea level...... 18 Figure 14. Daily rainfall and elevation of Hicklin Lake 2013-2015...... 22 Figure 15. Water temperature isotherms and water level for Lake Hicklin 2013-2015. ....23 Figure 16. Dissolved oxygen isopleths and water level for Lake Hicklin 2013-2015...... 24 Figure 17. Conductance isopleths and water level for Lake Hicklin 2013-2015...... 25 Figure 18. pH isopleths and water level for Lake Hicklin 2013-2015...... 26 Figure 19. Whole-lake, volume-weighted nutrient concentrations 1996-2015...... 27 Figure 20. Whole-lake, volume-weighted nutrient concentrations by month...... 29 Figure 21. Surface mass-based N:P ratio 1996-2015...... 30 Figure 22. Surface chlorophyll a concentrations 1996-2015...... 31

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Figure 23. Monthly chlorophyll a concentrations 2013‐2015...... 32 Figure 24. Secchi transparency at Hicklin Lake...... 33 Figure 25. Trophic state indicies for Hicklin Lake 1996 to 2015...... 34 Figure 26. Microcystin concentrations in Hicklin Lake during targetted scum sampling...... 35 Figure 27. Total metal concentrations 2013‐2015...... 40

Tables Table 1. Location data for sample sites along transect across Hicklin Lake...... 13 Table 2. Parameters sampled during between May 2013 and October 2015...... 15 Table 3. Standard Analytical Procedures for Hicklin Lake sample analysis...... 17 Table 4. Hicklin Lake morphology (depth‐area‐volume)...... 19 Table 5. Lake elevations on Lake Hicklin sampling dates. Differences between field and gage measurements are bolded...... 21 Table 6. Total metals measured in Hicklin Lake 2013‐2015...... 37 Table 7. Fecal coliform summary statistics 2013‐2015...... 41 Table 8. Comparison to fecal coliform water quality standards...... 41 Table 9. Mass of total nitrogen and total phosphorus detected in biofilm samples from the west and east floating islands and the associate N:P ratio...... 42 Table 10. Estimated nutrient uptake by the floating island biofilm...... 42

Appendices Appendix A: Water Quality Data Summary 2013‐2015 Appendix B: Comparison between A745, A745C, and A745D

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EXECUTIVE SUMMARY In 2013, Washington Department of Ecology (WDOE) grant G1300120 partially funded the acquisition, planting, installation, and monitoring of two floating wetland treatment systems on the surface of Hicklin Lake. Hicklin Lake is located in Dick Thurnau (formerly Lakewood) Park in the White Center neighborhood in unincorporated King County. The overarching goal of this project was to remove excess nutrients that have frequently caused toxic algal blooms in the lake.

Two 600-ft2 floating islands were installed on Hicklin Lake in July 2013. The islands cover about 0.5 percent of the lake surface. The islands’ manufacturer recommended at least 3 percent coverage, and other studies support coverage from 10 to 50 percent of the lake surface to effectively remove excess nutrients. Project cost constraints prevented increasing the island sizing for Hicklin Lake.

King County monitored the lake monthly between May/June and October from 2004 to 2015. Monitoring data show water quality concerns related to fecal coliform bacteria, nutrients and harmful algal blooms, copper, lead, and zinc. Hicklin Lake water quality did not appear to improve during the two years of monitoring following installation of the floating islands. It is apparent that these islands did not provide a quick fix to Hicklin Lake water quality concerns. Toxic algal blooms were detected in 2013, 2014, and 2015.

The long-term effectiveness of the floating islands to improve Hicklin Lake water quality is unknown. As the two islands further establish, increased uptake and sequestration of nutrients may be occur. However, it not known if that will be enough to cause the algal blooms to subside.

To mitigate toxic algal blooms in Hicklin Lake, three primary options to decrease nutrient inputs remain, including: • further alum treatment to prevent to nutrient loading from the lake sediment, • continued stormwater mitigation to further decrease loads from outside the lake, and • the addition of more floating islands to increase their treatment capacity.

Floating islands have not yet proved to be a viable method for treating excess phosphorus and toxic algal blooms in Hicklin Lake. However, floating islands have shown to be an opportunity for public education efforts concerning the lake and water quality in general. The islands may be leveraged in future water quality education campaigns in White Center.

The maintenance of the islands is straightforward and not time-intensive. To retain the diversity and aesthetics of the islands, the islands need to be visited semiannually: once in the early spring for pruning and fence repair and again in the late summer to pull invasive weeds and administer any further repairs. The structural integrity of the islands has not worsened over the course of their application. The ability of the islands to cope with sudden and large changes in the lake level is a tremendous asset.

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1.0 INTRODUCTION

1.1 Project Background Information

In 2013, Washington Department of Ecology (WDOE) grant G1300120 partially funded the acquisition, planting, installation, and effectiveness monitoring of two floating wetland treatment systems on the surface of Hicklin Lake, located in Dick Thurnau (formerly Lakewood) Park, in the White Center neighborhood in unincorporated King County. The overarching goal was to reduce concentrations of nutrients available to algae in order to prevent blooms that may potentially produce toxins. Other goals were to address possible accumulations of metals due to stormwater runoff from the urbanized watershed and to improve the lake’s overall suitability for recreational purposes as one of the park’s amenities. The natural character of the floating wetland islands was attractive to the community. This more natural approach was in contrast to the previous applications of aluminum sulfate (“alum”) to reduce phosphorus concentrations in the water. An additional goal of the project was to measure water quality parameters over the remaining grant period to begin assessing the efficacy of the islands in contributing to a discernable difference of available nutrients and pollutants in the lake water.

Before implementation, it was recognized that it would take longer than the life of the grant to validate the degree to which the islands contribute to water quality improvements. The purpose of the grant work was to design a monitoring program and begin to collect important data for addressing the question. If it is found the floating islands significantly contribute to water quality, such islands could become an important new tool available for increasing stormwater quality across the region.

1.2 History and Geography of the Watershed

Western settlers arrived in the White Center area in the 1870s and began harvesting lumber and clearing land. These early settlers used Hicklin Lake as a mill pond for a shingle and saw mill operation. When most of the old growth had been harvested, land was converted to small farms, and use of Hicklin Lake became focused on informal recreational activities such as swimming and fishing.

In the 1930s, the land surrounding the lake was purchased by L.B. Garrett, who dredged the lake to increase storage capacity as an irrigation water holding pond and used the dredge spoils to construct a golf course. Garret additionally constructed a pump house. By the 1940s, the federal government had purchased land nearby to build housing to support workers for the war effort at the nearby Boeing facilities. This increase in population necessitated an expansion of the combined sewer pipe system to carry wastewater and stormwater directly into Puget Sound.

The land under the golf course land was divided and sold to King County and the North Highline School District in the late 1940s. King County established a park on its portion of

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the property, and the Highline School District began planning for schools. Evergreen High School was completed and opened in 1955, and Cascade Middle School opened in 1957. In the early 1960s, a sandy bathing beach with steps and a large fishing pier that connected to the shoreline at both ends were constructed in the park. The beach was manned by lifeguards off and on until 1991, when it was permanently closed due to health and safety considerations.

After World War II, the federal government turned over the management of the sewer system to the Southwest Suburban Sewer District. The Southwest Suburban Sewer District split the combined sewer system flows into separate wastewater and stormwater conveyance systems. Following separation, wastewater was diverted into a new pipeline that carried waste to a treatment plant near the shoreline of Puget Sound. Stormwater flows remained in the original pipe system and continued to discharge to Puget Sound. Over multiple years, the separated stormwater system was amended, patched, and rerouted numerous times as new demands, changes in street configurations, or maintenance issues arose.

In the early 1960s, the stormwater conveyance system was modified to discharge directly into Hicklin Lake. Winter stormwater flows into Hicklin Lake caused large fluctuations in lake levels and local flooding since Hicklin Lake is a closed basin with no natural outlet. The outlet pump station was upgraded in the early 1980s, increasing the maximum flowrate from 2 cfs to 4.5 cfs. Today, the Hicklin Lake watershed consists primarily of a system of stormwater pipes (Figure 1). Some open water exists immediately upstream of Hicklin Lake, Mallard Lake, White Center Pond, and a wetland in White Center Heights Park.

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Figure 1. Map of Hicklin Lake watershed and stormwater flows to lake.

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1.3 Historic Water Quality and Contaminants of Concern

Over time, untreated stormwater inputs into Hicklin Lake caused nutrient accumulation in sediments and elevated bacteria levels. Phosphorus and fecal coliform bacteria are the contaminants of greatest concern in Hicklin Lake.

Excess phosphorus in lakes can lead to excess algae growth, oxygen depletion, nuisance odor from decaying algae, and toxic algal blooms that negatively impact recreational use. Based on King County monitoring data, the Washington State Department of Ecology has listed phosphorus in Hicklin Lake as a Category 5 impairment (i.e., polluted waters that require remediation through a Total Maximum Daily Load [TMDL] project) since 1996. To date, a TMDL and water clean-up plan has not been completed.

Fecal coliform bacteria are used in water quality monitoring programs to indicate the potential presence of pathogens associated with the feces of warm-blood animals. Ecology listed fecal coliform bacteria as a lake impairment in the 1998 303d list. The category was changed to Category 2 (i.e., waters of concern but inadequate evidence to support TMDL production) in 2008 and subsequent years. King County monitoring data show frequent exceedances of the fecal coliform water quality standard.

