St. Louis County. wq-s2-08p

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1 St. Louis County This county-based case study was developed in support of a report entitled A review of transparency trends in Minnesota lakes. It is one of several county-based case studies, which provide a brief lake-bylake description of Secchi transparency and TP trends and potential reasons for the observed trends. Corresponding transparency (R-generated seasonal Kendall with median, max, and min for each year) and summer-mean TP graphs for each lake are included following the lake-by-lake descriptions (Figure 1). Further details on these charts and overall trend assessments, are found in the report cited above. St. Louis County had 21 lakes exhibiting significant transparency trends, of these, 16 were increasing, and five were decreasing. Very few lakes had sufficient TP data to allow for a comparison of transparency and TP trends. Of the three, with four or more years of TP data, Shagawa, East Vermilion, and Dodo, all exhibited good correspondence of transparency and TP trends. Spiny waterflea was the only aquatic invasive confirmed in these lakes and included Shagawa (2013), Namakan (2006), East Vermilion (2015), Kabetogama (2007), and Island Lake Reservoir (2007). Where possible, we provided observations on potential explanations for the transparency trends. Jesse Anderson, MPCA, EAO Duluth offered insights from his monitoring of several of these lakes. Narratives on some of the lakes were included in the Kawishiwi Watershed report (Anderson et al. 2011). Some observations were drawn from MDNR s LakeFinder as well. Increasing transparency Shagawa is a 2,300-acre, 48-foot deep lake located at Ely. It has one of the best water quality databases of any lake in St. Louis County. TP and transparency data dated to 1979 when MPCA was studying the impact of the Ely wastewater treatment facility (WWTF) discharge on the quality of the lake. USEPA data, which are not in EQuIS, dated to the early 1970s when they were involved in this same issue. The City of Ely was one of the first cities in the Nation to treat WWTF effluent to very low levels (referred to as tertiary treatment). The transparency data were continuous since 1979 and exhibited a significant increase over time. This trend corresponded directly to the reduction in in-lake TP over time, which was a function of reduced TP loading from the Ely WWTF. The upgrade to the WWTF resulted in a 70 percent reduction in TP load to Shagawa during , based on USEPA monitoring at that time. Before the wastewater upgrade, it was estimated that the WWTF accounted for 81 percent of the lake s TP load from (Larsen et. al., 1975 in Anderson et al. 2011). In 2009, the TP contribution from the WWTF was down to 98 kg (with an annual average TP concentration of 110 μg/l; MPCA Delta database). As such, wastewater s contribution was estimated at just 5.7 percent of the lakes total TP load, reflecting further improvements to WWTF and the lakes continued recovery from cultural eutrophication. Summer-mean TP since 1994 is at or below the 30 ppb water quality standard. The lake was deemed fully supporting for aquatic recreation when it was assessed. The lake was confirmed for spiny waterflea in 2013 and it is too recent to discern if it has any impact on water quality of the lake. Sabin (Embarrass Mine) is a 126-acre, 465-foot former mine pit at Aurora. It routinely has among the highest transparency of any lake in the state. It is a unique body of water, with essentially no surface water inflow, just groundwater and precipitation on the surface. It exhibited a significant increase in transparency over time. Because of its very high transparency, it is difficult to make an accurate Secchi disk reading and that may contribute to the high variability in measurements. It is a designated stream trout lake. From 1984 to 2010, various sizes and strains of rainbow trout, brook trout, lake trout, and wq-s2-08p 1