The central water quality station (A745) at the deepest part of the lake has been monitored by • CH2M Hill (1982) – March 1981 to February 1982 • CH2M Hill (1987) – February to December 1986 • King County Lake Stewardship volunteer – May through October 1996 to 1998 • King County staff – May/June through October 2004 to 2015

Hicklin Lake was initially monitored by the King County Health Department for total coliforms, albeit infrequently, in the 1960s and 1970s. Large concentrations of bacteria were recorded at the bathing beach as far back as 1961. Hicklin Lake was identified as eutrophic in the early 1980s (CH2M Hill, 1982). In 1986, King County constructed a detention basin upstream to divert high flows around the lake and extended the pump intake pipe to the deepest point of the lake (CH2M Hill, 1987). Degraded water quality continued through the mid-2000s.

Hicklin Lake received alum treatments in 2005 and 2011 to combat the frequent and sometimes toxic algal blooms that plague it. The 2005 treatment successfully reduced the levels of bioavailable phosphorus in the lake, leading to decreased chlorophyll a concentrations and increased clarity (King County, 2006). However, water quality conditions gradually deteriorated until 2010 when conditions were similar to those before treatment. An alum treatment was completed in 2011, which lead to improved conditions but only for a short period. Toxic algal blooms were detected every summer from 2012 to

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2015. In the late 2000s, King County invested in regional stormwater improvements in White Center, including: • Retrofit of White Center Pond (Cell 1) • Restoration of White Center Heights Pond • Construction of Mallard Lake Wetland facility • Repair of Hicklin Lake inlet bioswales • Illicit Discharge Detection Elimination and education

1.4 Floating Islands

Floating wetland treatment systems (floating islands) are engineered, vegetated rafts made of natural or inert materials that mimic floating bog mats. The root systems of the vegetation on the floating islands dangle under the islands into the water. Floating islands are designed to allow vegetation to take up both nutrients and other pollutants, and provide a substrate for extensive biofilms that also work to improve water quality.

Because the water level fluctuates widely through the year, Hicklin Lake’s shoreline is essentially devoid of submerged and emergent plants. Several park and community planting projects have attempted to increase vegetation. These plantings met with little success, due to both vandalism and the variable water levels. Floating islands may be a useful surrogate for the missing shoreline vegetation.

Floating islands are not a new technology, but they have not been used very often in the Pacific Northwest. Those installed in Washington State’s public lakes have been to decrease water temperature rather than the occurrence of toxic algal blooms. Floating islands have been used in other areas around the world, most often in stormwater detention ponds, sewage treatment lagoons, and urban canals for nutrient removal to inhibit algal blooms. Multiple studies have shown that floating wetlands have been shown to be effective in reducing nutrient concentrations in stormwater detention ponds (e.g., Headley and Tanner, 2011; White and Cousins, 2013; Wang and Sample, 2014).

Limited effectiveness data are available for floating wetland treatment systems in natural lakes or other water bodies. Even lakes with nuisance algal blooms have nutrient concentrations substantially lower than in sewage treatment lagoons or stormwater detention ponds. Vendor-supplied effectiveness data (Floating Islands International, unpublished data), demonstrate floating island effectiveness for phosphorus levels about 10 times higher than phosphorus levels in Hicklin Lake.

The lack of data does not necessarily suggest that the islands would not work as effectively in natural lakes. They simply have not been tested in situations with lower nutrient content, or nuisance algae blooms. Hicklin Lake provides a good opportunity to test the effectiveness of floating islands in removing nutrients and pollutants from a small lake with lower overall concentrations, while concurrently looking at algae production as measured by chlorophyll a concentrations.

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2.0 FLOATING ISLAND INSTALLATION AND MAINTENANCE

2.1 Island Design

Several possible layouts were considered, ranging from one large island to four smaller islands. Biomatrix Water recommended about 3 percent surface area coverage (~5,000 ft2). Budget constraints limited construction to two 600-ft2 islands, which represents about 0.5 percent coverage.

Seattle-based Herrera Environmental, representing the international firm Biomatrix Water, was selected to guide island design, provide platforms, and direct island installation. The planting list was completed by King County staff and contractors. The planting list was created with consideration to habitat, ultimate plant size, and aesthetics. The list included sedges, rushes, and bulrush, with native ornamentals such as Nootka Rose, Pacific Ninebark, and red-twig dogwood. Willows were added for visual appeal. The islands were each planted with 18 shrubs and approximately 500 rushes, sedges, and other grassy wetland plants (Sparganium spp. and Scirpus spp.). Approximately 50 artificial dynamic media columns were hooked underneath the islands to act as substrates for biofilm formation (Figure 2).

Figure 2. Biomatrix Water floating island design, media column weight, and dynamic media columns (source: Biomatrix Water).

2.2 Island Installation

The two floating islands were installed in Hicklin Lake on July 17, 2013. They were anchored well offshore to guard against possible vandalism and were located equidistant from the routine monitoring site A745 in the middle of the lake over the deepest part. The islands were anchored at three points with heavy concrete cinderblocks to allow for shifting water level.

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Several different groups assisted with the construction, planting and anchoring of the floating islands (Figure 3). Groups assisting the installation were: • King County staff and contractors, • Washington Conservation Corps team, • KC Youth Source interns, and • University of Washington students

Figure 3. Team that installed floating islands: YouthSource, UW students, WCC, and King County staff and contractors.

Installation and placement of the islands consisted of several steps. First, the construction team physically removed the island components from the shipping container and placed them in the appropriate positions in order to fasten them together. The floating island portions are several shapes (triangles, rectangles and half circles) and were placed together in an S shape. They were bolted together with plates. Island construction occurred on the shore (some portions were in the water) due to the heavy nature of the fully constructed islands (Figure 4). After the islands were constructed the dynamic media columns were attached to the islands using stainless steel D clips. The D clips were looped around the top end of the media columns and then clipped to the underside of the islands.

The construction team installed the plants after the islands were bolted into the appropriate shape. Plant locations were selected and holes were cut in the jute/plastic mesh for each plant. After the holes were cut the plants were rinsed of any sediment on their roots to reduce external nutrient inputs to the lake. Purchased coir bricks were

King County Science and Technical Support Section 7 March 2017 Hicklin Lake Floating Islands Final Report for WDOE Grant G1300120 soaked in lake water filled buckets to break them up, and coir fiber was placed in the plant holes along with the plants (Figure 5).

After the islands were planted, the construction team installed vertical posts along the edges of the island. Mesh was secured to the posts around the exterior of the islands to act as a bird deterrent. The plastic mesh deer fencing was wrapped around the islands and attached to a stainless steel cable that was threaded through the posts. The bottom of the mesh was zip-tied to the plastic floats of the island creating a mesh barrier around the islands.

Finally, the construction team towed the islands out to their selected locations out on the lake. This was done using a canoe with two paddlers with one person on the island (Figure 6). The islands were towed out and 3 large cinder blocks with lines attached were tied to the exterior floats around the islands. The blocks were then dropped into the water and the lines tightened to allow some freedom of movement with the wind and water level fluctuations (Figure 7).

Waterfowl were seen on the islands soon after installation. To prevent damage to the vegetation, two people canoed out and placed twine across the interior of the islands. Mylar ribbons were attached to the twine to act as a further bird deterrent. Since the mylar ribbons were installed there has been little observed bird usage on the islands.

Figure 4. Construction of the islands was completed on shore.

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Figure 5. Holes were cut in the jute/plastic mesh and plants were installed in coir fiber.

Figure 6. Towing the floating islands into place.

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Figure 7. Floating islands installed in Hicklin Lake in July 2013.

2.3 Island Maintenance

Maintenance of the floating islands has been done several times a year since the initial installation. Activities include dead organic material removal, fence repair, weeding, and trimming of overgrown vegetation.

Plant survival on both islands has been extremely good. Less than five percent of the plants were removed because they had died. Those plants that did die were generally planted too high on the island for immediate contact with the water, which resulted in them dying. Twice a year teams of two or three people canoed out to the islands to remove dead organic material and weeds. Staff climbs onto the island and remove leaf litter (Figure 8).

Over the course of several seasons, unplanted species of vegetation have been found on the islands. In 2015 reed canary grass appeared on the north island. This was addressed by trimming the grass down to the surface of the island and placing heavy black garbage bags over the remaining grass/roots. The bags were weighted down with bricks and left in place for several months to drown the grass. Several additional weed species were removed as necessary.

Since the islands were installed in 2013, there have been several breaks in the deer fencing mesh that wraps around the islands. These breaks are believed to be caused by people throwing objects at the islands (primarily rocks). The mesh fencing was repaired several times. The twine used for suspending the mylar ribbons has stretched and sagged over time and was replaced.

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Birds or bird feces/feathers have rarely been observed on the island. Bird use of the island appears to be dependent on breaks in the mesh fencing. The combination of mylar ribbon and fencing appears to be an adequate deterrent.

Future maintenance may include pruning some of the larger species planted on the islands (willow, dogwood and ninebark). It is suspected that the willows may become large enough to overgrow the other species. It is also possible that large willows may exceed the weight limits of the islands, forcing the islands down in the water and drowning out other plants. To address this issue, larger plant varieties will be pruned as needed.

Figure 8. King County staff maintaining floating islands.

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3.0 SAMPLING AND ANALYSIS METHODS

3.1 Sampling Locations

Water quality was sampled in Hicklin Lake at stations established along an east-west trending transect across the lake along its long axis (Figure 9, Table 1). The transect passes through the historic central station (A745). Two stations were located on either side to look for patchiness in analyte concentrations (A745C,D). Two further stations (A745A,B) were established along the east and west shorelines for assessing cyanobacterial scum accumulation and to measure potential exposure by shoreline users to fecal coliform bacteria.

Figure 9. Location of installed floating islands (in pink) and stations (dots) set up for the water quality monitoring component of the project.

All water quality stations were sampled once monthly from May or June to October. Site A745 was sampled from 1996-1998 by volunteers as part of King County’s Lake Stewardship Monitoring Program. King County has sampled this site since 2004. Sites

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A745A, A745B, A745FI-East, and A745-West were sampled 2013 through 2015. Sites A745C and A754D were sampled in 2013 and 2014. Sites A745C and A745D were discontinued at the end of 2014 following the end of grant funding through Ecology. The King County Stormwater Services Section continues to support the project through ongoing monitoring of the A745, A745A, and A745B sites.

3.2 Sampling Methods

King County field staff collects water for analysis of nutrients, chlorophyll a, bacteria (as fecal coliform), and total metals. Water column profile data are collected for specific conductance, temperature, dissolved oxygen, and pH using a Hydrolab MS5 or YSI EXO sonde at 0.5 m intervals at sites A745, A745C, and A745D. Secchi transparency was measured at these sites as well. Due to the fluctuating nature of the surface elevation of Hicklin Lake, the maximum depth sampled varied between sampling events. A staff plate is installed in Hicklin Lake with a reference point of 340.66 ft above sea level (NGVD 88) and lake elevation was noted by staff. King County maintains a water level gage that records level every 15 minutes inside the pump house at Hicklin Lake (gage: 50L) as well.

In addition, approximately 50 artificial dynamic media columns hook underneath the islands and act as substrates for biofilm formation. Two of these structures, one from each islands, were unhooked from underneath in the islands in spring during the first sampling trip and again in September in the years 2014 and 2015 (Figure 10). Biofilm was sampled by ringing the media column over a bucket. King County staff occasionally wore gloves for this procedure. Due to the high concentration of nutrients in the biofilm, it is not believed that contamination from staff hands was an issue.

In 2005, the Washington State Legislature established funding for an algae control program. Ecology developed the program which focuses on providing local governments with the tools they need to manage algae problems. Under the Northwest Toxic Algae Program, local jurisdictions, lake managers, and Washington residents can report an algae bloom and sample it to test for potential toxins produced by algae. The cyanotoxins microcystin and anatoxin-a were measured. Algal toxin samples were taken frequently as part of this program.

Location data for sample sites along transect across Hicklin Lake. Discrete Years Parameters Depths Locator Description Latitude Longitude Sampled Analyzed Sampled Deepest part of lake (5 m), Chlorophyll a, 1 m historical 1996-1998, nutrients, metals, 2.5 m sampling A745 47.50314 -122.34504 2004 - 2015 Secchi 3.5, 4, 4.5, or 5 point, a transparency, m between physical profiles floating islands

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Discrete Years Parameters Depths Locator Description Latitude Longitude Sampled Analyzed Sampled East 2013 – Fecal coliform, A745A 47.50340 -122.34422 Surface shoreline 2015 Chlorophyll a West 2013 – Fecal coliform, A745B 47.50295 -122.36409 Surface shoreline 2015 Chlorophyll a West of 1 m Chlorlophyll a, A745C western 47.50300 -122.34560 2013-2014 2.5, 3.0, or 3.5 nutrients island m East of Chlorlophyll a, 1 m A745D 47.50328 -122.34460 2013-2014 eastern island nutrients 3 or 3.5 m A745FI- Eastern NA NA 2013-2015 Total nutrients NA East floating island A745FI- Western NA NA 2013-2015 Total nutrients NA West floating island a. Sampling from 1996 to 1998 was completed by volunteers as part of the King County Lake Stewardship Program; chlorophyll a, Secchi transparency, and total nutrients were the only parameters analyzed for this program. In 2004, King County staff began routinely sampling the lake.

Figure 10. King County staff extracting biofilm from dynamic media column recovered from beneath floating island.

The sampling frequency for May 2013 through October 2015 is displayed in Table 2. Figure 11 provides the sampling frequency for conventionals (nutrients, chlorophyll a), total metals, and microbial (fecal coliform) parameters across discrete sampling depths. Figure 12 provides the same information over the entire sampling history for site A745.

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Parameters sampled during between May 2013 and October 2015. A745 A745A,B A745C,D A745FI-WEST Sampling Conven- A745 Chl-a and Conven- and EAST Date (Y-M-D) tionals Metals Fecal Coliform tionals Biofilm 2013-05-14 X X 2013-06-11 X X 2013-07-08 X X X X 2013-08-20 X X X X 2013-09-17 X X X X 2013-10-15 X X X X 2014-05-13 X X 2014-06-10 X X X X 2014-07-15 X X X X 2014-08-19 X X X X 2014-09-16 X X X X 2014-09-17 X 2014-10-14 X X X X 2015-06-23 X X X X 2015-07-21 X X 2015-08-18 X X X 2015-09-16 X X X 2015-10-15 X X X

Figure 11. Sampling frequency at Hicklin Lake sites from May 2013 to October 2015. A745C in green and A745D in blue.

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Figure 12. Sampling frequency for the A745 site in central Hicklin Lake from 1997 to 2015. Bottom depth varies with changes in lake level.

3.3 Analytical Methods

Table 3 displays the laboratory methods employed, the method and reporting detection limits, and units for each analyte.

Algal scums were sampled as part of the Department of Ecology’s Freshwater Algae Program. These samples were analyzed for the cyanotoxins, microcystin, and anatoxin-a by the King County Environmental Laboratory (Methods: ENVIROLOGIX 2003 and KCEL SOP#466 LCMS, respectively).

Hicklin Lake was sampled for two common cyanotoxins when a blue-green algal bloom was observed by King County staff. If the detected cyanotoxin levels were above the Washington State guidelines for either toxin (6 µg/L for microcystin and 1 µg/L for anatoxin-a), the lake was typically resampled weekly until two consecutive weeks below the guidelines, per state Department of Health protocol.

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Standard Analytical Procedures for Hicklin Lake sample analysis. Analyte Method MDL RDL Units Nutrients KEROUEL & Ammonia Nitrogen 0.002 0.01 mg/L AMINOT 1997 Nitrate/Nitrite Nitrogen SM4500-NO3-F 0.01 0.04 mg/L Total Nitrogen SM4500-N-C 0.05 0.1 mg/L Orthophosphate Phosphorus SM4500-P-F 0.0005 0.002 mg/L Total Phosphorus SM4500-P-B, F 0.005 0.01 mg/L Physical Parameters Chlorophyll a EPA 446.0 0.5 1.0 μg/L Phaeophytin a EPA 446.0 1.0 2.0 μg/L Microbiology CFU/ Fecal Coliform SM9222D, 20th ed. 1 1 100 mL Metals Aluminum, Total, ICP-MS 2 10 Antimony, Total, ICP-MS 0.3 1 Arsenic, Total, ICP-MS 0.1 0.5 Beryllium, Total, ICP-MS 0.1 0.5 Cadmium, Total, ICP-MS 0.05 0.25 Calcium, Total, ICP-MS 50 50 Chromium, Total, ICP-MS 0.2 1 Copper, Total, ICP-MS 0.4 2 EPA 200.8* Lead, Total, ICP-MS 0.1 0.5 µg/L SW846 6020A Magnesium, Total, ICP-MS 50 50 Manganese, Total, ICP-MS 0.1 0.5 Nickel, Total, ICP-MS 0.1 0.5 Selenium, Total, ICP-MS 0.5 1 Silver, Total, ICP-MS 0.04 0.2 Sodium, Total, ICP-MS 100 100 Thallium, Total, ICP-MS 0.04 0.2 Zinc, Total, ICP-MS 0.5 2.5

3.4 Data Analysis Methods

Whole-lake nutrient concentrations were estimated using volume weighting. The representative volume associated with each sampled depth was calculated based on lake bathymetry and the lake surface elevation. Lake bathymetry data presented by CH2MHill (1982) and King County surface elevation contour data (King County, 2009) were used to determine the morphology of Hicklin Lake (Figure 13; Table 4).

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Figure 13. Hicklin Lake bathymetry and surrounding surface elevation (ft) releative to sea level. Average lake elevation (344 ft) shown with bold line.

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For the purposes of whole-lake concentrations, the arithmetic means of concentrations of samples taken at the same depth region from different sites (i.e., A745, A745C, and A745D) were calculated. These values were used to calculate the whole-lake concentration for a sampling date based on the fraction of the lake volume a sample is expected to represent, i.e, the 1 m sample represents the surface to 1.5 m, the 2.5 m samples represents 1.6 to 3.5 m, and the 4 m sample represents 3.6 m to the lake bottom. The fraction of the lake volume each sample represents is dependent on lake surface elevation. Therefore, whole-lake concentrations were calculated for each sampling event based on measured lake elevation during that sampling event.

Hicklin Lake morphology (depth-area-volume). Elevation (ft Area Area Strata Volume above sea level) (acres) (ha) Volume (m3) below (m3) 360 13.76 5.57 72,000 197,000 355 9.45 3.82 43,000 125,000 350 4.65 1.88 31,000 81,800 344 (Average Lake 3.83 1.55 9,100 50,400 Elevation) 342 3.52 1.43 8,300 41,400 340 3.19 1.29 7,400 33,100 338 2.78 1.13 6,400 25,000 336 2.38 0.96 5,500 19,400 334 2.06 0.83 4,700 13,900 332 1.74 0.70 3,900 9,210 330 1.40 0.57 3,000 5,350 328 1.01 0.41 1,700 2,380 326 0.37 0.15 610 688 324 0.13 0.05 78 77.9 323 0 0 - - (lake bottom)

A common method of tracking water quality trends in lakes is by calculating the Trophic State Index (TSI) (Carlson, 1977). TSI values predict the primary productivity of the lake based on three parameters: water clarity (Secchi), total phosphorus, and chlorophyll a. The values are scaled from 0 to 100, which allow them to be used for comparisons of water quality over time and between lakes. If all of the assumptions about a lake ecosystem are met, the three TSI values should be very close together for a particular lake. When they are far apart in value, lake conditions and measurements should be examined to understand what special conditions might exist at the lake that are different from Carlson’s assumptions, or alternatively if data should be evaluated for errors. The index assumes that higher nutrient availability equates to more phytoplankton biovolume and more phytoplankton particles in the water contribute to decreased clarity, and vice versa.