2 even Atlantic salmon were stocked. Lake trout adults were only stocked in 1984 and After 1985, only rainbow trout and brook trout have been stocked (MDNR LakeFinder). The changes in fish stocking over time, may have had an impact on lake transparency (via the food web) but we were not aware of any specific studies that document this. Long ( ) is a 151-acre, 33-foot deep lake south of Eveleth. It exhibited a significant increase in transparency over time based on a continuous record since Long Lake is the last in a small chain of lakes, draining Horseshoe and Mud Lakes to the north and outlets to the St. Louis River. The lake s watershed is a mix of forest and wetlands with developed lands comprising most of the shoreline. The lake is highly developed compared to other lakes in the NLF ecoregion, with over 100 homes and cabins. Properties around the lake are serviced by a sanitary sewer system that was installed in the 1990 s. The lake was the subject of a 1992 LAP study, follow-up study in 1997, and was included in the 2012 National Lakes Assessment. Based on data from these monitoring efforts TP decreased from 31 ppb in 1992, to 21 ppb in 1997, and a single sample in 2012 was 10 ppb. Though this was a limited data set, it appears that TP has likely decreased over time and accounted for the increase in transparency. Namakan is a 12,000-acre, 150-foot deep lake that is part of an expansive flowage. It exhibited a significant increase in transparency over time based on a record that dates to Namakan and Kabetogama were recently studied by USGS and Voyageur s National Park. They found a statistically significant improvement in water quality, which was associated with more natural lake level management -- as mandated by the International Joint Commission. Details on that study may be found in Kabetogama is a 22,000-acre, 50-foot deep lake that is part of a very large flowage. It exhibited a significant increase in transparency based on data since It was studied by USGS and VNP along with Namakan Lake and the trend was attributed to lake level management. Maple Leaf is a 98-acre, 51-foot deep lake located near Alborn. It exhibited a significant increase in transparency based on a continuous database since It was the subject of a 1994 LAP study. TP averaged 27 ppb in The lakeshore was already developed at the time of the LAP study. There is a lack of more recent TP data. Though it is unknown, improvement in septic systems over time could account for the increased transparency, since the lake had a relatively low TP value in 1995 and small reductions in TP loading can result in measurable changes in algal levels and transparency. Bassett is a 410-acre, 20-foot deep lake near Fairbanks. It exhibited a significant increase in transparency based on data since While it is a headwater lake in Superior National Forest, it does have a high amount of development. TP averaged 27 ppb in 1994 MPCA monitoring. Given its relatively low TP in 1995, small reductions in in-lake TP could yield measurable increases in transparency. Eagles Nest No. Four is a 175-acre, 49-foot deep lake that is part of a chain of lakes, west of Ely. It exhibited a subtle but significant increase in transparency since It is a headwater lake (flows to L. Vermilion). It does not have a public access and is a high quality lake. The only TP data was from summer of 1998 and the lake averaged 15 ppb. As with other lakes with low TP -- small reductions can yield measurable increases in transparency. East Vermilion is a 25,000-acre, 57-foot deep lake near Tower and is heavily influenced by inflow from the Pike River. It exhibited a subtle but significant increase in transparency, based on a record dating to 2