The Index relates to three commonly used productivity categories: • oligotrophy (low productivity, below 40 on the TSI scale – low in nutrient concentrations, small amount of algae growth);

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• mesotrophy (moderate productivity, between 40 and 50 on TSI scale – moderate nutrient concentrations, moderate growth of algae growth); and • eutrophy (high productivity, above 50 – high nutrient concentrations, high level of algae growth).

A lake may fall into any of these categories naturally, depending on the conditions in the watershed, climate characteristics, vegetation, rock and soil types, as well as the shape and volume characteristics of the lake basin. Activities of people, such as land development, sanitary waste systems, and agricultural practices can also increase productivity, which is known as “cultural eutrophication.”

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4.0 WATER QUALITY RESULTS The water quality results presented herein are organized by parameter. The first group of parameters presented is physical: the level/elevation of the lake, water temperature, dissolved oxygen, conductance, and pH. The next group presented is nutrients: orthophosphate, total phosphorus, nitrate+nitrite nitrogen, ammonia nitrogen, and total nitrogen. Chlorophyll a, Secchi transparency, and the calculated trophic state indices are presented thereafter. Cyanotoxins, metals, and fecal coliform bacteria data are then presented. Finally, an analysis of the biofilm monitoring data is presented. The summary statistics for monitored parameters are presented in Appendix A. A comparison of spatial differences in observed values is presented in Appendix B.

4.1 Physical Parameters

4.1.1 Lake Level The field measurements and gage readings at 50L are in close agreement (Table 5) – the greatest recorded difference was 0.05 ft (0.6 in or 1.5 cm). The differences may be related to changes in the lake level over the day, a lag between water level and the level inside the pump house, or a slightly misread staff level by the user. Figure 14 below summarizes the lake level between 2013 and 2015.

Lake elevations on Lake Hicklin sampling dates. Differences between field and gage measurements are bolded. Lake Level Mean Daily Staff Level (Field (converted from Lake Level (50L Measurement) field measurement) Gage) (ft above Difference (ft) Date (ft) (ft above sea level) sea level) (Field – 50L) 5/14/2013 No plate installed 342.40 6/11/2013 1.52 342.18 342.18 0.00 7/8/2013 1.38 342.04 342.04 0.00 8/20/2013 0.06 340.72 340.72 0.00 9/17/2013 2.24 342.90 342.90 0.00 10/15/2013 Not measured 343.49 5/13/2014 Not measured 346.33 6/10/2014 Not measured 345.21 7/15/2014 3.06 343.72 343.67 0.05 8/19/2014 Above staff plate ?? 343.89 9/16/2014 2.20 342.86 342.85 0.01 10/14/2014 Above staff plate ?? 346.17 6/22/2015 Not measured 342.67 7/20/2015 0.81 341.47 341.50 -0.03 8/18/2015 1.76 342.42 342.40 0.02 9/16/2015 Above staff plate 345.45 10/15/2015 Not measured 343.80

The level of Hicklin Lake fluctuates greatly throughout the year (Figure 14). The greatest lake elevation between 2013 and 2015 occurred in December 2015, when levels reached

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356 ft above sea level. This resulted in flooding of the parking lot and park area. The lake levels during the 2014 sampling season were noticeably greater than during the 2013 or 2015 seasons. The level was between 2 and 4 feet higher in summer 2014 with notably high levels observed in August (343.89 ft above sea level).

Figure 14. Daily rainfall and elevation of Hicklin Lake 2013-2015. Sampling dates shown in green squares and field level elevation measurements (corrected to feet above sea level) in addition to sampling are shown in red diamonds.

4.1.2 Water Temperature Hicklin Lake is a warm, monomictic lake that stratifies before May and turns over between September and October, with water mixing isothermally in fall and winter. Destratification is closely linked to decreasing water temperatures, increasing inflow from the watershed, and strong winds.

In 2013 through 2015, thermal stratification was observed in the first sampling event of each year (May in 2013 and 2014; and June in 2015) (Figure 15). Surface temperatures increased and the depth of the thermocline (the density gradient) deepened over the course of the summer. Thermal stratification was observed in September sampling events each year, and had completely deteriorated by the October sampling events.

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Hicklin Lake does not strongly stratify. Lake mixing has been previously observed in mid- summer due to large rain events. These mixing events can bring a large amount of nutrients up from the hypolimnion to the lake surface.

Figure 15. Water temperature isotherms and water level for Lake Hicklin 2013-2015. Sampling dates denoted by ticks; temperature interpolated between depths and sampling dates. Lake elevation shown as dashed line.

4.1.3 Dissolved Oxygen Hicklin Lake surface water (sampled at 0.2 m below the surface) dissolved oxygen (DO) concentration typically ranges from 3 to 10 mg/L between May and October. The highest oxygen levels are generally coupled with a spring algal bloom (Figure 16). Mid- to late summer blooms have also been observed, causing an increase in DO. Lower surface DO levels occur in late summer.

With the onset of stratification, DO in the hypolimnion decreases with depth to below the method detection limit (0.5 mg/L). The hypolimnion remains anoxic through the course of stratification. With fall turnover, DO becomes approximately equal throughout the water column.

DO concentrations throughout the water column during August 2015 were substantially lower than in 2013 and 2014. DO on 8/18/2013 was about 3 mg/L at the surface and dropped to less than 0.5 mg/L in the first 2 meters. The July 2015 DO was not measured

King County Science and Technical Support Section 23 March 2017 Hicklin Lake Floating Islands Final Report for WDOE Grant G1300120 due to a malfunction of the sonde probe and thereby cannot be used for comparison. A 1.26 inch rain event on August 14, 2015 may have caused an influx of organic material from the watershed, as well as some mixing up of hypolimnetic organic material, resulting in a drop in DO.

Figure 16. Dissolved oxygen isopleths and water level for Lake Hicklin 2013-2015. Sampling dates denoted by ticks; concentrations interpolated between depths and sampling dates. Lake elevation shown as dashed line.

4.1.4 Conductance Hicklin Lake conductance is typically about 60 µS/cm throughout the water column. Higher conductance is observed near the lake bottom due to sediment resuspension along the water-sediment interface (Figure 17).

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Figure 17. Conductance isopleths and water level for Lake Hicklin 2013-2015. Sampling dates denoted by ticks; conductance interpolated between depths and sampling dates. Lake elevation shown as dashed line.

4.1.5 pH Lake Hicklin pH ranges from about 6 to above 10. The highest pH values occur in surface waters during summer months and are strongly linked to biological activity (Figure 18). Elevated pH was seen during phytoplankton blooms. As phytoplankton photosynthesize they consume dissolved CO2 (H2CO3), thereby removing acid from the lake.

During summer, the lake’s lower layer is typically slightly acidic. With the onset of stratification, the pH in the hypolimnion decreases as heterotrophic organisms consume DO and detritus, increasing the levels of bicarbonate (HCO3-) and CO2/H2CO3. When oxygen levels drop to concentrations below levels that support aerobic decomposition, anaerobic bacteria in the hypolimnion chemically reduce iron, manganese, sulfate, and nitrate. These chemical reductions contribute to acid-neutralizing capacity and mitigate decreases in pH. Fall turnover equalizes pH throughout the water column.

The pH profiles indicate the presence and extent of phytoplankton blooms in Hicklin Lake. In 2013, a bloom was evident in the surface 2 m in the August sample. In 2014, a surface bloom was evident in the May and August samples. In 2015, an intense bloom (pH>10) was observed in the July sample.

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Figure 18. pH isopleths and water level for Lake Hicklin 2013-2015. Sampling dates denoted by ticks; pH values interpolated between depths and sampling dates. Lake elevation shown as dashed line.

4.2 Nutrients

The April 2005 and May 2011 alum treatments substantially reduced the orthophosphate, total phosphorus, and total nitrogen concentrations relative to 2004 and 2010 concentrations (Figure 19). Surface total phosphorus concentrations in Hicklin Lake were between 50 and 65 µg/L during the volunteer monitoring between 1996 and 1998. Whole- lake, volume-weighted concentrations were between 40 and 115 µg/L in 2004. Total Phosphorus dropped to 20 to 40 µg/L in 2005 following the alum treatment and climbed steadily to between 75 and 110 µg/L by 2010. The 2011 alum treatment saw a drop in total phosphorus to levels similar to 2005, but 2012 through 2015 surface levels were similar to pre-treatment levels observed in 1996-1998.

Volume-weighted orthophosphate concentrations were substantially greater in 2004 and 2010 relative to other years (averages of 42 and 55 µg/L versus less than 5 µg/L). This was driven by high concentrations detected in the hypolimnion (above 100 µg/L). These data suggest that the alum treatments may have effectively reduced the loading of orthophosphate from the lake sediments. The 2005 treatment reduced loading between 2005 and 2009, and the 2011 treatment reduced loading between 2011 and at least 2015.

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Figure 19. Whole-lake, volume-weighted nutrient concentrations 1996-2015. Note that 1996-1998 samples were typically only collected at 1m; these data could not be volume-weighted and the mean surface concentrations are presented here. The box shows the interquartile (25th to 75th percentile) range, whiskers are 5th to 95th percentile, outliers are dots, and median is the solid line in box.

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Little historic ammonia and nitrate data are available. The two parameters were analyzed in 2004 and not again until 2011. The impact of the alum treatments and floating islands on these parameters cannot be determined with the available data.

Following the installation of the floating islands in 2013, no obvious decreases in nutrient concentrations were observed. By 2015 when the island plantings were well-established, whole-lake average nutrient concentrations, except orthophosphate, were greater than those observed since the alum treatment in 2011. Orthophosphate concentrations have remained stable from 2011 to 2015.

Figure 19 displays whole-lake nutrient concentrations from 2013 through 2015 by month. The general seasonal progressions are expected for the lake and are as follows: • Ammonia concentrations appear to increase over the course of the summer. This is likely due to the release of ammonium from the sediments under anoxic conditions. The high October values may also be related to increased stormwater input. • Nitrate+nitrite concentrations were near or below the detection limit in all months except October 2013 and 2015. These increased levels are likely linked to stormwater input of detritus. • Total phosphorus and total nitrogen concentrations were greatest from August through October in 2013 and 2014. In July 2015, total nitrogen peaked and total phosphorus was elevated relative to the previous years. • Orthophosphate concentrations were elevated in May 2013 and 2014 and October 2013, coinciding with wetter weather. The lower summer concentrations are influenced by the uptake by phytoplankton in the euphotic zone. This is expected in lakes where phosphorus is limiting phytoplankton. August 2015 orthophosphate levels were elevated following a summer rain event. The ratio of total nitrogen to total phosphorus (N:P) in surface water is used to indicate which nutrient is limiting algal growth. Lake water typically is considered to be nitrogen limited if the mass-based N:P ratio is less than 10 and to be phosphorus limited if the mass- based N:P ratio is greater than 17 (Carroll and Pelletier, 1991). Certain cyanobacteria species may have an advantage in more nitrogen-limiting conditions (ratio less than 25) because they can fix molecular nitrogen.

Hicklin Lake is generally phosphorus limited with some shifts toward co-limitation. This may be conducive to cyanobacteria able to fix nitrogen and/or uptake phosphorus when available for later utilization (luxury uptake) (Figure 20).

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Figure 20. Whole-lake, volume-weighted nutrient concentrations by month.

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Figure 21. Surface mass-based N:P ratio 1996-2015. Ratios less than 10 are considered nitrogen limited and greater than 17 are phophorus limited. Ratios below 25 may favor cyanobacteria.

4.3 Chlorophyll a

Chlorophyll a concentrations can be viewed as a proxy for phytoplankton biovolume. Similar to nutrients, the alum treatments in April 2005 and May 2011 substantial reduced chlorophyll a concentrations in 2005 and 2011 relative to 2004 and 2010 (Figure 21). The 2011 alum treatment saw a drop in 2011 chlorophyll a to levels similar to 2005. Thereafter, the 2012 through 2015 levels were similar to pre-treatment levels observed in 1996-1998 and 2007-2009.

In 2013 and 2014, chlorophyll a were elevated in August through October, and in 2015, July levels exceeded 100 µg/L (Figure 22). Chlorophyll a concentrations throughout the lake were typically similar. One exception was the 2013-10-15 sample that found the west beach (A745B) at about 350 µg/L and the east beach (A745A) at about 30 µg/L. On this date, an algal scum was observed on the west shoreline. The scum was likely pushed towards the west shore by winds or incoming flow from the NE stormwater outfall, increasing algal density along the shoreline.

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Figure 22. Surface chlorophyll a concentrations 1996-2015. Note log-scale.

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Figure 23. Monthly chlorophyll a concentrations 2013-2015. Note log-scale.

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4.4 Secchi Transparency

Secchi transparency is typically greatest in late spring when sampling begins. The Secchi depth decreases over the course of sampling through summer and early fall. Historically, the greatest transparencies were observed following the alum treatments in 2005 and 2011 (Figure 24).

Figure 24. Secchi transparency at Hicklin Lake.

4.5 Trophic State Indices

Hicklin Lake has been classified as eutrophic throughout monitoring (Figure 25). The 2005 and 2011 alum treatment decreased summer TSI values to marginally eutrophic. Recent TSI values indicate that Hicklin Lake continues to be eutrophic with TSI values upwards of 60. The TSI values associated with total phosphorus and chlorophyll a are close together on the scale, whereas the Secchi TSI values are typically lower, indicating that transparency is greater than the index would predict.

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Figure 25. Trophic state indicies for Hicklin Lake 1996 to 2015.

4.6 Cyanotoxins

Hicklin Lake microcystin concentrations frequently exceeded the Washington State recreational use guideline (6 µg/L) during the May-October sampling period (Figure 26). No microcystin data are available from November through April. In 2007, 2008, and 2011 (a year with alum treatment), no samples exceeded the Washington State recreational use guideline. Concentrations above 100 µg/L were observed in the summers of 2013, 2014, and 2015.

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Figure 26. Microcystin concentrations in Hicklin Lake during targetted scum sampling. Dashed line signifies Washington guideline threshold. Non-detects shown as hollow points.

Anatoxin-a was detected in one out of 33 samples from 2009 through 2015. In October, 2012, an Anatoxin-a concentration of 0.055 µg/L was measured, which is below the Washington State recreational guideline of 1 µg/L.

4.7 Metals

This section presents summary statistics for total metals measured in Hicklin Lake and, where applicable, comparison to Washington State water quality standards. Because only total metals were analyzed, Washington State aquatic life water quality standards for dissolved metals were back-calculated based on the conversion factors presented in WAC 173-201A-240. Washington State human health standard for the consumption of organisms are also presented.

Some metals have water quality standards that are dependent on water hardness. The water hardness data indicates that Hicklin Lake is soft at about 20 mg CaCO3/L, consistent with other Puget Lowland seepage lakes. Hardness was slightly greater at depth.

Generally, concentrations of metals were greatest near the lake bottom (Table 6). The exceptions to this were total copper and total antimony, where surface concentrations were greater than that of the near-bottom. Metal concentrations in the mid-water layer were only measured in 2013. In 2013, aluminum, antimony, chromium, copper, lead, nickel, sodium, and zinc concentrations appeared to be higher across all depths.

The elevated metals concentrations observed in 2013 were seen prior to the installation of the islands in July (Figure 27). The cause(s) of the lower metal concentrations seen in 2014 and 2015 is unknown, but potential contributing factors include precipitation events and

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Total metals measured in Hicklin Lake 2013-2015. All values in µg/L unless otherwise noted. Mid-depths were measured only in 2013 and do not include data from 2014 or 2015. Detects Detects Human Chronic Acute Above Above Health Metal Water Layer FOD Mean Median Min Max MDL Criteriaa,b Criteriaa,b Chronic Acute Criteria Near-Surface 15/15 145 139 56.2 350 2 Aluminum, Mid (2013) 4/4 223 193 172 287 2 Total Near-Bottom 15/15 159 151 69.4 280 2 Near-Surface 14/15 0.54 0.49 0.34 0.92 0.3 Antimony, Mid (2013) 4/4 0.63 0.57 0.56 0.72 0.3 180 Total Near-Bottom 6/15 0.37 NA 0.31 0.56 0.3 Near-Surface 15/15 1.96 1.85 0.847 3.15 0.1 200 379 0/15 0/15 Arsenic, Mid (2013) 4/4 2.21 2.2 1.47 2.61 0.1 200 379 0/4 0/4 10 Total Near-Bottom 15/15 1.57 1.5 0.918 2.59 0.1 200 379 0/15 0/15 Near-Surface 15/15 6810 6830 5970 7400 50 Calcium, Mid (2013) 4/4 6780 6950 5980 7250 50 Total Near-Bottom 15/15 8660 8070 6090 12500 50 Near-Surface 15/15 0.32 0.32 0.23 0.44 0.2 50.0 154 0/15 0/15 Chromium, Mid (2013) 4/4 0.40 0.38 0.33 0.48 0.2 50.6 156 0/4 0/4 Total Near-Bottom 15/15 0.38 0.36 0.26 0.54 0.2 56.8 175 0/15 0/15 Near-Surface 15/15 3.48 3.13 2.86 4.29 0.4 3.14 4.11 9/15 2/15 Copper, Mid (2013) 4/4 3.50 3.11 2.84 4.18 0.4 3.19 4.17 2/4 1/4 Total Near-Bottom 15/15 2.64 2.64 1.7 4.03 0.4 3.59 4.76 3/15 1/15

Hardness Near-Surface 15/15 21.2 21.2 18.5 22.9 0.331 (mg Mid (2013) 4/4 21.2 21.3 18.5 23 0.331 CaCO3/L Near-Bottom 15/15 26.2 24.8 18.9 37.3 0.331 Near-Surface 15/15 2.16 2.17 1.23 3.04 0.1 0.44 11.3 15/15 0/15 Lead, Total Mid (2013) 4/4 3.07 2.82 2.23 4.29 0.1 0.45 11.6 4/4 0/4 Near-Bottom 15/15 2.53 2.62 1.24 3.8 0.1 0.54 13.8 15/15 0/15