3 1976 and a continuous record since TP data are spotty but spread across the entire record and suggested a decrease over time. Flowage is a 111-acre, 15-foot deep lake north of Duluth. It exhibited a significant increase in transparency based on data since There is little information on the lake since it s fishery is not actively managed and the lake lacks a public access. Lake levels vary somewhat but were higher in recent years as compared to 2006 and 2007 when the transparency readings were initiated. Lake levels are controlled indirectly by lake level management in Island Lake Reservoir. TP in the summers of 2010 and 2011 was 21 and 13 ppb respectively. Dodo is an 88-acre, 53-foot deep lake near Shaw. Dodo is connected to Elora and Rose Lakes and all have much shoreline development. Dodo exhibited a significant increase in transparency based on a record that dates to 1995, when a MPCA LAP study was conducted. There was a reasonably good TP database available for comparison. However, several summers were represented by a single sample, the ones for 1995, 2004, and were based on multiple samples and overall suggest a decrease in TP over time. Schubert, also referred to as East Bass, is a 209-acre, 24-foot deep lake, NE of Cotton. It exhibited a significant increase in transparency based on a record that dates to Transparency peaked in 2007 and decreased slightly thereafter. The lakes shoreline is somewhat developed. There was no TP data for the lake so no trend comparisons were made. St. Mary's is a 240-acre, 44-foot deep lake that has served as a drinking water source for the City of Eveleth. It exhibited a significant increase in transparency based on a discontinuous record since There was no recent TP data and the only historical data available indicated TP in the ppb range. It is adjacent to Ely Lake and is periodically augmented by it. Ely is a 710-acre, 70-foot deep lake at the City of Eveleth. It is a high quality lake and serves as Eveleth s drinking water source via St. Mary s Lake. It exhibited a significant increase in transparency based on a record since The only TP data was from 1997 and the average was 14 ppb. Majestic is a 49-acre, 51-foot deep lake near Wolf and south of Mountain Iron. It exhibited a significant increase in transparency based on a record that dates to The lakes fishery is not actively managed and there is modest development around the lake. There was no TP data available for the lake, so no further explanation can be offered. Ban is a 388-acre, 15-foot deep lake near Orr. The MPCA conducted a LAP study on the lake in 2006, prior to shoreline development. It is located in a very remote area and there has been limited development around the lake. It exhibited a significant increase in transparency, with the first dataset running from and the second dataset from The only TP data was from the MPCA study and that indicated a summer-mean of 25 ppb. No further information was available that would help to explain the increase in transparency. Decreasing transparency Pequaywan is a 418-acre, 33-foot deep lake near Rollins. It exhibited a significant decrease in transparency since It has no public access, is very developed, and water levels are heavily influenced by Cloquet River system. This watershed has had extremes in low and high water the last five 3

4 years or more and this quite likely had an influence on TP loading, shoreline erosion, and transport of humic water into the lake -- all of which can affect transparency. The only TP data were from 2009 and 2011 and indicated TP was in the ppb range. Briar is an 80-acre, 21-foot deep lake near Palmers. It exhibited a significant decrease in transparency that was most pronounced from and thereafter there was a slight increase. It is a heavily developed seepage lake, likely a result of being near Duluth. Since it has a small watershed, its water quality would be strongly influenced by near shore overland runoff and surficial groundwater. It has been managed as a put-and-take rainbow trout fishery since Since there is no TP data for the lake, we cannot discern whether the transparency trend was a function of changes in TP or is perhaps related to fishery management. Thompson is 197-acre, 9-foot deep lake near Duluth. It is a bog stained lake and part of the Cloquet River system. It exhibited a significant decrease in transparency based on a continuous record since though there was some oscillation in the measures. A 2000 fishery survey indicated the lake had no improved public access, extensive macrophytes, and periodic low dissolved oxygen in the winter. There was no TP data for the lake. Management of flows in the Cloquet River system and wet to dry year cycles likely have a big influence on the water quality and transparency of Thompson Lake. Loon is a 270-acre, 85-foot deep lake near Aurora. The lake has moderate development. It exhibited a significant decrease in transparency based on a record that dates to The only TP data were from and TP averaged 9 ppb. Island Lake Reservoir (East Basin) is a 1,500-acre, 94-foot deep reservoir on the Cloquet River system ten miles north of Duluth. It exhibited a linear decrease in transparency based on a continuous database since A single summer in 1990 (a dry year) had a much higher transparency as well. It should be noted that the June flood of 2012 might have contributed to the very low transparency for that summer. Decreased transparency may relate to hydropower management and perhaps changes in climate. During droughty periods, lake levels can be extremely low and during wet periods, water residence time is very short. 4

5 Figure 1. Transparency and TP trend charts for St. Louis County case study. Increasing transparency Shagawa Sabin (Embarrass Mine) Long

6 Namakan Kabetogama Maple Leaf

7 Bassett Eagles Nest No. Four East Vermilion

8 Flowage Dodo Schubert

9 St. Mary's Ely Majestic

10 Ban Decreasing transparency Pequaywan Briar

11 Thompson Loon Island Lake Reservoir (East Basin)