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Detects Detects Human Chronic Acute Above Above Health Metal Water Layer FOD Mean Median Min Max MDL Criteriaa,b Criteriaa,b Chronic Acute Criteria Near-Surface 15/15 1020 1050 875 1100 50 Magnesium, Mid (2013) 4/4 1020 957 872 1180 50 Total Near-Bottom 15/15 1110 1120 886 1460 50 Near-Surface 15/15 23.5 17.1 4.81 45.5 0.1 Manganese, Mid (2013) 4/4 52 33.5 16 113 0.1 Total Near-Bottom 15/15 255 240 34.6 586 0.1 Near-Surface 15/15 0.841 0.824 0.618 1.25 0.1 42.4 382 0/15 0/15 Nickel, Total Mid (2013) 4/4 0.98 0.984 0.945 1 0.1 43.0 387 0/4 0/4 190 Near-Bottom 15/15 0.952 0.986 0.746 1.23 0.1 48.5 436 0/15 0/15 Near-Surface 15/15 2500 2460 2040 3290 100 Sodium, Mid (2013) 4/4 2760 2600 2290 3320 100 Total Near-Bottom 15/15 2640 2570 1920 3730 100 Near-Surface 15/15 17.3 19.3 6.74 32.1 0.5 28.5 31.4 2/15 1/15 Zinc, Total Mid (2013) 4/4 14.2 10.2 10.1 20.1 0.5 28.9 31.9 0/4 0/4 2,900 Near-Bottom 15/15 19.7 17.8 11 45.3 0.5 32.5 35.9 1/15 1/15 FOD = Frequency of Detection a. Criteria back-calculated from dissolved metal criteria based on conversion factors presented in WAC 173-201A-240, except for Total Chromium. b. Where criteria are hardness-based, criteria are shown based on the median hardness for the water layer.

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The following metals exceeded Washington State aquatic life water quality standards: • Copper concentrations were greater than the chronic standard in 15 of 34 samples (9 of 15 sampling events) and greater than the acute standard in 4 of 34 samples (2 of 15 events). Three of the acute exceedances were observed on Oct. 15, 2013 at all three sampled depths – the other event was on May 14, 2013 at the near-surface. • Lead concentrations exceeded the chronic standard in all samples (34 of 34 samples – 15 of 15 events). The acute standard was not exceeded. • Zinc concentrations were greater than the chronic standard in 3 of 34 samples (3 of 15 sampling events) and greater than the acute standard in 2 of 24 34 samples (2 of 15 events). The acute events were on May 14, 2013 at 3.5 m and on June 23, 2015 at 1 m. All arsenic, chromium, and nickel samples were below the acute and chronic water quality standards. Finally, no metals exceeded the Washington State water quality standards for the consumption of organisms.

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Figure 27. Total metal concentrations 2013-2015. No mid-depth samples were collected in 2014 or 2015. The box shows the interquartile (25th to 75th percentile) range, whiskers are 5th to 95th percentile, outliers are dots, and median is the solid line in box.

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4.8 Fecal Coliform

Fecal coliform bacteria are used as indicators of pathogens found in warm-blooded animal feces. Hicklin Lake is designated for extraordinary primary contact recreation (e.g., swimming, wading) and has the following bacteria Washington State water quality standard: • Fecal coliform organism levels must not exceed a geometric mean value of 50 colonies/100 mL. At least 5 samples must be used to calculate the geometric mean (known as the geometric mean standard). • No more than 10 percent of all samples (or any single sample when less than ten sample points exist) obtained for calculating the geometric mean value may exceed 100 colonies/100 mL (known as the peak standard). Hicklin Lake fecal coliform concentrations exceeded both the geometric mean and the peak standards in 2013 through 2015. The geometric mean standard was exceeded along the west shoreline (A745B) only in 2013 and 2015 (Table 8). The peak standard was exceeded in all years at both shoreline sites (A745A and A745B) (Table 8).

Fecal coliform summary statistics 2013-2015. Locator Detections Mean Median Min Max A745A 17/17 70.6 41 2 440 A745B 19/19 113 60 3 460

Comparison to fecal coliform water quality standards. 2013 (n=6) 2014 (n=6) 2015 (n=5) Geometric Geometric Geometric Locator mean Max mean Max mean Max A745A 28 140 35 110 34 440 A745B 54 220 35 220 116 460

4.9 Biofilm Monitoring

The biofilm attached to the artificial dynamic media columns were sampled in June and September of 2014 and 2015 to determine the nutrient uptake over the course of the summer. The concentrations of total nitrogen and total phosphorus were multiplied by the volume extracted from each column to estimate the mass of total phosphorus and total nitrogen within the biofilm attached to the columns (Table 9).

The N:P ratio detected in the biofilm ranged between 6 and 10 with a higher ratio in the early summer than the late summer. The N:P ratio in the biofilm was lower than that of the lake, indicating a relatively greater level of phosphorus in the biofilm (Table 9).

The change in the nutrient content in the biofilm between June and September was used to estimate the total amount of nutrients taken up by biofilm on all 100 of the dynamic media

King County Science and Technical Support Section 41 March 2017 Hicklin Lake Floating Islands Final Report for WDOE Grant G1300120 columns. This estimate was based on the assumptions that all media columns on an island take up the same amount of nutrients, that all of the biofilm on a column was removed by the field staff, and that there is no settling of sloughed or senescent biofilm from the column to the sediments.1 Total phosphorus and total nitrogen uptake by the biofilms was calculated for each island for each year (Table 10). The nutrient uptake in 2015 was notably lower than in 2014.

Mass of total nitrogen and total phosphorus detected in biofilm samples from the west and east floating islands and the associate N:P ratio. Volume Mass Mass Biofilm Lake Sample Collected TN TN TP TP N:P N:P Island Date Number (L) (mg/L) (mg) (mg/L) (mg) Ratio Ratio L60423-5 4.40 2.81 12.36 0.409 1.80 6.87 13.66 6/10/2014 L60423-6 4.20 2.70 11.34 0.367 1.54 7.36 13.66 East 9/17/2014 L61163-10 4.59 14.5 66.56 2.23 10.24 6.50 14.89 6/23/2015 L63050-6 2.70 6.17 16.66 0.662 1.79 9.32 18.95 9/16/2015 L63729-6 4.10 8.59 35.22 1.39 5.70 6.18 15.72 L60423-7 5.35 2.01 10.75 0.267 1.43 7.53 13.66 6/10/2014 L60423-8 4.00 2.28 9.12 0.329 1.32 6.93 13.66 West 9/17/2014 L61163-11 2.77 19.8 54.75 3.15 8.71 6.29 14.89 6/23/2015 L63050-7 3.65 5.92 21.61 0.592 2.16 10.00 18.95 9/16/2015 L63729-7 3.21 8.08 25.94 1.36 4.37 5.94 15.72

Estimated nutrient uptake by the floating island biofilm. Change Summer Uptake per Per Island (g) June September column (change * 50 Parameter Island Year (mg) (mg) (mg) columns) 2014 1.67 10.24 8.57 0.43 East Total 2015 1.79 5.70 3.91 0.20 Phosphorus 2014 1.38 8.71 7.33 0.37 West 2015 2.16 4.37 2.21 0.11 2014 11.85 66.56 54.71 2.74 East Total 2015 16.66 35.22 18.56 0.93 Nitrogen 2014 9.94 54.75 44.81 2.24 West 2015 21.61 25.94 4.33 0.22

Summing removal across both islands, 0.8 g of total phosphorus was removed by the biofilm in 2014 and 0.31 g in 2015, and 4.98 g of total nitrogen was removed in 2014 and 1.15 g in 2015. The fraction of nutrient removal from the surface layer of the lake can be estimated. The volume of the epilimnion is about 18,000 m3 (between 342 and 333 ft above sea level). Therefore, the reduction in total phosphorus concentration in the surface layer

1 Biofilm and plant biomass settling to the lake bottom may release sequestered nutrients due to aerobic or anaerobic decomposition. Nutrients associated with the settled biofilm and biomass may also be removed from the lake by burial or mineralization.

King County Science and Technical Support Section 42 March 2017 Hicklin Lake Floating Islands Final Report for WDOE Grant G1300120 was about 0.044 µg/L. The average concentration of the summer epilimnion is 58.3 µg/L, therefore the removal would account for about 0.075 percent of the surface concentration.

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5.0 DISCUSSION The floating islands were installed on Hicklin Lake in July 2013. King County monitored lake water quality monthly between May/June and October since 2004. These data confirm water quality concerns for fecal coliform bacteria, nutrients and harmful algal blooms, copper, lead, and zinc. Hicklin Lake water levels are unnaturally variable due to stormwater inputs, amplifying the challenges in lake management. Relatively low total phosphorus and chlorophyll a levels were observed in 2005 and 2011 following alum treatment of the lake. After the 2005 treatment, total phosphorus and chlorophyll a levels slowly increased, whereas the 2011 treatment was less enduring, and a toxic bloom occurred the following year.

Insufficient data are available to fully assess the floating island’s efficacy at removing nutrients from Hicklin Lake’s surface water. Hicklin Lake monitoring does not show substantial differences in water quality pre- and post-installation. The data from biofilm sampling indicates that the biofilm attached to the dynamic media columns removed a small fraction of nutrients from the lake surface layer during the sampling period. Sampling of the root and shoot biomass from the plants could be useful to determine the total amount of nutrients sequestered by the plants (as well as the biofilm attached to the plant roots). Zhang et al. (2016) found that plant uptake accounted for about 60 and 90 percent of total nitrogen and phosphorus uptake by a floating treatment wetland.

The data presented in this report extends for only two years following the installation of the floating islands. It is apparent that the islands did not provide a quick fix to Hicklin Lake water quality concerns, as toxic algal blooms were detected in 2013, 2014, and 2015.

The long-term effectiveness of the floating islands in Lake Hicklin is unknown. As the two 600-ft2 islands further establish, increased uptake and sequestration of nutrients may occur, especially in the plant biomass. However, it is not known if the expected increase in nutrient removal will be sufficient to cause the algal blooms to subside.

Biomatrix Water recommended at least 3 percent coverage, and the current islands cover about 0.5 percent of the lake surface. Other studies have recommended coverage from 10 to 50 percent (Marimom et al., 2013; Winston et al., 2013; WQGIT, 2016). Increasing coverage to 5 or 10 percent of lake could result in a more marked change in water quality.

To mitigate toxic algal blooms in Hicklin Lake, three primary options to decrease nutrient inputs remain, including: • further alum treatment to prevent to nutrient loading from the lake sediment, • continued stormwater mitigation to further decrease loads from outside the lake, and • the addition of more floating islands to increase their treatment capacity.

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Further analysis is recommended to identify which of these approaches would provide the greatest likelihood of improving Hicklin Lake water quality cost effectively over the long term.

The presence of emergent and submerged aquatic plants could reduce the frequency and severity of algal blooms (Wetzel, 2001). Due to issues with fluctuating water levels in Hicklin Lake, planting along the shoreline has not been successful in the past and therefore is not recommended. Increasing the coverage of floating islands may prove a suitable substitution for the missing shoreline and in-water vegetation.

The floating islands have shown to be an opportunity for public education efforts concerning Hicklin Lake and water quality in general. The islands may be leveraged in future water quality education campaigns in White Center.

The maintenance of the islands is straightforward and not time-intensive. To retain the diversity and aesthetics of the islands, the islands need to be visited semiannually: once in the early spring for pruning and fence repair and again in the late summer to pull invasive weeds and administer any further repairs. Pruning the decorative shrubs may need to be done every few years as well. The structural integrity of the islands has not worsened over time after their installation in the lake. The ability of the anchoring system of the islands to cope with sudden and large changes in the lake level is a tremendous asset.

Several next steps are recommended for continued evaluation of the effectiveness of the floating islands in Hicklin Lake: • Evaluate planted species for ultimate size, growth rate, and ease of maintenance. • Evaluate island structural components for longevity and durability. • Evaluate annual biomass production and nutrient uptake by above-ground vegetation, roots, and root-attached biofilm. • Evaluate the phosphorus budget for Hicklin Lake, including stormwater inputs, released from the sediments, and additional pathways. King County plans to continue to monitor the water quality of Hicklin Lake and maintain the floating islands.

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6.0 REFERENCES Carroll, J.V., and G.J. Pelletier. 1991. Diagnostic Study of Lake Sawyer. Washington State Department of Ecology. Olympia, WA.

CH2M Hill. 1982. Lake Hicks Restoration Study. Prepared for: King County Division of Parks and Recreation. Seattle, WA.

CH2M Hill. 1987. Lake Hicks Post-Restoration Study. Prepared for: King County Division of Parks and Recreation. Seattle, WA.

Headley, T.R., and C.C. Tanner. 2012. Constructed Wetlands With Floating Emergent Macrophytes: An Innovative Stormwater Treatment Technology. Critical Reviews in Environmental Science and Technology 42: 2261-2310.

King County. 2005. Lake Hicks Integrated Phosphorus Management Plan. Water and Land Resources Division. Seattle, WA.

King County. 2006. Lake Hicks Alum Treatment Report. Water and Land Resources Division. Seattle, WA.

King County. 2008. Quality Assurance Project Plan for White Center Regional Stormwater Improvements. Water and Land Resources Division.

King County. 2009. Five (5) foot-interval index contour isolines and index contours (10 foot, 20 foot, 40 foot, 50 foot 7 100 foot). King County GIS Center. http://www5.kingcounty.gov/sdc/Metadata.aspx?Layer=contour005

King County. 2013. Final Project report for Application Number G0900041 “White Center Regional Stormwater Improvement Project.” Water and Land Resources Division.

Marimom, Z.A., Z. Xuan, and N. Chang. 2013. System dynamics modeling with sensitivity analysis for floating treatment wetlands in a stormwater wet pond. Ecological Modelling 267: 66-79.

Water Quality Goal Implementation Team (WQGIT). 2016. Recommendations of the Expert Panel to Define Removal Rates for Floating Treatment Wetlands in Existing Wet Ponds. Prepared by T. Schueler and C. Lane, Chesapeake Stormwater Network, and D. Wood, Chesapeake Research Consortium. US EPA Chesapeake Bay Program. Annapolis, MD.

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Wang, C.Y., and D.J. Sample. 2014. Assessment of the nutrient removal effectiveness of floating treatment wetlands applied to urban retention ponds. Journal of Environmental Management 137: 23-35.

Wetzel, R.G. 2001. Limnology: lake and river ecosystems. Elsevier. San Diego: Academic Press.

White, S.A., and M.M. Cousins. 2013. Floating treatment wetland aided remediation of nitrogen and phosphorus from simulated stormwater runoff. Ecological Engineering 61: 207-215.

Winston, R.J., W.F. Hunt, S.G. Kennedy, L.S. Merriman, J. Chandler, and D. Brown. 2013. Evaluation of floating treatment wetlands as retrofits to existing stormwater retention ponds. Ecological Engineering 54: 254-265.

Zhang, L, J. Zhao, N. Cui, Y. Dai, L. Kong, J. Wu, and S. Cheng. 2016. Enhancing the water purification efficiency of a floating treatment wetland using a biofilm carrier. Environmental Science and Pollution Research 23: 7437-7443.

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APPENDIX A: WATER QUALITY DATA SUMMARY 2013-2015

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Table A-1. Physical parameters summary statistics 2011-2013.

Parameter Locator Layer Detections Mean Median Min Max Near-Surface 51/51 56.3 56.2 46.9 86.7 A745 Mid 34/34 56.1 55.5 47.2 65.7 Near-Bottom 68/68 84.5 67.7 47.8 176.5 Near-Surface 33/33 54.4 54.4 47.5 79.6 Conductance A745C (µS/cm) Mid 22/22 54.4 54.3 47.4 65.8 Near-Bottom 22/22 69.3 59.7 47.9 145.9 Near-Surface 33/33 54.6 54.6 47.3 86.9 A745D Mid 22/22 54.5 54.8 47.4 67.6 Near-Bottom 19/19 63.9 57.4 47.9 159.6 Near-Surface 48/48 6.98 7.53 0.83 11.66 A745 Mid 30/32 4.31 4.28 0.07 9.21 Near-Bottom 52/65 1.55 0.13 0.01 7.11 Dissolved Near-Surface 27/27 7.76 7.44 3.84 11.16 Oxygen A745C Mid 16/18 4.87 4.96 0.91 8.5 (mg/L) Near-Bottom 15/19 2.56 0.56 0.14 6.67 Near-Surface 27/27 7.7 7.37 4.24 11.71 A745D Mid 17/18 4.71 4.75 0.03 9.19 Near-Bottom 15/16 3.06 1.57 0.09 6.94 Near-Surface 51/51 7.48 7.3 6.17 10.35 A745 Mid 34/34 6.87 6.76 6.12 7.98 Near-Bottom 68/68 6.45 6.4 5.94 7.08 Near-Surface 33/33 7.62 7.32 6.4 10.16 pH A745C Mid 22/22 7.02 7.03 6.42 7.78 Near-Bottom 22/22 6.62 6.61 6.17 7.07 Near-Surface 33/33 7.61 7.43 6.37 10.32 A745D Mid 22/22 6.9 6.85 6.29 7.63 Near-Bottom 19/19 6.59 6.53 5.91 7.16 Near-Surface 51/51 20 20.5 11.9 25.6 A745 Mid 34/34 18.5 18.7 11.9 23.5 Near-Bottom 68/68 14.9 15 11.2 20.4 Water Near-Surface 33/33 20.4 21.3 11.9 25.6 Temperature A745C Mid 22/22 19 19.4 11.9 23.7 (°C) Near-Bottom 22/22 16.8 17 11.9 20.5 Near-Surface 33/33 20.5 21.4 12 25.5 A745D Mid 22/22 19 19.4 11.9 23.5 Near-Bottom 19/19 16.7 16.9 11.8 20.7 Secchi A745 NA 17/17 1.28 1.2 0.3 2.5 Transparency A745C NA 11/11 1.12 1 0.3 2.25 (m) A745D NA 11/11 1.16 1 0.3 2.3

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Table A-2. Nutrients summary statistics 2011-2013.

Parameter Locator Layer Detections Mean Median Min Max Near-Surface 16/17 0.103 0.057 0.0046 0.564 A745 Mid 11/13 0.153 0.0823 0.0042 0.541 Near-Bottom 17/17 0.839 0.489 0.0232 3.18 Ammonia Near-Surface 7/9 0.0674 0.0159 0.0038 0.279 Nitrogen A745C Mid 2/2 NA NA 0.109 0.138 Near-Bottom 6/7 0.117 0.137 0.0026 0.284 Near-Surface 8/9 0.0712 0.0173 0.0022 0.29 A745D Near-Bottom 9/9 0.149 0.102 0.0023 0.506 Near-Surface 6/17 0.0287 NA 0.011 0.141 A745 Mid 5/13 0.0303 NA 0.013 0.142 Near-Bottom 4/17 0.033 NA 0.022 0.138 Nitrite + Nitrate Near-Surface 2/9 NA NA 0.011 0.142 Nitrogen A745C Mid 0/2 NA NA NA NA Near-Bottom 2/7 NA NA 0.015 0.148 Near-Surface 1/9 0.142 NA 0.142 0.142 A745D Near-Bottom 1/9 0.14 NA 0.14 0.14 Near-Surface 15/16 0.0031 0.00296 0.00062 0.00645 A745 Mid 12/12 0.00283 0.00249 0.00076 0.00602 Near-Bottom 15/16 0.00285 0.002 0.00072 0.0139 Orthophosphate Near-Surface 8/8 0.00255 0.0017 0.00059 0.00628 Phosphorus A745C Mid 2/2 0.00125 NA 0.0011 0.0014 Near-Bottom 6/6 0.00234 0.0012 0.001 0.00555 Near-Surface 8/8 0.00314 0.00205 0.00078 0.00787 A745D Near-Bottom 8/8 0.00231 0.0016 0.0013 0.00653 Near-Surface 17/17 1 1.02 0.449 2.27 A745 Mid 13/13 1.06 1.13 0.474 1.57 Near-Bottom 17/17 1.64 1.37 0.819 3.6 Near-Surface 9/9 0.967 1.15 0.437 1.42 Total Nitrogen A745C Mid 2/2 1.32 NA 1.09 1.55 Near-Bottom 7/7 0.971 0.987 0.57 1.33 Near-Surface 9/9 0.98 1.15 0.458 1.47 A745D Near-Bottom 9/9 1.18 1.11 0.594 2.15 Near-Surface 16/16 0.0582 0.0649 0.0272 0.0877 A745 Mid 12/12 0.069 0.0701 0.0328 0.1 Near-Bottom 16/16 0.0823 0.0744 0.0465 0.12 Total Near-Surface 8/8 0.0604 0.0657 0.0277 0.0804 Phosphorus A745C Mid 2/2 0.0927 NA 0.0734 0.112 Near-Bottom 6/6 0.066 0.0679 0.0481 0.0806 Near-Surface 8/8 0.0609 0.0651 0.0283 0.0824 A745D Near-Bottom 8/8 0.0906 0.0716 0.0454 0.25

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Table A-3. Cholorophyll-a and fecal coliform summary statistics 2011-2013.

Parameter Locator Layer Detections Mean Median Min Max A745 Near-Surface 17/17 28.9 17.6 3.39 116 A745A Near-Surface 13/13 33.4 33.8 5.55 99.7 Chlorophyll a (µg/L) A745B Near-Surface 13/13 69.8 44.6 4.75 348 A745C Near-Surface 8/8 38.2 29.3 4.35 81.8 A745D Near-Surface 8/8 31.2 22.7 4.95 70.1 Fecal Coliform A745A Near-Surface 17/17 70.6 41 2 440 (CFU/100 mL A745B Near-Surface 19/19 113 60 3 460

Table A-4. Volume-weighted nutrient summary statistics by year (May – October).

Parameter Year Mean Min Max # Samples 2004 0.711 0.142 1.90 6 Ammonia 2013 0.239 0.138 0.457 6 Nitrogen (mg/L) 2014 0.110 0.029 0.213 6 2015 0.330 0.009 0.691 5 2004 0.030 0.020 0.055 6 Nitrite + Nitrate 2013 0.032 0.010 0.142 6 Nitrogen (mg/L) 2014 0.014 0.010 0.030 6 2015 0.034 0.010 0.083 5 1996 0.885 0.544 1.570 12 1997 0.893 0.223 3.000 12 1998 0.972 0.552 1.710 13 2004 1.55 0.574 2.97 12 2005 0.686 0.523 0.859 6 2006 0.876 0.633 1.079 5 2007 1.180 0.757 2.149 5 Total Nitrogen (mg/L) 2008 1.353 0.780 2.204 5 2009 1.777 1.526 2.061 3 2010 2.293 1.500 2.990 4 2011 0.503 0.422 0.597 6 2012 1.377 0.654 2.102 6 2013 1.100 0.653 1.820 6 2014 0.892 0.537 1.336 6 2015 1.320 0.828 1.759 5

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Parameter Year Mean Min Max # Samples 2004 0.042 0.003 0.144 12 2005 0.002 0.002 0.003 6 2006 0.002 0.002 0.003 5 2007 0.003 0.002 0.005 5 2008 0.004 0.002 0.007 5 Orthophosphate 2009 0.004 0.002 0.006 3 Phosphorus (mg/L) 2010 0.055 0.006 0.089 4 2011 0.002 0.002 0.004 6 2012 0.004 0.002 0.007 6 2013 0.003 0.002 0.006 5 2014 0.003 0.001 0.008 6 2015 0.003 0.001 0.005 5 1996 0.063 0.028 0.101 12 1997 0.089 0.030 0.489 12 1998 0.053 0.035 0.083 13 2004 0.082 0.030 0.146 12 2005 0.029 0.022 0.038 6 2006 0.037 0.032 0.045 5 Total 2007 0.055 0.044 0.065 5 Phosphorus 2008 0.068 0.046 0.089 5 (mg/L) 2009 0.123 0.084 0.184 3 2010 0.128 0.074 0.156 4 2011 0.026 0.015 0.038 6 2012 0.052 0.042 0.073 6 2013 0.070 0.044 0.101 5 2014 0.055 0.038 0.075 6 2015 0.073 0.052 0.086 5

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Table A-5. Chlorophyll a and Secchi transparency summary statistics by year (May – October).

Parameter Year Mean Min Max # Samples 1996 1.5 0.5 2.5 12 1997 1.8 0.5 3.0 12 1998 1.8 0.5 3.0 13 2004 0.9 0.2 2.2 12 2005 2.7 1.7 4.0 5 2006 1.8 0.9 3.8 5 Secchi 2007 1.9 1.1 2.8 5 transparency 2008 1.8 1.2 2.8 5 (m) 2009 1.2 0.4 2.2 3 2010 0.4 0.4 0.4 2 2011 2.3 0.7 4.0 7 2012 1.1 0.4 1.5 3 2013 1.1 0.5 2.4 6 2014 1.5 0.9 2.5 6 2015 1.2 0.3 1.6 5 1996 21.8 1.70 105 12 1997 62.0 0.54 500 12 1998 26.6 2.50 112 13 2004 57.0 7.37 195 12 2005 14.8 1.40 62.0 6 2006 11.6 2.42 19.8 5 2007 14.5 3.30 23.4 5 Chlorophyll a (µg/L) 2008 55.7 3.20 168 5 2009 20.1 4.11 30.0 3 2010 53.6 29.6 75.4 4 2011 12.1 1.00 37.6 7 2012 25.9 10.2 54.9 6 2013 26.5 3.39 78.8 6 2014 26.7 3.45 63.9 6 2015 34.5 8.20 116.0 5

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APPENDIX B: COMPARISON BETWEEN A745, A745C, AND A745D

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Profiles and discrete sampling was performed at site A745, A745C, and A745D. The following plots compare the reported values for nutrients (ammonia, nitrite+nitrate, total nitrogen, orthophosphate, and total phosphorus), Secchi transparency, chlorophyll a, temperature, dissolved oxygen, pH, and conductance. Samples collected from the same depth with more than 20 percent difference between sites are labeled with the date of sampling.

Few samples collected on the same date at similar depths were found to substantially differ between sites. Surface chlorophyll a concencentrations were found to be spatially heterogenous. Additionally, dissolved oxygen concentrations were found to be highly variable at depth. A possible explanation is the steep decreasing gradient in dissolved oxygen during stratification; a small difference in depth sampled could result in very different concentrations recorded. Similarly, much variability was seen for nutrient concentrations collected within the metalimnion.

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Figure B-1. Ammonia concentrations compared between A745, A745C, and A745D. All values in mg/L. Solid diagonal line represents equal concentrations and dashed line represent 20 percent tolerance.

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Figure B-2. Nitrite+nitrate concentrations compared between A745, A745C, and A745D. All values in mg/L. Solid diagonal line represents equal concentrations and dashed line represent 20 percent tolerance.

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Figure B-3. Orthophosphate concentrations compared between A745, A745C, and A745D. All values in mg/L. Solid diagonal line represents equal concentrations and dashed line represent 20 percent tolerance.

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Figure B-4. Total nitrogen concentrations compared between A745, A745C, and A745D. All values in mg/L. Solid diagonal line represents equal concentrations and dashed line represent 20 percent tolerance.

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Figure B-5. Total phosphorus concentrations compared between A745, A745C, and A745D. All values in mg/L. Solid diagonal line represents equal concentrations and dashed line represent 20 percent tolerance.

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Figure B-6. Secchi transparency compared between A745, A745C, and A745D. All values in m. Solid diagonal line represents equal values and dashed line represent 20 percent tolerance.

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Figure B-7. Chlorophyll a concentrations compared between A745, A745C, and A745D. All values in µg/L. Solid diagonal line represents equal concentrations and dashed line represent 20 percent tolerance.

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Figure B-8. Pheophytin concentrations compared between A745, A745C, and A745D. All values in mg/L. Solid diagonal line represents equal concentrations and dashed line represent 20 percent tolerance.

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Figure B-9. Conductance values compared between A745, A745C, and A745D. All values in µS/cm. Solid diagonal line represents equal values and dashed line represent 20 percent tolerance.

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Figure B-10. Dissolved oxygen concentrations compared between A745, A745C, and A745D. All values in mg/L. Solid diagonal line represents equal values and dashed line represent 20 percent tolerance.

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Figure B-11. Water temperature compared between A745, A745C, and A745D. All values in °C. Solid diagonal line represents equal values and dashed line represent 20 percent tolerance.

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Figure B-12. pH field compared between A745, A745C, and A745D. Solid diagonal line represents equal values and dashed line represent 20 percent tolerance.

B-14